Voltage smoothing circuit for smoothing voltage from power supply

This U.S. National stage application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application Nos. 2009-184413, filed in Japan on Aug. 7, 2009 and 2010-091946, filed in Japan on Apr. 13, 2010, the entire contents of which are hereby incorporated herein by reference.

The present invention relates to a voltage smoothing circuit and in particular to a circuit that smoothes a voltage outputted from a power supply portion.

A motor driver for driving a motor generates a motor drive voltage in an inverter portion and supplies the motor drive voltage to the motor. Generally, an AC voltage outputted from a power supply is smoothed and is thereafter supplied to the inverter portion.

As a technique for smoothing the voltage from the power source, a technique that utilizes smoothing capacitors that are connected in parallel to the power supply is often used as disclosed in Japanese Laid-open Patent Application Publication No. 2003-8814499, for example. Specifically, in the technique pertaining to Patent Document 1, two smoothing capacitors are connected in series to each other and are connected in parallel to the power supply. Moreover, a balancing resistor whose resistance value is smaller than those of internal resistors of the smoothing capacitors is connected in parallel to the smoothing capacitors. The balancing resistor is a resistor for maintaining a balance between the voltages applied to the smoothing capacitors so that the voltages applied to the smoothing capacitors fall within the rated voltage of the capacitors.

Further, as a related technology other than Japanese Laid-open Patent Application Publication No. 2003-8814499, there is the technology disclosed in Japanese Laid-open Patent Application Publication No. 1-169516.

Technical Problem

In the technique pertaining to Japanese Laid-open Patent Application Publication No. 2003-8814499, a relatively large current always flows to the balancing resistor, so the need to use a resistor of a specification able to withstand that current as the balancing resistor arises. As such a resistor, a resistor whose dimensions are relatively large, like a cement resistor for example, is predominantly utilized, and the size of the printed board on which the balancing resistor and so forth are mounted inevitably ends up becoming large. Further, in the technique pertaining to Japanese Laid-open Patent Application Publication No. 2003-8814499, because a large current always flows to the balancing resistor, the amount of heat emitted in the balancing resistor is also large and there is the concern that this will have adverse effects on electronic parts near the balancing resistor.

In particular, there are individual differences in the values of internal resistors of smoothing capacitors. For that reason, for example, even if two of the same type of smoothing capacitors whose capacitance value is 2880 μF are used, the internal resistors of the smoothing capacitors do not become exactly the same value but vary in the range of 420 kΩ to 1075 kΩ. In the technique of Japanese Laid-open Patent Application Publication No. 2003-8814499, even in light of variations between the internal resistors of the smoothing capacitors, a balancing resistor with a relatively large resistance value ends up becoming necessary.

Further, in Japanese Laid-open Patent Application Publication No. 1-169516, by using an op-amp or the like to increase and decrease the amount of current flowing to the balancing resistor, the amount of current flowing to the balancing resistor is alleviated compared to Japanese Laid-open Patent Application Publication No. 2003-8814499. However, in this technique, the number of elements configuring a circuit for maintaining a balance between the voltages of the smoothing capacitors and making the voltages applied to the smoothing capacitors fall within the rated voltages of those capacitors is many, and the circuit is also complicated.

Therefore, it is a problem of the present invention to provide a voltage smoothing circuit which, even if there are variations between internal resistors of smoothing capacitors, can with a simple configuration prevent a voltage equal to or greater than the rated voltage of a smoothing capacitor from being applied to that capacitor. It is also a problem of the present invention to provide a voltage smoothing circuit that can with a simple configuration maintain a balance between voltages applied to smoothing capacitors.

Solution to Problem

A voltage smoothing circuit pertaining to a first aspect of the invention is a circuit that smoothes a voltage outputted from a power supply portion. The voltage smoothing circuit comprises a first smoothing capacitor, a second smoothing capacitor, a first balancing resistor, and a second conduction regulating portion. The first smoothing capacitor and the second smoothing capacitor are connected in series to each other and are connected in parallel to the power supply portion. The first balancing resistor is connected in parallel to the first smoothing capacitor. The second conduction regulating portion is connected on a current path in parallel with the second smoothing capacitor. The second conduction regulating portion conducts current in one direction on the current path in a case where a voltage equal to or greater than a second predetermined voltage has been applied.

Examples of the second conduction regulating portion include a Zener diode. When a voltage equal to or greater than a predetermined voltage is applied to the second conduction regulating portion, currents flow from the power supply portion to the first smoothing capacitor and the first balancing resistor. The currents thereafter flow mainly on a current path (the second conduction regulating portion) whose impedance is lower than that on an internal resistor of the second smoothing capacitor, for example. Consequently, the end-to-end voltage of the second smoothing capacitor can be lowered with a simple configuration regardless of variations between the internal resistors of the smoothing capacitors, and a voltage equal to or greater than the rated voltage can be prevented from being applied to the second smoothing capacitor, for example.

A voltage smoothing circuit pertaining to a second aspect of the invention is the voltage smoothing circuit pertaining to the first aspect, wherein the second predetermined voltage is lower than the rated voltage of the second smoothing capacitor. The second conduction regulating portion maintains its inter-terminal voltage at the second predetermined voltage in a case where a voltage equal to or greater than the second predetermined voltage has been applied.

In this voltage smoothing circuit, in a state where a voltage equal to or greater than the second predetermined voltage is not being applied to the second conduction regulating portion, the second conduction regulating portion does not operate and, for example, the currents flowing from the power supply portion to the first smoothing capacitor (specifically, the internal resistor of the first smoothing capacitor) and the first balancing resistor merge and flow to the second smoothing capacitor. When a voltage equal to or greater than the second predetermined voltage is applied to the second conduction regulating portion, the second conduction regulating portion operates, its inter-terminal voltage is maintained at the second predetermined voltage, and the current that had flowed to the second smoothing capacitor at the time when the second conduction regulating portion was not operating branches and flows to the second smoothing capacitor and the second conduction regulating portion connected in parallel to that capacitor. Additionally, the end-to-end voltage of the second smoothing capacitor is maintained (clipped) at the second predetermined voltage that is lower than the rated voltage of the second smoothing capacitor. Consequently, at least the end-to-end voltage of the second smoothing capacitor can be prevented from becoming equal to or greater than the rated voltage of the second smoothing capacitor.

A voltage smoothing circuit pertaining to a third aspect of the invention is the voltage smoothing circuit pertaining to the second aspect, further comprising a second balancing resistor. The second balancing resistor connected on the current path in such a way as to become in parallel with the second smoothing capacitor and in series with the second conduction regulating portion. The current flows in one direction to the second balancing resistor in a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion.

According to this voltage smoothing circuit, the second balancing resistor in parallel with the second smoothing capacitor and in series with the second conduction regulating portion is disposed on the current path, so when a voltage equal to or greater than the second predetermined voltage is applied to the second conduction regulating portion, current flows also to the second balancing resistor. Because of this, adverse effects resulting from power loss in the second conduction regulating portion configured by a Zener diode, for example, ending up exceeding the rating and heat being emitted to parts near the second conduction regulating portion can be controlled.

Further, supposing that the second conduction regulating portion is configured by a Zener diode, for example, it is not always the case that a Zener diode where the second predetermined voltage is the desired value is commercially available. Depending on the value of the second predetermined voltage, sometimes cases arise where the voltage applied to the second smoothing capacitor connected in parallel to the Zener diode becomes lower and the voltage applied to the first smoothing capacitor becomes higher or where, conversely, the voltage applied to the second smoothing capacitor becomes higher than the desired value. However, according to this voltage smoothing circuit, the value of the voltage applied to the second smoothing capacitor is, in terms of the circuit configuration, equal to the sum of the voltage applied to the second balancing resistor and the voltage applied to the Zener diode. For this reason, the second predetermined voltage can be set while considering the voltage applied to the second balancing resistor, and in correspondence thereto the range of options for the Zener diode expands. Thus, the second predetermined voltage can be freely set, and it becomes possible to adjust the voltages applied to the first and second smoothing capacitors. Consequently, even if inexpensive capacitors whose rated voltages are low, for example, are used for the first and second smoothing capacitors, this voltage smoothing circuit is applicable also to devices where the operating range of the voltage from the power supply portion is relatively large. Moreover, by setting the second predetermined voltage to an optimum value, it also becomes possible to make the heat emission amounts of configural parts of the voltage smoothing circuit other than the second conduction regulating portion smaller and to make the power loss lower.

A voltage smoothing circuit pertaining to a fourth aspect of the invention is the voltage smoothing circuit pertaining to the third aspect, wherein the resistance value of at least one of the first balancing resistor and the second balancing resistor is decided in such a way as to satisfy a condition where a first end-to-end voltage representing the end-to-end voltage of the first smoothing capacitor becomes lower than the rated voltage of the first smoothing capacitor and a second end-to-end voltage representing the end-to-end voltage of the second smoothing capacitor becomes tower than the rated voltage of the second smoothing capacitor. Additionally, the second predetermined voltage is substantially the same as or less than the second end-to-end voltage.

For the sake of simplifying the description, as an example, a circuit configuration where the second conduction regulating portion is configured by a Zener diode, the second balancing resistor is not disposed on the current path, and only the second conduction regulating portion is disposed on the current path will be taken as an example. In this circuit configuration, the second end-to-end voltage of the second smoothing capacitor is equal to the inter-terminal voltage of the second conduction regulating portion, so when a voltage equal to or greater than the second predetermined voltage is applied to the second conduction regulating portion and current flows on the current path, the second end-to-end voltage becomes the inter-terminal voltage of the second conduction regulating portion that has been clipped—that is, the second predetermined voltage. In this state, when the voltage from the power supply portion rises, in terms of the circuit configuration there is the concern that the first end-to-end voltage of the first smoothing capacitor will rise and end up exceeding the rated voltage of the first smoothing capacitor.

However, in this voltage smoothing circuit, the balancing resistors are decided in such a way that the first end-to-end voltage becomes lower than the rated voltage of the first smoothing capacitor and the second end-to-end voltage becomes lower than the rated voltage of the second smoothing capacitor. Additionally, the second predetermined voltage is substantially the same as or less than the second end-to-end voltage. Consequently, even if the first end-to-end voltage rises due to a rise in the voltage from the power supply portion, the first end-to-end voltage does not exceed the rated voltage of the first smoothing capacitor.

A voltage smoothing circuit pertaining to a fifth aspect of the invention is the voltage smoothing circuit pertaining to any of the second aspect to the fourth aspect, wherein the resistance value of the first balancing resistor is decided in such a way as to satisfy a condition where a first end-to-end voltage representing the end-to-end voltage of the first smoothing capacitor becomes equal to or less than a second end-to-end voltage representing the end-to-end voltage of the second smoothing capacitor and the second end-to-end voltage is lower than the rated voltage of the second smoothing capacitor.

For the sake of simplifying the description, as an example, a circuit configuration where the second conduction regulating portion is configured by a Zener diode, the second balancing resistor is not disposed on the current path, and only the second conduction regulating portion is disposed on the current path will be taken as an example. A case will be considered where, in this circuit configuration, the second predetermined voltage is not applied to the second conduction regulating portion and the second conduction regulating portion does not operate due to a factor such as the difference between the internal resistors of the smoothing capacitors being large or the voltage from the power supply portion being low, for example. In this case, the end-to-end voltage of the second smoothing capacitor connected in parallel to the second conduction regulating portion is always kept equal to or less than the second predetermined voltage. However, in terms of the circuit configuration, the first end-to-end voltage of the first smoothing capacitor becomes a voltage obtained by subtracting the second end-to-end voltage of the second smoothing capacitor from the voltage from the power supply portion, and depending on the case the concern that the first end-to-end voltage of the first smoothing capacitor will reach a voltage equal to or greater than the rated voltage of the first smoothing capacitor is also not inconceivable.

However, according to this voltage smoothing circuit, the resistance value of the first balancing resistor is decided in such a way that the first end-to-end voltage of the first smoothing capacitor to which the second conduction regulating portion is not connected in parallel becomes equal to or less than the second end-to-end voltage of the second smoothing capacitor to which the second conduction regulating portion is connected in parallel. For that reason, the first end-to-end voltage of the first smoothing capacitor is always kept equal to or less than the second predetermined voltage of the second conduction regulating portion, and consequently the concern that a voltage equal to or greater than the rated voltage wilt be applied to the first smoothing capacitor can be avoided.

A voltage smoothing circuit pertaining to a sixth aspect of the invention is the voltage smoothing circuit pertaining to any of the second aspect to the fifth aspect, further comprising either of a first auxiliary resistor and a second auxiliary resistor. The first auxiliary resistor is connected in parallel to the second conduction regulating portion. The second auxiliary resistor is connected in parallel to the first smoothing capacitor and the second smoothing capacitor connected in series to each other.

According to this voltage smoothing circuit, the current that has flowed through the second conduction regulating portion in the circuit configuration where the first auxiliary resistor or the second auxiliary resistor was not disposed branches and flows to the first auxiliary resistor or the second auxiliary resistor and the second conduction regulating portion. Because of this, the amount of current flowing to the second conduction regulating portion becomes smaller, so the operating voltage and the rated power of the second conduction regulating portion can be set low, and a portion whose rated current is relatively small can be used for the second conduction regulating portion. Consequently, costs pertaining to the voltage smoothing circuit can be reduced (in particular, the cost of the second conduction regulating portion can be cut).

A voltage smoothing circuit pertaining to a seventh aspect of the invention is the voltage smoothing circuit pertaining to the first aspect, further comprising a second balancing resistor and a first conduction regulating portion. The second balancing resistor is connected on the current path in such a way as to become in parallel with the second smoothing capacitor and in series with the second conduction regulating portion. The first conduction regulating portion is connected in series to the first balancing resistor and conducts current in one direction to the first balancing resistor in a case where a voltage equal to or greater than a predetermined first voltage has been applied. Additionally, current flows in one direction to the second balancing resistor in a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion.

In this voltage smoothing circuit, in a case where a voltage equal to or greater than the first predetermined voltage has been applied to the first conduction regulating portion, current flows to the first balancing resistor, and the current flows to the second smoothing capacitor without flowing to the second balancing resistor, for example. In a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion, current flows to the second balancing resistor, whereby current flows also to the first smoothing capacitor, for example. In a case where current has flowed to the first smoothing capacitor, the end-to-end voltage of the first smoothing capacitor rises, and in a case where current has flowed to the second smoothing capacitor, the end-to-end voltage of the second smoothing capacitor arises, so a balance between the voltages applied to the smoothing capacitors can be maintained with a simple configuration.

A voltage smoothing circuit pertaining to an eighth aspect of the invention is the voltage smoothing circuit pertaining to the seventh aspect, further comprising a third auxiliary resistor and a fourth auxiliary resistor. The third auxiliary resistor is connected in parallel to both ends of the first conduction regulating portion. The fourth auxiliary resistor is connected in parallel to both ends of the second conduction regulating portion.

Current flowing on the current path including the first balancing resistor branches and flows to the first conduction regulating portion and the third auxiliary resistor, and current flowing on the current path including the second balancing resistor branches and flows to the second conduction regulating portion and the fourth auxiliary resistor. Because of this, the amounts of current flowing to the first and second conduction regulating portions become smaller, so the operating voltages and the rated power of the first and second conduction regulating portions can be set low, and portions whose rated currents are relatively small can be used for the first and second conduction regulating portions. Consequently, costs pertaining to the voltage smoothing circuit can be reduced (in particular, the cost of the first and second conduction regulating portions can be cut).

A voltage smoothing circuit pertaining to a ninth aspect of the invention is the voltage smoothing circuit pertaining to the seventh aspect or the eighth aspect, wherein a voltage equal to or greater than the second predetermined voltage is not applied to the second conduction regulating portion in a case where a voltage equal to or greater than the first predetermined voltage has been applied to the first conduction regulating portion. A voltage equal to or greater than the first predetermined voltage is not applied to the first conduction regulating portion in a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion.

In this voltage smoothing circuit, in a case where a voltage equal to or greater than the first predetermined voltage has been applied to the first conduction regulating portion, current that has flowed through the first balancing resistor flows to the second smoothing capacitor without flowing to the second balancing resistor. In a case where a voltage equal to or greater than the second predetermined voltage has been applied to the second conduction regulating portion, current flows to the second balancing resistor, whereby current flows also to the first smoothing capacitor, but current does not flow to the first balancing resistor. That is, in this voltage smoothing circuit, a voltage equal to or greater than the first predetermined voltage or equal to or greater than the second predetermined voltage is applied only to either one of the first conduction regulating portion and the second conduction regulating portion, so current does not always flow to the first and second balancing resistors. For that reason, resistors whose dimensions are relatively small can be utilized for the first and second balancing resistors, and the amounts of heat emitted in the first and second balancing resistors can be alleviated. Consequently, the printed board on which the first and second balancing resistors are mounted can be made smaller.

A voltage smoothing circuit pertaining to a tenth aspect of the invention is the voltage smoothing circuit pertaining to the ninth aspect, wherein the first conduction regulating portion is configured by a first Zener diode. The second conduction regulating portion is configured by a second Zener diode. The first predetermined voltage and second predetermined voltage are decided, on the basis of the value of the voltage that the power supply portion outputs, in such a way that current flows only to either one of the first Zener diode and the second Zener diode.

For example, in a case supposing that the value of the voltage that the power supply portion outputs is “718 V”, the first predetermined voltage and the second predetermined voltage that are the Zener voltages of the Zener diodes are both decided as “360 V”. Because of this, current flows only to either one of the first Zener diode and the second Zener diode, so the amounts of heat emitted in the first and second balancing resistors can be alleviated with a simple configuration.

A voltage smoothing circuit pertaining to an eleventh aspect of the invention is the voltage smoothing circuit pertaining to the tenth aspect, wherein the first predetermined voltage and the second predetermined voltage are equal to or less than the rated voltages of the first smoothing capacitor and the second smoothing capacitor.

Because of this, voltages that are larger than the values of the first predetermined voltage and the second predetermined voltage that are Zener voltages are applied to the first and second smoothing capacitors.

A voltage smoothing circuit pertaining to a twelfth aspect of the invention is the voltage smoothing circuit pertaining to the seventh aspect or the eighth aspect, wherein a voltage equal to or greater than the first predetermined voltage is applied to the first conduction regulating portion and a voltage equal to or greater than the second predetermined voltage is applied also to the second conduction regulating portion.

According to this voltage smoothing circuit, a voltage equal to or greater than the first predetermined voltage is applied to the first conduction regulating portion and a voltage equal to or greater than the second predetermined voltage is applied also to the second conduction regulating portion, so currents are applied to both of the first conduction regulating portion and the second conduction regulating portion.

A voltage smoothing circuit pertaining to a thirteenth aspect of the invention is the voltage smoothing circuit pertaining to the twelfth aspect, wherein the voltage smoothing circuit can take either of a first state and a second state. The first state is a state where a voltage equal to or greater than the first predetermined voltage is applied to the first conduction regulating portion and thereafter a voltage equal to or greater than the second predetermined voltage is applied also to the second conduction regulating portion. The second state is a state where a voltage equal to or greater than the second predetermined voltage is applied to the second conduction regulating portion and thereafter a voltage equal to or greater than the first predetermined voltage is applied also to the first conduction regulating portion.

According to this voltage smoothing circuit, a voltage equal to or greater than a predetermined voltage is applied to either one of the conduction regulating portions and that conduction regulating portion starts operating, whereby a voltage equal to or greater than a predetermined voltage is applied also the other of the conducting regulating portions and that conduction regulating portion also starts operating, and a balance between the voltages applied to the smoothing capacitors is maintained.

A voltage smoothing circuit pertaining to a fourteenth aspect of the invention is the voltage smoothing circuit pertaining to the twelfth aspect or the thirteenth aspect, wherein the first conduction regulating portion is configured by a first Zener diode, and the second conduction regulating portion is configured by a second Zener diode.

According to this voltage smoothing circuit, current flows to the first Zener diode as a result of a voltage equal to or greater than the first predetermined voltage that is a Zener voltage being applied to the first Zener diode. Current flows to the second Zener diode as a result of a voltage equal to or greater than the second predetermined voltage that is a Zener voltage being applied to the second Zener diode. The voltages in the first Zener diode and the second Zener diode are respectively clipped to the first predetermined voltage and the second predetermined voltage. For that reason, a difference voltage between the end-to-end voltage of the first smoothing capacitor and the first predetermined voltage is applied to the first balancing resistor, and a difference voltage between the end-to-end voltage of the second smoothing capacitor and the second predetermined voltage is applied to the second balancing resistor. Consequently, the values of the currents flowing to the first and second balancing resistors can be made smaller than conventionally with a simple configuration, and thus the amounts of heat emitted in the first and second balancing resistors can be alleviated.

A voltage smoothing circuit pertaining to a fifteenth aspect of the invention is the voltage smoothing circuit pertaining to the fourteenth aspect, wherein the first predetermined voltage and the second predetermined voltage are equal to or less than the rated voltages of the first smoothing capacitor and the second smoothing capacitor.

