Protection Circuit, Battery Pack, and Operating Method of Protection Circuit

Abstract

The present invention can reliably prevent overcurrent or creeping current after disconnection to improve safety, and can reduce costs by a device structure simpler than before, and further can reduce the failure rate of the device. In the protection circuit (1), when an overcurrent flows through the conduction path, after one of the two fuse elements provided in each of the plurality of protection elements (10A, 10B, 10C) is fused, the heater provided in at least one of the plurality of protection elements generates heat due to the creeping current flowing through the plurality of protection elements (10A, 10B, 10C) on the remaining conduction path, and fuses the other of the two fuse elements provided in the at least one protection element.

Description

Technical Field

[0001] The present invention relates to a protection circuit, a battery pack, and a method of operating the protection circuit, for example, a protection circuit provided between a secondary battery and a charger in a charge and discharge circuit of a secondary battery.

[0002] This application claims priority based on Japanese Patent Application No. 2019-203245 filed on November 8, 2019, and incorporates its content herein by reference. Background Art

[0003] Conventionally, a protection circuit has been installed in various mobile devices equipped with secondary batteries, such as mobile phones and laptop computers. As an existing protection circuit, for example, there is a secondary battery device configured to include a power storage device, a plurality of protection circuits, and first and second output terminals. Each of the protection circuits has two fuse elements connected in series. When an external circuit is connected to the first and second output terminals, a discharge current supplied from the power storage device to the external circuit and a charging current supplied from the external circuit to the power storage device flow through the two fuse elements connected in series within the plurality of protection circuits (Patent Document 1).

[0004] This secondary battery device is configured to include a heater having one end connected to a connection point between the fuse elements. One end of a rectifying element is connected to the other end of each heater, and a switching element is connected to the other end of each rectifying element. When the switching element is turned on, current flows through the switching element and each rectifying element to the heater of each protection circuit.

[0005] Further, in this secondary battery device, at least two rectifying elements are inserted in the middle of a current path connecting the terminals of the heaters of the protection circuits. In a state where a short-circuit current flows and one of the fuse elements is blown, even if a voltage difference is generated between the terminals of the heaters of the two protection circuits, at least one rectifying element is reverse-biased. Therefore, current does not flow from the terminal of the heater of one protection circuit into the terminal of the heater of another protection circuit, and no residual current is generated due to this situation.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Patent No. 4095426 Gazette Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] However, in the protection circuit of the above-mentioned Patent Document 1, since the fuse with a heater (hereinafter also referred to as SCP) has a left-right symmetric structure, when the current is cut off, the probability that one of the two fuse elements is cut off is 50%. Therefore, when a plurality of SCPs are connected in parallel in the protection circuit, it is impossible to determine which one of the two fuse elements in each SCP is cut off by the current. Therefore, depending on the cut-off location generated in each SCP, a sneak current may sometimes be generated in the protection circuit, and the overcurrent flows from the power storage device to the external circuit. Therefore, as a whole system, in order to prevent overcurrent, it is necessary to install a plurality of rectifying elements (diodes) corresponding one by one to the plurality of SCPs, resulting in circuit complexity, cost increase, and an increase in the device failure rate accompanied by an increase in the number of components.

[0011] In addition, consider a structure in which by changing the left-right balance of the two fuse elements of the SCP, it is possible to determine which one of the two fuse elements is cut off by the current. However, in this structure, due to the state of the heat capacity balance including circuit components around the SCP and the housing of the SCP, the possibility of the fuse element on the undesired side melting cannot be completely denied, and due to the continuous energization state of the heater, undesired circuit heating may occur, and further, there may be a risk of smoking, fire, etc.

[0012] In recent years, due to the further development of the high performance and high functionality of mobile devices, as the charging capacity of secondary batteries further increases, a protection circuit with high safety that can reliably prevent overcurrent is required.

[0013] An object of the present invention is to provide a protection circuit, a battery pack, and a method of operating the protection circuit, which can reliably prevent overcurrent or sneak current after cut-off to improve safety, and can reduce costs by a device structure simpler than before, and further can reduce the device failure rate.

[0014] Means for Solving the Problem

[0015] In order to achieve the above object, the present invention provides the following means.

[0016] [1] A protection circuit, which has a plurality of protection elements connected in parallel on the current path between a battery and an external circuit, wherein,

[0017] The protection element has two fuse elements connected in series on the current path and a heating element that melts the fuse element due to energization.

[0018] By passing an overcurrent through the conduction path, after one of the two fuse elements provided in each of the plurality of protection elements is blown, the heating element of at least one protection element among the plurality of protection elements generates heat due to the sneak current flowing through the plurality of protection elements on the remaining conduction path, and the other of the two fuse elements provided in the at least one protection element is blown.

[0019] [2] The protection circuit according to the above [1], wherein, by the sneak current flowing through the remaining conduction path, a power greater than the operating power of the protection element is applied to the heating element of at least one protection element provided on the remaining conduction path.

[0020] [3] The protection circuit according to the above [1] or [2], wherein the lower limit value of the operating power of the protection element is set to be equal to or less than the power calculated based on the voltage of the battery and the resistance including the combined resistance of the plurality of heating elements on the remaining conduction path.

[0021] [4] The protection circuit according to the above [3], wherein

[0022] the voltage of the battery is the lower limit value of the voltage range of the battery,

[0023] the combined resistance of the plurality of heating elements is calculated based on the lower limit value and the upper limit value of the resistance tolerance of the heating element,

[0024] the lower limit value of the operating power of the protection element is calculated based on the lower limit value of the voltage range during charging and discharging of the battery and the lower limit value and the upper limit value of the resistance tolerance of the heating element.

