JP2008148419A - Battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the safety by breaking a charge current surely in condition that the temperature of a battery goes higher while allowing quick charge with a large current. <P>SOLUTION: A battery pack includes a switching element 2 for charge for breaking the charge current of a battery 1, a switching element 3 for discharge for breaking a discharge current, a control circuit 4 which controls the switching element 2 for charge and the switching element 3 for discharge, a temperature sensor 5 which detects the temperature of the battery, and a protective FET 6. Though the protective FET 6 breaks a charge current in off state, it is connected in series with a battery 1 so as to let the charge current of the battery 1 flow via a parasitic diode 6a. Furthermore, the protective FET 6 connects an input circuit 7, which switches on or switches off the protective FET6 with a signal from the temperature sensor 5 and the voltage of the battery, to its input side. This input circuit 7 switches off the protective FET 6 in condition that the temperature of the battery 1 is higher than charge stop temperature and that the voltage of the battery 1 is higher than the off voltage to switch off the protective FET 6. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a battery pack in which a switching element for controlling charging / discharging of a battery in series with the battery and an FET for cutting off current at battery temperature are connected.

  A battery pack in which a switching element made of an FET is connected as a battery protection circuit in series with the battery has been developed. In this battery pack, a charge control switching element and a discharge control switching element are connected in series with the battery. The switching element for charge control is switched off when the voltage of the battery to be charged becomes higher than the set voltage, thereby preventing overcharging of the battery. The discharge control switching element is switched off when the voltage of the discharged battery is lower than the set voltage, thereby preventing overdischarge of the battery. It is also possible to protect the battery by detecting that an overcurrent flows through the battery and switching off the charge control switching element and the discharge control switching element. This battery pack is discharged while protecting the battery with a switching element for charge control and a switching element for discharge control provided as a protection circuit. However, if the protection circuit fails, the battery becomes abnormal and the temperature becomes abnormally high. Sometimes.

  In order to prevent this problem, in addition to a switching element serving as a protection circuit, a battery pack in which a PTC and a fuse are connected in series has been developed. In the PTC, when an overcurrent flows through the battery or when the battery temperature becomes abnormally high, the electric resistance rapidly increases and the battery current is effectively cut off. The fuse is also blown by overcurrent or battery temperature to protect the battery. However, since recent battery packs are rapidly charged with a large current, it is difficult to realize a characteristic that PTC and fuses are not interrupted by rapid charging while the current is reliably interrupted in the event of an abnormality. This is because a PTC or fuse that allows rapid charging with a large current also increases the current value to be cut off.

This problem can be solved by a circuit that detects the temperature of the battery and interrupts the current of the battery, as described in Patent Document 1, for example. As shown in FIG. 1, the battery pack of Patent Document 1 detects the temperature of the battery 91 with a temperature sensor 95, and switches off the protection FET 96 connected in series with the battery 91 using a signal from the temperature sensor 95. .
No. 2000-152516

  In the battery pack of Patent Document 1, a protection FET is connected so as to control the discharge current. This protection FET is switched off to interrupt the discharge current. This battery pack does not cut off the charging current with the parasitic diode of the off-state protection FET. Therefore, the battery pack is charged while the protection FET is off. A battery pack that can be charged while the battery is heated to an abnormal temperature cannot ensure safety. Further, the charging current flowing in the reverse direction to the FET in the off state causes a large voltage drop by the parasitic diode. For this reason, the FET in the off state generates a large amount of heat due to the charging current, and there is a problem that it is heated by the charging current.

  The present invention has been developed for the purpose of solving this drawback. An important object of the present invention is to provide a battery pack capable of improving safety by reliably interrupting the charging current in a state where the battery temperature is high while allowing rapid charging with a large current.

The battery pack of the present invention has the following configuration in order to achieve the aforementioned object.
The battery pack is connected in series with a rechargeable battery 1 to cut off the charging current of the battery 1 and charging switching element 2 connected in series with the battery 1 to cut off the discharging current of the battery 1. An element 3, a control circuit 4 that detects battery voltage and controls on / off of the switching element 2 for charging and the switching element 3 for discharging, a temperature sensor 5 that detects the temperature of the battery 1, and the temperature sensor 5 A protection FET 6 that is switched on and off at the detected battery temperature and that is connected in series with the battery 1 is provided. The protection FET 6 is an FET having a parasitic diode 6a. The protection FET 6 is connected in series with the battery 1 so as to cut off the charging current in the off state but allow the discharging current of the battery 1 to flow through the parasitic diode 6a. Further, the protection FET 6 is connected to an input side of an input circuit 7 for switching the protection FET 6 on and off by a signal from the temperature sensor 5 and a battery voltage. The input circuit 7 switches the protection FET 6 to the off state in a state where the temperature of the battery 1 is higher than the charging stop temperature and the voltage of the battery 1 is higher than the off voltage that turns off the protection FET 6.

