Protection circuit, battery pack and electrical device

Abstract

A protection circuit is provided in a battery pack including a battery including at least one battery cell of a secondary battery, a first external terminal, and a second external terminal. The protection circuit includes a protection element including a fuse element provided between the battery and the first external terminal, and a heat generating resistor for heating the fuse element; a first switch element having one end connected to the battery and the second external terminal and the other end connected to the heat generating resistor; a second switch element and a resistance element provided in parallel with the first switch element; and a control portion for controlling the operation of the first switch element and the second switch element in accordance with the voltage of the battery cell or the battery. The control portion switches the protection circuit to a first state in which the first switch element is set to an on state to energize the heat generating resistor, and a second state in which the second switch element is set to an on state to energize the heat generating resistor via the resistance element.

Description

TECHNICAL FIELD

[0001] The present application relates to a protection circuit, a battery pack, and an electrical device, which include a protection element including a heat generating resistor and a fuse element. BACKGROUND

[0002] A secondary battery such as a lithium ion battery is commercialized in the form of a battery pack. Even in the case where a secondary battery such as a lithium ion battery is used in a single cell, a protection circuit (safety unit) is installed in a case. This is because it is difficult to achieve sufficient protection by only the cell of a secondary battery such as a lithium ion battery. The lithium ion battery is weak in the ability to resist overcharging and overheat.

[0003] Therefore, in the battery pack, a protection circuit including a protection element is provided in conjunction with a secondary battery, and is housed in an outer can such as a plastic case. A charge and discharge control system (battery management system, BMS) controls the charge and discharge of the secondary battery while detecting the voltage, current, temperature, and the like of the secondary battery.

[0004] In a battery pack mounted on a notebook computer or the like, a battery including a plurality of cells such as lithium ion batteries is included. In recent years, due to the necessity of double protection against overcharging, overheat, and overdischarge, a second protection device is generally mounted in a battery pack of a lithium ion battery.

[0005] In this second protection device, a protection element (including a fuse element) called SCP (self-controlled protection device) irreversibly cuts off the charge and discharge path. Specifically, the second protection device 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.

[0006] A heat generating resistor is built in the protection element, and for example, when the battery is charged to exceed a reference value, the heat generating resistor is energized by the second protection device IC to heat and melt a fuse element of a low melting point metal in a short time. In addition, the protection element also operates due to abnormal current of the battery. When abnormal current occurs, the fuse element is melted by Joule heat generated by the overcurrent (see Japanese Patent Application Publication No. 2017-228379).

[0007] The above protection element is included in a protection circuit of a battery pack. The protection circuit includes a second protection device IC that monitors the voltage of the battery or each cell, and a switching element such as an FET. The operation of the fuse element is controlled by the second protection device IC.

[0008] For example, Japanese Patent Application Laid-Open No. 2012-231649 describes a protective element used in a battery pack charge and discharge control circuit. In response to overcurrent in the battery pack and a rise in ambient temperature, the fuse melts, thereby shutting off the circuit. Furthermore, by energizing a heating resistor under specified conditions, the fuse is forcibly blown, shutting off the circuit.

[0009] Specifically, the protection element can melt the fuse element when an overcurrent occurs, thereby disconnecting the circuit. Furthermore, when the protection circuit detects an abnormality in the device, the protection element heats the resistor element with a signal current. This heat can melt the fuse element, which is made of a fusible alloy, thereby disconnecting the circuit.

[0010] In a conventional protection circuit, for example, in a battery pack whose charging voltage is controlled to a range of 8.4 to 19.1V, if the charging voltage exceeds 19.1V, the second protection device IC determines that the battery is overcharged. The second protection device IC energizes the heating resistor of the protection element via an FET, heating the heating resistor and melting the fuse element. Furthermore, if the charging voltage falls below 8.4V, the second protection device IC determines that the battery is overdischarged and melts the fuse element.

[0011] Therefore, in the conventional protection circuit, when the voltage deviates from a relatively narrow voltage range, the circuit is cut off to protect the battery and the electrical equipment (see Japanese Patent Application Laid-Open No. 2018-060659). Summary of the Invention

[0012] Problems to be solved by the invention

[0013] An object of the present invention is to provide a protection circuit, a battery pack, and an electrical device, which can be used in a wide voltage range to provide protection against overcharging, overheating, and overdischarging.

