Protection element and protection circuit

Abstract

A protection element (1) comprises: an insulating substrate (2); a first electrode (11) and a second electrode (12); a first lower electrode (21) and a second lower electrode (22); a heat-generating body (3); a first heat-generating body electrode and a second heat-generating body electrode; an insulating member (5); a third lower electrode (13); and a fusible conductor (4). In a plan view seen from a first surface (2a) side of the insulating substrate (2), the fusible conductor (4) is connected to the first electrode (11) and the second electrode (12) in a manner of bridging between the first electrode (11) and the second electrode (12). In the plan view, a portion of the heat-generating body (3), a portion of the first electrode (11), and a portion of the fusible conductor (4) are provided overlapping each other.

Description

Protection elements and protection circuits

[0001] The present invention relates to a protective element and a protective circuit. The present invention claims priority based on Japanese Patent Application No. 2024-228465 filed in Japan on December 25, 2024, Japanese Patent Application No. 2025-061058 filed in Japan on April 2, 2025, and Japanese Patent Application No. 2025-246374 filed in Japan on December 12, 2025, the contents of which are incorporated herein by reference.

[0002] Conventionally, protection circuits have been implemented in various mobile devices equipped with secondary batteries, such as mobile phones and portable computers. A conventional protection circuit is a secondary battery device having a power storage device, multiple protection circuits, and first and second output terminals (Patent Document 1). In the secondary battery device of Patent Document 1, each of the multiple protection circuits has two fuse elements connected in series. The secondary battery device of Patent Document 1 is configured such that when an external circuit is connected to the first and second output terminals, the discharge current supplied from the power storage device to the external circuit and the charging current supplied from the external circuit to the power storage device flow through the two fuse elements connected in series within the multiple protection circuits.

[0003] In the secondary battery device of Patent Document 1, each protection circuit has a heater, one end of which is connected to the connection point between fuse elements. The other end of each heater is connected to one end of a rectifier element. The other end of each rectifier element is connected to a switch element. The secondary battery device is configured such that when the switch element conducts, current flows to the heater of each protection circuit through the switch element and each rectifier element.

[0004] In addition, in the secondary battery device of Patent Document 1, at least two rectifying elements are inserted in the middle of the current path connecting the terminals of the heater of the protection circuit. In the secondary battery device of Patent Document 1, even when a short-circuit current flows and a voltage difference occurs between the terminals of the heaters of the two protection circuits in a state where one fuse element is blown, at least one rectifying element is reverse-biased. In the secondary battery device of Patent Document 1, no current flows from the terminal of the heater of one protection circuit to the terminal of the heater of the other protection circuit, so that no residual current is generated thereby.

[0005] Japanese Patent No. 4095426

[0006] In the protection circuit of Patent Document 1, since the fuse with a heater has a bilaterally symmetric structure, when current interruption is performed, the probability that one of the two fuse elements is interrupted is 50%. Therefore, when a plurality of protection circuits are connected in parallel, it is impossible to specify which of the two fuse elements in each protection circuit is the part where the current is interrupted. Therefore, depending on the part where the interruption occurs in each protection circuit, a circulating current may occur in the secondary battery device, and an overcurrent may flow from the power storage device to the external circuit. Therefore, in order to prevent an overcurrent in the entire system, a plurality of rectifying elements (diodes) corresponding one-to-one to the plurality of protection circuits must be mounted. When a plurality of rectifying elements (diodes) are mounted, there are problems such as circuit complexity, cost increase, and an increase in the failure rate of the device due to an increase in the number of parts.

[0007] In addition, since the protection circuit has two fuse elements connected in series, there is a problem that the resistance value (conductor resistance) during energization becomes high. In addition, in recent years, as mobile devices have become more high-performance and highly functional, with a further increase in the charging capacity of secondary batteries, a highly safe protection circuit that can surely prevent overcurrents is required.

[0008] One of the objectives of the present invention is to provide a protective element and protective circuit that can reliably prevent overcurrent and improve safety, achieve cost reduction with a simpler device configuration than conventional devices, further reduce the failure rate of the device, and lower the conductor resistance when energized.

[0009] To solve the above problems, the present invention provides the following means.

[0010] [Aspect 1 of the present invention] An insulating substrate; a first electrode and a second electrode provided on the first surface of the insulating substrate so as to face each other; a first lower electrode provided on the second surface of the insulating substrate opposite to the first surface and connected to the first electrode; a second lower electrode provided on the second surface of the insulating substrate and connected to the second electrode; a heating element provided on the first surface or the second surface of the insulating substrate; a first heating element electrode connected to one end of the heating element and the first electrode; a second heating element electrode connected to the other end of the heating element opposite to the one end; an insulating member covering the surface of the heating element; a third lower electrode provided on the second surface of the insulating substrate and connected to the second heating element electrode; and a fusible conductor provided on the first surface of the insulating substrate, wherein in a plan view from the first surface of the insulating substrate, the fusible conductor is connected to the first electrode and the second electrode so as to span between them. In the plan view, a protective element is provided such that a part of the heating element, a part of the first electrode, and a part of the fusible conductor overlap each other.

[0011] [Aspect 2 of the present invention] The protective element according to aspect 1, wherein, in the plan view, the area of ​​the first electrode is larger than the area of ​​the second electrode.

[0012] [Aspect 3 of the present invention] The protective element according to aspect 2, wherein, in the plan view, when the area of ​​the insulating substrate is A0 and the area of ​​the first electrode is A1, the condition 0.15 ≤ A1 / A0 ≤ 0.70 is satisfied.

[0013] [Aspect 4 of the present invention] The protective element according to any one of aspects 1 to 3, wherein the fusible conductor is a laminate comprising a high-melting-point metal layer and a low-melting-point metal layer.

[0014] [Aspect 5 of the present invention] The protective element according to aspect 4, wherein the high melting point metal layer is made of Ag or Cu, or a metal mainly composed of Ag or Cu, and the low melting point metal layer is made of Sn or a metal mainly composed of Sn.

[0015] [Aspect 6 of the present invention] The protective element according to any one of aspects 1 to 5, wherein the heating element is provided on the first surface side of the insulating substrate, and the insulating member is provided between the heating element and the first electrode, or both between the heating element and the first electrode and between the heating element and the insulating substrate, in the portion where the heating element and the first electrode overlap each other in the plan view.

[0016] [Aspect 7 of the present invention] The protective element according to any one of claims 1 to 5, wherein the heating element is provided on the second surface side of the insulating substrate.

[0017] [Aspect 8 of the present invention] The protective element according to any one of claims 1 to 7, wherein the fusible conductor is connected to the first electrode and the second electrode via a connecting member made of solder.

[0018] [Aspect 9 of the present invention] The protective element according to aspect 4 or 5, wherein the fusible conductor is connected to the first electrode and the second electrode via a connecting member made of solder or via the low-melting-point metal layer.

[0019] [Aspect 10 of the present invention] A protective circuit comprising one or more protective elements, wherein the protective element comprises: an insulating substrate; a first electrode and a second electrode provided on the first surface side of the insulating substrate so as to face each other; a first lower electrode provided on the second surface side of the insulating substrate opposite to the first surface side and connected to the first electrode; a second lower electrode provided on the second surface side of the insulating substrate and connected to the second electrode; a heating element provided on the first surface side or the second surface side of the insulating substrate; a first heating element electrode connected to one end of the heating element and the first electrode; a second heating element electrode connected to the other end of the heating element opposite to the one end; an insulating member covering the surface of the heating element; a third lower electrode provided on the second surface side of the insulating substrate and connected to the second heating element electrode; and a fusible conductor provided on the first surface side of the insulating substrate. In a plan view from the first surface side of the insulating substrate, the fusible conductor is connected to the first electrode and the second electrode so as to span between them, and in the plan view, a part of the heating element, a part of the first electrode, and a part of the fusible conductor are arranged to overlap each other, in a protective circuit.

[0020] [Aspect 11 of the present invention] A protection circuit according to aspect 10, further comprising a secondary battery, an external positive terminal and an external negative terminal, a switching element, and a control device, wherein the protection element is provided in the current path between the positive terminal of the secondary battery and the external positive terminal, or between the negative terminal of the secondary battery and the external negative terminal, and the switching element is switched to conduct current by a signal from the control device, thereby blocking the connection between the secondary battery and the external positive terminal, or between the secondary battery and the external negative terminal.

[0021] [Aspect 12 of the present invention] A protection circuit according to aspect 10, further comprising: a secondary battery; an external positive terminal and an external negative terminal; a switching element; and a control device, wherein a plurality of protection elements are provided; the plurality of protection elements are connected in parallel between the positive terminal of the secondary battery and the external positive terminal, or between the negative terminal of the secondary battery and the external negative terminal; all of the first lower electrodes of each of the plurality of protection elements are connected to the same terminal; all of the second lower electrodes of each of the plurality of protection elements are connected to the same terminal; all of the third lower electrodes of each of the plurality of protection elements are connected to the same terminal in the switching element; and the switching element is switched to conduct electricity by a signal from the control device, thereby blocking the connection between the secondary battery and the external positive terminal, or between the secondary battery and the external negative terminal.

[0022] [Aspect 13 of the present invention] The protection circuit according to aspect 11 or 12, wherein the control device stops supplying power to the heating element after a predetermined time has elapsed since the switching element was switched to be energized.

[0023] According to the above-mentioned aspects of the present invention, overcurrent can be reliably prevented to improve safety, costs can be reduced with a simpler device configuration than conventional devices, the failure rate of the device can be reduced, and the conductor resistance during energization can be lowered.

[0024] This is a top view of the protective element of the first embodiment. This is a bottom view of the protective element of the first embodiment. This is a cross-sectional view taken along the line III-III in Figure 1, where Figure 3(A) shows the protective element of the first embodiment and Figure 3(B) shows the protective element of the first modified example of the first embodiment. This is a cross-sectional view taken along the line IV-IV in Figure 1. This shows the circuit configuration of the protective element of the first embodiment. This is a diagram illustrating a first example of the protective element of the comparative example before and after the operation of the heating element. This is a diagram illustrating a first example of the protective element of the first embodiment before and after the operation of the heating element. This is a diagram illustrating a second example of the protective element of the comparative example before and after the operation of the heating element. This is a diagram illustrating a second example of the protective element of the first embodiment before and after the operation of the heating element. This is a schematic circuit diagram showing the configuration of the protective circuit of the first embodiment. This is a diagram illustrating an example of current interruption performed by the protective circuit of Figure 10. This is a top view of the protective element of the second embodiment. This is a cross-sectional view taken along the line XIII-XIII in Figure 12. This shows the circuit configuration of the protective element of the second embodiment. This is a schematic circuit diagram showing the configuration of the protective circuit of the second embodiment. This is a diagram illustrating an example of current interruption performed by the protective circuit of Figure 15. This is a schematic circuit diagram showing the configuration of the protection circuit of the third embodiment. This is a diagram illustrating an example of current interruption performed by the protection circuit of Figure 17. This is a schematic circuit diagram showing the configuration of the protection circuit of the fourth embodiment. This is a diagram illustrating an example of current interruption performed by the protection circuit of Figure 19. This is a diagram showing the protection element of the fifth embodiment, and is a cross-sectional view corresponding to Figure 3. This is a top view of the protection element of the sixth embodiment. This is a bottom view of the protection element of the sixth embodiment. This is a cross-sectional view taken from XXIV-XXIV in Figure 23. This is a top view showing the protection element of the first modified example of the sixth embodiment. This is a cross-sectional view taken from XXVI-XXVI in Figure 25. This is a top view of the protection element of the seventh embodiment. This is a cross-sectional view taken from XXVIII-XXVIII in Figure 27. This is a diagram showing the electrical characteristics of the comparative example and the example.