  In the battery pack of the present invention, the control circuit 4 switches off the charging switching element 2 when the voltage of the battery 1 becomes higher than the overcharge voltage, and discharges when the voltage of the battery 1 becomes lower than the overdischarge voltage. The switching element 3 is switched off, and the off voltage at which the input circuit 7 switches off the protection FET 6 can be made higher than the overcharge voltage.

  The battery pack of the present invention uses a rechargeable battery 1 as a lithium ion secondary battery, an overcharge voltage of 4.1 V to 4.3 V / cell, an overdischarge voltage of 2.6 V to 3.2 V / cell, and an off-state. The voltage can be 4.4 V / cell or higher.

  In the battery pack of the present invention, the charge stop temperature at which the protection FET 6 is turned off can be set to 50 ° C to 70 ° C.

  In the battery pack of the present invention, the input circuit 7 includes a discharge current detection circuit 10 that detects the discharge current, and the discharge current detection circuit 10 can detect the discharge current and switch the protection FET 6 in the off state on.

  In the battery pack of the present invention, the control circuit 4 switches off the charging switching element 2 when the voltage of the battery 1 becomes higher than the overcharge voltage, and discharges when the voltage of the battery 1 becomes lower than the overdischarge voltage. The switching element 3 is switched off, and the off voltage at which the input circuit 7 switches off the protection FET 6 can be made lower than the overcharge voltage and higher than the overdischarge voltage. Furthermore, in the battery pack of the present invention, the charge stop temperature at which the input circuit 7 switches off the protection FET 6 can be set to 40 ° C. to 50 ° C.

  The battery pack of the present invention is characterized in that safety can be improved by reliably interrupting the charging current in a state where the battery temperature is high while allowing rapid charging with a large current. This is because the battery pack of the present invention connects the FET having the parasitic diode in series with the battery so that the charging current is cut off and the discharging current flows through the parasitic diode in the off state. Connected to the input side of the FET is an input circuit that switches the protection FET on and off with both the signal from the temperature sensor and the battery voltage. With this input circuit, the temperature of the battery is higher than the charge stop temperature and the voltage of the battery This is because the protection FET is switched to the off state in a state higher than the off voltage for turning off the protection FET.

  In particular, in the battery pack according to claim 2 of the present invention, in addition to the configuration of claim 1, the control circuit switches off the charging switching element when the battery voltage becomes higher than the overcharge voltage. When the voltage becomes lower than the overdischarge voltage, the switching element for discharging is switched off, and the input circuit makes the off voltage for switching off the protection FET higher than the overcharge voltage. In this battery pack, the protection FET is not switched off in a normal use state in which the charging switching element and the discharging switching element are normally operated. However, when the charging switching element breaks down, the battery temperature becomes abnormally high, and the battery voltage becomes abnormally high, the protection FET is switched off to reliably prevent the battery temperature from rising. Therefore, even if the switching element for charging the protection circuit breaks down, it can be used safely.

The battery pack according to claim 5 of the present invention is provided with a discharge current detection circuit for detecting a discharge current in the input circuit in addition to the configuration of claim 1, and the discharge current detection circuit detects the discharge current. Since the protection FET in the off state is switched on, even if the battery pack is discharged with the protection FET switched off, the protection FET can be prevented from being heated, and the protection FET can be turned on / off when the battery temperature is high. There is a feature capable of preventing chattering described below that can be switched.
For example, even when a discharge current is detected by such a discharge current detection circuit, the configuration of claim 1 includes an input circuit that switches the protection FET on and off by both the signal from the temperature sensor and the battery voltage. Thus, such chattering can be prevented. In other words, if the protection FET is turned on / off only by a signal from the temperature sensor without using the battery voltage, the protection FET is turned off even when the temperature rises in the discharge state. After that, if discharge is requested from an electronic device using a battery pack, the discharge resumes when the temperature drops (detects the discharge and turns on the protection FET), the temperature rises, and the protection FET is turned off. . There is a problem that this continues and chattering occurs thereafter. Such a problem is solved by the structure of claim 5.

