JP2015173569A - Battery pack with auxiliary charging/discharging function - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a protection circuit board small-sized by reducing a space occupied in packaging a current reduction resistor forming an auxiliary charging circuit or an auxiliary discharging circuit.SOLUTION: A battery pack includes: a secondary battery (2); a charging/discharging switch circuit (6) including a charging control switch element (12) and a discharging control switch element (13) inserted into a charging/discharging line (5) from the secondary battery; and a protection circuit (7) for protecting charging/discharging through the charging/discharging line by turning on/off the charging control switch element and the discharging control switch element. An auxiliary charging circuit (14) is further included which is connected in parallel with the charging control switch element. The auxiliary charging circuit is formed from a serial circuit of an auxiliary charging control switch element (15) of which the ON/OFF is controlled by the protection circuit, and an inorganic PTC thermistor (16).

Description

  The present invention relates to a battery pack having a protection circuit that cuts off charging / discharging of a built-in secondary battery in response to occurrence of an abnormal situation, and in particular, has a protection function for a secondary battery by adding a function of pre-charging or pre-discharging. The present invention relates to an improved battery pack.

  The battery pack generally includes a plurality of secondary batteries, and is provided in a state where charge and discharge are possible via positive and negative external terminals. In order to protect the built-in secondary battery from an abnormal situation such as overcharge or overdischarge, a protection circuit is provided for performing control to stop charging / discharging in response to the occurrence of the abnormal situation. That is, a charge / discharge switch circuit is interposed between the external terminal and the secondary battery, and the control circuit performs control to shut off the charge / discharge switch circuit when an abnormal situation is detected. Further, charge / discharge control by the charge / discharge switch circuit is performed so as to cope with various abnormalities such as an abnormal temperature rise in the battery pack as well as overcharge or overdischarge.

  Patent Document 1 discloses a configuration example such as a protection circuit provided in a battery pack. In FIG. 5, the circuit diagram of the battery pack 100 disclosed by patent document 1 is shown. However, illustrations of parts unnecessary for the description of the prior art relating to the present invention are omitted.

  The battery pack 100 includes a secondary battery 101 in which a plurality of unit cells 101a such as lithium ion batteries are connected. The battery pack 100 is detachably attached to the portable device 102. The portable device 102 is supplied with DC power obtained by converting AC commercial power, and is provided with control / power supply means 103 that controls and supplies this power. The power output from the control / power supply means 103 is supplied to the load 104 of the portable device 102 and is supplied to charge the secondary battery 101 of the battery pack 100. When there is no power supply from commercial power, power is supplied from the battery pack 100 to the control / power supply means 103.

  The secondary battery 101 discharges from the charge / discharge external terminals T1 and T2 connected via the charge / discharge line 105 to the control / power supply means 103, while the control / power supply means 103 supplies the charging power. Is done. A charge / discharge switch circuit 106 is inserted in the charge / discharge line 105. The charge / discharge switch circuit 106 includes a charge control FET 107 and a discharge control FET 108. A precharge circuit 109 is connected in parallel with the charge control FET 107. The preliminary charging circuit 109 includes a resistor 110 for reducing the charging current and a preliminary charging control FET 111.

  The battery pack 100 includes a protection circuit 112 including a microprocessor unit that monitors and controls charging / discharging of the secondary battery 101. In addition, a current detection unit 113 including a resistor or the like that detects a current during charging / discharging of the secondary battery 101 and a temperature detection unit 114 disposed in close contact with the secondary battery 101 are provided.

  The protection circuit 112 is provided with an A / D conversion unit 115, which converts the total battery voltage (measurement point d), the output from the current detection unit 113, and the output voltage from the temperature detection unit 114 into a digital voltage and outputs an actual voltage [mV]. Or actual current value [mA] or the like. An output from the A / D conversion unit 115 is input to the control / calculation unit 116 to perform calculation, comparison, determination, and the like. On / off of the charge / discharge switch circuit 106 is controlled by a signal from the control / calculation unit 116. That is, when detecting an abnormal current, abnormal temperature, abnormal voltage, or the like, the control / calculation unit 116 controls the charge / discharge switch circuit 106 to cut off the current. Thereby, protection of the secondary battery 101 or accident occurrence is prevented.

