Circuit protection device

Abstract

To provide a circuit protection device capable of suppressing a discharge current at the time of interruption of a circuit protection element.SOLUTION: A circuit protection device for protecting a monitoring circuit 22 includes an overvoltage protection element 212, a circuit protection element 211, and an impedance 25. The overvoltage protection element is connected between a plurality of detection lines M that connect a power supply unit and a monitoring circuit and fails in a short circuit when an overvoltage is applied. The circuit protection element is provided on each detection line and breaks the electrical connection between the power supply and the monitoring circuit when a current equal to or greater than a predetermined current value flows through any of the detection lines. The impedance is provided on at least one of the detection lines and arranged between the power supply and the circuit protection element. In the event of an overvoltage, the overvoltage protection element fails to short-circuit and maintains a short-circuit state between detection lines, and the circuit protection element breaks the electrical connection between the power supply and the monitoring circuit due to short-circuit current flowing between the detection lines through the overvoltage protection element. The impedance suppresses the generation of discharge current when the circuit protection element breaks the electrical connection between the power supply and the monitoring circuit due to the short-circuit current.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a circuit protection device that protects a monitoring circuit that monitors the voltage of a power supply unit. [Background technology]

[0002] For example, hybrid cars and electric cars are equipped with a battery pack in which many battery cells are connected in series as a power supply unit, and the electric motor for driving the car is driven by the voltage generated by the power supply unit. As disclosed in Patent Document 1, this type of power supply unit is connected to a monitoring circuit that monitors the voltage in order to prevent heat generation, burning, deterioration, etc., associated with voltage abnormalities, and a circuit protection device that protects the monitoring circuit is provided between the power supply unit and the monitoring circuit.

[0003] Here, the power supply unit and the monitoring circuit are electrically connected by multiple detection lines for voltage detection, and if an overvoltage occurs in the power supply unit due to the influence of peripheral devices, etc., or if a large current flows through the detection lines, there is a risk that the monitoring circuit will be destroyed. Therefore, it is necessary to provide a circuit protection device between the power supply unit and the monitoring circuit to protect the monitoring circuit.

[0004] The circuit protection device of Patent Document 1 includes an overvoltage protection element (e.g., a Zener diode) that is connected between a plurality of detection lines for voltage detection that connect a power supply unit and a monitoring circuit and that short-circuits when an overvoltage is applied, and a circuit protection element (e.g., a fuse) that is provided on each of the plurality of detection lines and that cuts off the electrical connection between the power supply unit and the monitoring circuit when a current equal to or greater than a predetermined current value flows through the detection line. When an overvoltage occurs in the power supply unit, the overvoltage protection element maintains the plurality of detection lines in a short-circuit state, and the circuit protection element cuts off the electrical connection between the power supply unit and the monitoring circuit, so that the monitoring circuit can be appropriately protected from the overvoltage occurring in the power supply unit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-7883 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the circuit protection device of Patent Document 1, a discharge current may flow due to arc discharge or the like at a point where the electrical connection between the power supply unit and the monitoring circuit is interrupted by a circuit protection element such as a fuse.

[0007] In view of the above, an object of the present invention is to provide a circuit protection device capable of suppressing a discharge current when a circuit protection element is cut off. [Means for solving the problem]

[0008] The present invention provides a circuit protection device for protecting a monitoring circuit that monitors the voltage of a power supply unit. The circuit protection device includes an overvoltage protection element connected between a plurality of detection lines for voltage detection that connect the power supply unit and the monitoring circuit and that short-circuits when an overvoltage is applied, a circuit protection element provided on each of the detection lines and that cuts off the electrical connection between the power supply unit and the monitoring circuit when a current equal to or greater than a predetermined current value flows through the detection line, and an impedance provided on at least one of the detection lines and located between the power supply unit and the circuit protection element. The overvoltage protection element is configured to short-circuit when an overvoltage occurs in the power supply unit, thereby maintaining a short state between the plurality of detection lines. The circuit protection element is configured to interrupt the electrical connection between the power supply unit and the monitoring circuit by a short-circuit current flowing between the detection line via the overvoltage protection element when an overvoltage occurs in the power supply unit, and the impedance is configured to suppress generation of a discharge current when the circuit protection element interrupts the electrical connection between the power supply unit and the monitoring circuit by the short-circuit current.