  Furthermore, in the battery pack of claim 6 of the present invention, in addition to the configuration of claim 1, the control circuit switches off the charging switching element when the battery voltage becomes higher than the overcharge voltage, When the voltage becomes lower than the overdischarge voltage, the switching element for discharging control is switched off, and the off voltage at which the input circuit switches off the protection FET is set lower than the overcharge voltage and higher than the overdischarge voltage. It has the feature that it can be charged while preventing deterioration due to high temperature charging.

  Embodiments of the present invention will be described below with reference to the drawings. However, the example shown below illustrates the battery pack for embodying the technical idea of the present invention, and the present invention does not specify the circuit configuration of the battery pack as follows.

  Further, in this specification, in order to facilitate understanding of the scope of claims, numbers corresponding to the members shown in the examples are indicated in the “claims” and “means for solving problems” sections. It is added to the members. However, the members shown in the claims are not limited to the members in the embodiments.

  The battery pack shown in the circuit diagram of FIG. 2 includes a charging switching element 2 that is connected in series with the rechargeable battery 1 to block the charging current of the battery 1, and a discharge current of the battery 1 that is connected in series with the battery 1. Switching element 3 for cutting off the battery, control circuit 4 for detecting the battery voltage and controlling switching element 2 for charging and switching element 3 for discharging on and off, and temperature sensor 5 for detecting the temperature of battery 1 And a protection FET 6 that is switched on and off at the battery temperature detected by the temperature sensor 5 and connected in series with the battery 1, and an input circuit 7 that switches the protection FET 6 on and off.

  The switching element 2 for charging, the switching element 3 for discharging, and the protection FET 6 are MOSFETs having parasitic diodes 2a and 3a that can be energized in the reverse direction. Since the charging switching element 2 controls the charging current of the battery 1, the charging switching element 2 is connected in a direction in which the charging current flows in the forward direction. Therefore, when the charging switching element 2 is switched off, the charging current of the battery 1 is cut off. Furthermore, since the discharge switching element 3 controls the discharge current of the battery 1, it is connected in the direction in which the discharge current flows in the forward direction. Therefore, when the discharge switching element 3 is switched off, the discharge current of the battery 1 is cut off.

  The control circuit 4 detects the voltage of the battery 1 and controls the charging switching element 2 and the discharging switching element 3 to be turned on and off. The control circuit 4 outputs an on signal or an off signal to the FET gates of the charging switching element 2 and the discharging switching element 3 to switch the FET on and off. FIG. 3 shows a state in which the control circuit 4 controls the switching element 2 for charging and the switching element 3 for discharging to be turned on and off. As shown in this figure, when the voltage of the battery 1 being charged becomes higher than the overcharge voltage, the control circuit 4 switches off the charging switching element 2 to prevent the battery 1 from being overcharged. At this time, the discharging switching element 3 is kept on. Further, when the voltage of the discharged battery 1 becomes lower than the overdischarge voltage, the control circuit 4 switches the discharge switching element 3 to OFF to prevent the battery 1 from being overdischarged. At this time, the charging switching element 2 is kept on. As shown in FIG. 3, the control circuit 4 has an overcharge voltage of 4.1 V to 4.3 V / cell and an overdischarge voltage of 2.6 V to 3.2 V / cell. When the voltage of the battery 1 is between the overcharge voltage and the overdischarge voltage, the control circuit 4 charges and discharges the battery pack by turning on both the charging switching element 2 and the discharging switching element 3. Make it ready. When the voltage of the battery 1 is higher than the overcharge voltage, the charging switching element 2 is turned off to prevent overcharging, and when the voltage is lower than the overdischarge voltage, the discharging switching element 3 is turned off. Stop discharge to prevent overdischarge.

  The protection FET 6 cuts off the charging current in the off state. Therefore, the protection FET 6 is connected in series with the battery 1 so as to cut off the charging current in the off state but allow the discharging current of the battery 1 to flow through the parasitic diode 6a.

  The input circuit 7 detects the battery temperature, the battery voltage, and the discharge state of the battery 1 to control the protection FET 6 on and off. The input circuit 7 is connected to a temperature sensor 5 in order to detect the temperature of the battery 1. The temperature sensor 5 is thermally coupled to the battery 1 and detects the temperature of the battery 1. The temperature sensor 5 is a sensor whose electrical resistance changes with respect to the battery temperature, such as a thermistor. The thermistor has a negative temperature characteristic in which the electrical resistance decreases as the temperature increases. Therefore, the temperature of the battery 1 can be detected from the electrical resistance of the thermistor.