[0025] [5] The protection circuit according to the above [4], wherein

[0026] an equivalent circuit formed by connecting two resistors connected in parallel and one resistor in series is used,

[0027] the lower limit value of the voltage range during charging and discharging of the battery is set as the voltage applied across the two ends of the equivalent circuit,

[0028] the lower limit value of the resistance tolerance of the heating element is set as the resistance value of the one resistor,

[0029] the upper limit value of the resistance tolerance of the heating element is set as the resistance value of the two resistors,

[0030] the power calculated based on the voltage applied across the two ends of the equivalent circuit and the combined resistance of the two resistors and the one resistor is set to be greater than or equal to the lower limit value of the operating power of the protection element.

[0031] [6] According to the protection circuit described in [1] above, wherein,

[0032] The protection element has:

[0033] A first fuse element and a second fuse element connected in series;

[0034] A first electrode portion connected to a side of the first fuse element opposite to the second fuse element;

[0035] A second electrode portion connected to a side of the second fuse element opposite to the first fuse element;

[0036] A third electrode portion connected between the first fuse element and the second fuse element and connected in series with the heating element; and

[0037] A fourth electrode portion connected to a side of the heating element opposite to the third electrode portion.

[0038] [7] According to the protection circuit described in [6] above, wherein,

[0039] The first fuse element is connected to the battery side,

[0040] The second fuse element is connected to the external circuit side,

[0041] One end of the heating element is connected to the first fuse element and the second fuse element via the third electrode portion, and the other end is connected to the battery via the fourth electrode portion.

[0042] [8] According to the protection circuit described in [7] above, wherein,

[0043] The protection circuit further has a switching element connected between the heating element and the battery.

[0044] [9] A battery pack, wherein the battery pack is equipped with the protection circuit described in any one of [1] to [8] above.

[0045]

[10] A method for operating a protection circuit, the protection circuit having a plurality of protection elements connected in parallel on a conduction path between a battery and an external circuit, wherein,

[0046] By flowing an overcurrent in the conduction path, after one of the two fuse elements provided in each of the plurality of protection elements is fused, the heating element provided in at least one of the plurality of protection elements generates heat due to the sneak current flowing through the plurality of protection elements on the remaining conduction path, and fuses the other of the two fuse elements provided in the at least one protection element.

[0047] Advantages of the Invention

[0048] According to the present invention, overcurrent or creeping current after disconnection can be reliably prevented, thereby improving safety. Moreover, cost reduction can be achieved with a circuit structure simpler than conventional ones, and further, the failure rate of the device can be reduced. Brief Description of the Drawings

[0049] Figure 1 It is a diagram schematically showing an example of the structure of a protection circuit according to an embodiment of the present invention.

[0050] Figure 2 It shows the setting in Figure 1 A schematic diagram showing an example of the structure of a protection element of a protection circuit.

[0051] Figure 3 It illustrates the first case of current interruption in the protection circuit of Figure 1 A diagram.

[0052] Figure 4 It shows the correspondence with Figure 3 A diagram of the equivalent circuit corresponding to the first case.

[0053] Figure 5 It illustrates the second case of current interruption in the protection circuit of Figure 1 A diagram.

[0054] Figure 6 It shows the correspondence with Figure 5 A diagram of the equivalent circuit corresponding to the second case.

[0055] Figure 7 It illustrates the third case of current interruption in a modified example of the protection circuit of Figure 1 A diagram.

[0056] Figure 8 It shows the correspondence with Figure 7 A diagram of the equivalent circuit corresponding to the third case.

[0057] Figure 9 It illustrates the fourth case of current interruption in a modified example of the protection circuit of Figure 1 A diagram.

[0058] Figure 10 It shows the correspondence with Figure 9 A diagram of the equivalent circuit corresponding to the fourth case.

[0059] Figure 11 (a) of Figure 11 and Figure 10 (b) are diagrams showing the subsequent

[0060] Figure 12 It illustrates the situation inFigure 1 Diagram of the fifth case where current is cut off in a modified example of the protection circuit.

[0061] Figure 13 It shows the relationship with Figure 12 Diagram of the equivalent circuit corresponding to the fifth case. Detailed Implementation Modes

[0062] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings used in the following description, in order to facilitate understanding of the features, the parts that become the features are sometimes enlarged for convenience, and the dimensional ratios of the respective components are sometimes different from the actual ones. The materials, dimensions, etc. exemplified in the following description are just examples, and the present invention is not limited thereto, and can be appropriately changed and implemented within the range that can achieve the effects of the present invention.

[0063] [Structure of the Protection Circuit]

[0064] Figure 1 It is a diagram schematically showing an example of the structure of the protection circuit according to the embodiment of the present invention. In the protection circuit of the present embodiment, a plurality of protection elements described later are surface-mounted. This protection circuit is mounted on a battery pack such as a lithium-ion secondary battery, for example.

