Regulator and electronic apparatus therewith

This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2005-017621 filed in Japan on Jan. 26, 2005, the entire contents of which are hereby incorporated by reference.

1. Field of the Invention

The present invention relates to a regulator incorporating an overvoltage protection circuit, and more particularly to a technique of reducing the electric power consumption thereof.

2. Description of Related Art

Conventionally, stabilized direct-current power supplies incorporate a regulator as means for yielding a constant output voltage without being influenced by the input voltage, the load current, the ambient temperature, etc. In particular, chopper-type regulators (switching regulators) that produce a constant output voltage by varying the duty of an output drive circuit offer the advantages of very low heat loss and efficient operation in cases where there is a great input-output voltage difference. Such regulators generally incorporate an overvoltage protection circuit (see, for example, Japanese Patent Application Laid-open No. 11-289759).

Certainly, with a conventional regulator incorporating an overvoltage protection circuit, when a voltage higher than the threshold value appears in the output stage, as when the load become open-circuited, the output operation of the regulator can be stopped. This helps prevent breakdown etc. of circuit elements due to overvoltage.

However, since the conventional regulator is so configured as to achieve overvoltage protection by constantly monitoring the output voltage without regard to whether it is in an operation-enabled or -disabled state or the state of the input and output voltages, it has the disadvantages of consuming unnecessary electric power in the overvoltage protection circuit. For example, in an overvoltage protection circuit that detects overvoltage based on the result of comparison between a division voltage obtained through resistor division of the output voltage and a predetermined reference voltage, electric power is lost by being steadily consumed by resistors, resulting in unnecessarily high electric power consumption. Thus, when the conventional regulator is adopted as a stabilized direct-current supply in a battery-operated electronic apparatus (such as a cellular phone), inconveniently, it tends to waste the electric power stored in the battery, unduly shortening the duration the electronic apparatus can be used.

In view of the conventionally experienced inconveniences discussed above, it is an object of the present invention to provide a regulator incorporating an overvoltage protection circuit that operates with reduced electric power consumption.

To achieve the above object, according to the present invention, in a regulator that produces a constant output voltage from an input voltage and that incorporates an overvoltage protection circuit that stops the output operation of the regulator when a voltage higher than a first threshold voltage appears, the overvoltage protection circuit includes switch means that turns on and off the overvoltage protection operation thereof according to a predetermined control signal. With this configuration, through the input of a proper control signal, it is possible to reduce the electric power wasted in the overvoltage protection circuit.

Moreover, according to the present invention, an electronic apparatus is provided with a battery that serves as an electric power source and a stabilized direct-current power supply that serves as means for converting the output of the battery. Adopted as the stabilized direct-current power supply here is the regulator described above. With this configuration, it is possible to prevent the electric power stored in the battery from being wasted in the overvoltage protection circuit, and thereby to lengthen the duration the electronic apparatus can be used.

FIG. 1A is a circuit diagram showing the electronic apparatus of a first embodiment of the present invention, and FIG. 1B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof;

FIG. 2A is a circuit diagram showing the electronic apparatus of a second embodiment of the present invention, and FIG. 2B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof;

FIG. 3A is a circuit diagram showing the electronic apparatus of a third embodiment of the present invention, FIG. 3B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof, and FIG. 3C is a circuit diagram showing an example of the configuration of the input voltage detection circuit thereof;

FIG. 4A is a circuit diagram showing the electronic apparatus of a fourth embodiment of the present invention, FIG. 4B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof, and FIG. 4C is a circuit diagram showing an example of the configuration of the output voltage detection circuit thereof;

FIG. 5A is a circuit diagram showing the electronic apparatus of a fifth embodiment of the present invention, and FIG. 5B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof;

First, the electronic apparatus of a first embodiment of the present invention will be described in detail with reference to FIGS. 1A and 1B . FIG. 1A is a circuit diagram showing the electronic apparatus of the first embodiment of the present invention, and FIG. 1B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof (each diagram partly presented as a block diagram). As shown in FIG. 1A , the electronic apparatus of this embodiment includes: a direct-current voltage source E 1 (for example, a lithium-ion battery) as the electric power source of the electronic apparatus; a stabilized direct-current power supply (a regulator IC 100 , smoothing capacitors C 1 and C 2 , a coil L 1 , a diode D 1 , and a resistor R 1 ) as means for converting the output of the direct-current voltage source E 1 ; and a light-emitting diode array LED as a load. The electronic apparatus is, for example, a cellular phone.

The stabilized direct-current power supply mentioned above is configured as a step-up chopper-type regulator composed of, as already described, a regulator IC 100 , smoothing capacitors C 1 and C 2 , a coil L 1 , a diode D 1 , and a resistor R 1 .