  The input circuit 7 converts the electrical resistance of the thermistor into a digital signal, calculates an A / D converter 8 that converts the voltage of the battery 1 into a digital signal, and calculates a digital signal output from the A / D converter 8. And an arithmetic circuit 9 for outputting an on / off signal to the gate of the protection FET 6. The A / D converter 8 also converts the battery voltage into a digital signal and outputs it to the arithmetic circuit 9. Further, the A / D converter 8 converts the voltage drop value of the parasitic diode 6 a generated by the discharge current into both ends of the protection FET 6 into a digital signal and inputs it to the arithmetic circuit 9. It is determined whether the protection FET 6 is in a discharged state.

  The arithmetic circuit 9 of the input circuit 7 calculates the temperature signal converted into a digital signal by the A / D converter 8 and the voltage signal of the battery 1 and outputs an on / off signal to the gate of the protection FET 6. The arithmetic circuit 9 outputs an off signal to the gate of the protection FET 6 in a state where the temperature of the battery 1 is higher than the charging stop temperature and the voltage of the battery 1 is higher than the off voltage for turning off the protection FET 6. Switch off. The charging stop temperature of the battery 1 is set to, for example, 50 ° C to 70 ° C, preferably 60 ° C to 70 ° C. The off voltage is set to 4.4 V or higher, for example.

  When the temperature of the battery 1 becomes higher than 50 ° C. to 70 ° C. and the voltage of the battery 1 becomes 4.4 V or higher, the input circuit 7 switches off the protective FET 6 to cut off the charging current of the battery pack. To do. The charging switching element 2 is switched off at a voltage lower than the off voltage of 4.4V. Therefore, as long as the charging switching element 2 operates normally, the voltage of the battery 1 does not rise to 4.4V. However, when the charging switching element 2 fails and the battery pack is charged, the battery voltage may rise to an off voltage of 4.4V. In the battery pack according to the present invention, when the battery voltage becomes higher than 4.4 V and the battery temperature becomes higher than the charge stop temperature, the protection FET 6 is turned off to stop the charge, so that the charging switching element 2 fails. But it can be used safely. As for the input circuit 7, other circuit configurations may be employed as long as the above-described functions are provided.

  When the battery pack is discharged with the protection FET 6 switched off, the discharge current flows through the parasitic diode 6a of the protection FET 6 and is supplied to the load. Since the voltage drop of the parasitic diode 6a due to the discharge current is large and the heat generation is also large, the input circuit 7 detects the discharged state and switches the protection FET 6 from OFF to ON. The input circuit 7 includes a discharge current detection circuit 10 that detects a discharge current. The discharge current detection circuit 10 detects the discharge current and switches on the protection FET 6 in the off state. The discharge current detection circuit 10 shown in the figure is an arithmetic circuit 9 that determines whether the battery pack is discharged by detecting the voltage drop due to the discharge current generated in the parasitic diode 6a of the protection FET 6. . When a discharge current flows through the protection FET 6 in the off state, a voltage drop of the parasitic diode 6a and a discharge voltage of 0.7V are generated. This discharge voltage is amplified by an amplifier circuit (not shown) built in the input circuit 7 and input to the A / D converter 8. When a discharge current flows through the protection FET 6, the A / D converter 8 converts the amplified discharge voltage into a digital signal and inputs the digital signal to the arithmetic circuit 9. The arithmetic circuit 9 which is the discharge current detection circuit 10 detects the discharge voltage input from the A / D converter 8 and detects the discharge current of the protection FET 6.

  When the discharge voltage is input in a state in which the protection FET 6 is switched off, the input circuit 7 switches the off protection FET 6 on. The protection FET 6 switched to the on state has a small internal resistance and remarkably reduces the voltage drop due to the discharge current. Therefore, the heat generation of the protection FET 6 due to the discharge current is reduced. This is because the heat generation of the protection FET 6 is proportional to the product of the voltage and current of the FET. Therefore, even if the battery pack is discharged in a state where the protection FET 6 is switched off, the protection FET 6 can be prevented from being heated. The magnitude of the discharge current is specified by the impedance of the load, but is smaller than the quick charge current of the battery pack, so that it is unlikely to discharge and become abnormal. However, although not shown in the drawing, a protection FET is connected in series with an FET that cuts off the charging current, and an FET that cuts off the discharging current (a state in which the direction of the parasitic diode is opposite to that of the parasitic diode 6a) is connected in series. When the temperature becomes abnormally high, both the charging current and the discharging current can be cut off. This battery pack has an FET that cuts off the discharge current as the lowest voltage at which the battery temperature is set higher than the discharge stop temperature, for example, 50 to 70 ° C., and the battery voltage is set lower than the overdischarge voltage, for example Switch off when below 2.5V.

