JP2010088179A - Battery equalization circuit, and battery power supply device - Google Patents

Abstract

A battery equalization circuit capable of detecting a failure of a circuit to be discharged in order to equalize the stored charge amount of each secondary battery used in an assembled battery including a plurality of secondary batteries, and the same A battery power supply is provided.
Discharge parts X1 to X10 connected in parallel to secondary batteries B1 to B10, a failure detection part 41 for detecting a failure of the discharge parts X1 to X10, and an imbalance in each secondary battery Are provided with an imbalance reduction circuit 5 that reduces the imbalance by using the discharge units X1 to X10. The discharge units X1 to X10 are controlled to be turned on and off by the photocouplers PC1 to PC10 and the imbalance reduction circuit 5. The switching elements SW1 to SW10 and the resistors R1 to R10 are connected in series. The presence / absence of X10 failure was determined.
[Selection] Figure 1

Description

  The present invention relates to a battery equalization circuit used for equalizing each secondary battery in an assembled battery including a plurality of secondary batteries, and a battery power supply apparatus using the same.

  In recent years, a battery pack that outputs a high voltage by connecting a large number of secondary batteries in series, as represented by in-vehicle secondary batteries that are mounted as a power source in hybrid cars and electric cars that use an engine and an electric motor together The use of is expanding. In such an assembled battery, for example, since 80 secondary batteries are connected in series, it is difficult to ensure the reliability of the entire assembled battery.

  Specifically, in such an assembled battery, the amount of stored charge charged in each secondary battery varies due to characteristic variations that occur during the manufacturing process of the secondary battery constituting the assembled battery.

  And if charging / discharging of an assembled battery is repeated in the state in which the amount of stored electric charge varies, there is a possibility that the deterioration of a secondary battery having a small stored charge amount may be accelerated. In other words, when charging a battery pack, a secondary battery with a larger amount of stored charge than other secondary batteries before charging is likely to be fully charged before other secondary batteries and become overcharged, and the deterioration is accelerated. There is a risk that. On the other hand, when discharging the assembled battery, the secondary battery having a smaller stored charge amount than other secondary batteries from before the discharge tends to be overdischarged because the stored charge amount becomes zero before the other secondary batteries, Deterioration may be accelerated.

  The secondary battery whose deterioration has been accelerated has a reduced capacity and a shortened life. In the case of an assembled battery, if some of the secondary batteries deteriorate, the entire assembled battery becomes unusable or decreases in reliability. Has a great impact. For this reason, in an assembled battery in which a large number of secondary batteries are connected in series, it is desired to equalize the stored charge amount of each secondary battery.

  As described above, when using an assembled battery in which a large number of secondary batteries are connected in series, a method for ensuring reliability as an assembled battery by performing equalization of the amount of stored charge is known (for example, a patent Reference 1).

  FIG. 3 is a circuit diagram showing a battery equalization circuit for equalizing a plurality of secondary batteries constituting the assembled battery described in Patent Document 1. This battery equalization circuit converts a serial signal output from the microcomputer into a parallel signal by the first control unit, and equalizes each secondary battery. The microcomputer outputs a serial signal designating the secondary battery to be discharged to the first control unit via the optical insulating element.

The first control unit converts the serial signal into a parallel signal, and outputs the parallel signal to a transistor that discharges each battery block via the level conversion circuit. Thereby, the amount of electricity stored in each secondary battery is equalized by turning on and discharging the transistor corresponding to the secondary battery having a high terminal voltage.
JP 2005-333717 A

  However, in the battery equalization circuit shown in FIG. 3, it is possible to equalize the secondary batteries constituting the assembled battery, but only the terminal voltage of each secondary battery is detected. For example, when a short circuit failure occurs in a transistor, it is distinguished whether the secondary battery terminal voltage has decreased due to a decrease in the stored charge amount of the secondary battery, or whether the secondary circuit terminal voltage has decreased due to a failure in the discharge circuit. It is not possible to detect the failure of the discharge circuit. For this reason, there are inconveniences that a failure of the discharge circuit causes a decrease in reliability and safety, and a maintenance service for the failure cannot be performed accurately.

  An object of the present invention is to provide a battery equalization circuit capable of detecting a failure of a circuit to be discharged in order to equalize the stored charge amount of each secondary battery used in an assembled battery composed of a plurality of secondary batteries, and this It is providing the battery power supply device using.