The regulator IC 100 includes, as the circuit blocks incorporated therein, an output drive circuit 101 , a soft start circuit 102 , an on/off control circuit 103 , an overheat protection circuit 104 , an overvoltage protection circuit 105 , an amplifier circuit 106 , an oscillation circuit 107 , an adder circuit 108 , a PWM (pulse width modulation) comparator circuit 109 , and an error amplifier circuit 110 . The regulator IC 100 further includes: a P-channel field-effect transistor FET 1 as means for controlling the output voltage; a P-channel field-effect transistor FET 2 and a resistor R 2 together as means for monitoring the output current; and a direct-current voltage source E 2 and resistors R 3 and R 4 together as means for setting the output voltage. The regulator IC 100 has all the just-mentioned circuit blocks and components thereof packaged into a semiconductor integrated circuit device.

The regulator IC 100 also has: an external terminal T 1 to which an input voltage Vin is applied; an external terminal T 2 to which a switching pulse voltage V SW is applied; an external terminal T 3 to which a drive control signal CTRL is applied; an external terminal T 4 to which the output voltage Vo is applied; an external terminal T 5 to which a voltage feedback signal FB is applied; and an external terminal T 6 that is grounded to a reference potential (GND potential).

The positive end of the direct-current voltage source E 1 is grounded via the smoothing capacitor C 1 , and is connected to one end of the coil L 1 and to the external terminal T 1 of the regulator IC 100 . The negative end of the direct-current voltage source E 1 is grounded. The other end of the coil L 1 is connected to the anode of the diode D 1 and to the external terminal T 2 of the regulator IC 100 . The cathode of the diode D 1 is grounded via the smoothing capacitor C 2 , and is connected to the anode-side end of the light-emitting diode array LED and to the external terminal T 4 of the regulator IC 100 . The cathode-side end of the light-emitting diode array LED is grounded via the resistor R 1 , and is connected to the external terminal T 5 of the regulator IC 100 .

Inside the regulator IC 100 , the sources of the transistors FET 1 and FET 2 are both connected to the external terminal T 2 , the drain of the transistor FET 1 is directly grounded, and the drain of the transistor FET 2 is grounded via the resistor R 2 . The gates of the transistors FET 1 and FET 2 are both connected to the gate signal output end of the output drive circuit 101 . The backgates of the transistors FET 1 and FET 2 are connected to their respective drains. One end of the resistor R 2 is connected to one input end of the amplifier circuit 106 , and the other end of the resistor R 2 is connected to the other input end of the amplifier circuit 106 . One input end of the adder circuit 108 is connected to the output end of the amplifier circuit 106 , and the other input end of the adder circuit 108 is connected to the output end of the oscillation circuit 107 . One input end of the PWM comparator circuit 109 is connected to the output end of the adder circuit 108 , and the other input end of the PWM comparator circuit 109 is connected to the output end of the error amplifier circuit 110 . The output end of the PWM comparator circuit 109 is connected to the PWM pulse signal input end of the output drive circuit 101 . One input end of the error amplifier circuit 110 is connected to the external terminal T 5 ; the other input end of the error amplifier circuit 110 is grounded via the resistor R 3 , and is connected via the resistor R 4 to the positive end of the direct-current voltage source E 2 . The negative end of the direct-current voltage source E 2 is grounded.

In the regulator IC 100 configured as described above, the error amplifier circuit 110 amplifies the error voltage between the voltage feedback signal FB (a monitoring voltage that varies with the output voltage Vo) applied to the external terminal T 5 and a predetermined reference voltage Vref (an output setting voltage that is produced by the direct-current voltage source E 2 and the resistors R 3 and R 4 ), and then feeds the amplified error signal to the PWM comparator circuit 109 . Thus, in this embodiment, the configuration is such that the voltage appearing at the node between the cathode-side end of the light-emitting diode array LED serving as the load and the resistor R 1 is fed back. This configuration, unlike one in which a voltage obtained through resistor division of the output voltage Vo is fed back, permits proper output stabilization operation that is not affected by variation of the forward voltage drop VF across the light-emitting diode array LED.

The current that is diverted from the external terminal T 2 to the transistor FET 2 is converted by the resistor R 2 into a voltage that serves as a current feedback signal (a monitoring voltage whose level varies with the output current). The amplifier circuit 106 amplifies this current feedback signal, and then feeds the amplified current feedback signal to the adder circuit 108 . The adder circuit 108 adds together the current feedback signal amplified by the amplifier circuit 106 and a triangular wave signal produced by the oscillation circuit 107 to give the triangular wave signal an offset commensurate with the output current. Through this feedback control of the output current, the output current can be kept constant.