[0009] The circuit protection device of the present invention has an impedance in at least one of the detection lines. The impedance is disposed at a position between the power supply unit and the circuit protection element. The concept of impedance includes resistance and reactance (inductive reactance and capacitive reactance), and specific configurations include impedance elements such as resistors, inductors, and capacitors, and wiring that functions as an impedance. When the circuit protection element cuts off the electrical connection between the power supply unit and the monitoring circuit due to a short-circuit current, the voltage drop of the impedance can reduce the electric field (i.e., potential difference) at the location where discharge may occur, so that the occurrence of a discharge current can be suppressed. Since the possibility that the monitoring circuit will be destroyed by the discharge current generated in the broken circuit protection element can be reduced, a circuit protection unit 20 that can protect the monitoring circuit 22 more reliably than before can be provided. [Brief description of the drawings]

[0010] [Figure 1] 1 is an overall view of a power supply system including a circuit protection device according to a first embodiment. [Diagram 2] 1 is a diagram showing a main part of a battery monitoring device including a circuit protection device according to a first embodiment. [Diagram 3] 2A to 2C are diagrams illustrating the function of the circuit protection device according to the first embodiment. [Figure 4] 13 is a diagram showing a main part of a battery monitoring device including a circuit protection device according to a modified example. [Diagram 5] 10 is a diagram showing a main part of a battery monitoring device including a circuit protection device according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] (First embodiment) In the first embodiment, the circuit protection device of the present invention is applied to a power supply system mounted on a hybrid vehicle or an electric vehicle. As shown in Fig. 1, the power supply system of this embodiment includes, as main components, a battery pack 1 and a battery monitoring device 2. Note that in the following embodiments, parts that are the same or equivalent to each other are given the same reference numerals in the drawings.

[0012] The battery pack 1 mainly supplies power to an electric motor for driving the vehicle (not shown) and various other on-board electrical loads, constituting the power supply section of the present invention. The battery pack 1 of this embodiment is configured by connecting a plurality of battery cells 10, each made of a secondary battery such as a lithium ion battery, in series, and is configured as a series-connected body of a plurality of battery blocks B1 to Bn, each grouped together with a predetermined number of adjacent battery cells 10.

[0013] The battery monitoring device 2 is a device that monitors the battery pack 1 by detecting various conditions such as the voltage of the battery pack 1, and is connected to both terminals of each battery cell 10 of the battery pack 1 via a detection line M for voltage detection.

[0014] The battery monitoring device 2 of this embodiment includes, as main components, a circuit protection unit 20, a plurality of monitoring circuits 22, a control unit 23, and an insulation unit 24.

[0015] The circuit protection unit 20 is a circuit protection device that protects the monitoring circuit 22 from the battery pack 1, and includes a circuit protection element 211, an overvoltage protection element 212, and an impedance element 25. The circuit protection element 211 and the overvoltage protection element 212 are provided on the same circuit board 21, and the impedance element 25 is provided outside the circuit board 21. Note that, as will be described later, the impedance element 25 may be provided on the circuit board 21.

[0016] The circuit protection elements 211 are provided on each detection line M, and are elements that cut off the electrical connection between the battery pack 1 and the monitoring circuit 22 when a current equal to or greater than a predetermined current value flows through the detection line M. The overvoltage protection elements 212 are connected between each detection line M, and are elements that maintain the voltage applied to the monitoring circuit 22 at a constant voltage. The overvoltage protection elements 212 are composed of elements that undergo a short circuit failure when an overvoltage is applied.

[0017] The impedance element 25 is provided on at least one of the detection lines M, and is disposed at a position between the power supply unit and the circuit protection element 211. In this embodiment, the impedance element 25 is provided on each of the detection lines M.

[0018] The circuit protection element 211, the overvoltage protection element 212, and the impedance element 25 in the circuit protection unit 20 will be described in detail later.

[0019] The monitoring circuits 22 are provided in plurality corresponding to the battery blocks B1-Bn of the battery pack 1, and are circuits that monitor the block voltages of the battery blocks B1-Bn and the cell voltages of the battery cells 10 in the battery pack 1. The monitoring circuits 22 in this embodiment are configured to output a signal indicating the voltage state, etc. of the battery pack 1 to the control unit 23 via an insulating unit 24.