Because of this, voltages that are larger than the values of the first predetermined voltage and the second predetermined voltage that are Zener voltages are applied to the first and second smoothing capacitors.

A voltage smoothing circuit pertaining to a sixteenth aspect of the invention is the voltage smoothing circuit pertaining to any of the third aspect to the fifteenth aspect, wherein the first balancing resistor has a resistance value that is smaller than the value of an internal resistor of the first smoothing capacitor. The second balancing resistor has a resistance value that is smaller than the value of an internal resistor of the second smoothing capacitor.

Because of this, the amounts of current flowing to the first balancing resistor and the second balancing resistor become larger than the amounts of current flowing to the internal resistors of the first smoothing capacitor and the second smoothing capacitor, so the amounts of current flowing to the first smoothing capacitor and the second smoothing capacitor can be controlled. Consequently, the voltages applied to the first smoothing capacitor and the second smoothing capacitor can be made lower.

Advantageous Effects of Invention

According to the voltage smoothing circuit pertaining to the first aspect of the invention, the end-to-end voltage of the second smoothing capacitor can be lowered with a simple configuration regardless of variations between the internal resistors of the smoothing capacitors.

According to the voltage smoothing circuit pertaining to the second aspect of the invention, at least a voltage equal to or greater than the rated voltage can be prevented from being applied to the second smoothing capacitor.

According to the voltage smoothing circuit pertaining to the third aspect of the invention, adverse effects resulting from power loss in the second conduction regulating portion ending up exceeding the rating and heat being emitted to parts near the second conduction regulating portion can be controlled. Further, the second predetermined voltage can be freely set, and it becomes possible to adjust the voltages applied to the first and second smoothing capacitors. Consequently, even if inexpensive capacitors whose rated voltages are low, for example, are used for the first and second smoothing capacitors, this voltage smoothing circuit is applicable also to devices where the operating range of the voltage from the power supply portion is relatively large. Moreover, by setting the second predetermined voltage to an optimum value, it also becomes possible to make the heat emission amounts of configural parts of the voltage smoothing circuit other than the second conduction regulating portion smaller and to make the power loss lower.

According to the voltage smoothing circuit pertaining to the fourth aspect of the invention, even if the first end-to-end voltage rises due to a rise in the voltage from the power supply portion, the first end-to-end voltage of the first smoothing capacitor does not exceed the rated voltage of that capacitor.

According to the voltage smoothing, circuit pertaining to the fifth aspect of the invention, the first end-to-end voltage of the first smoothing capacitor is always kept equal to or less than the second predetermined voltage of the second conduction regulating portion, so the concern that a voltage equal to or greater than the rated voltage will be applied to the first smoothing capacitor can be avoided.

According to the voltage smoothing circuit pertaining to the sixth aspect of the invention, costs pertaining to the voltage smoothing circuit can be reduced (in particular, the cost of the second conduction regulating portion can be cut).

According to the voltage smoothing circuit pertaining to the seventh aspect of the invention, a balance between the voltages applied to the smoothing capacitors can be maintained with a simple configuration.

According to the voltage smoothing circuit pertaining to the eighth aspect of the invention, the operating voltages and the rated power of the first and second conduction regulating portions can be set low, and portions whose rated currents are relatively small can be used for the first and second conduction regulating portions. Consequently, costs pertaining to the voltage smoothing circuit can be reduced (in particular, the cost of the first and second conduction regulating portions can be cut).

According to the voltage smoothing circuit pertaining to the ninth aspect of the invention, current does not always flow to both of the first and second balancing resistors, so resistors whose dimensions are relatively small can be utilized for the first and second balancing resistors, and the amounts of heat emitted in the first and second balancing resistors can be alleviated. Consequently, the printed board on which the first and second balancing resistors are mounted can be made smaller.

According to the voltage smoothing circuit pertaining to the tenth aspect of the invention, the amounts of heat emitted in the first and second balancing resistors can be alleviated with a simple configuration.

According to the voltage smoothing circuit pertaining to the eleventh aspect of the invention, voltages that are larger than the values of the first predetermined voltage and the second predetermined voltage that are Zener voltages are applied to the first and second smoothing capacitors.

According to the voltage smoothing circuit pertaining to the twelfth aspect of the invention, currents are flowed to both of the first conduction regulating portion and the second conduction regulating portion.

According to the voltage smoothing circuit pertaining to the thirteenth aspect of the invention, a balance between the voltages applied to the smoothing capacitors is maintained.

According to the voltage smoothing circuit pertaining to the fourteenth aspect of the invention, the values of the currents flowing to the first and second balancing resistors can be made smaller than conventionally with a simple configuration, and thus the amounts of heat emitted in the first and second balancing resistors can be alleviated.

According to the voltage smoothing circuit pertaining to the fifteenth aspect of the invention, voltages that are larger than the values of the first predetermined voltage and the second predetermined voltage that are Zener voltages are applied to the first and second smoothing capacitors.

According to the voltage smoothing circuit pertaining to the sixteenth aspect of the invention, the amounts of current flowing to the first smoothing capacitor and the second smoothing capacitor can be controlled, and the voltages applied to the first smoothing capacitor and the second smoothing capacitor can be made lower.

FIG. 1 is a configuration diagram of a motor driver that is equipped with a voltage smoothing circuit pertaining to a first embodiment;

FIG. 2 is a circuit diagram of the voltage smoothing circuit pertaining to the first embodiment;

FIG. 3 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where the end-to-end voltage of a second smoothing capacitor is lower than a. Zener voltage in the voltage smoothing circuit of FIG. 2 ;

FIG. 4 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where the end-to-end voltage of the second smoothing capacitor is equal to or greater than the Zener voltage in the voltage smoothing circuit of FIG. 2 ;

FIG. 5 is a circuit diagram of a voltage smoothing circuit pertaining to modification (a) of the first embodiment and shows a case where an auxiliary resistor is connected in parallel to the Zener diode;

FIG. 6 is a circuit diagram of the voltage smoothing circuit pertaining to modification (a) of the first embodiment and shows a case where an auxiliary resistor is connected in parallel to first and second smoothing capacitors;

FIG. 7 is a circuit diagram of a voltage smoothing circuit pertaining to modification (b) of the first embodiment and shows a case where the positions of a Zener diode and a balancing resistor are the opposite of the positions shown in FIG. 2 ;

FIG. 8 is a circuit diagram of a voltage smoothing circuit pertaining to a second embodiment;

FIG. 9 is a circuit diagram of a voltage smoothing circuit pertaining to a third embodiment;

FIG. 10 is a circuit diagram of the voltage smoothing circuit pertaining to the third embodiment and shows flows of currents used when deciding the resistance values of balancing resistors;

FIG. 11 is a circuit diagram of the voltage smoothing circuit pertaining to the third embodiment and shows flows of currents used when deciding the resistance values of the balancing resistors;

FIG. 12 is a circuit diagram of a voltage smoothing circuit pertaining to modification (a) of the third embodiment and shows a case where an auxiliary resistor is connected in parallel to a Zener diode;

FIG. 13 is a circuit diagram of the voltage smoothing circuit pertaining to modification (a) of the third embodiment and shows a case where an auxiliary resistor is connected in parallel to the Zener diode and a second smoothing capacitor;

FIG. 14 is a circuit diagram of a voltage smoothing circuit pertaining to modification (b) of the third embodiment and shows a case where the positions of a Zener diode and balancing resistors are the opposite of the positions shown in FIG. 9 ;

FIG. 15 is a circuit diagram of a voltage smoothing circuit pertaining to a fourth embodiment;

FIG. 16 is a circuit diagram of a voltage smoothing circuit pertaining to a fifth embodiment and shows flows of currents used when deciding the resistance values of balancing resistors;

FIG. 17 is a circuit diagram of the voltage smoothing circuit pertaining to the fifth embodiment and shows flows of currents used when deciding the resistance values of the balancing resistors;

FIG. 18 is a circuit diagram of a voltage smoothing circuit pertaining to a sixth embodiment;

FIG. 19 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where a voltage equal to or greater than a first Zener voltage has been applied to both ends of a first smoothing capacitor in the sixth embodiment;

FIG. 20 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where a voltage equal to or greater than a second Zener voltage has been applied to both ends of a second smoothing capacitor in the sixth embodiment;

FIG. 21 is a circuit diagram of a voltage smoothing circuit pertaining to modification of the sixth embodiment;

FIG. 22 is a diagram showing paths of currents flowing in a voltage smoothing circuit in a case where a balance between the end-to-end voltage of a first smoothing capacitor and the end-to-end voltage of a second smoothing capacitor is maintained in a seventh embodiment;

FIG. 23 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where the end-to-end voltage of the first smoothing capacitor is larger than the end-to-end voltage of the second smoothing capacitor in the seventh embodiment;

FIG. 24 is a diagram showing paths of currents flowing in the voltage smoothing circuit in a case where the end-to-end voltage of the first smoothing capacitor is smaller than the end-to-end voltage of the second smoothing capacitor in the seventh embodiment; and

FIG. 25 is a circuit diagram of a voltage smoothing circuit pertaining to modification (a) of the seventh embodiment.

A voltage smoothing circuit pertaining to the present invention will be described in detail below using the drawings.

First Embodiment

(1) Brief

FIG. 1 is a configuration diagram of a motor driver 1 that is equipped with a voltage smoothing circuit 14 pertaining to the present embodiment. The motor driver 1 is utilized for driving a compressor-use motor 52 that is a drive source of a compressor of an air conditioning apparatus, for example. Examples of types of the compressor-use motor 52 include a 3-phase brushless DC motor.

The motor driver 1 is mainly equipped with a power supply portion 13 , the voltage smoothing circuit 14 , an inverter portion 15 , and a current detecting portion 16 . The power supply portion 13 has a diode bridge 11 and a reactor 12 , and the diode bridge 11 , the voltage smoothing circuit 14 , the inverter portion 15 , and the current detecting portion 16 are configured on a single printed board P 1 . The reactor 12 is externally connected to the printed board P 1 via interfaces IF 4 and IF 5 of the printed board P 1 .

The diode bridge 11 is configured by six diodes D 1 a , D 1 b , D 1 c , D 1 d , D 1 e , and D 1 f The diodes D 1 a and D 1 b , D 1 e and D 1 d , and D 1 e and D 1 f are respectively connected in series to each other, and these are connected so as to become in parallel with each other. Points-of-connection between the diodes D 1 a and D 1 b , D 1 e and D 1 d , and D 1 e and D 1 f that are connected in series are connected to a 3-phase commercial power supply 51 via interfaces IF 1 , IF 2 , and IF 3 on the printed board P 1 . An AC voltage outputted from the commercial power supply 51 is rectified by the diode bridge 11 . The reactor 12 is connected in series on a power supply line L 1 to which the cathodes of the diodes D 1 a , D 1 c , and D 1 e are connected. The voltage rectified by the diode bridge 11 comes to have a waveform close to a DC voltage because of the reactor 12 and is applied to the voltage smoothing circuit 14 . The anodes of the diodes D 1 b , D 1 d , and D 1 f are connected to a GND line L 2 .

The voltage smoothing circuit 14 is a circuit for smoothing the voltage outputted from the power supply portion 13 and is placed between the power supply portion 13 and the inverter portion 15 . Details of the voltage smoothing circuit 14 wilt be described later.

The inverter portion 15 is configured by insulated gate bipolar transistors Q 5 a , Q 5 b , Q 5 c , Q 5 d , Q 5 e , and Q 5 f (below, simply called “transistors”) and reflux-use diodes D 5 a , D 5 b , D 5 c , D 5 d , D 5 e , and D 5 f . The transistors Q 5 a and Q 5 b , Q 5 c and Q 5 d , and Q 5 e and Q 5 f are connected in series between the power supply line L 1 and the GND line L 2 . Points-of-connection NU, NV, and NW between the transistors Q 5 a and Q 5 b , Q 5 c and Q 5 d , and Q 5 e and Q 5 f are connected to the compressor-use motor 52 via interfaces IF 6 , IF 7 , and IF 8 on the printed board P 1 . The diodes D 5 a to D 5 f have the characteristic that they conduct current in a case where a reverse voltage has been applied to the transistors Q 5 a to Q 5 f , and the diodes D 5 a to D 5 f are connected in parallel to the transistors Q 5 a to Q 5 f . The inverter portion 15 having this configuration generates a drive voltage for driving the compressor-use motor 52 when the transistors Q 5 a to Q 5 f are switched ON and OFF on the basis of a gate control voltage sent from a microcomputer (not shown in the drawings). The compressor-use motor 52 is driven to rotate by the drive voltage.

The current detecting portion 16 detects a motor current that has flowed to the compressor-use motor 52 . The current detecting portion 16 is mainly configured by a shunt resistor, which is connected in series on the GND line L 2 between the voltage smoothing circuit 14 and the inverter portion 15 , and a microcomputer (not shown in the drawings), which computes the motor current on the basis of the end-to-end voltage of the shunt resistor.

(2) Configuration of Voltage Smoothing Circuit

Next, the configuration of the voltage smoothing circuit 14 pertaining to the present embodiment will be specifically described using FIGS. 2 to 4 . In FIGS. 2 to 4 , for the sake of simplifying the drawings, only the power supply portion 13 and the voltage smoothing circuit 14 are extracted from FIG. 1 and shown. Further, as has already been described, because the voltage from the commercial power supply 51 that has come to have a waveform close to a DC voltage is applied by the power supply portion 13 via the power supply line L 1 to the voltage smoothing circuit 14 , the power supply portion 13 is represented as a “DC power supply”. In FIGS. 2 to 4 , the value of the DC voltage outputted from the power supply portion 13 is represented as “Vdc”. Supposing, thr example, that the AC voltage outputted from the commercial power supply 51 is a voltage within a range whose upper limit is about 470 V±10% and whose lower limit is about 380 V−10%, the voltage Vdc can be a voltage within a range of about 731 V to about 483 V.

The voltage smoothing circuit 14 is equipped with a first smoothing capacitor C 1 , a second smoothing capacitor C 2 , a balancing resistor R 3 (which corresponds to a first balancing resistor), and a Zener diode RZ 4 (which corresponds to a second conduction regulating portion).

(2-1) First Smoothing Capacitor and Second Smoothing Capacitor

The first smoothing capacitor C 1 and the second smoothing capacitor C 2 are connected in series to each other and are connected in parallel to the power supply portion 13 . Specifically, one end of the first smoothing capacitor C 1 is connected to the power supply line L 1 , and one end of the second smoothing capacitor C 2 is connected to the GND line L 2 . The other ends of the first smoothing capacitor C 1 and the second smoothing capacitor C 2 are connected to each other. The first smoothing capacitor C 1 and the second smoothing capacitor C 2 further smooth the voltage outputted from the power supply portion 13 .

Here, generally, the equivalent circuit of a capacitor is configured by a capacitance component and a resistance component (below, called an “internal resistor”) that are connected in parallel to each other and also by an inductance component that is connected in series to these components. In FIG. 2 , for the sake of simplifying the description, the inductance component is omitted and the first and second smoothing capacitors C 1 and C 2 are respectively represented by internal resistors R 1 a and R 2 a and capacitance components C 1 a and C 2 a . The internal resistor R 1 a and the capacitance component C 1 a of the first smoothing capacitor C 1 are connected in parallel to each other. The internal resistor R 2 a and the capacitance component C 2 a of the second smoothing capacitor C 2 are connected in parallel to each other.

The first smoothing capacitor C 1 and the second smoothing capacitor C 2 have the same capacitance values; as an example, 1920 μC and 2880 μC can be given. Supposing that the capacitance values of the smoothing capacitors C 1 and C 2 are 2880 μC, for example, values in a range whose upper limit is 1075 kΩ and whose lower limit is 420 kΩ can be given for the resistance values of the internal resistors R 1 a and R 2 a . Moreover, supposing that the voltage Vdc is “718 V”, for example, smoothing capacitors whose rated voltages Vrt 1 and Vrt 2 are about 400 V to about 450 V, for example, are utilized for the first smoothing capacitor C 1 and the second smoothing capacitor C 2 . That is, it can be said that the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 are values that are around about 1.1 times to about 1.3 times about one-half of the value of the voltage Vdc. Further, examples of types of capacitors that may be used for the first smoothing capacitor C 1 and the second smoothing capacitor C 2 include electrolytic capacitors, tantalum capacitors, ceramic capacitors, and so forth, but in the present embodiment, electrolytic capacitors are used for the first smoothing capacitor C 1 and the second smoothing capacitor C 2 .

(2-2) Balancing Resistor

The balancing resistor R 3 is connected on a current path I 3 in parallel with the first smoothing capacitor C 1 . Specifically, one end of the current path I 3 is connected to the power supply line L 1 , the other end of the current path I 3 is connected to a point-of-connection s 1 between the first smoothing capacitor C 1 and the second smoothing capacitor C 2 , and the balancing resistor R 3 is connected in series on this current path I 3 .

The balancing resistor R 3 has a resistance value that is smaller than the value of the internal resistor R 1 a of the first smoothing capacitor C 1 . This is to control the amount of current flowing to the first smoothing capacitor C 1 . That is, this is because the amount of current flowing to the balancing resistor R 3 becomes larger than the amount of current flowing to the internal resistor R 1 a of the first smoothing capacitor C 1 , and the more the resistance value of the balancing resistor R 3 is decided to be a small value, the more the controllability of the amount of current flowing to the first smoothing capacitor C 1 improves.

Moreover, the resistance value of the balancing resistor R 3 pertaining to the present embodiment is decided in such a way as to not only satisfy the above-described condition (that is, the value of the balancing resistor R 3 is smaller than the value of the internal resistor R 1 a of the first smoothing capacitor C 1 ) but also satisfy other conditions, but a detailed method of deciding the resistance value of the balancing resistor R 3 will be described later.

(2-3) Zener Diode

The Zener diode RZ 4 is connected on a current path I 4 in parallel with the second smoothing capacitor C 2 to which the balancing resistor R 3 is not connected in parallel. More specifically, the anode of the Zener diode RZ 4 is connected to the GND line L 2 side and the cathode of the Zener diode RZ 4 is connected to the point-of-connection s 1 side between the first smoothing capacitor C 1 and the second smoothing capacitor C 2 ; because of this, the current path I 4 is formed.

The voltage applied to the Zener diode RZ 4 is, terms of the circuit configuration, equal to an end-to-end voltage V 2 (which corresponds to a second end-to-end voltage) of the second smoothing capacitor C 2 connected in parallel to the Zener diode RZ 4 . Thus, if the end-to-end voltage V 2 is lower than a Zener voltage Vr 4 (which corresponds to a second predetermined voltage) (V 2 <Vr 4 ), a voltage less than the Zener voltage Vr 4 is applied to the Zener diode RZ 4 and the Zener diode RZ 4 does not operate (see FIG. 3 ). Conversely, if the end-to-end voltage V 2 is equal to or greater than the Zener voltage Vr 4 (V 2 ≧Vr 4 ), a voltage equal to or greater than the Zener voltage Vr 4 is applied to the Zener diode RZ 4 , current flows in one direction on the current path I 4 including the Zener diode RZ 4 , and the voltage between the anode and the cathode of the Zener diode RZ 4 (below, called an “inter-terminal voltage”) is maintained at the Zener voltage Vr 4 (see FIG. 4 ). The one direction referred to here is a direction from the cathode to the anode of the Zener diode RZ 4 .

Here, in the present embodiment, the Zener voltage Vr 4 is decided in such a way as to become lower than the rated voltage Vrt 2 of the second smoothing capacitor C 2 (Vr 4 <Vrt 2 ). This is so that when a voltage equal to or greater than the Zener voltage Vr 4 is applied to the Zener diode RZ 4 , the characteristic whereby the end-to-end voltage V 2 of the second smoothing capacitor C 2 is clipped to the Zener voltage Vr 4 by the operation of the Zener diode RZ 4 is utilized to prevent the end-to-end voltage V 2 of the second smoothing capacitor C 2 that is clipped from becoming equal to or greater than the rated voltage Vrt 2 of that capacitor C 2 . Moreover, the Zener voltage Vr 4 may also be decided on the basis of the voltage Vdc from the power supply portion 13 . As an example, supposing that the rated voltage Vrt 2 of the second smoothing capacitor C 2 is 400 V, for example, and the voltage Vdc is 718 V, the Zener voltage Vr 4 is decided as “376 V” in such a way as to become smaller than the rated voltage of the second smoothing capacitor C 2 and equal to or less than the voltage Vdc and larger than one-half of the voltage Vdc. Because of this, when a voltage equal to or greater than 376 V is applied to the Zener diode RZ 4 due to, for example, variations between the internal resistors R 1 a and R 2 a of the first smoothing capacitor C 1 and the second smoothing capacitor C 2 , the Zener diode RZ 4 operates and the end-to-end voltage V 2 of the second smoothing capacitor C 2 is clipped to 376 V. In this case, a voltage obtained by subtracting the end-to-end voltage V 2 of the second smoothing capacitor C 2 from the voltage Vdc of the power supply portion 13 (V 1 =Vdc−V 2 , and specifically 718 V−376 V=342 V) becomes an end-to-end voltage V 1 of the first smoothing capacitor C 1 .

