TWI813352B - Safety unit, battery pack, and electrical device - Google Patents

Abstract

A safety unit is provided in a battery pack including a battery including at least one cell of a secondary battery, a first external terminal, and a second external terminal. The safety unit includes a safety element including a fuse element provided between the battery and the first external terminal and a heat-generating resistor that heats the fuse element, a first switching element having one terminal connected to the battery and the second external terminal and having the other terminal connected to the heat-generating resistor, a second switching element and a resistive element provided in parallel to the first switching element, and a controller that controls operations of the first switching element and the second switching element in accordance with a voltage of the cell or the battery. The controller switches the safety unit to a first state in which the first switching element is turned on to render the heat-generating resistor conducting and to a second state in which the second switching element is turned on to render the heat-generating resistor conducting through the resistive element.

Description

Protect circuits, battery packs and electronic equipment

The present invention relates to a protection circuit, a battery pack and an electronic device provided with a protection element including a heating resistor and a fuse element.

Even when used as a single cell like a secondary battery for a mobile phone, secondary batteries such as lithium-ion batteries are commercialized in the form of a battery pack in which a protection circuit (Safety Unit) is built into a casing. It is difficult to achieve sufficient protection only with secondary battery cells such as lithium-ion batteries. Characteristics of lithium-ion batteries include susceptibility to overcharging and overheating.

Therefore, in a battery pack, a protection circuit including a protection element is combined with a secondary battery and housed in an external container such as a plastic case. The charge and discharge control system (battery management system, BMS) controls the charge and discharge of the secondary battery while detecting the voltage, current, temperature, etc. of the secondary battery.

A battery pack installed in a notebook computer or the like includes a battery pack in which a plurality of cells such as a lithium ion battery or the like are connected. In recent years, due to the necessity of dual protection against overcharge, overheating and over-discharge, lithium-ion battery packs are usually equipped with secondary protection (second protection).

In this secondary protection, the charge and discharge path is irreversibly cut off by a protection element (including a fuse element) called a self-control protector. Specifically, the secondary protection integrated circuit (IC) controls and operates the protection element connected in series with the battery to cut off the current when the battery is charged and discharged in an abnormal state.

The protection element has a built-in heating resistor. When the battery exceeds the reference value and is charged, for example, the heating resistor is energized through the secondary protection IC and heats and blows the fuse element of the low-melting-point metal in a short period of time. In addition, the protective element also operates due to the abnormal current of the battery. When an abnormal current occurs, the fuse element melts due to Joule heat caused by the overcurrent (see Japanese Patent Application Laid-Open No. 2017-228379).

The above protection components are included in the protection circuit of the battery pack. The protection circuit includes secondary protection ICs that monitor the voltage of the battery or each unit, and switching elements such as field effect transistors (FETs). The operation of the fuse element is controlled through the secondary protection IC.

For example, the protective element used in the charge and discharge control circuit of the battery pack described in Japanese Patent Application Laid-Open No. 2012-231649 senses an overcurrent of the battery pack and an increase in ambient temperature, blows the fuse, and cuts off the electronic circuit. In addition, by energizing the heating resistor under specific conditions, the fuse is forcibly blown and the electronic circuit is cut off.

That is to say, this protection element can blow the fuse element and cut off the circuit through overcurrent. In addition, when this protection element detects an abnormality in the equipment through the protection circuit, it can heat the resistor element through the signal current, and use its heat to melt the fuse element made of fusible alloy and cut off the circuit.

In a conventional protection circuit, for example, in a battery pack whose voltage is controlled within the charging voltage range of 8.4 to 19.1V, when the charging voltage exceeds 19.1V, the secondary protection IC determines that the battery is overcharged. The secondary protection IC energizes the heating resistor of the protection element through the FET, causing the heating resistor to heat and fuse the fuse element. In addition, when the charging voltage is lower than 8.4V, the secondary protection IC determines that it is over-discharge and blows the fuse element.

Therefore, in a conventional protection circuit, when the voltage exceeds a relatively narrow range, the circuit is cut off to protect the battery and electronic equipment (see Japanese Patent Application Laid-Open No. 2018-060659).

The purpose of the present invention is to provide a protection circuit and circuit that can be used in a wider voltage range. In battery packs and electronic equipment, protection circuits, battery packs and electronic equipment are used to protect overcharge, overheating and over-discharge.

