Protection circuit

Abstract

The protection circuit includes a plurality of protection elements connected in series on the conduction path between the battery and the external circuit. Each of the plurality of protection elements has a fuse unit connected in series on the conduction path and a heating element that generates heat due to energization to heat the fuse unit and cause it to melt. The resistance values of the heating elements of the respective plurality of protection elements are different.

Description

Technical Field

[0001] The present invention relates to a protection circuit.

[0002] This application claims priority based on Japanese Patent Application No. 2019-205362 filed in Japan on November 13, 2019, and the content thereof is incorporated herein by reference. Background Art

[0003] Currently, a protection circuit for cutting off a conduction path in the event of an abnormality such as an overcurrent is provided in the conduction path between a battery and an external circuit. As a protection element, a fuse with a heater (hereinafter also referred to as SCP) is known, which has a fuse unit connected in series in the conduction path and a heating element that generates heat due to energization to heat the fuse unit to cause it to melt (Patent Document 1).

[0004] When an overcurrent exceeding the rated value occurs in the conduction path, the fuse unit of the SCP heats itself and melts, thereby cutting off the conduction path. In addition, in the event of an abnormality other than an overcurrent, the heating element is heated by energization to heat the fuse unit to cause it to melt, thereby cutting off the conduction path.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 2790433 Gazette Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] A current for energizing the heating element of the SCP is supplied from the battery. Therefore, the resistance value of the heating element of the SCP is set to be able to heat the fuse unit to a meltable temperature within the operating voltage range of the battery. However, depending on the use of the battery, sometimes the maximum voltage during charging is much different from the minimum voltage during discharging. Especially in a battery composed of a battery pack formed by combining a plurality of single cells, the voltage difference between the maximum voltage during charging and the minimum voltage during discharging is large. Therefore, if the resistance value of the heating element is set according to the maximum voltage during charging, when an abnormality occurs during discharging, the current flowing through the heating element becomes small, and the heating element sometimes does not heat up to a temperature capable of melting the fuse unit. On the other hand, if the resistance value of the heating element is set according to the minimum voltage during discharging, when an abnormality occurs during charging, an excessive current flows through the heating element, the temperature rapidly becomes high, and the heating element itself sometimes melts. In addition, in recent years, due to changes in the electrode materials of single cells, the operating voltage sometimes varies even with the same number of single cells, and it may deviate from the operating voltage range of the SCP and cannot operate normally.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a protection circuit having a wide voltage range capable of cutting off a conduction path when an abnormality occurs in a conduction path between a battery and an external circuit.

[0011] Means for Solving the Problem

[0012] In order to solve the above problems, the present invention provides the following means.

[0013] (1) The protection circuit according to one aspect of the present invention has a plurality of protection elements connected in series in a conduction path between a battery and an external circuit. Each of the plurality of protection elements has a fuse unit connected in series in the conduction path, and a heating element that generates heat due to energization and heats the fuse unit to melt it. The resistance values of the heating elements of the plurality of protection elements are different from each other.

[0014] (2) In the aspect described in (1) above, it may be configured such that the protection element having the lowest resistance value of the heating element among the plurality of protection elements is arranged on the battery side.

[0015] (3) In the aspect described in (1) or (2) above, it may be configured such that the resistance values of the heating elements of the plurality of protection elements differ by 1 Ω or more.

[0016] Advantages of the Invention

[0017] According to the present invention, it is possible to provide a protection circuit having a wide voltage range capable of cutting off a conduction path when an abnormality occurs in a conduction path between a battery and an external circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 An example of the structure of the protection circuit according to the first embodiment of the present invention is schematically shown.

[0019] Figure 2 An example of the structure of the protection circuit according to the second embodiment of the present invention is schematically shown.

[0020] Figure 3 An example of the structure of the protection circuit according to the third embodiment of the present invention is schematically shown. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, in order to facilitate understanding of the features, parts that become the features may sometimes be enlarged for convenience, and the dimensional ratios of the respective components may sometimes be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and can be appropriately modified within the range that achieves the effects of the present invention for implementation.

[0022] (First Embodiment)

[0023] Figure 1 An example of the structure of the protection circuit according to the first embodiment of the present invention is schematically shown.