[0025] The embodiments will be described in detail below, with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience to clearly illustrate the features, and the dimensional ratios of each component may differ from those in reality. The materials, dimensions, etc., exemplified in the following description are examples only, and the present invention is not limited to them. It is possible to modify and implement the invention as appropriate within the scope of achieving its effects.

[0026] (Protection Element) Figure 1 is a top view of the protection element 1 of the first embodiment. Figure 2 is a bottom view of the protection element 1 of the first embodiment. Figure 3 is a cross-sectional view taken along line III-III of Figure 1, where Figure 3(A) shows the protection element 1 of the first embodiment, and Figure 3(B) shows the protection element 1A of the first modified example of the first embodiment. Figure 4 is a cross-sectional view taken along line IV-IV of Figure 1. Figure 5 shows the circuit configuration of the protection element 1 of the first embodiment. Figure 1 corresponds to a plan view taken from the first surface 2a side of the insulating substrate 2. Figure 2 corresponds to a plan view taken from the second surface 2b side of the insulating substrate 2. Referring to Figures 1 to 5, the protective element 1 comprises an insulating substrate 2, a first electrode 11 and a second electrode 12, a first lower electrode 21, a second lower electrode 22, a heating element 3, a first heating element electrode 23, a second heating element electrode 24, an insulating member 5, a third lower electrode 13, and a fusible conductor 4. In Figure 3, the third lower electrode 13 is shown by a dashed line.

[0027] The insulating substrate 2 is not particularly limited as long as it is made of an insulating material. For example, the insulating substrate 2 can be a ceramic substrate or a glass epoxy substrate, which are substrates used in printed circuit boards, as well as a glass substrate, a resin substrate, an insulating treated metal substrate, etc. Among the above, a ceramic substrate is preferred as the insulating substrate 2 because it has excellent heat resistance and good thermal conductivity.

[0028] The insulating substrate 2 is formed in the shape of a rectangular plate when viewed from above. In the example shown in Figure 1, the insulating substrate 2 is formed in the shape of a rectangle. The insulating substrate 2 has a first surface 2a on one side in the thickness direction of the insulating substrate 2. The insulating substrate 2 has a second surface 2b on the other side (opposite to the first surface 2a) in the thickness direction of the insulating substrate 2.

[0029] In the following, we will set an XYZ Cartesian coordinate system (3D Cartesian coordinate system) in each figure and explain each configuration. In a plan view, the longitudinal direction of the insulating substrate 2 corresponds to the X direction in each figure. In a plan view, the short direction of the insulating substrate 2 corresponds to the Y direction in each figure. The thickness direction of the insulating substrate 2 corresponds to the Z direction in each figure. In the Z direction, the +Z side corresponds to the upper side, and the -Z side corresponds to the lower side.

[0030] In the following explanation, "upper side" and "lower side" are convenient names used to clearly explain the relative positional relationship of each component, and the actual arrangement may differ from those indicated by these names.

[0031] The first electrode 11 and the second electrode 12 function as fuse terminals. The first electrode 11 and the second electrode 12 are provided on the first surface 2a side of the insulating substrate 2, facing each other. Metal materials such as Ag (silver) and Cu (copper) can be used as the materials constituting the first electrode 11 and the second electrode 12. The surfaces of the first electrode 11 and the second electrode 12 may be coated with a metal or alloy such as Ag, Ag-Pt (platinum), Ag-Pd (palladium), Au (gold), or Ni (nickel)-Au. It is preferable that the materials constituting the first electrode 11 and the second electrode 12 are the same, but they may be different. The materials constituting the first electrode 11 and the second electrode 12 are not limited to those described above and can be changed according to the design specifications.

[0032] The first electrode 11 is formed in a shape that is elongated in the X direction when viewed from above. When viewed from above, the maximum dimension of the first electrode 11 in the X direction is larger than the dimension of the fusible conductor 4 in the X direction, and is larger on the -Y side than the first end 4a of the fusible conductor 4. The first electrode 11 has a portion that contains the molten fusible conductor 4 (molten material). The first electrode 11 is the electrode into which the molten fusible conductor 4 flows. Preferably, the first electrode 11 is a metal that has good wettability with the molten fusible conductor 4. The first electrode 11 may be composed of multiple printed layers.

[0033] In the example shown in Figure 3, the first electrode 11 has a crank shape that is elongated in the Y direction when viewed in cross-section. The first electrode 11 has, when viewed in cross-section, a base portion 11a formed on the -Y end side of the insulating substrate 2 and having a Z-direction dimension (thickness) that is thicker than the thickness of the fusible conductor 4, and an extended portion 11b that is integrally formed with the base portion 11a, having a uniform thickness that extends from the +Y end and upper end side of the base portion 11a to the +Y side of the insulating member 5, and having a thickness that is thinner than the base portion 11a. The thickness of the base portion 11a may be less than or equal to the thickness of the fusible conductor 4. The thickness of the extended portion 11b may be greater than or equal to the thickness of the base portion 11a.

[0034] The second electrode 12 is formed in a shape that is elongated in the Y direction when viewed from above. When viewed from above, the maximum dimension of the second electrode 12 in the X direction is larger than the X-direction dimension of the fusible conductor 4, and is larger on the +Y side than the second end 4b of the fusible conductor 4. The second electrode 12 has a portion that contains the molten fusible conductor 4 (molten material). The second electrode 12 is the electrode into which the molten fusible conductor 4 flows. Preferably, the second electrode 12 is a metal with good wettability with the molten fusible conductor 4. The second electrode 12 may be composed of multiple printed layers.

[0035] In the example shown in Figure 3, the second electrode 12 is formed on the +Y end side of the insulating substrate 2 in cross-sectional view and has a shape in which the Z-direction dimension (thickness) is thicker than the thickness of the fusible conductor 4. Preferably, the thickness of the second electrode 12 is the same as the thickness of the base portion 11a of the first electrode 11, but it may be different. The thickness of the second electrode 12 may be less than or equal to the thickness of the fusible conductor 4.

[0036] The first lower electrode 21 is provided on the second surface 2b of the insulating substrate 2, opposite to the first surface 2a. The first lower electrode 21 is connected to the first electrode 11. The first lower electrode 21 is formed on the -Y end side of the lower surface of the insulating substrate 2. The first lower electrode 21 is connected, for example, to the wiring of a circuit board.

[0037] The second lower electrode 22 is provided on the second surface 2b side of the insulating substrate 2. The second lower electrode 22 is connected to the second electrode 12. The second lower electrode 22 is formed on the +Y end side of the lower surface of the insulating substrate 2, spaced apart from the first lower electrode 21 in the Y direction. The second lower electrode 22 is connected, for example, to the wiring of a circuit board.

[0038] Metallic materials such as Ag (silver) and Cu (copper) can be used as the materials constituting the first lower electrode 21 and the second lower electrode 22. The materials constituting the first lower electrode 21 and the second lower electrode 22 may be the same as or different from the materials constituting the first electrode 11 and the second electrode 12.

[0039] At positions corresponding to the first lower electrode 21 and the second lower electrode 22, through holes 35 and 36 that are perfect circles in plan view are provided respectively. The first lower electrode 21 and the second lower electrode 22 are connected to the first electrode 11 and the second electrode 12 through conductive portions 27 and 28 such as solder in the through holes 35 and 36 respectively.

[0040] In the examples of FIGS. 3 and 5, only one heating element 3 is provided in the protection element 1. Note that the number of heating elements 3 provided in the protection element 1 may be two or more and can be changed according to the design specifications.

[0041] The heating element 3 is formed of a high-resistance conductive material that has a relatively high resistance compared to the third lower electrode 13 and is likely to generate heat when energized. As the material constituting the heating element 3, for example, conductive materials such as ruthenium oxide and carbon black can be used. The material constituting the heating element 3 is not limited to the above and can be changed according to the design specifications.

[0042] The heating element 3 is provided on the first surface 2a side of the insulating substrate 2. The heating element 3 is disposed below the central portion of the soluble conductor 4 in the Y direction on the central side in the Y direction on the first surface 2a of the insulating substrate 2. The heating element 3 is disposed on the central side in the Y direction of the upper surface of the insulating substrate 2 with a gap from the base portion 11a of the first electrode 11 and a gap from the second electrode 12 in the Y direction.

[0043] The heating element 3 is covered with an insulating member 5. The material constituting the insulating member 5 is not particularly limited as long as it can insulate the heating element 3 from the outside. For example, insulating materials such as ceramics and glass can be used.

[0044] The insulating member 5 is provided between the heating element 3 and the first electrode 11 at a portion where the heating element 3 and the first electrode 11 overlap each other in plan view. In the example of FIG. 3(A), the insulating member 5 is formed so as to cover the outer surface of the heating element 3 in cross-sectional view and is interposed between the lower surface of the extending portion 11b of the first electrode 11 and the upper surface of the heating element 3.

[0045] In the example of FIG. 3(B), the protection element 1A includes insulating members 5 and 6 both between the heating element 3 and the first electrode 11 and between the heating element 3 and the insulating substrate 2. In the example of FIG. 3(B), the insulating member 5 is formed so as to cover the outer surface of the heating element 3 in a cross-sectional view and is interposed between the lower surface of the extending portion 11b of the first electrode 11 and the upper surface of the insulating member 6. The insulating member 6 is interposed between the upper surface of the insulating substrate 2 and the lower surface of the heating element 3.

[0046] The heating element 3 is connected to the third lower electrode 13 and the fourth electrode 14 (see FIG. 5). The third lower electrode 13 functions as a heater terminal. The fourth electrode 14 functions as a heating element lead-out electrode. In the example of FIG. 2, the third lower electrode 13 is provided on the second surface 2b side of the insulating substrate 2. The third lower electrode 13 is connected to the second heating element electrode 24. The third lower electrode 13 is formed at the +X end side of the lower surface of the insulating substrate 2.

[0047] As materials constituting the third lower electrode 13 and the fourth electrode 14, metal materials such as Ag (silver) and Cu (copper) can be used. The materials constituting the third lower electrode 13 and the fourth electrode 14 may be the same as or different from the materials constituting the first electrode 11 and the second electrode 12.

