Cell voltage detecting apparatus

The present application claims benefit of the filing date of Japanese Patent Application No. 2007-309021 filed on Nov. 29, 2007 which is incorporated herein by reference.

The present invention relates to a cell voltage detecting apparatus for detecting voltage across terminals of a cell module in which cells are connected in series, and more particularly, to the cell voltage detecting apparatus for detecting voltage by converting voltage across the cell module into current.

Vehicles having traveling motors such as electric cars and hybrid cars are equipped with battery packs each of which is made up of a plurality of serially connected cell modules each of which is made up of a plurality of serially connected cells so as to supply power to the motor. In the battery pack, the charged state of each of a plurality of cell modules may be different each other after repeated charging/discharging. For this reason, each of voltages (module voltage) across the cell modules is monitored.

In order to detect the module voltages across these cell modules, an operational amplifier is used so as to convert the module voltage of each cell module into a constant current which is proportional to the module voltage, and so as to convert the constant current into the voltage again (see, for example, “Design of OP AMP Circuit”, by Michio OKAMURA, published by CQ Publishing Co., Ltd., Tokyo, Japan, pp. 252-257). In this detecting method, a constant current circuit including an operational amplifier, etc. is used so as to precisely send/receive analog quantities between circuits having different potentials such as the cell modules in which cells are serially connected, etc.

Also, it is well known that a “cell voltage detecting circuit” detects the cell voltage of the battery pack by converting the cell voltage of the battery pack into a current using the constant current circuit, allowing this current to pass through a resistor with reference to a minus terminal (ground terminal) of the battery pack, and measuring a voltage across the terminals of the resistor so as to detect the cell voltage (for example, see JP 3721839 B2 ([0035]-[0046], FIG. 2)).

Also, in the battery packs of electric cars and hybrid cars, a manual service plug or switch is often provided near the center of the serially connected cell modules. This service plug or switch electrically divides the serially connected cells near the center of the battery pack to divide a voltage across the battery pack in half so as to facilitate handling the battery pack at the time of maintenance. Consequently, there is a standard which recommends to provide the switch, etc. at the center of the battery pack (for example, see SAE J2344 (Guidelines for Electric Vehicle Safety)).

However, because the cell voltage across the cell is detected by allowing a constant current to pass through a resistor used for detecting voltage with reference to a minus terminal (ground terminal) of the battery pack in the “cell voltage detecting circuit” (see JP 3721839 B2 ([0035]-[0046], FIG. 2)), a total voltage of the battery pack (for example, in the case of the battery pack including ten cells, 200 volts), not each cell voltage across the cell (e.g., 20 volts), is applied to each semiconductor device (e.g., P-channel MOS FET) which constitutes the constant current circuit. For this reason, a power semiconductor device driven by the operational amplifier needs to have enough voltage endurance (source-to-drain voltage endurance) to endure the total voltage of the battery pack (200 volts). However, a problem arises that the P-channel power MOS FETs having voltage endurance over 200 volts are generally expensive because such P-channel power MOS FETs are limited in model numbers and production volume.

Further, as defined in the SAE J2344, in the case where a switch is provided near the center of the cell modules which constitute the battery pack to cut off the cell modules, if some load is connected between an upper terminal and a lower terminal of the battery pack, an upper end potential of the battery pack becomes zero when a lower end potential of the battery pack is made to be zero. As a result, the potential of a connection point just above a cut-off point by the switch (i.e., the minus terminal of the cell module just above the cut-off point by the switch) becomes less than zero (e.g., −100 volts). Accordingly, in the case where a discharge type constant current circuit is used to detect the voltage of the cell module, a problem arises that an unnecessary discharge of the cell occurs because the current of the cell module continues passing through a discharge type constant current circuit when the switch is turned off. Also, for example, a protection circuit is needed to be added because a voltage which is out of range of a power supply voltage may be applied to terminals of the operational amplifier used in the constant current circuit and a current-voltage converter circuit. As a method for adding the protection circuit, a voltage limiting device such as a zener diode, etc. may be connected to each terminals of the operational amplifier. However, a problem arises that voltage measurement accuracy is deteriorated by a leakage current of the added device.

In view of the foregoing, an object of the present invention is to provide a low cost and easy to produce cell voltage detecting apparatus using a semiconductor having low voltage endurance. Another object of the present invention is to provide a cell voltage detecting apparatus which suppresses unnecessary discharge current which continues passing through the cell module when the switch at the center of the battery pack is turned off.

In order to achieve the above objects, in accordance with a first aspect of the present invention, there is provided a cell module voltage detecting apparatus connected to a battery pack made up of a plurality of serially connected cell modules each of which is made up of one or more cells, for detecting a voltage between terminals of the cell module including: discharge type constant current circuits where any one of mutual connection points of the cell modules except both ends of the battery pack is used as a middle point, a potential of the middle point is set to a reference potential, each of the discharge type constant current circuits is provided for each of the cell modules on a higher potential side of the middle point and outputs a current representative of a voltage of the cell module; first current-voltage converter circuits each of which is provided for each of the discharge type constant current circuits and converts the current outputted from the discharge type constant current circuit to a voltage; induction type constant current circuits each of which is provided for each of the cell modules on a lower potential side of the middle point and outputs a current representative of a voltage of the cell module; and second current-voltage converter circuits each of which is provided for each of the induction type constant current circuits and converts a current outputted from the induction type constant current circuit to a voltage.

