JP2007006559A - Protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection circuit capable of protecting a secondary battery from overcharge and overcurrent with a simple circuit.
A comparator A1 outputs a high level signal when the voltage of a secondary battery 6 exceeds a predetermined reference voltage (overcharge protection voltage) Ref1, turns on a transistor Q1, energizes a heater R1, The bimetal switch SW1 is turned off to protect the secondary battery 6 from overcharging. The counter C1 counts up every time the comparator A1 outputs a high level signal. When the count value exceeds a predetermined value, the counter C1 outputs a high level signal, turns on the transistor Q2, and energizes the heater R2. The thermal fuse F1 is turned off.
[Selection] Figure 2

Description

  The present invention relates to a protection circuit that protects a secondary battery from excessive charging and overcurrent.

  FIG. 3 is a circuit diagram showing a configuration of a battery pack according to the background art. A battery pack 101 shown in FIG. 3 includes a protection circuit 102 and a secondary battery 103. The secondary battery 103 is a rechargeable secondary battery such as a lithium ion secondary battery, a lithium polymer secondary battery, a nickel hydride secondary battery, or a nickel cadmium secondary battery. If such a secondary battery is excessively charged or the discharge current becomes excessive, characteristics such as cycle life may be deteriorated, or the battery may be expanded or deformed. Therefore, the battery pack 101 includes a protection circuit 102 that protects the secondary battery 103 from excessive charging (overcharge) and excessive discharge current (overcurrent) (see, for example, Patent Document 1).

  The protection circuit 102 includes external connection terminals 104 and 105, FETs (Field Effect Transistors) 106 and 107, reference voltage sources 108 and 109, comparators 110 and 111, a resistor 112, and a logic circuit 113. .

  The external connection terminals 104 and 105 are connected to a charging device for charging the secondary battery 103, mobile devices such as mobile phones and digital cameras driven by the discharge current from the secondary battery 103, electric tools, robots This is a connection terminal for connecting a driving power source such as an electric bicycle. The external connection terminal 104, the secondary battery 103, the FET 106, the FET 107, and the external connection terminal 105 are connected in series.

  The FET 106 has a direction in which the anode of the parasitic diode is on the secondary battery 103 side, and the FET 107 has a direction in which the anode of the parasitic diode is on the external connection terminal 105 side. The FET 106 is used as a switch for overcurrent protection that cuts off the discharge current when an overcurrent flows through the secondary battery 103, and the FET 107 is used to charge the current when the secondary battery 103 is overcharged. Used as an overcharge protection switch to shut off.

  The positive terminal of the secondary battery 103 is applied to the + terminal of the comparator 110, the reference voltage VRef 1 output from the reference voltage source 108 is applied to the − terminal of the comparator 110, and the output terminal of the comparator 110 is connected to the logic circuit 113. It is connected. As the reference voltage VRef1, a voltage for detecting overcharge of the secondary battery 103 is set. The comparator 110 detects overcharge when the secondary battery 103 is charged by a charging device (not shown) connected to the external connection terminals 104 and 105 and the terminal voltage of the secondary battery 103 exceeds the reference voltage VRef1. The signal is output to the logic circuit 113.

  The connection point between the FET 106 and the FET 107 is connected to the negative terminal of the comparator 111 via the resistor 112, and the reference voltage VRef 2 output from the reference voltage source 109 is applied to the positive terminal of the comparator 111. As a result, the discharge current from the secondary battery 103 flows through the FET 106, and a voltage drop caused by the on-resistance of the FET 106 is applied to the negative terminal of the comparator 111 via the resistor 112. For example, the reference voltage VRef2 is set to a voltage corresponding to a voltage drop caused by the on-resistance of the FET 106 when the maximum discharge current in the range that does not cause deterioration of the characteristics of the secondary battery 103 flows through the FET 106.

  The comparator 111 is short-circuited, for example, when the external connection terminals 104 and 105 come into contact with a metal piece, or when a load device connected to the external connection terminals 104 and 105 breaks down. When an overcurrent flows, an increase in voltage drop in the FET 106 is detected, and a detection signal indicating the overcurrent is output to the logic circuit 113.