[0024] In Figure 1 , the protection circuit 1 includes a first protection element 20a and a second protection element 20b connected in series on the conduction path between the battery 10 and the external circuit. The first protection element 20a is arranged on the side closer to the battery 10, and the second protection element 20b is arranged on the side closer to the external device (not shown). That is, the first protection element 20a is located on the side closer to the positive electrode of the battery 10 than the second protection element 20b.

[0025] The battery 10 is a battery pack formed by combining a plurality of single cells 11. The single cell 11 is a secondary battery, for example, a lithium-ion secondary battery. In Figure 1 , four single cells 11 are connected in series to the battery 10, but the number of single cells 11 is not particularly limited, and the single cells 11 may also be connected in parallel. In addition, the battery 10 may also be a single cell 11.

[0026] The first protection element 20a is an SCP having a first fuse unit 21a and a first heating element 22a connected in series with the positive electrode of the battery 10. One end of the first heating element 22a is connected to the first fuse unit 21a, and the other end is connected to the switching element 40 via the first rectifying element 30a. The switching element 40 is connected to the negative electrode of the battery 10 and the protection IC 50.

[0027] The second protection element 20b is an SCP having a second fuse unit 21b and a second heating element 22b connected in series with the positive electrode of the battery 10. One end of the second heating element 22b is connected to the second fuse unit 21b, and the other end is connected to the switching element 40 via the second rectifying element 30b. In this way, the fuse units of the plurality of protection elements are connected to the same switching element via the heating elements and the rectifying elements. This switching element is connected to the protection.

[0028] The first fuse unit 21a and the second fuse unit 21b have a resistance value such that when an overcurrent exceeding the rated value is generated in the conduction path, they heat up and fuse themselves, thereby being able to cut off the conduction path. Preferably, the current values at which the first fuse unit 21a and the second fuse unit 21b fuse are the same. There are no particular limitations on the structures and materials of the first fuse unit 21a and the second fuse unit 21b. For example, they can be a single metal, or a laminate in which the outer side is a high-melting-point metal layer with a relatively high melting point and the inner side is a low-melting-point metal layer with a relatively low melting point. In the case of a single metal, as its material, In (indium), Pb (lead), Ag (silver), Cu (copper), or an alloy mainly composed of any one of them can be used. In the case of a laminate, preferably, the material of the low-melting-point metal layer is tin or an alloy mainly composed of tin (tin alloy). Preferably, the tin content of the tin alloy is 40% or more by mass, and more preferably 60% or more by mass. Examples of the tin alloy include Sn-Bi alloy, In-Sn alloy, and Sn-Ag-Cu alloy. Preferably, the high-melting-point metal layer is composed of a metal material that is melted by the melt of the low-melting-point metal layer. When the material of the low-melting-point metal layer is tin or a tin alloy, preferably, the material of the high-melting-point metal layer is silver or an alloy mainly composed of silver (silver alloy). Preferably, the silver content of the silver alloy is 40% or more by mass, and more preferably 60% or more by mass. Examples of the silver alloy include Ag-Pd alloy.

[0029] The first heating element 22a and the second heating element 22b each have a resistance value such that they generate heat due to energization and can heat the first fuse unit 21a or the second fuse unit 21b to fuse it. The resistance values of the first heating element 22a and the second heating element 22b are different from each other. That is, the electric powers required for the first heating element 22a and the second heating element 22b to be heated to the temperature at which the fuse unit can be fused are different. Preferably, the difference in the resistance values of the first heating element 22a and the second heating element 22b is 1 Ω or more.

[0030] In the protection circuit 1 of the present embodiment, the resistance value of the first heating element 22a of the first protection element 20a disposed closer to the battery 10 is lower than the resistance value of the second heating element 22b of the second protection element 20b. That is, the first heating element 22a can be heated to the temperature at which the fuse unit can be fused with a small amount of electric power. In the protection circuit of the present embodiment, for example, a plurality of protection elements can be arranged such that the closer the protection element is to the positive electrode side of the battery, the lower its resistance value.

[0031] As long as the first heating element 22a and the second heating element 22b generate heat due to energization, there are no particular restrictions on the structure or material. As the materials constituting the first heating element 22a and the second heating element 22b, ruthenium oxide or carbon black can be used. The resistance values of the first heating element 22a and the second heating element 22b can be adjusted by the dimensions such as the width and thickness, and the composition of the materials of the first heating element 22a and the second heating element 22b.

