JP3798218B2 - Secondary battery protection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a secondary battery protection circuit that uses a PTC element to suppress overcharge of a secondary battery that performs charging and discharging.
[0002]
[Prior art]
Rechargeable secondary batteries such as nickel, cadmium and nickel metal hydride have been used in portable electronic devices (portable radios, portable tape recorders, portable optical disk players, portable video recorders, portable telephones, notebook personal computers) Computer). Since these electronic devices are becoming smaller and lighter year by year, and a long continuous driving time is required, demand for lithium ion secondary batteries having a large discharge capacity per volume is increasing.
[0003]
The lithium ion secondary battery has the above-mentioned advantages, but has a disadvantage that the characteristic deterioration due to the extreme rise and fall of the voltage is large. Moreover, in order to prevent destruction at the time of a short circuit, it is normal to have a protection circuit that performs precise battery voltage management.
[0004]
That is, the secondary battery is charged by monitoring the battery voltage and continuing charging at a constant voltage so that the charging voltage does not increase beyond that voltage after reaching the set voltage. However, in a lithium ion type secondary battery, if the charging voltage rises above a set value for some reason, an irreversible reaction such as thermal decomposition of the electrolytic solution, decomposition of the electrode plate occurs, and a thermal runaway state occurs and the worst battery is It becomes a dangerous state of smoking and ignition.
[0005]
Therefore, when charging a lithium ion type secondary battery, a protection circuit is usually provided that monitors the charging voltage and stops charging when there is a risk that the charging voltage will rise beyond a set value. In the event that this protection circuit does not function or is damaged, double and triple protection means are provided to prevent the occurrence of a thermal runaway state of the lithium ion secondary battery. .
[0006]
As one of the protection means, a PTC (Positive Temperature Coefficient) element having a characteristic that the resistance value increases as the temperature rises is used. A PTC element usually has a characteristic (PTC characteristic) in which a resistance value rapidly increases at a certain temperature, and a resistance change rate is 3 digits or more, and some materials reach 6 digits or more. The PTC element is used as a heating protection element or an overcurrent protection element by utilizing the fact that the resistance value increases when heated in an external atmosphere or warmed by generation of Joule heat due to a large current flowing.
[0007]
In the protection circuit for the secondary battery, the PTC element is connected in series to the secondary battery, and a load (during discharging) and a charger (during charging) are connected to both ends of the series circuit. With this configuration, when an overcurrent due to a short circuit at the time of discharge or an overcharge current due to a failure of the protection circuit at the time of charging flows, the resistance value of the PTC elements connected in series rapidly increases due to Joule heat, and the overcurrent is reduced. Acts to suppress. In order to connect in series with the secondary battery, it is desirable that the resistance value of the PTC element is normally low. This is because the continuous energization time is shortened by consuming useless power during discharging, and the charging time is extended during charging.
[0008]
Moreover, since lithium ion secondary batteries are inherently low in thermal stability, it is desirable to limit charging and discharging when the ambient temperature rises. Therefore, the PTC element is electrically connected in series with the lithium ion secondary battery and is disposed in thermal contact. Thereby, the temperature rise of the lithium ion type secondary battery is detected by the PTC element itself so that the resistance value is increased and the charging current can be suppressed.
[0009]
[Problems to be solved by the invention]
As already described, since heat generation due to overcharging of the lithium ion secondary battery involves a risk of causing thermal runaway, a protection circuit using a PTC element needs to exhibit a desired function in a very short time. In addition, once a lithium-ion type secondary battery or the like generates abnormal heat due to overcharging or the like, the performance and stability deteriorate, so it is dangerous to recharge even after the battery temperature is lowered by the protection circuit. Is accompanied. Therefore, it is necessary to be able to maintain a state where the charging current is reduced even when the battery temperature decreases.
[0010]
The object of the present invention is to detect a rise in battery temperature due to overvoltage charging to effectively reduce the charging current, and to keep the charging current in a reduced state even when the battery temperature is lowered, thereby protecting the secondary battery safely. Another object of the present invention is to provide a secondary battery protection circuit.