  For example, when the voltage of the secondary battery 101 becomes equal to or higher than the overcharge voltage, the control / calculation unit 116 controls the charge control FET 107 to be turned off, and charging is stopped. The charge control FET 107 is connected so that the parasitic diode 107a is in the reverse direction with respect to the charging current. Further, when the voltage of the secondary battery 101 becomes equal to or lower than the overdischarge voltage, the discharge control FET 108 is controlled to be off, and the discharge is stopped. The discharge control FET 108 is connected so that the parasitic diode 108a is in the reverse direction with respect to the discharge current.

  The preliminary charging circuit 109 is provided to perform preliminary charging with a reduced current value instead of the above-described normal charging when the secondary battery 101 is held in a state of an overdischarge voltage or less. The preliminary charging control FET 111 of the preliminary charging circuit 109 is controlled to be turned on / off by an instruction from the control / calculation unit 116, and energizes the reduced charging current via the resistor 110. The precharge control FET 111 is connected such that the parasitic diode 111a is in the reverse direction with respect to the charging current.

  That is, at the start of charging, when the battery voltage is equal to or lower than the overdischarge voltage, the control / calculation unit 116 turns off the charge control FET 107 and turns on the preliminary charge control FET 111. Under this operation, when a charging current is supplied from the portable device 102, the charging current is reduced by the resistor 110, and the secondary battery 101 is charged via the precharge control FET 111 in the on state. If the battery voltage becomes equal to or higher than a predetermined value within a predetermined time from the start of charging, the control / calculation unit 116 turns off the preliminary charge control FET 111 and turns on the charge control FET 107 to perform normal charging. Thereby, it is avoided that the charging current to the secondary battery 101 becomes excessive.

JP 2008-288046 A

  In the battery pack disclosed in Patent Document 1, the resistor 110 for reducing the charging current in the preliminary charging circuit 109 is required to have high power and high resistance characteristics. For this reason, for example, cement resistors are used in the conventional battery packs. However, since they are large, they occupy a large space for mounting, making it difficult to reduce the size of the protection circuit board.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a battery pack that can reduce the space occupied in mounting a current reducing resistor constituting a precharge circuit or a predischarge circuit, thereby enabling downsizing of a protection circuit board. .

  On the other hand, the preliminary discharge function has not been sufficiently considered. However, if the discharge control FET 108 is immediately turned on when discharging from the battery pack to the external circuit, depending on the state of the external circuit, there is a risk of cell deterioration, rush current, charge / discharge FET failure, and the like. In particular, a battery pack with a high voltage can be a serious problem.

  In view of this, the present invention obtains effects such as suppression of unit cell deterioration and suppression of rush current by appropriately functioning preliminary discharge at a suppressed current prior to normal discharge when discharging to an external circuit. It is a further object to provide a battery pack that is capable of satisfying the requirements.

  The battery pack of the present invention includes, as a basic configuration, a secondary battery, a charge control switch element inserted in a charge / discharge line from the secondary battery, a charge / discharge switch circuit including a discharge control switch element, and the charge control switch. And a protection circuit for controlling charge / discharge through the charge / discharge line by turning on / off the element and the discharge control switch element.

  In order to solve the above problem, the battery pack of the first configuration of the present invention further includes a precharge circuit connected in parallel with the charge control switch element, and the precharge circuit is controlled to be turned on and off by the protection circuit. It is characterized by comprising a series circuit of a precharge control switch element and an inorganic PTC thermistor.

  The battery pack of the second configuration of the present invention further includes a preliminary discharge circuit connected in parallel with the discharge control switch element, and the preliminary discharge circuit includes a preliminary discharge control switch element whose on / off is controlled by the protection circuit; It is comprised by the series circuit of an inorganic PTC thermistor.

