JP2013135479A - Threshold voltage decision method for detection circuit, overvoltage detection circuit, and battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a threshold voltage decision method for a detection circuit, an overvoltage detection circuit, and a battery pack which can reduce the power consumption of the detection circuit before secondary batteries fall to an overdischarged state.SOLUTION: While a difference between an open voltage of the secondary battery that has the highest voltage, indicated by a full line, of three secondary batteries connected in series and a voltage of 1.3 V at an upper limit of an overdischarged state of the secondary batteries (that is, a boundary voltage to a deep discharge region) is surely greater than a voltage difference between the highest and lowest open voltages of the secondary batteries (that is, a vertical difference between characteristic curves indicated by full and broken lines), when the voltage of the secondary battery that has the highest voltage becomes equal to or lower than a shutdown threshold voltage (3.1 V-3.9 V) lower than an overvoltage detection voltage of 4.35 V, a protection IC (detection circuit) shuts down to reduce power consumption.

Description

  The present invention detects a threshold voltage determination method for a detection circuit that detects that each of a plurality of secondary batteries connected in series is in an overvoltage state and enters a power saving state at a predetermined threshold voltage, an overvoltage detection circuit, and The present invention relates to a battery pack provided with the overvoltage detection circuit.

  Conventionally, in the charging of a secondary battery represented by a lithium ion battery, constant current charging is performed at a predetermined current, and the terminal voltage (hereinafter referred to as battery voltage or cell voltage) is lower than the maximum voltage allowed for the secondary battery. A so-called constant current / constant voltage charging method in which charging is performed by constant voltage charging after reaching a set predetermined voltage is widely used. When the battery voltage exceeds the maximum voltage, the life and charge / discharge capacity of the battery are impaired, and there is a risk of ignition. Therefore, the battery voltage is controlled not to exceed the maximum voltage during charging.

  By the way, when charging a battery pack including an assembled battery in which two or more secondary batteries (cells) are connected in series, when the cell voltage balance is lost, the cell voltage is “1 / series connected to the charging voltage. It can normally occur that the voltage of the “number of cells” is exceeded. In addition, an overvoltage may be applied due to a failure of the charger on the main body side. For this reason, in the battery pack including the assembled battery as described above, an overvoltage is often detected twice by a hardware overvoltage detection circuit and a control circuit controlled by software in order to ensure certainty (patents). Reference 1). In a battery pack having a small capacity, an overvoltage may be detected only by an overvoltage detection circuit.

  The control circuit monitors the cell voltage of each cell, and when any cell drops to the discharge end voltage, in order to prevent overdischarge, a discharge circuit interposed in the charging / discharging path of the assembled battery is used. Turn off the switch. Also in this case, since the overvoltage detection circuit is connected to each cell, the cell voltage continues to decrease slightly, so that some cells fall into an overdischarged state, and copper ions eluted from the negative electrode are inside the battery. There is a risk that the container of the battery pack may swell up due to gas deposited in the cell or gas generated inside the cell.

  On the other hand, in some overvoltage detection circuits, when it is detected that the cell voltage has dropped to a predetermined threshold voltage (power-down threshold voltage), the overvoltage detection circuit powers itself down to reduce current consumption. . By using such an overvoltage detection circuit, further voltage drop of each cell is prevented.

JP 2004-127532 A

  However, an overvoltage detection circuit capable of powering down powers down only when the cell voltage of all cells to be detected falls below the power-down threshold voltage. There is a possibility that a cell having a low value falls into an overdischarge state.

  The present invention has been made in view of such circumstances, and an object of the present invention is to detect the threshold voltage of the detection circuit that can reduce the power consumption of the detection circuit before the secondary battery falls into an overdischarged state. A determination method, an overvoltage detection circuit, and a battery pack including the overvoltage detection circuit.

  The threshold voltage determination method of the detection circuit according to the present invention is such that each secondary battery is in a predetermined overvoltage state when the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time or more. A method for detecting in advance and predetermining the second voltage of a detection circuit that operates with reduced power consumption when the voltages of all the secondary batteries are equal to or lower than a second voltage lower than the first voltage. A discharge characteristic indicating a relationship between a discharge capacity of the secondary battery and a maximum and minimum open voltage, and the maximum open voltage and the secondary battery are overdischarged for one discharge capacity in the discharge characteristic. And calculating the difference between the maximum and minimum open circuit voltages and determining whether or not the calculated difference is greater than the voltage difference. Maximum open circuit voltage Characterized by a serial second voltage.