[0011]
[Means for Solving the Problems]
The object is to provide a PTC element electrically connected in series and in thermal contact with a secondary battery, and electrically connected in parallel to the secondary battery and the PTC element and with the PTC element. A secondary battery protection circuit comprising a resistance heating element that is in thermal contact and increases a current value of a flowing current by increasing a resistance value of the PTC element due to heat generation of the secondary battery. Achieved by:
[0012]
According to the present invention, when the secondary battery abnormally generates heat during charging, the PTC element first increases the resistance value to suppress the charging current. Then, most of the current flows through the heating resistance element, the heating resistance element generates heat, and the PTC element is heated. Thereby, the suppression operation of charging current can be continued. This current suppression operation is maintained even when the battery temperature decreases.
[0013]
Further, the secondary battery protection circuit of the present invention is characterized in that it has switching means for connecting the resistance heating element to the circuit when the secondary battery is charged and disconnecting when the secondary battery is discharged. According to the present invention, not only can secondary battery protection be effective during charging, but also power consumption during discharging can be suppressed.
[0014]
Further, the secondary battery protection circuit of the present invention includes a common electrode formed between the PTC element and the resistance heating element, a PTC side electrode disposed to face the common electrode via the PTC element, A heating element side electrode disposed opposite to the common electrode through the resistance heating element, and the PTC side electrode, the PTC element, the common electrode, the resistance heating element, and the heating element side electrode are laminated in order and integrated It is characterized by being formed.
According to the present invention, the thermal contact between the PTC element and the resistance heating element can be ensured, and the circuit can be miniaturized.
[0015]
In the secondary battery protection circuit of the present invention, the operating temperature of the PTC element is 100 ° C. or lower. According to the present invention, the protection operation can be surely started before the secondary battery reaches a dangerous temperature state.
[0016]
In the secondary battery protection circuit of the present invention, the resistance heating element has a PTC characteristic. According to the present invention, the heat generation characteristics of the resistance heating element can be matched with those of the PTC element.
[0017]
In the protection circuit for a secondary battery of the present invention, an operating temperature of the resistance heating element is higher than an operating temperature of the PTC element. According to the present invention, the resistance heating element can start the heat generation operation after the PTC element starts the current suppressing operation.
[0018]
In the protection circuit for a secondary battery of the present invention, the PTC element includes a conductive polymer material in which conductive particles are dispersed in a thermoplastic polymer. By doing so, the room temperature resistance value can be reduced, and the protection circuit can be easily formed.
Furthermore, in the secondary battery protection circuit according to the present invention, once the PTC element is in a trip state, the resistance heating element continues to be heated and does not return from the trip state. By doing so, it is possible to maintain a state where the charging current is reduced even when the secondary battery temperature is lowered, and to prevent dangerous charging from being resumed.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
A protection circuit for a secondary battery according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a secondary battery protection circuit according to the present embodiment. As shown in FIG. 1, the secondary battery protection circuit is configured by connecting a resistance heating element 5 in parallel to a PTC element 3 connected in series with the secondary battery 1. This series-parallel circuit is connected between the input / output terminals 7 and 9. The secondary battery 1 and the PTC element 3 are disposed in thermal contact. Similarly, the PTC element 3 and the resistance heating element 5 are also arranged in thermal contact with each other. A load is connected between the input / output terminals 7 and 9 during discharging, and a charger is connected during charging.
[0020]
As shown in FIG. 1, the positive electrode of the secondary battery 1 is connected to the input / output terminal 9 and one end of the resistance heating element 5. The negative electrode of the secondary battery 1 is connected to the input / output terminal 7 and the other end of the resistance heating element 5 through the PTC element 3. In the present embodiment, a lithium ion secondary battery is used as the secondary battery 1, but the present embodiment can be applied to other secondary batteries.
[0021]
Materials having PTC characteristics are roughly classified into inorganic ceramic systems and organic polymer systems. The former includes doped barium titanate, and the latter mainly includes a conductive polymer material in which conductive particles are dispersed in a thermoplastic polymer. The organic polymer system is disclosed in US Pat. Nos. 3,243,753 and 3,351,882. In this embodiment, it is preferable to use the latter conductive polymer material because the room temperature (steady state) resistance value can be reduced and molding is easy.
[0022]
The room temperature resistance value of the PTC element 3 is preferably equal to or less than the internal resistance value of the secondary battery 1, specifically 100 mΩ or less, more preferably 50 mΩ or less, and even more preferably 20 mΩ or less. With the miniaturization of the secondary battery 1, a small PTC element is desired. However, in order to reduce the resistance value of the PTC element 3, it is necessary to increase the surface area. Therefore, the lower the volume resistance value of the material, the better.