[0048] The first heating element electrode 23 is connected to one end of the heating element 3 and the first electrode 11. In the example of FIG. 1, the first heating element electrode 23 is connected to the -X end of the heating element 3 and the -X end of the first electrode 11. The first heating element electrode 23 is provided on the first surface 2a side of the insulating substrate 2. The first heating element electrode 23 is formed at the -X end side of the upper surface of the insulating substrate 2.

[0049] The second heating element electrode 24 is connected to the other end facing one end of the heating element 3. In the example of FIG. 1, the second heating element electrode 24 is connected to the +X end of the heating element 3. The second heating element electrode 24 is provided on the first surface 2a side of the insulating substrate 2. The second heating element electrode 24 is formed at the +X end side of the upper surface of the insulating substrate 2 with a gap from the first heating element electrode 23 in the X direction.

[0050] Metallic materials such as Ag (silver) and Cu (copper) can be used as the materials constituting the first heating element electrode 23 and the second heating element electrode 24. The materials constituting the first heating element electrode 23 and the second heating element electrode 24 may be the same as or different from the materials constituting the first electrode 11 and the second electrode 12.

[0051] In the examples shown in Figures 3 and 5, only one fusible conductor 4 is provided in the protective element 1. However, the number of fusible conductors 4 installed in the protective element 1 may be two or more, and can be changed according to the design specifications.

[0052] The fusible conductor 4 is not particularly limited in its composition or material as long as it can be melted and cut by heat, but it is preferably made of a low-melting-point metal. Low-melting-point metals are composed of, for example, Sn or alloys mainly composed of Sn. Since the melting point of Sn is 232°C, metals mainly composed of Sn have a low melting point and become soft at low temperatures. In addition, various low-melting-point metals that have been conventionally used as fuse materials can be used. Examples of low-melting-point metals include SnSb alloy, BiSnPb alloy, BiPbSn alloy, BiPb alloy, BiSn alloy, SnPb alloy, SnAg alloy, PbIn alloy, ZnAl alloy, InSn alloy, PbAgSn alloy, etc. The material constituting the fusible conductor 4 is not limited to the above and can be changed according to the design specifications.

[0053] The fusible conductor 4 is provided on the first surface 2a side of the insulating substrate 2. In the example shown in Figure 1, the fusible conductor 4 is formed in a rectangular shape that is elongated in the Y direction when viewed from above. The fusible conductor 4 has a first end 4a and a second end 4b that face each other. The first end 4a of the fusible conductor 4 corresponds to the -Y end of the fusible conductor 4. The second end 4b of the fusible conductor 4 corresponds to the +Y end of the fusible conductor 4. In a plan view from the first surface 2a side of the insulating substrate 2, the fusible conductor 4 is connected to the first electrode 11 and the second electrode 12 so as to span between them. The first end 4a of the fusible conductor 4 is connected to the first electrode 11. The second end 4b of the fusible conductor 4 is connected to the second electrode 12.

[0054] It should be noted that the fusible conductor 4 is not limited to being formed in a rectangular shape when viewed from above, with its first end 4a connected to the first electrode 11 and its second end 4b connected to the second electrode 12. For example, if the fusible conductor 4 is formed in a circular shape when viewed from above, or in a shape without ends, it is sufficient if a part of the fusible conductor 4 is connected to each electrode 11, 12.

[0055] The fusible conductor 4 is connected to the first electrode 11 and the second electrode 12 via connecting members 25 and 26 made of solder. In the example shown in Figure 3, the first end 4a of the fusible conductor 4 is connected to the upper surface of the first electrode 11 via the connecting member 25 made of solder. The second end 4b of the fusible conductor 4 is connected to the upper surface of the second electrode 12 via the connecting member 26 made of solder. Note that the fusible conductor 4 may be connected to the first electrode 11 and the second electrode 12 via conductive connecting members other than solder.

[0056] The fusible conductor 4 is made of a metal plate-like member, sheet-like member, or metal foil, etc. The fusible conductor 4 has a shape that extends in a plane direction perpendicular to the Z direction (XY plane direction). In the example in Figure 1, the fusible conductor 4 has a rectangular plate shape in plan view, where the dimension in the Y direction is larger than the dimension in the X direction. In the example in Figure 3, the fusible conductor 4 has a uniform thickness along the Y direction. The shape of the fusible conductor 4 is not limited to the above, and may be, for example, a thin flake or a rod.

[0057] Semicircular half-through holes (castellars) 31, 32, 33, and 34 are provided in plan view at positions corresponding to the first electrode 11, the second electrode 12, the first heating element electrode 23, and the second heating element electrode 24, respectively. The first electrode 11, the second electrode 12, the first heating element electrode 23, and the second heating element electrode 24 are connected to an external circuit (protection circuit 100) via solder at the castellars 31, 32, 33, and 34, respectively.

[0058] In the protective element 1 of this embodiment, when a large current exceeding the rated value flows through the protective element 1, the fusible conductor 4 (fuse element) melts due to self-heating (Joule heating), or the fusible conductor 4 melts due to the heat generated by the heating element 3, thereby interrupting the current path.

[0059] For example, the first electrode 11, the second electrode 12, the first heating element electrode 23, and the second heating element electrode 24 are connected to the wiring of the circuit board via solder in castellations 31, 32, 33, and 34, respectively. When an overcurrent flows through the wiring of the circuit board, the overcurrent flows to the fusible conductor 4 via the first electrode 11 and the second electrode 12 of the protection element 1. When an overcurrent flows through the fusible conductor 4, Joule heat is generated in the fusible conductor 4, and this heat causes the fusible conductor 4 to melt and break, thereby interrupting the current path of the circuit board. Also, when an abnormality other than an overcurrent occurs in the circuit board, current flows through the third lower electrode 13, causing the heating element 3 to heat up, and this heat is transferred to the fusible conductor 4, causing the fusible conductor 4 to melt and break, thereby interrupting the current path of the circuit board. The molten material of the fusible conductor 4 after melting is held on the first electrode 11.

[0060] Next, an example of the portion in which the heating element 3, the first electrode 11, and the fusible conductor 4 overlap in the protective element 1 of this embodiment will be described. In this embodiment, in a plan view, a part of the heating element 3, a part of the first electrode 11, and a part of the fusible conductor 4 are arranged to overlap each other. In the example of Figure 3, the protective element 1 has an overlapping portion 40 in which the heating element 3, the extended portion 11b of the first electrode 11, the +Y side portion of the connecting member 25, and the Y-direction central portion of the fusible conductor 4 overlap each other in the Z direction. In the Y direction, a space 41 is formed between the overlapping portion 40 and the second electrode 12 and the connecting member 26.

[0061] In this embodiment, in a plan view, the area A1 of the first electrode 11 is larger than the area A2 of the second electrode 12. In a plan view, the area A1 of the first electrode 11 corresponds to the area of ​​the upper surface of the first electrode 11. When the entire upper surface of the first electrode 11 is covered by the connecting member 25, in a plan view, the area A1 of the first electrode 11 corresponds to the area of ​​the upper surface of the connecting member 25. In a plan view, the area A2 of the second electrode 12 corresponds to the area of ​​the upper surface of the second electrode 12. When the entire upper surface of the second electrode 12 is covered by the connecting member 26, in a plan view, the area A2 of the second electrode 12 corresponds to the area of ​​the upper surface of the connecting member 26.

[0062] In a plan view, when the area of ​​the insulating substrate 2 is A0 and the area of ​​the first electrode 11 is A1, the following conditions are met: 0.15 ≤ A1 / A0 ≤ 0.70. In a plan view, the area A0 of the insulating substrate 2 corresponds to the area of ​​the upper surface of the insulating substrate 2. It is more preferable that the following conditions are met: 0.20 ≤ A1 / A0 ≤ 0.65, and even more preferable that the following conditions are met: 0.25 ≤ A1 / A0 ≤ 0.60.

[0063] Next, we will describe examples of the operation of the heating element 3 of the protective element 1 of this embodiment before and after, together with a comparative example. Figure 6 is a diagram illustrating a first example of the operation of the heating element 3X of the protective element 1X of the comparative example before and after. Figures 6(a) and (b) correspond to the plan view and cross-sectional view of the heating element 3X of the protective element 1X of the comparative example before operation, respectively. Figures 6(c) and (d) correspond to the plan view and cross-sectional view of the heating element 3X of the protective element 1X of the comparative example after operation, respectively. As shown in Figure 6, the protective element 1X of the comparative example has two fuse elements 4AX and 4BX connected in series, and a heating element 3X and a central electrode 15X that overlap between the two fuse elements 4AX and 4BX in a plan view.

[0064] In the comparative example, after the operation of the heating element 3X shown in Figures 6(c) and 6(d), the molten material of the two fuse elements 4AX and 4BX (the molten material of the fuse elements 4AX and 4BX on both sides of the central electrode 15X) that melted due to the operation of the heating element 3X is contained on the central electrode 15X. In the comparative example, the molten material on the central electrode 15X is formed in a semi-circular shape when viewed in cross-section. In the comparative example, it may be difficult to secure space on the central electrode 15X to contain the molten material when the heating element 3X is operating.

[0065] Figure 7 illustrates a first example of the protective element 1's heating element 3 before and after operation. Figures 7(a) and 7(b) correspond to a plan view and a cross-sectional view of the protective element 1's heating element 3 before operation, respectively. Figures 7(c) and 7(d) correspond to a plan view and a cross-sectional view of the protective element 1's heating element 3 after operation, respectively. As shown in Figure 7, in this embodiment, after the heating element 3 is operated as shown in Figures 7(c) and 7(d), the molten material of the fusible conductor 4 melted by the operation of the heating element 3 is contained on the connecting member 25 (first electrode 11). In this embodiment, compared to the central electrode 15X of the comparative example, the area for containing the molten material on the connecting member 25 (first electrode 11) is larger, allowing for the containment of more molten material. In this embodiment, compared to the comparative example, it is easier to secure space for containing the molten material on the first electrode 11 during the operation of the heating element 3.

[0066] Incidentally, in order to reduce the conductor resistance of the fuse element in order to cope with high currents, the cross-sectional area (volume) of the fuse element is sometimes increased. Next, referring to Figures 8 and 9, other examples of the operation of the heating element 3 of the protection element 1 of this embodiment (examples in which the cross-sectional area of ​​the fuse element is larger than that of the examples in Figures 6 and 7) will be explained, along with comparative examples.