  When the detection signal indicating the overcharge is output from the comparator 110, the logic circuit 113 turns off the FET 107 to stop the charging of the secondary battery 103, and when the detection signal indicating the overcurrent is output from the comparator 111, The FET 106 is turned off to stop the discharge of the secondary battery 103. Thereby, the protection circuit 102 protects the secondary battery 103 from overcharge and overcurrent.

  Further, as a protection circuit for protecting the secondary battery from overcharging and overcurrent in this way, a secondary battery 122 and a bimetal switch 123 are connected in series as in the battery pack 121 shown in FIG. When the charging device connected to the external connection terminals 124 and 125 fails, the bimetal switch 123 is heated by overcharging and the secondary battery 122 generates heat or the bimetal switch 123 self-heats. In this case, a battery in which the bimetal switch 123 is turned off to interrupt the charging current and protect the secondary battery 122 is known.

Further, as in the battery pack 131 shown in FIG. 5, a secondary battery 133 and a PTC element 132 are used by using a PTC element 132 that is a PTC (Positive Temperature Coefficient) element that is a thermistor that is turned off when a predetermined temperature is exceeded. Are connected in series, for example, when the charging device 136 connected to the external connection terminals 134 and 135 breaks down, the secondary battery 133 generates heat or the PTC element 132 self-heats due to excessive charging. Thus, it is known that when the PTC element 132 is heated, the PTC element 132 is turned off to interrupt the charging current and protect the secondary battery 133.
JP-A-11-262270

  However, since the FET has a parasitic diode, the protection circuit 102 shown in FIG. 3 cannot cut off the discharge current and the charge current in different directions of current flow with one FET, and cut off the discharge current. It is necessary to provide the FET 106 and the FET 107 that cuts off the charging current. Further, a reference voltage source 108 and a comparator 110 are required to detect overcharge, a reference voltage source 109 and a comparator 111, and a resistor 112 as necessary are required to detect overcurrent. Since the logic circuit 113 for turning on and off the two FETs 106 and 107 based on the output signal 111 is required, there is a disadvantage that the circuit scale of the protection circuit 102 increases.

  Furthermore, as shown in FIG. 4 and FIG. 5, in the configuration in which the secondary battery is protected from overcharging by connecting the temperature switch that operates according to the temperature of the bimetal switch or the PTC element in series with the secondary battery, Because the detection accuracy is low, the secondary battery can be charged with a charging current that does not cause the temperature to rise suddenly, such as when the battery pack is charged by a poor charging device with low charging voltage control accuracy. If the operation is continued, the secondary battery is overcharged without operating the temperature switch, and there is a problem that the characteristics of the secondary battery may be deteriorated or the battery may be expanded or deformed. Furthermore, since the bimetal switch is a mechanical contact, its operating life is about 100 times, and if it is used beyond its operating life, the contact and the bimetal are welded to prevent overcharging and overcurrent. In addition to being unable to protect the secondary battery, there is a problem that safety for the user cannot be ensured.

  The present invention has been made in view of such a problem, and protects a secondary battery from overcharging and overcurrent with a simple circuit, prevents welding of a bimetal switch, and ensures safety for a user. It is an object of the present invention to provide a protection circuit that can be used.

  The protection circuit according to the present invention includes a charging device for charging a secondary battery and / or first and second connection terminals for connecting a load device driven by a discharge current from the secondary battery, and a secondary battery. Third and fourth connection terminals connected to the two electrodes, a bimetal switch connected to the first connection terminal, a first heater for heating the bimetal switch, and the third and fourth connections When the voltage between the terminals exceeds a predetermined overcharge protection voltage, the overcharge protection means for energizing the first heater and turning off the bimetal switch, and the number of times the overcharge protection means turns off the bimetal switch are set. Counting means, and when the count value exceeds a predetermined value determined based on the guaranteed number of operations of the bimetal switch, a cutoff means for cutting off the electrical connection with the secondary battery is provided. And features.

