JP2010259240A - Protection circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protection circuit for correctly detecting a temperature abnormality of a secondary battery and improving safety on use. <P>SOLUTION: A TH terminal for detecting a temperature of a secondary battery 110, an overcharging detection circuit and a voltage adjusting circuit are installed in double protection IC 300. When the temperature of the secondary battery 100 comes out of a prescribed range, the voltage adjusting circuit adjusts overcharging detection voltage in the overcharging detection circuit. Thus, the temperature of the secondary battery 110 is protected in double protection IC 300. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a protection circuit provided with a double protection circuit for double protection of a secondary battery.

  In recent years, portable devices such as digital cameras and mobile phones that are driven by a secondary battery such as a lithium ion battery have become widespread. A secondary battery such as a lithium ion battery is used in the form of a battery pack provided with a protection circuit in order to ensure safety in use.

  In the conventional battery pack, there is a battery pack provided with a double protection circuit for double protection of the secondary battery separately from the protection time for controlling the charge / discharge to protect the secondary battery from overcharge and overdischarge. is there. In the conventional battery pack, even if the protection circuit performs the secondary battery protection operation based on the battery temperature or the like of the secondary battery, the protection operation by the double protection circuit is performed when the secondary battery cannot be protected. For example, Patent Document 1 discloses a battery pack provided with a control IC that controls charging / discharging of a secondary battery and a double protection IC for double protection of the secondary battery.

  By the way, in recent years, portable devices are becoming more multifunctional, and the temperature of the device body tends to be higher. When the temperature of the device main body becomes high with the battery pack mounted on the portable device, the temperature of the battery pack also rises. At this time, the battery pack may determine that the temperature of the secondary battery has increased, and may activate the protection circuit.

  Therefore, the conventional portable device recognizes the battery temperature detected by the temperature detection element in the battery pack as a temperature lower than the actual temperature so that the protection circuit does not operate when the temperature of the battery pack rises due to the temperature rise of the device body. Ingenuity has been made such as making it happen.

JP 2007-141572 A

  In the above conventional technique, the temperature of the secondary battery detected by the temperature detection element can be recognized lower than the actual from the outside of the battery pack. There is a problem with safety.

  The present invention has been made to solve this problem in view of the above circumstances, and provides a protection circuit that can correctly detect a temperature abnormality of a secondary battery and can improve safety in use. It is intended to provide.

  The present invention employs the following configuration in order to achieve the above object.

The present invention is a protection circuit (110) that is connected between a secondary battery (110) and a load (120) and protects the secondary battery (110),
A temperature detection element (Rs) for detecting the temperature of the secondary battery (110);
Switch means (M10, M20) provided on the wiring connecting the negative electrode of the secondary battery (110) and the negative electrode of the load (120);
A switch for controlling on / off of the switch means (M10, M20) based on the temperature of the secondary battery (110) detected by the temperature detection element (Rs) and the battery voltage of the secondary battery (110). A protection circuit (200);
A fuse (400) provided in a wiring connecting the positive electrode of the secondary battery (110) and the positive electrode of the load (120);
Based on the temperature of the secondary battery (110) detected by the temperature detection element (Rs) and the battery voltage of the secondary battery (110), the overcharge of the secondary battery (110) is detected and the fuse ( 400) and a second protection circuit (300) for controlling fusing.

In the protection circuit of the present invention, the second protection circuit (300)
A voltage source (314) for generating an overcharge detection voltage that is a threshold voltage for detecting overcharge of the secondary battery (110);
An overcharge detection circuit (310) having a comparator (311) for comparing the battery voltage of the secondary battery (110) with the overcharge detection voltage;
And a voltage adjustment circuit (320) that outputs a control signal for causing the voltage source (314) to change the overcharge detection voltage based on the temperature detected by the temperature detection element (Rs).

In the protection circuit of the present invention, the voltage adjustment circuit (320) includes:
When it is detected that the temperature detected by the temperature detection element (Rs) is outside a predetermined range, a control signal for changing the overcharge detection voltage of the voltage source (314) is output.