[0067] Figure 8 illustrates a second example of the heating element 3X of the comparative example's protective element 1X before and after operation. Figures 8(a) and 8(b) correspond to the plan view and cross-sectional view of the heating element 3X of the comparative example's protective element 1X before operation, respectively. Figures 8(c) and 8(d) correspond to the plan view and cross-sectional view of the heating element 3X of the comparative example's protective element 1X after operation, respectively. As shown in Figure 8, in the comparative example, if the cross-sectional area of ​​the fuse elements 4AX and 4BX is larger than a predetermined value, it becomes difficult for the heating element 3X to melt and cut the fuse elements 4AX and 4BX. In the comparative example, if the cross-sectional area of ​​the fuse elements 4AX and 4BX is too large, the molten material of the two fuse elements 4AX and 4BX melted by the operation of the heating element 3X may not be able to be contained on the central electrode 15X.

[0068] Figure 9 illustrates a second example of the operation of the heating element 3 of the protective element 1 in the first embodiment, before and after operation. Figures 9(a) and 9(b) correspond to the plan view and cross-sectional view of the heating element 3 of the protective element 1 in this embodiment before operation, respectively. Figures 9(c) and 9(d) correspond to the plan view and cross-sectional view of the heating element 3 of the protective element 1 in this embodiment after operation, respectively. As shown in Figure 9, in this embodiment, the central electrode 15X of the comparative example is replaced with a first electrode 11, and the molten material containment area (area that can contain) is larger than that of the comparative example, so even if the cross-sectional area of ​​the fusible conductor 4 is larger than a predetermined size, it is easy to melt and cut the fusible conductor 4 with the operation of the heating element 3.

[0069] (Protection Circuit) Figure 10 is a schematic circuit diagram showing the configuration of the protection circuit 100 of the first embodiment. The protection circuit 100 comprises one or more protection elements 1. In the example of Figure 10, two protection elements 1 shown in Figure 5 are mounted on the protection circuit 100. The protection circuit 100 constitutes a circuit within a battery pack of a lithium-ion secondary battery, for example. The number of protection elements 1 mounted on the protection circuit 100 may be one or three or more, and can be changed according to the design specifications.

[0070] As shown in Figure 10, in the protection circuit 100, two protection elements 1 are connected in parallel. The protection circuit 100 further comprises a secondary battery 50, an external positive terminal 61 and an external negative terminal 62, switching elements 71, 72, and 73, and control devices 81 and 82. Multiple protection elements 1 are provided. Multiple protection elements 1 are connected in parallel between the positive terminal of the secondary battery 50 and the external positive terminal 61.

[0071] All of the first lower electrodes 21 of each of the multiple protection elements 1 are connected to the same terminal. Specifically, all of the first lower electrodes 21 of each of the multiple protection elements 1 are connected to the positive terminal of the same secondary battery 50 via the conductive portion 27 and the first electrode 11. All of the second lower electrodes 22 of each of the multiple protection elements 1 are connected to the same terminal. Specifically, all of the second lower electrodes 22 of each of the multiple protection elements 1 are connected to the same external positive terminal 61 via the conductive portion 28 and the second electrode 12. All of the third lower electrodes 13 of each of the multiple protection elements 1 are connected to the same terminal on the switching element 71. The switching element 71 is switched to conduct electricity by a signal from the control device 81, interrupting the connection between the secondary battery 50 and the external positive terminal 61.

[0072] The first electrodes 11 of the two protective elements 1 are connected to a first connection point P1 via a current-carrying path and are also connected to the positive terminal of the secondary battery 50. The second electrodes 12 of the two protective elements 1 are connected to a second connection point P2 via a current-carrying path and are also connected to the external positive terminal 61. The third lower electrodes 13 of the two protective elements 1 are connected to a fourth electrode 14 via a heating element 3. The third lower electrodes 13 of the two protective elements 1 are connected to a third connection point P3 via a current-carrying path and are also connected to the switching element 71.

[0073] In this embodiment, the fusible conductors 4 of the two protective elements 1 are connected to the external positive electrode terminal 61 side (charging device side). One end of the heating element 3 of the two protective elements 1 is connected to the fusible conductor 4 via the fourth electrode 14, and the other end is connected to the switching element 71 via the third lower electrode 13 and the third connection point P3.

[0074] The secondary battery 50 is composed of one or more battery cells 51. In this embodiment, multiple battery cells 51 are connected in series. The positive terminals of the multiple battery cells 51 are connected to an external positive terminal 61, and the negative terminals are connected to an external negative terminal 62. The protection circuit 100 is connected to an external charging device via the external positive terminal 61 and the external negative terminal 62. When the secondary battery 50 is being charged, power is supplied to the secondary battery 50 from the external charging device via the power supply path. When the secondary battery 50 is being discharged, power is supplied from the secondary battery 50 to the power supply path.

[0075] The switching elements 71, 72, and 73 are composed of, for example, field-effect transistors (hereinafter also referred to as "FETs"). In the example shown in Figure 10, the protection circuit 100 is provided with three switching elements 71, 72, and 73. The heating elements 3 of two protection elements 1 are connected to a third connection point P3 via a current path and to one switching element 71. In the protection circuit 100, two switching elements 72 and 73 are provided on the current path between the second connection point P2 and the external positive terminal 61.

[0076] In the example shown in Figure 10, the protection circuit 100 is provided with two control devices 81 and 82 (a first control device 81 and a second control device 82). The first control device 81 is connected to a plurality of battery cells 51 of the secondary battery 50. The first control device 81 monitors the voltage of one or more of the plurality of battery cells 51, detects abnormalities, and outputs a signal. The first control device 81 is, for example, an IC (Integrated Circuit). The first control device 81 detects the voltage of each of the plurality of battery cells 51 and determines whether or not an abnormality such as overcharging has occurred in the battery cell 51 based on the detected voltage. If an abnormality occurs in the secondary battery 50, the first control device 81 activates the protection element 1 to cut off the power supply path.

[0077] The switching element 71 is connected to the first control device 81. The switching element 71 is turned on or off by a control signal output from the first control device 81. The signal from the first control device 81 switches the switching element 71 to conduct electricity (turns it on). When the switching element 71 is turned on, the heating element 3 of the protection element 1 heats up, and the fusible conductor 4 of the protection element 1 melts, interrupting the connection between the secondary battery 50 and the external positive terminal 61.

[0078] The portion consisting of the two switching elements 72 and 73 and the second control device 82 is responsible for the primary protection of the protection circuit 100. The second control device 82 is, for example, an IC (Integrated Circuit). When an abnormality such as overcharging or over-discharging is detected in the charge / discharge path, the second control device 82 controls the operation of the switching elements 72 and 73 to cut off the power supply to the charge / discharge path.

[0079] The two switching elements 72 and 73 are connected to the second control device 82. The switching elements 72 and 73 are turned on or off by a control signal output from the second control device 82. By switching the on or off operation of the switching elements 72 and 73, the charging path and the discharging path are switched. When the switching elements 72 and 73 are turned off, the current path between the second connection point P2 and the external positive terminal 61 is interrupted.

[0080] The protection circuit 100 may have a detection element (not shown) connected to each of the multiple battery cells 51 and also connected to the switching element 71. This detection element constantly monitors whether a high voltage state, particularly an overvoltage state, is present, and outputs a control signal to the switching element 71 when a high voltage state is detected. In this case, the switching element 71 generates heat in the heating element 3 by supplying current from the secondary battery 50 to the heating element 3 in response to the detection signal. This allows the fusible conductor 4 to be melted.

[0081] In the control (primary protection) of the part consisting of the two switching elements 72 and 73 and the second control device 82, the fusible conductor 4 is not melted, so the protection circuit 100 returns to normal once the abnormality is resolved. On the other hand, the part consisting of the protection element 1 and the first control device 81 is responsible for the secondary protection of the protection circuit 100. For example, if an electronic component such as a switch malfunctions and the power supply cannot be cut off in the event of an abnormality, the control (secondary protection) of the part consisting of the protection element 1 and the first control device 81 melts the fusible conductor 4, irreversibly cutting off the power supply.

[0082] Figure 11 illustrates an example of current interruption performed by the protection circuit 100 in Figure 10. As shown in Figure 11, it is assumed that an overcurrent flows due to an external short circuit or the like, causing the fusible conductor 4 to melt. In the example in Figure 11, since all of the fusible conductors 4 are located on the external positive terminal 61 side, the melting of the fusible conductors 4 interrupts the current in both the circuit on the external positive terminal 61 side and the circuit on the secondary battery 50 side. In this embodiment, since one fusible conductor 4 is provided inside each of the two protection elements 1, the melting of the fusible conductor 4 in each protection element 1 allows for current interruption in both the circuit on the external positive terminal 61 side and the circuit on the secondary battery 50 side in a parallel circuit without the need for a rectifier element (diode).

[0083] (Effects of this embodiment) The protective element 1 of this embodiment described above comprises an insulating substrate 2, a first electrode 11 and a second electrode 12 provided on the first surface 2a side of the insulating substrate 2 so as to face each other, a first lower electrode 21 provided on the second surface 2b side of the insulating substrate 2 opposite to the first surface 2a side and connected to the first electrode 11, a second lower electrode 22 provided on the second surface 2b side of the insulating substrate 2 and connected to the second electrode 12, a heating element 3 provided on the first surface 2a side of the insulating substrate 2, a first heating element electrode 23 connected to one end of the heating element 3 and the first electrode 11, a second heating element electrode 24 connected to the other end facing the one end of the heating element 3, an insulating member 5 covering the surface of the heating element 3, a third lower electrode 13 provided on the second surface 2b side of the insulating substrate 2 and connected to the second heating element electrode 24, and a fusible conductor 4 provided on the first surface 2a side of the insulating substrate 2. In a plan view from the first surface 2a of the insulating substrate 2, the fusible conductor 4 is connected to the first electrode 11 and the second electrode 12 so as to span between them. In a plan view, a part of the heating element 3, a part of the first electrode 11, and a part of the fusible conductor 4 are arranged to overlap each other. With this configuration, a part of the fusible conductor 4 between the first end 4a and the second end 4b (the part that overlaps with the space between the first electrode 11 and the second electrode 12 in a plan view) melts, thereby interrupting the circuit on the first end 4a side and the circuit on the second end 4b side of the fusible conductor 4. Therefore, when forming a protection circuit 100 equipped with multiple protection elements 1 connected in parallel, overcurrent can be reliably prevented without providing rectifying elements such as diodes. Furthermore, the protection element 1 is equipped with one fusible conductor 4 and one heating element 3, and does not have a central electrode. For this reason, it is a simpler and easier configuration to form compared to a configuration having two fuse elements connected in series and a central electrode. Furthermore, in a configuration where the heating element 3 and a portion of either the first electrode 11 or the second electrode 12 overlap with a portion of the fusible conductor 4 in a plan view, the cross-sectional area of ​​the conductor increases in the overlapping portion (overlapping portion 40) compared to other portions. For this reason, the resistance value (conductor resistance) when energized can be lowered compared to a configuration with two fuse elements connected in series.Therefore, it is possible to reliably prevent overcurrents and improve safety, reduce costs with a simpler device configuration than conventional methods, further reduce the device failure rate, and lower the conductor resistance during energization.