[0020] The control unit 23 is composed of a microcomputer consisting of a CPU, ROM, RAM, EEPROM (registered trademark), etc., and its peripheral devices, and is configured to execute various processes such as control processing of each monitoring circuit 22 and determination processing of voltage abnormality in the battery pack 1 in accordance with a control program stored in a storage means such as a ROM.

[0021] The insulating unit 24 is a signal transmitting means for transmitting signals in both directions while insulating each of the monitoring circuits 22 and the control unit 23 from each other, and is constituted by, for example, a photocoupler.

[0022] Next, details of the circuit protection unit 20 of this embodiment will be described with reference to the configuration diagram of the main parts shown in Fig. 2. For ease of explanation, Fig. 2 illustrates one battery block Bi among the multiple battery blocks B1 to Bn, a monitoring circuit 22 that monitors the battery block Bi, and the circuit protection unit 20 that protects the monitoring circuit 22.

[0023] The overvoltage protection element 212 of this embodiment is an element that prevents an overvoltage generated in a battery block Bi from being applied to the monitoring circuit 22, and is configured to maintain a short-circuit state (conductive state) between the detection lines connected to both terminals of the battery cell 10 when an overvoltage occurs in one of the battery cells 10 that constitutes the battery block Bi.

[0024] In this embodiment, the overvoltage protection element 212 is configured with a Zener diode ZD, and as shown in FIG. 2, the Zener diodes ZD1 to ZDn are connected between the detection lines M1 to Mn+1.

[0025] The Zener diode ZD of this embodiment has a breakdown voltage (for example, several times the fully charged voltage of the battery cell 10) set in consideration of the voltage of the battery cell 10 and the withstand voltage of the monitoring circuit 22. Note that, of a pair of detection lines connected to both terminals of the battery cell 10, each of the Zener diodes ZD1 to ZDn has a cathode connected to the detection line connected to the high potential terminal of the battery cell 10 and an anode connected to the detection line connected to the low potential terminal.

[0026] In addition, in this embodiment, a Zener diode ZD having a structure that causes a short circuit failure (short circuit failure) when an overvoltage is applied is adopted. Specifically, for example, the Zener diode ZD may be composed of a PN junction type IC chip, a pair of lead frames that sandwich the IC chip at one end, and a resin exterior that covers the IC chip and a part of the lead frame. If the Zener diode ZD has a structure in which the IC chip and the lead frame are bonded with wires, there is a possibility that the wires will break and cause an open circuit failure when an overvoltage is applied. For this reason, it is preferable to adopt a Zener diode ZD having a structure in which the IC chip is directly sandwiched between a pair of lead frames.

[0027] Next, the circuit protection element 211 of this embodiment is configured to cut off the electrical connection between the monitoring circuit 22 and both terminals of the battery cell 10 in which an overcurrent has occurred, due to a short-circuit current flowing between the detection lines M via the overvoltage protection element 212 when an overvoltage occurs. In other words, the circuit protection element 211 uses an element that breaks down due to a short-circuit current flowing between the detection lines M via the overvoltage protection element 212 when an overvoltage occurs.

[0028] Specifically, in this embodiment, the circuit protection element 211 is configured with a fuse F that breaks when a current equal to or greater than a rated current flows, and as shown in FIG. 2, fuses F1 to Fn+1 are provided on the detection lines M1 to Mn+1.

[0029] The fuse F of this embodiment is configured to break when the Zener diode ZD shorts out due to an overvoltage, due to a large current flowing through the detection line M. In other words, the rated current of the fuse F is set based on the large current flowing through the detection line M when the Zener diode ZD shorts out due to an overvoltage. If the resistance component of the fuse F is large, it will affect the accuracy of voltage monitoring in the monitoring circuit 22, so it is desirable to select a fuse F with a small resistance value.

[0030] The impedance element 25 of this embodiment is provided on at least one of the detection lines M, and is disposed at a position between the assembled battery 1 and the circuit protection element 211. The impedance element 25 is configured to suppress the generation of a discharge current in the circuit protection element 211 when the circuit protection element 211 cuts off the electrical connection between both terminals of the battery cell 10 in which an overcurrent has occurred and the monitoring circuit 22 due to a short-circuit current flowing between the detection lines M via the overvoltage protection element 212 in the event of an overvoltage. For example, the impedance element 25 has electrical characteristics such as a resistance value and inductance designed to suppress the generation of a discharge current in the circuit protection element 211 when the circuit protection element 211 cuts off the electrical connection between both terminals of the battery cell 10 in which an overcurrent has occurred and the monitoring circuit 22 due to a short-circuit current flowing between the detection lines M via the overvoltage protection element 212 in the event of an overvoltage.