  The overvoltage detection circuit according to the present invention has means for determining whether or not the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time or more, and when determining that the means is high And means for detecting that each secondary battery is in a predetermined overvoltage state, and reduces the power consumption when the voltage of all the secondary batteries is equal to or lower than the second voltage lower than the first voltage. The maximum voltage and the upper limit voltage at which the secondary battery is in an overdischarged state with respect to one discharge capacity in the discharge characteristics indicating the relationship between the discharge capacity of the secondary battery and the maximum and minimum voltages. The second voltage is the maximum voltage when the difference between the two is larger than the voltage difference between the maximum and minimum voltages.

  In the overvoltage detection circuit according to the present invention, the secondary battery is a lithium ion battery, and the second voltage is 3.1V to 3.9V.

  In the overvoltage detection circuit according to the present invention, the second voltage is 3.5 V or more.

  The overvoltage detection circuit according to the present invention has means for determining whether or not the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time or more, and when determining that the means is high Means for detecting that each secondary battery is in a predetermined overvoltage state, and the voltage of all the secondary batteries is lower than the first voltage and lower than the second voltage higher than the end-of-discharge voltage. In this case, the power consumption is reduced.

  The overvoltage detection circuit according to the present invention is characterized in that the voltage at the end of discharge is 3.0 V or more.

  The battery pack according to the present invention includes the above-described overvoltage detection circuit and a plurality of series-connected secondary batteries that are detected to be in an overvoltage state by the overvoltage detection circuit.

In the present invention, when the second voltage of the detection circuit that reduces the power consumption when all of the plurality of secondary batteries connected in series are equal to or lower than the second voltage, the secondary voltage is determined in advance. In the discharge characteristics showing the relationship between the discharge capacity of the battery and the maximum and minimum open voltage, the difference between the maximum open voltage for one discharge capacity and the upper limit voltage at which the secondary battery is overdischarged is the same. When it is larger than the voltage difference between the maximum and minimum open circuit voltages with respect to the discharge capacity, the maximum open circuit voltage at that time is set as the second voltage.
That is, the threshold value of the voltage monitored by the detection circuit is determined so that the detection circuit is in the power saving state when the voltage of the secondary battery having the lowest voltage is higher than the upper limit voltage of the overdischarge state.

In the present invention, since the second voltage, which is the voltage of the secondary battery when the detection circuit is switched to the power saving state, is set to 3.1 V to 3.9 V, which is higher than the conventional voltage, the detection circuit Is suitably used for detecting an overvoltage of a lithium ion battery.
In other words, by setting the lower limit value of the second voltage to 3.1 V, the detection circuit enters a power saving state before the voltage difference between the secondary batteries expands and the voltage balance is largely lost. In addition, when the upper limit value of the second voltage is set to 3.9 V with respect to the overvoltage detection voltage that is normally set to 4.1 V or higher, reliable detection of the overvoltage is ensured. When the detection circuit is composed of a semiconductor integrated circuit, it is difficult to manufacture the size of the variation range of the second voltage below 0.8V.

In the present invention, the second voltage is preferably 3.5 V or higher.
When the second voltage is set lower than 3.5 V, it is detected that the voltage of the secondary battery having the highest voltage is lower than the second voltage and the detection circuit is in the power saving state. As a result, the voltage difference is increased, and the voltage balance is easily lost.

In the present invention, when the second voltage of the detection circuit that reduces the power consumption when all of the plurality of secondary batteries connected in series are equal to or lower than the second voltage, the secondary voltage is determined in advance. A voltage lower than the first voltage at which each of the batteries is detected to be in an overvoltage state and higher than the voltage at the end of discharge of the secondary battery is defined as the second voltage.
That is, the threshold value of the voltage monitored by the detection circuit is determined so that the detection circuit enters the power saving state before the voltage of the secondary battery having the highest voltage becomes lower than at least the voltage at the end of discharge.

  In the present invention, since the detection circuit is in a power saving state before the voltage of the secondary battery having the highest voltage is lower than at least 3.0 V, the secondary battery having the lowest voltage is in an overdischarged state. There is a high probability that it will be prevented.