The arithmetic circuit 9 of the input circuit 7 switches the protection FET 6 on and off in the flowchart of FIG.
[Step of n = 1]
At the start, the protection FET 6 is controlled to be on. In this step, it is determined whether or not the battery temperature is higher than the charge stop temperature. When the battery temperature is lower than the charge stop temperature, this step is looped.
[Step of n = 2]
If the battery temperature is higher than the charge stop temperature, it is determined in this step whether or not the battery voltage is higher than the off voltage. When the battery voltage is not higher than the off voltage, the process jumps to the step of n = 1 and loops the steps of n = 1 and 2.
[Step n = 3]
When the battery temperature is higher than the charge stop temperature and the battery voltage is higher than the off voltage, the signal input to the gate of the protection FET 6 is switched from the on signal to off, and the protection FET 6 is switched off.
[Steps n = 4, 5]
Thereafter, in this step, it is determined whether or not a discharge current flows through the protection FET 6. When the discharge current is flowing, the protection FET 6 is switched from OFF to ON, and then jumps to the step of n = 4, and the steps of n = 4 and 5 are looped. If no discharge current flows through the protection FET 6, the process jumps to the step of n = 1.

  Furthermore, in the battery pack of the present invention, the off voltage at which the input circuit 7 switches the protection FET 6 off is lower than the overcharge voltage and higher than the overdischarge voltage, for example, 4 V / cell, and further the protection FET 6 is turned off. By setting the charge stop temperature to be switched to 40 ° C. to 50 ° C., the battery 1 can be charged while preventing deterioration due to high temperature charging. This battery pack does not switch off the protective FET 6 due to the failure of the charging switching element 2 but switches off the protective FET 6 first, and then switches off the switching element 2 for charging. Improve sexiness. That is, since the protection FET 6 is switched off before the charging switching element 2 is switched off, even if the charging switching element 2 fails, the protection FET 6 cuts off the charging current to improve safety. Let

  Furthermore, the following configuration can be added to the battery pack of the present invention. In the following embodiments, the same components as those in the above-described embodiments are denoted by the same reference numerals and description thereof is omitted. The battery pack shown in the circuit diagrams of FIGS. 5 and 6 has a structure in which the input circuit 27 performs the temperature protection operation only when the charger 20 is connected. In order to realize this, the battery pack shown in the figure is provided with a detection terminal 12 for detecting the connection of the charger 20 in addition to the positive and negative output terminals 11. As the detection terminal 12, for example, a thermistor terminal or a model discrimination resistor terminal can be used. When the battery pack is connected to the charger 20, the input circuit 27 shown in the figure detects this by a signal from the detection terminal 12, and performs the temperature protection operation only in this state. In other words, the input circuit 27 turns off the protection FET 6 when the battery 1 is connected to the charger 20 and the temperature of the battery 1 exceeds a predetermined temperature and the voltage of the battery 1 exceeds the OFF voltage. Switch to cut off the battery pack charging current. The input circuit 27 controls the protection FET 6 to be in an on state when the battery pack is not connected to the charger 20. Since the battery pack having this structure is used after being removed from the charger 20 in the discharging state of the battery 1, the input circuit 27 controls the protection FET 6 to be in an ON state. Therefore, since the discharge current flows through the protection FET 6 in the ON state without flowing through the parasitic diode 6a of the protection FET 6, the heat generation of the protection FET 6 due to the discharge current can be greatly reduced.

  Furthermore, the battery pack shown in FIG. 6 has a structure capable of detecting that the protection FET 6 is controlled to be in an off state on the electronic device side to which the battery pack is connected. In the battery pack shown in this figure, a temperature sensor 5 and a detection resistor 13 are connected in series to a detection terminal 12 which is a thermistor terminal, one end of this series circuit is connected to an input circuit 27 and the other end is negative of the battery pack. Connected to the output side. Further, the drain and source of the detection FET 14 are connected to both ends of the detection resistor 13, and the gate of the detection FET 14 is connected to the gate of the protection FET 6. According to this circuit configuration, when the input circuit 27 controls the protection FET 6 to be turned on / off, the detection FET 14 is similarly controlled to be turned on / off. For this reason, when the protection FET 6 is controlled to be turned off, the detection FET 14 is also turned off, and the detection FET 14 does not bypass both ends of the detection resistor 13. As a result, the resistance value of the resistance component connected to the detection terminal 12 is increased by the detection resistance 13. Therefore, it can be recognized that the protection FET 6 is in the OFF state by detecting this resistance change on the electronic device side to which the battery pack is connected.