[0031] 2, in this embodiment, for example, an inductor L is used as the impedance element 25, and inductors L1 to Ln+1 are arranged on all of the detection lines M1 to Mn+1. Specifically, the inductors L1 to Ln+1 are designed to have an inductance that suppresses the generation of a discharge current in a blown fuse when the corresponding fuse F1 to Fn+1 is blown. The inductance of the inductors L1 to Ln+1 can be designed based on an experimental method, for example, by setting the inductance based on an inductance that does not flow an arc current that is obtained by actually blowing any of the fuses F1 to Fn+1.

[0032] Next, we will explain the operation of the circuit protection unit 20 when an overvoltage occurs in the battery pack 1. When an overvoltage occurs in the battery pack 1 and a voltage exceeding the breakdown voltage is applied to the Zener diodes ZD1 to ZDn, a large current (short-circuit current) flows through the closed circuit formed between the battery pack 1 and the Zener diodes ZD1 to ZDn.

[0033] At this time, if the Zener diodes ZD1 to ZDn short-circuit, a large current (short-circuit current) continues to flow through the closed circuit formed between the battery pack 1 and the Zener diodes ZD1 to ZDn, and the electrical connection between the battery pack 1 and the monitoring circuit 22 is interrupted. As a result, no overvoltage is applied to the monitoring circuit 22, so the monitoring circuit 22 is appropriately protected from the overvoltage generated in the battery pack 1.

[0034] For example, if an overvoltage occurs in the battery cell 10 with the second highest potential in the battery block Bi shown in FIG. 2 and a voltage exceeding the breakdown voltage is applied to the Zener diode ZD2, a large current (short-circuit current) will flow in the closed circuit formed by the battery cell 10, the detection lines M2 and M3, and the Zener diode ZD2, as shown by the arrows in FIG. 2.

[0035] At this time, as shown in Fig. 3(a), if the Zener diodes ZD1 to ZDn are short-circuited, a large current (short-circuit current) continues to flow in the closed circuit formed between the battery cell 101 and the Zener diode ZD2. At this time, an electromotive force in a direction that prevents the short-circuit current is generated in the inductor L2 as a counter electromotive force. As shown in Fig. 3(b), when the short-circuit current flows through the fuse F2 and the fuse F2 breaks as shown in Fig. 3(c), the electrical connection between the battery cell 10 and the monitoring circuit 22 is interrupted. At this time, an electromotive force in a direction that tries to continue the flow of the short-circuit current is generated in the inductor L2 as a counter electromotive force. In addition, the potential difference across the blown fuse F2 becomes large, and the electric field also becomes large.

[0036] In the fuse F2 whose electrical connection has been cut off by rupture, a discharge current may flow due to arc discharge or the like, as shown by the arrow in Fig. 3(d). At this time, an electromotive force in a direction that hinders the discharge current is generated in the inductor L2 as a counter electromotive force. The inductor L2 is designed to have an inductance that suppresses the generation of a discharge current in the fuse F2 when the corresponding fuse F2 is ruptured. Therefore, the counter electromotive force generated in the inductor L2 can reduce the potential difference across the fused fuse F2, making it possible to reduce the electric field and suppress the generation of a discharge current.

[0037] As described above, the circuit protection unit 20 of this embodiment includes the overvoltage protection element 212, the circuit protection element 211, and the impedance element 25. The overvoltage protection element 212 is configured by an element that short-circuits when an overvoltage is applied, and when an overvoltage occurs in the battery pack 1, it short-circuits and maintains the detection lines M in a short-circuited state. The circuit protection element 211 breaks due to a short-circuit current that flows between the detection lines M via the overvoltage protection element 212 when an overvoltage occurs in the battery pack 1. As a result, when an overvoltage occurs in the battery pack 1, the detection lines M are maintained in a short-circuited state by the overvoltage protection element 212, and the electrical connection between the battery pack 1 and the monitoring circuit 22 is interrupted by the circuit protection element 211, so that the monitoring circuit 22 can be appropriately protected from the overvoltage occurring in the battery pack 1.