[0032] The first rectifying element 30a suppresses the current flowing through the second protection element 20b from flowing into the first protection element 20a via the second heating element 22b. The second rectifying element 30b suppresses the current flowing through the first protection element 20a from flowing into the second protection element 20b via the first heating element 22a.

[0033] The protection IC 50 detects an abnormality other than an overcurrent such as the voltage of the conduction path becoming a high voltage, for example, and causes the switching element 40 to operate when an abnormality is detected. By causing the switching element 40 to operate, current flows from the battery 10 to the first heating element 22a via the first rectifying element 30a and to the second heating element 22b via the second rectifying element 30b.

[0034] In the protection circuit 1 of the present embodiment, when an overcurrent exceeding the rated value occurs in the conduction path, the first fuse unit 21a or the second fuse unit 21b generates heat and melts, thereby cutting off the conduction path. The melted fuse unit may be the first fuse unit 21a or the second fuse unit 21b.

[0035] In addition, when an abnormality other than an overcurrent occurs in the conduction path, the protection IC 50 causes the switching element 40 to operate, and current flows from the battery 10 to the first heating element 22a via the first rectifying element 30a and to the second heating element 22b via the second rectifying element 30b. By this energization, both the first heating element 22a and the second heating element 22b generate heat, and one of the first fuse unit 21a or the second fuse unit 21b melts, thereby cutting off the conduction path.

[0036] When an abnormality occurs in a state where the operating voltage of the battery 10 is high (for example, 13V or more and 18.5V or less when four lithium-ion secondary batteries are connected in series), the current flowing through the first heating element 22a and the second heating element 22b increases. At this time, even if the fuse unit is blown due to the rapid temperature rise of the first heating element 22a with a low resistance value, the second heating element 22b with a high resistance value will generate heat and heat the second fuse unit 21b to blow it, thereby cutting off the conduction path. On the other hand, when an abnormality occurs in a state where the operating voltage of the battery 10 is low (for example, 9V or more and less than 13V when four lithium-ion secondary batteries are connected in series), the current flowing through the first heating element 22a and the second heating element 22b decreases. In this case, even if the second heating element 22b with a high resistance value does not heat up to a temperature capable of blowing the second fuse unit 21b, the first heating element 22a with a low resistance value will generate heat and heat the first fuse unit 21a to blow it, thereby cutting off the conduction path.

[0037] In the protection circuit 1 of the present embodiment configured as described above, since the resistance values of the first heating element 22a of the first protection element 20a and the second heating element 22b of the second protection element 20b are different, the voltage range in which the conduction path can be cut off becomes wider. In addition, in the protection circuit 1 of the present embodiment, the first heating element 22a having the first heating element 22a with a low resistance value is arranged closer to the battery 10. Thus, when an abnormality occurs in a state where the operating voltage of the battery 10 is low, the first fuse unit 21a is blown to cut off the conduction path, so that current does not flow through the second protection element 20b. On the other hand, when an abnormality occurs in a state where the operating voltage of the battery 10 is high, the second fuse unit 21b is blown to cut off the conduction path, and the first heating element 22a is blown, so that current does not flow through the first protection element 20a. And, in the protection circuit 1 of the present embodiment, when the difference in resistance values between the first heating element 22a and the second heating element 22b is 1Ω or more, the voltage range in which the conduction path can be cut off can be reliably widened.

[0038] (Second Embodiment)

[0039] Figure 2 Schematically shows an example of the structure of the protection circuit according to the second embodiment of the present invention.

[0040] The difference between the protection circuit 2 of the second embodiment and that of the first embodiment is that two heating elements are respectively connected to switching elements instead of rectifying elements. That is, the first heating element 22a is connected to the first switching element 40a, and the second heating element 22b is connected to the second switching element 40b. The first switching element 40a and the second switching element 40b are respectively connected to the protection IC 50. In this way, in the second embodiment, each heating element of the plurality of protection elements is connected to a switching element. In addition, the switching elements to which the respective heating elements of the plurality of protection elements are connected are connected to the same protection. The protection IC 50 switches the switching element that operates according to the operating voltage of the battery 10. For the parts common to the protection circuit 2 of the second embodiment and the protection circuit 1 of the first embodiment, the same reference numerals are used and the description is omitted.