The PWM comparator circuit 109 compares the output signal of the error amplifier circuit 110 and the triangular wave signal from the adder circuit 108 to produce a PWM pulse signal, and feeds the produced PWM pulse signal to the output drive circuit 101 . Thus, the ratio of the period during which the PWM pulse signal remains at logical high to the period during which it remains at logical low keeps varying according to the result of the comparison between the output signal of the error amplifier circuit 110 and the triangular wave signal.

According to the PWM pulse signal from the PWM comparator circuit 109 , the output drive circuit 101 determines the output duty, and varies the on-state periods of the transistors FET 1 and FET 2 accordingly. Incidentally, when the transistor FET 1 is on, the current from the direct-current voltage source E 1 flows through the coil L 1 , and thus electrical energy is stored in the coil L 1 . On the other hand, when the transistor FET 1 is off, the electrical energy stored in the coil L 1 produces a back electromotive force in the coil L 1 . The back electromotive force produced in the coil L 1 adds to the voltage of the direct-current voltage source E 1 , and the resulting sum voltage charges the smoothing capacitor C 2 via the diode D 1 . These operations are repeated, so that the light-emitting diode array LED serving as the load is supplied with a direct-current output smoothed by the smoothing capacitor C 2 .

Parallel with the above sequence of operations, for the purpose of avoiding rush current at the startup of the regulator IC 100 , according to the drive control signal applied to the external terminal T 3 , the soft start circuit 102 starts the output drive circuit 101 softly. Moreover, according to the drive control signal applied to the external terminal T 3 , the on/off control circuit 103 enables and disables the output drive circuit 101 .

Moreover, the overheat protection circuit 104 enables and disables the output drive circuit 101 so that, when the chip temperature of the regulator IC 100 becomes higher than a threshold value, the output operation of the regulator IC 100 is stopped. Moreover, by monitoring the output voltage Vo applied to the external terminal T 4 , the overvoltage protection circuit 105 enables and disables the output drive circuit 101 so that, when a voltage higher than a threshold value appears in the output stage, as when the light-emitting diode array LED serving as the load becomes open-circuited, the output operation of the regulator IC 100 is stopped.

In this embodiment, as shown in FIG. 1B , the overvoltage protection circuit 105 includes: a comparator circuit CMP 1 , a direct-current voltage source E 3 , resistors R 5 and R 6 , and a P-channel field-effect transistor FET 3 . The transistor FET 3 serves as switch means for turning on and off the overvoltage protection operation of the overvoltage protection circuit 105 according to a predetermined control signal.

One input end of the comparator circuit CMP 1 is connected to the positive end of the direct-current voltage source E 3 . The negative end of the direct-current voltage source E 3 is grounded. The other input end of the comparator circuit CMP 1 is connected via the resistor R 5 to the drain of the transistor FET 3 , and is grounded via the resistor R 6 . The source of the transistor FET 3 is connected to the external terminal T 4 . The backgate of the transistor FET 3 is connected to the drain of the transistor FET 3 itself. A predetermined control signal is applied to the gate of the transistor FET 3 .

In the overvoltage protection circuit 105 configured as described above, when the transistor FET 3 is on, the comparator circuit CMP 1 compares the output voltage Vo applied to the external terminal T 4 with a first threshold voltage Vth 1 (the voltage at the positive end of the direct-current voltage source E 3 ), and enables and disables the output drive circuit 101 so that, if a voltage higher than the first threshold voltage Vth 1 appears in the output voltage Vo, the output operation of the regulator IC 100 is stopped.

On the other hand, when the transistor FET 3 is off, the monitoring of the output voltage Vo by the comparator circuit CMP 1 is suspended, and the overvoltage protection operation of the overvoltage protection circuit 105 is kept off. In this state, the current path leading from the external terminal T 4 through the resistors R 5 and R 6 to ground is cut off by the transistor FET 3 in an off state, and therefore no electric power is lost in the resistors R 5 and R 6 .

As described above, in this embodiment, the overvoltage protection circuit 105 includes switching means (the transistor FET 3 ) that turns on and off the overvoltage protection operation thereof according to a predetermined control signal. With this configuration, through the input of a proper control signal to the switch means, it is possible to reduce the electric power wasted in the overvoltage protection circuit 105 (that is, the waste of the electric power of the direct-current voltage source E 1 , which is a battery), and thereby to lengthen the duration the electronic apparatus can be used.