  According to the battery pack having the above configuration, the PTC thermistor is used instead of the conventional cement resistor as an element for reducing the current in the precharge circuit or the precharge circuit. It is possible to significantly reduce the size of the protective circuit board by reducing the space occupied by mounting on the protective circuit board.

  In addition, according to the battery pack of the second configuration, when discharging to the external circuit, the preliminary discharge with the suppressed current is appropriately functioned before the normal discharge, thereby suppressing the deterioration of the unit cell and the rush current. Etc. can be obtained.

FIG. 3 is a block diagram showing a battery pack in the first embodiment. Block diagram showing a battery pack in Embodiment 2 Flow chart showing operation at the start of discharge in the battery pack Block diagram showing a battery pack in Embodiment 3 Block diagram showing a conventional battery pack

  The battery pack of the present invention can take the following aspects based on the above configuration.

  That is, the first configuration further includes a preliminary discharge circuit connected in parallel with the discharge control switch element, and the preliminary discharge circuit includes a preliminary discharge control switch element whose on / off is controlled by the protection circuit and an inorganic PTC thermistor. It is comprised by the series circuit of. By using the PTC thermistor, even if the preliminary charging circuit and the preliminary discharging circuit are provided, the space occupied for mounting on the protective circuit board is suppressed, and it is easy to ensure miniaturization of the protective circuit board.

  In this configuration, the preliminary charging circuit and the preliminary discharging circuit are connected in series and connected in parallel with the charging / discharging switch circuit, and the PTC thermistor is integrated into one, the preliminary discharging circuit and the preliminary charging circuit. Can be configured to be shared by each other. Thus, by sharing a single PTC thermistor for predischarge and precharge, the space saving effect is improved and the precharge circuit and the predischarge circuit can be more easily provided.

  In any one of the configurations described above, when the protection circuit starts the transition operation from the OFF state to the ON state of the discharge control switch element, the protection circuit first controls the preliminary discharge control switch element to turn on to perform preliminary discharge. And detecting whether or not a pack voltage, which is a voltage at the output terminal of the charge / discharge line, exceeds a release voltage set to a predetermined value, and the discharge control when the pack voltage exceeds the release voltage The pre-discharge is stopped by controlling the switch element to be on, and when the pre-discharge operation has elapsed for a predetermined time without the pack voltage exceeding the release voltage, the pre-discharge is stopped and a predetermined waiting time is reached. After the lapse of time, it is detected whether or not the pack voltage exceeds the release voltage while performing the preliminary discharge again, and the discharge control is performed when the pack voltage exceeds the release voltage. After the preliminary discharge is stopped by controlling the switch element to be turned on and the pack voltage does not exceed the release voltage and the preliminary discharge operation is repeated a predetermined number of times, the discharge control switch element is A configuration may be adopted in which the preliminary discharge is stopped and the transition operation is terminated without shifting to the on state. Thus, preliminary discharge with reduced current through the preliminary discharge circuit is performed, and the presence or absence of an abnormality such as a short circuit of the external circuit is detected based on the change in the pack voltage when the discharge from the battery pack to the external circuit is started. Can do. And since it is preliminary discharge, even if it is a case where it is short-circuited, a big rush current can be avoided.

  The PTC thermistor is mounted in a direction in which the longitudinal direction intersects the circuit board. Thereby, the heat transfer from the PTC thermistor to the circuit board can be suppressed, and the possibility that the heat generated by energizing the PTC thermistor affects the characteristics of other circuit components can be reduced.

  The switch element is configured by any of a MOSFET, a transistor, an IGBT, or a relay.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

<Embodiment 1>
The battery pack according to Embodiment 1 will be described with reference to the block diagram of FIG. The battery pack 1 includes a secondary battery 2 in which a plurality of unit cells 2a such as lithium ion batteries are connected. The battery pack 1 is detachably attached to an electronic device 4 including an external circuit 3. The external circuit 3 is supplied with DC power converted from AC commercial power or DC power from the battery pack 1. The DC power converted from the AC commercial power is consumed in the external circuit 3 and also supplied for charging the battery pack 1.

