In-vehicle cutoff device

Abstract

An in-vehicle cut-off device (10) has: a control unit (30) that controls a first cutoff unit (21); and a specific cutoff unit (for example, a thermal fuse (40)). Only when a vehicle is in a first state among the first state and a second state, the control unit (30) switches the first cutoff unit (21) to the first cutoff state on the basis of the fact that a current exceeding a first threshold value (TH1) flows from a second power supply unit side to a first power supply unit side. When the vehicle is at least in the second state, the specific cutoff unit cuts off the current flowing from the second power supply unit side to the first power supply unit side on the basis of the fact that a current exceeding a second threshold value (TH2) larger than the first threshold value (TH1) flows from the second power supply unit side to the first power supply unit side.

Description

Vehicle-mounted circuit breaker

[0001] The present disclosure relates to an on-vehicle shutoff device.

[0002] Patent Literature 1 discloses a power supply system that prevents current from passing from a sub-power source to a main power source when power from the main power source is interrupted. This power supply system determines whether power from the main power source has been interrupted, for example, based on the current flowing to the main power source.

[0003] Japanese Patent Application Laid-Open No. 2020-182318

[0004] In the configuration of Patent Document 1, even when an attempt is made to supply power from the sub-power source to the main power source, the system may determine that there has been an interruption in power from the main power source, and the power supply to the main power source may be cut off. Therefore, when power is to be supplied from the sub-power source to the main power source, it may be possible to disable the cutoff function and allow the power supply to the main power source. However, disabling the cutoff function creates the problem of not being able to cut off the power even if an overcurrent flows.

[0005] The present disclosure aims to provide a technology that makes it easy to appropriately interrupt current.

[0006] An on-board circuit breaker of the present disclosure is an on-board circuit breaker included in an on-board system including: a first power supply unit; a second power supply unit; a conductive path provided between the first power supply unit and the second power supply unit; and a load electrically connected to the conductive path, the on-board circuit breaker having: a first circuit breaker provided between the first power supply unit and the conductive path; a control unit that controls the first circuit breaker; and a specific circuit breaker, wherein the first circuit breaker switches between a first permissive state that allows current to flow from the second power supply unit side to the first power supply unit side and a first blocked state that blocks current from flowing from the second power supply unit side to the first power supply unit side, and the control unit switches the first circuit breaker to the first blocked state based on a current exceeding a first threshold value flowing from the second power supply unit side to the first power supply unit side only when the vehicle is in the first state out of a first state and a second state, The specific cut-off unit cuts off the current flowing from the second power supply unit side to the first power supply unit side based on the fact that a current exceeding a second threshold value, which is greater than the first threshold value, flows from the second power supply unit side to the first power supply unit side when the vehicle is in at least the second state.

[0007] The technology disclosed herein makes it easy to appropriately interrupt current.

[0008] FIG. 1 is a schematic diagram illustrating an in-vehicle system including an in-vehicle circuit breaker according to a first embodiment. FIG. 2 is an explanatory diagram illustrating the operation of the in-vehicle system according to the first embodiment during precharging. FIG. 3 is an explanatory diagram illustrating the operation of the in-vehicle system according to the first embodiment while the vehicle is traveling. FIG. 4 is an explanatory diagram illustrating a state in which a ground fault occurs in the second conduction path in the state shown in FIG. 2. FIG. 5 is an explanatory diagram illustrating a state in which a thermal fuse has melted in the state shown in FIG. 4. FIG. 6 is an explanatory diagram illustrating a state in which a ground fault occurs in the second conduction path in the state shown in FIG. 3. FIG. 7 is an explanatory diagram illustrating a state in which the first circuit breaker has switched from the state shown in FIG. 6 to the first circuit breaker state. FIG. 8 is a schematic diagram illustrating an in-vehicle system including an in-vehicle circuit breaker according to a second embodiment. FIG. 9 is an explanatory diagram illustrating the operation of the in-vehicle system according to the second embodiment during precharging. FIG. 10 is an explanatory diagram illustrating the operation of the in-vehicle system according to the second embodiment while the vehicle is traveling. FIG. 11 is an explanatory diagram illustrating a state in which a ground fault occurs in the second conduction path in the state shown in FIG. 9. Fig. 12 is an explanatory diagram showing a state in which the second interrupting unit has switched to the second interrupting state from the state shown in Fig. 11. Fig. 13 is an explanatory diagram showing a state in which a ground fault occurs in the second conductive path in the state shown in Fig. 10. Fig. 14 is an explanatory diagram showing a state in which the first interrupting unit has switched to the first interrupting state from the state shown in Fig. 13.