[0065] As Figure 1 shown, the protection circuit 1 includes a plurality of protection elements 10A, 10B, 10C connected in parallel on the conduction path between the secondary battery 2 (battery) and the external circuit. Specifically, the plurality of first electrode portions 15A, 15B, 15C of the plurality of protection elements 10A, 10B, 10C are connected to the parallel connection point A via the conduction path and are connected to the positive electrodes of the secondary batteries 2, 2, ···. In addition, the plurality of second electrode portions 16A, 16B, 16C of the plurality of protection elements 10A, 10B, 10C are connected to the parallel connection point B via the conduction path and are connected to the positive electrode of the charger 3. The plurality of third electrode portions 17A, 17B, 17C of the plurality of protection elements 10A, 10B, 10C are respectively connected to the fourth electrode portions 18A, 18B, 18C via heaters 14A, 14B, 14C (heating elements). The fourth electrode portions 18A, 18B, 18C are connected to both the negative electrodes of the secondary batteries 2, 2, ··· and the negative electrode of the charger 3, for example. A switching element 4 such as a FET is provided on the downstream side of the fourth electrode portions 18A, 18B, 18C.

[0066] The secondary battery 2 is composed of one or more battery cells 20, 20, ···. In the present embodiment, the plurality of battery cells 20, 20, ··· are connected in series. When the secondary battery 2 is charged, power is supplied from the charger 3 to the secondary battery 2 via the conduction path. In addition, when the secondary battery discharges, power is supplied from the secondary battery 2 to the conduction path. Thus, in either case of charging and discharging of the secondary battery 2, the same power is supplied to both the first fuse element 12A (12B, 12C) and the second fuse element 13A (13B, 13C).

[0067] The protection circuit 1 may also have a detection element (not shown) that is connected to each of the plurality of battery cells 20, 20... and is connected to the switching element 4. This detection element always monitors whether a high voltage state, particularly an overvoltage, occurs, and outputs a control signal to the switching element 4 in the case of a high voltage state. In this case, the switching element 4 causes current to flow from the secondary battery 2 to the heater 14A (14B, 14C) according to the detection signal, thereby heating the heater 14A (14B, 14C). As a result, the first fuse element 12A (12B, 12C) and / or the second fuse element 13A (13B, 13C) can be melted.

[0068] [Structure of protection element]

[0069] Figure 2 It shows an example of the structure of the protection element 10A of the protection circuit 1 provided in Figure 1 . The structures of the protection elements 10B and 10C are the same as that of the protection element 10A, and thus their descriptions are omitted.

[0070] As Figure 2 shown, the protection element 10A has: a substrate 11A; a first fuse element 12A and a second fuse element 13A (two fuse elements) connected in series on the substrate 11A; and a heater 14A (heating element) connected between the first fuse element 12A and the second fuse element 13A, which melts the first fuse element 12A and / or the second fuse element 13A by energization. In addition, the protection element 10A has: a first electrode portion 15A connected to the side of the first fuse element 12A opposite to the second fuse element 13A; a second electrode portion 16A connected to the side of the second fuse element 13A opposite to the first fuse element 12A; a third electrode portion 17A connected between the first fuse element 12A and the second fuse element 13A and connected in series with the heater 14A; and a fourth electrode portion 18A connected to the side of the heater 14A opposite to the third electrode portion 17A.

[0071] In this embodiment, the first fuse element 12A is connected to the secondary battery 2 side, and the second fuse element 13A is connected to the charger 3 side (external circuit side). One end of the heater 14A is connected to the first fuse element 12A and the second fuse element 13A via the third electrode portion 17A, and the other end is connected to the secondary battery 2 via the fourth electrode portion 18A.

[0072] The substrate 11A may be any substrate made of an insulating material and is not particularly limited. For example, in addition to substrates for printed wiring boards such as ceramic substrates and glass epoxy substrates, glass substrates, resin substrates, insulated metal substrates, etc. can also be used. Among them, a ceramic substrate, which is an insulating substrate with excellent heat resistance and good thermal conductivity, is preferably used.

[0073] The first fuse element 12A is provided, for example, on one main surface side of the substrate 11A, and the second fuse element 13A is similarly provided on one main surface side of the substrate 11A. The first fuse element 12A and the second fuse element 13A may be integrally formed or may be composed of different components. In addition, the shapes of the first fuse element 12A and the second fuse element 13A are, for example, sheet-like, but are not limited thereto, and may also be rod-shaped.

[0074] The first fuse element 12A and the second fuse element 13A have, for example, a sheet shape with the same width and thickness, and the length of the first fuse element 12A is the same as the length of the second fuse element 13A. In this case, the thermal resistance of the first fuse element 12A is the same as the thermal resistance of the second fuse element 13A.

[0075] As the materials constituting the first fuse element 12A and the second fuse element 13A, various low-melting-point metals that have been used as fuse materials can be used. Examples of low-melting-point metals include SnSb alloys, BiSnPb alloys, BiPbSn alloys, BiPb alloys, BiSn alloys, SnPb alloys, SnAg alloys, PbIn alloys, ZnAl alloys, InSn alloys, PbAgSn alloys, etc. The materials constituting the first fuse element 12A and the second fuse element 13A are preferably the same, but may also be different.

[0076] The heater 14A is provided, for example, on the other main surface side of the substrate 11A. The heater 14A is configured to abut against the other main surface of the substrate 11A and is disposed directly below the third electrode portion 17A. The heater 14A is provided on the side of the substrate 11A opposite to the first fuse element 12A and the second fuse element 13A, but is not limited thereto, and may also be provided on the same side of the substrate 11A as the first fuse element 12A and the second fuse element 13A.

[0077] The heater 14A is formed, for example, by coating a resistive paste composed of a conductive material such as ruthenium oxide and carbon black, an inorganic binder such as sodium silicate, and an organic binder such as a thermosetting resin, and firing as needed. Alternatively, as the heater 14A, a thin film of ruthenium oxide, carbon black, etc. can be formed through processes such as printing, plating, evaporation, and sputtering, or it can be formed by pasting and laminating these films.