In the protection circuit of the present invention, the overcharge detection circuit (310) includes:
When the control signal is output from the voltage adjustment circuit (320), the temperature detected by the temperature detection element (Rs) is the predetermined range within which the overcharge detection voltage generated by the voltage source (314) is detected. It was set as the structure made lower than the overcharge detection voltage when it is in.

In the protection circuit of the present invention, the voltage adjustment circuit (320) includes:
A first comparator in which the voltage of the temperature detection terminal (TH terminal) connected to the temperature detection element (Rs) is supplied to the non-inverting input terminal and the first predetermined voltage (Vz1) is supplied to the inverting input terminal. (321),
A second comparator in which the voltage of the temperature detection terminal (TH terminal) connected to the temperature detection element (Rs) is supplied to the inverting input terminal and the second predetermined voltage (Vz2) is supplied to the non-inverting input terminal. (322),
An OR circuit (325) to which an output signal of the first comparator (321) and an output signal of the second comparator (322) are input;
A delay circuit (326) for delaying the output signal of the OR circuit (325) for a predetermined time.

In the protection circuit of the present invention, the secondary battery (110) is configured by connecting a plurality of battery cells (111 to 114) in series,
The overcharge detection circuit (310A)
Having the same number of comparators (311A to 311D) as the plurality of battery cells (111 to 114),
The voltage at the connection point between the battery cells is supplied to the inverting input terminals of the plurality of comparators (311A to 311D), and the overcharge detection voltage is supplied to the non-inverting input terminals of the plurality of comparators (311A to 311D). ,
It is good also as a structure which detects the overcharge for every said battery cell (111-114).

The present invention is a protection circuit (300) connected between a secondary battery (110) and a load (120) for protecting the secondary battery (110),
A voltage source (314) for generating an overcharge detection voltage that is a threshold voltage for detecting overcharge of the secondary battery (110);
An overcharge detection circuit (310) having a comparator (311) for comparing the battery voltage of the secondary battery (110) with the overcharge detection voltage;
A voltage adjustment circuit that outputs a control signal for causing the voltage source (314) to change the overcharge detection voltage based on a temperature detected by a temperature detection element (Rs) that detects the temperature of the secondary battery (110). (320).

  Note that the reference numerals in the parentheses are given for ease of understanding, are merely examples, and are not limited to the illustrated modes.

  According to the present invention, the temperature abnormality of the secondary battery can be correctly detected, and the safety in use can be improved.

It is a figure for demonstrating the protection circuit of this embodiment. It is a figure explaining the double protection IC of 1st embodiment. It is a figure which shows an example of the relationship between the temperature of the secondary battery and overcharge detection voltage in the protection circuit of 1st embodiment. It is a figure explaining the double protection IC of 2nd embodiment.

  The present invention is provided with a temperature detection terminal for detecting the temperature of the secondary battery, an overcharge detection circuit, and a voltage adjustment circuit in the double protection IC, and the temperature of the secondary battery is out of the predetermined range. At this time, by adjusting the overcharge detection voltage in the overcharge detection circuit by the voltage adjustment circuit, the temperature of the secondary battery is also protected in the double protection IC.

(First embodiment)
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining the protection circuit of the present embodiment.

  The protection circuit 100 according to the present embodiment is connected between the secondary battery 110 and the load 120 to protect the secondary battery 110.

  The protection circuit 100 of this embodiment includes a protection IC 200, a double protection IC 300, and a fuse 400. The protection circuit 100 includes transistors M10, M20, and M30, and a thermistor Rs that is a temperature detection element.

  The protection circuit 100 of the present embodiment performs temperature protection of the secondary battery 110 using the thermistor Rs in the protection IC 200, and when the secondary battery 110 cannot be protected even by the protection IC 200, the double protection IC 300 and the fuse 400 are protected. Thus, the secondary battery 110 is protected. In the double protection IC 300 of this embodiment, a voltage at a TH terminal (described later) connected to the thermistor Rs is monitored, and protection is performed based on the temperature of the secondary battery 110.