[0041] In the protection circuit 2 of this embodiment, when an abnormality occurs in a state where the operating voltage of the battery 10 is low, the protection IC 50 causes the first switching element 40a to operate, thereby heating the first heating element 22a to fuse the first fuse unit 21a and cut off the conduction path. On the other hand, when an abnormality occurs in a state where the operating voltage of the battery 10 is high, the protection IC 50 causes the second switching element 40b to operate, heating the second heating element 22b to fuse the second fuse unit 21b and cut off the conduction path.

[0042] The protection circuit 2 of this embodiment configured as described above selects the heating element required to cut off the conduction path through the protection IC 50, and allows the current to flow only through one of the first heating element 22a and the second heating element 22b, so that the heat generated by the protection circuit 2 can be reduced. In addition, since rectifying elements are not used, the number of components can be reduced.

[0043] (Third Embodiment)

[0044] Figure 3 An example of the structure of the protection circuit of the third embodiment of the present invention is schematically shown. The difference between the protection circuit 3 of the third embodiment and that of the first embodiment is that two heating elements are respectively connected to switching elements instead of rectifying elements, and the switching elements are respectively connected to protection ICs. That is, the first heating element 22a is connected to the first switching element 40a, and the first switching element 40a is connected to the first protection IC 50a. On the other hand, the second heating element 22b is connected to the second switching element 40b, and the second switching element 40b is connected to the second protection IC 50b. The abnormal voltage ranges detected by the first protection IC 50a and the second protection IC 50b are different. For the parts common to the protection circuit 3 of the third embodiment and the protection circuit 1 of the first embodiment, the same reference numerals are used and the description is omitted.

[0045] In the protection circuit 3 of the present embodiment, when an abnormality occurs in a state where the operating voltage of the battery 10 is low, the first protection IC 50a detects the abnormality and operates the first switching element 40a, thereby heating the first heating element 22a to fuse the first fuse unit 21a to cut off the conduction path. On the other hand, when an abnormality occurs in a state where the operating voltage of the battery 10 is high, the second protection IC 50b detects the abnormality and operates the second switching element 40b, thereby heating the second heating element 22b to fuse the second fuse unit 21b to cut off the conduction path. Thus, in the third embodiment, the plurality of fuse units are connected to their respective protections via their respective heating elements and switching elements.

[0046] In the protection circuit 3 of the present embodiment configured as described above, current only flows through one of the first heating element 22a and the second heating element 22b, so the heat generated in the protection circuit 3 can be reduced. In addition, since rectifying elements are not used, the number of components can be reduced. Moreover, since there is no need for a protection IC to switch the operating switching element, the structure of the protection IC can be simplified.

[0047] As described above, the embodiments of the present invention have been described in detail, but the present invention is not limited to the above embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the protection scope.

[0048] For example, in the present embodiment, two protection elements, i.e., the first protection element 20a and the second protection element 20b, are used, but as long as there are two or more protection elements, the number thereof is not limited. When three or more protection elements are used, it is preferable to arrange the protection elements with lower resistance values of the heating elements in order starting from the side closer to the battery 10.

[0049] Industrial application

[0050] The protection circuit of the present invention can be used as a battery management system (BMS: Battery Management System) for a battery with a wide operating voltage range.

[0051] Explanation of reference numerals

[0052] 1, 2, 3 Protection circuit

[0053] 10 Battery

[0054] 11 Single cell

[0055] 20a First protection element

[0056] 20b Second protection element

[0057] 21a First fuse unit

[0058] 21b Second fuse unit

[0059] 22a First heating element

[0060] 22b Second heating element

[0061] 30a First rectifying element

[0062] 30b Second rectifying element

[0063] 40 Switching element

[0064] 40a First switching element

[0065] 40b Second switching element

[0066] 50 Protection IC

[0067] 50a First protection IC

[0068] 50b Second protection IC.

Claims

1. A protection circuit, characterized in that, the protection circuit includes a plurality of protection elements connected in series on the conduction path between the battery and the external circuit, each of the plurality of protection elements connected in series has two fuse units connected in series on the conduction path, and a heating element with one end connected to the connection point of the two fuse units connected in series and the other end connected to the battery via a switching element, which generates heat due to energization to heat the fuse unit and cause it to melt, the resistance values of the heating elements respectively included in the plurality of protection elements are set such that the closer the protection element is to the positive electrode side of the battery, the lower the resistance value.

2. The protection circuit according to claim 1, characterized in that, the resistance values of the heating elements of the plurality of protection elements differ by 1 Ω or more.

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