[0014] Means used to solve the problem

[0015] The protection circuit of the present invention is provided in a battery pack, the battery pack comprising: a battery including at least one secondary battery cell, a first external terminal, and a second external terminal. The protection circuit includes: a protection element comprising: a fuse element disposed between the battery and the first external terminal, and a heating resistor for heating the fuse element; a first switching element having one end connected to the battery and the second external terminal and the other end connected to the heating resistor; a second switching element and a resistor disposed in parallel with the first switching element; and a control unit configured to control the operation of the first and second switching elements based on the voltage of the battery cell or the battery. The control unit switches the protection circuit between a first state in which the first switching element is turned on, energizing the heating resistor, and a second state in which the second switching element is turned on, energizing the heating resistor via the resistor.

[0016] In the above-mentioned protection circuit, when the voltage value of the above-mentioned battery cell or the above-mentioned battery is lower than the specified voltage range, the above-mentioned control unit can switch the above-mentioned protection circuit to the above-mentioned first state; when the voltage value of the above-mentioned battery cell or the above-mentioned battery is higher than the above-mentioned specified voltage range, the above-mentioned control unit can switch the above-mentioned protection circuit to the above-mentioned second state.

[0017] For example, when the specified voltage range is set to 8.4 to 43.3V, when the discharge voltage is lower than 8.4V, the control unit turns on the first switch element, switching to the first state, causing the heating resistor to heat up, thereby blowing the fuse element. When the charging voltage exceeds 43.3V, the control unit turns on the second switch element, switching to the second state, energizing the heating resistor via the resistor element, causing the heating resistor to heat up, thereby blowing the fuse element. Even in the case of a high voltage, such as a charging voltage of 43.3V, by energizing the heating resistor via the resistor element, the heating resistor can be heated without damaging the heating resistor. Thus, even in a battery pack used within a wide voltage range, such as 8.4V to 43.3V, protection against overcharge, overheating, and overdischarge can be achieved.

[0018] In the above-mentioned protection circuit, when the resistance value of the above-mentioned heating resistor is set to R1, the rated voltage value of the above-mentioned protection element is set to V1, and the voltage of the above-mentioned battery cell or the above-mentioned battery is set to V2, the resistance value R2 of the above-mentioned resistance element can satisfy the relationship R2 = {R1×(V2-V1)} / V1.

[0019] For example, when the resistance value R1 of the heating resistor is set to 31Ω and the specified 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 can use the first switching element when the battery voltage is lower than 33.6V and use the second switching element when the battery voltage is higher than 51.0V, thereby causing the heating resistor to heat up.

[0020] The switching element of the present invention is composed of a switching transistor such as a field effect transistor (FET) or a MOSFET, or a protection circuit module including the switching element.

[0021] In the protection circuit, the battery includes a plurality of battery cells; and the control unit may control the operation of the first switching element and the second switching element according to the voltage of any one or more of the battery cells.

[0022] The battery pack including the above-mentioned protection circuit further includes a battery including at least one battery cell of a secondary battery, a first external terminal, and a second external terminal.

[0023] The electrical device including the battery pack further includes: a charging and discharging device for charging and discharging the battery pack; and a device body on which the battery pack is detachably mounted.

[0024] According to the above-mentioned protection circuit, when the voltage value of the battery cell or battery is lower than the specified voltage range, the heating resistor can be energized via the first switching element, causing the heating resistor to heat up, thereby causing the fuse element of the protection element to melt. In addition, when the voltage value of the battery cell or battery exceeds the specified voltage range, the heating resistor can be energized via the second switching element and the resistance element, causing the heating resistor to heat up, thereby causing the fuse element of the protection element to melt. By configuring the first switching element and the second switching element and the resistance element connected in parallel therewith, an appropriate voltage can be applied to the heating resistor regardless of whether the battery voltage is high or low. As a result, it can be used at a higher voltage value without exceeding the withstand voltage of the heating resistor included in the protection element. As a result, the protection circuit can be used in a wider voltage range.

[0025] Effects of the Invention

[0026] A protection circuit, a battery pack, and an electrical device can be provided, which can realize protection against overcharge, overheating, and overdischarge in a battery pack used in a wide voltage range.