Further, the value of the Zener voltage Vr 4 may also be decided considering not only the rated voltage Vrt 2 of the second smoothing capacitor C 2 , the voltage Vdc from the power supply portion 13 , and so forth but also the rated voltage Vrt 1 of the first smoothing capacitor C 1 , the value of the balancing resistor R 3 , and so forth. An example where the Zener voltage Vr 4 is decided also considering the rated voltage Vrt 2 , the value of the balancing resistor R 3 , and so forth will be described below together with a method of deciding the resistance value of the balancing resistor R 3 .

(3) Method of Deciding Resistance Value of Balancing Resistor and Zener Voltage

First, a case will be considered where the Zener diode RZ 4 is switched ON by a voltage equal to or greater than the Zener voltage Vr 4 being applied to the Zener diode RZ 4 and current flows in the one direction on the current path I 4 . In this case, as described above, the end-to-end voltage V 2 of the second smoothing capacitor C 2 is held at a constant voltage (the Zener voltage Vr 4 ).

Therefore, the balancing resistor R 3 pertaining to the present embodiment is decided in such a way as to satisfy a condition where the end-to-end voltage V 1 (which corresponds to a first end-to-end voltage) of the first smoothing capacitor C 1 becomes lower than the rated voltage Vrt 1 of that capacitor C 1 (V 1 <Vrt 1 ) and the end-to-end voltage V 2 of the second smoothing capacitor C 2 becomes lower than the rated voltage Vrt 2 of that capacitor C 2 (V 2 <Vrt 2 ). Because of this, even if the end-to-end voltage V 2 of the second smoothing capacitor C 2 rises, the value of that end-to-end voltage V 2 does not exceed the rated voltage Vrt 2 of that capacitor C 2 , and in particular a rise in the end-to-end voltage V 2 equal to or greater than the rated voltage Vrt 2 is avoided because of the Zener diode RZ 4 . Additionally, although there is the potential for the end-to-end voltage V 1 of the first smoothing capacitor C 1 to rise due to a rise in the voltage Vdc from the power supply portion 13 even while the end-to-end voltage V 2 of the second smoothing capacitor C 2 is being clipped to the Zener voltage Vr 4 (V 2 ≈Vr 4 ), the value of the balancing resistor R 3 is decided in such a way as to satisfy the condition described above, so a voltage equal to or greater than the rated voltage Vrt 1 can be prevented from being applied to the first smoothing capacitor C 1 .

This will be specifically described below. In terms of the circuit configuration of the voltage smoothing circuit 14 , the inter-terminal voltage of the Zener diode RZ 4 is always equal to the end-to-end voltage V 2 of the second smoothing capacitor C 2 . Additionally, the voltage Vdc from the power supply portion 13 is equal to the sum of the end-to-end voltage V 1 of the first smoothing capacitor C 1 and the end-to-end voltage V 2 of the second smoothing capacitor C 2 (see the following equation (1)).

<Equation 1>

Vdc=V 1 +V 2  (1)

From the above equation (1) and the relationship between the end-to-end voltage V 2 and the inter-terminal voltage of the Zener diode RZ 4 , the end-to-end voltage V 2 of the second smoothing capacitor C 2 takes a maximum value in a case where the internal resistor R 1 a of the first smoothing capacitor C 1 and the balancing resistor R 3 are both minimum values and the internal resistor R 2 a of the second smoothing capacitor C 2 is a maximum value. Thus, as a first condition for deciding the Zener voltage Vr 4 and the balancing resistor R 3 , the maximum value of the end-to-end voltage V 2 becoming lower than the rated voltage Vrt 2 of the second smoothing capacitor can be given (see the following equation (2)).

<Equation 2>

V 2(max)≈ Vr 4 <Vrt 2  (2)

“V 2 (max)” represents the maximum value of the end-to-end voltage V 2 of the second smoothing capacitor C 2 .

Conversely, the end-to-end voltage V 2 of the second smoothing capacitor C 2 takes a minimum value in a case where the internal resistor R 1 a of the first smoothing capacitor C 1 and the balancing resistor R 3 are both maximum values and the internal resistor R 2 a of the second smoothing capacitor C 2 is a minimum value. At a time when the end-to-end voltage V 2 of the second smoothing capacitor C 2 takes a minimum value, the end-to-end voltage V 1 of the first smoothing capacitor C 1 takes a maximum value. Therefore, as a second condition for deciding the Zener voltage Vr 4 and the balancing resistor R 3 , the maximum value of the end-to-end voltage V 1 of the first smoothing capacitor C 1 becoming lower than the rated voltage Vrt 1 of the first smoothing capacitor C 1 can be given (see the following equation (3)).

<Equation 3>

V 1(max)= Vdc (max)− V 2(min)< Vrt 1  (3)

“V 1 (max)” represents the maximum value of the end-to-end voltage V 1 of the first smoothing capacitor C 1 , and “Vdc(max)” represents the maximum value of the voltage Vdc from the power supply portion 13 . “V 2 (min)” represents the minimum value of the end-to-end voltage V 2 of the second smoothing capacitor C 2 .

The Zener voltage Vr 4 and the resistance value of the balancing resistor R 3 are decided on the basis of the above equations (2) and (3) and in such a way that the resistance value of the balancing resistor R 3 becomes smaller than the internal resistor R 1 a of the first smoothing capacitor C 1 . The internal resistors R 1 a and R 2 a and the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 are values unique to capacitors and are known values, and the range of the value of the voltage Vdc from the power supply portion 13 is decided, so what becomes variables in the above equations (2) and (3) are the Zener voltage Vr 4 and the value of the balancing resistor R 3 . For that reason, the Zener voltage Vr 4 and the resistance value of the balancing resistor R 3 can be decided from the above equations (2) and (3) and the conditions of the balancing resistor R 3 and the internal resistor Ma.

The resistance value of the balancing resistor R 3 that has been decided by the method described above may also be adjusted considering the lower limit value of variations between the internal resistors R 1 a and R 2 a of the smoothing capacitors C 1 and C 2 . Further, considering also power loss in the balancing resistor R 3 and the Zener diode RZ 4 , it is preferred that the resistance value of the balancing resistor R 3 be decided in such a way that that power loss becomes a target power loss amount.

Here, as an example of the resistance value of the balancing resistor R 3 that has been decided by the method described above, the resistance value of the balancing resistor R 3 may be “350 kΩ” in a case supposing that the internal resistor R 1 a of the first smoothing capacitor C 1 is “1075 kΩ”. In this way, the voltage applied to the balancing resistor R 3 pertaining to the present embodiment can be made significantly lower compared to the value of the balancing resistor in the conventional techniques, so loss can be made smaller and a relatively small-sized resistor like a chip resistor can be used. In contrast, in the conventional techniques, the balancing resistor had a relative large value, like “3 series of 5.6 kΩ (10 W)”, for example, so using a cement resistor whose dimensions are large has been predominant.

(4) Operation of Voltage Smoothing Circuit

Next, the operation of the voltage smoothing circuit 14 will be described using FIGS. 3 and 4 .

First, the same capacitors are used for the smoothing capacitors C 1 and C 2 , on ideally there should be substantially no variations between the internal resistors R 1 a and R 2 a or any variations should be small (R 1 a ≈R 2 a ), and thus the end-to-end voltage V 1 of the first smoothing capacitor C 1 and the end-to-end voltage V 2 of the second smoothing capacitor C 2 should be in a state in which they become equal to or less than the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 , respectively, and become substantially equal. In this ideal state, the end-to-end voltage V 2 of the second smoothing capacitor C 2 —that is, the inter-terminal voltage of the Zener diode RZ 4 —becomes lower than the Zener voltage Vr 4 (V 2 <Vr 4 ) and current does not flow to the current path I 4 . In this ideal state, as shown in FIG. 3 , current flows from the power supply portion 13 via the power supply line L 1 and branches to the internal resistor R 1 a side of the first smoothing capacitor C 1 and the current path I 3 side, the branch currents merge at the point-of-connection s 1 , and thereafter the current flows via the internal resistor R 2 a of the second smoothing capacitor C 2 to the GND line L 2 . In this case, the first and second smoothing capacitors C 1 and C 2 take a state where a balance between their end-to-end voltages is maintained.

However, if there are variations between the internal resistor R 1 a of the first smoothing capacitor C 1 and the internal resistor R 2 a of the second smoothing capacitor C 2 , the balance between the end-to-end voltages V 1 and V 2 of the smoothing capacitors C 1 and C 2 becomes disrupted and a magnitude relation arises between the end-to-end voltages V 1 and V 2 . In particular, depending on the values of the end-to-end voltages V 1 and V 2 , there is also the concern that they will exceed the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 , so in the present embodiment, considering such variations between the internal resistors R 1 a and R 2 a , the Zener voltage Vr 4 and the value of the balancing resistor R 3 are decided in such a way that the end-to-end voltages V 1 and V 2 never exceed the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 .

If the end-to-end voltage V 2 of the second smoothing capacitor C 2 —that is, the inter-terminal voltage of the Zener diode RZ 4 —is equal to or greater than the Zener voltage Vr 4 , the Zener diode RZ 4 operates as shown in FIG. 4 . When this happens, the end-to-end voltage V 2 is clipped to a constant voltage—that is, the Zener voltage Vr 4 . As indicated by the bold arrow in FIG. 4 , part of the sum of the currents that have flowed on the internal resistor R 1 a of the first smoothing capacitor C 1 and the balancing resistor R 3 flows on the current path I 4 . Between the current path I 4 and the second smoothing capacitor C 2 side, impedance is lower on the current path I 4 side, so much of the current that has flowed on the internal resistor R 1 a of the first smoothing capacitor C 1 and the balancing resistor R 3 flows through the current path I 4 side. At this time, the Zener voltage Vr 4 is decided in such a way as to become equal to or less than the rated voltage Vrt 2 of the second smoothing capacitor C 2 , so a voltage equal to or greater than the rated voltage Vrt 2 can be prevented from being applied to the second smoothing capacitor C 2 . Further, the balancing resistor R 3 is decided in such a way that the end-to-end voltages V 1 and V 2 become equal to or less than the rated voltages Vrt 1 and Vrt 2 of the smoothing capacitors C 1 and C 2 , so, for example, even if the voltage Vdc rises in a state where the end-to-end voltage V 2 has been clipped to the Zener voltage Vr 4 and the end-to-end voltage V 1 rises, the end-to-end voltage V 1 does not exceed the rated voltage Vrt 1 of the first smoothing capacitor C 1 .

(5) Characteristics

(A)

In the voltage smoothing circuit 14 pertaining to the present embodiment, when a voltage equal to or greater than the Zener voltage Vr 4 that is a second predetermined voltage is applied to the Zener diode RZ 4 that is a second conduction regulating portion, currents flow from the power supply portion 13 to the internal resistor a of the first smoothing capacitor C 1 and the first balancing resistor R 3 . The currents thereafter flow mainly on the current path I 4 (that is, the Zener diode RZ 4 ) whose impedance is lower than that on the internal resistor R 2 a of the second smoothing capacitor C 2 . Consequently, the end-to-end voltage V 2 of the second smoothing capacitor C 2 can be lowered with a simple configuration regardless of variations between the internal resistors R 1 a and R 2 a of the smoothing capacitors C 1 and C 2 , and a voltage equal to or greater than the rated voltage Vrt 2 can be prevented from being applied to the second smoothing capacitor C 2 .

(B)

In particular, when a voltage equal hour greater than the Zener voltage Vr 4 is applied to the Zener diode RZ 4 , the Zener diode RZ 4 operates. Current flows in the Zener diode RZ 4 in a direction heading from the point-of-connection s 1 to the GND line L 2 , and the end-to-end voltage V 2 of the second smoothing capacitor C 2 is clipped to the Zener voltage Vr 4 . The Zener voltage Vr 4 is lower than the rated voltage Vrt 2 of the second smoothing capacitor C 2 , so the end-to-end voltage V 2 of the second smoothing capacitor C 2 connected in parallel to the Zener diode RZ 4 is clipped to the Zener voltage Vr 4 that is lower than the rated voltage Vrt 2 of the second smoothing capacitor C 2 . Consequently, with a simple configuration a voltage equal to or greater than the rated voltage Vrt 2 can be reliably prevented from being applied to the second smoothing capacitor C 2 to which the Zener diode RZ 4 is connected in parallel.

(C)

Incidentally, as described above, when the voltage Vdc from the power supply portion 13 rises in a state where the end-to-end voltage V 2 of the second smoothing capacitor C 2 is being clipped to the Zener voltage Vr 4 , in terms of the circuit configuration there is the concern that the end-to-end voltage V 1 of the first smoothing capacitor C 1 will rise and end up exceeding the rated voltage Vrt 1 of the first smoothing capacitor C 1 .

However, in this voltage smoothing circuit 14 , the resistance value of the balancing resistor R 3 is decided in such a way that the end-to-end voltage V 1 of the first smoothing capacitor C 1 becomes lower than the rated voltage Vrt 1 of that capacitor C 1 (V 1 <Vrt 1 ) and the end-to-end voltage V 2 of the second smoothing capacitor C 2 becomes lower than the rated voltage Vrt 2 of that capacitor C 2 (V 2 <Vrt 2 ). Additionally, the Zener voltage Vr 4 is substantially the same as the end-to-end voltage V 2 of the second smoothing capacitor C 2 . Consequently, even if the end-to-end voltage V 1 rises, the end-to-end voltage V 1 does not exceed the rate age Vrt 1 of the first smoothing capacitor C 1 .

(D)

Further, according to the voltage smoothing circuit 14 pertaining to the present embodiment, the amount of current flowing to the balancing resistor R 3 becomes larger than the amount of current flowing to the internal resistor R 1 a of the first smoothing capacitor C 1 , so the amount of current flowing to the first smoothing capacitor C 1 can be controlled.

(6) Modifications

(a)

In the present embodiment, a case where the voltage smoothing circuit 14 has the configuration shown in FIGS. 2 to 4 has been described. However, the voltage smoothing circuit 14 may also have the configuration shown in FIG. 5 . A voltage smoothing circuit 14 ′ in FIG. 5 is further equipped with an auxiliary resistor R 5 (which corresponds to a first auxiliary resistor) in addition to the configuration of the voltage smoothing circuit 14 already described. The auxiliary resistor R 5 is connected in parallel to both ends of the Zener diode RZ 4 .

According to the voltage smoothing circuit 14 ′ in FIG. 5 , when the end-to-end voltage V 2 of the second smoothing capacitor C 2 becomes equal to or greater than the Zener voltage Vr 4 (V 2 ≧Vr 4 ), the current flowing on the current path I 4 branches and flows to the Zener diode RZ 4 and the auxiliary resistor R 5 . Because of this, the amount of current flowing to the Zener diode RZ 4 can be reduced, so the operating voltage and the rated power of the Zener diode RZ 4 can be set low, and a diode whose rated current is relatively small can be used for the Zener diode RZ 4 . Consequently, costs pertaining to the voltage smoothing circuit 14 ′ can be reduced (in particular, the cost of the Zener diode RZ 4 can be cut).

Further, the auxiliary resistor R 5 can also function as a discharge circuit of the first smoothing capacitor C 1 and the second smoothing capacitor C 2 at the time of power shutdown of the motor driver 1 . Consequently, it is not necessary to separately dispose a discharge circuit of the first smoothing capacitor C 1 and the second smoothing capacitor C 2 .

Further, the auxiliary resistor is not limited to FIG. 5 and may also be disposed like in FIG. 6 (which corresponds to a second auxiliary resistor). An auxiliary resistor R 6 pertaining to FIG. 6 is connected in parallel to the first and second smoothing capacitors C 1 and C 2 connected in series to each other. In this configuration also, the same effects as FIG. 5 can be provided.

(b)

In the present embodiment, a case where, as shown in FIG. 2 to FIG. 4 , the balancing resistor R 3 is disposed on the power supply line L 1 side and the Zener diode RZ 4 is disposed on the GND line L 2 side with respect to the point-of-connection s 1 between the first and second smoothing capacitors C 1 and C 2 has been described. However, the positions where the balancing resistor R 3 and the Zener diode RZ 4 are disposed are not limited to FIGS. 2 to 4 and may also, as shown in FIG. 7 , be mutually opposite with respect to the point-of-connection s 1 . In a voltage smoothing circuit 14 ″ in FIG. 7 , a Zener diode RZ 4 ′ is disposed on the power supply line L 1 side and a balancing resistor R 3 ′ is disposed on the GND line L 2 side with respect to the point-of-connection s 1 between the first and second smoothing capacitors C 1 and C 2 .

That is, it suffices for the Zener diode to be disposed in such a way as to become in parallel with either one of the smoothing capacitors C 1 and C 2 and for the balancing resistor to be disposed in such a way as to become in parallel with the other of the smoothing capacitors C 1 and C 2 .

Further, in this case also, an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the Zener diode RZ 4 ′, or an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the first and second smoothing capacitors connected in series to each other.

Second Embodiment

In the first embodiment, a case where the resistance value of the balancing resistor R 3 is decided as described in “(3) Method of Deciding Resistance Value of Balancing Resistor and Zener Voltage” was described. In the present embodiment, a case where the resistance value of the balancing resistor R 3 is decided by a method differing from the above deciding method will be described.

(1) Configuration of Voltage Smoothing Circuit

FIG. 8 is a circuit diagram of a voltage smoothing circuit 114 pertaining to the present embodiment. The configuration of the voltage smoothing circuit 114 is the same as that of the voltage smoothing circuit 14 of the above-described first embodiment except that the method of deciding the resistance value of the balancing resistor R 3 differs. In the present embodiment, configural elements other than the configural elements configuring the voltage smoothing circuit 114 are the same as those in the first embodiment, so reference signs that are the same as those in the first embodiment will be given to configural elements (specifically, the power supply portion 13 ) other than the configural elements of the voltage smoothing circuit 114 .

That is, the voltage smoothing circuit 114 is equipped with a first smoothing capacitor C 11 , a second smoothing capacitor C 12 , a balancing resistor R 13 (which corresponds to a first balancing resistor), and a Zener diode RZ 14 (which corresponds to a second conduction regulating portion). The first smoothing capacitor C 11 and the second smoothing capacitor C 12 are connected in series to each other and are connected in parallel to the power supply portion 13 . The first smoothing capacitor C 11 and the second smoothing capacitor C 12 are respectively configured by capacitance elements C 11 a and C 12 a and internal resistors R 11 a and R 12 a . The balancing resistor R 13 is connected on a current path I 13 in parallel with the first smoothing capacitor. The Zener diode RZ 14 is connected on a current path I 14 in parallel with the second smoothing capacitor C 12 . The Zener diode RZ 14 conducts current in one direction on the current path I 14 in a case where a voltage equal to or greater than a Zener voltage Vr 14 (which corresponds to a second predetermined voltage) that is lower than a rated voltage Vrt 12 of the second smoothing capacitor C 12 has been applied and maintains its inter-terminal voltage at the Zener voltage Vr 14 .

(2) Method of Deciding Resistance Value of Balancing Resistor

In the method of deciding the resistance value of the balancing resistor R 3 pertaining to the first embodiment, it was assumed that a voltage equal to or greater than the Zener voltage Vr 4 is applied to the first smoothing capacitor C 1 , the Zener diode RZ 4 operates, and current flows in one direction on the current path I 4 . However, due to factors such as the difference between the resistance values of the internal resistors R 1 a and R 2 a of the smoothing capacitors C 1 and C 2 being larger than a predetermined difference due to variations between those internal resistors R 1 a and R 2 a or the voltage Vdc from the power supply portion 13 being low, depending on the case there is the concern that a voltage equal to or greater than the Zener voltage Vr 4 will not be applied to the Zener diode RZ 4 . The Zener diode RZ 4 not operating means that a voltage equal to or greater than the rated voltage Vrt 2 is not applied to the second smoothing capacitor C 2 , and there is no problem regarding the second smoothing capacitor C 2 . However, the potential for the end-to-end voltage V 1 of the first smoothing capacitor C 1 to end up becoming equal to or greater than the rated voltage Vrt 1 cannot be denied.

Therefore, the balancing resistor R 13 pertaining to the present embodiment is decided to be a resistance value that is smaller than the value of the internal resistor R 11 a of the first smoothing capacitor C 11 and is decided in such a way that an end-to-end voltage V 11 of the first smoothing capacitor C 11 becomes equal to or less than an end-to-end voltage V 12 of the second smoothing capacitor C 12 (V 11 ≦V 12 ) and is decided in such a way as to satisfy a condition where the end-to-end voltage V 12 of the second smoothing capacitor C 12 is lower than the rated voltage Vrt 12 of the second smoothing capacitor C 12 (V 12 <Vrt 12 ). That is, the balancing resistor R 13 pertaining to the present embodiment is decided in such a way as to satisfy relative conditions of the end-to-end voltage V 11 of the first smoothing capacitor C 11 and the end-to-end voltage V 12 of the second smoothing capacitor C 12 .