  A battery equalization circuit according to the present invention includes a plurality of discharge units connected in parallel to a plurality of secondary batteries connected in series, a failure detection unit that detects a failure of each discharge unit, and each secondary battery And an imbalance reduction unit that reduces the imbalance by using each of the discharge units when the imbalance occurs in each of the discharge units, wherein each of the discharge units converts the flowing current to light to insulate the current. A photo-isolating element that outputs a current detection signal, a switching element that is controlled to be turned on and off by the imbalance reduction unit, and a resistor are connected in series. Based on the current detection signal output from the element, the presence / absence of a failure of each discharge unit is determined.

  According to this configuration, the plurality of discharge units are connected in parallel to the plurality of secondary batteries connected in series. In addition, in each discharge unit, a flowing current is converted into light and insulated, and a photo-insulating element that outputs a current detection signal indicating the current, a switching element, and a resistor are connected in series. When an imbalance occurs in each secondary battery, the switching element of each discharge unit is turned on and off by the imbalance reduction unit so as to reduce the imbalance, and the discharge of each secondary battery is controlled. . At this time, depending on whether the switching element is turned on or off, whether the current actually flows or is interrupted is notified to the failure detection unit by the current detection signal of the photo-insulating element. By determining the presence or absence of a failure in each discharge unit based on the current detection signal output from the optical insulating element, it is possible to detect a failure in a circuit that is discharged in order to equalize the stored charge amount of each secondary battery. .

  In addition, a voltage detection unit that detects a terminal voltage of each secondary battery and a period during which any one of the terminal voltages detected by the voltage detection unit exceeds a preset discharge start voltage. It is preferable to further include an imbalance reduction unit that turns on the switching element of the discharge unit connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the start voltage.

  According to this configuration, when the terminal voltage of each secondary battery exceeds the discharge start voltage, the switching of the discharge unit connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the discharge start voltage by the imbalance reduction unit is performed. Since the element is turned on and discharged until the terminal voltage of the secondary battery becomes equal to or lower than the discharge start voltage, when the plurality of secondary batteries are charged, the terminal voltage of each secondary battery finally becomes the discharge start voltage. As a result, the secondary batteries can be equalized.

  Moreover, it is preferable that the said discharge start voltage is a full charge voltage of each said secondary battery.

  According to this configuration, when the plurality of secondary batteries are charged, the terminal voltages of the respective secondary batteries are finally aligned at the full charge voltage, so that each secondary battery can be equalized while being fully charged. .

  In addition, a voltage detection unit that detects a terminal voltage of each secondary battery, and whether or not an imbalance has occurred in the terminal voltage of each secondary battery based on each terminal voltage detected by the voltage detection unit. If the imbalance determination unit and the imbalance determination unit determine that an imbalance has occurred, at least the secondary battery having the highest terminal voltage detected by the voltage detection unit among the secondary batteries. You may make it further provide the imbalance reduction part which turns on the said switching element in the discharge part connected in parallel with the battery.

  According to this configuration, when the imbalance determining unit determines that an imbalance has occurred, the secondary voltage having the highest terminal voltage detected by the voltage detecting unit among at least each of the secondary batteries is determined by the imbalance reducing unit. When the switching element in the discharge unit connected in parallel with the battery is turned on and the secondary battery is discharged, the imbalance of each secondary battery is reduced. In this case, since equalization can be performed without charging each secondary battery to the discharge start voltage, the degree of freedom of timing for performing equalization increases.

  When the current detection signal output from the optical isolation element connected in series with the switching element turned off by the imbalance reduction unit indicates that a current is flowing, the fault detection unit It is preferable to determine that a failure has occurred in the discharge part including

  If the switching element turned off by the imbalance reduction unit is actually turned off, no current flows through the optical insulating element connected in series with the switching element. However, if the current detection signal output from the optical isolation element indicates that a current is flowing, it is considered that a failure has occurred in the discharge unit including the optical isolation element. It can be determined that a failure has occurred in the part.

  In addition, when the current detection signal output from the optical isolation element connected in series with the switching element turned on by the imbalance reduction unit indicates that no current flows, the failure detection unit It is preferable to determine that a failure has occurred in the discharge part including

  If the switching element turned on by the imbalance reduction unit is actually turned on, a current flows through the optical insulating element connected in series with the switching element. However, if the current detection signal output from the photo-isolation element indicates that no current flows, it is considered that some failure has occurred in the discharge unit including the photo-isolation element. It can be determined that a failure has occurred in the part.