  Both electrode terminals of the secondary battery 2 are connected to the external terminals T1 and T2 for charging / discharging through the charging / discharging line 5, and are connected to the external circuit 3 through the external terminals T1 and T2. A charge / discharge switch circuit 6 is inserted in the charge / discharge line 5 between the positive electrode terminal of the secondary battery 2 and the external terminal T1. The charge / discharge switch circuit 6 is controlled to be turned on / off by the protection circuit 7 and controls the charge / discharge operation by the secondary battery 2. The protection circuit 7 includes a switch circuit control unit 8, a voltage detection unit 9, a current detection unit 10, and a temperature detection unit 11.

  The voltage detector 9 monitors the charge / discharge voltage of the secondary battery 2 and generates a predetermined detection signal when overdischarge or overcharge voltage is detected. The current detection unit 10 monitors the current flowing through the secondary battery 2 via the resistor R inserted on the negative electrode side of the charge / discharge line 5 and generates a predetermined detection signal when an overcurrent is detected. The temperature detector 11 monitors the temperature in the battery pack 1 and generates a predetermined detection signal when a temperature abnormality is detected. These are examples of abnormality detection means for detecting an abnormality in the state of the secondary battery 2 or its surroundings.

  The charge / discharge switch circuit 6 is configured by connecting a charge control FET 12 (charge control switch element) and a discharge control FET 13 (discharge control switch element) made of MOSFETs in series. The charge control FET 12 is connected such that the parasitic diode 12a existing between the drain and the source is in the forward direction with respect to the discharge current. The discharge control FET 13 is connected so that the parasitic diode 13a is in the forward direction with respect to the charging current.

  In the protection circuit 7, detection signals generated by the voltage detection unit 9, the current detection unit 10, and the temperature detection unit 11 are supplied to the switch circuit control unit 8. The switch circuit control unit 8 controls charging / discharging through the charging / discharging line 5 by switching conduction (on state) or non-conduction (off state) of the charge control FET 12 and the discharge control FET 13 based on the detection signals. That is, when an abnormality such as overcharge or overdischarge occurs, the charge / discharge line 5 is cut off to protect the secondary battery 2 or prevent an accident from occurring.

  A preliminary charging circuit 14 is connected in parallel with the charging control FET 12. The preliminary charging circuit 14 is configured by a series circuit of a preliminary charging control FET 15 (preliminary charging control switch element) whose on / off is controlled by the protection circuit 7 and an inorganic PTC thermistor 16. The PTC thermistor 16 is an element for reducing the charging current, and is used in place of the resistor 110 of the conventional example shown in FIG.

  The preliminary charging circuit 14 is provided with the same function as the above-described conventional example, for example, and is reduced in place of normal charging when the secondary battery 2 is held in a state of an overdischarge voltage or less. It is made to operate | move so that it may charge with a preset current value. On / off of the precharge control FET 15 of the precharge circuit 14 is controlled by an instruction from the switch circuit control unit 8.

  That is, at the start of charging, when the battery voltage is equal to or lower than the overdischarge voltage, the switch circuit control unit 8 turns off the charge control FET 12 and turns on the preliminary charge control FET 15. When a charging current is supplied from the external circuit 3 under this state, the charging current is reduced by the PTC thermistor 19 to charge the secondary battery 2. If the battery voltage becomes equal to or higher than a predetermined value within a predetermined time from the start of charging, the switch circuit control unit 8 turns off the preliminary charging control FET 15 and turns on the charging control FET 12 to perform normal charging.

  The switch circuit control unit 8 includes an FET gate voltage control circuit. In this embodiment, n-ch FETs are used as the charge control FET 12, the discharge control FET 13, and the precharge control FET 15. In this case, the switch circuit control unit 8 includes a booster circuit, an insulation circuit, and the like.