The protection circuit according to the present invention is provided in a battery pack, the battery pack includes a battery of at least one unit including a secondary battery, a first external terminal and a second external terminal, and includes a protection element provided in the battery. a fuse element between the first external terminal and the heating resistor for heating the fuse element; a first switch element with one end connected to the battery and the second external terminal, and the other end connected to the heating resistor; a second switch The element and the resistive element are arranged in parallel with the first switching element; and the control section controls the operations of the first switching element and the second switching element based on the voltage of the unit or the battery. The control unit switches the protection circuit between a first state and a second state. In the first state, the first switching element is turned on and the heating resistor is energized. In the second state, the second switching element is turned on. Turn on and energize the heating resistor through the resistor element.

In the above protection circuit, the control unit may switch the protection circuit to the first state when the voltage value of the unit or battery exceeds the specific voltage range. When the voltage falls within the voltage range, the protection circuit is switched to the second state.

For example, when the specific voltage range is set to 8.4~43.3V, when the discharge voltage is lower than 8.4V, the control unit turns on the first switching element and switches to the above-mentioned first state to cause the heating resistor to heat and blow the fuse element. When the charging voltage exceeds 43.3V, the control unit turns on the second switching element and switches to the second state, energizes the heating resistor through the resistive element, and causes the heating resistor to heat and melt the fuse element. Even when the charging voltage is as high as 43.3V, for example, the heating resistor can be heated without damaging the heating resistor by energizing the heating resistor through the resistor element. Therefore, even in a battery pack used in a wide voltage range, such as 8.4V to 43.3V, protection against overcharge, overheating, and overdischarge can be achieved.

In the above protection circuit, the resistance value of the aforementioned heating resistor is R1, and the rated value of the aforementioned protection element is When the voltage is V1 and the voltage of the aforementioned unit or battery is V2, the resistance value R2 of the aforementioned resistive element may also satisfy the relationship of R2={R1×(V2-V1)}/V1.

For example, when the resistance value R1 of the heating resistor is set to 31Ω and the specific voltage range is set to 33.6~51.0V, by setting the resistance value R2 of the resistor element connected to the second switching element to 10Ω, the control unit controls the control unit when the battery voltage is low. The first switching element is used when 33.6V, and the second switching element is used when the battery voltage exceeds 51.0V, so that the heating resistor can heat.

The switching element of the present invention is composed of a switching transistor such as a field effect transistor (FET) or a metal oxide semifield effect transistor (MOSFET), or a protection circuit module including the switching element.

In the above protection circuit, the battery may include a plurality of the above units, and the control unit may control the operation of the first switching element and the second switching element based on the voltage of any one or more of the above units.

The battery pack including the above protection circuit further includes a battery of at least one unit including a secondary battery, a first external terminal, and a second external terminal.

The electronic equipment including the battery pack further includes a charging and discharging device for charging and discharging the battery pack; and an equipment body for detachably installing the battery pack.

With the above protection circuit, when the voltage value of the unit or battery is lower than a specific voltage range, the heating resistor is energized through the first switching element, so that the heating resistor can heat and blow out the fuse element of the protection element. In addition, when the voltage value of the unit or battery exceeds a specific voltage range, the heating resistor is energized through the second switching element and the resistor element, so that the heating resistor can heat and blow the fuse element of the protection element. By arranging the second switching element and the resistor element in parallel with the first switching element, an appropriate voltage can be applied to the heating resistor both when the voltage of the battery is high and when the voltage of the battery is low. Therefore, a higher voltage value can be used without exceeding the withstand voltage of the heating resistor included in the protective element. Therefore, the protection circuit can be used over a wider voltage range.

It can provide protection circuits, battery packs and electronic equipment that can protect overcharge, overheating and over-discharge in battery packs used in a wide voltage range.

The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the present invention taken in conjunction with the accompanying drawings.

10: Protection circuit

11:Unit

12:Battery

12a: 1st electrode

12b: 2nd electrode

13: 1st external terminal

14: 2nd external terminal

15:Control Department

15a: Terminal 1

15b: Terminal 2

15c: Terminal 3

15d: Terminal 4

16: Fuse component

17: Heating resistor

18: Protective components

19: 1st switching element

20: Protection circuit

200: 2nd switching element

201:Resistance element

21:Unit

21a:Electrode

22:Battery

22a: 1st electrode

22b: 2nd electrode

23: 1st external terminal

24: 2nd external terminal

25:Control Department

25a: Terminal 1

25b: Terminal 2

25c: Terminal 3

25d: Terminal 4

25e: Terminal 5

26: Fuse component

27:Heating resistor

28:Protective components

29: 1st switching element

300: 2nd switching element

301:Resistance element

FIG. 1 is a diagram showing a protection circuit according to an embodiment of the present invention.