  The protection IC 200 includes a VDD terminal, a VTH terminal, a VSSTH terminal, a VSS terminal, a DOUT terminal, a COUT terminal, and a V− terminal. The VDD terminal is connected to the positive electrode side of the secondary battery 110 via the resistor R10, and the VSS terminal is connected to the negative electrode side of the secondary battery 110. The VDD terminal is connected to the negative electrode side of the secondary battery 110 via the capacitor C10. The VTH terminal is connected to one end of the thermistor Rs and the TH terminal of the double protection IC 300. The VSSTH terminal is connected to one end of the thermistor Rs via the resistor R20. The other end of the thermistor Rs is connected to the positive electrode of the secondary battery 110.

  The DOUT terminal is connected to the gate of the transistor M10, and the COUT terminal is connected to the gate of the transistor M20. The V-terminal is connected to the negative electrode side of the load via a resistor R30.

  The double protection IC 300 has a VDD terminal, a VSS terminal, a V1 terminal, a V2 terminal, a V3 terminal, an OV terminal, and a TH terminal. The VDD terminal is connected to a connection point between the resistor R40 and the capacitor C20 connected in series between the positive electrode and the negative electrode of the secondary battery 110. The VSS terminal, V1 terminal, V2 terminal, and V3 terminal are grounded to the negative electrode side of the secondary battery 110. The OV terminal is connected to the gate of the transistor M30, and the TH terminal is connected to one end of the thermistor Rs and the VTH terminal.

  The fuse 400 includes fuses 410 and 420 and resistors R50 and R60 connected in series. The fuses 410 and 420 are connected in series between the positive electrode of the secondary battery 110 and the negative electrode of the load 120. A resistor R50 and a resistor R60 are connected in parallel between a connection point between the fuse 410 and the fuse 420 and the drain of the transistor M30. The source of the transistor M30 is connected to the negative electrode of the secondary battery 110.

  The transistor M10 and the transistor M20 are connected between the negative electrode side of the load 120 and the negative electrode side of the secondary battery 110, and ON / OFF is controlled by signals output from the COUT terminal and the DOUT terminal of the protection IC 200. Is done. In the protection circuit 100, discharging the secondary battery 110 is prohibited when the transistor M10 is turned off, and charging from the secondary battery 110 is stopped when the transistor M20 is turned off.

  The protection IC 200 of this embodiment includes a temperature abnormality detection circuit 210, an overcharge detection circuit 220, an overdischarge detection circuit 230, a charge overcurrent detection circuit 240, a discharge overcurrent detection circuit 250, an oscillator 260, a counter 270, a logic circuit 280, A logic circuit 290, a level shift 291, a delay circuit 292, and a short circuit detection circuit 293 are included.

  The temperature abnormality detection circuit 210 detects a temperature abnormality by monitoring the voltage of the VTH terminal connected to the thermistor Rs. When the temperature detection circuit 210 detects a temperature abnormality, it outputs a temperature abnormality detection signal to the oscillator 260 and the logic circuit 280. When a predetermined delay time is counted by the counter 270 after the temperature abnormality detection signal is output to the logic circuit 280, the logic circuit 280 outputs a control signal from the COUT terminal via the level shift 291 to turn off the transistor M20. Prohibit charging.

  The overcharge detection circuit 220 monitors the voltage at the VDD terminal and detects overcharge. When the overcharge detection circuit 220 detects overcharge, it outputs an overcharge detection signal to the oscillator 260 and the logic circuit 280. When a predetermined delay time is counted by the counter 270 after the overcharge detection signal is output to the logic circuit 280, the logic circuit 280 outputs a control signal from the COUT terminal via the level shift 291 to turn off the transistor M20. Prohibit charging.

  The overdischarge detection circuit 230 monitors the VDD terminal and detects overdischarge. When overdischarge is detected, overdischarge detection circuit 230 outputs an overdischarge detection signal to oscillator 260 and logic circuit 290. When a predetermined delay time is counted by the counter 270 after the overdischarge detection signal is output to the logic circuit 290, the logic circuit 290 outputs a control signal from the DOUT terminal and turns off the transistor M10 to inhibit discharge.