[0078] An insulating member (not shown) may be provided on the heater 14A so as to cover its outer surface.

[0079] As the material constituting the insulating member, any material can be used as long as it can insulate the heater 14A from the outside, and there is no particular limitation. For example, glass (SiO2) can be cited.

[0080] When the heater 14A has a resistance tolerance, it is preferable to consider this resistance tolerance in the calculation of the power of the protection element described later. The range of the resistance tolerance of the heater 14A is not particularly limited. For example, it is 4.8 Ω to 8.0 Ω.

[0081] The first electrode portion 15A, the second electrode portion 16A, and the third electrode portion 17A are electrodes into which the melted first fuse element 12A or the second fuse element 13A flows, respectively. The materials constituting these first electrode portion 15A, second electrode portion 16A, and third electrode portion 17A are not particularly limited, and metals having good wettability with the melted first fuse element 12A or the second fuse element 13A can be cited. As the materials constituting the first electrode portion 15A, second electrode portion 16A, and third electrode portion 17A, a metal monomer such as copper (Cu) or a material having at least its surface formed of Ag (silver), Ag (silver)-Pt (platinum), Ag (silver)-Pd (palladium), Au (gold), etc. can be used.

[0082] Solder portions (not shown) are provided at positions corresponding to the first electrode portion 15A, the second electrode portion 16A, and the fourth electrode portion 18A, respectively. The first electrode portion 15A, the second electrode portion 16A, and the fourth electrode portion 18A are respectively connected to the protection circuit 1 via the solder portions (not shown).

[0083] In the protection element 10A, when a large current (overcurrent) exceeding the rated value flows through the protection element 10A, the first fuse element 12A and / or the second fuse element 13A melts due to its own heat generation (Joule heat), or a detection element (not shown) constantly monitors whether the battery becomes a high voltage state, particularly an overvoltage state, and outputs a control signal to the switching element 4 in the case of a high voltage state. As a result, the first fuse element 12A and / or the second fuse element 13A melts due to the heat generation of the heater 14A, thereby cutting off the conduction path.

[0084] In the protection circuit 1 configured as described above, when an overcurrent flows through the conduction path, after one of the two fuse elements respectively provided in the plurality of protection elements 10A, 10B, and 10C is melted, due to the sneak current flowing through the plurality of protection elements 10A, 10B, and 10C on the remaining conduction path, the heater of at least one protection element among the plurality of protection elements 10A, 10B, and 10C generates heat, and the other of the two fuse elements provided in the at least one protection element is melted.

[0085] In order to perform the above operation in the protection circuit 1, for example, the lower limit value of the operating power of each protection element is preferably set to be equal to or lower than the power calculated based on the voltage of the secondary battery 2 and the resistance of the combined resistance including the plurality of heaters 14A, 14B, and 14C on the remaining conduction path.

[0086] The "resistance including the combined resistance" means, when there are other components (not shown) mounted on the above conduction path, the sum of the combined resistance of the plurality of heaters 14A, 14B, and 14C on the remaining conduction path and the resistance of the other component, and when there are no such other components mounted on the above conduction path, it means the combined resistance of the plurality of heaters 14A, 14B, and 14C on the remaining conduction path itself.

[0087] The operating power of the protection element refers to the power value or power range required to normally melt the first fuse element and / or the second fuse element in each protection element, and is a value provided as a characteristic (specification) of each protection element. The range of the operating power of the protection element is not particularly limited, for example, it is 13W to 130W.

[0088] The voltage of the secondary battery 2 refers to the value provided as a characteristic (specification) of the cell voltage when the secondary battery 2 is composed of one battery cell. When the secondary battery 2 is composed of a plurality of battery cells, the voltage of the secondary battery 2 refers to the value provided as a characteristic (specification) of the combined voltage (battery pack voltage) of these battery cells. The range of the battery voltage is not particularly limited, for example, it is 3.0V to 4.5V. The range of the pack voltage is also not particularly limited, for example, in the case of a structure in which five of the above cell voltages are connected in series, it is 15.0V to 22.5V.

[0089] In addition, the remaining conduction path refers to the path through which the sneak current flows through the plurality of protection elements 10A, 10B, and 10C in a state where one of the two fuse elements provided in each of the plurality of protection elements 10A, 10B, and 10C is melted.

[0090] Thus, in the protection circuit 1, the power above the operating power of at least one protection element provided on the remaining current-carrying path is applied to the heater of the protection element by the sneak current flowing in the remaining current-carrying path.

[0091] [Operating Method and Principle of Protection Circuit]

[0092] Next, the operating principle of the protection circuit of the present embodiment will be specifically described by taking the following first case to sixth case as examples. In the first case to sixth case, for the sake of convenience of explanation, the case where no other components are mounted on the current-carrying path will be described.

[0093] Figure 3 It is to illustrate Figure 1 FIG. showing the first case of current cut-off in the protection circuit 1. As the first case, it is assumed that an overcurrent flows due to an external short circuit or the like, and the first fuse element 12A and the second fuse elements 13B and 13C are blown.

[0094] In this case, since the first fuse element 12A is a fuse element on the secondary battery side and the second fuse elements 13B and 13C are fuse elements on the charger side, the secondary battery 2 side and the charger 3 side are in a state where the current is not cut off, and a sneak current flows through the first fuse elements 12B and 12C and the second fuse element 13A. If the second fuse element 13A is blown due to this sneak current, the secondary battery 2 side and the charger 3 side are cut off from the current.