This will be specifically described below. If the Zener diode RZ 14 does not operate, in terms of the circuit configuration of the voltage smoothing circuit 114 the end-to-end voltages V 11 and V 12 of the smoothing capacitors C 11 and C 12 become values obtained by dividing the voltage Vdc supplied from the power supply portion 13 by the combined resistance value of the balancing resistor R 13 and the internal resistor R 11 a of the first smoothing capacitor C 11 (that is, the combined resistance value of the resistors R 13 and R 11 a connected in parallel) and by the resistance value of the internal resistor R 12 a of the second smoothing capacitor C 12 (see the following equations (4) and (5)).

In the above equations (4) and (5), reference signs are used as is for the resistance values of the resistors R 11 a , R 12 a , and R 13 .

In this case also, the Zener voltage Vr 14 of the Zener diode RZ 14 is decided to be a value that is smaller than the rated voltage Vrt 12 of the second smoothing capacitor C 12 . Consequently, the end-to-end voltage V 12 of the second smoothing capacitor C 12 to which the Zener diode RZ 14 is connected in parallel is protected by the Zener diode RZ 14 . That is, in the present embodiment, a voltage equal to or greater than the Zener voltage Vr 14 is not applied to the Zener diode RZ 14 and the Zener diode RZ 14 does not operate, so the end-to-end voltage V 12 of the second smoothing capacitor C 12 always becomes equal to or less than the Zener voltage Vr 14 , and a voltage equal to or greater than the rated voltage Vrt 12 of the second smoothing capacitor C 12 is not applied to that capacitor C 12 .

Otherwise, the end-to-end voltage V 11 of the first smoothing capacitor C 11 to which the Zener diode RZ 14 is not connected in parallel is represented by a value decided by the division of the voltage Vdc as described above—that is, a value obtained by subtracting the end-to-end voltage V 12 of the second smoothing capacitor C 12 from the voltage Vdc (V 11 =Vdc−V 12 )—so there is the concern that the end-to-end voltage of the first smoothing capacitor C 11 will end up exceeding the rated voltage Vrt 11 of the capacitor C 11 because of the value of the voltage Vdc or the values of the internal resistors R 11 a and R 12 a.

In order to prevent this, the balancing resistor R 13 is decided in such a way as to satisfy the condition of the following equation (6).

In the above equation (6), “R 13 (max)” represents the maximum value of the resistance value of the balancing resistor R 13 . “R 11 a (max)” represents the maximum value of the resistance value of the internal resistor R 11 a of the first smoothing capacitor C 11 . “R 12 a (min)” represents the minimum value of the resistance value of the internal resistor R 12 a of the second smoothing capacitor C 12 . In the above equation (6), the reason the minimum value is utilized for the internal resistor R 12 a of the second smoothing capacitor C 12 and maximum values are utilized for the internal resistor R 11 a of the first smoothing capacitor C 11 and the balancing resistor R 13 is to ensure that the resistance value of the balancing resistor R 13 satisfies the strictest condition in light of the fact that voltage is proportional to resistance value. That is, the larger the resistance values of the internal resistor R 11 a of the first smoothing capacitor C 11 and the balancing resistor R 13 in parallel to each other are, the larger the end-to-end voltage V 11 of the first smoothing capacitor C 11 becomes, and the smaller the resistance value of the internal resistor R 11 a of the second smoothing capacitor C 12 is, the smaller the end-to-end voltage V 12 of the second smoothing capacitor C 12 becomes. Consequently, a case where the Zener diode RIM does not operate and the end-to-end voltage of the first smoothing capacitor C 11 becomes a maximum voltage equal to or greater than the rated voltage Vrt 11 of the capacitor C 11 is considered to be a case where the resistance values of the internal resistor R 11 a of the first smoothing capacitor C 11 and the balancing resistor R 13 become maximum values and the resistance value of the internal resistor R 12 a of the second smoothing capacitor C 12 becomes a minimum value.

By deciding the resistance value of the balancing resistor R 13 in such a way as to satisfy the above equation (6), the following equation (7) is always satisfied.

<Equation 7>

V 11≦ V 12≦ Vr 14< Vrt 12  (7)

That is, the resistance value of the balancing resistor R 13 is decided in such a way that the end-to-end voltage of the first smoothing capacitor C 11 becomes equal to or less than the end-to-end voltage V 12 of the second smoothing capacitor C 12 and the Zener voltage Vr 14 and in such a way that the end-to-end voltage V 12 of the second smoothing capacitor C 12 becomes equal to or less than the rated voltage Vrt 12 of the second smoothing capacitor C 12 . Because of this, even if the end-to-end voltage V 12 of the second smoothing capacitor C 12 does not exceed the Zener voltage Vr 14 and the Zener diode RZ 14 does not operate, the end-to-end voltage V 11 of the first smoothing capacitor C 11 always becomes substantially the same as or lower than the end-to-end voltage V 12 of the second smoothing capacitor C 12 . Consequently, the end-to-end voltage V 11 of the first smoothing capacitor C 11 does not become equal to or greater than the rated voltage Vrt 11 of the first smoothing capacitor C 11 comprising the same capacitor as the second smoothing capacitor C 12 .

(3) Characteristics

(A)

The voltage smoothing circuit 114 pertaining to the present embodiment has the same configuration as that of the voltage smoothing circuit 14 of the first embodiment, but the resistance value of the balancing resistor R 13 is decided in such a way as to satisfy a condition where the end-to-end voltage V 11 of the first smoothing capacitor C 11 to which the Zener diode RZ 14 is not connected in parallel becomes equal to or less than the end-to-end voltage V 12 of the second smoothing capacitor C 12 to which the Zener diode RZ 14 is connected in parallel (V 11 ≦V 12 ) and the end-to-end voltage V 12 of the second smoothing capacitor C 12 is lower than the rated voltage Vrt 12 of that capacitor C 12 (V 12 <Vrt 12 ). Because of this, even in a case where the Zener diode RZ 14 does not operate due to there being a factor such as a voltage equal to or greater than the Zener voltage Vr 14 not being applied to the Zener diode RZ 14 , the end-to-end voltage V 12 of the second smoothing capacitor C 12 connected in parallel to the Zener diode RZ 14 is always kept equal to or less than the Zener voltage Vr 14 that is lower than the rated voltage Vrt 12 of the second smoothing capacitor C 12 . Additionally, the end-to-end voltage V 11 of the first smoothing capacitor C 11 becomes a voltage obtained by subtracting the end-to-end voltage V 12 of the second smoothing capacitor C 12 from the voltage Vdc, but that end-to-end voltage is always kept equal to or less than the Zener voltage Vr 14 of the Zener diode RZ 14 .

Consequently, with a simple configuration the concern that voltages equal to or greater than the rated voltages Vrt 11 and Vrt 12 will be applied to the smoothing capacitors C 11 and C 12 can be avoided.

In a case where there is no concern that the end-to-end voltages of the first and second smoothing capacitors C 11 and C 12 will exceed the rated voltages Vrt 11 and Vrt 12 even considering the range of Vdc and variations between the resistance values of the internal resistors R 11 a and R 12 a , the resistance value of the balancing resistor R 13 does not have to be decided by the deciding method of the present embodiment. In this case, it suffices for the resistance value of the balancing resistor R 13 to be decided by the deciding method of the first embodiment.

(B)

Further, according to the voltage smoothing circuit 114 pertaining to the present embodiment, the balancing resistor R 13 has a value that is smaller than the value of the internal resistor R 11 a of the first smoothing capacitor C 11 , so the amount of current flowing to the internal resistor R 11 a of the first smoothing capacitor C 11 can be controlled.

(4) Modifications

(a)

The method of deciding the resistance value of the balancing resistor R 13 described in the present embodiment can be applied also to a configuration of a voltage smoothing circuit where an auxiliary resistor is disposed like in FIGS. 5 and 6 pertaining to the first embodiment.

(b)

Further, in the method of deciding the resistance value of the balancing resistor R 13 described in the present embodiment, the positions where the Zener diode RZ 14 and the balancing resistor R 13 are disposed may also be mutually opposite with respect to the point-of-connection s 1 like in FIG. 7 pertaining to the first embodiment. That is, it suffices for the Zener diode RZ 14 to be disposed in such a way as to become in parallel with either one of the smoothing capacitors C 11 and C 12 and for the balancing resistor R 13 to be disposed in such a way as to become in parallel with the other of the smoothing capacitors C 11 and C 12 .

Moreover, in this case also, an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the Zener diode, or an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the first and second smoothing capacitors C 11 and C 12 connected in series to each other.

Third Embodiment

In the first and second embodiments, it was described that only the Zener diodes RZ 4 and RZ 14 are connected on the current paths I 4 and I 14 . However, in the voltage smoothing circuits 14 and 114 pertaining to the first and second embodiments, depending on the amount of current flowing on the Zener diodes RZ 4 and RZ 14 , there is a concern about effects resulting from power loss in the Zener diodes RZ 4 and RZ 14 ending up exceeding the rating and heat being emitted to other parts near the Zener diodes RZ 4 and RZ 14 . Therefore, a balancing resistor may also be disposed on the current path.

(1) Configuration of Voltage Smoothing Circuit

FIG. 9 is a circuit diagram of a voltage smoothing circuit 214 pertaining to the present embodiment. Configural elements other than the configural elements configuring the voltage smoothing circuit 214 are the same as those in the first embodiment, on reference signs that are the same as those in the first embodiment will be given to configural elements (specifically, the power supply portion 13 ) other than the configural elements of the voltage smoothing circuit 214 . The voltage smoothing circuit 214 is further equipped with one more balancing resistor in addition to the configurations of the voltage smoothing circuits 14 and 114 pertaining to the first and second embodiments.

That is, the voltage smoothing circuit 214 is equipped with a first smoothing capacitor C 21 , a second smoothing capacitor C 22 , a first balancing resistor R 23 , a Zener diode RZ 24 (which corresponds to a second conduction regulating portion), and a second balancing resistor R 24 . The first smoothing capacitor C 21 and the second smoothing capacitor C 22 are connected in series to each other and are connected in parallel to the power supply portion 13 . The first smoothing capacitor C 21 and the second smoothing capacitor C 22 are respectively configured by capacitance elements C 21 a and C 22 a and internal resistors R 21 a and R 22 a . The first balancing resistor R 23 is connected on a current path I 23 in parallel with the first smoothing capacitor C 211 . The Zener diode RZ 24 is connected on a current path I 24 in parallel with the second smoothing capacitor C 22 . The Zener diode RZ 24 conducts current in one direction on the current path I 24 in a case where a voltage equal to or greater than a Zener voltage Vr 24 (which corresponds to a second predetermined voltage) has been applied and maintains its inter-terminal voltage at the Zener voltage Vr 24 . The second balancing resistor R 24 is connected on the current path I 24 in such a way as to become in parallel with the second smoothing capacitor C 22 and in series with the Zener diode RZ 24 . The second balancing resistor R 24 is a resistor for deciding a bias point of the Zener diode RZ 24 , and current flows in one direction to the second balancing resistor R 24 when a voltage equal to or greater than the Zener voltage Vr 24 is applied between the terminals of the Zener diode RZ 24 .

(2) Method of Deciding Resistance Values of Balancing Resistors and Zener Voltage

A method of deciding the resistance values of the balancing resistors 823 and Z 24 and the Zener voltage Vr 24 in the voltage smoothing circuit 214 of FIG. 9 in a case where it is supposed that the Zener diode always operates will be described below. Here, in the present embodiment, the resistance value of the first balancing resistor R 23 is decided in such a way as to become smaller than that the internal resistor R 21 a of the first smoothing capacitor C 21 , and the resistance value of the second balancing resistor R 24 is decided in such a way as to become smaller than that of the internal resistor R 22 a of the second smoothing capacitor C 22 . Further, the Zener voltage Vr 24 is decided in such a way as to become lower than a rated voltage Vrt 22 of the second smoothing capacitor C 22 .

(2-1) Overview

The Zener voltage Vr 24 , the resistance values of the first balancing resistor R 23 and the second balancing resistor R 24 are decided by further considering a condition in regard to the second balancing resistor R 24 in addition to the condition of the case described in the first embodiment.

Specifically, in terms of the circuit configuration of the voltage smoothing circuit 214 , an end-to-end voltage V 22 of the second smoothing capacitor C 22 is equal to the sum of the inter-terminal voltage of the Zener diode RZ 24 and an end-to-end voltage VX of the second balancing resistor R 24 . Additionally, the voltage Vdc from the power supply portion 13 is equal to the sum of an end-to-end voltage V 21 of the first smoothing capacitor C 21 and the end-to-end voltage V 22 of the second smoothing capacitor C 22 .

From these relations, the end-to-end voltage V 22 of the second smoothing capacitor C 22 takes a maximum value in a case where the internal resistor R 21 a of the first smoothing capacitor C 21 and the first balancing resistor R 23 are both minimum values and the internal resistor R 22 a of the second smoothing capacitor C 22 is a maximum value. Thus, as a first condition for deciding the Zener voltage Vr 24 and the balancing resistors R 23 and R 24 , the maximum value of the end-to-end voltage V 22 becoming lower than the rated voltage Vrt 22 of the second smoothing capacitor C 22 can be given (see the following equation (8)).

<Equation 8>

V 22(max)< Vrt 22  (8)

“V 22 (max)” represents the maximum value of the end-to-end voltage V 22 of the second smoothing capacitor C 22 . Additionally, supposing that the Zener diode RZ 24 is operating at the maximum value of the end-to-end voltage V 22 , the following condition can be given (see the following equation (9)).

<Equation 9>

V 22(max)= Vr 24 +VX   (9)

That is, the above equation (9) represents, in contrast to (2) equation of the first embodiment, the Zener voltage Vr 24 being equal to or less than the end-to-end voltage V 22 .

Conversely, the end-to-end voltage V 22 of the second smoothing capacitor C 22 takes a minimum value in a case where the internal resistor R 21 a of the first smoothing capacitor C 21 and the first balancing resistor R 23 are both maximum values and the internal resistor R 22 a of the second smoothing capacitor C 22 is a minimum value. At a time when the end-to-end voltage V 22 of the second smoothing capacitor C 22 takes a minimum value, the end-to-end voltage V 21 of the first smoothing capacitor C 21 takes a maximum value. Therefore, as a second condition for deciding the Zener voltage Vr 24 and the balancing resistors R 23 and R 24 , the maximum value of the end-to-end voltage V 21 of the first smoothing capacitor C 21 becoming lower than a rated voltage Vrt 21 of the first smoothing capacitor C 21 can be given (see the following equation (10)).

<Equation 10>

V 21(max)= Vdc (max)− V 22(min)< Vrt 21  (10)

“V 21 (max)” represents the maximum value of the end-to-end voltage V 21 of the first smoothing capacitor C 21 , and “Vdc(max)” represents the maximum value of the voltage Vdc from the power supply portion 13 . “V 22 (min)” represents the minimum value of the end-to-end voltage V 22 attic second smoothing capacitor C 22 .

Moreover, as a condition of the balancing resistors R 23 and R 24 , the resistance values of the balancing resistors R 23 and R 24 being respectively smaller than those of the internal resistors R 21 a and R 22 a of the smoothing capacitors C 21 and C 22 can be given. Further, as a condition of the Zener voltage Vr 24 , the Zener voltage Vr 24 being lower than the rated voltage Vrt 22 of the second smoothing capacitor C 22 can be given.

On the basis of the above equations (8) to (10) and the conditions described above, the voltage value of the Zener voltage Vr 24 and the resistance values of the balancing resistors R 23 and R 24 are decided.

The resistance values of the balancing resistors R 23 and R 24 that have been decided by the method described above may also be adjusted considering the lower limit value of variations between the internal resistors R 21 a and R 22 a of the smoothing capacitors C 21 and C 22 . Further, considering also power loss in the balancing resistors R 23 and R 24 and the Zener diode RZ 24 , it is preferred that the resistance values of the balancing resistors R 23 and R 24 be decided in such a way that that power loss becomes a target power loss amount.

To summarize, the balancing resistors R 23 and R 24 are decided in such a way as to satisfy a condition where the end-to-end voltage V 21 of the first smoothing capacitor C 21 becomes lower than the rated voltage Vrt 21 of that capacitor C 21 (V 21 <Vrt 21 ) and the end-to-end voltage V 22 of the second smoothing capacitor C 22 becomes lower than the rated voltage Vrt 22 of that capacitor C 22 (V 22 <Vrt 22 ). Because of this, even if the end-to-end voltage V 22 of the second smoothing capacitor C 22 rises, the value of that end-to-end voltage V 22 does not exceed the rated voltage Vrt 22 of that capacitor C 22 . In particular, the end-to-end voltage V 22 is kept substantially constant at the sum of the Zener voltage Vr 24 and the inter-terminal voltage VX of the second balancing resistor R 24 (V 22 ≈Vr 24 +VX), so a rise in the end-to-end voltage V 22 to become equal to or greater than the rated voltage Vrt 22 is avoided. Further, although there is the potential for the end-to-end voltage V 21 of the first smoothing capacitor C 21 to rise due to arise in the voltage Vdc from the power supply portion 13 even while the end-to-end voltage V 22 is being kept constant, the value of the first balancing resistor R 23 is, as has already been described, decided in such a way as to become smaller than the value of the internal resistor R 21 a of the first smoothing capacitor C 21 and in such a way that the end-to-end voltage V 21 of the first smoothing capacitor C 21 becomes lower than the rated voltage Vrt 21 of that capacitor C 21 , so a voltage equal to or greater than the rated voltage Vrt 21 can be prevented from being applied to the first smoothing capacitor C 21 .

(2-2) Specific Example

Next, a specific example of the method described above will be described below using FIG. 10 and FIG. 11 .

To begin, the voltage Vdc of the power supply portion 13 (below, called the power supply voltage Vdc), the values of the internal resistors R 21 a and R 22 a of the smoothing capacitors C 21 and C 22 , the end-to-end voltages V 21 and V 22 of the smoothing capacitors C 21 and C 22 , and the value of the Zener voltage Vr 24 of the Zener diode RZ 24 are decided as a precondition before deciding the first and second balancing resistors R 23 and R 24 .

Specifically, it will be supposed that the power supply voltage Vdc is a maximum value in an operating range having the potential to fluctuate. Here, as an example, it will be supposed that the power supply voltage Vdc is 700 V. The resistance values of the internal resistors R 21 a and R 22 a of the smoothing capacitors C 21 and C 22 are known values that have been decided from types and capacitance values of capacitors that are actually used. For that reason, it will be supposed that the resistance values of the internal resistors R 21 a and R 22 a are maximum values or minimum values of a range resulting from variations between capacitors that are actually used. Here, as an example, it will be supposed that the internal resistors R 21 a and R 22 a can take resistance values in the range of 400 kΩ to 1000 kΩ, from variations between the capacitors.

Further, the end-to-end voltages V 21 and V 22 of the smoothing capacitors C 21 and C 22 are, here, as a guide, hypothetically decided in such a way as to become equal to or less than “Vdc/2±X %” on the basis of the power supply voltage Vdc. In particular, even if the end-to-end voltages V 21 and V 22 take the maximum value of “Vdc/2+X %”, this maximum value is decided in such a way as to become equal to or less than the rated voltages Vrt 21 and Vrt 22 of the smoothing capacitors C 21 and C 22 . Here, “±X %” represents the operating range of the end-to-end voltages V 21 and V 22 and is appropriately decided by desktop calculation, simulation, experiment, or the like depending on the characteristics and so forth of the power supply portion 13 , for example. Specifically, in a case supposing that the internal resistor R 21 a of the first smoothing capacitor C 21 is the maximum value “1000 kΩ” and the internal resistor R 22 a of the second smoothing capacitor C 22 is the minimum value “400 kΩ”, the end-to-end voltage V 21 of the first smoothing capacitor C 21 that is proportional to the value of the internal resistor R 21 a becomes higher and the end-to-end voltage V 22 of the second smoothing capacitor C 22 that is proportional to the value of the internal resistor R 22 a becomes lower. In this case, as an example, supposing that the rated voltages of the smoothing capacitors C 21 and C 22 are 450 V the end-to-end voltage V 21 is decided as “380 V” and the end-to-end voltage V 22 is decided as “320 V”. Conversely, in a case supposing that the internal resistor R 21 a of the first smoothing capacitor C 21 is the minimum value “400 kΩ” and the internal resistor R 22 a of the second smoothing capacitor C 22 is the maximum value “1000 kΩ”, the end-to-end voltage V 21 of the first smoothing capacitor C 21 that is proportional to the value of the internal resistor R 21 a becomes lower and the end-to-end voltage V 22 of the second smoothing capacitor C 22 that is proportional to the value of the internal resistor R 22 a becomes higher. In this case, as an example, supposing that the rated voltages of the smoothing capacitors C 21 and C 22 are 450 V, the end-to-end voltage V 21 is decided as “320 V” and the end-to-end voltage V 22 is decided as “380 V”.