[0027] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a diagram showing a protection circuit according to an embodiment of the present invention.

[0029] Figure 2 It is a diagram showing a protection circuit according to an embodiment of the present invention.

[0030] Description of Reference Numerals

[0031] 10, 20 protection circuit, 11, 21 battery cell, 12, 22 battery, 12a, 22a first electrode, 12b, 22b second electrode, 13, 23 first external terminal, 14, 24 second external terminal, 15, 25 control unit, 15a, 25a first terminal, 15b, 25b second terminal, 15c, 25c third terminal, 15d, 25d fourth terminal, 16, 26 fuse element, 17, 27 heating resistor, 18, 28 protection element, 19, 29 first switching element, 21a electrode, 25e fifth terminal, 200, 300 second switching element, 201, 301 resistor element. DETAILED DESCRIPTION

[0032] Hereinafter, a protection circuit, a battery pack, and an electric device according to this embodiment will be described.

[0033] The protection circuit of this embodiment is provided in a battery pack, the battery pack comprising: a battery (battery pack) including at least one secondary battery cell, a first external terminal, and a second external terminal. The protection circuit includes a protection element comprising: a fuse element disposed between the battery cell and the first external terminal, and a heating resistor for heating the fuse element; a first switching element having one end connected to the battery cell and the second external terminal and the other end connected to the heating resistor; a second switching element and a resistor disposed in parallel with the first switching element; and a control unit that controls the operation of the first and second switching elements based on the voltage of the battery cell or battery. The control unit switches the protection circuit between a first state in which the first switching element is turned on, energizing the heating resistor, and a second state in which the second switching element is turned on, energizing the heating resistor via the resistor.

[0034] In the above-mentioned protection circuit, when the voltage value of the above-mentioned battery cell or the above-mentioned battery is lower than the specified voltage range, the above-mentioned control unit switches the above-mentioned protection circuit to the above-mentioned first state; when the voltage value of the above-mentioned battery cell or the above-mentioned battery is higher than the above-mentioned specified voltage range, the above-mentioned control unit switches the above-mentioned protection circuit to the above-mentioned second state.

[0035] The control section outputs a control signal in accordance with the voltage of the battery cell or the 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 the off state of the first switching element and the second switching element are switched by the control signal output from the control section in accordance with the voltage of the battery.

[0036] For example, when the prescribed voltage range is set to 8.4 to 43.3 V, the control section sets the first switching element to the on state and switches to the first state described above to cause the heat generating resistor to generate heat and thereby cause the fuse element to fuse when the discharge voltage of the battery is lower than 8.4 V. The control section sets the second switching element to the on state and switches to the second state to cause the heat generating resistor to generate heat by passing current through the heat generating resistor via the resistance element and thereby cause the fuse element to fuse when the charge voltage exceeds 43.3 V.

[0037] For example, even in the case of a high voltage of 43.3 V, the heat generating resistor can be caused to generate heat without damaging the heat generating resistor by passing current through the heat generating resistor via the resistance element. Thus, even in a battery pack used in a wide voltage range of, for example, 8.4 to 43.3 V, protection against overcharge, overheat, and overdischarge can be achieved.

[0038] The 8.4 to 43.3 V prescribed voltage range in the above example is divided into a first voltage range of 8.4 to 19.1 V and a second voltage range of 19.2 to 43.3 V. When the discharge voltage of the battery is within the first voltage range, i.e., 8.4 to 19.1 V, the control section controls the voltage of the battery to be maintained within the first voltage range. When the discharge voltage of the battery is lower than 8.4 V (lower than the first voltage range), the second protection device IC that constitutes the control section sets the first switching element to the on state to pass current through the heat generating resistor and cause the heat generating resistor to generate heat and thereby cause the fuse element to fuse (cause the protection element to act). When the charge voltage of the battery exceeds 19.1 V (exceeds the first voltage range), the control section controls the voltage of the battery to be within the second voltage range, i.e., 19.2 to 43.3 V. When the voltage of the battery exceeds 43.3 V (exceeds the second voltage range), the second protection device IC that constitutes the control section sets the second switching element to the on state to pass current through the heat generating resistor via the resistance element and cause the heat generating resistor to generate heat and thereby cause the fuse element to fuse (cause the protection element to act). Even in the case of a relatively high voltage, the heat generating resistor can be caused to generate heat without damaging the heat generating resistor by passing current through the resistance element.