[0095] Therefore, in the present embodiment, it is preferable to set the lower limit value of the operating power of the protection element 10A to be equal to or lower than the power calculated based on the voltage of the secondary battery 2 and the combined resistance of the heaters 14A, 14B, and 14C on the remaining current-carrying path. Thus, the power above the operating power of the protection element 10A can be reliably applied to the protection element 10A on the remaining current-carrying path by the sneak current flowing in the remaining current-carrying path, and the second fuse element 13A can be blown by the operation of the protection element 10A.

[0096] The secondary battery 2 generally has a voltage range as a normal region except for the over-discharge region and the over-charge region. Therefore, the voltage of the secondary battery 2 used when calculating the power W is preferably the lower limit value of the voltage range of the secondary battery. Further, when the heaters of the respective protection elements have a resistance tolerance, it is preferable to calculate the combined resistance of the heaters 14A, 14B, and 14C on the remaining conduction path according to the lower limit value and the upper limit value of the resistance tolerance of the heater. In this case, the lower limit value of the operating power of the protection element 10A is calculated based on the lower limit value of the voltage range during charging and discharging of the secondary battery 2, and the lower limit value and the upper limit value of the resistance tolerance of the heater. Thereby, even when the power applied to the protection element 10A deviates due to the leakage current flowing through the remaining conduction path, the protection element 10A can be sufficiently operated, and the second fuse element 13A can be reliably fused.

[0097] As Figure 4 shown, Figure 3 the protection circuit 1 in the state can be represented by an equivalent circuit EC1 formed by connecting two resistors R2 and R3 connected in parallel and one resistor R1 in series. When a current I EC1 (leakage current) flows through this equivalent circuit EC1 and the fuse H1 is blown, the parallel connection point A and the parallel connection point B are cut off by the current.

[0098] Therefore, in Figure 4 the equivalent circuit EC1, the combined resistance R0 of the resistors R1, R2, and R3 in the equivalent circuit EC1 is obtained, and the current I EC1 flowing from this combined resistance to the equivalent circuit EC1 is obtained using Ohm's law. Further, the power W1 at the resistor R1 is calculated based on the voltage V between the parallel connection point A and the parallel connection point B (W1 = (I EC1 ) 2 × R1). And the operating power below the power W1 calculated above can be set as the operating power of the protection element 10A.

[0099] As an example of the calculation, for example, consider a case where the voltage range during charging and discharging of the secondary battery 2 is 15.0 V to 22.5 V, and the resistance tolerance of the heaters 14A, 14B, and 14C is 4.8 Ω to 8.0 Ω. In this case, the lower limit value of the voltage range of the secondary battery 2 is 15.0 V, the lower limit value of the resistance tolerance of the heaters 14A, 14B, and 14C is 4.8 Ω, and the upper limit value is 8.0 Ω.

[0100] When using the lower limit value and the upper limit value of the resistance tolerance of the heater, there are four combination patterns of the resistance values of the resistors R1, R2, and R3 in the equivalent circuit EC1. Table 1 shows the results of calculating the powers W1, W2, and W3 using each combination pattern.

[0101] [Table 1]

[0102]

[0103] In Table 1, in combination mode 1, the lower limit value (15.0 V) of the voltage range in the charge and discharge of the secondary battery 2 is set as the voltage V applied across both ends of the equivalent circuit EC1. In addition, the lower limit value (4.8 V) of the resistance tolerance of the heater 14A is set as the resistance value of the resistor R1, and the upper limit value (8.0 V) of the resistance tolerance of the heaters 14B and 14C is set as the resistance values of the resistors R2 and R3. Moreover, in this combination mode 1, the power W1 (13.9 W) applied to the resistor R1 becomes the minimum value. Therefore, in this first case, it is preferable to set the power W1 calculated based on the voltage V applied across both ends of the equivalent circuit EC1 and the combined resistance R0 of the resistors R1, R2, and R3 to be equal to or higher than the lower limit value of the operating power of the protection element 10A.

[0104] Figure 5 It is to illustrate Figure 1 the second case where current is cut off in the protection circuit 1. In the second case, it is assumed that an overcurrent flows due to an external short circuit or the like, and the first fuse elements 12A and 12B and the second fuse element 13C are blown.

[0105] In this case, since the first fuse elements 12A and 12B are fuse elements on the secondary battery side and the second fuse element 13C is a fuse element on the charger side, the secondary battery 2 side and the charger 3 side are in a state where the current is not cut off, and a leakage current flows through the first fuse element 12C and the second fuse elements 13A and 13B. If the first fuse element 12C is blown due to this leakage current, the secondary battery 2 side and the charger 3 side are cut off from the current.

[0106] As Figure 6 shown, Figure 5 the protection circuit 1 in this state can be represented by an equivalent circuit EC2 formed by connecting one resistor R3 and two resistors R1 and R2 connected in parallel in series. When a current I EC2 (leakage current) flows through this equivalent circuit EC2 and the fuse H3 is blown, the parallel connection points A and B are cut off from the current.

[0107] In Figure 6 the equivalent circuit EC2, similar to Figure 4 the equivalent circuit EC1, the combined resistance R0 of the resistors R1, R2, and R3 inside the equivalent circuit EC2 is obtained, and Ohm's law is used to find the current I EC2, Further, the power W3 at the resistor R3 is calculated based on the voltage V between the parallel connection point A and the parallel connection point B (W3 = (I EC2 ) 2 × R3). And the operating power below the calculated power W3 can be set as the operating power of the protection element 10C.