  The apparatus further comprises a selection unit that selects one of the current detection signals output from each of the optical isolation elements and supplies the current detection signal to the failure detection unit. The failure detection unit is configured to detect the current detection by the selection unit. It is preferable to select the signals sequentially.

  According to this configuration, even if the number of secondary batteries increases and the number of discharge units increases, it is not necessary to increase the signal input port of the failure detection unit only by increasing the selection number of the selection unit, It becomes easy to use a large number of discharge parts.

  Moreover, the battery power supply device according to the present invention includes the above-described battery equalization circuit and the plurality of secondary batteries.

  According to this configuration, in a battery power supply device including a plurality of secondary batteries, it is possible to detect a failure of a circuit that is discharged in order to equalize the stored charge amount of each secondary battery.

  In the battery equalization circuit and the battery power supply device configured as described above, when an imbalance occurs in each secondary battery, the switching element of each discharge unit is turned on so that the imbalance reduction unit reduces the imbalance. The secondary battery is turned off to control the discharge of each secondary battery. At this time, depending on whether the switching element is turned on or off, whether the current actually flows or is interrupted is notified to the failure detection unit by the current detection signal of the photo-insulating element. By determining the presence or absence of a failure in each discharge unit based on the current detection signal output from the optical insulating element, it is possible to detect a failure in a circuit that is discharged in order to equalize the stored charge amount of each secondary battery. .

  Embodiments according to the present invention will be described below with reference to the drawings. In addition, the structure which attached | subjected the same code | symbol in each figure shows that it is the same structure, The description is abbreviate | omitted. FIG. 1 is a block diagram showing an example of the configuration of a battery power supply device using a battery equalization circuit according to an embodiment of the present invention.

  A battery power supply device 1 shown in FIG. 1 includes a battery equalization circuit 2 and an assembled battery 3. The assembled battery 3 is configured by, for example, ten secondary batteries B1, B2,..., B10 connected in series. As the secondary batteries B1, B2,..., B10, various secondary batteries such as nickel hydrogen secondary batteries and lithium ion secondary batteries can be used.

  In addition, the number of the secondary batteries which comprise the assembled battery 3 should just be two or more, and is not limited to ten pieces. Further, the secondary batteries B1, B2,..., B10 may each be a battery block in which a plurality of cells are configured in series, parallel, or a combination of series and parallel.

  Moreover, the positive electrode of the assembled battery 3 is connected to the connection terminal T1, and the negative electrode is connected to the connection terminal T2. Then, for example, a charging device such as a generator or a solar cell, or a load device such as a motor is connected to the connection terminals T1 and T2. Then, by supplying a charging current from the charging device to the connection terminals T1, T2, the secondary batteries B1, B2,..., B10 are charged, and the secondary batteries B1, B2,. When the current is supplied to the load device via the connection terminals T1 and T2, the load device is driven.

  The battery equalization circuit 2 includes discharge units X1, X2,..., X10, resistors R1 to R10, R11 to R21, a control unit 4, an imbalance reduction circuit 5, and a multiplexer 6 (selection unit). I have. The discharge part X1 is configured by connecting a photocoupler PC1 (photo insulating element), a switching element SW1, and a resistor R1 in series. Similarly, the discharge units X2 to X10 are configured by a series circuit of a photocoupler PC, a switching element SW, and a resistor R having the same reference numerals as the corresponding discharge units.

  Each of the photocouplers PC1 to PC10 includes an LED (Light Emitting Diode) and a phototransistor that receives light from the LED. And LED of photocoupler PC1-PC10 is connected in series with each switching element SW and resistance R in corresponding discharge part X1-X10. The collector of each phototransistor is connected to the operating power supply VDD via the corresponding resistors R1 to R10, and the emitter of each phototransistor is connected to the ground.