  In the above configuration, the shut-off means includes a temperature fuse connected between the bimetal switch and the third connection terminal, a second heater that heats the temperature fuse, and the count value is the predetermined value. It is preferable to include a thermal fuse control means for energizing the second heater and blowing the thermal fuse when the value exceeds.

  Further, in the above configuration, the overcharge protection unit includes a comparator and a first transistor, the thermal fuse control unit includes a counter and a second transistor, and the comparator includes the third and fourth transistors. When the voltage between the connection terminals exceeds the overcharge protection voltage, the first transistor is turned on to energize the first heater, and the counter is counted up. When a predetermined value is exceeded, it is preferable that the second transistor is turned on to energize the second heater.

  In the above configuration, the first heater is composed of the first transistor, the second heater is composed of the second transistor, and the bimetal switch is turned on when the first transistor is turned on. Preferably, the thermal fuse is heated by the generated heat, and the thermal fuse is heated by the heat generated when the second transistor is turned on.

  According to the first aspect of the present invention, the overcharge protection means is configured such that when the voltage between the third and fourth connection terminals (the voltage of the secondary battery) exceeds a preset overcharge protection voltage, Since the heater is energized, the bimetal switch is turned off, and the energization of the charging current is interrupted, the secondary battery can be protected from overcharging.

  Further, when the discharge current from the secondary battery exceeds a predetermined current value, the bimetal switch is turned off by self-heating to cut off the discharge current, so that the secondary battery can be protected from overcurrent. Therefore, the overcurrent prevention FET 106, the reference voltage source 109, and the comparator 111 for detecting overcurrent as shown in FIG. 3 are not necessary, and the circuit can be simplified.

  Furthermore, the number of times the bimetal switch is turned off is counted, and if the count value exceeds a predetermined value determined based on the guaranteed number of operations of the bimetal switch, the electrical connection with the secondary battery is interrupted. As a result, the charging / discharging of the secondary battery can be stopped before the number of operations of the bimetal switch exceeds the number of times of operation compensation. As a result, welding of the bimetal switch can be prevented, and the secondary battery can be overcharged or overcharged. In addition to being able to protect from current, safety for the user can be ensured.

  According to the second aspect of the present invention, when the count value exceeds a predetermined value, the second heater is energized and the temperature fuse is blown, so that the electrical connection with the secondary battery is reliably cut off. Therefore, the safety of the user can be ensured more reliably.

  According to the invention described in claim 3, since the overcharge protection means is constituted by the comparator and the first transistor, and the thermal fuse control means is constituted by the counter and the second transistor, the voltage of the secondary battery is overcharged. When the protection voltage is exceeded, the bimetal switch can be turned off more reliably and the counter can be counted up more reliably.

  According to the fourth aspect of the present invention, the first heater and the second heater can be omitted, and the circuit can be simplified and the cost can be reduced.

  Embodiments of the present invention will be described below. FIG. 1 is an exploded perspective view showing an example of a battery pack according to Embodiment 1 of the present invention. A battery pack 1 shown in FIG. 1 includes a bottomed cylindrical container 2, an external terminal connection unit 3, and a plate-like spacer 4 inserted between the container 2 and the external terminal connection unit 3. . The container 2 accommodates a secondary battery 6 and is sealed by caulking, and a positive electrode terminal 6 a provided in a convex shape on the secondary battery 6 projects from the opening end of the container 2. The container 2 is made of a steel plate with nickel plating on the surface, and the negative electrode of the secondary battery 6 is connected to the container 2 inside the container 2.

  The external terminal connection unit 3 includes, for example, a resin-molded case 31, and connection terminals T <b> 1 and T <b> 2 for connecting a charging device and a load device are exposed on the surface of the case 31. Further, a connection terminal T4 made of, for example, a plate-like metal connected to the connection terminal T2 is provided so as to protrude in the direction in which the container 2 is connected.