[0108] In addition, in this second case, it is preferable to set the voltage V applied across both ends of the equivalent circuit EC2 to the lower limit value of the voltage range during charging and discharging of the secondary battery 2. Further, the resistance value of the resistor R3 is set to the lower limit value of the resistance tolerance of the heater 14C, and the resistance values of the resistors R1 and R2 are set to the upper limit values of the resistance tolerances of the heaters 14A and 14B. In this case, similarly to the above first case, it is preferable to set the power W3 calculated based on the voltage V applied across both ends of the equivalent circuit EC2 and the combined resistance R0 of the resistors R1, R2, and R3 to be above the lower limit value of the operating power of the protection element 10C.

[0109] And the lower limit value of the operating power of the protection element 10B can also be set based on the same calculation as above. In addition, since the equivalent circuit EC2 is substantially the same as the equivalent circuit EC1, the power W3 is the same as the power W1.

[0110] Therefore, in the protection circuit 1 in which 3 protection elements are connected in parallel as Figure 1 shown, it is only necessary to set the lower limit values of the operating powers of the protection elements 10A, 10B, and 10C to be below the power W1 (= W3).

[0111] Figure 7 is a diagram for explaining a third case where current is cut off in a modified example of the protection circuit 1 in Figure 1 . In this third case, it is assumed that 2 protection elements 10A and 10B are provided in the protection circuit 1, and an overcurrent flows due to an external short circuit or the like, and the first fuse element 12A and the second fuse element 13B are blown.

[0112] In this case, since the first fuse element 12A is a fuse element on the secondary battery side and the second fuse element 13B is a fuse element on the charger side, the secondary battery 2 side and the charger 3 side are in a state where the current is not cut off, and a sneak current flows through the first fuse element 12B and the second fuse element 13A. If the first fuse element 12B or the second fuse element 13A is blown due to this sneak current, the secondary battery 2 side and the charger 3 side are cut off from the current.

[0113] As Figure 8 shown, Figure 7 the protection circuit in the state can be represented by an equivalent circuit EC3 formed by connecting 2 resistors R1 and R2 in series. The current IEC3 (The leakage current) flows through the equivalent circuit EC3, and the fuse H1 or the fuse H2 blows, whereby the parallel connection points A and B are cut off by the current.

[0114] Therefore, in Figure 8 the equivalent circuit EC3, the combined resistance R0 of the resistors R1 and R2 in the equivalent circuit EC3 is also obtained, and Ohm's law is used to obtain the current I flowing from this combined resistance to the equivalent circuit EC3 EC3 , and further, the power W1 at the resistor R1 is calculated based on the voltage V between the parallel connection points A and B (W1 = (I EC3 ) 2 ×R1). And the operating power below the above-calculated power W1 can be set as the operating power of the protection element 10A.

[0115] In addition, in this third case, it is preferable to set the voltage V applied across the two ends of the equivalent circuit EC3 to the lower limit value of the voltage range during the charge and discharge of the secondary battery 2, and to set the resistance values of the resistor R1 and the resistor R2 to the upper limit value of the resistance tolerance of the heaters 14A and 14B. In this case, the power W1 (or power W2) calculated based on the voltage V applied across the two ends of the equivalent circuit EC3 and the combined resistance R0 of the resistors R1 and R2 can be set to be above the lower limit value of the operating power of the protection elements 10A and 10B.

[0116] Figure 9 is a diagram illustrating a fourth case where current is cut off in a modified example of the protection circuit 1 in Figure 1 . As the fourth case, consider the following situation: Four protection elements 10A, 10B, 10C, and 10D are provided in the protection circuit, and an overcurrent flows due to an external short circuit or the like, and the first fuse elements 12A, 12B and the second fuse elements 13C, 13D blow. In addition, the protection elements 10A, 10B, 10C, and 10D have substantially the same structure.

[0117] In this case, since the first fuse elements 12A, 12B are the fuse elements on the secondary battery side and the second fuse elements 13C, 13D are the fuse elements on the charger side, the secondary battery 2 side and the charger 3 side are in a state where they are not cut off by the current, and the leakage current flows through the first fuse elements 12C, 12D and the second fuse elements 13A, 13B. As Figure 10 shown, Figure 9 the protection circuit in this state can be represented by an equivalent circuit EC4 formed by connecting in series two resistors R3 and R4 connected in parallel and two resistors R1 and R2 connected in parallel.

[0118] After that, a sneak current continuously flows through the remaining conduction paths of the protection circuit, and as a result, one of the first fuse elements 12C, 12D and the second fuse elements 13A, 13B is blown. For example, when the second fuse element 13B is blown due to the sneak current, as shown in (a) of Figure 11 , the path of the fuse H2 corresponding to the second fuse element 13B disappears, and the equivalent circuit EC4 becomes the same equivalent circuit EC5 as the Figure 4 equivalent circuit EC1. Therefore, in the fourth case shown in Figure 9 , as the protection element 10A, a protection element with a lower limit value of the operating power of W1 or less can be selected.

[0119] In addition, when the second fuse element 13A is blown due to the sneak current from the state of Figure 10 , the equivalent circuit EC4 also becomes the same equivalent circuit as the equivalent circuit EC5 in (a) of Figure 11 . Therefore, in the fourth case shown in Figure 9 , as the protection element 10B, a protection element with a lower limit value of the operating power of W1 or less can be selected.