  The short circuit detection circuit 293 monitors the voltage at the V− terminal, detects a short circuit between the secondary battery 110 and the load 120, and outputs a short circuit detection signal to the delay circuit 292. When a predetermined delay time elapses in the delay circuit 292, the short circuit detection signal is supplied to the logic circuit 290. The logic circuit 290 receives the short circuit detection signal, outputs a control signal from the DOUT terminal, turns off the transistor M10, and inhibits discharge.

  The double protection IC 300 of this embodiment has a TH terminal connected to the thermistor Rs, and protects the temperature of the secondary battery 110 by monitoring the voltage Vth of the TH terminal. In the double protection IC 300 of the present embodiment, the overcharge detection voltage serving as a threshold for detecting overcharge is changed in accordance with the temperature detected by the thermistor Rs.

  FIG. 2 is a diagram for explaining the double protection IC of the first embodiment. The double protection IC 300 of this embodiment includes an overcharge detection circuit 310 and a voltage adjustment circuit 320. In the double protection IC 300, the voltage adjustment circuit 320 adjusts the overcharge detection voltage when the overcharge detection circuit 310 detects overcharge according to the temperature of the secondary battery 110 detected by the thermistor Rs.

  The overcharge detection circuit 310 includes a comparator 311, a delay circuit 312, an inverter 313, a reference voltage source 314, and resistors R31 and R32.

  The resistors R31 and R32 are connected in series between the VDD terminal and the ground. The voltage Va at the connection point A between the resistors R31 and R32 is supplied to the inverting input terminal of the comparator 311. The reference voltage Vref generated by the reference voltage source 314 is supplied to the non-inverting input terminal of the comparator 311. In the present embodiment, the reference voltage Vref generated by the reference voltage source 314 is a threshold voltage for detecting overcharge. Note that the reference voltage source 314 of the present embodiment is configured to be able to change the value of the reference voltage Vref to be generated based on the output signal of the voltage adjustment circuit 320.

  The output of the comparator 311 is supplied to the delay circuit 312. The output of the delay circuit 312 is output from the OV terminal via the inverter 313. The OV terminal is connected to the gate of the transistor M30, and a signal output from the OV terminal controls on / off of the transistor M30.

  In the overcharge detection circuit 310 of this embodiment, when the voltage Va at the connection point A becomes higher than the reference voltage Vref, the comparator 311 outputs an output from a high level (hereinafter referred to as H level) on the assumption that overcharge is detected. Invert to low level (hereinafter L level). The L level signal is delayed for a predetermined time by the delay circuit 312, then inverted to an H level signal by the inverter 313, and output from the OV terminal.

  The H level signal output from the OV terminal turns on the transistor M30. When the transistor M30 is turned on, the fuse 410 and the fuse 420 of the fuse 400 are blown, and charging of the secondary battery 110 is prohibited.

  The voltage adjustment circuit 320 includes comparators 321 and 322, constant voltage sources 323 and 324, an OR circuit 325, and a delay circuit 326.

  The non-inverting input terminal of the comparator 321 and the inverting input terminal of the comparator 322 are connected, and are connected to the TH terminal. The TH terminal is connected to one end of the thermistor Rs. A voltage Vz <b> 1 generated by the constant voltage source 323 is supplied to the inverting input terminal of the comparator 321. A voltage Vz <b> 2 generated by the constant voltage source 324 is supplied to the non-inverting input terminal of the comparator 322.

  The output of the comparator 321 is supplied to one input of the OR circuit 325, and the output of the comparator 322 is supplied to the other input of the OR circuit 325. The signal output from the OR circuit 325 is delayed by a predetermined time by the delay circuit 326 and then supplied to the reference voltage source 314 of the overcharge detection circuit 310 as an output signal of the voltage adjustment circuit 320. The reference voltage source 314 adjusts the value of the voltage generated by the reference voltage source 314 based on the output signal of the voltage adjustment circuit 320. For example, when the reference voltage generated when the output signal of the voltage adjustment circuit 320 is at the L level is Vref1 and the output signal of the voltage adjustment circuit 320 is at the H level, The configuration may be such that Vref2, which is a voltage lower than the reference voltage Vref1, is generated.