  FIG. 2 shows a circuit diagram of the battery pack 1 shown in FIG. The battery pack 1 includes a protection circuit 5 and a secondary battery 6. The secondary battery 6 is a rechargeable secondary battery such as a lithium ion secondary battery, a lithium lithium polymer secondary battery, a nickel hydride secondary battery, or a nickel cadmium secondary battery. The protection circuit 5 is a circuit that protects the secondary battery 6 from overcharging and overcurrent.

  The protection circuit 5 includes connection terminals T1 to T4 (first to fourth connection terminals), a bimetal switch SW1, a thermal fuse F1, heaters R1 and R2, an overcharge protection unit 51, and a thermal fuse control unit 52. The overcharge protection unit 51 includes a comparator A1, a reference voltage source E1, and a transistor Q1. The thermal fuse control unit 52 includes a counter C1 and a transistor Q2.

  The connection terminal T <b> 1 and the connection terminal T <b> 2 are connection terminals for connecting a charging device (not shown) that charges the secondary battery 6 and / or a load device that is driven by a discharge current from the secondary battery 6. The load device is various electric devices driven by a battery such as a mobile phone, a digital camera, a video camera, a portable personal computer, and an electric tool. The connection terminal T3 is connected to the positive electrode of the secondary battery 6, and the connection terminal T4 is connected to the negative electrode of the secondary battery 6.

  The bimetal switch SW1 is a thermal switch that is turned off when a predetermined operating temperature Tsw1 that is set in advance is exceeded. The operating temperature Tsw1 is set to a maximum temperature in a temperature range that does not deteriorate the characteristics of the secondary battery 6, for example. Yes.

  The bimetal switch SW1 is a return-type thermal switch that turns on again when the temperature drops after the temperature rises and turns off. In addition, as a thermal switch, instead of a bimetal switch, a switch using a shape memory alloy (for example, one described in Japanese Utility Model Publication Nos. 7-4770 and 11-224579), or a switch using a shape memory resin, It can be used similarly.

  The shape memory alloy may be a shape memory alloy having a restoring force based on thermoelastic martensitic transformation and reverse transformation such as nickel-titanium alloy, copper-zinc-aluminum alloy, and these alloys are deformed. The shape change temperature range in which the shape is restored to the restored shape can be changed by appropriately selecting the shape memory alloy composition or changing the heat treatment process.

  As the shape memory resin, resins such as polyester, polyurethane, styrene / butadiene, and transpolyisoprene in which a cross-linked or partially crystallized stationary phase and a reversible phase are mixed can be used.

The thermal fuse F1 is heated by the heater R2, melted by the heat, and disposed close to the secondary battery 6 or in close contact with an insulator so that the secondary battery 6 is overcharged or oversized. It is a fuse that is blown by the heat when heat is generated by a simple discharge. The operating temperature Tfuse1 at which the thermal fuse F1 blows is set to a temperature higher than the operating temperature Tsw1 of the bimetal switch SW1. Further, the fusing characteristics are set so that the operating speed of the thermal fuse F1 is slower than that of the bimetal switch SW1. The thermal fuse F1 is a non-returnable thermal switch that does not return to a conductive state once it is blown. In this case, the operating temperature Tsw1 of the bimetal switch SW1, the final reached temperature Th1 of the heater R1, the operating temperature Tfuse1 of the thermal fuse F1, and the final reached temperature Th2 of the heater R2 have a relationship represented by the following formula (1).
Tsw1 <Th1 <Tfuse1 <Th2 (1)

  In addition, the setting of the operating temperature and operating speed of the bimetal switch SW1 and the thermal fuse F1 sets the characteristics of the components of the bimetal switch SW1 and the thermal fuse F1 itself, and operates the bimetal switch SW1 before the thermal fuse F1. Therefore, for example, the bimetal switch SW1 and the secondary battery 6 are placed close to each other so that the thermal resistance between the bimetal switch SW1 and the secondary battery 6 is smaller than the thermal resistance between the thermal fuse F1 and the secondary battery 6. For example, the contact resistance of the bimetal switch SW1 or the resistance at the movable piece is increased to increase the amount of self-heating, or the thermal resistance to the surroundings when the bimetal switch SW1 dissipates heat is increased. Reduce the heat capacity by reducing the size of the bimetal switch SW1. The bimetal switch SW1 may be a temperature rise easily formed by self-heating by benefit.