FIG. 2 is a diagram showing a protection circuit according to an embodiment of the present invention.

[Preferred embodiment]

The following describes the protection circuit, battery pack, and electronic equipment of this embodiment.

The protection circuit of this embodiment is provided in a battery pack including at least one unit battery (assembly battery) including a secondary battery, a first external terminal, and a second external terminal, and includes a protection element. , including a fuse element disposed between the battery and the first external terminal and a heating resistor for heating the fuse element; the first switching element has one end connected to the above-mentioned battery and the above-mentioned second external terminal, and the other end connected to the above-mentioned a heating resistor; a second switching element and a resistive element arranged in parallel with the first switching element; and a control section that controls the operations of the first switching element and the second switching element according to the voltage of the unit or the battery; wherein , the control unit switches the protection circuit between a first state and a second state. The first state turns on the first switching element and energizes the heating resistor. The second state turns the second switching element on. Set to on and energize the heating resistor via the resistive element.

In the above-mentioned protection circuit, the above-mentioned control unit operates when the voltage value of the above-mentioned unit or the above-mentioned battery is lower than a specific value. When the voltage value of the unit or battery exceeds the specific voltage range, the protection circuit is switched to the second state.

The control unit outputs a control signal based on the voltage of the unit or battery. The first switching element is connected to the control section, and the second switching element is connected to the control section. The on-state and off-state of the first switching element and the second switching element are switched by a control signal output from the control unit according to the voltage of the battery.

For example, when the specific voltage range is set to 8.4~43.3V, when the discharge voltage of the battery is lower than 8.4V, the control unit turns on the first switching element and switches to the above-mentioned first state, causing the heating resistor to heat and fuse the fuse. wire components. When the charging voltage exceeds 43.3V, the control unit turns on the second switching element and switches to the second state, energizes the heating resistor through the resistive element, and causes the heating resistor to heat and melt the fuse element.

Even when the charging voltage is as high as 43.3V, for example, the heating resistor can be heated without damaging the heating resistor by energizing the heating resistor through the resistor element. Therefore, even in a battery pack used in a wide voltage range, such as 8.4V to 43.3V, protection against overcharge, overheating, and overdischarge can be achieved.

In the above example, the specific voltage range of 8.4~43.3V is divided into a first voltage range of 8.4~19.1V and a second voltage range of 19.2V~43.3V. When the discharge voltage of the battery is 8.4V to 19.1V in the first voltage range, the control unit controls the voltage of the battery to maintain the first voltage range. When the discharge voltage of the battery is lower than 8.4V (when it is lower than the first voltage range), the second protection integrated circuit (IC) constituting the control unit turns on the first switching element to energize the heating resistor. Heat and blow the fuse element (activate the protective element). When the charging voltage of the battery exceeds 19.1V (exceeds the first voltage range), the control unit controls the voltage of the battery to maintain the voltage in the second voltage range of 19.2V to 43.3V. When the voltage of the battery exceeds 43.3V (exceeds the second voltage range), the second protection integrated circuit (IC) constituting the control unit turns on the second switching element, energizes the heating resistor through the resistive element, and heats the heating resistor. Blowing the fuse element (activating the protective element). Even when the voltage is high, heating can be achieved without damaging the heating resistor by passing electricity through the resistive element.

In this way, by arranging the first switching element and the second switching element and the resistor element in parallel with the first switching element, a protection circuit capable of corresponding to a wider voltage range combining the first voltage range and the second voltage range can be constructed.

In the above protection circuit, when the resistance value of the above heating resistor is R1, the rated voltage of the above protection element is V1, and the voltage of the above unit or the above battery is V2, the resistance value R2 of the above resistance element satisfies R2={R1×(V2 -V1)}/V1 relationship.

For example, when the resistance value R1 of the heating resistor is 31Ω and the specific voltage range is 33.6~51.0V, by setting the resistance value R2 of the resistor element connected to the second switching element to 10Ω, the control unit (second protection IC) When the battery voltage is lower than 33.6V, the first switching element is used. When the battery voltage exceeds 51.0V, the second switching element is used to heat the heating resistor.