[0038] Furthermore, when the circuit protection element 211 cuts off the electrical connection between the battery pack 1 and the monitoring circuit 22, the voltage drop across the impedance element 25 reduces the potential difference at the fractured portion of the fractured circuit protection element 211, thereby reducing the electric field in the space between the fractured portions, thereby preventing a discharge current from occurring in the fractured circuit protection element 211. Since the possibility that the monitoring circuit 22 will be destroyed by the discharge current occurring in the fractured circuit protection element 211 can be reduced, a circuit protection unit 20 can be provided that can protect the monitoring circuit 22 more reliably than before.

[0039] Furthermore, the impedance element 25 is inductors L1 to Ln+1, and can be designed to have an inductance that suppresses the generation of a discharge current when the circuit protection element 211 cuts off the electrical connection between the assembled battery 1 and the monitoring circuit 22. Furthermore, the inductors L1 to Ln+1 are not provided on the circuit board 21 on which the circuit protection element 211 and the overvoltage protection element 212 are provided, but are provided outside the circuit board 21, between the assembled battery 1 and the circuit board 21. For this reason, the circuit protection unit 20 according to this embodiment can be realized simply by adding the inductor L to the circuit board 21 on which the circuit protection element 211 and the overvoltage protection element 212 are provided as in the conventional case.

[0040] In this embodiment, since the overvoltage protection element 212 is configured with the Zener diode ZD which short-circuits when an overvoltage is applied, any circuit protection element 211 can be used as long as it cuts off each detection line M by a short-circuit current flowing between each detection line M when the Zener diode ZD short-circuits. This increases the number of options for the circuit protection element 211, making it easier to select the circuit protection element 211.

[0041] (Modification) As shown in Fig. 4, the circuit protection element 211, the overvoltage protection element 212, and the inductor L may all be provided on the same circuit board 21. Even if the inductor L is provided on the circuit board 21 as in the circuit protection unit 20 shown in Fig. 4, it is possible to provide a circuit protection unit 20 that can prevent a discharge current from occurring in a broken circuit protection element 211, similar to the circuit protection unit 20 shown in Fig. 2, and can protect the monitoring circuit 22 more reliably than before. A power supply system including the circuit protection device according to the present application can be realized by simply installing the circuit board 21 including the circuit protection element 211, the overvoltage protection element 212, and the inductor L in a power supply system including the monitoring circuit 22 and a power supply unit.

[0042] Furthermore, the inductor L may be provided at least in the top detection line M1, which is the highest potential side, and the bottom detection line Mn+1, which is the lowest potential side, of the detection lines M. That is, the circuit protection unit 20 may include at least the inductor L1 and the inductor Ln+1 as the inductor L.

[0043] For example, in FIG. 1, when the connection members connecting the battery blocks B1 to Bn to each other come off, an overvoltage occurs at the point where the connection members come off, and the fuses provided in the detection lines are broken. For example, when the connection members connecting the battery blocks B1 and B2 come off, the fuses Fn+1 provided in the lowest detection line Mn+1 of the battery block B1 and the fuses F1 provided in the highest detection line M1 of the battery block B2 are broken. Then, in the battery block B1, the fuses are broken in a chain reaction from the lowest detection line Mn+1 to the highest detection line M1. In the battery block B2, the fuses are broken in a chain reaction from the highest detection line M1 to the lowest detection line Mn+1. As the chain reaction of fuse breaking progresses, the overvoltage increases. Finally, in the battery block B1, the overvoltage generated in the highest detection line M1 becomes the largest, and the fuse F1 is broken. For this reason, by providing the inductor L1 in the highest detection line M1, it is possible to suppress the generation of a discharge current. Finally, in battery block B2, the overvoltage occurring in the lowest detection line Mn+1 becomes the largest, causing fuse Fn+1 to break. For this reason, by providing inductor Ln+1 in the lowest detection line Mn+1, it is possible to suppress the occurrence of a discharge current. When only inductor L1 and inductor Ln+1 are provided, for example in a power supply system for a hybrid vehicle or electric vehicle, the inductance of inductor L1 and inductor Ln+1 can be designed by calculating the path current from the voltage charged in the smoothing capacitor connected in parallel to the battery pack 1 and the path resistance of the final current path after the fuses break in a chain reaction.