[0039] In this way, by providing the first switching element, the second switching element connected in parallel to the first switching element, and the resistance element, a protection circuit suitable for a wide voltage range including a first voltage range and a second voltage range can be constituted.

[0040] In the above-mentioned protection circuit, when the resistance value of the above-mentioned heating resistor is set to R1, the rated voltage value of the above-mentioned protection element is set to V1, and the voltage of the above-mentioned battery cell or the above-mentioned battery is set to V2, the resistance value R2 of the above-mentioned resistance element satisfies the relationship R2 = {R1×(V2-V1)} / V1.

[0041] For example, when the resistance value R1 of the heating resistor is set to 31Ω and the specified 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 (second protection device IC) can use the first switching element when the battery voltage is lower than 33.6V and use the second switching element when the battery voltage is higher than 51.0V, thereby causing the heating resistor to heat up.

[0042] The above-mentioned specified voltage range of 33.6 to 51.0V is divided into: a first voltage range of 33.6 to 46.9V and a second voltage range of 47.0 to 51.0V. When the battery voltage is lower than the first voltage range of 33.6 to 46.9V, the control unit uses the first switching element to energize the heating resistor. When the battery voltage exceeds the second voltage range of 47.0 to 51.0V, the second switching element can be used to energize the heating resistor via the resistor element, thereby causing the heating resistor to generate heat. 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 pack used in a wide voltage range including the first voltage range and the second voltage range.

[0043] According to the above-mentioned protection circuit, when the voltage of the battery cell or battery is lower than the specified voltage range, the heating resistor can be energized via the first switching element, causing the heating resistor to generate heat, thereby causing the fuse element of the protection element to melt. In addition, when the voltage of the battery cell or battery exceeds the specified voltage range, the heating resistor can be energized via the second switching element and the resistance element, causing the heating resistor to generate heat, thereby causing the fuse element of the protection element to melt. By configuring the first switching element and the second switching element and the resistance element connected in parallel therewith, an appropriate voltage can be applied to the heating resistor regardless of whether the battery voltage is high or low. As a result, it can be used at a higher voltage without exceeding the withstand voltage of the heating resistor included in the protection element. In addition, the heating resistor can be effectively operated even at low voltage. As a result, the protection circuit can be used in a wider voltage range.

[0044] According to the protection circuit of this embodiment, protection against overcharge, overheating, and overdischarge can be achieved in a battery pack used in a wide voltage range.

[0045] It is known that in both overcharge and overdischarge states, a short circuit between the electrodes of a battery cell generates an excessive current, causing the battery cell temperature to rise. According to the protection circuit of this embodiment, protection can be achieved by activating the protection element regardless of overcharge or overdischarge.

[0046] The switching element of this embodiment is composed of a switching transistor such as a field effect transistor (FET) or a MOSFET, or a protection circuit module including the switching element.

[0047] The protection circuit of this embodiment can be mounted on a battery pack to protect the charging and discharging device.

[0048] The protection circuit of this embodiment is applicable to a battery pack. The battery pack including the protection circuit further includes a battery including at least one battery cell of a secondary battery, a first external terminal, and a second external terminal.

[0049] The battery pack of this embodiment is used in cordless electrical equipment such as mobile devices. The electrical equipment further includes: a charging and discharging device for charging and discharging the battery pack; and an equipment body to which the battery pack is detachably mounted.

[0050] In the protection circuit, the battery includes a plurality of battery cells; and the control unit may control the operation of the first switching element and the second switching element according to the voltage of any one or more of the battery cells.

[0051] Multiple secondary battery cells are connected in series. A control unit outputs a control signal based on the voltage of the battery cells or battery (battery pack). When the first voltage range of one or more battery cells is set to VR1, when the voltage falls below VR1, the heating resistor is energized via the first switching element, causing the fuse element of the protection element to melt. When the second voltage range is set to VR2, when the voltage exceeds VR2, the heating resistor is energized via the second switching element and the resistance element, causing the fuse element of the protection element to melt.