  A connection point between the collector of each phototransistor and the resistors R <b> 1 to R <b> 10 is connected to the input terminal of the multiplexer 6. As a result, when no current flows through the discharge portions X1 to X10, the LEDs of the photocouplers PC1 to PC10 are turned off, the phototransistors are turned off, and pulled up by the resistors R1 to R10 to be a high level current detection signal. Scd is input to the multiplexer 6. On the other hand, when current flows through the discharge parts X1 to X10, the LEDs of the photocouplers PC1 to PC10 emit light, each phototransistor is turned on, and low level current detection signals Scd1 to Scd10 are input to the multiplexer 6, respectively. It has become so.

  The multiplexer 6 selects one of the current detection signals Scd <b> 1 to Scd <b> 10 indicating the presence / absence of the current output from the photocouplers PC <b> 1 to PC <b> 10 according to the control signal from the control unit 4, and outputs it to the control unit 4. As a result, even if the number of discharge units increases, it is not necessary to increase the signal input port of the control unit 4 only by increasing the number of multiplexers 6 to be selected, so that it becomes easy to use a large number of discharge units.

  The current detection signals Scd <b> 1 to Scd <b> 10 may be directly input to the control unit 4 without using the multiplexer 6.

  Both ends of the secondary batteries B1, B2,..., B10 are connected to the imbalance reduction circuit 5 via resistors R11 to R21, respectively.

  When any one of the terminal voltages of the secondary batteries B1, B2,..., B10 input via the resistors R11 to R21 exceeds the preset discharge start voltage Vr, the imbalance reduction circuit 5 During the period when the terminal voltage exceeds the discharge start voltage Vr, the switching element of the discharge unit connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the discharge start voltage Vr is turned on. Further, the imbalance reduction circuit 5 outputs a switch state signal Ssw indicating the on / off states of the switching elements SW <b> 1 to SW <b> 10 to the control unit 4. In this case, the imbalance reduction circuit 5 corresponds to an example of a voltage detection unit and an imbalance reduction unit in the claims.

  The imbalance reduction circuit 5 may be configured using, for example, a plurality of comparators that compare the terminal voltages of the secondary batteries B1, B2,..., B10 with the discharge start voltage Vr. In this case, when each terminal voltage of the corresponding secondary battery exceeds the discharge start voltage Vr, each comparator outputs its output signal to the switching element of the discharge unit connected in parallel with the corresponding secondary battery, While each terminal voltage exceeds the discharge start voltage Vr, the switching element of the discharge unit connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the discharge start voltage Vr can be turned on.

  In this case, by supplying a charging current from the charging device to the connection terminals T1, T2, the secondary batteries B1, B2,..., B10 are charged, and the secondary batteries B1, B2,. When the terminal voltage increases, the switching element of the discharge unit connected in parallel with the secondary battery is turned on by the imbalance reduction circuit 5 in order from the secondary battery whose terminal voltage has reached the discharge start voltage Vr, and the secondary battery is turned on. Since the charging current of the battery is bypassed, finally, the secondary batteries B1, B2,..., B10 are charged equally up to the discharge start voltage Vr as a result of the secondary batteries B1, B2,. ..., the terminal voltage of B10 is equalized.

  And since there is a correlation between the terminal voltage of the secondary battery and the stored charge amount, when the terminal voltages of the secondary batteries B1, B2,..., B10 are equalized, the stored charge amount of the secondary battery. Are equalized. In this way, the imbalance reduction circuit 5 can equalize the stored charge amount of the secondary batteries B1, B2,..., B10.

  In addition, if the discharge start voltage Vr is set to the full charge voltage of the secondary batteries B1, B2,..., B10, the stored charge amount while the secondary batteries B1, B2,. Can be reduced.

  Although the imbalance reduction circuit 5 is shown as a single circuit block, it may be divided into a plurality of circuit blocks.

  The control unit 4 includes, for example, a CPU (Central Processing Unit) that executes predetermined arithmetic processing, a nonvolatile ROM (Read Only Memory) in which a predetermined control program is stored, and a RAM (Random) that temporarily stores data. Access Memory) and its peripheral circuits and the like. And the control part 4 functions as the failure detection part 41 by running the control program memorize | stored in ROM, for example.