Further, the Zener voltage Vr 24 of the Zener diode RZ 24 is decided as a value that is about half the power supply voltage Vdc. For example, since the power supply voltage Vdc is 700 V, the Zener voltage Vr 24 can be decided as about 350 V. However, in the marketplace, it is not always the case that a Zener diode whose Zener voltage is 350 V is commercially available. For that reason, in a case where a Zener diode whose Zener voltage is 350 V is not commercially available, it is best for a Zener diode whose Zener voltage is a value close to 350 V to be used. Here, as an example, a case where a Zener diode whose Zener voltage is 300 V is used because there was not a Zener diode whose Zener voltage is 350 V will be taken as an example.

—Case where Internal Resistor R 21 a is Maximum Value and Internal Resistor R 22 a is Minimum Value—

In a case supposing that the internal resistor R 21 a of the first smoothing capacitor C 21 is the maximum value “1000 kΩ” and the internal resistor R 22 a of the second smoothing capacitor C 22 is the minimum value “400 kΩ”, the following equation (11) is true assuming that i 1 represents the current flowing through the internal resistor R 21 a and i 2 represents the current flowing through the first balancing resistor R 23 ( FIG. 10 ).

<Equation 11>

i 1×1000 =i 2 ×R 23 =V 21=380  (11)

In the above equation (11), the reference sign is used as is for the resistance value of the first balancing resistor R 23 .

Because the end-to-end voltage V 22 of the second smoothing capacitor C 22 is lower than the Zener voltage Vr 24 (V 22 >Vr 24 , and specifically 320 V>300 V), the next equations (12) and (13) are true. In the next equations (12) and (13), i 3 represents the current flowing through the internal resistor R 22 a , i 4 represents the current flowing through the second balancing resistor R 24 , and the reference sign is used as is thr the resistance value of the internal resistor R 22 a.

<Equation 12>

i 3×400 =i 4 ×R 24+300 =V 22=320  (12)

<Equation 13>

i 1 +i 2 =i 3 +i 4  (13)

—Case where Internal Resistor R 21 a is Minimum Value and Internal Resistor R 22 a , is Maximum Value—

In a case supposing that the internal resistor R 21 a of the first smoothing capacitor C 21 is the minimum value “400 kΩ” and the internal resistor R 22 a of the second smoothing capacitor C 22 is the maximum value “1000 kΩ”, the next equations (14) to (16) are true assuming that i 5 represents the current flowing through the internal resistor 21 a , i 6 represents the current flowing through the first balancing resistor R 23 , i 7 represents the current flowing through the internal resistor R 22 a , and i 8 represents the current flowing through the second balancing resistor R 24 ( FIG. 11 ).

<Equation 14>

i 5×400 =i 6 ×R 23 =V 21=320  (14)

<Equation 15>

i 7×1000 =i 8 ×R 24+300 =V 22=380  (15)

<Equation 16>

i 5 +i 6 =i 7 +i 8  (16)

By calculating the above equations (11) to (16), the first balancing resistor R 23 can be decided as “571 kΩ” and the second balancing resistor R 24 can be decided as “81.6 kΩ”. In this way, the resistance values of the balancing resistors R 23 and R 24 pertaining to the present embodiment are respectively equal to or less than those of the internal resistors R 21 a and R 22 a.

(3) Operation of Voltage Smoothing Circuit

The balancing resistors R 23 and R 24 and the Zener voltage Vr 24 are decided by the method described above. It will be supposed that, in this state, the end-to-end voltage V 22 of the second smoothing capacitor C 22 rises due to variations between the internal resistor R 21 a of the first smoothing capacitor C 21 and the internal resistor R 22 a of the second smoothing capacitor C 22 .

Even if the end-to-end voltage V 22 rises, the Zener diode ZR 24 does not operate if the inter-terminal voltage of the Zener diode RZ 24 is lower than the Zener voltage Vr 24 . For that reason, the current that has flowed from the power supply portion 13 and branched to the internal resistor R 21 a side of the first smoothing capacitor C 21 and the current path I 23 does not flow to the current path I 24 but all flows into the internal resistor R 22 a of the second smoothing capacitor C 22 . From the minimum value (e.g., 420 kΩ) of variations in the internal resistor R 21 a of the first smoothing capacitor C 21 also, the current flowing to the current path I 23 is larger than the current flowing through that internal resistor R 21 a because that internal resistor B 214 is larger than the first balancing resistor R 23 .

However, if the inter-terminal voltage of the Zener diode RZ 24 becomes equal to or greater than the Zener voltage Vr 24 , the Zener diode RZ 24 operates and the inter-terminal voltage of the Zener diode RZ 24 is clipped to the Zener voltage Vr 24 . The current that has flowed from the power supply portion 13 and branched to the internal resistor R 21 a side of the first smoothing capacitor C 21 and the current path I 23 is divided and flows to the current path I 24 and the internal resistor R 22 a of the second smoothing capacitor C 22 . From the minimum value (e.g., 420 kΩ) of variations in the internal resistor R 22 a of the second smoothing capacitor C 22 also, the current flowing to the current path I 24 is larger than the current flowing through that internal resistor R 22 a because that internal resistor R 22 is larger than the second balancing resistor R 24 . Moreover, the end-to-end voltage V 22 of the second smoothing capacitor C 22 is equal to the sum of the inter-terminal voltage of the Zener diode RZ 24 that has been clipped (that is, the Zener voltage Vr 24 ) and the end-to-end voltage VX of the second balancing resistor R 24 , so the larger the difference (that is, the voltage VX) between the end-to-end voltage V 22 and the Zener voltage Vr 24 becomes, the more the current flows to the current path I 24 side. Because of this, the current flowing to the internal resistor R 22 a of the second smoothing capacitor C 22 becomes lesser and the end-to-end voltage V 22 drops, so the end-to-end voltage V 22 can be kept equal to or less than the rated voltage Vrt 22 of the second smoothing capacitor C 22 .

The first balancing resistor R 23 is decided in such a way that the end-to-end voltages V 21 and V 22 become equal to or less than the rated voltages Vrt 21 and Vrt 22 of the smoothing capacitors C 21 and C 22 , on even if the end-to-end voltage V 21 rises, the end-to-end voltage V 21 does not exceed the rated voltage Vrt 21 of the first smoothing capacitor C 21 .

(4) Characteristics

(A)

In a case where only the Zener diodes RZ 4 and RZ 14 are disposed on the current paths I 4 and I 14 like in the voltage smoothing circuits 14 and 114 pertaining to the first embodiment and the second embodiment, Zener diodes where the values of the Zener voltages Vr 4 and Vr 14 are desired values are selected from among commercially available Zener diodes and used for the Zener diodes RZ 4 and RZ 14 . However, it is not always the case that Zener diodes where the Zener voltages Vr 4 and Vr 14 are desired values are commercially available. Depending on the values of the Zener voltages Vr 4 and Vr 14 , sometimes cases arise where the voltages V 2 and V 12 applied to the second smoothing capacitors C 2 and C 12 connected in parallel to the Zener diodes RZ 4 and RZ 14 become lower and the voltages V 1 and V 11 applied to the first smoothing capacitors C 1 and C 11 become higher or where, conversely, the voltages applied to the second smoothing capacitors C 2 and C 12 become higher than the desired values. In particular, if only the Zener diodes RZ 4 and RZ 14 are disposed on the current paths I 4 and I 14 , there is the concern that the currents flowing to the Zener diodes RZ 4 and RZ 14 will end up becoming larger in a case where the internal resistors R 1 a , R 11 a , R 2 a , and R 12 a of the smoothing capacitors C 1 , C 11 , C 2 , and C 12 take maximum values or minimum values due to variations. In this case, there are the concerns that the amount of heat emitted in the Zener diodes RZ 4 and RZ 14 will increase or that the end-to-end voltages V 2 and V 12 cannot be made into optimum values because the end-to-end voltages V 2 and V 12 of the second smoothing capacitors C 2 and C 12 are fixed to the Zener voltages Vr 4 and Vr 14 . For this reason, cases arise where the values of the end-to-end voltages V 1 , V 11 , V 2 , and V 12 of the smoothing capacitors C 1 , C 11 , C 2 , and C 12 greatly differ due to which of maximum values and minimum values the internal resistors R 1 a , R 11 a , R 2 a , and R 12 a take, the operating range of the voltage from the power supply portion 13 resultantly ends up becoming narrower, and there becomes no other choice but to select capacitors whose rated voltages Vrt 1 , Vrt 11 , Vrt 2 , and Vrt 12 are high as the first and second smoothing capacitors C 1 , C 11 , C 2 , and C 12 .

However, in the voltage smoothing circuit 214 pertaining to the present embodiment, the second balancing resistor R 24 is disposed in series with the Zener diode RZ 24 . For that reason, when a voltage equal to or greater than the Zener voltage Vr 24 that is lower than the rated voltage Vrt 22 of the second smoothing capacitor C 22 is applied to the Zener diode RZ 24 , current flows also to the second balancing resistor R 24 . Because of this, adverse effects resulting from power loss in the Zener diode RZ 24 ending up exceeding the rating and heat being emitted to other parts near the Zener diode RZ 24 can be controlled with a simple configuration.

Further, the end-to-end voltage V 22 of the second smoothing capacitor C 22 pertaining to the present embodiment is, in terms of the circuit configuration, equal to the sum of the inter-terminal voltage of the Zener diode RZ 24 and the end-to-end voltage VX of the second balancing resistor R 24 . For this reason, the Zener voltage Vr 24 can be set while considering the voltage applied to the second balancing resistor R 24 , and in correspondence thereto the options for the Zener diode expand. Thus, the Zener voltage Vr 24 can be freely set such as making the Zener voltage Vr 24 of the Zener diode RZ 24 lower compared to the Zener voltage in a case where the second balancing resistor R 24 is not disposed and it becomes possible to adjust the voltages applied to the first and second smoothing capacitors C 21 and C 22 . Consequently, even if inexpensive capacitors whose rated voltages are low, for example, are used for the first and second smoothing capacitors C 21 and C 22 , this voltage smoothing circuit 214 is applicable also to devices where the operating range of the voltage Vdc from the power supply portion 13 is relatively large. Moreover, by setting the Zener voltage Vr 24 to an optimum value, it also becomes possible to make the heat emission amounts of configural parts of the voltage smoothing circuit 214 other than the Zener diode RZ 24 smaller and to make the power loss lower.

(B)

Further, in a case where a voltage equal to or greater than the Zener voltage Vr 24 is applied to the Zener diode RZ 24 and current is flowing on the current path I 24 , a rise in the end-to-end voltage V 22 of the second smoothing capacitor C 22 is controlled by the Zener diode RZ 24 connected in parallel to the second smoothing capacitor C 22 . However, if the voltage Vdc from the power supply portion 13 rises in this state, in terms of the circuit configuration there is the concern that the end-to-end voltage V 21 of the first smoothing capacitor C 21 will rise and end up exceeding the rated voltage Vrt 21 of that capacitor C 21 .

However, in this voltage smoothing circuit 214 , the resistance values of the balancing resistors R 23 and R 24 are decided in such a way that the end-to-end voltage V 21 becomes lower than the rated voltage Vrt 21 of the first smoothing capacitor C 21 (V 21 <Vrt 21 ) and the end-to-end voltage V 22 becomes lower than the rated voltage Vrt 22 of the second smoothing capacitor (V 22 <Vrt 22 ). Additionally, the Zener voltage Vr 24 becomes equal to or less than the end-to-end voltage V 22 of the second smoothing capacitor C 22 . Consequently, even if the end-to-end voltage V 21 of the first smoothing capacitor C 21 rises, the end-to-end voltage V 21 does not exceed the rated voltage Vrt 21 of the first smoothing capacitor C 21 .

(C)

Further, according to this voltage smoothing circuit 214 , the amounts of current flowing to the balancing resistors R 23 and R 24 become larger than the amounts of current flowing to the internal resistors R 21 a and R 22 a of the smoothing capacitors C 21 and C 22 , on the amounts of current flowing to the first and second smoothing capacitors C 21 and C 22 can be controlled.

(5) Modifications

(a)

In the voltage smoothing circuit 214 pertaining to the present embodiment also, an auxiliary resistor may also be disposed like in the first and second embodiments. FIG. 12 shows a voltage smoothing circuit 214 ′ where an auxiliary resistor R 25 is connected in parallel to both ends of the Zener diode RZ 24 , and FIG. 13 shows a voltage smoothing circuit 214 ′ where an auxiliary resistor R 26 is connected in parallel to the Zener diode RZ 24 and the second balancing resistor R 24 (both of the auxiliary resistors R 25 and R 26 correspond to a first auxiliary resistor).

In both of the voltage smoothing circuits 214 ′ of FIGS. 12 and 13 also, if the end-to-end voltage V 22 of the second smoothing capacitor C 22 becomes equal to or greater than the Zener voltage Vr 24 (V 22 ≧Vr 24 ), the current flowing on the current path I 24 branches and flows to the Zener diode RZ 24 side and the auxiliary resistors R 25 and R 26 side, so the amount of current flowing to the Zener diode RZ 24 can be made smaller. For that reason, the operating voltage and the rated power of the Zener diode RZ 24 can be set low, and a Zener diode whose rated current is relatively small can be used for the Zener diode RZ 24 . Consequently, costs pertaining to the voltage smoothing circuits 214 ′ can be reduce particular, the cost of the Zener diode RZ 24 can be cut).

Further, the auxiliary resistors R 25 and R 26 can also function as a discharge circuit of the first smoothing capacitor C 21 and the second smoothing capacitor C 22 at the time of power shutdown of the motor driver 1 . Consequently, it is not necessary to separately dispose a discharge circuit of the first smoothing capacitor C 21 and the second smoothing capacitor C 22 .

Although it is not illustrated, an auxiliary resistor may also, like in FIG. 6 pertaining to the first embodiment, be connected in parallel to the first and second smoothing capacitors C 21 and C 22 connected in series to each other (second auxiliary resistor).

(b)

Further, in the voltage smoothing circuit 214 pertaining to the present embodiment also, as shown in FIG. 14 , the positions where the balancing resistor and the Zener diode are disposed may also be mutually opposite with respect to the point-of-connection s 1 . In a voltage smoothing circuit 214 ″ pertaining to FIG. 14 , a second balancing resistor R 24 ′ and a Zener diode R 24 ′ are disposed on the power supply line L 1 side and a first balancing resistor R 23 ′ is disposed on the GND line L 2 side with respect to the point-of-connection s 1 between the first and second smoothing capacitors C 21 and C 22 .

That is, it suffices for the Zener diode and the second balancing resistor to be disposed in such a way as to become in parallel with either one of the smoothing capacitors C 21 and C 22 and for the balancing resistor to be disposed in such a way as to become in parallel with the other of the smoothing capacitors C 21 and C 22 .

Further, in this case also, an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the Zener diode RZ 24 ′, or an auxiliary resistor (not shown in the drawings) may also be disposed in parallel with the first and second smoothing capacitors C 21 and C 22 connected in series to each other,

Fourth Embodiment

Next, a method of deciding the resistance values of balancing resistors in a case where the voltage smoothing circuit is equipped with two balancing resistors like in the third embodiment and there is also the concern that the Zener diode will not operate like in the second embodiment will be described.

(1) Configuration of Voltage Smoothing Circuit

FIG. 15 is a circuit diagram of a voltage smoothing circuit 314 pertaining to the present embodiment. The configuration of the voltage smoothing circuit 314 is the same as that of the voltage smoothing circuit 214 of the third embodiment except that the method of deciding the resistance values of the first and second balancing resistors differs.

That is, the voltage smoothing circuit 314 is equipped with a first smoothing capacitor C 31 , a second smoothing capacitor C 32 , a first balancing resistor R 33 , a second balancing resistor R 34 , and a Zener diode RZ 34 (which corresponds to a second conduction regulating portion). The first smoothing capacitor C 31 and the second smoothing capacitor C 32 are connected in series to each other and are connected in parallel to the power supply portion 13 . The first smoothing capacitor C 31 and the second smoothing capacitor C 32 are respectively configured by capacitance elements C 31 a and C 32 a and internal resistors R 31 a and R 32 a . The first balancing resistor R 33 is connected on a current path I 33 in parallel with the first smoothing capacitor C 31 . The second balancing resistor R 34 and the Zener diode RZ 34 are connected in series on a current path I 34 in parallel with the second smoothing capacitor C 32 . The Zener diode RZ 34 conducts current in one direction on the current path I 34 in a case where a voltage equal to or greater than a Zener voltage Vrt 34 (which corresponds to a second predetermined voltage) that is lower than a rated voltage Vrt 32 of the second smoothing capacitor C 32 has been applied and maintains its inter-terminal voltage at the Zener voltage Vr 34 .

(2) Method of Deciding Resistance Values of Balancing Resistors and Zener Voltage

A method of deciding the balancing resistors R 33 and R 34 in a case where there is the concern that the Zener diode will not operate will be described below.

In a case where there is the concern that the Zener diode RZ 34 will not operate due to factors such as the difference between the resistance values of the internal resistors R 31 a and R 32 a , being larger than a predetermined difference due to variations between the smoothing capacitors C 31 and C 32 or the voltage Vdc from the power supply portion 13 being low, the resistance value of the first balancing resistor R 33 can be decided like in the deciding method described in the second embodiment.

That is, in order to avoid the concern that an end-to-end voltage V 31 of the first smoothing capacitor C 31 will end up exceeding a rated voltage Vrt 31 of that capacitor C 31 due to the value of the voltage Vdc or the values of the internal resistors R 31 a and R 32 a , the first balancing resistor R 33 is decided in such a way as to satisfy the condition of the following equation (17).

In the above equation (17), “R 33 (max)” represents the maximum value of the resistance value of the first balancing resistor R 33 . “R 31 a (max)” represents the maximum value of the resistance value of the internal resistor R 31 a of the first smoothing capacitor C 31 . “R 32 a (min)” represents the minimum value of the resistance value of the internal resistor R 32 a of the second smoothing capacitor C 32 .

The resistance value of the first balancing resistor R 33 is decided in such a way as to satisfy the above equation (17) and in such a way that a condition where the resistance value of the first balancing resistor R 33 is smaller than that of the internal resistor R 31 a of the first smoothing capacitor C 31 is satisfied, whereby the following equation (18) is satisfied.

<Equation 18>

V 31≦ V 32≦ Vr 34< V 32  (18)

That is, the resistance value of the first balancing resistor R 33 is decided in such a way that the end-to-end voltage V 31 of the first smoothing capacitor C 31 becomes equal to or less than an end-to-end voltage V 32 of the second smoothing capacitor C 32 and the Zener voltage Vr 34 and in such a way that the end-to-end voltage V 32 of the second smoothing capacitor C 32 becomes equal to or less than the rated voltage Vrt 32 of the second smoothing capacitor C 32 . Because of this, even if the end-to-end voltage V 32 of the second smoothing capacitor C 32 does not exceed the Zener voltage Vr 34 and the Zener diode R 234 does not operate, the end-to-end voltage V 31 of the first smoothing capacitor C 31 always becomes substantially the same as or lower than the end-to-end voltage V 32 of the second smoothing capacitor C 32 . Consequently, the end-to-end voltage V 31 of the first smoothing capacitor C 31 does not become equal to or greater than the rated voltage Vrt 31 of the first smoothing capacitor C 31 comprising the same capacitor as the second smoothing capacitor C 32 .

It suffices for the Zener voltage Vr 34 to be decided in such a way as to become equal to or less than the rated voltage Vrt 32 of the second smoothing capacitor C 32 and for the resistance value of the second balancing resistor R 34 to be decided in such a way as to become equal to or less than that of the internal resistor R 32 a of the second smoothing capacitor C 32 . This is because as long as the Zener diode RZ 34 does not operate, a voltage equal to or greater than the rated voltage Vrt 32 of the second smoothing capacitor C 32 will not be applied to that capacitor C 32 . Further, even if the Zener diode RZ 34 operates, the end-to-end voltage V 32 of the second smoothing capacitor C 32 does not exceed the rated voltage Vrt 32 of that capacitor C 32 due to the Zener diode RZ 34 .

(3) Operation of Voltage Smoothing Circuit

The balancing resistors R 33 and R 34 and the Zener voltage Vr 34 are decided by the method described above. It will be supposed that, in this state, the end-to-end voltage V 32 of the second smoothing capacitor C 32 rises due to variations between the internal resistor R 31 a of the first smoothing capacitor C 31 and the internal resistor R 32 a of the second smoothing capacitor C 32 .

In this case, the end-to-end voltage V 32 of the second smoothing capacitor C 32 does not exceed the rated voltage Vrt 32 of that capacitor C 32 due to the same operation as in (3) of the third embodiment.

Further, the value of the first balancing resistor R 33 is decided in such a way that the end-to-end voltage V 31 of the first smoothing capacitor C 31 always becomes lower than the end-to-end voltage V 32 of the second smoothing capacitor C 32 , so even if the end-to-end voltage V 31 rises, the end-to-end voltage V 31 does not exceed the rated voltage Vrt 31 of the first smoothing capacitor C 31 .