In the present invention, the detection circuit described above detects that the secondary battery is in an overvoltage state.
Thereby, before the voltage of the secondary battery with the lowest voltage drops to the upper limit voltage at which it becomes an overdischarged state, the dark current flowing from each secondary battery is greatly reduced by entering the power saving state. A detection circuit capable of the above is applied to the battery pack.

According to the present invention, the threshold value of the voltage monitored by the detection circuit is determined so that the detection circuit is in the power saving state when the voltage of the secondary battery having the lowest voltage is higher than the upper limit voltage of the overdischarge state. .
Therefore, the power consumption of the detection circuit can be reduced before the secondary battery enters the overdischarged state, and the dark current flowing from each secondary battery into the detection circuit can be greatly reduced.

It is a circuit diagram which illustrates the connection configuration of the battery pack according to the embodiment of the present invention. It is a circuit diagram which illustrates the connection structure of the battery pack which concerns on other embodiment of this invention. It is a characteristic view which illustrates the change of the open circuit voltage with respect to the discharge capacity of a secondary battery.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
FIG. 1 is a circuit diagram illustrating a connection configuration of a battery pack according to an embodiment of the present invention. In the figure, 1 is a secondary battery, and the secondary batteries 1, 1, 1 are composed of three lithium ion batteries connected in series. The number of secondary batteries 1 connected in series is not limited to three, and the type is not limited to a lithium ion battery.

  The negative terminal of the secondary battery 1 to be arranged on the lowest potential side is connected to the ground potential. The positive terminal of the secondary battery 1 on the highest potential side is connected to a plus (+) terminal 81 exposed outside the case (not shown). The positive terminals of the secondary batteries 1, 1, 1 connected in series are connected to the input terminals 41, 42, 43 of the protection IC 4 via resistors 2, 2, 2. Capacitors 3 and 3 are respectively connected between the input terminals 41 and 42 and 42 and 43. Another capacitor 3 is connected between the input terminal 43 and the ground potential. Resistors 2, 2, 2 and capacitors 3, 3, 3 are for operating the protection IC 4 stably.

  In the protection IC 4, a power terminal 44 and a ground terminal 45 are connected to a plus (+) terminal 81 and a ground potential, respectively, and the three secondary batteries 1, 1, 1 are connected by the five terminals described above. Detect overvoltage separately. The detection signal terminal 46 from which the protection IC 4 outputs an overvoltage detection signal has a negative (−) terminal 82 exposed outside the case and an N-channel MOSFET (hereinafter referred to as FET) 51 connected in series between the ground potential. 52 is connected to the gate. The FETs 51 and 52 have their drains butted together.

  A case (not shown) of the battery pack is provided with a temperature (T) terminal 83, and between the temperature terminal 83 and the negative terminal 82, a thermal element thermally coupled to the secondary batteries 1, 1, 1. 6 and a thermal fuse 7 thermally coupled to the FETs 51 and 52 are connected in series. In FIG. 1, the broken line represents thermal coupling. When the FETs 51 and 52 fail and overheat, the temperature fuse 7 is blown. The battery pack is detachably attached to an electric device (not shown) such as a portable terminal via a plus terminal 81, a minus terminal 82, and a temperature terminal 83.

  The external electric device detects the voltage between the temperature terminal 83 and the minus terminal 82 to calculate the resistance value of the thermal element 6, and based on the temperature of the thermal element 6 converted from the calculated resistance value, the secondary battery 1 1 and 1 temperatures are detected. When the FETs 51 and 52 are overheated and the thermal fuse 7 is blown, the resistance value of the thermal element 6 is converted to a very large value, so that an abnormality in the FETs 51 and 52 is detected from the outside.

  In the circuit configuration of the battery pack described above, for example, when the state where the voltage of each of the secondary batteries 1, 1, 1 is higher than 4.35 V continues for 2 seconds or more, the protection IC 4 detects that the secondary battery 1, 1, 1 Are detected separately and a detection signal terminal 46 outputs a low (L) level detection signal. By supplying this detection signal to the gates of the FETs 51 and 52, the FETs 51 and 52 are turned off and charging of the secondary batteries 1, 1, and 1 is prohibited. Protected from. The protection IC 4 consumes a maximum current of about 5 μA from the secondary batteries 1, 1, 1 while monitoring the overvoltage of the secondary batteries 1, 1, 1.