[0052] A battery pack equipped with a battery composed of a plurality of connected secondary battery cells can be configured. An electric device equipped with a battery pack equipped with a battery composed of a plurality of connected secondary battery cells can be configured.

[0053] [Example]

[0054] like Figure 1 As shown, the protection circuit 10 of the first embodiment is a protection circuit for protecting a battery pack of secondary batteries such as lithium-ion batteries from overcharge, overheating, and overdischarge. 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 201.

[0055] In Example 1, one or more secondary battery cells 11 are connected in series to form a battery 12. The battery 12 is mounted in a battery pack. The battery pack has a first external terminal 13 and a second external terminal 14.

[0056] A first terminal 15a of the control unit 15 is connected to the first electrode 12a of the battery 12 and the protection element 18. A 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. By connecting the first terminal 15a and the second terminal 15b of the control unit 15 to the first electrode 12a and the second electrode 12b of the battery 12, respectively, the control unit 15 monitors the voltage of the battery 12. A third terminal 15c of the control unit 15 is connected to the first switching element 19. A fourth terminal 15d of the control unit 15 is connected to the second switching element 200. The control unit 15 selectively outputs control signals to the first switching element 19 and the second switching element 200 based on the voltage of the battery 12.

[0057] A fuse element 16 of a protection element 18 is connected in series between the first electrode 12a of the battery 12 and the first external terminal 13. The protection element 18 includes the fuse element 16 and a heating resistor 17 for heating the fuse element 16. The heating resistor 17 can be provided on the same side of the substrate as the fuse element 16 so as to overlap, or it can be provided on the other side of the substrate so as to transfer heat to the fuse element 16 via the substrate.

[0058] One end of the first switching element 19 is connected to the second electrode 12b 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. The first switching element 19 is connected to the control unit 15. The control unit 15 switches between one end and the other end of the first switching element 19 between a conductive state (on state) and a non-conductive state (off state) by outputting a control signal.

[0059] The second switching element 200 and the resistor 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 between one end and the other end of the second switching element 200 between a conductive state (on state) and a non-conductive state (off state) by outputting a control signal.

[0060] The second switching element 200 and the resistance element 201 are connected in series. The first switching element 19 and the second switching element 200 and the resistance element 201 provided in parallel are connected to the heating resistor 17. The heating resistor 17 is also electrically connected to the middle point of the fuse element 16.

[0061] The control unit 15 switches between 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 less than 8.4V, the control unit 15 (second protection device IC) turns on the first switching element 19 (first state), energizing the heating resistor 17, causing it to heat up, thereby activating the protection element (melting the fuse element 16 of the protection element 18). When the charging voltage exceeds 43.3V, the control unit 15 (second protection device IC) turns on the second switching element 200 (second state), energizing the heating resistor 17 via the resistor element 201, causing it to heat up, thereby activating the protection element.

[0062] like Figure 2 As shown, the protection circuit 20 of the second embodiment is a protection circuit for protecting a battery pack containing secondary batteries such as lithium-ion batteries from overcharge, overheating, and overdischarge. The protection circuit 20 includes a protection element 28, a first switching element 29, a second switching element 300, a control unit 25, and a resistor 301.

[0063] In Example 2, one or more secondary battery cells 21 are connected in series to form a battery 22. The battery 22 is mounted in a battery pack. The battery pack has a first external terminal 23 and a second external terminal 24.

[0064] 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. A plurality of fifth terminals 25e of the control unit 25 are connected to the electrodes 21a between the battery cells 21. By connecting the first terminal 25a, the second terminal 25b, and the fifth terminal 25e of the control unit 25 to the first electrode 22a, the second electrode 22b of the battery 22, and the electrode 21a between the battery cells 21, respectively, the control unit 25 monitors the voltage of the battery 22 and the voltage of each battery cell 21.

[0065] 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 control signals to the first switching element 29 and the second switching element 300 according to the voltage of the battery 22 or the battery cell 21.

[0066] A fuse element 26 of a protection element 28 is connected between the first electrode 22a of the battery 22 and the first external terminal 23. The protection element 28 includes the fuse element 26 and a heating resistor 27 for heating the fuse element 26.