  A feature of the present embodiment having the above configuration is that a PTC thermistor 16 is used as an element for reducing the charging current in the preliminary charging circuit 14 instead of the cement resistance of the conventional example. The PTC thermistor 16 is extremely small as compared with various resistors for high power and high resistance, and its volume is about several tenths compared with cement resistance. Thereby, the space which occupies for the mounting to a protection circuit board can fully be reduced, and size reduction of a protection circuit board can be achieved.

  The PTC thermistor 16 is mounted in a direction in which the longitudinal direction intersects with the protection circuit board, that is, in a state where the PTC thermistor 16 stands on the circuit board. Since the PTC thermistor 16 generates a large amount of heat due to energization, the characteristics of other circuit components may be affected by the heat. By mounting the PTC thermistor 16 upright, it is possible to suppress heat transfer to the circuit board and avoid such a fear.

  Normally, in a battery pack, an organic PTC thermistor is used for current interruption when an abnormality occurs, whereas an inorganic PTC thermistor is used in the present embodiment. This is because the use of the PTC thermistor is different from the conventional example, and in this embodiment, it is necessary to ensure the reversibility of the thermistor characteristics.

  In addition, as a switch element which comprises the charging / discharging switch circuit 6 and the precharge circuit 14, not only MOSFET but various elements, such as a transistor, IGBT, a relay, can be used.

<Embodiment 2>
A battery pack according to Embodiment 2 will be described with reference to the block diagram of FIG. In the battery pack 20 of the present embodiment, a preliminary discharge circuit 17 is added to the configuration of the first embodiment. Further, a pack voltage that is a voltage at the output terminal of the charge / discharge line 5, that is, a voltage at a point P on the external terminal T <b> 1 side is connected so as to be detected by the voltage detection unit 9. Other components are the same as those in the first embodiment, and the same reference numerals are assigned and the description is not repeated.

  The preliminary discharge circuit 17 is connected in parallel to the discharge control FET 13. The preliminary discharge circuit 17 is configured by a series circuit of a preliminary discharge control FET 18 (preliminary discharge control switch element) whose on / off is controlled by the protection circuit 7 and an inorganic PTC thermistor 19. The PTC thermistor 19 is an element for reducing the discharge current. By using the PTC thermistors 16 and 19, a space saving effect is greater than in the case of using a resistor, and this facilitates the provision of the preliminary charging circuit 14 and the preliminary discharging circuit 17. It should be noted that only the preliminary discharge circuit 17 may be provided without providing the preliminary charge circuit 14 and the preliminary discharge circuit 17, and a corresponding effect can be obtained.

  The purpose of providing the preliminary discharge circuit 17 to perform the preliminary discharge with the reduced current is, for example, as follows. That is, when the discharge control FET 13 shifts from the OFF state to the ON state, that is, when the discharge operation from the secondary battery 2 is started, the preliminary discharge control FET 18 is always turned on prior to the on control of the discharge control FET 13. Thereby, after performing preliminary discharge to the external circuit 3, the charge / discharge control FETs 12 and 13 are turned on. By performing preliminary discharge, it is possible to suppress the deterioration of the unit cell 2a, suppress the rush current when the battery pack 1 is incorporated in the device, suppress the failure of the charge / discharge control FETs 12 and 13, or detect the abnormality of the external circuit 3. And the like can be obtained.

  For example, in order to suppress the rush current, the discharge control FET 13 may be turned on after detecting that the external circuit 3 is not short-circuited. Prior to the transition of the discharge control FET 13 to the on state, the preliminary discharge control FET 18 is turned on to perform preliminary discharge, thereby detecting the presence or absence of a short circuit in the external circuit 3. That is, when the discharge from the battery pack 20 to the external circuit 3 is started, if the pack voltage reaches a predetermined voltage, it is understood that there is no short circuit. However, if normal discharge is performed with the discharge control FET 13 turned on, if there is a short circuit, a large rush current will flow. In order to avoid this, preliminary discharge with reduced current through the preliminary discharge circuit 17 is effective.