According to the first aspect of the present invention, an approximately middle point except both ends of the battery pack is set to the reference potential (ground), and corresponding to each of the cell modules on the higher potential side of the middle point, the discharge type constant current circuit and the current-voltage converter circuit which converts a current outputted from the discharge type constant current circuit to a voltage are provided. Further, corresponding to each of the cell modules on the lower potential side of the middle point, the induction type constant current circuit and the current-voltage converter circuit which converts a current inputted into the induction type constant current circuit into a voltage. Therefore, because only a lower voltage (for example, half of the total voltage) than the total voltage of the battery pack in which all cell modules are serially connected is applied to a semiconductor used in the discharge type constant current circuit or the induction type constant current circuit, the semiconductor having relatively low voltage endurance may be used.

In addition, the middle point of the battery pack which is set to the reference potential is any one of mutual connection points of the cell module except both ends of the battery pack. Preferably, a plurality of serially connected cell modules are evenly or approximately evenly divided on opposite sides of this middle point.

Preferably, according to a second aspect of the present invention, in addition to the first aspect, there is provided the cell module voltage detecting apparatus further including: a cut-off switch provided between the middle point and a terminal of the cell module on the lower potential side of the middle point; and diodes each of which is inserted between the induction type constant current circuit and the current-voltage converter circuit for locating a cathode at an output terminal of the induction type constant current circuit, and for locating an anode at an input terminal of the current-voltage converter circuit.

That is, in the case where the reference potential (ground) is provided on the higher potential side of the switch located at the middle point of the cell modules which constitute the battery pack, if the diode to allow a current to pass in a direction from the current-voltage converter circuit to the corresponding induction type constant current circuit is located between the induction type constant current circuit on the lower potential side of the switch and the current-voltage converter circuit, an unnecessary discharge current passing through the cell modules is suppressed when the switch is turned off.

Also, preferably, according to a third aspect of the present invention, in addition to the first aspect, there is provided the cell module voltage detecting apparatus further including: a cut-off switch provided between the middle point and a terminal of the cell module on the higher potential side of the middle point; and diodes each of which is inserted between the discharge type constant current circuit and the current-voltage converter circuit for locating an anode at an output terminal of the discharge type constant current circuit, and for locating a cathode at an input terminal of the current-voltage converter circuit.

That is, in the case where the reference potential (ground) is provided on the lower potential side of the switch located at the middle point of the cell modules which constitute the battery pack, if the diode to allow a current to pass in a direction from the discharge type constant current circuit to the corresponding current-voltage converter circuit is located between the discharge type constant current circuit on the higher potential side of the switch and the current-voltage converter circuit, an unnecessary discharge current passing through the cell modules is suppressed when the switch is turned off.

Also, in accordance with a fourth aspect of the present invention, there is provided a cell module voltage detecting apparatus connected to a battery pack made up of a plurality of serially connected cell modules each of which is made up of one or more cells, for detecting a voltage between terminals of the cell module including: discharge type constant current circuits where one terminal having the lowest potential of all is set to the reference potential, any one of mutual connection points of the cell modules except both ends of the battery pack is used as a middle point, a cut-off switch is provided at the middle point, each of the discharge type constant current circuits is provided for each of the cell modules and outputs a current representative of a voltage of the cell module; current-voltage converter circuits each of which is provided for each of the discharge type constant current circuits and converts the current outputted from the discharge type constant current circuit into a voltage; and diodes each of which is inserted between an output terminal of the discharge type constant current circuit connected to the cell module on the lower potential side of the middle point and the current-voltage converter circuit connected to the discharge type constant current circuit for locating an anode at an output terminal of the discharge type constant current circuit, and for locating a cathode at an input terminal of the current-voltage converter circuit.

That is, in the case where the switch is provided at the middle point of a plurality of serially connected cell modules, and where the discharge type constant current circuit and the current-voltage converter circuit are provided for each of a plurality of cell modules, if the diode to allow a current to pass in a direction from the discharge type constant current circuits to the corresponding current-voltage converter circuit is connected, an unnecessary discharge current passing through the cell modules is suppressed when the switch is turned off.

The object and features of the present invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of a cell voltage detecting circuit of a first embodiment according to the present invention.

FIG. 2 is a circuit diagram of the discharge type constant current circuit.

FIG. 3A is a first example circuit diagram of the current-voltage converter circuit corresponding to the discharge type constant current circuit shown in FIG. 2 .

FIG. 3B is a second example circuit diagram of the current-voltage converter circuit corresponding to the discharge type constant current circuit shown in FIG. 2 .

FIG. 4 is a circuit diagram of the induction type constant current circuit.

FIG. 5A is a first example circuit diagram of the current-voltage converter circuit corresponding to the induction type constant current circuit shown in FIG. 4 .

FIG. 5B is a second example circuit diagram of the current-voltage converter circuit corresponding to the induction type constant current circuit shown in FIG. 4 .

FIG. 6 is a block diagram of a cell voltage detecting circuit of a second embodiment according to the present invention.

FIG. 7 is a block diagram of a cell voltage detecting circuit of a third embodiment according to the present invention.

FIG. 8 is a block diagram of a cell voltage detecting circuit of a fourth embodiment according to the present invention.

FIG. 9 is a block diagram of a cell voltage detecting circuit of a first comparative example.

FIG. 10 is a block diagram of a cell voltage detecting circuit of a second comparative example.

The above and other advantages of the invention will become more apparent in the following description and the accompanying drawings in which like numerals refer like parts.

First Embodiment

FIG. 1 is a block diagram of a cell voltage detecting circuit 11 of a first embodiment according to the present invention.

A battery pack BB is a detected object by the cell voltage detecting circuit 11 , and is made up of serially connected cell modules B 1 , B 2 , . . . , B 10 . Each of the cell modules B 1 , B 2 , . . . , B 10 is made up of one or a given number of serially connected cells. Therefore, a plus terminal of the cell module at the highest potential is also a plus terminal of the battery pack BB, and a minus terminal of the cell module at the lowest potential is also a minus terminal of the battery pack BB.