[0023]
In order to ensure the safety of the secondary battery 1, the operating temperature of the PTC element 3 is preferably set to 100 ° C., preferably around 70 to 90 ° C. at the highest. If the operating temperature is too high, the resistance value of the PTC element 3 becomes high and the secondary battery 1 may have already shifted to a dangerous state of a thermal runaway state when it enters a trip state in which a current suppressing operation is performed. Because there is sex.
[0024]
Such a PTC element 3 is disclosed in, for example, Japanese Patent Laid-Open Nos. 10-214705, 11-168005, and 11-195506 proposed by the inventors of the present application.
[0025]
On the other hand, regarding the resistance heating element 5, when there is no abnormality in the secondary battery 1, it is necessary to make the charging current flow mainly to the secondary battery 1 to the PTC element 3 side having a low resistance value. Moreover, it is necessary not to consume useless power in the normal state. Therefore, the resistance value of the resistance heating element 5 is set higher than the sum of the internal resistance value of the secondary battery 1 and the resistance value of the PTC element 3, and is set higher by at least one digit, preferably two digits or more. As the resistance heating element 5, a self-temperature controllable PTC heater can be used in addition to a normal resistance heater. At that time, it is desirable to set the operating temperature slightly higher than that of the PTC element 3.
[0026]
As a preferred example of the present embodiment, the PTC element 3 and the resistance heating element 5 may be integrated. Thereby, the stable thermal contact of both can be obtained reliably. FIG. 2 is a configuration example of a protection circuit for a secondary battery using a protection element 21 in which the PTC element 3 and the resistance heating element 5 are integrated. As shown in FIG. 2, the protection element 21 includes a PTC layer 25 and a resistance heating layer 27 that face each other with the common electrode 23 interposed therebetween. An electrode 29 is attached to the surface of the PTC layer 25 that faces the contact surface with the common electrode 23. An electrode 31 is attached to the surface of the resistance heating layer 27 that faces the contact surface with the common electrode 23. As described above, the protection element 21 is integrally formed by sequentially stacking the PTC side electrode 29, the PTC layer 25, the common electrode 23, the resistance heating layer 27, and the heating element side electrode 31. The layer 27 can be thermally connected well.
[0027]
The common electrode 23 of the protection element 21 is connected to the input / output terminal 7. The electrode 31 on the resistance heating layer 27 side is connected to the input / output terminal 9 and the positive electrode of the secondary battery 1. The electrode 29 on the PTC layer 25 side is connected to the negative electrode of the secondary battery 1. Thereby, the electrical connection relationship similar to the circuit configuration shown in FIG. 1 is obtained.
[0028]
A protective element in which a PTC element and a resistance heating element, or a PTC element and a resistance heating element having PTC characteristics are stacked and integrated is disclosed in, for example, Japanese Patent Publication No. 60-4446789 (Reference 1). This publication discloses an electric device in which a heat supply device is provided in a PTC element. In Japanese Examined Patent Publication No. 62-45673 (Document 2), a PTC sheet having a high resistance value is in close contact with a low resistance sheet having a resistance value of 10 ⁻³ times Ω · cm or less, and an electrode is provided thereon. Further, a self-temperature control type heating element is disclosed. Japanese Patent Application Laid-Open No. 55-95203 (Reference 3) discloses an electrode in which an electric current flows along an electric circuit that sequentially passes through a CW element and a PTC element containing carbon black having a defined particle system and surface area. An electrical device provided with a is disclosed.
[0029]
However, in all of these documents 1 to 3, the PTC element and the resistance heating element are electrically connected in series, and wasteful power consumption is inevitable when the secondary battery is discharged in a normal state. Has the disadvantages.
[0030]
Now, an operation during charging of the secondary battery protection circuit according to the present embodiment will be described with reference to FIG. When there is no heat generation abnormality in the secondary battery 1, the charging current flows mainly to the PTC element 3 and the secondary battery 1 side having a low resistance value. The amount of heat generated by the resistance heating element 5 is negligibly small.
[0031]
When the secondary battery 1 is abnormally heated due to an increase in the charging voltage due to an abnormality in the secondary battery 1 or a failure of the charger, the temperature of the PTC element 3 in thermal contact rises and its resistance value increases (trip state). Thereby, the protection operation which suppresses the charging current which flows into the secondary battery 1 connected in series is started. Further, when the sum of the internal resistance value of the secondary battery 1 and the resistance value of the PTC element 3 exceeds the resistance value of the resistance heating element 5, a current flows mainly through the resistance heating element 5, and the secondary battery 1. The value of the charging current that flows is further reduced.