[0084] In this embodiment, in a plan view, the area A1 of the first electrode 11 is larger than the area A2 of the second electrode 12. With this configuration, compared to the case where the area A1 of the first electrode 11 is less than or equal to the area A2 of the second electrode 12 in a plan view, it is easier to contain the molten material (the melted portion of the fusible conductor 4) on the first electrode 11 when the fusible conductor 4 melts. For example, in a configuration having two fuse elements connected in series and a central electrode in a plan view, it is conceivable to make the central electrode larger in order to contain the melted portion of the fuse elements. However, in this case, the conductor resistance increases as the conductor distance increases, and the product size increases, making it difficult to achieve both low resistance and miniaturization (securing space to contain the molten material when the heating element is operating). In contrast, with this configuration, a configuration without a central electrode is sufficient, and the molten material can be contained on the first electrode 11, making it easy to achieve both low resistance and miniaturization (securing space to contain the molten material when the heating element 3 is operating).

[0085] In this embodiment, when viewed from above, the area of ​​the insulating substrate 2 is A0 and the area of ​​the first electrode 11 is A1, the condition 0.15 ≤ A1 / A0 ≤ 0.70 is satisfied. With this configuration, compared to the case where 0.15 > A1 / A0, the molten material of the fusible conductor 4 can be easily contained, and the performance is more stable. Also, when the fusible conductor 4 is cut, the greater the distance between the first electrode 11 and the second electrode 12 (distance between electrodes), the more stable the performance. Therefore, compared to the case where A1 / A0 > 0.70, it is possible to maintain a sufficient distance between electrodes, and the performance is more stable.

[0086] In this embodiment, the heating element 3 is provided on the first surface 2a side of the insulating substrate 2. In the portion where the heating element 3 and the first electrode 11 overlap each other in a plan view, insulating members 5 and 6 are further provided between the heating element 3 and the first electrode 11, or both between the heating element 3 and the first electrode 11 and between the heating element 3 and the insulating substrate 2. With this configuration, since the heating element 3 is provided on the same side of the insulating substrate 2 as the fusible conductor 4, the heating efficiency when melting the fusible conductor 4 can be improved. As a result, the current path can be interrupted with high precision.

[0087] In this embodiment, the fusible conductor 4 is connected to the first electrode 11 and the second electrode 12 via connecting members 25 and 26 made of solder.

[0088] The protection circuit 100 of this embodiment is a protection circuit 100 that includes one or more of the above-mentioned protection elements 1. With this configuration, because the above-mentioned protection elements 1 are included, overcurrent can be reliably prevented and safety can be improved, and a simpler device configuration can be achieved to reduce costs compared to conventional devices, further reducing the failure rate of the device and lowering the conductor resistance when energized.

[0089] In this embodiment, the protection circuit 100 further comprises a secondary battery 50, an external positive terminal 61 and an external negative terminal 62, switching elements 71, 72, and 73, and control devices 81 and 82. Multiple protection elements 1 are provided. Multiple protection elements 1 are connected in parallel between the positive terminal of the secondary battery 50 and the external positive terminal 61. All of the first lower electrodes 21 of each of the multiple protection elements 1 are connected to the same terminal. All of the second lower electrodes 22 of each of the multiple protection elements 1 are connected to the same terminal. All of the third lower electrodes 13 of each of the multiple protection elements 1 are connected to the same terminal on the switching element 71. The switching element 71 is switched to conduct electricity by a signal from the control device 81, thereby interrupting the connection between the secondary battery 50 and the external positive terminal 61. With this configuration, the switching element 71 is switched to conduct electricity by a signal from the control device 81, thereby interrupting the power supply to the charge / discharge path and isolating the connection between the secondary battery 50 and the external positive terminal 61.

[0090] (Second Embodiment) The protective element 201 according to the second embodiment of the present invention will be described with reference to Figures 12 to 14. The protective element 201 of the second embodiment differs from the first embodiment mainly in that the shapes of the first electrode 211 and the second electrode 212 and the arrangement of the fusible conductor 4 are reversed from those of the first embodiment. In the figures of this embodiment, components similar to those of the first embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0091] Figure 12 is a top view of the protection element 201 of the second embodiment. Figure 13 is a cross-sectional view taken along line XIII-XIII in Figure 12. Figure 14 is a diagram showing the circuit configuration of the protection element 201 of the second embodiment. Referring together to Figures 12 to 14, the protection element 201 comprises an insulating substrate 2, a first electrode 211 and a second electrode 212, a first lower electrode 21, a second lower electrode 22, a heating element 3, a first heating element electrode 23, a second heating element electrode 24, an insulating member 5, a third lower electrode 13, and a fusible conductor 4.

[0092] The first electrode 211 is formed in a shape that is elongated in the X direction when viewed from above. In the example of Figure 12, when viewed from above, the maximum dimension of the first electrode 211 in the X direction is larger than the X-direction dimension of the fusible conductor 4, and is larger on the -Y side than the first end 4a of the fusible conductor 4. The first electrode 211 has a portion that contains the molten fusible conductor 4 (molten material). The first electrode 211 is the electrode into which the molten fusible conductor 4 flows. Preferably, the first electrode 211 is a metal with good wettability with the molten fusible conductor 4.

[0093] In the example shown in Figure 13, the first electrode 211 is formed on the -Y end side of the insulating substrate 2 in cross-sectional view and has a shape in which the Z-direction dimension (thickness) is thicker than the thickness of the fusible conductor 4. Preferably, the thickness of the first electrode 211 is the same as the thickness of the base portion 212a of the second electrode 212, but they may be different. The thickness of the first electrode 211 may be less than or equal to the thickness of the fusible conductor 4.

[0094] The second electrode 212, when viewed from above, has a maximum dimension in the X direction that is greater than the X-direction dimension of the fusible conductor 4, and is greater on the +Y side than the second end 4b of the fusible conductor 4. The second electrode 212 has a portion that accommodates the molten fusible conductor 4 (molten material). The second electrode 212 is the electrode into which the molten fusible conductor 4 flows. Preferably, the second electrode 212 is made of a metal with good wettability with the molten fusible conductor 4.

[0095] In the example shown in Figure 13, the second electrode 212 has a crank shape that is elongated in the Y direction when viewed in cross-section. The second electrode 212 has, when viewed in cross-section, a base portion 212a formed on the +Y end side of the edge substrate 2 and having a Z-direction dimension (thickness) that is thicker than the thickness of the fusible conductor 4, and an extended portion 212b that is integrally formed with a uniform thickness extending from the -Y end and upper end side of the base portion 212a to the -Y end of the connecting member 26 and having a thickness that is thinner than the base portion 212a. The thickness of the base portion 212a may be less than or equal to the thickness of the fusible conductor 4. The thickness of the extended portion 212b may be greater than or equal to the thickness of the base portion 212a.

[0096] In the protective element 201 of this embodiment, when a large current exceeding the rated value flows through the protective element 201, the fusible conductor 4 (fuse element) melts due to self-heating (Joule heating), or the fusible conductor 4 melts due to the heat generated by the heating element 3, thereby interrupting the current path.

[0097] For example, the first electrode 211, the second electrode 212, the first heating element electrode 23, and the second heating element electrode 24 are connected to the wiring of the circuit board via solder in castellations 31, 32, 33, and 34, respectively. When an overcurrent flows through the wiring of the circuit board, the overcurrent flows to the fusible conductor 4 via the first electrode 211 and the second electrode 212 of the protection element 201. When an overcurrent flows through the fusible conductor 4, Joule heat is generated in the fusible conductor 4, and this heat causes the fusible conductor 4 to melt and break, thereby interrupting the current path of the circuit board. Also, when an abnormality other than an overcurrent occurs in the circuit board, current flows through the third lower electrode 13, causing the heating element 3 to heat up, and this heat is transferred to the fusible conductor 4, causing the fusible conductor 4 to melt and break, thereby interrupting the current path of the circuit board. The molten material of the fusible conductor 4 after melting is held on the second electrode 212.

[0098] Next, an example of the portion in which the heating element 3, the second electrode 212, and the fusible conductor 4 overlap in the protective element 201 of this embodiment will be described. In this embodiment, in a plan view, a part of the heating element 3, a part of the second electrode 212, and a part of the fusible conductor 4 are arranged to overlap each other. In the example of Figure 13, the protective element 201 has an overlapping portion 40 in which the heating element 3, the extended portion 212b of the second electrode 212, the -Y side portion of the connecting member 26, and the Y-direction central portion of the fusible conductor 4 overlap each other in the Z direction. In the Y direction, a space 41 is formed between the overlapping portion 40 and the first electrode 211 and the connecting member 25.

[0099] In this embodiment, in a plan view, the area A2 of the second electrode 212 is larger than the area A1 of the first electrode 211. In a plan view, the area A1 of the first electrode 211 corresponds to the area of ​​the upper surface of the first electrode 211. When the entire upper surface of the first electrode 211 is covered by the connecting member 25, in a plan view, the area A1 of the first electrode 211 corresponds to the area of ​​the upper surface of the connecting member 25. In a plan view, the area A2 of the second electrode 212 corresponds to the area of ​​the upper surface of the second electrode 212. When the entire upper surface of the second electrode 212 is covered by the connecting member 26, in a plan view, the area A2 of the second electrode 212 corresponds to the area of ​​the upper surface of the connecting member 26.

[0100] In a plan view, when the area of ​​the insulating substrate 2 is A0 and the area of ​​the second electrode 212 is A2, the following conditions are met: 0.15 ≤ A2 / A0 ≤ 0.70. In a plan view, the area of ​​the insulating substrate 2 corresponds to the area of ​​the upper surface of the insulating substrate 2. It is more preferable that the following conditions are met: 0.20 ≤ A2 / A0 ≤ 0.65, and even more preferable that the following conditions are met: 0.25 ≤ A2 / A0 ≤ 0.60.

[0101] Figure 15 is a schematic circuit diagram showing the configuration of the protection circuit 200 of the second embodiment. In the example of Figure 15, two protection elements 201, as shown in Figure 14, are mounted on the protection circuit 200. The protection circuit 200 constitutes, for example, a circuit within a battery pack of a lithium-ion secondary battery. The number of protection elements 201 mounted on the protection circuit 200 can be one or three or more, and can be changed according to the design specifications.

[0102] As shown in Figure 15, in the protection circuit 200, two protection elements 201 are connected in parallel. The protection circuit 200 includes a secondary battery 50, an external positive terminal 61 and an external negative terminal 62, switching elements 71, 72, and 73, and control devices 81 and 82. Multiple protection elements 201 are provided. Multiple protection elements 201 are connected in parallel between the positive terminal of the secondary battery 50 and the external positive terminal 61.