(4) Effects

(A)

In the voltage smoothing circuit 314 pertaining to the present embodiment, the second balancing resistor R 34 is disposed in series with the Zener diode RZ 34 like in the third embodiment. For that reason, when a voltage equal to or greater than the Zener voltage Vr 34 that is lower than the rated voltage Vrt 32 of the second smoothing capacitor C 32 is applied to the Zener diode RZ 34 , current flows also to the second balancing resistor R 34 . Because of this, adverse effects resulting from power loss in the Zener diode RZ 34 ending up exceeding the rating and heat being emitted to other parts near the Zener diode RZ 34 can be controlled with a simple configuration.

Further, the Zener voltage Vr 34 can be set while considering the voltage applied to the second balancing resistor R 34 , so in correspondence thereto the options for the Zener diode expand. Thus, the Zener voltage Vr 34 can be freely set—such as making the Zener voltage Vr 34 of the Zener diode RZ 34 lower compared to the Zener voltage in a case where the second balancing resistor R 34 is not disposed—and it becomes possible to adjust the voltages applied to the first and second smoothing capacitors C 31 and C 32 . Consequently, even if inexpensive capacitors whose rated voltages are low, for example, are used for the first and second smoothing capacitors C 31 and C 32 , this voltage smoothing circuit 314 is applicable also to devices where the operating range of the voltage Vdc from the power supply portion 13 is relatively large. Moreover, by setting the Zener voltage Vr 34 to an optimum value, it also becomes possible to make the heat emission amounts of configural parts of the voltage smoothing circuit 314 other than the Zener diode RZ 34 smaller and to make the power loss lower.

(B)

In a case where the Zener voltage Vr 34 is not applied to the Zener diode RZ 34 and the Zener diode RZ 34 does not operate due to a factor such as the difference between the internal resistors R 31 a and R 32 a of the smoothing capacitors C 31 and C 32 being large or the voltage Vdc from the power supply portion 13 being low, for example, the end-to-end voltage V 32 of the second smoothing capacitor C 32 connected in parallel to the Zener diode RZ 34 is kept equal or less than the Zener voltage Vr 34 . However, in terms of the circuit configuration, the end-to-end voltage V 31 of the first smoothing capacitor C 31 becomes a voltage obtained by subtracting the end-to-end voltage V 32 of the second smoothing capacitor C 32 from the voltage Vdc from the power supply portion 13 , and depending on the case the concern that the end-to-end voltage V 31 of the first smoothing capacitor C 31 will reach a voltage equal to or greater than the rated voltage Vrt 31 of the first smoothing capacitor C 31 is also not inconceivable.

However, according to this voltage smoothing circuit 314 , the resistance value of the first balancing resistor R 33 is decided in such a way that the end-to-end voltage V 31 of the first smoothing capacitor C 31 becomes lower than the end-to-end voltage V 32 of the second smoothing capacitor C 32 (V 31 <V 32 ). For that reason, the end-to-end voltage V 31 of the first smoothing capacitor C 31 is always kept equal to or less than the Zener voltage Vr 34 of the Zener diode RZ 34 . Consequently, the concern that a voltage equal to or greater than the rated voltage Vrt 31 will be applied to the first smoothing capacitor C 31 can be avoided.

(C)

Further, according to this voltage smoothing circuit 314 , the amounts of current flowing to the balancing resistors R 33 and R 34 become larger than the amounts of current flowing to the internal resistors R 31 a and R 32 a of the smoothing capacitors C 31 and C 32 , so the amounts of current flowing to the first and second smoothing capacitors C 31 and C 32 can be controlled.

(5) Modifications

(a)

In the voltage smoothing circuit 314 pertaining to the present embodiment also, an auxiliary resistor may also be disposed like in FIGS. 12 and 13 .

(b)

Further, in the voltage smoothing circuit 314 pertaining to the present embodiment also, the positions where the balancing resistors and the Zener diode are disposed may also be mutually opposite with respect to the point-of-connection s 1 like in FIG. 14 . Moreover, an auxiliary resistor may also be disposed in parallel with the Zener diode, or an auxiliary resistor may also be disposed in parallel with the first and second smoothing capacitors connected in series to each other.

Fifth Embodiment

In the fourth embodiment, a case where the second balancing resistor R 34 is decided in such a way as to become equal to or less than the internal resistor R 32 a of the second smoothing capacitor C 32 was described. Here, a case where the first balancing resistor is decided more simply compared to the fourth embodiment and the second balancing resistor is decided by a method other than the one in the fourth embodiment will be described.

(1) Configuration of Voltage Smoothing Circuit

FIG. 16 is a circuit diagram of a voltage smoothing circuit 414 pertaining to the present embodiment. The configuration of the voltage smoothing circuit 414 is mainly the same as that of the voltage smoothing circuit 314 of the fourth embodiment except that the method of deciding the resistance value of the second balancing resistor differs.

That is, the voltage smoothing circuit 414 is equipped with a first smoothing capacitor C 41 , a second smoothing capacitor C 42 , a first balancing resistor R 43 , a second balancing resistor R 44 , and a Zener diode RZ 44 (which corresponds to a second conduction regulating portion). The first smoothing capacitor C 41 and the second smoothing capacitor C 42 are connected in series to each other and are connected in parallel to the power supply portion i 3 . The first smoothing capacitor C 41 and the second smoothing capacitor C 42 are respectively configured by capacitance elements C 41 a and C 42 a and internal resistors R 41 a and R 42 a . The first balancing resistor R 43 is connected on a current path I 43 parallel with the first smoothing capacitor C 41 . The second balancing resistor R 44 and the Zener diode RZ 44 are connected in series on a current path I 44 in parallel with the second smoothing capacitor C 42 . The Zener diode RZ 44 conducts current in one direction on the current path I 44 in a case where a voltage equal to or greater than a Zener voltage Vr 44 (which corresponds to a second predetermined voltage) that is lower than a rated voltage Vrt 42 of the second smoothing capacitor C 42 has been applied to the Zener diode RZ 44 and maintains its inter-terminal voltage at the Zener voltage Vr 44 .

(2) Method of Deciding Resistance Values of Balancing Resistors and Zener Voltage

To begin, the voltage Vdc of the power supply portion 13 (here, below, called the power supply voltage Vdc), the values of the internal resistors R 41 a and R 42 a of the smoothing capacitors C 41 and C 42 , end-to-end voltages V 41 and V 42 of the smoothing capacitors C 41 and C 42 , and the value of the Zener voltage Vr 44 of the Zener diode RZ 44 are decided as a precondition.

Specifically, it will be supposed that the power supply voltage Vdc is a maximum value in an operating range having the potential to fluctuate. Here, as an example, it will be supposed that the power supply voltage Vdc is 700 V. It will be supposed that the resistance values of the internal resistors R 41 a and R 42 a are maximum values or minimum values of a range resulting from variations between capacitors that are actually used. Here, as an example, it will be supposed that the internal resistors R 41 a and R 42 a can take resistance values in the range of 400 kΩ to 1000 kΩ from variations between the capacitors.

Further, the end-to-end voltages V 41 and V 42 of the smoothing capacitors C 41 and C 42 are hypothetically decided in such a way as to become equal to or less than “Vdc/2±X %” on the basis of the power supply voltage Vdc. In particular, even if the end-to-end voltages V 41 and V 42 take the maximum value of “Vdc/2+X %”, this maximum value is decided in such a way as to become equal to or less than rated voltages Vrt 41 and Vrt 42 of the smoothing capacitors C 41 and C 42 . Here, “±X %” represents the operating range of the end-to-end voltages V 41 and V 42 like in the third embodiment. Specifically, in a case supposing that the internal resistor R 41 a of the first smoothing capacitor C 41 is the maximum value “1000 kΩ” and the internal resistor R 42 a of the second smoothing capacitor C 42 is the minimum value “400 kΩ”, assuming that the rated voltages of the smoothing capacitors C 41 and C 42 are 450 V as an example the end-to-end voltage V 41 is decided as “420 V” and the end-to-end voltage V 42 is decided as “280 V”. Conversely, in a case supposing that the internal resistor R 41 a of the first smoothing capacitor C 41 is the minimum value “400 kΩ” and the internal resistor R 42 a of the second smoothing capacitor C 42 is the maximum value “1000 kΩ”, the end-to-end voltage V 41 is decided as “280 V” and the end-to-end voltage V 42 is decided as “420 V”.

Further, the Zener voltage Vr 44 of the Zener diode RZ 44 is decided as a value (specifically, about 350 V) that is about half the power supply voltage Vdc, but here, like in the third embodiment, a case where the Zener voltage Vr 44 of the Zener diode RZ 44 is decided as 300 V will be taken as an example,

—Case where Internal Resistor R 41 a is Maximum Value and Internal Resistor R 42 a is Minimum Value—

In a case supposing that the internal resistor R 41 a of the first smoothing capacitor C 41 is the maximum value “1000 kΩ” and the internal resistor R 42 a of the second smoothing capacitor C 42 is the minimum value “400 kΩ”, the next equation (19) is true assuming that i 11 represents the current flowing through the internal resistor R 41 a and i 12 represents the current flowing through the first balancing resistor R 43 ( FIG. 16 ).

<Equation 19>

i 11×1000 =i 12 ×R 43 =V 41=420  (19)

In the above equation (19), the reference sign is used as is for the resistance value of the first balancing resistor R 43 .

Moreover, in this case, because the end-to-end voltage V 41 is “420 V” and the end-to-end voltage V 42 is “280 V”, the end-to-end voltage V 42 of the second smoothing capacitor C 42 becomes lower than the Zener voltage Vr 44 (V 42 <Vr 44 , and specifically 280 V<300 V) and the next equation (20) is true. Current does not flow to the second balancing resistor R 44 (i 14 pertaining to FIG. 16 =0 A), so the next equation (21) is true,

<Equation 20>

i 13×400=280  (20)

<Equation 21>

i 11 +i 12 =i 13  (21)

—Case where Internal Resistor R 41 a is Minimum Value and Internal Resistor R 42 a is Maximum Value—

In a case supposing that the internal resistor R 41 a of the first smoothing capacitor C 41 is the minimum value “400 kΩ” and the internal resistor R 42 a of the second smoothing capacitor C 42 is the maximum value “1000 kΩ”, the end-to-end voltage V 41 is “280 V” and the end-to-end voltage V 42 is “420 V”, so the end-to-end voltage V 42 becomes lower than the Zener voltage Vr 44 (V 42 >Vr 44 ). Consequently, the Zener diode RZ 44 switches ON and current flows on the current path I 44 . Assuming that i 15 represents the current flowing through the internal resistor R 41 a , i 16 represents the current flowing through the first balancing resistor R 43 , i 17 represents the current flowing through the internal resistor R 42 a , and 8 represents the current flowing through the second balancing resistor R 44 ( FIG. 17 ), the next equations (22) to (24) are true.

<Equation 22>

i 15×400 =i 16 ×R 43 =V 41=280  (22)

<Equation 23>

i 17×1000 =i 18 ×R 44+300 =V 42=420  (23)

<Equation 24>

i 15 +i 16 =i 17 +i 18  (24)

By calculating the above equations (19) to (24), the first balancing resistor R 43 can be decided as “1500 kΩ” and the second balancing resistor R 44 can be decided as “256 kΩ”.

In the method described above, the end-to-end voltages V 41 and V 42 of the smoothing capacitors C 41 and C 42 satisfy the condition of being respectively equal to or less than the rated voltages Vrt 41 and Vrt 42 of the smoothing capacitors C 41 and C 42 , but the obtained second balancing resistor R 44 is equal to or less than the internal resistor R 42 a of the second smoothing capacitor C 42 and the first balancing resistor R 43 is equal to or greater than the internal resistor R 41 a of the first smoothing capacitor C 41 .

(3) Effects

In the method pertaining to the present embodiment, the values of the first and second balancing resistors R 43 and R 44 are simply decided considering both a case where the Zener diode RZ 44 does not operate and a case where the Zener diode RZ 44 operates. In the present embodiment, as described in the fourth embodiment, the end-to-end voltage V 41 of the first smoothing capacitor C 41 does not always satisfy the condition of being equal to or less than the end-to-end voltage V 42 of the second smoothing capacitor C 42 . However, in the present embodiment, the condition that the end-to-end voltage V 41 of the first smoothing capacitor C 41 is lower than the rated voltage Vrt 41 of that capacitor C 41 (V 41 <Vrt 41 ) and the end-to-end voltage V 42 of the second smoothing capacitor C 42 is lower than the rated voltage Vrt 42 of that capacitor C 42 (V 42 <Vrt 42 ) is satisfied, and voltages equal to or greater than the rated voltages Vrt 41 and Vrt 42 are not applied to the smoothing capacitors C 41 and C 42 .

(4) Modifications

(a)

In the voltage smoothing circuit 414 pertaining to the present embodiment also, an auxiliary resistor may also be disposed like in FIGS. 12 and 13 .

(b)

Further, in the voltage smoothing circuit 414 pertaining to the present embodiment also, the positions where the balancing resistors and the Zener diode are disposed may also be mutually opposite with respect to the point-of-connection s 1 like in FIG. 14 . Moreover, an auxiliary resistor may also be disposed in parallel with the Zener diode, or an auxiliary resistor may also be disposed in parallel with the first and second smoothing capacitors connected in series to each other.

Sixth Embodiment

Next, a voltage smoothing circuit 514 that is further equipped with one more Zener diode in contrast to the first embodiment to the fifth embodiment will be described.

(1) Configuration of Voltage Smoothing Circuit

FIG. 18 is a circuit diagram of a voltage smoothing circuit 514 pertaining to the present embodiment. The voltage smoothing circuit 514 is equipped with a first smoothing capacitor C 51 , a second smoothing capacitor C 52 , a first balancing resistor R 53 , a second balancing resistor R 54 , a first Zener diode RZ 53 (which corresponds to a first conduction regulating portion), and a second Zener diode RZ 54 (which corresponds to a second conduction regulating portion).

(1-1) First Smoothing Capacitor and Second Smoothing Capacitor

The first smoothing capacitor C 51 and the second smoothing capacitor C 52 are, like in the first embodiment, connected in series to each other and are connected in parallel to the power supply portion 13 . The first smoothing capacitor C 51 and the second smoothing capacitor C 52 are respectively configured by capacitance elements C 51 a and C 52 a and internal resistors R 51 a and R 52 a.

The first smoothing capacitor C 51 and the second smoothing capacitor C 52 pertaining to the present embodiment have the same capacitance values; 1920 μC can be given as an example. Further, examples of types of capacitors that may be used for the first smoothing capacitor C 51 and the second smoothing capacitor C 52 include, like in the first embodiment, electrolytic capacitors, tantalum capacitors, ceramic resistors, and so forth, but in the present embodiment, electrolytic capacitors are used for the first smoothing capacitor C 51 and the second smoothing capacitor C 52 .

(1-2) First Balancing Resistor and Second Balancing Resistor

The first balancing resistor R 53 is connected in parallel to the first smoothing capacitor C 51 , and the second balancing resistor R 54 is connected in parallel to the second smoothing capacitor C 52 . That is, the first balancing resistor R 53 is disposed on the power supply line L 1 side (that is, the upper side), and the second balancing resistor R 54 is disposed on the GND line L 2 side (that is, the lower side). Specifically, one end of the first balancing resistor R 53 is connected to the power supply line L 1 , and the other end of the first balancing resistor R 53 is connected to the cathode of the first Zener diode RZ 53 . One end of the second balancing resistor R 54 is connected to the point-of-connection s 1 between the first smoothing capacitor C 51 and the second smoothing capacitor C 52 , and the other end of the second balancing resistor R 54 is connected to the cathode of the second Zener diode RZ 54 .

Further, the first balancing resistor R 53 has a resistance value that is smatter than the value of the internal resistor R 51 a of the first smoothing capacitor C 51 , and the second balancing resistor R 54 has a resistance value that is smaller than the value of the internal resistor R 52 a of the second smoothing capacitor C 52 . This is because controllability improves the more the resistance values of the first balancing resistor R 53 and the second balancing resistor R 54 are set to small values, and thus a balance between both of the voltages applied to the first smoothing capacitor C 51 and the second smoothing capacitor C 52 can be achieved. Therefore, in the present embodiment, the resistance values of the first balancing resistor R 53 and the second balancing resistor R 54 are decided to be sufficiently small values with respect to the lower limit value of variations between the internal resistor R 51 a of the first smoothing capacitor C 51 and the internal resistor R 52 a of the second smoothing capacitor C 52 . As an example, the first balancing resistor R 53 and the second balancing resistor R 54 are respectively decided to be about 1/10 to about 1/20 of the internal resistors R 51 a and R 52 a . However, the smaller the values of the first balancing resistor R 53 and the second balancing resistor R 54 are made, the larger the currents flowing to the first balancing resistor R 53 and the second balancing resistor R 54 become, so power loss in the balancing resistors R 53 and R 54 ends up becoming larger. For that reason, in consideration of that power loss, it is preferred that the resistance values of the first balancing resistor R 53 and the second balancing resistor R 54 be decided in such a way that that power loss becomes a target power loss amount.

As a specific example of the first balancing resistor R 53 and the second balancing resistor R 54 , the resistance values of the first balancing resistor R 53 and the second balancing resistor R 54 can both be decided as “50 kΩ (⅛ W)” in a case supposing that the internal resistor R 51 a of the first smoothing capacitor C 51 is “1075 kΩ” and the internal resistor R 52 a of the second smoothing capacitor C 52 is “420 kΩ”. In this way, the voltages applied to the first balancing resistor R 53 and the second balancing resistor R 54 pertaining to the present embodiment can be made significantly lower compared to the value of the balancing resistor in the conventional techniques, so loss can be made smaller and a relatively small-sized resistor like a chip resistor can be used. In contrast, in the conventional techniques the balancing resistor had a relative large value, like “3 series of 5.6 kΩ (10 W)”, for example, so using a cement resistor whose dimensions are large has been predominant.

(1-3) First Zener Diode and Second Zener Diode

The first Zener diode RZ 53 is connected in series to the first balancing resistor R 53 . The anode of the first Zener diode RZ 53 is connected to the point-of-connection s 1 between the first smoothing capacitor C 51 and the second smoothing capacitor C 52 , and the cathode of the first Zener diode RZ 53 is connected to the first balancing resistor R 53 . The first Zener diode RZ 53 conducts current in one direction to the first balancing resistor R 53 in a case where a voltage equal to or greater than a first Zener voltage Vr 53 (which corresponds to a first predetermined voltage) has been applied to the first Zener diode RZ 53 (see FIG. 19 ). The one direction referred to here is the opposite direction of the first Zener diode RZ 53 —that is, a direction from the cathode to the anode.

The second Zener diode RZ 54 is connected in series to the second balancing resistor R 54 . More specifically, the anode of the second Zener diode RZ 54 is connected to the GND line L 2 , and the cathode of the second Zener diode RZ 54 is connected to the second balancing resistor R 54 . The second Zener diode RZ 54 conducts current in one direction to the second balancing resistor R 54 in a case where a voltage equal to or greater than a second Zener voltage Vr 54 (which corresponds to a second predetermined voltage) has been applied to the second Zener diode RZ 54 (see FIG. 20 ). The one direction referred to here is the opposite direction of the second Zener diode RZ 54 —that is, from the cathode to the anode.

In particular, in the present embodiment, in a case supposing that the voltage Vdc is “718 V”, for example, the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are both decided as “360 V” on the basis of the value of the voltage Vdc. The first Zener voltage Vr 53 and the second Zener voltage Vr 54 are both values equal to or less than the voltage Vdc but are decided in such a way that the total of these becomes equal to or greater than the voltage Vdc. Because of this, voltages that become equal to or greater than the first Zener voltage Vr 53 and equal to or greater than the second Zener voltage Vr 54 are not applied to both the first Zener diode RZ 53 and the second Zener diode RZ 54 , and a voltage equal to or greater than the first Zener voltage Vr 53 or greater than the second Zener voltage Vr 54 is applied only to either one of the first Zener diode RZ 53 or the second Zener diode RZ 54 . That is, in a case where a voltage equal to or greater than the first Zener voltage Vr 53 has been applied to the first Zener diode RZ 53 , a voltage equal to or greater than the second Zener voltage Vr 54 is not applied to the second Zener diode RZ 54 . Conversely, in a case where a voltage equal or greater than the second Zener voltage Vr 54 has been applied to the second Zener diode RZ 54 , a voltage equal to or greater than the first Zener voltage Vr 53 is not applied to the first Zener diode RZ 53 .

Consequently, if a voltage equal to or greater than the first Zener voltage Vr 53 is applied to the first Zener diode RZ 53 due to variations between the internal resistors R 51 a and R 52 a of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 , current flows to a current path I 53 on the upper side including the first balancing resistor R 53 , but current does not flow to a current path I 54 on the lower side including the second balancing resistor R 54 . Thus, the current that has flowed on the current path I 53 flows into the internal resistor R 52 a of the second smoothing capacitor C 52 . Conversely, if a voltage equal to or greater than the second Zener voltage Vr 54 is applied to the second Zener diode RZ 54 due to variations between the internal resistors R 51 a and R 52 a , current flows to the current path I 54 on the lower side, but current does not flow to the current path I 53 on the upper side. Thus, the current flowing on the current path I 54 flows from the internal resistor R 51 a of the first smoothing capacitor C 51 . That is, it can be said that the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are decided in such a way that current flows only to either one of the first Zener diode RZ 53 or the second Zener diode RZ 54 .