[0032]
When a current flows through the resistance heating element 5 to generate heat and the temperature rises, the temperature of the PTC element 3 in thermal contact with the resistance heating element 5 further increases and the resistance value is further increased. To do. As a result, the temperature of the secondary battery 1 drops without reaching a dangerous temperature state. Thus, the provision of the resistance heating element 5 allows the PTC element 3 to quickly perform a current suppression protection operation.
[0033]
Lithium-ion type secondary batteries, etc., once they generate abnormal heat due to overcharging, etc., will degrade performance and stability, so there is a risk of recharging even after the battery temperature has been lowered by the protection circuit. . On the other hand, in the protection circuit according to the present embodiment, even if the battery temperature is lowered by reducing the charging current, the PTC element 3 continues to be heated by the resistance heating element 5 that is electrically connected in parallel, and thus from the trip state. Does not return. For this reason, even when the battery temperature is lowered, the state where the charging current is reduced can be maintained, and dangerous charging can be prevented from being resumed.
[0034]
If the resistance heating element 5 is connected in series to the PTC element 3 as described in the above documents 1 to 3, if the current decreases due to the operation of the PTC element 3, the heating by the resistance heating element 5 is insufficient. Become. As a result, when the temperature of the PTC element 3 decreases and the resistance value decreases, recharging may occur depending on the degree of decrease in battery temperature. On the other hand, since the resistance heating element 5 is connected in parallel to the PTC element 3 in this embodiment, the resistance heating element 5 can continue to heat the PTC element 3 and prevent recharging of the secondary battery. Can do.
[0035]
When the current flowing through the resistance heating element 5 is reduced for some reason and the heating by the resistance heating element 5 becomes insufficient for the PTC element 3 in a tripped state, the resistance value of the PTC element 3 becomes low. However, even if the resistance value of the PTC element 3 falls below the resistance value of the resistance heating element 5, the charging current flows to the PTC element 3 at that time, so that the PTC element 3 generates heat due to Joule heat. Therefore, the current suppression by the PTC element 3 is continued and the charging current does not increase again.
[0036]
Thus, according to the present embodiment, dangerous recharging can be prevented from occurring. In order to resume the charging, the energization from the charger is once cut off and the temperature of the PTC element 3 is completely lowered. By doing so, it is possible to prevent an unintended return from the protective operation of the PTC element 3.
[0037]
The secondary battery protection circuit shown in FIGS. 1 and 2 has a configuration in which the resistance heating element 5 (the resistance heating layer 27 in FIG. 2) remains connected to the circuit in both charging and discharging of the secondary battery. Yes. However, in this configuration, the load and the resistance heating element 5 are connected in parallel during discharge, and there is a possibility that almost no current flows through the load depending on the resistance value of the load. Therefore, the resistance heating element 5 may be connected only at the time of charging and may be provided with a switching means for disconnecting from the circuit at the time of discharging. 3 to 5 show an example of a secondary battery protection circuit including a switching unit.
[0038]
In FIG. 3, a load 11 is connected between the input / output terminals 7 and 9. For example, a switch 13 is provided between the input / output terminal 9 and one end of the resistance heating element 5. As the switch 13, a switch having a mechanical contact or a circuit switch that is electrically disconnected can be used.
[0039]
In FIG. 4, the battery pack containing the protection element 21 is provided with a third terminal (charging terminal) 41 for connection between the electrode 31 on the resistance heating layer 27 side and the input / output terminal 9 (see FIG. 2). In other words, the electrode 31 is connected to a third terminal (charging terminal) 41. During charging, the charging terminal 41 and the input / output terminal 9 are short-circuited on the charger side, and during discharging (when connected to a load), the resistance heating element 5 is disconnected without being connected to the charging terminal 41.
[0040]
In FIG. 5, the push switch 15 is provided in the battery pack that houses the protection element 21, the connection between the electrode 31 on the resistance heating layer 27 side and the input / output terminal 9 is cut off (see FIG. 2), and the electrode 31 is pushed. The input / output terminal 9 is connected to the other end of the push switch 15. At the time of discharging, the push switch 15 is turned off to electrically disconnect between the electrode 31 and the input / output terminal 9. When the battery pack is inserted into the charger, the push switch 15 is pushed and the electrode 31 and the input / output terminal 9 are connected.