[0103] All of the first lower electrodes 21 of each of the multiple protection elements 201 are connected to the same terminal. Specifically, all of the first lower electrodes 21 of each of the multiple protection elements 201 are connected to the same positive terminal of the secondary battery 50 via the conductive portion 27 and the first electrode 211. All of the second lower electrodes 22 of each of the multiple protection elements 201 are connected to the same terminal. Specifically, all of the second lower electrodes 22 of each of the multiple protection elements 201 are connected to the same external positive terminal 61 via the conductive portion 28 and the second electrode 212. All of the third lower electrodes 13 of each of the multiple protection elements 201 are connected to the same terminal on the switching element 71. The switching element 71 is switched to conduct electricity by a signal from the control device 81, interrupting the connection between the secondary battery 50 and the external positive terminal 61.

[0104] The first electrodes 211 of the two protective elements 201 are connected to a first connection point P1 via a current-carrying path and are also connected to the positive terminal of the secondary battery 50. The second electrodes 212 of the two protective elements 201 are connected to a second connection point P2 via a current-carrying path and are also connected to the external positive terminal 61. The third lower electrodes 13 of the two protective elements 201 are connected to a fourth electrode 14 via a heating element 3. The third lower electrodes 13 of the two protective elements 201 are connected to a third connection point P3 via a current-carrying path and are also connected to the switching element 71.

[0105] In this embodiment, the fusible conductors 4 of the two protective elements 201 are connected to the secondary battery 50 side (opposite side from the charging device side). One end of the heating element 3 of the two protective elements 201 is connected to the fusible conductor 4 via the fourth electrode 14, and the other end is connected to the switching element 71 via the third lower electrode 13 and the third connection point P3.

[0106] Figure 16 illustrates an example of current interruption performed by the protection circuit 200 in Figure 15. As shown in Figure 16, it is assumed that an overcurrent flows due to an external short circuit or the like, causing the fusible conductor 4 to melt. In the example in Figure 16, since all of the fusible conductors 4 are provided on the secondary battery 50 side, the melting of the fusible conductors 4 interrupts the current in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side. In this embodiment, since one fusible conductor 4 is provided inside each of the two protection elements 201, the melting of the fusible conductor 4 in each protection element 201 allows for current interruption in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side in a parallel circuit without the need for a rectifier element (diode).

[0107] (Third Embodiment) A protection circuit 300 according to the third embodiment of the present invention will be described with reference to Figures 17 and 18. The protection circuit 300 of the third embodiment differs from the second embodiment described above mainly in that it stops supplying power to the heating element 3 after a predetermined time has elapsed. In the figures of this embodiment, components similar to those in the second embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0108] Figure 17 is a schematic circuit diagram showing the configuration of the protection circuit 300 of the third embodiment. The protection circuit 300 comprises one or more protection elements 201. In the example of Figure 17, one protection element 201 shown in Figure 14 is mounted on the protection circuit 300. The protection circuit 300 constitutes a circuit within a battery pack of a lithium-ion secondary battery, for example. Note that the number of protection elements 201 mounted on the protection circuit 300 may be two or more and can be changed according to the design specifications.

[0109] As shown in Figure 17, the protection circuit 300 is provided with one protection element 201. The protection element 201 is located in the current path between the positive terminal of the secondary battery 50 and the external positive terminal 61. A signal from the control device 81 switches the switching element 71 to conduct electricity, thereby interrupting the connection between the secondary battery 50 and the external positive terminal 61.

[0110] The first electrode 211 of the protection element 201 is connected to the positive terminal of the secondary battery 50 via a current-carrying path. The second electrode 212 of the protection element 201 is connected to the external positive terminal 61 via a current-carrying path. The third lower electrode 13 of the protection element 201 is connected to the fourth electrode 14 via a heating element 3. The third lower electrode 13 of the protection element 201 is connected to the switching element 71 via a current-carrying path.

[0111] In this embodiment, the fusible conductor 4 of the protective element 201 is connected to the secondary battery 50 side (opposite side from the charging device side). One end of the heating element 3 of the protective element 201 is connected to the fusible conductor 4 via the fourth electrode 14, and the other end is connected to the switching element 71 via the third lower electrode 13.

[0112] Figure 18 illustrates an example of current interruption by the protection circuit 300 in Figure 17. As shown in Figure 18, it is assumed that an overcurrent flows due to an external short circuit or the like, causing the fusible conductor 4 to melt. In the example in Figure 18, since all of the fusible conductors 4 are located on the secondary battery 50 side, the melting of the fusible conductors 4 interrupts the current in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side. In this embodiment, since one fusible conductor 4 is provided inside one protection element 201, the melting of the fusible conductor 4 in the protection element 201 can interrupt the current in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side without the need for a rectifier element (diode).

[0113] In this embodiment, the control device 81 stops supplying power to the heating element 3 after a predetermined time has elapsed from the time the switching element 71 is switched to energize. In the example shown in Figure 18, the second control device 82 controls the first control device 81 to stop supplying power to the heating element 3 after a predetermined time has elapsed from the time the switching element 71 is switched to energize (turns on). The predetermined time can be set, for example, in the range of 0.1 seconds to 60 seconds.

[0114] Specifically, the first control device 81 turns on the switching element 71 when it detects an abnormality such as overcharging or over-discharging in the charge / discharge path. This cuts off the power supply to the charge / discharge path. After a predetermined time has elapsed (for example, 10 seconds) since the switching element 71 was turned on, the second control device 82 turns off the switching element 71, and the power supply to the heating element 3 is stopped. In this way, the power supply to the heating element 3 is stopped by the timer control of the second control device 82.

[0115] In this embodiment, the second control device 82 controls the first control device 81 to stop supplying power to the heating element 3 after a predetermined time has elapsed since the switching element 71 was switched to energize. For example, if the switching element is switched to energize, the power supply may continue, which could result in the heating element continuing to operate. In contrast, with this configuration, the control is performed to stop supplying power to the heating element 3 after a predetermined time has elapsed since the switching element 71 was switched to energize, thereby preventing the heating element 3 from continuing to operate.

[0116] (Fourth Embodiment) A protection circuit 400 according to the fourth embodiment of the present invention will be described with reference to Figures 19 and 20. The protection circuit 400 of the fourth embodiment differs from the third embodiment described above mainly in that it is provided with two protection elements 201. In the figures of this embodiment, components similar to those in the third embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0117] Figure 19 is a schematic circuit diagram showing the configuration of the protection circuit 400 of the fourth embodiment. In the example of Figure 19, two protection elements 201, as shown in Figure 14, are mounted on the protection circuit 400. The protection circuit 400 constitutes, for example, a circuit within a battery pack of a lithium-ion secondary battery. The number of protection elements 201 mounted on the protection circuit 400 can be one or three or more, and can be changed according to the design specifications.

[0118] As shown in Figure 19, in the protection circuit 400, two protection elements 201 are connected in parallel. The protection circuit 400 includes a secondary battery 50, an external positive terminal 61 and an external negative terminal 62, switching elements 71, 72, and 73, and control devices 81 and 82. Multiple protection elements 201 are provided. Multiple protection elements 201 are connected in parallel between the positive terminal of the secondary battery 50 and the external positive terminal 61.

[0119] All of the first lower electrodes 21 of each of the multiple protection elements 201 are connected to the same terminal. Specifically, all of the first lower electrodes 21 of each of the multiple protection elements 201 are connected to the same positive terminal of the secondary battery 50 via the conductive portion 27 and the first electrode 211. All of the second lower electrodes 22 of each of the multiple protection elements 201 are connected to the same terminal. Specifically, all of the second lower electrodes 22 of each of the multiple protection elements 201 are connected to the same external positive terminal 61 via the conductive portion 28 and the second electrode 212. All of the third lower electrodes 13 of each of the multiple protection elements 201 are connected to the same terminal on the switching element 71. The switching element 71 is switched to conduct electricity by a signal from the control device 81, and the fusible conductor 4 of the protection element 201 is melted, interrupting the connection between the secondary battery 50 and the external positive terminal 61.

[0120] The first electrodes 211 of the two protective elements 201 are connected to a first connection point P1 via a current-carrying path and are also connected to the positive terminal of the secondary battery 50. The second electrodes 212 of the two protective elements 201 are connected to a second connection point P2 via a current-carrying path and are also connected to the external positive terminal 61. The third lower electrodes 13 of the two protective elements 201 are connected to a fourth electrode 14 via a heating element 3. The third lower electrodes 13 of the two protective elements 201 are connected to a third connection point P3 via a current-carrying path and are also connected to the switching element 71.

[0121] In this embodiment, the fusible conductors 4 of the two protective elements 201 are connected to the secondary battery 50 side (opposite side from the charging device side). One end of the heating element 3 of the two protective elements 201 is connected to the fusible conductor 4 via the fourth electrode 14, and the other end is connected to the switching element 71 via the third lower electrode 13 and the third connection point P3.

[0122] Figure 20 illustrates an example of current interruption by the protection circuit 400 in Figure 19. As shown in Figure 20, it is assumed that an overcurrent flows due to an external short circuit or the like, causing the fusible conductor 4 to melt. In the example in Figure 20, all of the fusible conductors 4 are provided on the secondary battery 50 side, so the melting of the fusible conductors 4 interrupts the current in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side. In this embodiment, since one fusible conductor 4 is provided inside each of the two protection elements 201, the melting of the fusible conductor 4 in each protection element 201 allows for current interruption in both the circuit on the secondary battery 50 side and the circuit on the external positive terminal 61 side in a parallel circuit without the need for a rectifier element (diode).

[0123] In this embodiment, the control device 81 stops supplying power to the heating element 3 after a predetermined time has elapsed since the switching element 71 was switched to energize. In the example shown in Figure 20, the first control device 81 stops supplying power to the heating element 3 after a predetermined time has elapsed since the switching element 71 was switched to energize (turned on). The predetermined time can be set, for example, in the range of 0.1 seconds to 60 seconds.

[0124] Specifically, the first control device 81 turns on the switching element 71 when an abnormality such as overcharging occurs in the battery cell 51 of the secondary battery 50. This cuts off the charging current to the secondary battery 50. After a predetermined time has elapsed (for example, 10 seconds) since the switching element 71 was turned on, the first control device 81 stops the power supply to the heating element 3. In this way, the power supply to the heating element 3 is stopped by the timer control of the first control device 81.

[0125] In this embodiment, the first control device 81 stops supplying power to the heating element 3 after a predetermined time has elapsed since the switching element 71 was switched to energize. With this configuration, by controlling the power supply to the heating element 3 to stop after a predetermined time has elapsed since the switching element 71 was switched to energize, it is possible to prevent the heating element 3 from continuing to operate.

[0126] (Fifth Embodiment) A protective element 501 according to the fifth embodiment of the present invention will be described with reference to Figure 21. The protective element 501 of the fifth embodiment differs from the first embodiment described above mainly in that the fusible conductor 504 is a laminate containing a high melting point metal layer 504A and a low melting point metal layer 504B. In the figures of this embodiment, components similar to those of the first embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0127] Figure 21 is a diagram showing a protective element 501 of the fifth embodiment, and is a cross-sectional view corresponding to Figure 3. As shown in Figure 21, the protective element 501 comprises an insulating substrate 2, a first electrode 11 and a second electrode 12, a first lower electrode 21, a second lower electrode 22, a heating element 3, a first heating element electrode 23, a second heating element electrode 24, an insulating member 5, a third lower electrode 13, and a fusible conductor 504.