Moreover, in the present embodiment, the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are decided in such a way as to become smaller than the rated voltages of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 . This is to ensure that the voltages applied to the first smoothing capacitor CSI and the second smoothing capacitor C 52 become larger than the values of the first Zener voltage Vr 53 and the second Zener voltage Vr 54 . Capacitors whose rated voltages are several hundred volts, such as 400 V, for example, are utilized for the first smoothing capacitor C 51 and the second smoothing capacitor C 52 . The more the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are decided to be large voltages, the smaller the power loss in the first balancing resistor R 53 and the second balancing resistor R 54 can be made, so the amounts of heat emitted in the first balancing resistor R 53 and the second balancing resistor R 54 also become smaller. Therefore, in the present embodiment, as described above, by deciding the Zener voltages Vr 53 and Vr 54 to be “360 V”, which is smaller than the rated voltages of the smoothing capacitors C 51 and C 52 , the power loss in the balancing resistors R 53 and R 54 is made smaller.

The values of the Zener voltages Vr 53 and Vr 54 are decided considering also the values of the first balancing resistor R 53 and the second balancing resistor R 54 in addition to the voltage Vdc and the rated voltages of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 .

(2) Operation of Voltage Smoothing Circuit

Next, the operation of the voltage smoothing circuit 514 will be described using FIGS. 19 and 20 .

First, according to the configuration of the voltage smoothing circuit 514 , a voltage V 51 applied to both ends of the first smoothing capacitor C 51 is equal to the voltage applied on the current path I 53 —that is, from the first balancing resistor R 53 to the first Zener diode RZ 53 . A voltage V 52 applied to both ends of the second smoothing capacitor C 52 is equal to the voltage applied on the current path I 54 —that is, from the second balancing resistor R 54 to the second Zener diode RZ 54 .

On the other hand, the same capacitors are used for the smoothing capacitors C 51 and C 52 , so ideally there would be substantially no variations between the internal resistors R 51 a and R 52 a or any variations would be small (R 51 a ≈R 52 a ) and thus the voltage V 51 applied to both ends of the first smoothing capacitor C 51 and the voltage V 52 applied to both ends of the second smoothing capacitor C 52 would be in a state in which they become equal to or less than the rated voltages of the smoothing capacitors C 51 and C 52 , respectively, and become substantially equal. In this ideal state, the voltages V 51 and V 52 applied to the current paths I 53 and I 54 respectively become equal to or less than the first Zener voltage Vr 53 and the second Zener voltage Vr 54 (V 51 <Vr 53 , V 52 <Vr 54 ). Current does not flow on the current paths I 53 and I 54 , and the first and second smoothing capacitors C 51 and C 52 take a state where a balance between their voltages is maintained.

However, if there are variations between the internal resistor R 51 a of the first smoothing capacitor C 51 and the internal resistor R 52 a of the second smoothing capacitor C 52 , a magnitude relation arises between the voltages V 51 and V 52 applied to the smoothing capacitors C 51 and C 52 and the Zener voltages Vr 53 and Vr 54 , and the voltage smoothing circuit takes a state where the balance between the voltages of the first and second smoothing capacitors C 51 and C 52 is disrupted. On the basis of that magnitude relation, the voltage smoothing circuit 514 takes either of the following operations.

(2-1) Case where Voltage Larger than First Zener Voltage Vr 53 has been Applied to Both Ends of First Smoothing Capacitor C 51 (V 51 >Vr 53 )

In this case, the voltage V 51 larger than the first Zener voltage Vr 53 is applied not only to both ends of the first smoothing capacitor C 51 but also to the first Zener diode RZ 53 , and the first Zener diode RZ 53 operates. When this happens, the end-to-end voltage of the first Zener diode RZ 53 is clipped to a constant voltage—that is, the first Zener voltage Vr 53 —and current flows on the current path I 53 in the order of the first balancing resistor R 53 and the first Zener diode RZ 53 as indicated by the arrows in FIG. 19 . The voltage V 52 applied to both ends of the second smoothing capacitor C 52 is expressed as “Vdc−V 51 ”, so that voltage V 52 is smaller than the second Zener voltage Vr 54 . Consequently, the second Zener diode RZ 54 does not operate and current does not flow on the current path I 54 .

The current that has flowed on the current path I 53 flows into the internal resistor R 52 a of the second smoothing capacitor C 52 via the point-of-connection s 1 . The larger the voltage V 51 applied to both ends of the first smoothing capacitor C 51 is, the more the amount of current flowing into the internal resistor R 52 a via the current path I 53 becomes.

In this way, the current flows into the internal resistor R 52 a , whereby the voltage V 52 applied to both ends of the second smoothing capacitor C 52 becomes larger. The voltage V 51 is expressed as “Vdc−V 52 ”, so it becomes smaller as the voltage V 52 becomes larger.

Because of the above operation, before long the voltage V 52 and the voltage V 51 become substantially equal and current no longer flows to the current path I 53 . That is, the above operation is continuously performed until the voltage V 51 applied to both ends of the first smoothing capacitor C 51 becomes substantially equal to the first Zener voltage Vr 53 and a state is reached where a balance between the voltages of the first and second smoothing capacitors C 51 and C 52 is maintained.

(2-2) Case where Voltage Larger than Second Zener Voltage Vr 54 has been Applied to Both Ends of Second Smoothing Capacitor C 52 (V 52 >Vr 54 )

In this case, the voltage V 52 larger than the second Zener voltage Vr 54 is applied not only to both ends of the second smoothing capacitor C 52 but also to the second Zener diode RZ 54 , and the second Zener diode RZ 54 operates. When this happens, the end-to-end voltage of the second Zener diode RZ 54 is clipped to a constant voltage—that is, the second Zener voltage Vr 54 —and a path where current flows on the current path I 54 in the order of the second balancing resistor R 54 and the second Zener diode RZ 54 as indicated by the arrows in FIG. 20 is formed. The voltage V 51 applied to both ends of the first smoothing capacitor C 51 is expressed as “Vdc−V 52 ”, so that voltage V 51 is smaller than the first Zener voltage Vr 53 . Consequently, the first Zener diode RZ 53 does not operate and current does not flow on the current path I 53 .

As described above, the current path I 54 becomes able to conduct but the current path I 53 is not able to conduct, so current flows through the internal resistor R 51 a of the first smoothing capacitor C 51 . That is, the current is drawn from the first smoothing capacitor C 51 side by the current path I 54 , and the current that has flowed through the internal resistor R 51 a flows to the current path I 54 via the point-of-connection s 1 . The larger the voltage V 52 applied to both ends of the second smoothing capacitor C 52 is, the more the amount of current flowing to the current path I 54 via the internal resistor R 51 a becomes.

In this way, the current flows to the internal resistor R 51 a , whereby the voltage V 51 applied to both ends of the first smoothing capacitor C 51 becomes larger. The voltage V 52 is expressed as “Vdc−V 51 ”, so it becomes smaller as the voltage V 51 becomes larger.

Because of the above operation, before long the voltage V 51 and the voltage V 52 become substantially equal and current no longer flows to the current path I 54 . That is, the above operation is continuously performed until the voltage V 52 applied to both ends of the second smoothing capacitor C 52 becomes substantially equal to the second Zener voltage Vr 54 and a state is reached where a balance between the voltages of the first and second smoothing capacitors C 51 and C 52 is maintained.

(3) Effects

(A)

In the voltage smoothing circuit 514 pertaining to the present embodiment, in a case where a voltage equal to or greater than the first Zener voltage Vr 53 that is a first predetermined voltage has been applied to the first Zener diode RZ 53 that is a first conduction regulating portion, current flows to the first balancing resistor R 53 , and this current flows, for example, to the internal resistor R 52 a of the second smoothing capacitor C 52 ( FIG. 19 ). Conversely, in a case where a voltage equal to or greater than the second Zener voltage Vr 54 that is a second predetermined voltage has been applied to the second Zener diode RZ 54 that is a second conduction regulating portion, current flows to the second balancing resistor R 54 , whereby current also flows, for example, to the internal resistor R 51 a of the first smoothing capacitor C 51 ( FIG. 20 ). In a case where current has flowed to the first smoothing capacitor C 51 , the end-to-end voltage V 51 of the first smoothing capacitor C 51 rises, and in a case where current has flowed to the second smoothing capacitor C 52 , the end-to-end voltage V 52 of the second smoothing capacitor C 52 rises, so a balance between the voltages applied to the smoothing capacitors C 51 and C 52 can be maintained with a simple configuration.

In the voltage smoothing circuit 514 pertaining to the present embodiment, depending on the way the voltage equal to or greater than the first Zener voltage Vr 53 or equal to or greater than the second Zener voltage Vr 54 is applied, current no longer always flows to both of the first and second balancing resistors R 53 and R 54 ; for the first and second balancing resistors R 53 and R 54 , it is alright not to use resistors equipped with conventional withstand performance (e.g., cement resistors), and resistors whose dimensions are relatively small (e.g., chip resistors) can be utilized. Consequently, in the printed board P 1 on which the first and second balancing resistors R 53 and R 54 are mounted, the area occupied by the first and second balancing resistors R 53 and R 54 becomes smaller, so the printed board P 1 can be made smaller. Further, if current no longer always flows to both the first and second balancing resistors R 53 and R 54 , the amounts of heat emitted in the first and second balancing resistors R 53 and R 54 can be alleviated, on the effect on electronic parts near the balancing resistors R 53 and R 54 can be controlled.

(B)

In particular, in the voltage smoothing circuit 514 pertaining to the present embodiment, a voltage equal to or greater than the first Zener voltage Vr 53 or equal to or greater than the second Zener voltage Vr 54 is applied only to either one of the first Zener diode RZ 53 or the second Zener diode RZ 54 , so current does not always flow to both of the first and second balancing resistors R 53 and R 54 . Consequently, resistors whose dimensions are relatively small (e.g., chip resistors) can be utilized tier the first and second balancing resistors R 53 and R 54 , and the amounts of heat emitted in the first and second balancing resistors R 53 and R 54 can be alleviated.

(C)

Further, in the voltage smoothing circuit 514 pertaining to the present embodiment, in a case supposing that the value of the voltage that the power supply portion 13 outputs is “718 V” for example, the Zener voltages Vr 53 and Vr 54 of the Zener diodes RZ 53 and RZ 54 are both decided as “360 V”. Because of this, current flows only to either one of the first Zener diode RZ 53 or the second Zener diode RZ 54 , so the amounts of heat emitted in the first and second balancing resistors R 53 and R 54 can be alleviated with a simple configuration.

(D)

Further, in the voltage smoothing circuit 514 pertaining to the present embodiment, the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are substantially the same as or less than the rated voltages of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 . Because of this, voltages that are the same as or larger than the values of the first Zener voltage Vr 53 and the second Zener voltage Vr 54 are applied to the first and second smoothing capacitors C 51 and C 52 .

(E)

Further, in the voltage smoothing circuit 514 pertaining to the present embodiment, the first balancing resistor R 53 has a resistance value that is smaller than the value of the internal resistor R 51 a of the first smoothing capacitor C 51 . The second balancing resistor R 54 has a resistance value that is smaller than the value of the internal resistor R 52 a of the second smoothing capacitor C 52 . Because of this, the amounts of current flowing to the first balancing resistor R 53 and the second balancing resistor R 54 become larger than the amounts of current flowing to the internal resistors R 51 a and R 52 a of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 , so the amount of currents flowing to the first smoothing capacitor C 51 and the second smoothing capacitor C 52 can be controlled. Consequently, the voltages applied to the first smoothing capacitor C 51 and the second smoothing capacitor C 52 can be made lower.

(4) Modification

In the present embodiment, a case where the voltage smoothing circuit 514 has the configuration shown in FIGS. 18 to 20 has been described. However, the voltage smoothing circuit may also have the configuration shown in FIG. 21 . A voltage smoothing circuit 514 ′ in FIG. 21 is further equipped with a third auxiliary resistor R 531 and a fourth auxiliary resistor R 532 in addition to the configuration of the voltage smoothing circuit 514 already described. The third auxiliary resistor R 531 is connected in parallel to both ends of the first Zener diode RZ 53 . The fourth auxiliary resistor R 532 is connected in parallel to both ends of the second Zener diode RZ 54 .

According to the voltage smoothing circuit 514 ′ pertaining to FIG. 21 , in a case where the voltage V 51 larger than the first Zener voltage Vr 53 has been applied to the first Zener diode RZ 53 (V 51 >Vr 53 ), the current flowing through the first balancing resistor R 53 branches and flows to the first Zener diode RZ 53 and the third auxiliary resistor R 531 . Conversely, in a case where the voltage V 52 larger than the second Zener voltage Vr 54 has been applied to the second Zener diode RZ 54 (V 52 >Vr 54 ), the current flowing through the second balancing resistor R 54 branches and flows to the second Zener diode RZ 54 and the fourth auxiliary resistor R 532 . Because of this, the amounts of current flowing to the first Zener diode RZ 53 and the second Zener diode RZ 54 become smaller compared to the voltage smoothing circuit 514 , so the operating voltages and the rated power of the first Zener diode RZ 53 and the second Zener diode RZ 54 can be set low, and diodes whose rated currents are relatively small can be used for the first Zener diode RZ 53 and the second Zener diode RZ 54 . Consequently, costs pertaining to the voltage smoothing circuit 514 ′ can be reduced (in particular, the cost of the first Zener diode RZ 53 and the second Zener diode RZ 54 can be cut).

Further, the third auxiliary resistor R 531 and the fourth auxiliary resistor R 532 can also function as a discharge circuit of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 at the time of power shutdown of the motor driver 1 . Consequently, it is not necessary to separately dispose a discharge circuit of the first smoothing capacitor C 51 and the second smoothing capacitor C 52 .

The voltage smoothing circuit 514 ′ has the same configuration as FIGS. 18 to 20 excluding the third auxiliary resistor R 531 and the fourth auxiliary resistor R 532 , so in FIG. 21 , the same reference signs as in FIGS. 18 to 20 are given excluding the third auxiliary resistor R 531 and the fourth auxiliary resistor R 532 .

Seventh Embodiment

In the sixth embodiment, a case where current flows only to either one of the first Zener diode RZ 53 or the second Zener diode RZ 54 was described, but in the present embodiment, a voltage smoothing circuit that performs an operation differing from the sixth embodiment will be described.

(1) Configuration of Voltage Smoothing Circuit

FIGS. 22 to 24 are circuit diagrams of a voltage smoothing circuit 614 pertaining to the present embodiment. The main circuit configuration of the voltage smoothing circuit 614 is the same as that of the voltage smoothing circuit 514 pertaining to the sixth embodiment. That is, the voltage smoothing circuit 614 is equipped with a first smoothing capacitor C 61 , a second smoothing capacitor C 62 , a first balancing resistor R 63 , a second balancing resistor R 64 , a first Zener diode RZ 63 (which corresponds to a first conduction regulating portion), and a second Zener diode RZ 64 (which corresponds to a second conduction regulating portion).

The first smoothing capacitor C 61 and the second smoothing capacitor C 62 are connected in series to each other and are connected in parallel to the power supply portion 13 . The first smoothing capacitor C 61 and the second smoothing capacitor C 62 respectively have internal resistors R 61 a and R 62 a and capacitance elements C 61 a and C 62 a and further smooth the voltage outputted from the power supply portion 13 .

The first balancing resistor R 63 is connected in parallel to the first smoothing capacitor C 61 , and the second balancing resistor R 64 is connected in parallel to the second smoothing capacitor C 62 . The first balancing resistor R 63 has a resistance value that is smaller than the value of the internal resistor R 61 a of the first smoothing capacitor C 61 , and the second balancing resistor R 64 has a resistance value that is smaller than the value of the internal resistor R 62 a of the second smoothing capacitor C 62 .

The first Zener diode RZ 63 is connected in series to the first balancing resistor R 63 , and the second Zener diode RZ 64 is connected in series to the second balancing resistor R 64 . The first Zener diode RZ 63 conducts current in one direction (that is, a direction from the cathode to the anode of the first Zener diode R 263 ) to the first balancing resistor R 63 in a case where a voltage equal to or greater than a first Zener voltage Vr 63 (a first predetermined voltage) has been applied. The second Zener diode RZ 64 conducts current in one direction (that is, a direction from the cathode to the anode of the second Zener diode RZ 64 ) to the second balancing resistor R 64 in a case where a voltage equal to or greater than a second Zener voltage Vr 64 (a second predetermined voltage) has been applied.

Further, the first Zener voltage Vr 63 is decided, on the basis of the value of the voltage Vdc of the power supply portion 13 , in such a way as to become a value that is lower than a voltage V 61 applied to both ends of the first smoothing capacitor C 61 . The second Zener voltage Vr 64 is decided, on the basis of the value of the voltage Vdc of the power supply portion 13 , in such a way as to become a value that is lower than a voltage V 62 applied to both ends of the second smoothing capacitor C 62 . As an example, in a case supposing that the voltage Vdc is “718 V”, the first Zener voltage Vr 63 and the second Zener voltage Vr 64 are respectively decided as “240 V”, which is equal to or less than the voltage Vdc. That is, in the present embodiment, the first Zener diode RZ 63 and the second Zener diode P 164 are configured more economically than in the sixth embodiment because Zener diodes whose Zener voltages are low compared to the first Zener diode RZ 53 and the second Zener diode RZ 54 pertaining to the sixth embodiment described above are utilized.

Because of this, supposing that the smoothing capacitors C 61 and C 62 have the same capacitances (as an example, 1920 μC), in a case where there are no variations between the internal resistors R 61 a and R 62 a of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 , the voltages V 61 and V 62 that are each 359 V are applied to both ends of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 . In this case, a voltage equal to or greater than the first Zener voltage Vr 63 is applied to the first Zener diode R 263 , and a voltage equal to or greater than the second Zener voltage Vr 64 is applied to the second Zener diode RZ 64 . When this happens, current flows to both a current path I 63 on the upper side configured by the first balancing resistor R 63 and the first Zener diode RZ 63 and a current path I 64 on the lower side configured by the second balancing resistor R 64 and the second Zener diode RZ 64 . At this time, current does not flow to the internal resistors R 61 a and R 62 a because the end-to-end voltages V 61 and V 62 of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 are equal.

On the other hand, also in a case where there are variations between the internal resistors R 61 a and R 62 a , sometimes a voltage equal to or greater than the first Zener voltage Vr 63 is applied to the first Zener diode RZ 63 and equal to or greater than the second Zener voltage Vr 64 is applied also to the second Zener diode RZ 64 . That is, in the present embodiment, sometimes voltages that become equal to or greater than the first Zener voltage Vr 63 and equal to or greater than the second Zener voltage Vr 64 are applied to both the first Zener diode RZ 63 and the second Zener diode RZ 64 . For example, in a case where the end-to-end voltage V 61 of the first smoothing capacitor C 61 is 310 V and the end-to-end voltage V 62 of the second smoothing capacitor C 62 is 408 V, a voltage equal to or greater than the first Zener voltage Vr 63 and a voltage equal to or greater than the second Zener voltage Vr 64 are respectively applied to the first Zener diode RZ 63 and the second Zener diode RZ 64 , so currents flow to the current path I 63 including the first Zener diode RZ 63 and the current path I 64 including the second Zener diode RZ 64 . As for the currents that have flowed through the current paths I 63 and I 64 in this way, the difference between these currents flows to the internal resistor R 61 a or the internal resistor R 62 a depending on the magnitudes of the end-to-end voltages V 61 and V 62 of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 .

Moreover, like in the first embodiment, the first Zener voltage Vr 63 is decided in such a way as to become equal to or less than the rated voltage of the first smoothing capacitor C 61 , and the second Zener voltage Vr 64 is decided in such a way as to become equal to or less than the rated voltage of the second smoothing capacitor C 62 .

Further, the values of the Zener voltages Vr 63 and Vr 64 are decided considering also the values of the first balancing resistor R 63 and the second balancing resistor R 64 in addition to the voltage Vdc and the rated voltages of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 .

(2) Operation

Next, the operation of the voltage smoothing circuit 614 will be described using FIGS. 22 and 24 . Below, for the sake of simplifying the description, it will be supposed that the resistance values of the balancing resistors R 63 and R 64 are equal, the first and second Zener voltages Vr 63 and Vr 64 are both “240 V”, and the voltage Vdc of the power supply portion 13 is 718 V.