The above-mentioned specific voltage range 33.6~51.0V is divided into a first voltage range 33.6~46.9V and a second voltage range 47.0V~51.0V. When the voltage of the battery is lower than the first voltage range of 33.6~46.9V, the control unit uses the first switching element to energize the heating resistor element. When the voltage of the battery exceeds the second voltage range of 47.0~51.0V, the second switching element is used to energize the heating resistor through the resistive element, so that the heating resistor can be heated. By selecting the resistance value R2 of the resistor element to satisfy the above relationship, protection can be achieved without damaging the heating resistor in a battery used in a wider voltage range that combines the first voltage range and the second voltage range.

According to the above protection circuit, when the voltage of the unit or battery is lower than a specific voltage range, the heating resistor is energized through the first switching element, so that the heating resistor can heat and blow out the fuse element of the protection element. In addition, when the voltage of the unit or battery exceeds a specific voltage range, the heating resistor is energized through the second switching element and the resistor element, so that the heating resistor can heat and blow out the fuse element of the protection element. By arranging the second switching element and the resistor element in parallel with the first switching element, an appropriate voltage can be applied to the heating resistor both when the voltage of the battery is high and when the voltage of the battery is low. Therefore, it can be used at a higher voltage without exceeding the withstand voltage of the heating resistor included in the protective element. Additionally, the heating resistor can be operated efficiently at low voltages. Therefore, the protection circuit can be used in a wider voltage range.

According to the protection circuit of this embodiment, protection against overcharge, overheating, and overdischarge can be achieved in a battery pack used in a wider voltage range.

It is known that in either overcharge or overdischarge state, a short circuit between electrodes of a cell generates an excessive current, causing the temperature of the cell to rise. According to the protection circuit of this embodiment, protection can be achieved by operating the protection element in both overcharge and overdischarge.

The switching element of this embodiment is composed of a switching transistor such as a field effect transistor (FET) or a metal oxide semifield effect transistor (MOSFET), or a protection circuit module including the switching element.

The protection circuit of this embodiment can be mounted on a battery pack to protect the charging and discharging device.

The protection circuit of this implementation type is suitable for battery packs. The battery pack including the above protection circuit further includes: a battery of at least one unit including a secondary battery, a first external terminal, and a second external terminal.

The battery pack of this embodiment is used in wireless electronic devices such as portable devices. The electronic equipment further includes a charging and discharging device for charging and discharging the above-mentioned battery pack; and an equipment body for detachably installing the above-mentioned battery pack.

In the above protection circuit, the battery includes a plurality of the units, and the control unit may control the operations of the first switching element and the second switching element based on the voltage of any one or more of the units.

The cells of a plurality of secondary batteries are connected in series. The control unit outputs a control signal based on the voltage of the unit or battery (assembly battery). When the first voltage range of any one or more cells of the battery is set to VR1, when the voltage is lower than VR1, the heating resistor is energized through the first switching element and the fuse element of the protection element is blown. When the second voltage range is VR2, when the voltage exceeds VR2, the heating resistor is energized through the second switching element and the resistor element, and the fuse element of the protection element is blown.

A battery pack equipped with batteries connected to a plurality of secondary battery cells can be constructed. It can constitute an electronic device equipped with a battery pack, and the electronic device is equipped with a battery connected to a plurality of secondary battery cells. battery pack.

[Example]

As shown in FIG. 1 , the protection circuit 10 of the first embodiment is a protection circuit for protecting a battery pack of a secondary battery such as a lithium ion battery from overcharging, overheating, and overdischarging. The protection circuit 10 includes a protection element 18 , a first switching element 19 , a second switching element 200 , a control unit 15 and a resistor element 201 .

In Example 1, one or more secondary battery cells 11 are connected in series to form the battery 12 . The battery 12 is contained in the battery pack. The battery pack includes a first external terminal 13 and a second external terminal 14 .

The first terminal 15 a of the control unit 15 is connected to the first electrode 12 a of the battery 12 and the protection element 18 . The second terminal 15b of the control unit 15 is connected to the second electrode 12b of the battery 12 and the second external terminal 14. The first terminal 15a and the second terminal 15b of the control unit 15 are respectively connected to the first electrode 12a and the second electrode 12b of the battery 12, and the control unit 15 monitors the voltage of the battery 12. The third terminal 15c of the control unit 15 is connected to the first switching element 19 . The fourth terminal 15d of the control unit 15 is connected to the second switching element 200. The control unit 15 selectively outputs a control signal to the first switching element 19 and the second switching element 200 according to the voltage of the battery 12 .