  The battery pack of the embodiment described above includes a control circuit 4 that detects battery voltage and controls the switching element 2 for charging and the switching element 3 for discharging to be turned on and off, and input circuits 7 and 27 that switch the protection FET 6 on and off. As a separate circuit. However, although not shown, the battery pack of the present invention can incorporate an input circuit for detecting the battery temperature and controlling the protection FET in the control circuit.

It is a circuit diagram of the conventional battery pack. 1 is a circuit diagram of a battery pack according to an embodiment of the present invention. It is a figure which shows the state in which a control circuit controls the switching element for charge and the switching element for discharge to on-off. It is a flowchart in which an input circuit switches a protection FET on and off. It is a circuit diagram of the battery pack according to another embodiment of the present invention. It is a circuit diagram of the battery pack according to another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Battery 2 ... Switching element for charge 2a ... Parasitic diode 3 ... Switching element for discharge 3a ... Parasitic diode 4 ... Control circuit 5 ... Temperature sensor 6 ... Protection FET 6a ... Parasitic diode 7 ... Input circuit 8 ... A / D Converter 9 ... Arithmetic circuit 10 ... Discharge current detection circuit 11 ... Output terminal 12 ... Detection terminal 13 ... Detection resistor 14 ... Detection switching element 20 ... Charger 27 ... Input circuit 91 ... Battery 95 ... Temperature sensor 96 ... Protection FET

Claims (7)

The charging switching element (2) connected in series with the rechargeable battery (1) to cut off the charging current of the battery (1), and the discharging current of the battery (1) connected in series with the battery (1) Discharging switching element (3) for cutting off, control circuit (4) for detecting battery voltage and controlling switching element for charging (2) and switching element for discharging (3) on and off, battery (1 ) And a protection FET (6) that is switched on and off at the battery temperature detected by the temperature sensor (5) and connected in series with the battery (1). A battery pack comprising:
When the protection FET (6) is an FET having a parasitic diode (6a) and is in an OFF state, the charging current is cut off, but the discharge current of the battery (1) is allowed to flow through the parasitic diode (6a). An input circuit (7) that is connected in series with the battery (1) and that switches the protection FET (6) on and off with the signal from the temperature sensor (5) and the battery voltage is connected to the input side of the protection FET (6). This input circuit (7) is in a state where the temperature of the battery (1) is higher than the charge stop temperature and the voltage of the battery (1) is higher than the off voltage that turns off the protection FET (6) A battery pack in which the protection FET (6) is switched off.   The control circuit (4) switches off the charging switching element (2) when the voltage of the battery (1) becomes higher than the overcharge voltage, and discharges when the voltage of the battery (1) becomes lower than the overdischarge voltage. The battery pack according to claim 1, wherein the switching element (3) is switched off and the off voltage at which the input circuit (7) switches off the protection FET (6) is higher than the overcharge voltage.   The rechargeable battery (1) is a lithium ion secondary battery, the overcharge voltage is 4.1 V to 4.3 V / cell, the overdischarge voltage is 2.6 V to 3.2 V / cell, and the off voltage is 4 The battery pack according to claim 2, which is 4 V / cell or more.   The battery pack according to claim 1, wherein a charge stop temperature at which the protection FET (6) is switched off is 50 ° C to 70 ° C.   The input circuit (7) comprises a discharge current detection circuit (10) for detecting the discharge current, and the discharge current detection circuit (10) detects the discharge current and switches on the off-state protection FET (6). 1. A battery pack described in 1.   The control circuit (4) switches off the charging switching element (2) when the voltage of the battery (1) becomes higher than the overcharge voltage, and discharges when the voltage of the battery (1) becomes lower than the overdischarge voltage. The switching element (3) is switched off and the off voltage at which the input circuit (7) switches off the protection FET (6) is lower than the overcharge voltage and higher than the overdischarge voltage. A battery pack described in 1.   The battery pack according to claim 6, wherein the charge stop temperature at which the input circuit (7) switches the protection FET (6) off is set to 40 ° C to 50 ° C.

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