[0044] Second embodiment As shown in the configuration diagram of Fig. 5, the circuit protection unit 20 according to the second embodiment differs from the circuit protection unit 20 according to the first embodiment shown in Fig. 2 in that the impedance element 25 is configured with a resistor R instead of an inductor L. Note that descriptions of the same or equivalent parts as those in the first embodiment will be omitted or simplified.

[0045] 5, in this embodiment, for example, a resistor R is used as the impedance element 25, and resistors R1 to Rn+1 are arranged on all of the detection lines M1 to Mn+1, respectively. Specifically, the resistors R1 to Rn+1 are designed to have resistance values ​​that suppress the generation of a discharge current in a blown fuse when the corresponding fuse F1 to Fn+1 is blown. The resistance values ​​of the resistors R1 to Rn+1 can be designed based on an experimental method, similar to the inductance of the inductors L1 to Ln+1 in the first embodiment.

[0046] As in the first embodiment, for example, when an overvoltage occurs in the battery cell 10 having the second highest potential in the battery block Bi shown in FIG. 5 and a voltage exceeding the breakdown voltage is applied to the Zener diode ZD2, a short-circuit current flows in the closed circuit formed by the battery cell 10, the detection lines M2, M3, and the Zener diode ZD2. When the Zener diodes ZD1 to ZDn short-circuit and the fuse F2 breaks, the electrical connection between the battery cell 10 and the monitoring circuit 22 is cut off. In the fuse F2 whose electrical connection has been cut off, a discharge current may flow due to an arc discharge or the like. The resistor R2 is designed to have a resistance value that suppresses the generation of a discharge current in the fuse F2. Therefore, the resistor R2 can reduce the potential difference across the blown fuse F2, reduce the electric field, and suppress the generation of a discharge current.

[0047] Even if the impedance element 25 is configured with a resistor R as in the present embodiment, the operational effect of being able to suppress the generation of a discharge current in the fuse F whose electrical connection has been cut off can be achieved in the same manner as in the first embodiment. Moreover, the resistors R1 to Rn+1 are not provided on the circuit board 21 on which the circuit protection element 211 and the overvoltage protection element 212 are provided, but are provided outside the circuit board 21, between the battery pack 1 and the circuit board 21. For this reason, the circuit protection unit 20 according to this embodiment can be realized simply by adding a resistor R to the circuit board 21 on which the circuit protection element 211 and the overvoltage protection element 212 are provided as in the conventional case.

[0048] 4, the circuit protection element 211, the overvoltage protection element 212, and the resistor R may all be provided on the same circuit board 21. Even in this case, like the circuit protection unit 20 shown in Fig. 4, it is possible to provide a circuit protection unit 20 that can prevent a discharge current from occurring in a broken circuit protection element 211 and protect the monitoring circuit 22 more reliably than before. A power supply system including the circuit protection device according to the present application can be realized by simply installing a circuit board 21 including the circuit protection element 211, the overvoltage protection element 212, and the resistor R in a power supply system including the monitoring circuit 22 and a power supply unit.

[0049] Moreover, it is sufficient that the resistor R is provided on at least one of the top detection line M1 or the bottom detection line Mn+1. That is, it is sufficient that the circuit protection unit 20 includes at least one of the resistor R1 or the resistor Rn+1 as the resistor R.

[0050] For example, in FIG. 1, if the connecting member connecting the battery block B1 and the battery block B2 is disconnected, as described above, the overvoltage generated in the highest detection line M1 in the battery block B1 will be the highest, and the fuse F1 will break. In the battery block B2, the overvoltage generated in the lowest detection line Mn+1 will be the highest, and the fuse Fn+1 will break. For this reason, by providing at least one of the resistor R1 or resistor Rn+1, the generation of a discharge current can be suppressed. When only one of the resistor R1 or resistor Rn+1 is provided, for example, in a power supply system for a hybrid vehicle or an electric vehicle, the resistance value of the resistor R1 or resistor Rn+1 can be designed by calculating the path current from the voltage charged in the smoothing capacitor connected in parallel to the battery pack 1 and the path resistance of the final current path after the fuses break in a chain reaction.