The middle point of the cell modules B 1 , B 2 , . . . , B 10 (in this case, a connection point between the cell module B 5 and the cell module B 6 ) is connected to a grounded (GND), and the potential of GND is set to a reference potential. Preferably, the connection point set to the reference potential is at or near a connection point (connection portion) which divides the voltage across the battery pack BB or the number of cell modules in half. However, any one of connection point except both ends of the battery pack BB may be used as the middle point, and the potential of the middle point may be set to the reference potential.

The cell voltage detecting circuit 11 is used to detect each voltage of the cell modules B 1 , B 2 , . . . , B 10 (module voltages V 1 , V 2 , V 10 ). The cell voltage detecting circuit 11 is provided with the discharge type constant current circuits VC 1 -VC 5 each of which is connected to each of the cell modules B 1 -B 5 on the higher potential side, and the induction type constant current circuits VS 6 -VS 10 each of which is connected to each of the cell modules B 6 -B 10 .

In the cell voltage detecting circuit 11 , each of the discharge type constant current circuits VC 1 -VC 5 is further connected to each of the current-voltage converter circuits CV 1 -CV 5 , and each of the induction type constant current circuits VS 6 -VS 10 is also connected to each of the current-voltage converter circuits SV 6 -SV 10 . And, detection signals are outputted from the current-voltage converter circuits CV 1 -SV 10 to module voltage monitoring terminals AD 1 -AD 10 of a voltage monitoring circuit ADC respectively. In addition, a resistor R 1 which simulates a load of the battery pack BB is connected between a plus terminal of the cell module B 1 at the highest potential of the battery pack BB and a minus terminal of the cell module B 10 at the lowest potential (i.e., both ends of the battery pack BB).

FIG. 2 is a circuit diagram of the discharge type constant current circuit VC 1 . The discharge type constant current circuits VC 2 , VC 3 , VC 10 may have the same configuration as that of the discharge type constant current circuit VC 1 . The discharge type constant current circuit VC 1 is provided with a P-channel FET (Ml) as an output device.

In the discharge type constant current circuit VC 1 , the module voltage V 1 of the cell module B 1 is divided by resistors R 11 and R 12 , and a current having a value of (divided voltage VR 11 /resistor R 13 ) flows through the P-channel FET (M 1 ). In this way, through the P-channel FET (M 1 ), an output current Jout, which is proportional to the module voltage V 1 of the cell module B 1 , is outputted from an output terminal lout of the discharge type constant current circuit VC 1 .

FIG. 3A is a first example circuit diagram of the current-voltage converter circuit CV 1 corresponding to the discharge type constant current circuit VC 1 shown in FIG. 2 (if necessary, see FIG. 1 ). The current-voltage converter circuits CV 2 , CV 3 , . . . , CV 10 may have the same configuration as that of the current-voltage converter circuit CV 1 .

The output current Jout is outputted from an output terminal lout of the discharge type constant current circuit VC 1 (see FIG. 2 ), and is inputted to an input terminal 1 in of the current-voltage converter circuit CV 1 . And, the output current Jout flows into GND through a resistor R 100 . A voltage VR 100 , which is generated by allowing an input current Jin to pass through the resistor R 100 , is inputted to a plus terminal of an operational amplifier U 11 , and an output voltage VEout, which is proportional to the output current Jout, is outputted from an output terminal OUT of the operational amplifier U 11 . In this way, an output voltage VEout, which is proportional to the output current Jout of the discharge type constant current circuit VC 1 , is outputted from an output terminal Vout of the current-voltage converter circuit CV 1 . That is, the output voltage VEout, which is proportional to the module voltage V 1 of the cell module B 1 , is outputted from the output terminal Vout of the current-voltage converter circuit CV 1 , where the VEout means a potential difference between the output terminal Vout and GND.

FIG. 3B is a second example circuit diagram of the current-voltage converter circuit CV 1 corresponding to the discharge type constant current circuit VC 1 . The current-voltage converter circuits CV 2 , CV 3 , . . . , CV 10 may have the same configuration as that of the current-voltage converter circuit CV 1 .

Although the first example of the current-voltage converter circuit CV 1 shown in FIG. 3A detects the output voltage VEout, which is proportional to the output current Jout of the discharge type constant current circuit VC 1 , with the resistor R 100 , the second example of the current-voltage converter circuit CV 1 shown in FIG. 3B detects the output voltage VEout, which is proportional to the output current Jout of the discharge type constant current circuit VC 1 , with a resistor R 101 , where VEout means a potential difference between a Vref and the Vout terminal.

When the discharge type constant current circuit VC 1 shown in FIG. 2 and the current-voltage converter circuit CV 1 shown in FIG. 3A or FIG. 3B are used in combination, if a voltage-current converting accuracy of the discharge type constant current circuit VC 1 and a current-voltage converting accuracy of the current-voltage converter circuit CV 1 are high enough, it is possible to detect each module voltages V 1 , V 2 , . . . , V 10 of the cell modules B 1 , B 2 , . . . , B 10 with a high degree of accuracy in spite of high or low total voltage across the battery pack BB.

FIG. 4 is a circuit diagram of the induction type constant current circuit VS 6 . The induction type constant current circuits VS 7 , VS 8 , . . . , VS 10 may have the same configuration as that of the induction type constant current circuit VS 6 . The induction type constant current circuit VS 6 is provided with a N-channel FET (M 2 ) as an output device.