[0120] In addition, when the first fuse element 12D is blown due to the sneak current from the state of Figure 10 , as shown in (b) of Figure 11 , the equivalent circuit EC4 becomes the same equivalent circuit EC6 as the Figure 6 equivalent circuit EC2. In addition, when the first fuse element 12C is blown due to the sneak current from the state of Figure 10 , the equivalent circuit EC4 also becomes the same equivalent circuit as the equivalent circuit EC6 in (b) of Figure 11 . Therefore, in the fourth case shown in Figure 9 , as the protection elements 10C, 10D, a protection element with a lower limit value of the operating power of W1 (= W3) or less can be selected.

[0121] Figure 12 is a diagram for explaining a fifth case of current interruption in a modified example of the protection circuit 1 in Figure 1 . As a sixth case, consider the following situation: In the protection circuit 1, four protection elements 10A, 10B, 10C, 10D are provided, and an overcurrent flows due to an external short circuit or the like, and the first fuse element 12A and the second fuse elements 13B, 13C, 13D are blown.

[0122] In this case, since the first fuse element 12A is a fuse element on the secondary battery side and the second fuse elements 13B, 13C, and 13D are fuse elements on the charger side, the secondary battery 2 side and the charger 3 side are in a state where they are not cut off by current, and a sneak current flows through the first fuse elements 12B, 12C, 12D and the second fuse element 13A. If the second fuse element 13A is blown due to this sneak current, the secondary battery 2 side and the charger 3 side are cut off by current.

[0123] As Figure 13 shown, Figure 12 the protection circuit in the state of can be represented by an equivalent circuit EC7 formed by connecting three resistors R2, R3, and R4 connected in parallel and one resistor R1 connected in series.

[0124] Current I EC7 (sneak current) flows through this equivalent circuit EC7, and the fuse H1 is blown, whereby the parallel connection point A and the parallel connection point B are cut off by current.

[0125] Therefore, in Figure 13 the equivalent circuit EC7 of, the combined resistance R0 of the resistors R1, R2, R3, and R4 in the equivalent circuit EC7 can also be obtained, and the current I EC7 flowing from this combined resistance to the equivalent circuit EC7 is obtained using Ohm's law. Furthermore, the power W1 at the resistor R1 is calculated based on the voltage V between the parallel connection point A and the parallel connection point B. However, the power W1 applied to the resistor R1 of the equivalent circuit EC7 of Figure 13 is greater than the power W1 applied to the resistor R1 of the equivalent circuit EC5 of (a) of Figure 11 . Therefore, if the lower limit value of the operating power of the protection element 10A is set to be equal to or lower than the power W1 applied to the resistor R1 of the equivalent circuit EC5, then in this fifth case, the second fuse element 13A will also be blown by the sneak current, and the secondary battery 2 side and the charger 3 side will be cut off by current.

[0126] In addition, in Figure 13 , the case where the first fuse element 12A and the second fuse elements 13B, 13C, and 13D are blown has been described. However, the same consideration as above can also be applied when one of the plurality of first fuse elements 12A, 12B, 12C, and 12D is blown and the second fuse element among all the protection elements other than the protection element having the blown first fuse element is blown.

[0127] Therefore, it is speculated that even for a protection circuit in which four protection elements are connected in parallel as Figure 9 shown, as long as the lower limit value of the operating power of the protection elements 10A, 10B, 10C, and 10D is also set to be equal to or lower than the power W1.

[0128] As described above, according to the present embodiment, by passing an overcurrent through the conduction path between the secondary battery 2 and the external circuit, after one of the two fuse elements provided in each of the plurality of protection elements 10A, 10B, ··· is fused, the heater provided in at least one of the plurality of protection elements generates heat due to the sneak current flowing through the remaining plurality of protection elements 10A, 10B, ··· on the conduction path, and fuses the other of the two fuse elements provided in the at least one protection element. Therefore, the circuit on one side of the first fuse element (or the second fuse element) can be disconnected from the circuit on the other side.

[0129] Therefore, without providing a rectifying element such as a diode in the protection circuit 1, an overcurrent or a sneak current after disconnection can be reliably prevented with a simple circuit structure. In addition, in the circuit design of the protection circuit 1, even without considering the heat capacity balance including circuit components around the SCP, the housing of the SCP, etc., the circuit can be reliably disconnected, an easy circuit design can be achieved, and the safety can be improved. Moreover, since there is no need to provide a rectifying element such as a diode, cost reduction can be achieved, and the number of components can be reduced to reduce the failure rate of the circuit.

[0130] In addition, the lower limit value of the operating power of each protection element is set to be equal to or lower than the power calculated based on the voltage of the secondary battery 2 and the resistance including the combined resistance of the plurality of heaters 14A, 14B, ··· on the remaining conduction path. Therefore, an overcurrent flowing through the remaining conduction path can reliably apply a power equal to or higher than the operating power of the protection element to the protection element on the remaining conduction path.

[0131] And the lower limit value of the operating power of each protection element is calculated based on the lower limit value of the voltage range during charging and discharging of the secondary battery 2, and the lower limit value and the upper limit value of the resistance tolerance of the heater. Therefore, a protection circuit 1 with higher operating accuracy can be constructed, and the reliability of the protection circuit 1 can be improved.

[0132] In addition, by screening the resistance of the heaters of each protection element, etc., the resistance tolerance can be reduced, thereby expanding the voltage operating range of each protection element. Therefore, by appropriately making such adjustments, the operating accuracy and reliability can also be improved.