  On the other hand, when the voltages of all the secondary batteries 1, 1, 1 become 3.5 V or less, which is a threshold voltage in a power saving state (hereinafter referred to as shutdown) in which the power consumption of the protection IC 4 is reduced, for example, The protection IC 4 is shut down. The current consumed from the secondary batteries 1, 1, 1 while the protection IC 4 is shut down is suppressed to about 0.1 μA at the maximum, so that the secondary batteries 1, 1, 1 are prevented from falling into an overdischarged state. The

In the above battery pack, the protection IC 4 outputs a low (L) level detection signal. However, the present invention is not limited to this, and the protection IC 4 may output a high (H) level detection signal. Good.
FIG. 2 is a circuit diagram illustrating a connection configuration of a battery pack according to another embodiment of the present invention. The battery pack includes secondary batteries 1, 1, 1 and a protection IC 4, and resistors 2, 2, 2 and capacitors 3, 3, 3 connected thereto, according to the embodiment shown in FIG. Since this is the same as the case, the description thereof is omitted.

  The battery pack shown in FIG. 2 includes a three-terminal non-return switch 9 having a first terminal connected to the positive terminal of the secondary battery 1 on the highest potential side, and a negative terminal 82 connected to the ground potential. . The non-return switch 9 has a second terminal connected to the plus terminal 81 and a third terminal connected to the drain of an N-channel FET 53 with a common source. The gate of the FET 53 is connected to the detection signal terminal 46 of the protection IC 4.

  The non-return switch 9 includes fuses 91 and 91 connected in series between the first and second terminals, and heating resistors 92 and 92 connected in parallel between the connection point of the fuses 91 and 91 and the third terminal. Have The fuses 91 and 91 are blown when the temperature rises to around 130 ° C., for example. When any of the voltages of the secondary batteries 1, 1, 1 becomes higher than the overvoltage detection voltage, the FET 53 is turned on by a high (H) level detection signal output from the detection signal terminal 46. As a result, a DC voltage is applied to the heating resistors 92, 92 from the secondary batteries 1, 1, 1 via the fuses 91, 91 to heat the fuses 91, 91. The charging / discharging current of the secondary batteries 1, 1, 1 is cut off. In this way, the secondary batteries 1, 1, 1 are protected from overvoltage.

  Instead of the non-return switch 9, two P-channel FETs with their drains butted in series are interposed in series between the positive terminal 81 and the positive terminal of the secondary battery 1 on the highest potential side. The detection signal terminal 46 may be connected to the gate of each FET. The operation of each FET in this case is the same as that of the FETs 51 and 52 in the embodiment shown in FIG. 1 except that the high / low polarities of the control signals applied to the respective gates are inverted. .

In the following, a method for shutting down the protection IC 4 in the battery pack according to the above-described embodiment and other embodiments before some of the secondary batteries 1 fall into an overdischarged state will be described.
FIG. 3 is a characteristic diagram illustrating the change of the open circuit voltage with respect to the discharge capacity of the secondary batteries 1, 1, 1. Here, the secondary batteries 1, 1, 1 are lithium ion batteries. The horizontal axis of the figure represents the discharge capacity from the fully charged state, that is, the capacity obtained by subtracting the remaining capacity from the full charge capacity, and the vertical axis represents the open circuit voltage of the secondary batteries 1, 1, 1. In the figure, the open circuit voltage of the secondary battery 1 with the highest voltage is displayed with a solid line, and the open circuit voltage of the secondary battery 1 with the lowest voltage is displayed with a broken line.

  When the secondary batteries 1, 1, 1 are fully charged and discharged, the discharge capacity of each secondary battery 1, 1, 1 is equal, whereas each secondary battery 1, 1, 1 Due to the difference in the discharge capacity-voltage characteristics of 1, the difference occurs in the open circuit voltage. This difference varies depending on the difference in discharge rate and the degree of deterioration of the secondary batteries 1, 1, 1, but becomes more prominent as the discharge capacity increases and the open circuit voltage decreases. In other words, when the discharge capacity of the secondary batteries 1, 1, 1 increases, the difference between the open circuit voltage of the secondary battery 1 having the highest voltage and the upper limit voltage at which the secondary battery 1 is overdischarged is While decreasing, the voltage difference between the maximum and minimum open-circuit voltage (or voltage during charging / discharging) in the secondary batteries 1, 1, 1 continues to increase.