[0041]
FIG. 6 is a diagram illustrating a mounting state of the secondary battery protection circuit according to the present embodiment. FIG. 6A is a perspective view showing the external appearance of the secondary battery 1, and FIG. 6B is a diagram for the secondary battery as viewed from the mounting direction side to the secondary battery 1 shown in FIG. It is a perspective view which shows the external appearance of a protection circuit. FIG. 6C shows the configuration of the protection element 21.
[0042]
As shown in FIG. 6A, the secondary battery 1 has a thin rectangular parallelepiped shape. The positive and negative electrodes of the battery are provided on both side surfaces of the attachment position 52 where the protective element 21 is attached in close contact. Only the positive electrode 50 is shown in the figure.
[0043]
As shown in FIGS. 6B and 6C, the lead wire 44 is drawn from the common electrode 23 of the protection element 21. A lead wire 40 is drawn from the PTC element side electrode 29, and a lead wire 42 is drawn from the resistance heating element side electrode 31. As shown in FIG. 6B, the lead wire 40 is connected to a wiring board 54 connected to a negative electrode (not shown) of the secondary battery 1. The lead wire 42 is connected to a wiring board 58 connected to the input / output terminal 9 (not shown). The wiring board 56 branched in the middle is connected to the positive electrode 50 of the secondary battery. The lead wire 44 is connected to the input / output terminal 7 (not shown).
[0044]
With such a configuration, the PTC element 25 side of the protection element 21 is attached in close contact with the attachment position 52 of the secondary battery 1 so that good thermal contact can be obtained. Hereinafter, the present embodiment will be described using specific examples and comparative examples.
[0045]
(Example)
[PTC layer]
High density polyethylene (Nippon Polychem, product name HY540) and equivalent amount of paraffin wax (Nippon Seiwa, product name HNP-10), filamentary Ni powder 4 times the total weight of both (INCO, product name) (Type 255 nickel powder) is kneaded in a mill at 150 ° C., and 1.0% by weight of the total weight of polyethylene and wax is a silane coupling agent (trade name KBE1003, manufactured by Shin-Etsu Chemical Co., Ltd.), 20% by weight of the organic solvent. An oxide (trade name Trigonox DT50, manufactured by Kayaku Akzo) was dropped into the kneaded product and kneaded for 60 minutes. The kneaded product was formed into a sheet having a thickness of about 0.6 mm at 150 ° C., immersed in a 20% by weight dibutyltin dilaurate emulsion, and subjected to crosslinking treatment at 65 ° C. for 8 hours.
[0046]
This sheet was sandwiched between two Ni foils with a thickness of 25 μm and heat-pressed at 150 ° C. to a total thickness of 0.4 mm, punched into a disk shape with a diameter of 10 mm, and a temperature-resistance curve was measured. The operating temperature was 75 ° C.
[0047]
[Resistance heating layer]
66% by weight of low density polyethylene (manufactured by Nippon Polychem, product name LC500) of 66% by weight of carbon black (manufactured by Tokai Carbon, trade name of Toka Black # 4500) is kneaded in a mill at 120 ° C., and 1.0% by weight of polyethylene in the kneaded product A silane coupling agent (trade name KBE1003, manufactured by Shin-Etsu Chemical Co., Ltd.) and 20% by weight of an organic peroxide (product name: Trigonox 29A, manufactured by Kayaku Akzo) were dropped into the kneaded product and kneaded for 20 minutes. The kneaded product was formed into a sheet having a thickness of about 0.6 mm at 120 ° C., immersed in a 20% by weight dibutyltin dilaurate emulsion, and subjected to crosslinking treatment at 65 ° C. for 8 hours.
[0048]
This sheet was sandwiched between two Ni foils with a thickness of 25 μm and heat-pressed at 150 ° C. to a total thickness of 0.4 mm, punched into a disk shape with a diameter of 10 mm, and a temperature-resistance curve was measured. 1.2Ω and the operating temperature was 90 ° C.
[0049]
[Protective element]
A 25 μm thick Ni foil / cross-linked PTC sheet / Ni foil / cross-linked resistance heating sheet / Ni foil are sandwiched in this order and heat-pressed at 150 ° C. to a total of 0.8 mm, and punched into a disk shape with a diameter of 10 mm It was.