  The failure detection unit 41 detects the presence or absence of current flowing through the discharge units X1, X2,..., X10 by causing the multiplexer 6 to sequentially select the current detection signals Scd1 to Scd10. Then, when the current detection signals Scd1 to Scd10 indicate that a current is flowing in the discharge unit including the switching element whose switch state signal Ssw is off, the failure detection unit 41 has a failure in the discharge unit. It is determined that

  Further, when the current detection signals Scd1 to Scd10 indicate that no current is flowing in the discharge unit including the switching element whose switch state signal Ssw is on, the failure detection unit 41 has a failure in the discharge unit. It is determined that

  Thereby, the battery equalization circuit 2 detects a failure of the discharge units X1, X2,..., X10 that are discharged in order to equalize the stored charge amount of the secondary batteries B1, B2,. be able to.

  When the failure detection unit 41 detects a failure in the discharge unit, the failure detection unit 41 may display, for example, that a failure has occurred by a display device (not shown), and a signal indicating that the failure has occurred is connected to the connection terminals T1 and T2. The failure may be notified by outputting to a connected charging device, load device, or other higher-level device. For example, the switching element (not shown) provided in the charging / discharging path of the assembled battery 3 is turned off. You may make it improve safety by prohibiting charging / discharging.

  In the battery equalization circuit 2, the example in which the imbalance reduction circuit 5 functions as the voltage detection unit and the imbalance reduction unit has been described. However, for example, a control unit may be used as the imbalance reduction unit.

  FIG. 2 is a block diagram showing an example of the configuration of the battery power supply device 1a including the battery equalization circuit 2a using the control unit as an imbalance reduction unit. The battery equalization circuit 2a shown in FIG. 2 includes a voltage detection unit 7 instead of the imbalance reduction circuit 5 of the battery equalization circuit 2 shown in FIG. The control unit 4a in the battery equalization circuit 2a functions as a failure detection unit 41a, an imbalance determination unit 42, and an imbalance reduction unit 43. Further, the switching elements SW <b> 1 to SW <b> 10 are turned on and off according to a control signal from the imbalance reduction unit 43. Since the other configuration is the same as that of the battery equalization circuit 2 shown in FIG.

  The voltage detection part 7 is comprised, for example using the analog-digital converter, detects each terminal voltage of secondary battery B1, B2, ..., B10, and outputs the detected value to the control part 4a.

  The imbalance determining unit 42 determines whether or not an imbalance has occurred in the terminal voltages of the secondary batteries B1, B2,..., B10 based on the terminal voltages detected by the voltage detecting unit 7. Specifically, the imbalance determination unit 42 calculates, for example, the difference between the maximum value and the minimum value of each terminal voltage, and if the calculated difference exceeds a preset reference voltage, the imbalance determination unit 42 calculates the difference. It is determined that an equilibrium has occurred. The imbalance determination unit 42 can use various other determination methods in order to determine whether an imbalance has occurred.

  When the imbalance determining unit 42 determines that an imbalance has occurred, the imbalance reducing unit 43 is in parallel with the secondary battery having the highest terminal voltage among at least the secondary batteries B1, B2,. By turning on and discharging the switching element in the connected discharge unit, the difference from other secondary batteries is reduced. More specifically, the imbalance reduction unit 43, for example, until the lowest terminal voltage among the terminal voltages of the secondary batteries B1, B2,..., B10 becomes equal to the other terminal voltages. By switching on and discharging the switching elements in the discharge unit connected in parallel with the secondary batteries other than the secondary battery having a low terminal voltage, all terminal voltages are aligned to the lowest terminal voltage, so that the terminal voltage Reduce imbalance.

  According to this configuration, each terminal voltage can be equalized only by discharging the secondary battery, and therefore, even if each secondary battery is not charged to the discharge start voltage Vr as in the battery equalization circuit 2, it is equalized. Can be executed.

  Note that the control unit 4a does not include the imbalance determination unit 42, and the imbalance reduction unit 43 starts discharging at which one of the terminal voltages detected by the voltage detection unit 7 is set to a full charge voltage, for example. During the period exceeding the voltage Vr, equalization may be performed by turning on the switching element of the discharge unit connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the discharge start voltage Vr, Other various methods can be used as other equalization means.