  For example, in the voltage adjustment circuit 320 of the present embodiment, when the voltage Vth at the TH terminal is between the voltage Vz1 of the constant voltage source 323 and the voltage Vz2 of the constant voltage source 324 (Vz1 <Vth <Vz2), the comparator 321 and the comparator Since the output of 322 is at L level, the output of the OR circuit 325 is at L level. Therefore, the output signal of the voltage adjustment circuit 320 becomes L level, and the reference voltage source 314 generates the reference voltage Vref1.

  When the voltage Vth becomes lower than the voltage Vz1 (Vth <Vz1 <Vz2) or when the voltage Vth becomes higher than the voltage Vz2 (Vz1 <Vz2 <Vth), the output of the OR circuit 325 becomes the H level. Therefore, the output signal of the voltage adjustment circuit 320 becomes H level. When the reference voltage source 314 receives an H level signal from the voltage adjustment circuit 320, the reference voltage source 314 generates a reference voltage Vref2 that is lower than the reference voltage Vref1.

  The change in the voltage Vth at the TH terminal of the double protection IC 300 is due to the change in the resistance value of the thermistor Rs. Therefore, in the double protection IC 300 of this embodiment, the overcharge detection voltage can be changed according to the temperature change of the secondary battery 110.

  FIG. 3 is a diagram illustrating an example of the relationship between the temperature of the secondary battery and the overcharge detection voltage in the protection circuit of the first embodiment.

  FIG. 3 shows the relationship between the temperature of the secondary battery 110 and the overcharge detection voltage V200 in the protection IC 200 and the relationship between the temperature of the secondary battery 110 and the overcharge detection voltage V300 in the double protection IC300. Yes.

  In the example of FIG. 3, when the temperature of the secondary battery 110 is higher than 10 ° C. and lower than 45 ° C., the protection IC 200 sets the overcharge detection voltage V200 = 4.3V, and the temperature of the secondary battery 110 is 10 ° C. or lower and 45 ° C. In the above case, the overcharge detection voltage V200 = 4.0V. Thus, in the protection IC 200, when the temperature of the secondary battery 110 is 10 ° C. or lower and 45 ° C. or higher, the overcharge is detected at an early stage, thereby ensuring the safety in use of the secondary battery 110. .

  In the example of FIG. 3, the double protection IC 300 sets the overcharge detection voltage V300 = Vref1 when the temperature of the secondary battery 110 is greater than 0 ° C. and less than 60 ° C., and the temperature of the secondary battery 110 is 0 ° C. or less 60 When it is higher than or equal to ° C., the overcharge detection voltage V300 = Vref2. Vref1 was set to a voltage higher than 4.3V, and Vref2 was set to a voltage higher than 4.0V.

  In the double protection IC 300 of the present embodiment, for example, the voltage Vz1 of the constant voltage source 323 and the voltage Vz2 of the constant voltage source 324 are set to values corresponding to the temperature at which the overcharge detection voltage is switched. For example, the voltage Vz1 is the TH terminal voltage Vth when the temperature of the secondary battery 110 is 0 ° C., and the voltage Vz2 is the TH terminal voltage Vth when the temperature of the secondary battery 110 is 60 ° C. . If the voltage Vz1 and the voltage Vz2 are set in this way, the voltage adjustment circuit 320 sets the overcharge detection voltage V300 of the overcharge detection circuit 310 when the temperature of the secondary battery 110 becomes 0 ° C. or lower and 60 ° C. or higher. Can be changed.

  As described above, in the protection circuit 100 of the present embodiment, when the secondary battery 110 is not recovered even after the temperature protection of the secondary battery 110 is performed by the protection IC 200, the secondary battery 110 is again used by the double protection IC 300. Temperature protection can be performed. Therefore, according to the protection circuit 100 of this embodiment, the temperature abnormality of the secondary battery 110 can be detected correctly, and the safety in use can be improved.

  Furthermore, in the protection circuit 100 of this embodiment, the thermistor Rs is disposed between the protection IC 200 and the double protection IC 300.