[0050]
[Protection circuit]
Each electrode of the protective element and a 0.55 Ahr lithium ion secondary battery 1 were connected as shown in FIG. 2, and a power supply for charging was connected to the input / output terminals 7 and 9.
[0051]
[Charge test]
Charging was performed under a constant current condition of 1 A up to a charging voltage of 5V. When the battery voltage reached about 4.3 V, the battery temperature began to rise, the PTC element operated at about 75 ° C., and the charging current was limited to 50 mA. Thereafter, the charging current did not increase even after standing for 3 hours.
[0052]
(Comparative example)
A disc-shaped PTC element having a thickness of 0.4 mm and a diameter of 10 mm is produced by sandwiching only the PTC element body of the example between the electrodes, connected in series between the battery and the power source, and the element and the battery are brought into thermal contact with each other. The same charge wiping test as in the example was performed.
[0053]
The residual current after the operation of the PTC element was 500 mA, which was 10 times that of the example.
[0054]
The present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the protection element in which the PTC element and the resistance heating element 5 are integrally configured has been described. However, the PTC element and the resistance heating element 5 may be configured by individual components.
[0055]
【The invention's effect】
As described above, according to the present invention, an increase in battery temperature due to overvoltage charging is detected and the charging current is effectively reduced, and even when the battery temperature decreases, the charging current is reduced and the secondary battery is maintained. Can be safely protected.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a protection circuit for a secondary battery according to an embodiment of the present invention.
FIG. 2 is a configuration example of a protection circuit for a secondary battery using a protection element in which a PTC element and a resistance heating element are integrated.
FIG. 3 is a configuration diagram of a secondary battery protection circuit including switching means for disconnecting the resistance heating element from the circuit during discharge.
FIG. 4 is a configuration diagram of a secondary battery protection circuit including switching means for disconnecting the resistance heating element from the circuit during discharge.
FIG. 5 is a configuration diagram of a secondary battery protection circuit including switching means for disconnecting the resistance heating element from the circuit during discharging.
FIG. 6 is a diagram illustrating a mounted state of the secondary battery protection circuit according to the embodiment of the present invention.
[Explanation of symbols]
1 Secondary battery 3 PTC element 5 Resistance heating element 7, 9 Input / output terminal 11 Load 13 Switch 15 Push switch 21 Protection element 23 Common electrode 25 PTC layer 27 Resistance heating layer 29, 31 Electrodes 40, 42, 44 Lead wire 41 First 3 terminal (charging terminal)
50 Positive electrode 52 Mounting position 54, 56, 58 Wiring board

Claims (7)

A PTC element electrically connected in series and in thermal contact with the secondary battery;
A current that flows when the secondary battery and the PTC element are electrically connected in parallel and are in thermal contact with the PTC element, and the resistance value of the PTC element increases due to the heat generated by the secondary battery. And a resistance heating element that increases the current value of the secondary battery. A protection circuit for a secondary battery according to claim 1,
A protective circuit for a secondary battery, comprising switching means for connecting the resistance heating element to the circuit when the secondary battery is charged and disconnecting when the secondary battery is discharged. The secondary battery protection circuit according to claim 1 or 2,
A common electrode formed between the PTC element and the resistance heating element;
A PTC side electrode disposed opposite to the common electrode through the PTC element;
A heating element side electrode disposed opposite to the common electrode via the resistance heating element;
The protective circuit for a secondary battery, wherein the PTC side electrode, the PTC element, the common electrode, the resistance heating element, and the heating element side electrode are laminated in order and integrally formed. The secondary battery protection circuit according to any one of claims 1 to 3,
The operating temperature of the PTC element is 100 ° C. or less. The secondary battery protection circuit according to any one of claims 1 to 4,
The said resistance heating element has a PTC characteristic. The protection circuit for secondary batteries characterized by the above-mentioned. A secondary battery protection circuit according to any one of claims 1 to 5,
The secondary battery protection circuit, wherein an operating temperature of the resistance heating element is higher than an operating temperature of the PTC element. The secondary battery protection circuit according to any one of claims 1 to 6,
The secondary battery protection circuit according to claim 1, wherein once the PTC element is in a trip state, the resistance heating element is continuously heated and does not return from the trip state .

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