[0133] In addition, in the design of the protection circuit 1, an equivalent circuit EC1 formed by connecting in series two resistors R2 and R3 connected in parallel and one resistor R1 is used. The lower limit value of the voltage range of the secondary battery 2 is set as the voltage V applied across both ends of the equivalent circuit EC1. The lower limit value of the resistance tolerance of the heater is set as the resistance value of the resistor R1, and the upper limit value of the resistance tolerance of the heater is set as the resistance values of the resistors R2 and R3. Moreover, the power W calculated based on the voltage V and the combined resistance R0 of the resistors R1, R2, and R3 is set to be above the lower limit value of the operating power of the protection elements 10A, 10B, and 10C. Therefore, it is possible to more easily design a protection circuit equipped with three or more protection elements.

[0134] As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

[0135] Reference Signs

[0136] 1 Protection Circuit

[0137] 2 Secondary Battery

[0138] 3 Charger

[0139] 4 Switching Element

[0140] 10A Protection Element

[0141] 10B Protection Element

[0142] 10C Protection Element

[0143] 10D Protection Element

[0144] 11A Substrate

[0145] 12A First Fuse Element

[0146] 12B First Fuse Element

[0147] 12C First Fuse Element

[0148] 12D First Fuse Element

[0149] 13A Second Fuse Element

[0150] 13B Second Fuse Element

[0151] 13C Second Fuse Element

[0152] 13D Second Fuse Element

[0153] 14A Heater

[0154] 14B Heater

[0155] 14C Heater

[0156] 15A First Electrode Part

[0157] 15B First Electrode Part

[0158] 15C First Electrode Part

[0159] 16A Second Electrode Part

[0160] 16B Second Electrode Part

[0161] 16C Second Electrode Part

[0162] 17A Third Electrode Part

[0163] 17B Third Electrode Part

[0164] 17C Third Electrode Part

[0165] 18A Fourth Electrode Part

[0166] 18B Fourth Electrode Part

[0167] 18C Fourth Electrode Part

[0168] 20 Battery Cell

Claims

1. A protection circuit having a plurality of protection elements connected in parallel on a conduction path between a battery and an external circuit, characterized in that the protection element has two fuse elements connected in series on the conduction path and a heating element that melts the fuse elements upon energization, when an overcurrent flows through the conduction path, after one of the two fuse elements provided in each of the plurality of protection elements is melted, the heating element provided in at least one of the plurality of protection elements generates heat due to the sneak current flowing through the plurality of protection elements on the remaining conduction path, and melts the other of the two fuse elements provided in the at least one protection element.

2. The protection circuit according to claim 1, characterized in that the sneak current flowing through the remaining conduction path applies a power greater than the operating power of the at least one protection element provided on the remaining conduction path to the heating element of the at least one protection element.

3. The protection circuit according to claim 1 or 2, characterized in that the lower limit value of the operating power of the at least one protection element is set to be less than or equal to the power calculated based on the voltage of the battery and the resistance including the combined resistance of the plurality of heating elements on the remaining conduction path.

4. The protection circuit according to claim 3, characterized in that the voltage of the battery is the lower limit value of the voltage range of the battery, the combined resistance of the plurality of heating elements is calculated based on the lower limit value and the upper limit value of the resistance tolerance of the heating elements, the lower limit value of the operating power of the at least one protection element is calculated based on the lower limit value of the voltage range during charging and discharging of the battery and the lower limit value and the upper limit value of the resistance tolerance of the heating elements.

5. The protection circuit according to claim 4, characterized in that an equivalent circuit formed by connecting two resistors connected in parallel and one resistor in series is used, the lower limit value of the voltage range during charging and discharging of the battery is set as the voltage applied across the two ends of the equivalent circuit, the lower limit value of the resistance tolerance of the heating elements is set as the resistance value of the one resistor, the upper limit value of the resistance tolerance of the heating elements is set as the resistance values of the two resistors, the power calculated based on the voltage applied across the two ends of the equivalent circuit and the combined resistance of the two resistors and the one resistor is set to be greater than or equal to the lower limit value of the operating power of the at least one protection element.

6. The protection circuit according to claim 1, characterized in that the protection element has: a first fuse element and a second fuse element connected in series; a first electrode portion connected to the side of the first fuse element opposite to the second fuse element; a second electrode portion connected to the side of the second fuse element opposite to the first fuse element; a third electrode portion connected between the first fuse element and the second fuse element and connected in series with the heating element; and a fourth electrode portion connected to the side of the heating element opposite to the third electrode portion.

7. The protection circuit according to claim 6, characterized in that The first fuse element is connected to the battery side. The second fuse element is connected to the external circuit side. One end of the heating element is connected to the first fuse element and the second fuse element via the third electrode portion, and the other end is connected to the battery via the fourth electrode portion.

8. The protection circuit according to claim 7, wherein: The protection circuit further has a switching element connected between the heating element and the battery.

9. A battery pack, wherein: The battery pack is equipped with the protection circuit according to any one of claims 1 to 8.

10. A method for operating a protection circuit, the protection circuit having a plurality of protection elements connected in parallel on a current-carrying path between a battery and an external circuit, wherein: By passing an overcurrent through the current-carrying path, after one of the two fuse elements provided in each of the plurality of protection elements is melted, the heating element provided in at least one of the plurality of protection elements generates heat due to the sneak current flowing through the plurality of protection elements on the remaining current-carrying path, and melts the other of the two fuse elements provided in the at least one protection element.

Images