In the induction type constant current circuit VS 6 , the module voltage V 6 of the cell module B 6 is divided by resistors R 61 and R 62 , and a current having a value of (divided voltage VR 62 /resistor R 63 ) flows through the N-channel FET (M 2 ). In this way, through the N-channel FET (M 2 ), an output current Jout, which is proportional to the module voltage V 6 of the cell module B 6 , is induced into an output terminal lout.

FIG. 5A is a first example circuit diagram of the current-voltage converter circuit SV 6 corresponding to the induction type constant current circuit VS 6 shown in FIG. 4 . The current-voltage converter circuits SV 7 -SV 10 may have the same configuration as that of the current-voltage converter circuit SV 6 .

The output current Jout is induced into the output terminal lout of the induction type constant current circuit VS 6 (see FIG. 4 ), and is inputted to an input terminal 1 in of the current-voltage converter circuit SV 6 as an input current Jin. And, in the current-voltage converter circuit SV 6 , because a voltage VR 106 between terminals of a resistor R 106 generated by the input current Jin is inputted to a plus terminal of an operational amplifier U 61 , an output voltage VEout, which is proportional to the output current Jout of the induction type constant current circuit VS 6 , is outputted from the output terminal Vout of the current-voltage converter circuit SV 6 . Referring back to FIG. 1 , in this way, the output voltage VEout, which is proportional to the module voltage V 6 of the cell module B 6 , is outputted from the output terminal Vout of the current-voltage converter circuit SV 6 , where the VEout means a potential difference between a Vref and the Vout terminal.

FIG. 5B is a second example circuit diagram of the current-voltage converter circuit SV 6 corresponding to the induction type constant current circuit VS 6 shown in FIG. 4 . The current-voltage converter circuits SV 7 -SV 10 may have the same configuration as that of the current-voltage converter circuit SV 6 .

The output current Jout is induced into the output terminal lout of the induction type constant current circuit VS 6 (see FIG. 4 ), and is inputted to the input terminal 1 in of the current-voltage converter circuit SV 6 as an input current Jin. And, in the current-voltage converter circuit SV 6 , a voltage VR 107 between terminals of a resistor R 107 is generated by the input current Jin, and the output voltage VEout, which is proportional to the voltage VR 107 between terminals, is outputted. Referring back to FIG. 1 , in this way, the output voltage VEout, which is proportional to the module voltage V 6 of the cell module B 6 , is outputted from the output terminal Vout of the current-voltage converter circuit SV 6 , where the VEout means a potential difference between the Vout terminal and a Vref.

As shown in FIG. 1 , when the module voltage V 1 of the cell module B 1 at the highest potential of the battery pack BB is inputted to the discharge type constant current circuit VC 1 , a gate voltage of the P-channel FET (M 1 ) is controlled by the operation of the operational amplifier U 1 shown in FIG. 2 to output the output current Jout expressed by a following equation (1) from the output terminal lout of the discharge type constant current circuit VC 1 .

J out=[ V 1*{ R 11/( R 11+ R 12)}]/ R 13  (1)

Next, in the first example of the current-voltage converter circuit CV 1 shown in FIG. 3A , because the output current Jout flows through the resistor R 100 , the potential difference VEout between the output terminal Vout of a voltage follower circuit, which is made up of an operational amplifier U 11 , and GND is expressed by a following equation (2).

That is, as can be seen from the equation (2), the module voltage V 1 of the cell module B 1 can be known from the output voltage VEout of the current-voltage converter circuit CV 1 . Likewise, the module voltages V 2 -V 5 of the cell modules B 2 -B 5 can be known from the output voltages VEout of the current-voltage converter circuits CV 2 -CV 5 .

On the other hand, in the second example of the current-voltage converter circuit CV 1 shown in FIG. 3B , any one voltage within the range of a source voltage of an operational amplifier U 10 is set to the Vref, and the potential difference VEout between the Vref and the output terminal Vout of the operational amplifier U 10 is expressed by a following equation (3).

VE out= V ref−[ R 101 *V 1*{ R 11/( R 11 +R 12)}]/ R 13  (3)

That is, as can be seen from the equation (3), the module voltage V 1 of the cell module B 1 can be measured from the output voltage VEout of the current-voltage converter circuit CV 1 . Likewise, the module voltages V 2 -V 5 of the cell modules B 2 -B 5 can be measured form the output voltages VEout of the current-voltage converter circuits CV 2 -CV 5 .

At this time, because the minus terminal of the cell module B 5 at the lowest potential of the five cell modules B 1 -B 5 is set to GND, when each module voltage of the cell modules B 1 -B 5 is set to 20 volts, a voltage on the order of only 100 volts is applied between a source and a drain of the P-channel FET (M 1 ) of the discharge type constant current circuit VC 1 at the highest potential. Therefore, a voltage endurance of a semiconductor device of the discharge type constant current circuit VC 1 may be half of that of a prior cell voltage detecting circuit 21 shown in FIG. 9 .

On the other hand, as shown in FIG. 1 , each of the cell modules B 6 -B 10 on the lower potential side uses each of the induction type constant current circuits VS 6 -VS 10 . In the induction type constant current circuit shown in FIG. 4 , when the module voltage V 10 of the cell module B 10 at the lowest potential is inputted to the induction type constant current circuit VS 10 , a gate voltage of the N-channel FET (M 2 ) is adjusted by the operation of the operational amplifier U 1 to output the output current Jout expressed by a following equation (4) from the output terminal lout of the induction type constant current circuit VS 10 .

I out= V 10* R 62/( R 61+ R 62)/ R 63  (4)

Next, in the current-voltage converter circuit shown in FIG. 5A , because the above described output current Jout flows through the resistor R 106 , when any one voltage within the range of a source voltage of an operational amplifier U 61 is set to the Vref, the potential difference VEout between the Vref and the output terminal Vout of the voltage follower circuit which is made up of the operational amplifier U 61 is expressed by a following equation (5).