The fuse element 16 of the protection element 18 is connected in series between the first electrode 12 a of the battery 12 and the first external terminal 13 . The protective element 18 includes a fuse element 16 and a heating resistor 17 for heating the fuse element 16 . The heating resistor 17 can be disposed on the same side as the substrate and overlap the fuse element 16 , or it can be disposed on the opposite side of the substrate to conduct heat through the substrate to the fuse element 16 .

One end of the first switching element 19 is connected to the second electrode 12 b of the battery 12 and the second external terminal 14 . The other end of the first switching element 19 is connected to the heating resistor 17 of the protection element 18 . In addition, the first switching element 19 is connected to the control unit 15 . The control unit 15 switches the conduction state (on state) and the non-conduction state (off state) between one end and the other end of the first switching element 19 by the output control signal.

The second switching element 200 and the resistive element 201 are provided in parallel with the first switching element 19 . The second switching element 200 is connected to the control unit 15 . The control unit 15 switches the conduction state (on state) and the non-conduction state (off state) between one end and the other end of the second switching element 200 by the output control signal.

The second switching element 200 and the resistive element 201 are connected in series. The heating resistor 17 is connected to the second switching element 200 and the resistive element 201 provided in parallel with the first switching element 19 . The heating resistor 17 is also electrically coupled to the middle point of the fuse element 16 .

The control unit 15 switches the first switching element 19 and the second switching element 200 to control the operation of the protection element 18 . For example, when the discharge voltage of the battery 12 is lower than 8.4V, the control unit 15 (second protection IC) turns the first switching element 19 into an on state (first state), energizes the heating resistor 17 and heats the heating resistor 17. The protective element is activated (the fuse element 16 of the protective element 18 is blown). When the charging voltage exceeds 43.3V, the control part 15 (secondary protection IC) turns the second switching element 200 into an on state (second state), and can energize the heating resistor 17 through the resistive element 201, so that the heating resistor 17 is heated and protected. Component action.

As shown in FIG. 2 , the protection circuit 20 of the second embodiment is a protection circuit for protecting a battery pack of a secondary battery such as a lithium ion battery from overcharging, overheating, and overdischarging. The protection circuit 20 includes a protection element 28 , a first switching element 29 , a second switching element 300 , a control section 25 , and a resistance element 301 .

In Example 2, one or more secondary battery cells 21 are connected in series to form the battery 22 . The battery 22 is contained in the battery pack. The battery pack includes a first external terminal 23 and a second external terminal 24 .

The first terminal 25a of the control unit 25 is connected to the first electrode 22a of the battery 22 and the protection element 28. The second terminal 25b of the control unit 25 is connected to the second electrode 22b of the battery 22 and the second external terminal 24. The plurality of fifth terminals 25e of the control unit 25 are connected to the electrodes 21a between the units 21. The first terminal 25a, the second terminal 25b and the fifth terminal 25e of the control part 25 are respectively connected to the first electrode 22a, the second electrode 22b of the battery 22 and the electrode 21a between the cells 21, and the control part 25 monitors the battery 22. voltage and the voltage of each unit 21.

The third terminal 25c of the control unit 25 is connected to the first switching element 29 . The fourth terminal 25d of the control unit 25 is connected to the second switching element 300. The control unit 25 selectively outputs a control signal to the first switching element 29 and the second switching element 300 according to the voltage of the battery 22 or the unit 21 .

The fuse element 26 of the protection element 28 is connected between the first electrode 22 a of the battery 22 and the first external terminal 23 . The protective element 28 includes a fuse element 26 and a heating resistor 27 that heats the fuse element 26 .

One end of the first switching element 29 is connected to the second electrode 22 b of the battery 22 and the second external terminal 24 . The other end of the first switching element 29 is connected to the heating resistor 27 of the protection element 28 . The first switching element 29 is connected to the control unit 25 . The control unit 25 switches the conduction state (on state) and the non-conduction state (off state) between one end and the other end of the first switching element 29 by the output control signal.

The second switching element 300 and the resistive element 301 are provided in parallel with the first switching element 29 . The second switching element 300 is connected to the control unit 25 . The control unit 25 switches the conduction state (on state) and the non-conduction state (off state) between one end and the other end of the second switching element 300 by the output control signal.