[0051] In addition, in each of the above embodiments, an example has been described in which the circuit protection element 211 is configured with the fuse F, but the circuit protection element 211 can be any element capable of performing a function equivalent to that of the fuse F. For example, a resistive element that breaks due to a short-circuit current that flows between the detection lines M via the overvoltage protection element 212 when an overvoltage occurs may be used as the circuit protection element 211. Note that it is preferable that the resistive element serving as the circuit protection element 211 is configured with a low resistance element having a low resistance value in order to suppress an effect on the voltage detection performance of the monitoring circuit 22.

[0052] In each of the above embodiments, an example has been described in which the overvoltage protection element 212 is configured with a Zener diode ZD. However, the overvoltage protection element 212 is not limited to the Zener diode ZD, and any element that can perform the same function as the Zener diode ZD can be adopted as the overvoltage protection element 212.

[0053] In each of the above embodiments, the circuit protection device using a resistor or an inductor as the impedance is described as an example, but is not limited thereto. The impedance may be an impedance element other than a resistor or an inductor (for example, a capacitor), or a wiring functioning as an impedance. In addition, the specific examples of the impedance exemplified above may be of the same type only, or may be of a combination of a plurality of types. For example, the circuit protection device may be equipped with both an inductor and a resistor as the impedance.

[0054] In each of the above embodiments, the circuit protection device of the present invention is applied to the monitoring circuit 22 related to the voltage of the battery pack 1 mounted on a vehicle, but the present invention is not limited to this and can be applied to a monitoring circuit related to the voltage of a power supply unit used for other purposes. Note that the power supply unit is not limited to a battery, and may be any power source capable of supplying power to various electrical loads.

[0055] According to each of the above embodiments, the following effects can be obtained.

[0056] The circuit protection unit 20 functions as a circuit protection device that protects the monitoring circuit 22 that monitors the voltage of the power supply unit (for example, the battery pack 1). The circuit protection unit 20 is connected between a plurality of detection lines M for voltage detection that connect the power supply unit and the monitoring circuit 22, and includes an overvoltage protection element 212, a circuit protection element 211, and an impedance element 25. The overvoltage protection element 212 is an element that short-circuits when an overvoltage is applied, and is configured to short-circuit and maintain a short state between the plurality of detection lines M when an overvoltage occurs in the power supply unit. The circuit protection element 211 is an element that is provided in each of the plurality of detection lines M, and is an element that cuts off the electrical connection between the power supply unit and the monitoring circuit 22 when a current equal to or greater than a predetermined current value flows through the detection line M, and is configured to cut off the electrical connection between the power supply unit and the monitoring circuit 22 by a short-circuit current that flows between the detection lines via the overvoltage protection element 212 when an overvoltage occurs in the power supply unit.

[0057] The impedance element 25 is provided on at least one of the detection lines M, and is positioned between the power supply unit and the circuit protection element 211, and is configured to suppress the generation of a discharge current when the circuit protection element 211 cuts off the electrical connection between the power supply unit and the monitoring circuit 22 due to a short-circuit current.

[0058] The impedance element 25 is an element that makes it difficult for a current to flow, and specific examples thereof include a resistor R and an inductor L. When the circuit protection element 211 cuts off the electrical connection between the power supply unit and the monitoring circuit 22 due to a short-circuit current, the voltage drop of the impedance element 25 reduces the electric field (i.e., the potential difference) at a location where a discharge may occur in the circuit protection element 211 that has cut off the electrical connection, and therefore the occurrence of a discharge current such as an arc discharge can be suppressed. Since the possibility that the monitoring circuit 22 will be destroyed by the discharge current can be reduced, it is possible to provide a circuit protection unit 20 that can protect the monitoring circuit 22 more reliably than before.

[0059] The impedance element 25 may be an inductor L (more specifically, inductors L1 to Ln+1) having an inductance that suppresses the occurrence of a discharge current when the circuit protection element 211 cuts off the electrical connection between the power supply unit and the monitoring circuit 22 due to a discharge current.

[0060] It is preferable that the inductor L is provided at least on the top sense line M1, which is the highest potential side of the sense lines M, and on the bottom sense line Mn+1, which is the lowest potential side.