VE out= R 106* V 10* R 62/( R 61+ R 62)/ R 63  (5)

That is, as can be seen from the equation (5), the module voltage V 10 of the cell module B 10 can be measured from the output voltage VEout of the current-voltage converter circuit SV 10 . Likewise, the module voltages V 6 -V 9 of the cell modules B 6 -B 9 can be measured from the output voltages VEout of the current-voltage converter circuits SV 6 -SV 10 .

On the other hand, in the current-voltage converter circuit SV 6 shown in FIG. 5B , when any one voltage within the range of a source voltage of an operational amplifier U 62 is set to the Vref, the potential difference VEout between the Vref and the output terminal Vout of the operational amplifier U 62 is expressed by a following equation (6).

VE out=[ R 107* V 10*{ R 61/( R 61+ R 62)}]/ R 63  (6)

Here, when each module voltage is set to 20 volts, a voltage of 100 volts is applied between a source and a drain of the N-channel FET (M 2 ) of the induction type constant current circuit VS 10 at the lowest potential of the battery pack BB. Therefore, a voltage endurance of a semiconductor device (N-channel FET) of the induction type constant current circuit VS 10 (see FIG. 4 ) may be half of that of the cell voltage detecting circuit 21 of below described first comparative example with reference to FIG. 9 .

In addition, instead of the P-channel FET (M 1 ), a PNP-type small signal bipolar transistor and a NPN-type power bipolar transistor may be used in combination as a Darlington circuit. In this configuration, two bipolar transistors can be treated as one PNP-type bipolar transistor. In this case, because a current amplification factor can be obtained by a product of those of the two transistor, a base current can be relatively reduced. Likewise, instead of the N-channel FET (M 2 ), a NPN-type small signal bipolar transistor and a NPN-type power bipolar transistor may be used in combination as a Darlington circuit. In this case, likewise, the same effect as above can be obtained.

According to the cell voltage detecting circuit 11 of the first embodiment, a voltage applied to a discharge type constant current circuit VCn can be reduced, and the circuit can be realized using a semiconductor device having low voltage endurance.

Second Embodiment

FIG. 6 is a block diagram of a cell voltage detecting circuit 12 of a second embodiment according to the present invention.

In the cell voltage detecting circuit 12 , backflow prevention diodes D 1 -D 5 are inserted so as to allow currents to pass in a direction from the discharge type constant current circuits VC 1 -VC 5 , which are connected to the cell modules B 1 -B 5 on the higher potential side of a switch SW 1 , to the current-voltage converter circuits CV 1 -CV 5 , and so as to prevent currents in a direction from the current-voltage converter circuits CV 1 -CV 5 to the discharge type constant current circuits VC 1 -VC 5 . For example, the diode D 1 is provided so as to prevent the current in the direction from the current-voltage converter circuit CV 1 to the discharge type constant current circuit VC 1 , and the diode D 2 is provided so as to prevent the current in the direction from the current-voltage converter circuit CV 2 to the discharge type constant current circuit VC 2 .

In the cell voltage detecting circuit 12 , a switch SW 1 to cut off the middle point of the cell modules B 1 -B 10 , which constitute the battery pack BB, is further provided. Also, each of the cell modules B 1 -B 10 is connected to each of the discharge type constant current circuits VC 1 -VC 10 , and each of the current-voltage converter circuits CV 1 -CV 10 , which are operated with reference to a low end of the cell module B 10 at the lowest potential as a reference point (GND), is correspondingly connected to each of the discharge type constant current circuits VC 1 -VC 10 .

That is, each of anodes of the diodes D 1 -D 5 is connected to each of the discharge type constant current circuits VC 1 -VC 5 on the higher potential side of the switch SW 1 to cut off the middle point, and each of cathodes of the diodes D 1 -D 5 is connected to each of the corresponding current-voltage converter circuits CV 1 -CV 10 .

With the switch SW 1 turned on, because potentials of all of the discharge type constant current circuits VC 1 -VC 10 are higher than those of the corresponding current-voltage converter circuits CV 1 -CV 10 , currents flow in the direction from the discharge type constant current circuits VC 1 -VC 5 to the current-voltage converter circuits CV 1 -CV 5 . Also, in a detecting system for the cell modules B 1 -B 5 on the higher potential side of the switch SW 1 , with the switch SW 1 turned on, because potentials of the discharge type constant current circuits VC 1 -VC 5 are higher than those of the corresponding current-voltage converter circuits CV 1 -CV 5 , currents flow in a forward direction from the discharge type constant current circuits VC 1 -VC 5 to the current-voltage converter circuits CV 1 -CV 5 through the diodes D 1 -D 5 . At this time, although a forward voltage drop of each of the diodes D 1 -D 5 is on the order of 0.6 volts, a measurement accuracy of voltage detection is not substantially affected because each of the discharge type constant current circuits VC 1 -VC 5 is in a feedback operation.

Also, with the switch SW 1 turned off, because each of the discharge type constant current circuits VC 6 -VC 10 on the lower potential side of the switch SW 1 is in the same condition as that when the switch SW 1 is turned on, a current flows in a direction from each of the discharge type constant current circuits VC 6 -VC 10 to each of the corresponding current-voltage converter circuits CV 6 -CV 10 .