  Therefore, the switch circuit control unit 8 is configured to control on / off of the preliminary discharge control FET 18 and the discharge control FET 13 based on the pack voltage detected by the voltage detection unit 9. The operation of controlling the preliminary discharge control FET 18 and the charge / discharge control FETs 12 and 13 by the switch circuit control unit 8 will be described with reference to the flowchart of FIG.

  When the transition operation from the OFF state to the ON state of the discharge control FET 13 is started (step S1), first, the preliminary discharge control FET 18 is controlled to be turned on to perform preliminary discharge (step S2). With the preliminary discharge, it is detected whether or not the pack voltage (the voltage at the point P at the output end) exceeds the release voltage set to a predetermined value (step S3). The pack voltage is detected during preliminary discharge, for example, at intervals of 0.2 seconds, and compared with the release voltage.

  When the pack voltage exceeds the release voltage (step S3, Yes), the discharge control FET 13 is controlled to be turned on (step S4), the preliminary discharge control FET 18 is controlled to be turned off (step S5), and the transition operation is completed (step S5). Step S6). As a result, a normal discharge state from the battery pack 20 is obtained.

  When the pack voltage does not exceed the release voltage (No in step S3), the preliminary discharge and the comparison operation between the pack voltage and the release voltage are continued for a predetermined time (for example, 10 seconds) (step S7). When the preliminary discharge operation has passed for 10 seconds without the pack voltage exceeding the release voltage (step S7, Yes), it is determined whether or not the repetition of the preliminary discharge operation for 10 seconds has reached a predetermined number of repetitions. (Step S8).

  If the predetermined number of repetitions has not been reached (No at Step S8), the preliminary discharge control FET 18 is controlled to be turned off (Step S9), and a predetermined time is waited (Step S10). After a certain waiting time has elapsed, the process returns to step S2, and it is detected whether or not the pack voltage exceeds the release voltage while performing preliminary discharge again (steps S2 and S3). When the pack voltage exceeds the release voltage, the process proceeds to step S4, where the transition operation is terminated and a normal discharge state from the battery pack 20 is entered as described above.

  When the pack voltage does not exceed the release voltage and the repetition of the operations of steps S2, S3, S7, S9, and S10 reaches a predetermined number of repetitions (step S8, Yes), the discharge control FET 13 is not turned on. Then, the preliminary discharge control FET 18 is controlled to be turned off (step S5), and the transition operation is ended (step S6). As a result, an error state occurs and the return to the normal discharge state is stopped.

<Embodiment 3>
A battery pack according to Embodiment 3 will be described with reference to the block diagram of FIG. The battery pack 21 of the present embodiment is obtained by changing the configuration of the preliminary charging circuit 14 and the preliminary discharging circuit 17 from the configuration of the second embodiment shown in FIG. Other components are the same as those in the second embodiment, and the same reference numerals are given and the description is not repeated.

  In the present embodiment, the preliminary charging circuit 14 and the preliminary discharging circuit 17 in FIG. 2 are integrated as the preliminary charging / discharging circuit 22. That is, one inorganic PTC thermistor 23 is connected in series to the series circuit of the preliminary charge control FET 15 and the preliminary discharge control FET 18. The node between the precharge control FET 15 and the predischarge control FET 18 in FIG. 2 and the node between the charge control FET 12 and the discharge control FET 13 are not connected. As a result, a current flows through the PTC thermistor 23 in both the preliminary charging and the preliminary discharging, and the PTC thermistor 23 is shared by the preliminary discharging circuit and the preliminary charging circuit.

  The preliminary charge control FET 15, the preliminary discharge control FET 18, and the PTC thermistor 23 are not limited to the illustrated arrangement, and may be arranged in any order.

  According to the present embodiment, by sharing the single PTC thermistor 23 for the preliminary discharge and the preliminary charging, it becomes easier to install the preliminary charging circuit and the preliminary discharging circuit by improving the space saving effect.