Next, the electronic apparatus of a second embodiment of the present invention will be described in detail with reference to FIGS. 2A and 2B . FIG. 2A is a circuit diagram showing the electronic apparatus of the second embodiment of the present invention, and FIG. 2 B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof (each diagram partly presented as a block diagram). As shown in FIGS. 2A and 2B , the electronic apparatus of this embodiment has largely the same configuration as the electronic apparatus of the first embodiment shown in FIGS. 1A and 1B described previously. Accordingly, such circuit blocks and components as find their counterparts in the first embodiment are identified with reference numerals and symbols common to FIGS. 1A and 1B , and no detailed explanations thereof will be repeated. Thus, the following description of this embodiment emphasizes the features unique thereto.

As shown in FIGS. 2A and 2B , in the regulator IC 100 of this embodiment, the on/off control circuit 103 enables and disables the output drive circuit 101 according to the drive control signal CTRL applied to the external terminal T 3 . In addition, the on/off control circuit 103 produces a control signal S 1 to turn on and off the overvoltage protection operation of the overvoltage protection circuit 105 synchronously with the timing with which the output operation of the regulator IC 100 is turned on and off. The on/off control circuit 103 feeds the thus produced control signal S 1 to the gate of the transistor FET 3 . With this configuration, when the output operation of the regulator IC 100 is turned off, the overvoltage protection operation is disabled from being unnecessarily continued. Thus, it is possible to reduce the electric power wasted in the overvoltage protection circuit 105 (that is, the waste of the electric power of the direct-current voltage source E 1 , which is a battery), and thereby to lengthen the duration the electronic apparatus can be used.

Next, the electronic apparatus of a third embodiment of the present invention will be described in detail with reference to FIGS. 3A to 3C . FIG. 3A is a circuit diagram showing the electronic apparatus of the third embodiment of the present invention, FIG. 3B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof, and FIG. 3C is a circuit diagram showing an example of the configuration of the input voltage monitoring circuit thereof (each diagram partly presented as a block diagram). As shown in FIGS. 3A to 3C , the electronic apparatus of this embodiment has largely the same configuration as the electronic apparatus of the first embodiment shown in FIGS. 1A and 1B described previously. Accordingly, such circuit blocks and components as find their counterparts in the first embodiment are identified with reference numerals and symbols common to FIGS. 1A and 1B , and no detailed explanations thereof will be repeated. Thus, the following description of this embodiment emphasizes the features unique thereto.

As shown in FIGS. 3A and 3B , the regulator IC 100 of this embodiment further includes, in addition to the circuit blocks and components already mentioned, an input voltage monitoring circuit 111 . The input voltage monitoring circuit 111 produces a control signal S 2 according to the result of monitoring of the input voltage Vin applied to the external terminal T 1 , and feeds the thus produced control signal S 2 to the gate of transistor FET 3 .

As shown in FIG. 3C , the input voltage monitoring circuit 111 includes a comparator circuit CMP 2 , a direct-current voltage source E 4 , and resistors R 7 and R 8 . One input end of the comparator circuit CMP 2 is connected to the external terminal T 1 ; the other input terminal of the comparator circuit CMP 2 is grounded via the resistor R 7 , and is connected via the resistor R 8 to the positive end of the direct-current voltage source E 4 . The negative end of the direct-current voltage source E 4 is grounded. Thus, the input voltage monitoring circuit 111 produces the control signal S 2 so that, when the input voltage Vin applied to the external terminal T 1 is lower than a second threshold voltage Vth 2 (a protection operation disabling voltage that is produced by the direct-current voltage source E 4 and the resistors R 7 and R 8 ), the overvoltage protection operation of the overvoltage protection circuit 105 is turned off.

Incidentally, the second threshold voltage Vth 2 can be set properly according to the mean voltage of the direct-current voltage source E 1 . For example, in a case where a lithium-ion battery is used as the direct-current voltage source E 1 , considering that its mean voltage is about 3.6 [V], the second threshold voltage Vth 2 is set to be lower than that voltage, specifically about 3.2 [V].

With this configuration, whenever the input voltage Vin (that is, the electric power stored in the direct-current voltage source E 1 ) lowers, and thus protection against overvoltage is found to be less necessary, the overvoltage protection operation can be disabled. Thus, it is possible to reduce the electric power wasted in the overvoltage protection circuit 105 (that is, the waste of the electric power of the direct-current voltage source E 1 , which is a battery), and thereby to lengthen the duration the electronic apparatus can be used.