[0128] The fusible conductor 504 is a laminate containing a low-melting-point metal layer 504B and a high-melting-point metal layer 504A composed of a high-melting-point metal with a higher melting point than the low-melting-point metal. The high-melting-point metal layer 504A is made of Ag or Cu, or a metal mainly composed of Ag or Cu. The low-melting-point metal layer 504B is made of Sn or a metal mainly composed of Sn.

[0129] Furthermore, the fusible conductor 504 may have a coating structure composed of a low-melting-point metal layer as an inner layer and a high-melting-point metal layer as an outer layer covering the low-melting-point metal layer as an inner layer. For example, the fusible conductor 504 may be a laminate with a three-layer structure in which an inner layer and an outer layer sandwiching it are stacked in the thickness direction, and the inner layer and the outer layer may be made of materials with different softening temperatures. In such a fusible conductor 504, among the inner and outer layers of the laminate, the solid-liquid phase mixture begins first in the layer of material with a lower softening temperature, and the layer of material with a higher softening temperature can be cut by the melting of the high-melting-point metal layer by the low-melting-point metal layer that has melted before the layer of material with a higher softening temperature reaches its softening temperature.

[0130] In the example shown in Figure 21, the fusible conductor 504 is provided as a laminate containing a high-melting-point metal layer 504A and a low-melting-point metal layer 504B, spanning between the first electrode 11 and the second electrode 12. The fusible conductor 504 has the high-melting-point metal layer 504A laminated on top of the low-melting-point metal layer 504B. The first end 4a of the low-melting-point metal layer 504B of the fusible conductor 504 is connected to the first electrode 11, and the second end 4b of the low-melting-point metal layer 504B is connected to the second electrode 12.

[0131] The fusible conductor 504 is connected to the first electrode 11 and the second electrode 12 via a connecting member made of solder or via a low-melting-point metal layer 504B. In the example shown in Figure 21, the portion of the fusible conductor 504 on the first end 4a side is connected to the upper surface of the first electrode 11 via the low-melting-point metal layer 504B. The portion of the fusible conductor 504 on the second end 4b side is connected to the upper surface of the second electrode 12 via the low-melting-point metal layer 504B. The high-melting-point metal layer 504A of the fusible conductor 504 is supported by the first electrode 11 and the second electrode 12 via the low-melting-point metal layer 504B.

[0132] In the example shown in Figure 21, the low-melting-point metal layer 504B and the high-melting-point metal layer 504A of the fusible conductor 504 each have a uniform thickness in the Y direction. In cross-sectional view, the low-melting-point metal layer 504B has a layered structure with a Y-direction dimension longer than that of the high-melting-point metal layer 504A and the Z-direction dimension (thickness) being the same as that of the high-melting-point metal layer 504A, and has a uniform thickness. The shape of the fusible conductor 504 is not limited to the above and can be changed according to the design specifications. The thickness of the low-melting-point metal layer 504B may be greater than or equal to the thickness of the high-melting-point metal layer 504A, or less than or equal to the thickness of the high-melting-point metal layer 504A.

[0133] In this embodiment, the fusible conductor 504 is a laminate containing a high-melting-point metal layer 504A and a low-melting-point metal layer 504B. The laminate containing the high-melting-point metal layer 504A and the low-melting-point metal layer 504B is provided to span between the first electrode 11 and the second electrode 12. In the fusible conductor 504, the high-melting-point metal layer 504A is laminated on top of the low-melting-point metal layer 504B. In the fusible conductor 504, the portion of the low-melting-point metal layer 504B on the first end 4a side is connected to the first electrode 11, and the portion of the low-melting-point metal layer 504B on the second end 4b side is connected to the second electrode 12. With this configuration, compared to a configuration in which the fusible conductor is a single layer, the cross-sectional area of ​​the conductor increases in the overlapping portion 40, so that the resistance value (conductor resistance) when energized can be reduced. Therefore, it is possible to reliably prevent overcurrents and improve safety, reduce costs with a simpler device configuration than conventional methods, further reduce the device failure rate, and lower the conductor resistance during energization.

[0134] (Sixth Embodiment) The protective element 601 according to the sixth embodiment of the present invention will be described with reference to Figures 22 to 26. The protective element 601 of the sixth embodiment differs from the first embodiment described above mainly in that the heating element 603 is provided on the second surface 2b side of the insulating substrate 2. In the figures of this embodiment, components similar to those of the first embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0135] Figure 22 is a top view of the protective element 601 of the sixth embodiment. Figure 23 is a bottom view of the protective element 601 of the sixth embodiment. Figure 24 is a cross-sectional view taken along line XXIV-XXIV of Figure 23. Figure 25 is a top view showing the protective element 601A of the first modified example of the sixth embodiment. Figure 26 is a cross-sectional view taken along line XXVI-XXVI of Figure 25. Referring together to Figures 22 to 26, the protective element 601 comprises an insulating substrate 2, a first electrode 611 and a second electrode 612, a first lower electrode 621 and a second lower electrode 622, a heating element 603, a first heating element electrode 623 and a second heating element electrode 624, an insulating member 605, a third lower electrode 613, and a fusible conductor 4.

[0136] In the example shown in Figure 24, the first electrode 611 is formed on the -Y end side of the insulating substrate 2 in cross-sectional view and has a shape in which the Z-direction dimension (thickness) is thicker than the thickness of the fusible conductor 4. The second electrode 612 is formed on the +Y end side of the insulating substrate 2 in cross-sectional view and has a shape in which the Z-direction dimension (thickness) is thicker than the thickness of the fusible conductor 4. The Y-direction dimension of the first electrode 611 is longer than the Y-direction dimension of the second electrode 612. The thickness of the first electrode 611 is preferably the same as the thickness of the second electrode 612, but they may be different. The thickness of the first electrode 611 may be less than or equal to the thickness of the fusible conductor 4.

[0137] The fusible conductor 4 is connected to the first electrode 611 and the second electrode 612 via a connecting member made of solder or a low-melting-point metal layer. In the example of Figure 24, the fusible conductor 4 is connected to the first electrode 611 and the second electrode 612 via connecting members 25 and 26 made of solder. In the example of Figure 26, the portion of the fusible conductor 4 on the first end 4a side is connected to the upper surface of the first electrode 611 via a low-melting-point metal layer 604B. The portion of the fusible conductor 4 on the second end 4b side is connected to the upper surface of the second electrode 612 via a low-melting-point metal layer 604B.

[0138] The heating element 603 is provided on the second surface 2b side of the insulating substrate 2. The heating element 603 is positioned on the center side in the Y direction on the second surface 2b of the insulating substrate 2. The heating element 603 is positioned on the center side in the Y direction on the lower surface of the insulating substrate 2, with a gap in the Y direction between it and the first lower electrode 621 and the second lower electrode 622.

[0139] The heating element 603 is covered with an insulating member 605. The insulating member 605 covers the surface of the heating element 603. In the example shown in Figure 24, the insulating member 605 is formed to cover the outer surface of the heating element 603 in cross-sectional view. The insulating member 605 may also be interposed between the lower surface of the insulating substrate 2 and the upper surface of the heating element 603.

[0140] In this embodiment, the heating element 603 is provided on the second surface 2b side of the insulating substrate 2. The surface of the heating element 603 is covered with an insulating member 605. With this configuration, the heating element 603 is provided on the side of the insulating substrate 2 opposite to the fusible conductor 4, which allows for a lower profile of the protective element 601. This increases the degree of freedom in mounting space when mounting the protective element 601 in the protective circuit.

[0141] (Seventh Embodiment) The protective element 701 according to the seventh embodiment of the present invention will be described with reference to Figures 27 and 28. The protective element 701 of the seventh embodiment differs from the first embodiment mainly in that the Y-direction dimension of the fusible conductor 704 is shorter than the Y-direction dimension of the fusible conductor 4 of the first embodiment. In the figures of this embodiment, components similar to those of the first embodiment may be given the same reference numerals or names and their descriptions may be omitted.

[0142] Figure 27 is a top view of the protection element 701 of the seventh embodiment. Figure 28 is a cross-sectional view taken along line XXVIII-XXVIII of Figure 27. Referring together to Figures 27 and 28, the protection element 701 comprises an insulating substrate 2, a first electrode 11 and a second electrode 12, a first lower electrode 21, a second lower electrode 22, a heating element 3, a first heating element electrode 23, a second heating element electrode 24, an insulating member 5, a third lower electrode 613, and a fusible conductor 704.

[0143] In this embodiment, in a plan view, a part of the heating element 3, a part of the first electrode 11, and a part of the fusible conductor 704 are arranged to overlap each other. In the example shown in Figure 28, the protective element 701 has an overlapping portion 740 in which the heating element 3, the extended portion 11b of the first electrode 11, the +Y side portion of the connecting member 25, and the first end 4a side portion of the fusible conductor 704 overlap each other in the Z direction. In the Y direction, a space 41 is formed between the overlapping portion 740 and the second electrode 12 and the connecting member 26.

[0144] In this embodiment, the Y-direction dimension of the fusible conductor 704 is shorter than the Y-direction dimension of the fusible conductor 4 in the first embodiment. In the example shown in Figure 27, in a plan view, the area where the portion of the fusible conductor 704 on the first end 4a side and the connecting member 25 overlap (the area of ​​the overlapping portion 740) is smaller than the area of ​​the overlapping portion 40 in the first embodiment.

[0145] In this embodiment, in a plan view, a part of the heating element 3, a part of the first electrode 11, and a part of the fusible conductor 704 are arranged to overlap each other. With this configuration, a part of the fusible conductor 704 between the first end 4a and the second end 4b (the part that overlaps with the space between the first electrode 11 and the second electrode 12 in a plan view) melts, thereby interrupting the circuit on the first end 4a side and the circuit on the second end 4b side of the fusible conductor 704. Therefore, when forming a protection circuit equipped with multiple protection elements 701 connected in parallel, overcurrent can be reliably prevented without providing rectifier elements such as diodes. Furthermore, the protection element 701 is equipped with one fusible conductor 704 and one heating element 3, and does not have a central electrode. For this reason, it is a simpler and easier configuration to form compared to a configuration having two fuse elements connected in series and a central electrode. Furthermore, in a plan view, the configuration in which the heating element 3 and a portion of either the first electrode 11 or the second electrode 12 and a portion of the fusible conductor 704 overlap each other results in a larger cross-sectional area of ​​the conductor in the overlapping portion (overlapping portion 740) compared to other portions. Therefore, compared to a configuration with two fuse elements connected in series, the resistance value (conductor resistance) during energization can be reduced. Consequently, overcurrent can be reliably prevented, safety can be improved, costs can be reduced with a simpler device configuration than conventional designs, and the failure rate of the device can be reduced, while the conductor resistance during energization can be lowered.