  The battery pack according to the present invention reduces the space occupied by the pre-charge or pre-discharge current reduction resistor in the mounting, and enables downsizing of the protection circuit board, which is useful for high-voltage battery packs and the like. It is.

DESCRIPTION OF SYMBOLS 1, 20, 100 Battery pack 2a, 101a Unit cell 2, 101 Secondary battery 3 External circuit 4 Electronic device 5, 105 Charge / discharge line 6, 106 Charge / discharge switch circuit 7, 112 Protection circuit 8 Switch circuit control part 9 Voltage detection Unit 10, 113 current detection unit 11, 114 temperature detection unit 12, 107 charge control FET
12a, 13a, 111a Parasitic diode 13 Discharge control FET
14, 109 Precharge circuit 15, 111 Precharge control FET
16, 19 PTC thermistor 17 Predischarge circuit 18 Predischarge control FET
102 portable device 103 control / power supply means 104 load 110 resistance 115 A / D conversion unit 116 control / calculation unit

Claims (7)

A secondary battery,
A charge / discharge switch circuit including a charge control switch element and a discharge control switch element inserted in a charge / discharge line from the secondary battery;
In a battery pack comprising a protection circuit that controls charge / discharge through the charge / discharge line by turning on / off the charge control switch element and the discharge control switch element,
A precharging circuit connected in parallel with the charging control switch element;
The battery pack is characterized in that the precharge circuit is configured by a series circuit of a precharge control switch element whose on / off is controlled by the protection circuit and an inorganic PTC thermistor. A preliminary discharge circuit connected in parallel with the discharge control switch element;
2. The battery pack according to claim 1, wherein the preliminary discharge circuit is configured by a series circuit of a preliminary discharge control switch element whose ON / OFF is controlled by the protection circuit and an inorganic PTC thermistor. The precharge circuit and the predischarge circuit are connected in series and connected in parallel with the charge / discharge switch circuit,
3. The battery pack according to claim 2, wherein the PTC thermistors are integrated into one and shared by the preliminary discharge circuit and the preliminary charging circuit. A secondary battery,
A charge / discharge switch circuit including a charge control switch element and a discharge control switch element inserted in a charge / discharge line from the secondary battery;
In a battery pack comprising a protection circuit that controls charge / discharge through the charge / discharge line by turning on / off the charge control switch element and the discharge control switch element,
A preliminary discharge circuit connected in parallel with the discharge control switch element;
The battery pack is characterized in that the preliminary discharge circuit is configured by a series circuit of a preliminary discharge control switch element whose ON / OFF is controlled by the protection circuit and an inorganic PTC thermistor. The protection circuit is
When starting the transition operation from the OFF state to the ON state of the discharge control switch element, the voltage at the output terminal of the charge / discharge line is first controlled while turning on the preliminary discharge control switch element to perform preliminary discharge. Detects whether the pack voltage exceeds the release voltage set to a predetermined value,
When the pack voltage exceeds the release voltage, the discharge control switch element is turned on to stop the preliminary discharge,
When the pre-discharge operation has passed for a predetermined time without the pack voltage exceeding the release voltage, the pre-discharge is stopped and the pack voltage is changed while performing the pre-discharge again after a certain waiting time has elapsed. Detecting whether or not the release voltage is exceeded, and when the pack voltage exceeds the release voltage, the discharge control switch element is turned on to stop the preliminary discharge,
The pack voltage does not exceed the release voltage, and after repeating the preliminary discharge operation for the predetermined time a predetermined number of times, the preliminary discharge is stopped and shifted without turning on the discharge control switch element. The battery pack according to claim 2, wherein the battery pack is controlled so as to end the operation.   The battery pack according to claim 1, wherein the PTC thermistor is mounted in a direction in which the longitudinal direction intersects the circuit board.   The battery switch according to claim 1, wherein the switch element is configured by any one of a MOSFET, a transistor, an IGBT, and a relay.

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