[0067] One end of the first switching element 29 is connected to the second electrode 22b 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 between one end and the other end of the first switching element 29 between a conductive state (on state) and a non-conductive state (off state) by outputting a control signal.

[0068] The second switching element 300 and the resistor 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 between one end and the other end of the second switching element 300 between a conductive state (on state) and a non-conductive state (off state) by outputting a control signal.

[0069] The second switching element 300 and the resistance element 301 are connected in series. The first switching element 29 and the second switching element 300 and the resistance element 301 provided in parallel are connected to the heating resistor 27. The heating resistor 27 is also electrically connected to the middle point of the fuse element 26.

[0070] The control unit 25 switches between 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 battery cell 21 is less than 8.4V, the control unit 25 (second protection device IC) turns on the first switching element 29, energizing the heating resistor 27, causing it to heat up and thereby activating the protection element (causing the fuse element 26 of the protection element 28 to melt). When the charging voltage exceeds 43.3V, the control unit 25 (second protection device IC) turns on the second switching element 300, energizing the heating resistor 27 via the resistor element 301, causing it to heat up and thereby activating the protection element.

[0071] The battery pack of Example 3 is a battery pack using the protection circuit 10 of Example 1. That is, it is a battery pack including battery cells of secondary batteries such as lithium-ion batteries, and includes the protection circuit 10 .

[0072] The battery pack of Example 4 is a battery pack using the protection circuit 20 of Example 2. That is, it is a battery pack including battery cells of secondary batteries such as lithium-ion batteries, and includes the protection circuit 20 .

[0073] The electrical device of Example 5 is an electrical device that utilizes the battery pack of Example 3 or the battery pack of Example 4. Specifically, it utilizes a battery pack comprising battery cells of secondary batteries such as lithium-ion batteries. The battery pack is detachably connected to the electrical device. The electrical device includes a device body that charges the battery pack or receives power from the battery pack. The electrical device also includes a charging and discharging device connected to the battery pack.

[0074] Industrial Applicability

[0075] The protection circuit, battery pack, and electrical device of the present invention can be used in electrical and electronic devices using a protection element including a heating resistor and a fuse element, and can be used particularly in a protection device for a battery pack containing a secondary battery.

[0076] While the embodiments of the present invention have been described, the embodiments disclosed herein are intended to be illustrative in all respects and not restrictive. The scope of the present invention is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A protection circuit is provided in a battery pack, which includes: A battery comprising at least one battery cell of a secondary battery, a first external terminal and a second external terminal, wherein the protection circuit comprises: a protection element comprising: a fuse element disposed between the battery and the first external terminal, and a heating resistor for heating the fuse element; a first switching element, one end of which is connected to the battery and the second external terminal, and the other end of which is connected to the heating resistor; A second switching element and a resistance element are arranged in parallel with the first switching element; and a control unit configured to control operations of the first switching element and the second switching element according to a voltage of the battery cell or the battery; The control unit switches the protection circuit between a first state in which the first switching element is turned on to energize the heating resistor and a second state in which the second switching element is turned on to energize the heating resistor via the resistor.

2. The protection circuit according to claim 1, wherein: When the voltage value of the battery cell or the battery is lower than the specified voltage range, the control unit switches the protection circuit to the first state; when the voltage value of the battery cell or the battery is higher than the specified voltage range, the control unit switches the protection circuit to the second state.

3. The protection circuit according to claim 1 or 2, characterized in that: When the resistance value of the heating resistor is set to R1, the rated voltage value of the protection element is set to V1, and the voltage of the battery cell or the battery is set to V2, the resistance value R2 of the resistor element satisfies the relationship R2 = {R1×(V2-V1)} / V1.

4. The protection circuit according to any one of claims 1 to 3, characterized in that: The battery includes a plurality of battery cells; and the control unit controls operations of the first switching element and the second switching element based on voltages of at least one of the battery cells.

5. A battery pack, characterized in that A battery pack comprising the protection circuit according to any one of claims 1 to 4, further comprising: A battery including at least one battery cell of a secondary battery, a first external terminal, and a second external terminal.

6. Electrical equipment, characterized in that The electrical device includes the battery pack according to claim 5, further comprising: a charging and discharging device for charging and discharging the battery pack; and A device main body to which the battery pack is detachably mounted.

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