On the other hand, with respect to the discharge type constant current circuits VC 1 -VC 5 on the higher potential side of the switch SW 1 , because a potential of each of minus terminals of the cell modules B 1 -B 5 drops to a lower potential than that of each of reference points (ground) of the corresponding current-voltage converter circuits CV 1 -CV 5 by a load resistor R 1 , a backward voltage is applied to each of the diodes D 1 -D 5 each of which connects each of the discharge type constant current circuits VC 1 -VC 5 to each of the current-voltage converter circuits CV 1 -CV 5 in a forward direction. Therefore, because a backward current is prevented from flowing from each of the current-voltage converter circuits CV 1 -CV 5 to each of the discharge type constant current circuits VC 1 -VC 5 by each of the diodes D 1 -D 5 , a current which causes a discharge at each of the cell modules B 1 -B 5 is not generated. Also, a negative voltage is not applied to each of the operational amplifiers U 11 of the current-voltage converter circuits CV 1 -CV 5 .

More particularly, in the cell voltage detecting circuit 12 , in the case where the switch SW 1 is opened, on the higher potential side of the switch SW 1 , a potential of a minus terminal (i.e., a minus terminal of the cell module Bn in question) of a input side of the discharge type constant current circuit VCn (see FIG. 2 ) is lower than that of GND of the current-voltage converter circuit CVn (first example)(see FIG. 3A ). As a result, a current tends to flow back from GND of the current-voltage converter circuit CVn (see FIG. 3A ) to the input side of the discharge type constant current circuit VCn (see FIG. 2 ) of the minus terminal. However, because backflow prevention diodes Dn (i.e., diodes D 1 -D 5 ) are inserted between the output terminal lout of the discharge type constant current circuit VCn (see FIG. 2 ) and the input terminal Iin of the current-voltage converter circuit CVn (see FIG. 3A ), a backflow current (i.e., a discharge current of each of the cell modules B 1 -B 5 ) is prevented.

According to the cell voltage detecting circuit 12 of the second embodiment, when the switch SW 1 located at any middle point of the cell modules B 1 , B 2 , . . . , B 12 is cut off, it is possible to suppress increasing in a quantity of discharge from a portion of the cell modules Bn. That is, when the switch SW 1 is cut off, it is possible to suppress a discharge current from any cell module Bn via the current-voltage converter circuit CVn and the discharge type constant current circuit VCn.

That is, according to the cell voltage detecting circuit 12 of the second embodiment, even though the switch SW 1 is located at the middle point of the cell modules B 1 , B 2 , . . . , B 10 to divide the voltage of the battery pack BB in half, it is possible to suppress increasing in a quantity of discharge from the cell modules B 1 , B 2 , . . . , B 10 when the switch SW 1 is cut off.

Third Embodiment

FIG. 7 is a block diagram of a cell voltage detecting circuit 13 of a third embodiment according to the present invention.

As shown in FIG. 7 , the switch SW 1 is located at a middle point of the cell modules B 1 -B 10 , the discharge type constant current circuits VC 1 -VC 5 are connected to the corresponding cell modules B 1 -B 5 , and the induction type constant current circuits VS 6 -VS 10 are connected to the corresponding cell modules B 6 -B 10 . Further, the current-voltage converter circuits CV 1 -CV 5 , which are operated with reference to a pole (upper pole) on the higher potential side of the switch SW 1 as a reference point (ground), are connected to the discharge type constant current circuits VC 1 -VC 5 respectively, and the current-voltage converter circuits SV 6 -SV 10 are connected to the induction type constant current circuits VS 6 -VS 10 respectively. Also, diodes D 6 -D 10 are connected respectively in a direction from the current-voltage converter circuits SV 6 -SV 10 to the corresponding induction type constant current circuits VS 6 -VS 10 .

According to the cell voltage detecting circuit 13 , as with the cell voltage detecting circuit 11 of the first embodiment (see FIG. 1 ), the P-channel FETs (M 1 ) of the discharge type constant current circuits VC 1 -VC 5 (see FIG. 2 ) and the N-channel FETs (M 2 ) of the induction type constant current circuits VS 6 -VS 10 (see FIG. 4 ) may have voltage endurance which is more than half of that of the total voltage of the battery pack BB.

Also, with the switch SW 1 turned on, the circuits on the higher potential side of the switch SW 1 are operated in the same manner as that of the first embodiment. In the circuits on the lower potential side of the switch SW 1 , because the potentials of the induction type constant current circuits VS 6 -VS 10 are lower than those of the corresponding current-voltage converter circuits SV 6 -SV 10 respectively, each of currents flows through each of the diodes D 6 -D 10 in a forward direction. Although forward voltage drop of each of the diodes D 6 -D 10 is on the order of 0.6 volts, a measurement accuracy of voltage detection is not substantially affected because each of the induction type constant current circuits VS 6 -VS 10 is in a feedback operation.

Also, with the switch SW 1 turned off, because potentials between the discharge type constant current circuits VC 1 -VC 5 and the corresponding current-voltage converter circuits CV 1 -CV 5 do not change, the circuits on the higher potential side of the switch SW 1 are operated in the same manner as those when the switch SW 1 is turned on. On the other hand, with respect to the circuits on the lower potential side of the switch SW 1 , because a potential of a minus terminal of the cell module B 10 becomes the same as that of a plus terminal of the cell module B 1 by the load resistor R 1 , a potential of a plus terminal of the cell module B 6 becomes higher than that of the higher potential side of the switch SW 1 which is set to the reference potential (GND) (i.e., a minus terminal of the cell module B 5 ) by 200 volts.