  In conventional protection circuits, the thermistor is often placed between the protection IC and the load. For this reason, in the conventional protection circuit, the temperature of the secondary battery detected by the thermistor is operated on the load side, and the temperature of the secondary battery can be recognized as a temperature lower than the actual temperature.

  In the protection circuit 100 of the present embodiment, the thermistor Rs is disposed between the protection IC 200 and the double protection IC 300, that is, in the vicinity of the secondary battery 110, so that it is detected on the load 120 side as in the conventional protection circuit. The temperature of the rechargeable secondary battery 110 cannot be manipulated.

  Therefore, in the present embodiment, the temperature of the secondary battery 110 can be accurately detected, and safety in use can be improved.

(Second embodiment)
A second embodiment of the present invention will be described below with reference to the drawings. The second embodiment of the present invention is different from the first embodiment only in that the double protection IC corresponds to multi-series connection of secondary batteries. Therefore, in the following description of the second embodiment, only differences from the first embodiment will be described, and those having the same functional configuration as the first embodiment will be used in the description of the first embodiment. The same reference numerals as those used are assigned, and the description thereof is omitted.

  FIG. 4 is a diagram for explaining the double protection IC of the second embodiment.

  In the present embodiment, the secondary battery 110A is configured by connecting four battery cells 111 to 114 in series.

  The double protection IC 300A of this embodiment includes an overcharge detection circuit 310A, a voltage adjustment circuit 320, a VDD terminal, a VSS terminal, an OV terminal, a TH terminal, a V1 terminal, a V2 terminal, and a V3 terminal.

  The VDD terminal of the double protection IC 300 is connected to a connection point between the resistor R40 and the capacitor C20 connected in series between the positive electrode and the negative electrode of the secondary battery 110A. The VSS terminal is connected to the negative electrode of the secondary battery 110A. The V1 terminal is connected to a connection point N between the battery cell 111 and the battery cell 112. The V2 terminal is connected to a connection point M between the battery cell 112 and the battery cell 113. The V3 terminal is connected to a connection point L between the battery cell 113 and the battery cell 114.

  The overcharge detection circuit 310A of this embodiment includes comparators 311A, 311B, 311C, 311D, resistors R31 to R38, a delay circuit 312, an inverter 313, a reference voltage source 314, and an OR circuit 315.

  The resistors R31 to R37 are connected in series between the VDD terminal and the VSS terminal.

  The overcharge detection circuit 310A of this embodiment includes comparators 311A, 311B, 311C, 311D, resistors R31 to R38, a delay circuit 312, an inverter 313, a reference voltage source 314, and an OR circuit 315.

  The inverting input terminal of the comparator 311A is connected to the connection point O between the resistors R31 and R32, and the non-inverting input terminal of the comparator 311A is connected to the reference voltage source 314. The inverting input terminal of the comparator 311B is connected to the connection points P and V3 of the resistors R32 and R33, and the non-inverting input terminal of the comparator 311B is connected to the reference voltage source 314.

  The inverting input terminal of the comparator 311C is connected to the connection points Q and V2 between the resistors R34 and R35, and the non-inverting input terminal of the comparator 311C is connected to the reference voltage source 314. The inverting input terminal of the comparator 311D is connected to the connection point R and V1 terminal of the resistor R36 and the resistor R37, and the non-inverting input terminal of the comparator 311D is connected to the reference voltage 314.

  The outputs of the comparators 311A to 311D are input to the OR circuit 315. The output of the OR circuit 314 is supplied to the delay circuit 312. The output of the delay circuit 312 is inverted by the inverter 313 and output from the OV terminal as an output signal of the overcharge detection circuit 310A.

  In the present embodiment, overcharge can be detected for each battery cell by connecting the connection point between the battery cells to the inverting input terminal of the comparator. Specifically, in this embodiment, the comparator 311A detects overcharge of the battery cell 114, the comparator 311B detects overcharge of the battery cell 113, the comparator C detects overcharge of the battery cell 112, and the comparator D detects overcharge of the battery cell 111.