[0009] [Description of Embodiments of the Present Disclosure] In the following, embodiments according to the present disclosure are listed and exemplified.

[0010] [1] An on-board circuit breaker included in an on-board system including a first power supply unit, a second power supply unit, a conductive path provided between the first power supply unit and the second power supply unit, and a load electrically connected to the conductive path, the on-board circuit breaker having a first circuit breaker provided between the first power supply unit and the conductive path, a control unit that controls the first circuit breaker, and a specific circuit breaker, the first circuit breaker being switched between a first permissive state that allows current to flow from the second power supply unit side to the first power supply unit side and a first blocked state that blocks current from flowing from the second power supply unit side to the first power supply unit side, and the control unit being configured to switch the first circuit breaker to the first blocked state based on the fact that current exceeding a first threshold has flowed from the second power supply unit side to the first power supply unit side only when the vehicle is in the first state out of a first state and a second state, The specific cutoff unit cuts off the current flowing from the second power supply unit side to the first power supply unit side based on the current flowing from the second power supply unit side to the first power supply unit side in a state where the vehicle is in at least the second state and the current exceeds a second threshold value that is greater than the first threshold value.

[0011] The above-mentioned vehicle circuit breaker device can switch the first circuit breaker unit to the first circuit breaker state based on the fact that a current exceeding a first threshold has flowed from the second power supply unit side to the first power supply unit side in the first state. That is, the above-mentioned vehicle circuit breaker device can quickly switch the first circuit breaker unit to the first circuit breaker state when a current flows backward from the second power supply unit side to the first power supply unit side in the first state. Furthermore, the above-mentioned vehicle circuit breaker device can interrupt the current flowing from the second power supply unit side to the first power supply unit side by using the specific circuit breaker unit based on the fact that a current exceeding a second threshold has flowed from the second power supply unit side to the first power supply unit side in the second state. In this way, the above-mentioned vehicle circuit breaker device can easily interrupt the current appropriately according to the state of the vehicle.

[0012] [2] The specific interrupter is provided between the connection point where the load is connected to the conductive path and the second power supply unit, and when the vehicle is in at least the second state, interrupts the current flowing from the second power supply unit to the first power supply unit and interrupts the current flowing from the first power supply unit to the second power supply unit based on the current flowing from the second power supply unit to the first power supply unit that exceeds the second threshold. The vehicle-mounted interrupter device described in [1].

[0013] The above-mentioned on-board circuit breaker device can supply power to the load from the first power supply unit as long as the first power supply unit is not faulty, even when the specific circuit breaker unit has cut off the current flowing from the second power supply unit to the first power supply unit.

[0014] [3] The vehicle-mounted circuit breaking device according to [1] or [2], wherein the specific circuit breaking unit is a thermal fuse that melts when a threshold temperature is exceeded.

[0015] According to this configuration, there is no need to control the specific interrupter.

[0016] [4] The on-board circuit breaking device described in [3] has a current detection unit that detects the current flowing from the conductive path side to the first power supply unit side, the control unit includes a first cut-off circuit, and the first cut-off circuit switches the first cut-off unit to the first cut-off state when the detection value of the current detection unit exceeds the first threshold value in the first state.

[0017] The above-mentioned on-board circuit breaker can quickly switch the first circuit breaker to the first circuit breaker state when the current flowing from the second power supply unit side to the first power supply unit side in the first state exceeds a first threshold value.

[0018] [5] The vehicle-mounted cutoff device described in [4], wherein the first cutoff circuit includes a comparator, the comparator outputs a cutoff signal when the detection value of the current detection unit exceeds the first threshold in the first state, the first cutoff unit switches to the first cutoff state when the cutoff signal is output from the comparator, and the comparator is OFF in the second state.

[0019] This configuration makes it easy to simplify the configuration of the first shutoff circuit.

[0020] [6] An on-board circuit breaking device according to any one of [3] to [5], further comprising a second circuit breaking unit provided between the second power supply unit and the conductive path, wherein the second circuit breaking unit is controlled by the control unit and switches between a second permissive state that allows current to flow from the second power supply unit side to the first power supply unit side and a second blocked state that blocks current from flowing from the second power supply unit side to the first power supply unit side, and wherein when the first circuit breaking unit is in the first permissive state and the second circuit breaking unit is in the second permissive state, the control unit switches the first circuit breaking unit to the first blocked state when the vehicle is in the first state, based on the fact that a current exceeding the first threshold has flowed from the second power supply unit side to the first power supply unit side.