[0146] In this embodiment, the Y-direction dimension of the fusible conductor 704 is shorter than the Y-direction dimension of the fusible conductor 4 in the first embodiment. In a plan view, the area of ​​the overlapping portion 740 of the fusible conductor 704 is smaller than the area of ​​the overlapping portion 40 in the first embodiment. With this configuration, compared to the configuration of the first embodiment, when the fusible conductor 704 is cut, it is easier to contain the molten material (the melted portion of the fusible conductor 704) on the first electrode 11.

[0147] (Modifications) In the above embodiment, the fusible conductor may be described as a laminate containing a high-melting-point metal layer and a low-melting-point metal layer, but it is not limited to this. For example, the fusible conductor may be composed of a single layer of the high-melting-point metal layer. For example, the fusible conductor may be composed of a single layer of the low-melting-point metal layer. The configuration of the fusible conductor can be changed according to the design specifications.

[0148] In the above embodiment, the protection circuit further comprises a secondary battery, an external positive terminal and an external negative terminal, a switching element, and a control device. The protection element is provided in the current path between the positive terminal of the secondary battery and the external positive terminal, and is switched to energize the switching element by a signal from the control device, thereby blocking the connection between the secondary battery and the external positive terminal. However, the embodiment is not limited to this example. For example, the protection element may be provided in the current path between the negative terminal of the secondary battery and the external negative terminal, and is switched to energize the switching element by a signal from the control device, thereby blocking the connection between the secondary battery and the external negative terminal. The configuration of the protection element in the protection circuit can be changed according to the design specifications.

[0149] In the above embodiment, the control device was described as stopping the power supply to the heating element after a predetermined time has elapsed since the switching element was switched to energize, but it is not limited to this. For example, the protection circuit may include a sensor that detects the voltage of multiple battery cells, and the control device may turn off the switching element and stop the power supply to the heating element when the voltage detected by the sensor falls below a predetermined voltage. The manner in which the power supply to the heating element is stopped can be changed according to the design specifications.

[0150] The present invention may be combined in any way that does not depart from the spirit of the invention, as described in the above embodiments and modifications, and the configurations may be added, omitted, substituted, or otherwise modified. Furthermore, the present invention is not limited by the above embodiments, but is limited only by the claims.

[0151] The protective element according to the above embodiment of the present invention will be described in detail below with reference to examples. Note that the following examples are specific examples to which the present invention is applied and do not limit the present invention.

[0152] Figure 29 shows the electrical characteristics of the comparative example and the embodiment. (Embodiment) As shown in Figure 29, the protective element of the embodiment includes an insulating substrate, a first electrode and a second electrode provided on the first surface side of the insulating substrate so as to face each other, a first lower electrode provided on the second surface side of the insulating substrate opposite to the first surface side and connected to the first electrode, a second lower electrode provided on the second surface side of the insulating substrate and connected to the second electrode, a heating element provided on the first surface side of the insulating substrate, a first heating element electrode connected to one end of the heating element and the first electrode, a second heating element electrode connected to the other end of the heating element opposite to the one end, an insulating member covering the surface of the heating element, and the second heating element electrode provided on the second surface side of the insulating substrate. A third lower electrode connected to the electrode and a fusible conductor provided on the first surface side of the insulating substrate were prepared, wherein in a plan view as seen from the first surface side of the insulating substrate, the fusible conductor is connected to the first electrode and the second electrode so as to span between them, and in the plan view, a part of the heating element, a part of the first electrode, and a part of the fusible conductor are arranged to overlap each other, and in the plan view, the area of ​​the first electrode is larger than the area of ​​the second electrode, and in the plan view, when the area of ​​the insulating substrate is A0 and the area of ​​the first electrode is A1, the condition 0.15 ≤ A1 / A0 ≤ 0.70 is satisfied (corresponding to the configuration shown in Figures 1 to 5).

[0153] (Comparative Example) The comparative example protection element was prepared having two fuse elements connected in series, a heating element and a central electrode that overlap between the two fuse elements in a plan view (corresponding to the configuration shown in Figure 8).

[0154] In the protective elements of the comparative example and the example, the fusible conductor was the same in size, measuring 2.2 mm in length, 1.9 mm in width, and 0.1 mm in thickness.

[0155] (Evaluation) The resistance value (FuseR) between the first and second electrodes of the fuse element of the protective device was measured. In addition, the number of times the fuse element did not blow when 44W of power was supplied to the third lower electrode (44W operation NG count) was measured.

[0156] As shown in Figure 29, the protective element of the embodiment exhibits a smaller resistance value (FuseR) between the first electrode and the second electrode compared to the protective element of the comparative example. This is thought to be because, in a plan view, the heating element, a portion of the first electrode, and a portion of the fusible conductor overlap each other, resulting in a larger cross-sectional area of ​​the conductor in the overlapping portion compared to other portions.

[0157] Furthermore, the protection element in the embodiment had zero failures at 44W operation in 12 evaluation tests. In other words, in all 12 evaluation tests, the fuse element of the protection element in the embodiment blew when 44W of power was supplied to the third lower electrode. Therefore, the protection element in the embodiment was found to be a protection element with lower resistance and more stable operation compared to the protection element of the comparative example.

[0158] 1, 201, 501, 601, 701…Protective elements 2…Insulating substrate 2a…First surface 2b…Second surface 3, 603…Heating element 4, 504, 704…Fusable conductor 4a…First end 4b…Second end 5, 6, 605…Insulating members 11, 611…First electrode 12, 612…Second electrode 13, 613…Third lower electrode 21…First lower electrode 22…Second lower electrode 23…First heating element electrode 24…Second heating element electrode 25, 26…Connecting members 40, 740…Superimposed parts 50…Secondary battery 51…Battery cell 61…External positive terminal 62…External negative terminal 71, 72, 73…Switching elements 81, 82…Control devices 100, 200, 300, 400... Protection circuit 504A... High melting point metal layer 504B... Low melting point metal layer A1... Area of ​​the first electrode A2... Area of ​​the second electrode P1... First connection point P2... Second connection point P3... Third connection point

Claims

1. The device comprises: an insulating substrate; a first electrode and a second electrode provided on the first surface of the insulating substrate so as to face each other; a first lower electrode provided on the second surface of the insulating substrate opposite to the first surface and connected to the first electrode; a second lower electrode provided on the second surface of the insulating substrate and connected to the second electrode; a heating element provided on the first or second surface of the insulating substrate; a first heating element electrode connected to one end of the heating element and the first electrode; a second heating element electrode connected to the other end of the heating element opposite to the one end; an insulating member covering the surface of the heating element; a third lower electrode provided on the second surface of the insulating substrate and connected to the second heating element electrode; and a fusible conductor provided on the first surface of the insulating substrate, wherein, in a plan view from the first surface of the insulating substrate, the fusible conductor is connected to the first electrode and the second electrode so as to span between them. In the plan view, a protective element is provided such that a part of the heating element, a part of the first electrode, and a part of the fusible conductor overlap each other.

2. The protective element according to claim 1, wherein, in a plan view, the area of ​​the first electrode is larger than the area of ​​the second electrode.

3. The protective element according to claim 2, wherein, in the plan view, when the area of ​​the insulating substrate is A0 and the area of ​​the first electrode is A1, the condition 0.15 ≤ A1 / A0 ≤ 0.70 is satisfied.

4. The protective element according to any one of claims 1 to 3, wherein the fusible conductor is a laminate comprising a high-melting-point metal layer and a low-melting-point metal layer.

5. The protective element according to claim 4, wherein the high-melting-point metal layer is made of Ag or Cu, or a metal mainly composed of Ag or Cu, and the low-melting-point metal layer is made of Sn or a metal mainly composed of Sn.

6. The protective element according to any one of claims 1 to 3, wherein the heating element is provided on the first surface side of the insulating substrate, and the insulating member is provided between the heating element and the first electrode, or both between the heating element and the first electrode and between the heating element and the insulating substrate, in the portion where the heating element and the first electrode overlap each other in the plan view.

7. The protective element according to any one of claims 1 to 3, wherein the heating element is provided on the second surface side of the insulating substrate.

8. The protective element according to any one of claims 1 to 3, wherein the fusible conductor is connected to the first electrode and the second electrode via a connecting member made of solder.

9. The protective element according to claim 4, wherein the fusible conductor is connected to the first electrode and the second electrode via a connecting member made of solder or via the low-melting-point metal layer.

10. A protective circuit comprising one or more protective elements, wherein the protective element comprises: an insulating substrate; a first electrode and a second electrode provided on the first surface of the insulating substrate so as to face each other; a first lower electrode provided on the second surface of the insulating substrate opposite to the first surface and connected to the first electrode; a second lower electrode provided on the second surface of the insulating substrate and connected to the second electrode; a heating element provided on the first or second surface of the insulating substrate; a first heating element electrode connected to one end of the heating element and the first electrode; a second heating element electrode connected to the other end of the heating element opposite to the one end; an insulating member covering the surface of the heating element; a third lower electrode provided on the second surface of the insulating substrate and connected to the second heating element electrode; and a fusible conductor provided on the first surface of the insulating substrate. In a plan view from the first surface side of the insulating substrate, the fusible conductor is connected to the first electrode and the second electrode so as to span between them, and in the plan view, a part of the heating element, a part of the first electrode, and a part of the fusible conductor are arranged to overlap each other, in a protective circuit.

11. The protection circuit according to claim 10, further comprising a secondary battery, an external positive terminal and an external negative terminal, a switching element, and a control device, wherein the protection element is provided in the current path between the positive terminal of the secondary battery and the external positive terminal, or between the negative terminal of the secondary battery and the external negative terminal, and is switched to conduct current by a signal from the control device, thereby blocking the connection between the secondary battery and the external positive terminal, or between the secondary battery and the external negative terminal.

12. The protection circuit according to claim 10, further comprising a secondary battery, an external positive terminal and an external negative terminal, a switching element, and a control device, wherein a plurality of protection elements are provided, the plurality of protection elements are connected in parallel between the positive terminal of the secondary battery and the external positive terminal, or between the negative terminal of the secondary battery and the external negative terminal, all of the first lower electrodes of each of the plurality of protection elements are connected to the same terminal, all of the second lower electrodes of each of the plurality of protection elements are connected to the same terminal, all of the third lower electrodes of each of the plurality of protection elements are connected to the same terminal in the switching element, and the switching element is switched to conduct electricity by a signal from the control device, thereby blocking the connection between the secondary battery and the external positive terminal, or between the secondary battery and the external negative terminal.

13. The protection circuit according to claim 11 or 12, wherein the control device stops supplying power to the heating element after a predetermined time has elapsed since the switching element was switched to be energized.

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