  In this embodiment, when overcharge is detected in any one of the battery cells 111 to 114 constituting the secondary battery 110A, an overcharge detection signal is output from the OV terminal and the fuses 410 and 420 are blown. To do.

  Therefore, in this embodiment, the safety in use can be improved also in the secondary battery 110A in which the battery cells are connected in multiple series.

  As mentioned above, although this invention has been demonstrated based on each embodiment, this invention is not limited to the requirements shown in the said embodiment. With respect to these points, the gist of the present invention can be changed without departing from the scope of the present invention, and can be appropriately determined according to the application form.

100 protection circuit 200 protection IC
210 Temperature Abnormality Detection Circuit 220, 310, 310A Charge Detection Circuit 230 Overdischarge Detection Circuit 240 Charge Overcurrent Detection Circuit 250 Discharge Overcurrent Detection Circuit 260 Oscillator 270 Counter 280, 290 Logic Circuit 300, 300A Double Protection IC
320 Voltage adjustment circuit

Claims (7)

A protection circuit connected between a secondary battery and a load for protecting the secondary battery,
A temperature detecting element for detecting the temperature of the secondary battery;
Switch means provided in wiring connecting the negative electrode of the secondary battery and the negative electrode of the load;
A first protection circuit for controlling on / off of the switch means based on the temperature of the secondary battery detected by the temperature detection element and the battery voltage of the secondary battery;
A fuse provided in a wiring connecting the positive electrode of the secondary battery and the positive electrode of the load;
A second protection circuit for detecting overcharge of the secondary battery based on the temperature of the secondary battery detected by the temperature detection element and the battery voltage of the secondary battery and controlling the blow of the fuse; Having protection circuit. The second protection circuit is:
A voltage source that generates an overcharge detection voltage that is a threshold voltage for detecting overcharge of the secondary battery;
A comparator for comparing a battery voltage of the secondary battery and the overcharge detection voltage;
The protection circuit according to claim 1, further comprising: a voltage adjustment circuit that outputs a control signal for causing the voltage source to change the overcharge detection voltage based on the temperature detected by the temperature detection element. The voltage adjustment circuit includes:
The protection circuit according to claim 2, wherein a control signal for changing the overcharge detection voltage of the voltage source is output when it is detected that the temperature detected by the temperature detection element is outside a predetermined range. The overcharge detection circuit is
When the control signal is output from the voltage adjustment circuit, the overcharge detection voltage generated by the voltage source is the overcharge detection voltage when the temperature detected by the temperature detection element is within the predetermined range. 4. The protection circuit according to claim 3, wherein the protection circuit is lower. The voltage adjustment circuit includes:
A voltage of a temperature detection terminal connected to the temperature detection element is supplied to a non-inverting input terminal, and a first comparator is supplied with a first predetermined voltage to the inverting input terminal;
A voltage at a temperature detection terminal connected to the temperature detection element is supplied to an inverting input terminal, and a second comparator is supplied with a second predetermined voltage to a non-inverting input terminal;
An OR circuit to which the output signal of the first comparator and the output signal of the second comparator are input;
The protection circuit according to claim 2, further comprising a delay circuit that delays an output signal of the OR circuit for a predetermined time. The secondary battery is composed of a plurality of battery cells connected in series,
The overcharge detection circuit is
Having the same number of comparators as the plurality of battery cells;
The voltage at the connection point between the battery cells is supplied to the inverting input terminals of the plurality of comparators, the overcharge detection voltage is supplied to the non-inverting input terminals of the plurality of comparators,
The protection circuit according to claim 2, wherein overcharge for each battery cell is detected. A protection circuit connected between a secondary battery and a load for protecting the secondary battery,
A voltage source that generates an overcharge detection voltage that is a threshold voltage for detecting overcharge of the secondary battery;
A comparator for comparing a battery voltage of the secondary battery and the overcharge detection voltage;
And a voltage adjustment circuit that outputs a control signal for causing the voltage source to change the overcharge detection voltage based on a temperature detected by a temperature detection element that detects a temperature of the secondary battery.

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