  Further, in order to delay the operation of the thermal fuse F1 from the bimetal switch SW1, for example, the thermal resistance to the surroundings when the thermal fuse F1 radiates heat is reduced, or the thermal fuse F1 is brought into contact with a material having good thermal conductivity, for example. The temperature fuse F1 may be configured not to easily rise in temperature by increasing the apparent heat capacity of the temperature fuse F1 without increasing the size of the temperature fuse F1 by a method.

  For the heaters R1 and R2, for example, a positive temperature characteristic, that is, a PTC (Positive Temperature Coefficient) thermistor whose resistance value increases or decreases in accordance with an increase or decrease in temperature is used. As a result, when a voltage is applied to the heater R1, the resistance value of the heater R1 increases due to the self-heating of the heater R1, and the current flowing through the heaters R1, R2 decreases. It becomes constant at the reached temperatures Th1 and Th2. The final temperature Th1 is a temperature that exceeds the operating temperature Tsw1 of the bimetal switch SW1, and is set to a temperature that does not damage the secondary battery 6 and the protection circuit 5. Thereby, it can suppress that the secondary battery 6 and the protection circuit 5 are damaged by the heat_generation | fever of heater R1. The final temperature Th2 is set to a temperature that exceeds the operating temperature Tfuse1 of the thermal fuse F1, and does not damage the secondary battery 6 and the protection circuit 5.

  The bimetal switch SW1 is connected between the connection terminal T1 and the thermal fuse F1. The thermal fuse F1 is connected between the bimetal switch SW1 and the connection terminal T3.

  The comparator A <b> 1 has a plus terminal and a power supply terminal connected to the connection terminal T <b> 3 via the temperature fuse F <b> 1 and is driven by power supplied from the secondary battery 6. The comparator A1 has a negative terminal connected to the positive electrode of the reference voltage source E1, an output terminal connected to the gate of the transistor Q1 and an input terminal of the counter C1, and a ground terminal connected to the connection terminals T2 and T4. The reference voltage source E1 is a voltage generation circuit that has a negative electrode connected to the connection terminals T2 and T4 and applies a predetermined overcharge protection voltage Ref1 to the negative terminal of the comparator A1.

  The transistor Q1 is composed of an n-channel field effect transistor, the drain is connected to the thermal fuse F1 via the heater R1, and the source is connected to the connection terminals T2 and T4. The transistor Q2 is composed of an n-channel field effect transistor, the gate is connected to the output terminal of the counter C1, the drain is connected to the thermal fuse F1 via the heater R2, and the source is connected to the connection terminals T2 and T4. Yes.

  When the voltage Va between the connection terminals T3 and T4 exceeds a predetermined overcharge protection voltage Ref1, the comparator A1 outputs a high level signal to turn on the transistor Q1, and the voltage Va is less than or equal to the overcharge protection voltage Ref1. In this case, a low level signal is output to turn off the transistor Q1. In the present embodiment, Ref1 = 4.3V is adopted as the overcharge protection voltage Ref1.

  The counter C1 is composed of a known counter, and counts up every time the signal output from the comparator A1 changes from low level to high level. When the count value exceeds a predetermined specified value, the high level signal is output. Output, turning on the transistor Q2.

  Next, the operation of the protection circuit 5 will be described. First, the overcharge protection operation by the protection circuit 5 will be described. When a charging device (not shown) is connected to the connection terminals T1 and T2, and the voltage Vb is applied between the connection terminals T1 and T2 from the charging device, the bimetal switch SW1 in the normal state where the voltage Va is equal to or lower than the overcharge protection voltage Ref1. Is turned on, and the secondary battery 6 is charged. Here, the voltage Vb is, for example, a maximum of 4.2 V when normal.