Also, each potential of each of the cell modules B 7 -B 10 becomes higher than that of the reference point by more than 100 volts. Therefore, although a large potential difference is generated between each of the induction type constant current circuits VS 6 -VS 10 connected to each of the cell modules B 6 -B 10 on the lower potential side of the switch SW 1 and each of the current-voltage converter circuits SV 6 -SV 10 , because each of the diodes D 6 -D 10 inserted between each of the induction type constant current circuits VS 6 -VS 10 and each of the current-voltage converter circuits SV 6 -SV 10 prevents a backward current, a discharge current from each of the cell modules B 6 -B 10 is suppressed. That is, a high voltage applied to each of the current-voltage converter circuits is suppressed.

According to the cell voltage detecting circuit 13 of the third embodiment, in the cell voltage detecting circuit 11 of the first embodiment shown in FIG. 1 , because the switch SW 1 is inserted between the discharge type constant current circuits VC 1 -VC 5 and the induction type constant current circuits VS 6 -VS 10 , when the switch SW 1 is cut off, it is possible to suppress a discharge current from any cell module Bn via the current-voltage converter circuit CVn and the induction type constant current circuit VSn.

Fourth Embodiment

FIG. 8 is a block diagram of a cell voltage detecting circuit 14 of a fourth embodiment according to the present invention.

In the third embodiment shown in FIG. 7 , the discharge type constant current circuits VC 1 -VC 5 and the induction type constant current circuits VS 6 -VS 10 are divided by the cell module B 5 and the cell module B 6 , the switch SW 1 is located between the cell module B 5 and the cell module B 6 , and GND is provided on the higher potential side of the switch SW 1 . However, in the fourth embodiment, GND is provided on the lower potential side of the switch SW 1 .

That is, as shown in FIG. 8 , the switch SW 1 is located at the middle point of the cell modules B 1 -B 10 , each of the discharge type constant current circuits VC 1 -VC 5 is correspondingly connected to each of the cell modules B 1 -B 5 , and each of the induction type constant current circuits VS 6 -VS 10 is correspondingly connected to each of the cell modules B 6 -B 10 . Further, each of the current-voltage converter circuits CV 1 -CV 5 , which are operated with reference to an electrode on the lower potential side of the switch SW 1 as a reference potential (GND), is correspondingly connected to each of the discharge type constant current circuits VC 1 -VC 5 , and each of the current-voltage converter circuits SV 6 -SV 10 is correspondingly connected to each of the induction type constant current circuits VS 6 -VS 10 . Also, each of the diodes D 1 -D 5 is correspondingly connected in a direction from each of the discharge type constant current circuits VC 1 -VC 6 to each of the current-voltage converter circuits CV 1 -CV 5 .

In this cell voltage detecting circuit 14 , with the switch SW 1 turned on, the circuits on the lower potential side of the switch SW 1 are operated in the same manner as that of the cell voltage detecting circuit 11 of the first embodiment shown in FIG. 1 . In the circuits on the higher potential side of the switch SW 1 , because the potentials of the discharge type constant current circuits VC 1 -VC 5 are higher than those of the corresponding current-voltage converter circuits CV 1 -CV 5 respectively, each of currents flows through each of the diodes D 1 -D 5 in a forward direction. At this time, although forward voltage drop of each of the diodes D 1 -D 5 is on the order of 0.6 volts, a measurement accuracy of voltage detection is not substantially affected because each of the discharge type constant current circuits VC 1 -VC 5 is in a feedback operation.

On the other hand, with the switch SW 1 turned off, because potentials between the current-voltage converter circuits SV 6 -SV 10 and the corresponding induction type constant current circuits VS 6 -VS 10 do not change, the circuits on the lower potential side of the switch SW 1 are operated in the same manner as those when the switch SW 1 is turned on. Also, with respect to circuits on the higher potential side of the switch SW 1 , because a potential of the plus terminal of the cell module B 1 becomes the same as that of the minus terminal of the cell module B 10 by the load resistor R 1 , a potential of the minus terminal of the cell module B 5 becomes lower than that of the switch SW 1 which is set to the reference potential (GND) by 200 volts. Also, each potential of the cell modules B 1 -B 4 becomes lower than that of the reference point (GND) by greater than or equal to 100 volts.

Therefore, in the circuits on the higher potential side of the switch SW 1 , although a large negative potential difference is generated between each of the discharge type constant current circuits VC 1 -VC 5 connected to the cell modules B 1 -B 5 and each of the current-voltage converter circuits CV 1 -CV 5 , a backward current is prevented from flowing from each of the current-voltage converter circuits CV 1 -CV 5 to each of the corresponding discharge type constant current circuits VC 1 -VC 5 by each of the diodes D 1 -D 5 . Therefore, a discharge current passing through each of the cell modules B 1 -B 5 is suppressed. That is, a negative voltage is not applied to each of the current-voltage converter circuits CV 1 -CV 5 .

In addition, in the case where the battery pack BB is made up of even numbers of cell modules B 1 , B 2 , . . . , the reference point is preferably provided at a center point of the battery pack BB so as to evenly divide the cell modules B 1 , B 2 , . . . . In the case where the battery pack BB is made up of odd numbers of cell modules B 1 , B 2 , the reference point is provided near the center point so as to approximately evenly divide the cell modules B 1 , B 2 , . . . . In the case where the reference point is provided as above, it is possible to make voltage endurances of semiconductor devices for output (such as, the P-channel FET (M 1 ) shown in FIG. 2 and the N-channel FET (M 2 ) shown in FIG. 4 ) to one-half or approximately one-half of the total voltage of the battery pack BB. The more the reference point comes close to the center point, the less the voltage endurance of the semiconductor device for output will be. When the reference point is provided at any mutual connection point of the cell modules 2 , except the plus terminal of the cell module 2 at the highest potential (the plus terminal of the battery pack BB) and the minus terminal of the cell module 2 at the lowest potential (the minus terminal of the battery pack BB), it is possible to make the voltage endurance of the semiconductor device for output lower than the total voltage of the battery pack BB.