First, according to the configuration of the voltage smoothing circuit 614 , the voltage V 61 applied to both ends of the first smoothing capacitor C 61 is equal to the voltage applied to the current path I 63 , and the voltage V 62 applied to both ends of the second smoothing capacitor C 62 is equal to the voltage applied to the current path I 64 . On the other hand, the same capacitors are used for the smoothing capacitors C 61 and C 62 , so ideally there would be substantially no variations between the internal resistors R 61 a and R 62 a or any variations would be small (R 61 a ≈R 62 a ), and thus the end-to-end voltage V 61 of the first smoothing capacitor C 61 and the end-to-end voltage V 62 of the second smoothing capacitor C 62 would be in a state in which they become equal to or less than the rated voltages of the smoothing capacitors C 61 and C 62 , respectively, and become substantially equal. In this ideal state, the voltages V 61 and V 62 applied to the current paths I 63 and I 64 are respectively larger than the first Zener voltage Vr 63 and the second Zener voltage Vr 64 (V 61 >Vr 63 , V 62 >Vr 64 ), current based on the difference voltage between the voltage V 61 and the first Zener voltage Vr 63 flows on the current path I 63 , and current based on the difference voltage between the voltage V 62 and the second Zener voltage Vr 64 flows on the current path I 64 . Current does not flow on the internal resistors R 61 a and R 62 a , and the first and second smoothing capacitors C 61 and C 62 take a state where a balance between their voltages is maintained ( FIG. 22 ).

However, if there are variations between the internal resistors R 61 a and R 6 a , a magnitude relation arises between the voltages V 61 and V 62 applied to the smoothing capacitors C 61 and C 62 , and the voltage smoothing circuit takes a state where the balance between the voltages of the first and second smoothing capacitors C 61 and C 62 is disrupted. On the basis of this magnitude relation, the voltage smoothing circuit 614 takes either of the following operations.

(2-1) Case where End-to-End Voltage V 61 of First Smoothing Capacitor C 61 is Larger than End-to-end Voltage V 62 of Second Smoothing Capacitor C 62 (V 61 >V 62 )

It will be supposed that the end-to-end voltage V 61 is 380 V and the end-to-end voltage V 62 is 338 V. Because the end-to-end voltages V 61 and V 62 are equal to or greater than the first and second Zener voltages Vr 63 and Vr 64 , the first and second Zener diodes RZ 63 and RZ 64 both operate, the end-to-end voltage of the first Zener diodes RZ 63 is clipped to the first Zener voltage Vr 63 , and the end-to-end voltage of the second Zener diode RZ 64 is clipped to the second Zener voltage Vr 64 . When this happens, current flows on the current path I 63 in the order of the first balancing resistor R 63 and the first Zener diode RZ 63 and current flows on the current path I 64 in the order from the second balancing resistor R 64 to the second Zener diode RZ 64 ( FIG. 23 ).

Further, the voltages acting on the balancing resistors R 63 and R 64 respectively become difference voltages between the end-to-end voltages V 61 and V 62 and the Zener voltages Vr 63 and Vr 64 (V 61 −Vr 63 , V 62 −Vr 64 ). Here, the end-to-end voltage V 61 is larger than the end-to-end voltage V 62 (V 61 >V 62 ), so the voltage acting on the first balancing resistor R 63 is larger than the voltage acting on the second balancing resistor R 64 . Thus, the current flowing through the first balancing resistor R 63 (that is, the current flowing on the current path I 63 ) becomes more than the current flowing through the second balancing resistor R 64 (that is, the current flowing on the current path I 64 ). That is, the current flowing on the current path I 63 branches and flows on the current path I 64 and on the internal resistor R 62 a of the second smoothing capacitor C 62 via the point-of-connection s 1 . That is, current does not flow to the internal resistor R 61 a of the first smoothing capacitor C 61 , but a difference current between the current flowing on the current path I 63 and the current flowing on the current path I 64 flows to the internal resistor R 62 a of the second smoothing capacitor C 62 . Because current flows into the internal resistor R 62 a in this way, the voltage V 62 applied to both ends of the second smoothing capacitor C 62 becomes larger. The voltage V 61 is expressed as “Vdc−V 62 ”, so it becomes smaller as the voltage V 62 becomes larger.

Because of the above operation, before long the end-to-end voltages V 61 and V 62 become substantially equal, and although currents based on the differences between the end-to-end voltages V 61 and V 62 and the Zener voltages Vr 63 and Vr 64 flow on the current path I 63 and the current path I 64 , current no longer flows to the internal resistor R 62 a of the second smoothing capacitor C 62 ( FIG. 22 ). In this way, because of the above operation, in a case where the end-to-end voltage V 61 is larger than the end-to-end voltage V 62 , the voltage smoothing circuit 614 works in such a way as to make smaller the end-to-end voltage V 61 of the first smoothing capacitor C 61 and make larger the end-to-end voltage V 62 of the second smoothing capacitor C 62 , so a state is reached where a balance between the end-to-end voltages V 61 and V 62 is maintained, and an excessive voltage application to the first smoothing capacitor C 61 can be avoided.

(2-2) Case where End-to-End Voltage V 61 of First Smoothing Capacitor C 61 is Smaller than End-to-End Voltage V 62 of Second Smoothing Capacitor C 62 (V 61 <V 62 )

It will be supposed that the end-to-end voltage V 61 is 338 V and the end-to-end voltage V 62 is 380 V. Because the end-to-end voltages V 61 and V 62 are equal to or greater than the first and second Zener voltages Vr 63 and Vr 64 , the first and second Zener diodes RZ 63 and RZ 64 both operate, the end-to-end voltage of the first Zener diodes RZ 63 is clipped to the first Zener voltage Vr 63 , and the end-to-end voltage of the second Zener diode RZ 64 is clipped to the second Zener voltage Vr 64 . When this happens, current flows on the current path I 63 in the order of the first balancing resistor R 63 and the first Zener diode RZ 63 , and current flows on the current path I 64 in the order from the second balancing resistor R 64 to the second Zener diode RZ 64 ( FIG. 24 ).

Further, the voltages acting on the balancing resistors R 63 and R 64 respectively become difference voltages between the end-to-end voltages V 61 and V 62 and the Zener voltages Vr 63 and Vr 64 (V 61 −Vr 63 , V 62 −Vr 64 ). Here, the end-to-end voltage V 62 is larger than the end-to-end voltage V 61 (V 61 <V 62 ), so the voltage acting on the second balancing resistor R 64 is larger than the voltage acting on the first balancing resistor R 63 . Thus, conversely from (2-1) described above, the current flowing through the second balancing resistor R 64 (that is, the current flowing on the current path I 64 ) becomes more than the current flowing through the first balancing resistor R 63 (that is, the current flowing on the current path I 63 ). That is, the current that has flowed from the power supply portion 13 branches and flows to the internal resistor R 61 a side of the first smoothing capacitor C 61 and the current path I 63 side, and thereafter the currents merge in the current path I 64 via the point-of-connection s 1 . That is, current does not flow to the internal resistor R 62 a of the second smoothing capacitor C 62 , but a difference current between the current flowing on the current path I 64 and the current flowing on the current path I 63 flows to the internal resistor R 61 a of the first smoothing capacitor C 61 . Because current flows into the internal resistor R 61 a in this way, the voltage V 61 applied to both ends of the first smoothing capacitor C 61 becomes larger. The voltage V 62 is expressed as “Vdc−V 61 ”, so it becomes smaller as the voltage V 61 becomes larger.

Because of the above operation, before long the end-to-end voltages V 61 and V 62 become substantially equal, and although currents based on the differences between the end-to-end voltages V 61 and V 62 and the Zener voltages Vr 63 and Vr 64 flow on the current path I 63 and the current path I 64 , current no longer flows to the internal resistor R 61 a of the first smoothing capacitor C 61 ( FIG. 22 ). In this way, because of the above operation, in a case where the end-to-end voltage V 62 is larger than the end-to-end voltage V 61 , the voltage smoothing circuit 614 works in such a way as to make smaller the end-to-end voltage V 62 of the second smoothing capacitor C 62 and make larger the end-to-end voltage V 61 of the first smoothing capacitor C 61 , so a state is reached where a balance between the end-to-end voltages V 61 and V 62 is maintained, and an excessive voltage application to the second smoothing capacitor C 62 can be avoided.

(3) Effects

(A)

According to the voltage smoothing circuit 614 pertaining to the present embodiment, a voltage equal to or greater than the first Zener voltage Vr 63 is applied to the first Zener diode RZ 63 , and a voltage equal to or greater than the second Zener voltage Vr 64 is applied also to the second Zener diode RZ 64 , so currents flow to both of the first Zener diode RZ 63 and the second Zener diode RZ 64 —that is, both of the first balancing resistor R 63 and the second balancing resistor R 64 .

In the present embodiment, the above operations are realized by utilizing Zener diodes whose Zener voltages are low compared to the sixth embodiment for the first Zener diode RZ 63 and the second Zener diode RZ 64 . For that reason, it can be said that the voltage smoothing circuit 614 pertaining to the present embodiment is a particularly effective method in a case where one wants to set the operating voltages and rated power of the Zener diodes that are conduction regulating portions low.

(B)

Further, according to the voltage smoothing circuit 614 pertaining to the present embodiment, current flows to the first Zener diode RZ 63 as a result of a voltage equal to or greater than the first Zener voltage Vr 63 being applied, and current flows to the second Zener diode RZ 64 as a result of a voltage equal to or greater than the second Zener voltage Vr 64 being applied. The voltages in the first Zener diode RZ 63 and the second. Zener diode RZ 64 are respectively clipped to the first Zener voltage Vr 63 and the second Zener voltage Vr 64 . For that reason, a difference voltage between the end-to-end voltage of the first smoothing capacitor C 61 and the first Zener voltage Vr 63 is applied to the first balancing resistor R 63 , and a difference voltage between the end-to-end voltage of the second smoothing capacitor C 62 and the second Zener voltage Vr 64 is applied to the second balancing resistor R 64 . Consequently, with a simple configuration the values of the currents flowing to the first and second balancing resistors R 63 and R 64 can be made smaller than conventionally, and the amounts of heat emitted in the first and second balancing resistors R 63 and R 64 can be alleviated, so the effects on electronic parts near the balancing resistors R 63 and R 64 can be controlled.

Consequently, with a simple configuration a balance between the voltages applied to the smoothing capacitors C 61 and C 62 can be maintained. Further, resistors whose dimensions are relatively small (e.g., chip resistors) can be utilized for the first balancing resistor R 63 and the second balancing resistor R 64 . In the printed board on which the first and second balancing resistors R 63 and R 64 are mounted, the area occupied by the first and second balancing resistors R 63 and R 64 becomes smaller, so the printed board can be made smaller.

(C)

Further, in the voltage smoothing circuit 614 pertaining to the present embodiment, the first Zener voltage Vr 63 and the second Zener voltage Vr 64 are equal to or less than the rated voltages of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 . Because of this, voltages that are larger than the values of the first Zener voltage Vr 63 and the second Zener voltage Vr 64 are respectively applied to the first and second smoothing capacitors C 61 and C 62 .

(D)

Further, according to the voltage smoothing circuit 614 pertaining to the present embodiment, the first balancing resistor R 63 has a resistance value that is smaller than the value of the internal resistor R 61 a of the first smoothing capacitor C 61 , and the second balancing resistor R 64 has a resistance value that is smaller than the value of the internal resistor R 62 a of the second smoothing capacitor C 62 . Because of this, the amounts of current flowing to the first balancing resistor R 63 and the second balancing resistor R 64 become more than the amounts of current flowing to the internal resistors R 61 a and R 62 a of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 , so the amounts of current flowing to the first smoothing capacitor C 61 and the second smoothing capacitor C 62 can be controlled. Consequently, the voltages applied to the first smoothing capacitor C 61 and the second smoothing capacitor C 62 can be made lower.

(4) Modifications

(a)

The voltage smoothing circuit pertaining to the present embodiment may also, like the voltage smoothing circuit 614 ′ pertaining to the sixth embodiment ( FIG. 21 ), have the configuration shown in FIG. 25 . A voltage smoothing circuit 614 ′ in FIG. 25 is further equipped with a third auxiliary resistor R 631 and a fourth auxiliary resistor R 632 in addition to the configuration of the voltage smoothing circuit 614 described in FIGS. 22 to 24 . The third auxiliary resistor R 631 is connected in parallel to both ends of the first Zener diode RZ 63 . The fourth auxiliary resistor R 632 is connected in parallel to both ends of the second Zener diode RZ 64 .

According to the voltage smoothing circuit 614 ′ pertaining to FIG. 25 , in a case where the Zener diodes RZ 63 and RZ 64 operate, the current flowing through the first balancing resistor R 63 branches and flows to the first Zener diode RZ 63 and the third auxiliary resistor R 631 , and the current flowing through the second balancing resistor R 64 branches and flows to the second Zener diode RZ 64 and the fourth auxiliary resistor R 632 . Because of this, the amounts of current flowing to the first Zener diode RZ 63 and the second Zener diode RZ 64 become smaller compared to the voltage smoothing circuit 614 , so the operating voltages and the rated power of the first Zener diode RZ 63 and the second Zener diode RZ 64 can be set low, and diodes whose rated currents are relatively small can be used for the first Zener diode RZ 63 and the second Zener diode RZ 64 . Consequently, costs pertaining to the voltage smoothing circuit 614 ′ can be reduced (in particular, the cost of the first Zener diode RZ 63 and the second Zener diode RZ 64 can be cut).

Further, the third auxiliary resistor R 631 and the fourth auxiliary resistor R 632 can also function as a discharge circuit of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 at the time of power shutdown of the motor driver 1 . Consequently, it is not necessary to separately dispose a discharge circuit of the first smoothing capacitor C 61 and the second smoothing capacitor C 62 .

The voltage smoothing circuit 614 has the same configuration as FIGS. 22 to 24 excluding the third auxiliary resistor R 631 and the fourth auxiliary resistor R 632 , so in FIG. 25 , the same reference signs as in FIGS. 22 to 24 are given excluding the third auxillary resistor R 631 and the fourth auxiliary resistor R 632 .

(b)

In “(2) Operation” of the present embodiment, a case where currents flow to both the current paths I 63 and I 64 even if there are variations between the internal resistors R 61 a and R 62 a and a magnitude relation arises between the end-to-end voltages V 61 and V 62 has been described. However, in the voltage smoothing circuit 614 pertaining to FIGS. 22 to 24 , in a case where the variations between the internal resistors R 61 a and R 62 a are extremely large and the difference between the end-to-end voltages V 61 and V 62 is large, it is conceivable that either one of the end-to-end voltages V 61 or V 62 will end up becoming smaller than the first Zener voltage Vr 63 or the second Zener voltage Vr 64 . In this case, first, only either one of the Zener diodes RZ 63 or RZ 64 to which the voltage equal to or greater than the Zener voltage Vr 63 or Vr 64 is being applied operates, and at the time when before long the difference between the end-to-end voltages V 61 and V 62 has become small, a voltage equal to or greater than the Zener voltage is applied also to the other Zener diode, and the Zener diode that was not operating also operates. Thereafter is the same as “(2) Operation” of the present embodiment. That is, the voltage smoothing circuit 614 in this case can take either of the following first state and second state.

First state: a state where a voltage equal to or greater than the first Zener voltage Vr 63 is applied to the first Zener diode RZ 63 and thereafter a voltage equal to or greater than the second Zener voltage Vr 64 is applied also to the second Zener diode RZ 64

Second state: a state where a voltage equal to or greater than the second Zener voltage Vr 64 is applied to the second Zener diode RZ 64 and thereafter a voltage equal to or greater than the first Zener voltage Vr 63 is applied also to the first Zener diode RZ 63

For the sake of describing a specific example of the first state, it will be supposed that the Zener voltages are “240 V”, the voltage Vdc of the power supply portion 13 is “718 V”, the end-to-end voltage V 61 is “500 V”, and the end-to-end voltage V 62 is “218 V”. In this case, first, only the first Zener diode RZ 63 operates and current flows into the internal resistor R 62 a like in FIG. 19 pertaining to the sixth embodiment. When this happens, the end-to-end voltage V 62 gradually becomes larger, so the value of the end-to-end voltage V 62 becomes equal to or greater than 240 V, whereby the second Zener diode RZ 64 that was not operating until then also starts to operate. Because of this, current flows as shown in FIG. 23 pertaining to the present embodiment, and before long astute is reached where a balance between the end-to-end voltages V 61 and V 62 is maintained.

Further, for the sake of describing a specific example of the second state, it will be supposed that the end-to-end voltage V 61 is “218 V” and the end-to-end voltage V 62 is “500 V”. In this case, first, only the second Zener diode RZ 64 operates and current flows to the internal resistor R 61 a like FIG. 20 pertaining to the sixth embodiment. When this happens, the end-to-end voltage V 61 gradually becomes larger, so the value of the end-to-end voltage V 61 becomes equal to or greater than 240 V, whereby the first Zener diode RZ 63 that was not operating until then also starts to operate. Because of this, current flows as shown in FIG. 24 pertaining to the present embodiment, and before long a state is reached where a balance between the end-to-end voltages V 61 and V 62 is maintained.

Other Embodiments

Embodiments of the present invention and modifications thereof have been described on the basis of the drawings, but the specific configurations are not limited these embodiments and their modifications and can be changed without departing from the scope of the invention.

(a)

In the voltage smoothing circuits 14 , 114 , and 214 pertaining to the first to third embodiments, cases were described where one Zener diode RZ 4 , RZ 14 , or RZ 24 is disposed and the Zener voltage Vr 4 , Vr 14 , or Vr 24 is 376 V, for example. However, there are few commonly available Zener diodes whose Zener voltage is relatively large (360 V, etc.). Therefore, plural Zener diodes may be connected in series and utilized for the Zener diodes RZ 4 , RZ 14 , and RZ 24 . For example, in a case where the Zener voltage is to be “376 V”, this can be accommodated by connecting in series eight Zener diodes whose Zener voltage is about 47 V.

However, in the case of using plural Zener diodes, parts costs inevitably end up becoming higher. Consequently, it is best to comprehensively consider the cost of the Zener diode to be utilized and the power loss target value of the balancing resistors R 3 and R 13 (or the first balancing resistor R 23 and the second balancing resistor R 24 ) and decide the Zener voltages Vr 4 , Vr 14 , and Vr 24 and the number of Zener diodes to be utilized.

Likewise, in the sixth embodiment and the seventh embodiment also, plural Zener diodes can be connected in series and utilized for the first Zener diodes RZ 53 and RZ 63 and the second Zener diodes RZ 54 and RZ 64 .

(b)

Further, in the voltage smoothing circuits 14 , 114 , and 214 pertaining to the first to third embodiments, cases were described where the “second conduction regulating portion” that conducts current in one direction on the current paths I 4 , I 14 , and I 24 in a case where a voltage equal to or greater than a predetermined voltage has been applied and maintains its end-to-end voltage at the predetermined voltage is configured by the Zener diodes RZ 4 , RZ 14 , and RZ 24 . However, as long as the second conduction regulating portion can conduct current in one direction to the balancing resistors R 3 and R 13 (or the first balancing resistor R 23 ) in a case where a voltage equal to or greater than the second predetermined voltage has been applied and maintain its end-to-end voltage at the second predetermined voltage, the second conduction regulating portion may be any kind of portion and may also be configured by something other than a Zener diode.

Likewise, in the sixth and seventh embodiments also, as long as the first conduction regulating portion and the second conduction regulating portion can conduct current in one direction to the first or second balancing resistors R 53 or R 63 and R 54 or R 64 in a case where a voltage equal to or greater than a predetermined voltage has been applied, the first conduction regulating portion and the second conduction regulating portion may be any kind of portion and may also be configured by something other than Zener diodes.

(c)

Further, in the first to fourth embodiments, cases satisfying the condition that the value of the balancing resistor is smaller than the value of the internal resistors of the smoothing capacitors have been described. However, this condition is not essential. In particular, in the method described in the third embodiment, the magnitude relation between the first balancing resistor and the internal resistor values of the smoothing capacitors changes depending on what values the various types of values included in the precondition are, such as the value of the Zener voltage, the value of “X %” representing the operating ranges of the end-to-end voltages in the smoothing capacitors, and so forth.

(d)

Further, in the first embodiment, only one method of deciding the balancing resistor R 1 and the Zener voltage Vr 4 was described in overview. However, the balancing resistor R 1 and the Zener voltage Vr 4 may also be decided like in “(2-2) Specific Example” of the third embodiment.

Further, as described in the second embodiment, in a case where there is only one balancing resistor, the value of this balancing resistor can be decided like in “(2) Method of Deciding Resistance Values of Balancing Resistors and Zener Voltage” in the fifth embodiment.

(e)

In the third embodiment, as shown in FIGS. 9 to 11 , a case where the Zener diode RZ 24 and the second balancing resistor R 24 are connected in order on the current path I 24 beginning with the side whose voltage is high was described. However, the order in which the elements are connected on the current path I 24 is not limited to this order; the elements may also be connected in the order of the second balancing resistor R 24 and the Zener diode RZ 24 .

Further, in the fourth to seventh embodiments also, the order in which the elements are connected on the current paths I 34 , I 44 , I 53 , I 54 , I 63 , and I 64 is not limited to the orders in FIGS. 15 to 20 and 22 to 24 .

The voltage smoothing circuit pertaining to the present invention can be utilized as a circuit for smoothing a power supply voltage supplied to an inverter portion in a motor driver tier driving a motor.