  For example, when voltage control cannot be performed due to a failure of a not-illustrated charging device, the voltage Va exceeds the overcharge protection voltage Ref1. Then, a high level signal is output from the comparator A1, the transistor Q1 is turned on, a current flows through the heater R1, and the bimetal switch SW1 is heated. When the temperature of the bimetal switch SW1 reaches the operating temperature Tsw1, the bimetal switch SW1 is turned off, the charging current is interrupted, and the overcharge protection state is set. Thereby, the secondary battery 6 is protected from overcharge.

  Next, overcurrent protection by the protection circuit 5 will be described. First, in a state where the bimetal switch SW1 is turned on, for example, a metal piece comes into contact with the connection terminals T1 and T2, or a load device such as a mobile phone (not shown) connected to the connection terminals T1 and T2 breaks down. Thus, when the connection terminals T1 and T2 are short-circuited or the resistance value between the connection terminals T1 and T2 becomes low resistance, an overcurrent flows from the secondary battery 6 via the temperature fuse F1 and the bimetal switch SW1. When an overcurrent flows, the bimetal switch SW1 is heated by the contact resistance.

  When the temperature reaches the operating temperature Tsw1, the bimetal switch SW1 is turned off to cut off the discharge current of the secondary battery 6, the protection circuit 5 enters the overcurrent protection state, and the secondary battery 6 is protected from the overcurrent. The At this time, since the output of the comparator A1 is at a low level and the heating of the heater R1 is stopped, the bimetal switch SW1 is naturally cooled. Then, when the bimetal switch SW1 becomes equal to or lower than the operating temperature Tsw1, the bimetal switch SW1 is turned on again, and the protection circuit 5 returns from the overcurrent protection state to the normal state.

  Next, the welding avoidance operation of the bimetal switch SW1 by the protection circuit 5 will be described. When the voltage Va exceeds the overcharge protection voltage Ref1, the comparator A1 turns on the transistor Q1, heats the heater R1, and turns off the bimetal switch SW1. On the other hand, when the voltage Va becomes equal to or lower than the overcharge protection voltage Ref1, the comparator A1 turns off the transistor Q1, stops the heating of the heater R1, and turns on the bimetal switch SW1.

  Therefore, when the signal output from the comparator A1 changes from the low level to the high level, the bimetal switch SW1 can be considered to generate a contact operation in which the bimetal and the contact change from the contact state to the non-contact state.

  Therefore, the counter C1 counts up every time the level of the signal output from the comparator A1 is switched. When the count value exceeds a predetermined value, the transistor Q2 is turned on, the heater R2 is heated, and the thermal fuse F1 is blown. This makes it possible to stop the charging / discharging of the secondary battery before the number of operations of the bimetal switch SW1 reaches the guaranteed number of operations, and the bimetal switch SW1 is welded to provide an overcharge protection function and an overcurrent protection function. It is possible to prevent the function from being lost and to protect the safety of the user.

  When the bimetal switch SW1 is protected against overcurrent, it is turned off by self-heating without being heated by the heater R1, so the count number of the counter C1 does not indicate an accurate value of the number of times the bimetal switch is turned off. However, since it is certain that the number of times the bimetal switch is turned off as the count number of the counter C1 increases, if the predetermined value is set in consideration of the number of times the bimetal switch SW1 is turned off by self-heating, Welding of the bimetal switch SW1 can be reliably prevented.

  As described above, according to the protection circuit 5, the secondary battery 6 can be protected from overcharging and overcurrent using the bimetal switch SW1, so that the protection circuit 102 according to the background art shown in FIG. In order to control on / off of the FET 106 that cuts off the discharge current, the FET 107 that cuts off the charging current, the reference voltage source 109 for detecting the overcurrent, the comparator 111, and the resistor 112, and the two FETs 106 and 107 The logic circuit 113 is not required, the circuit of the protection circuit 5 can be simplified, and the protection circuit 5 can be easily downsized.