The second switching element 300 and the resistive element 301 are connected in series. The heating resistor 27 is connected to the second switching element 300 and the resistive element 301 provided in parallel with the first switching element 29 . The heating resistor 27 is also electrically coupled to the midpoint of the fuse element 26 .

The control unit 25 switches the first switching element 29 and the second switching element 300 to control the operation of the protection element 28 . For example, when the discharge voltage of the battery 22 or the unit 21 is lower than 8.4V, the control unit 25 (second protection IC) turns the first switching element 29 on, energizes the heating resistor 27 and heats the heating resistor 27, causing the protection element to Action (blows the fuse element 26 of the protection element 28). When the charging voltage exceeds 43.3V, the control unit 25 (secondary protection IC) turns on the second switching element 300 and can energize the heating resistor 27 through the resistive element 301 to heat the heating resistor 27 and activate the protection element.

The battery pack of Embodiment 3 is a battery pack using the protection circuit 10 of Embodiment 1. This means a battery pack including cells of secondary batteries such as lithium ion batteries, and includes the protection circuit 10 .

The battery pack of Embodiment 4 is a battery pack using the protection circuit 20 of Embodiment 2. This means a battery pack including cells of secondary batteries such as lithium ion batteries, and includes the protection circuit 20 .

The electronic device of Example 5 is an electronic device using the battery pack of Example 3 or the battery pack of Example 4. It means an electronic device that uses a battery pack including cells of secondary batteries such as lithium ion batteries. The battery pack is removably connected to the electronic device. The electronic device includes a device body that charges a battery pack or receives power supply from the battery pack and is driven. Electronic equipment includes charging and discharging devices connected to the battery pack electrical devices.

[Industrial availability]

The protection circuit, battery pack and electronic equipment of the present invention can be used in electrical appliances or electronic equipment using a protection element including a heating battery and a fuse element. In particular, it can be used in a protection device such as a battery pack including a secondary battery.

Although the embodiments of the present invention are described, it should be understood that the embodiments of the present disclosure are only illustrative and not intended to limit the present invention. The scope of the present invention is shown by the scope of the patent application, and includes all changes within the scope and meanings equivalent to the scope of the patent application.

10: Protection circuit

11:Unit

12:Battery

12a: 1st electrode

12b: 2nd electrode

13: 1st external terminal

14: 2nd external terminal

15:Control Department

15a: Terminal 1

15b: Terminal 2

15c: Terminal 3

15d: Terminal 4

16: Fuse component

17: Heating resistor

18: Protective components

19: 1st switching element

200: 2nd switching element

201:Resistance element

Claims (6)

A protection circuit is provided in a battery pack, the battery pack includes a battery including at least one unit of a secondary battery, a first external terminal, and a second external terminal, including a protection element provided between the battery and the third external terminal. 1. A fuse element between the external terminals and a heating resistor for heating the fuse element; a first switching element with one end connected to the aforementioned battery and the aforementioned second external terminal, and the other end connected to the aforementioned heating resistor; a second switching element and a resistor The element is arranged in parallel with the first switching element; and the control section controls the operation of the first switching element and the second switching element according to the voltage of the unit or the battery; wherein the control section controls the protection circuit Switching between a first state and a second state, the first state turns on the first switching element and energizes the heating resistor, and the second state turns on the second switching element and energizes the heating resistor through the resistor element. The aforementioned heating resistor is energized. The protection circuit of claim 1, wherein the control unit switches the protection circuit to the first state when the voltage value of the unit or battery is lower than a specific voltage range, and when the voltage value of the unit or battery exceeds the specific voltage range, When the voltage falls within the voltage range, the aforementioned protection circuit is switched to the second state. For the protection circuit of claim 1 or 2, when the resistance value of the aforementioned heating resistor is R1, the rated voltage of the aforementioned protection element is V1, and the voltage of the aforementioned unit or the aforementioned battery is V2, the resistance value R2 of the aforementioned resistive element satisfies R2= The relationship of {R1×(V2-V1)}/V1. The protection circuit of claim 1 or 2, wherein the battery includes a plurality of the units, and the control unit controls the operation of the first switching element and the second switching element based on the voltage of any one or more of the units. A battery pack including the protection circuit of any one of claims 1 to 4, and more It includes a battery of at least one unit including a secondary battery, a first external terminal, and a second external terminal. An electronic device includes the battery pack of claim 5, and further includes: a charging and discharging device to charge and discharge the battery pack; and an equipment body to detachably install the battery pack.