First Comparative Example

FIG. 9 is a block diagram of a cell voltage detecting circuit 21 of a first comparative example.

Each of the module voltages V 1 , V 2 , . . . , V 10 , which are voltages between terminals of the cell modules B 1 , B 2 , . . . , B 10 , is detected by each of series circuits, each of which is made up of each of the discharge type constant current circuits VC 1 , VC 2 , . . . , VC 10 and each of the current-voltage converter circuits CV 1 , CV 2 , . . . , CV 10 , and is outputted to each of module voltage monitoring terminals AD 1 , AD 2 , . . . , AD 10 of the voltage monitoring circuit ADC. In addition, the minus terminal of the cell module B 10 at the lowest potential of the battery pack BB is connected to GND, and the resistor R 1 which simulates a load of the battery pack BB is connected between the plus terminal of the cell module B 1 at the highest potential of the battery pack BB and the minus terminal of the cell module B 10 at the lowest potential (GND).

In this cell voltage detecting circuit 21 , for example, the module voltage V 1 of the cell module B 1 is converted into a current by the discharge type constant current circuit VC 1 , is further converted into a voltage which is proportional to the module voltage V 1 of the cell module B 1 by the current-voltage converter circuit CV 1 , and is outputted to the module voltage monitoring terminal AD 1 of the voltage monitoring circuit ADC. Also, the module voltage V 2 of the cell module B 2 is converted into a current by the discharge type constant current circuit VC 2 , is further converted into a voltage which is proportional to the module voltage V 2 of the cell module B 2 by the current-voltage converter circuit CV 2 , and is outputted to the module voltage monitoring terminal AD 2 of the voltage monitoring circuit ADC. Hereinafter, each of the module voltages V 3 , V 4 , . . . , V 10 of each of the cell modules B 3 , B 4 , . . . , B 10 is detected in the same manner.

In this cell voltage detecting circuit 21 , for example, when each of the module voltages V 1 , V 2 , . . . , V 10 of each of the cell modules B 1 , B 2 , . . . , B 10 is set to 20 volts, the P-channel FET (M 1 ) (see FIG. 2 ), which is an output device of the discharge type constant current circuit VC 1 connected to the cell module B 1 , requires a voltage endurance more than or equal to 200 volts. That is, because the lowest potential minus terminal of the battery pack BB which is made up of the cell modules B 1 , B 2 , . . . , B 10 is set to the reference potential (GND), and the discharge type constant current circuits VC 1 , VC 2 , . . . , VC 10 are serially connected (see FIG. 2 ), a voltage, which is obtained by multiplying the voltage per the cell module (B 1 , etc.) by the number of cell modules (B 1 , etc.) which constitutes the battery pack BB, is applied to the P-channel FET (M 1 ) of the discharge type constant current circuit VC 1 located at the highest potential. The P-channel FET (M 1 ) requires the voltage endurance to endure this applied voltage. Because each of the discharge type constant current circuits VC 1 , VC 2 , . . . , VC 10 requires the semiconductor device (P-channel FET) having high voltage endurance, parts procurement may become difficult to obtain and the product price may become expensive.

Second Comparative Example

FIG. 10 is a block diagram of a cell voltage detecting circuit 22 of a second comparative example.

This cell voltage detecting circuit 22 has a configuration in which the switch SW 1 is provided at the middle point of the cell modules B 1 -B 10 (i.e., between the cell module B 5 and the cell module B 6 ) in the cell voltage detecting circuit 21 shown in FIG. 9 .

In this cell voltage detecting circuit 22 , because the resistor R 1 is connected between both ends of the cell modules B 1 -B 10 , when the cell modules B 1 -B 10 are cut off by the switch SW 1 at the middle point, if the lower end of the cell module B 10 is connected to GND, the upper end potential of the cell module B 1 becomes zero. For this reason, the potential just above the cut-off point by the switch SW 1 (i.e., the minus terminal of the cell module B 5 ) becomes less than zero. That is, with the switch SW 1 turned off, the potential of the plus terminal of the cell module B 1 becomes equal to that of the minus terminal of the cell module B 10 by the resistor R 1 . As a result, provided that the voltage per one of the cell modules B 1 , B 2 , . . . , B 10 is 20 volts, the potential of the minus terminal of the cell module B 5 becomes −100 volts. Likewise, the potential of the minus terminal of the cell module B 4 becomes −80 volts, the potential of the minus terminal of the cell module B 3 becomes −60 volts, the potential of the minus terminal of the cell module B 2 becomes −40 volts, and the potential of the minus terminal of the cell module B 1 becomes −20 volts.

Therefore, even if the switch SW 1 is turned off, a discharge current continues passing through the cell modules B 1 -B 5 on the higher potential side of the switch SW 1 . For example, in the cell module B 1 , because a current continues passing through GND (i.e., the plus terminal of the cell module B 1 ) of the current-voltage converter circuit CV 1 (see FIG. 3A ), the resistor R 100 , a parasitic diode of the P-channel FET (M 1 ) of the discharge type constant current circuit VC 1 (see FIG. 2 ), the operational amplifier U 1 , and the minus terminal of the cell module B 1 , a quantity of discharge from the cell module B 1 is increased (first example). In the cell modules B 2 -B 5 , the discharge current continues passing through like paths. Also, in the cell voltage detecting circuit 22 shown in FIG. 10 , because a negative voltage is applied to the operational amplifier U 11 used in each of the current-voltage converter circuits CV 1 -CV 5 connected to each of the cell modules B 1 -B 5 , the protection circuit is needed to be added, and current-voltage converting accuracy is deteriorated.