  In the example of FIG. 3, when the secondary batteries 1, 1, 1 are in a fully charged state, the voltage difference between the maximum and minimum open circuit voltages in the secondary batteries 1, 1, 1 is so small that it can be ignored. The voltage difference between the maximum and minimum open-circuit voltage is well within 0.1V until the open-circuit voltage of the secondary batteries 1, 1, 1 falls below 3.9V and drops to around 3.5V. ing. Even when the discharge capacity increases and the open circuit voltage of the secondary battery 1 having the highest voltage decreases to 3.1 V, the voltage difference between the maximum and minimum open circuit voltages of the secondary batteries 1, 1, 1 is , About 0.3V (3.1V-2.8V).

When the discharge capacity further increases and the open circuit voltage of the secondary battery 1 with the highest voltage drops to 3.0 V, the voltage difference between the maximum and minimum open circuit voltages of the secondary batteries 1, 1, 1 expands all at once. In addition, it can be seen that the open-circuit voltage of the secondary battery 1 having the lowest voltage is reduced to 1.3 V and enters an overdischarged state (that is, enters a deep discharge region). At this time, the difference between the open voltage of the secondary battery 1 having the highest voltage and the upper limit voltage at which the secondary battery 1 is in an overdischarged state is the maximum and minimum open voltage of the secondary batteries 1, 1, 1. Is equivalent to the voltage difference.
The discharge characteristics shown in FIG. 3 are merely examples, and there are various other discharge characteristics. It is preferable that the shutdown threshold voltage is higher than the voltage at the end of discharge.

  From the above, when the voltage of the secondary battery 1 with the highest voltage is higher than 3.0V, the protection IC 4 is shut down, so that the secondary battery 1 with the lowest voltage is put into the overdischarge state before the secondary battery 1 falls into the overdischarge state. It can be said that the power consumption of the secondary battery 1, 1, 1 can be prevented from being lowered any further.

  Therefore, in the present embodiment, the shutdown threshold voltage in the protection IC 4, that is, the lower limit value of the voltage that causes the protection IC 4 to shut down when the voltages of all the secondary batteries 1, 1, 1 fall below that voltage is 3.1 V. And As described above, by setting the shutdown threshold voltage in the protection IC 4 to be higher than 3.5V, the consumption of the protection IC 4 while the voltage difference between the secondary batteries 1, 1, 1 is within 0.1V. The current can be reduced. When the protection IC 4 is formed of a semiconductor integrated circuit, the threshold voltage range is set to 3.1 V to 3.9 V in consideration of manufacturing variations.

As described above, according to the present embodiment, the difference between the maximum open-circuit voltage for the discharge capacity of the secondary battery at that time and 1.3 V, which is the upper limit voltage at which the secondary battery is in an overdischarged state, is obtained. Shutdown of the highest voltage secondary battery below the overvoltage detection voltage of 4.35V, while being guaranteed to be greater than the voltage difference between the maximum and minimum open circuit voltage for the same discharge capacity When the threshold voltage is lower than the threshold voltage, the protection IC (detection circuit) is shut down to reduce power consumption.
That is, the detection circuit is in the power saving state when the voltage of the secondary battery having the lowest voltage is higher than the upper limit voltage that causes the overdischarge state.
Therefore, it is possible to significantly reduce the dark current flowing from each secondary battery into the detection circuit by shutting down the detection circuit before the secondary battery enters an overdischarged state.

In addition, since the shutdown threshold voltage is set to 3.1 V to 3.9 V, which is higher than the conventional one, the protection IC (detection circuit) is preferably used for detecting the overvoltage of the lithium ion battery.
In other words, by setting the lower limit value of the shutdown threshold voltage to 3.1 V, the detection circuit can be put into a power saving state before the voltage difference between the secondary batteries is enlarged and the voltage balance is largely lost. . In addition, when the upper limit value of the shutdown threshold voltage is set to 3.9 V with respect to the overvoltage detection voltage that is normally set to 4.1 V or higher, it is possible to ensure the reliable detection of the overvoltage.