  The failure detection unit 41a detects the presence / absence of current flowing in the discharge units X1, X2,..., X10 by sequentially selecting the current detection signals Scd1 to Scd10 using the multiplexer 6. When the current detection signals Scd1 to Scd10 indicate that a current is flowing in the discharge unit including the switching element turned off by the imbalance reduction unit 43, the failure detection unit 41a has a failure in the discharge unit. It is determined that

  Further, when the failure detection unit 41a indicates that the current detection signals Scd1 to Scd10 indicate that no current flows in the discharge unit including the switching element turned on by the imbalance reduction unit 43, a failure occurs in the discharge unit. It is determined that

  According to this, by making the control part 4a function as the imbalance determination part 42 and the imbalance reduction part 43, for example, the imbalance reduction circuit 5 is the same number as secondary battery B1, B2, ..., B10. The circuit scale can be easily reduced as compared with the case where the comparator is configured.

  A battery equalization circuit according to the present invention, and a battery power supply using the same, include a portable personal computer, a digital camera, an electronic device such as a mobile phone, a vehicle such as an electric vehicle and a hybrid car, a hybrid elevator, a solar cell, and a power generator. It can be suitably used in battery-mounted devices and systems such as a power supply system in which the device and the secondary battery are combined.

It is a block diagram which shows an example of a structure of the battery power supply device using the battery equalization circuit which concerns on one Embodiment of this invention. It is a block diagram which shows the modification of the battery power supply device shown in FIG. It is a circuit diagram which shows the battery equalization circuit which concerns on background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 1a Battery power supply device 2, 2a Battery equalization circuit 3 Battery assembly 4, 4a Control part 5 Imbalance reduction circuit 6 Multiplexer 7 Voltage detection part 10 Battery assembly 41, 41a Fault detection part 42 Imbalance determination part 43 Imbalance reduction Part B1, B2,..., B10 Secondary batteries PC1, PC2,..., PC10 Photocouplers R1 to R10, R11 to R21 Resistors SW1, SW2,. Switch status signal T1, T2 connection terminal X1, X2, ..., X10 Discharge unit

Claims (8)

A plurality of discharge units respectively connected in parallel to a plurality of secondary batteries connected in series;
A failure detection unit for detecting a failure of each discharge unit;
An imbalance reduction unit that reduces the imbalance by using each discharge unit when an imbalance occurs in each secondary battery,
Each discharge part is
An optical insulating element that converts the flowing current into light to insulate and outputs a current detection signal indicating the current, a switching element that is controlled to be turned on and off by the imbalance reduction unit, and a resistor are connected in series. And
The failure detection unit is
A battery equalization circuit, wherein the presence or absence of a failure of each discharge unit is determined based on a current detection signal output from each photo-isolation element. A voltage detector for detecting a terminal voltage of each of the secondary batteries;
One of the terminal voltages detected by the voltage detection unit is connected in parallel with the secondary battery corresponding to the terminal voltage exceeding the discharge start voltage for a period exceeding the preset discharge start voltage. The battery equalization circuit according to claim 1, further comprising: an imbalance reduction unit that turns on a switching element of the discharge unit. The discharge start voltage is
The battery equalization circuit according to claim 2, wherein the battery is a full charge voltage of each secondary battery. A voltage detector for detecting a terminal voltage of each of the secondary batteries;
Based on each terminal voltage detected by the voltage detection unit, an imbalance determination unit that determines whether an imbalance has occurred in the terminal voltage of each secondary battery;
In the discharge unit connected in parallel with the secondary battery having the highest terminal voltage detected by the voltage detection unit among the respective secondary batteries when the imbalance determination unit determines that an imbalance has occurred. The battery equalization circuit according to claim 1, further comprising an imbalance reduction unit that turns on the switching element. The failure detection unit is
When the current detection signal output from the optical isolation element connected in series with the switching element turned off by the imbalance reduction unit indicates that a current flows, a failure occurs in the discharge unit including the optical isolation element. The battery equalization circuit according to any one of claims 2 to 4, wherein the battery equalization circuit is determined. The failure detection unit is
When the current detection signal output from the optical isolation element connected in series with the switching element turned on by the imbalance reduction unit indicates that no current flows, a failure occurs in the discharge unit including the optical isolation element. The battery equalization circuit according to any one of claims 2 to 5, wherein the battery equalization circuit is determined. Selecting one of the current detection signals output from each of the optical isolation elements, further comprising a selection unit for supplying to the failure detection unit,
The failure detection unit is
The battery equalization circuit according to claim 1, wherein the current detection signals are sequentially selected by the selection unit. The battery equalization circuit according to any one of claims 1 to 7,
A battery power supply device comprising: the plurality of secondary batteries.

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