Next, the electronic apparatus of a fourth embodiment of the present invention will be described in detail with reference to FIGS. 4A to 4C . FIG. 4A is a circuit diagram showing the electronic apparatus of the fourth embodiment of the present invention, FIG. 4B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof, and FIG. 4C is a circuit diagram showing an example of the configuration of the input voltage monitoring circuit thereof (each diagram partly presented as a block diagram). As shown in FIGS. 4A to 4C , the electronic apparatus of this embodiment has largely the same configuration as the electronic apparatus of the first embodiment shown in FIGS. 1A and 1B described previously. Accordingly, such circuit blocks and components as find their counterparts in the first embodiment are identified with reference numerals and symbols common to FIGS. 1A and 1B , and no detailed explanations thereof will be repeated. Thus, the following description of this embodiment emphasizes the features unique thereto.

As shown in FIGS. 4A and 4B , the regulator IC 100 of this embodiment further includes, in addition to the circuit blocks and components already mentioned, an output voltage monitoring circuit 112 . The output voltage monitoring circuit 112 produces a control signal S 3 according to the result of monitoring of the output voltage Vo applied to the external terminal T 4 , and feeds the thus produced control signal S 3 to the gate of transistor FET 3 .

As shown in FIG. 4C , the output voltage monitoring circuit 112 includes a comparator circuit CMP 3 , a direct-current voltage source E 5 , and resistors R 9 and R 10 . One input end of the comparator circuit CMP 3 is connected to the external terminal T 4 ; the other input terminal of the comparator circuit CMP 3 is grounded via the resistor R 9 , and is connected via the resistor R 10 to the positive end of the direct-current voltage source E 5 . The negative end of the direct-current voltage source E 5 is grounded. Thus, the output voltage monitoring circuit 112 produces the control signal S 3 so that, when the output voltage Vo applied to the external terminal T 4 is lower than a third threshold voltage Vth 3 (a protection operation disabling voltage that is produced by the direct-current voltage source E 5 and the resistors R 9 and R 10 ), the overvoltage protection operation of the overvoltage protection circuit 105 is turned off.

Incidentally, the third threshold voltage Vth 3 can be set properly according to the mean voltage of the direct-current voltage source E 1 . For example, in a case where a lithium-ion battery is used as the direct-current voltage source E 1 , considering that its mean voltage is about 3.6 [V], the third threshold voltage Vth 3 is set to be approximately equal to that voltage, specifically about 3.6 [V].

With this configuration, when the light emission operation of the light-emitting diode array LED serving as the load is turned off, the overvoltage protection operation is disabled from being unnecessarily continued. Thus, it is possible to reduce the electric power wasted in the overvoltage protection circuit 105 (that is, the waste of the electric power of the direct-current voltage source E 1 , which is a battery), and thereby to lengthen the duration the electronic apparatus can be used.

Lastly, the electronic apparatus of a fifth embodiment of the present invention will be described in detail with reference to FIGS. 5A and 5B . FIG. 5A is a circuit diagram showing the electronic apparatus of the fifth embodiment of the present invention, and FIG. 5B is a circuit diagram showing an example of the configuration of the overvoltage protection circuit thereof (each diagram partly presented as a block diagram). As shown in FIGS. 5A and 5B , the electronic apparatus of this embodiment has largely the same configuration as the electronic apparatus of the first embodiment shown in FIGS. 1A and 1B described previously. Accordingly, such circuit blocks and components as find their counterparts in the first embodiment are identified with reference numerals and symbols common to FIGS. 1A and 1B , and no detailed explanations thereof will be repeated. Thus, the following description of this embodiment emphasizes the features unique thereto.

As shown in FIGS. 5A and 5B , the regulator IC 100 of this embodiment further includes, in addition to the circuit blocks and components already mentioned, an external terminal T 7 for receiving, from outside the IC, a control signal S 4 to be applied to the gate of the transistor FET 3 . With this configuration, through the input of a proper control signal S 4 to the transistor FET 3 from outside the IC, it is possible to reduce the electric power wasted in the overvoltage protection circuit 105 (that is, the waste of the electric power of the direct-current voltage source E 1 , which is a battery), and thereby to lengthen the duration the electronic apparatus can be used.

The embodiments described above all deal with cases where the present invention is applied to a step-up chopper type regulator. This, however, is not meant to limit the application of the present invention to such regulators. It should be understood that the present invention is applicable to regulators in general that produce a constant output voltage from an input voltage and that incorporate an overvoltage protection circuit that stops the output operation of the regulator when the output voltage becomes higher than a predetermined threshold voltage.

That is, the present invention is suitable in regulators in general that incorporate an overvoltage protection circuit, and particularly useful in reducing the electric power consumption thereof.

It should be understood that the present invention may be practiced in any manner other than specifically described as embodiments above, and many modifications and variations are possible within the spirit of the present invention.