Furthermore, it can be said that the shutdown threshold voltage by the protection IC (detection circuit) is preferably 3.5 V or more.
In other words, by setting the shutdown threshold voltage to 3.5 V or higher, the voltage of the secondary battery with the highest voltage is shut down before the voltage difference between the secondary batteries increases and the voltage balance tends to be lost. It becomes possible to shut down the detection circuit by detecting that the voltage is lower than the threshold voltage.

Furthermore, a voltage lower than the overvoltage detection voltage of 4.35 V and higher than the end-of-discharge voltage is set as the shutdown threshold voltage.
Therefore, the detection circuit can be shut down before the voltage of the secondary battery having the highest voltage becomes lower than at least the voltage at the end of discharge.

  Furthermore, since the protection IC shuts down before the voltage (maximum cell voltage) of the secondary battery with the highest voltage falls below at least 3.0V, the secondary battery with the lowest voltage is prevented from being overdischarged. It is possible to increase the probability of being done.

Furthermore, it is detected by the protection IC (detection circuit) described above that the secondary battery is in an overvoltage state.
As a result, the detection circuit that can shut down before the voltage of the secondary battery with the lowest voltage drops to the upper limit voltage that causes an overdischarged state to significantly reduce the dark current flowing from each secondary battery. Can be applied to a battery pack.

  In the present embodiment, the voltage of the secondary batteries 1, 1, 1 is monitored only by the protection IC 4. However, for example, a control unit having a CPU is provided, and the control unit is monitored by the protection IC 4. The overvoltage lower than the overvoltage to be monitored may be monitored, and the overdischarge of the secondary batteries 1, 1, 1 may be further monitored.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Secondary battery 4 Protection IC (detection circuit)
51, 52, 53 FET
9 Non-return switch

Claims (7)

When the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time or more, it is detected that each secondary battery is in a predetermined overvoltage state, and all the secondary batteries are In the method of predetermining the second voltage of the detection circuit that operates with reduced power consumption when the voltage is equal to or lower than the second voltage lower than the first voltage,
Prepare discharge characteristics showing the relationship between the discharge capacity of the secondary battery and the maximum and minimum open circuit voltage,
For one discharge capacity in the discharge characteristics, calculate the difference between the maximum open voltage and the upper limit voltage at which the secondary battery is overdischarged, and calculate the voltage difference between the maximum and minimum open voltage,
Determine whether the calculated difference is greater than the voltage difference,
A threshold voltage determination method for a detection circuit, wherein, when the value is larger, the maximum open-circuit voltage for the one discharge capacity is the second voltage. Means for determining whether the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time;
And a means for detecting that each secondary battery is in a predetermined overvoltage state when it is determined that the means is high,
When the voltage of all the secondary batteries is equal to or lower than the second voltage lower than the first voltage, power consumption is reduced.
For one discharge capacity in the discharge characteristics indicating the relationship between the discharge capacity of the secondary battery and the maximum and minimum voltage, the difference between the maximum voltage and the upper limit voltage at which the secondary battery is overdischarged is the maximum. An overvoltage detection circuit, wherein the second voltage is a maximum voltage that is larger than a voltage difference between the minimum voltages. The secondary battery is a lithium ion battery,
The overvoltage detection circuit according to claim 2, wherein the second voltage is 3.1V to 3.9V. The overvoltage detection circuit according to claim 3, wherein the second voltage is 3.5 V or more. Means for determining whether the voltage of each of the plurality of secondary batteries connected in series is continuously higher than the first voltage for a predetermined time;
And a means for detecting that each secondary battery is in a predetermined overvoltage state when it is determined that the means is high,
An overvoltage detection circuit, wherein when all the secondary batteries have a voltage lower than the first voltage and lower than a second voltage higher than the end-of-discharge voltage, the power consumption is reduced.   6. The overvoltage detection circuit according to claim 5, wherein the voltage at the end of discharge is 3.0 V or more.   A pack comprising: the overvoltage detection circuit according to any one of claims 2 to 6; and a plurality of series-connected secondary batteries that are detected to be in an overvoltage state by the overvoltage detection circuit. battery.

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