[0061] The overvoltage protection element 212 and the circuit protection element 211 may be provided on the same circuit board 21, and the inductor L may be provided outside the circuit board 21. This configuration can be easily realized by adding the inductor L to a conventional circuit board 21 including the overvoltage protection element 212 and the circuit protection element 211. The overvoltage protection element 212, the circuit protection element 211, and the inductor L may be provided on the same circuit board 21. A power supply system including the circuit protection device according to the present application can be realized by simply installing the circuit board 21 in a power supply system including the monitoring circuit 22 and the power supply unit. Furthermore, the inductor L may be provided both on the circuit board 21 and outside the circuit board.

[0062] The impedance element 25 may be a resistor R (more specifically, resistors R1 to Rn+1) having a resistance value that suppresses the occurrence of a discharge current when the circuit protection element 211 cuts off the electrical connection between the power supply unit and the monitoring circuit 22 due to a discharge current.

[0063] A resistor R is preferably provided at least on either the top sense line M1 or the bottom sense line Mn+1.

[0064] The overvoltage protection element 212 and the circuit protection element 211 may be provided on the same circuit board 21, and the resistor R may be provided outside the circuit board 21. This configuration can be easily realized by adding the resistor R to a conventional circuit board 21 including the overvoltage protection element 212 and the circuit protection element 211. The overvoltage protection element 212, the circuit protection element 211, and the resistor R may be provided on the same circuit board 21. A power supply system including the circuit protection device according to the present application can be realized by simply installing the circuit board 21 in a power supply system including the monitoring circuit 22 and the power supply unit. Furthermore, the resistor R may be provided both on the circuit board 21 and outside the circuit board.

[0065] The control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the control unit and the method described in the present disclosure may be realized by a special-purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the control unit and the method described in the present disclosure may be realized by one or more special-purpose computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by a computer. [Explanation of symbols]

[0066] 1... battery pack (power supply section), 20... circuit protection section (circuit protection device), 21... board, 211... circuit protection element, 212... overvoltage protection element, 22... monitoring circuit, 25... impedance element, M... detection line

Claims

1. A circuit protection device for protecting a monitoring circuit (22) that monitors the voltage of a power supply unit (1), comprising: an overvoltage protection element (212) connected between a plurality of detection lines (M) for detecting voltage that connect the power supply unit and the monitoring circuit, and which short-circuits when an overvoltage is applied; a circuit protection element (211) provided on each of the plurality of detection lines, the circuit protection element cutting off an electrical connection between the power supply unit and the monitoring circuit when a current equal to or greater than a predetermined current value flows through the detection line; an impedance (25) provided on at least one of the detection lines and disposed between the power supply unit and the circuit protection element; the overvoltage protection element is configured to cause a short-circuit failure and maintain a short-circuit state between the plurality of detection lines when an overvoltage occurs in the power supply unit; the circuit protection element is configured to cut off an electrical connection between the power supply unit and the monitoring circuit by a short-circuit current flowing between the detection lines via the overvoltage protection element when an overvoltage occurs in the power supply unit; The impedance is configured to suppress generation of a discharge current when the short-circuit current causes the circuit protection element to interrupt the electrical connection between the power supply unit and the monitoring circuit.

2. The circuit protection device according to claim 1, wherein the impedance is an inductor (L1 to Ln+1) having an inductance that suppresses the generation of a discharge current when the circuit protection element cuts off the electrical connection between the power supply unit and the monitoring circuit due to the short-circuit current.

3. The overvoltage protection element and the circuit protection element are provided on the same circuit board (21); 3. The circuit protection device of claim 2, wherein the inductor is provided outside the circuit board or on the circuit board, and is provided at least on a top detection line (M1) that is the highest potential side of the detection lines and a bottom detection line (Mn+1) that is the lowest potential side of the detection lines.

4. 2. The circuit protection device according to claim 1, wherein the impedance is a resistor (R1 to Rn+1) having a resistance value that suppresses the generation of a discharge current when the circuit protection element cuts off the electrical connection between the power supply unit and the monitoring circuit due to the short-circuit current.

5. The overvoltage protection element and the circuit protection element are provided on the same circuit board (21); 5. The circuit protection device of claim 4, wherein the resistor is provided outside or on the circuit board, and is provided on at least one of the top detection line (M1), which is the highest potential side of the detection lines, or the bottom detection line (Mn+1), which is the lowest potential side of the detection lines.

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