  Further, the overcharge is detected by the comparator A1, and the bimetal switch SW1 is turned off by heating the bimetal switch SW1 by the heater R1, so that it is connected in series with the secondary battery 122, for example, as shown in FIGS. The accuracy of detecting overcharge can be improved as compared with the case where overcharge protection is performed only by the bimetal switch 123 or the PTC element 132, and the secondary battery 6 is overcharged without performing the overcharge protection operation. The possibility that the characteristics of the secondary battery 6 deteriorate or the secondary battery 6 expands or deforms can be reduced. Further, the number of times that the signal of the comparator A1 changes from low level to high level is counted, and when the count number reaches a predetermined value, the heater R2 is heated and the thermal fuse F1 is blown. In addition to preventing the overcharge protection function and the overcurrent protection function by the protection circuit 5 from functioning by welding, the secondary battery 6 can be protected, and safety for the user can be ensured.

  In the above embodiment, the bimetal switch SW1 may be heated by heat generated when the transistor Q1 is turned on, and the thermal fuse F1 may be heated by heat generated when the transistor Q2 is turned on. In this case, the heaters R1 and R2 are not necessary, and the circuit can be simplified and the cost can be reduced. Further, the overcharge protection unit 51 and the thermal fuse control unit 52 are constituted by an integrated circuit IC, and the thermal fuse F1 and the bimetal switch SW1 are arranged so that heat of the integrated circuit IC is transmitted to the thermal fuse F1 and the bimetal switch SW1. May be. In this case, the circuit can be reduced in size. Further, when a self-holding bimetal switch is used as the bimetal SW1, the overcurrent protection state can be continued.

  The protection circuit and the battery pack of the present invention can realize a protection circuit and a battery pack that can protect the secondary battery from excessive charging and excessive discharge current with a simple circuit, and can be used for mobile devices and driving power supplies. Useful as.

It is a disassembled perspective view which shows an example of the battery pack which concerns on Embodiment 1 of this invention. The circuit diagram of the battery pack shown in FIG. 1 is shown. It is drawing which shows the protection circuit which concerns on background art. It is drawing which shows the protection circuit which concerns on background art. It is drawing which shows the protection circuit which concerns on background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery pack 2 Container 3 External terminal connection unit 4 Spacer 5 Protection circuit 6 Secondary battery 6a Positive electrode terminal 31 Case 51 Overcharge protection part 52 Thermal fuse control part A1 Comparator E1 Reference voltage source F1 Thermal fuse Q1 Q2 Transistor R1 R2 Heater SW1 Bimetal switch T1-T4 connection terminal

Claims (4)

A first and second connection terminals for connecting a charging device for charging a secondary battery and / or a load device driven by a discharge current from the secondary battery;
Third and fourth connection terminals connected to both electrodes of the secondary battery;
A bimetal switch connected to the first connection terminal;
A first heater for heating the bimetal switch;
Overcharge protection means for energizing the first heater and turning off the bimetal switch when the voltage between the third and fourth connection terminals exceeds a predetermined overcharge protection voltage;
The overcharge protection means counts the number of times the bimetal switch is turned off, and when the count value exceeds a predetermined value determined based on the guaranteed number of operations of the bimetal switch, A protection circuit comprising: a blocking means for blocking the connection. The blocking means is
A thermal fuse connected between the bimetal switch and the third connection terminal;
A second heater for heating the thermal fuse;
2. The protection circuit according to claim 1, further comprising: a thermal fuse control unit that energizes the second heater and blows the thermal fuse when the count value exceeds the predetermined value. The overcharge protection means includes a comparator and a first transistor,
The thermal fuse control means includes a counter and a second transistor,
The comparator turns on the first transistor to energize the first heater and counts the counter when the voltage between the third and fourth connection terminals exceeds the overcharge protection voltage. Let me up
3. The protection circuit according to claim 2, wherein when the count value exceeds the predetermined value, the counter turns on the second transistor and energizes the second heater.   The first heater is composed of the first transistor, the second heater is composed of the second transistor, and the bimetal switch is heated by heat generated when the first transistor is turned on. 4. The protection circuit according to claim 3, wherein the thermal fuse is heated by heat generated when the second transistor is turned on.

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