[0021] The vehicle-mounted circuit breaker device switches the first circuit breaker unit to the first circuit breaker state when the first circuit breaker unit is in the first permissive state and the second circuit breaker unit is in the second permissive state. Therefore, even when the first circuit breaker unit is switched to the first circuit breaker state, the vehicle-mounted circuit breaker device can supply power from the second power supply unit to the load without interrupting the power supply to the load.

[0022] [7] The specific interrupter is a second interrupter provided between the second power supply unit and the conductive path, and the second interrupter is controlled by the control unit and switches between a second permissive state that allows current to flow from the second power supply unit side to the first power supply unit side and a second interrupted state that blocks current from flowing from the second power supply unit side to the first power supply unit side, and when the vehicle is in the first state, the control unit switches the first interrupter to the first interrupted state based on a current exceeding the first threshold flowing from the second power supply unit side to the first power supply unit side, and when the vehicle is in the second state, the control unit switches the second interrupter to the second interrupted state based on a current exceeding the second threshold flowing from the second power supply unit side to the first power supply unit side. An on-board interrupter device as described in [1] or [2].

[0023] According to this configuration, the specific interrupter can be controlled.

[0024] [8] The control unit includes a first shutoff circuit and a second shutoff circuit, the first shutoff circuit switches the first shutoff unit to the first shutoff state when the current flowing from the second power supply unit side to the first power supply unit side in the first state exceeds the first threshold, and the second shutoff circuit switches the second shutoff unit to the second shutoff state when the current flowing from the second power supply unit side to the first power supply unit side in the second state exceeds the second threshold. The vehicle-mounted shutoff device described in [7].

[0025] The above-mentioned vehicle-mounted circuit breaker can quickly switch the first circuit breaker to the first circuit breaker state by the first circuit breaker circuit when the current flowing from the second power supply unit side to the first power supply unit side exceeds a first threshold value in the first state. Also, the above-mentioned vehicle-mounted circuit breaker can quickly switch the second circuit breaker to the second circuit breaker state by the second circuit breaker circuit when the current flowing from the second power supply unit side to the first power supply unit side exceeds a second threshold value in the second state.

[0026] [9] The vehicle-mounted shutdown device according to [8], wherein the first shutdown circuit includes a first comparator, the second shutdown circuit includes a second comparator, the first comparator outputs a first shutdown signal when the current flowing from the second power supply unit side to the first power supply unit side in the first state exceeds the first threshold, the second comparator outputs a second shutdown signal when the current flowing from the second power supply unit side to the first power supply unit side in the second state exceeds the second threshold, the first shutdown unit switches to the first shutdown state when the first shutdown signal is output from the first comparator, the second shutdown unit switches to the second shutdown state when the second shutdown signal is output from the second comparator, and the first comparator is OFF in the second state.

[0027] This configuration makes it easy to simplify the configurations of the first shutoff circuit and the second shutoff circuit.

[0028]

[10] The first state is a state in which power is supplied from the first power supply unit to the conductive path side, and the second state is a state in which power is supplied from the second power supply unit to the first power supply unit. An on-board circuit breaker device described in any one of [1] to [9].

[0029] When power is supplied from the first power supply unit to the conduction path side, the vehicle circuit breaker can immediately switch the first circuit breaker to the first circuit breaker state if a backflow to the first power supply unit occurs. Also, when power is supplied from the second power supply unit to the first power supply unit, the vehicle circuit breaker can interrupt the current using the specific circuit breaker if an overcurrent occurs.

[0030]

[11] The in-vehicle system comprises a high-voltage battery, a system main relay, and a capacitor, wherein the second power supply unit is a low-voltage battery, and the first power supply unit is a voltage conversion unit provided between the high-voltage battery and the low-voltage battery, and the voltage conversion unit performs a first conversion operation of stepping up or stepping down a voltage input from the high-voltage battery side and outputting the voltage to the low-voltage battery side, and a second conversion operation of stepping up or stepping down a voltage input from the low-voltage battery side and outputting the voltage to the high-voltage battery side, the system main relay is provided between the high-voltage battery and the voltage conversion unit, and the capacitor is electrically connected to a power path between the system main relay and the voltage conversion unit, and when a start switch of the vehicle is switched on, the in-vehicle system causes the voltage conversion unit to perform the second conversion operation while the system main relay is off to pre-charge the capacitor, and switches the system main relay on after the capacitor has been pre-charged, The vehicle-mounted cutoff device according to

[10] , wherein the first state is a state in which the start switch is ON and the system main relay is ON, and the second state is a state in which the start switch is ON and the system main relay is OFF.

[0031] The above-mentioned on-board circuit breaker can immediately switch the first circuit breaker to the first circuit breaker state when a backflow to the first power supply unit occurs while the vehicle is running. Also, the above-mentioned on-board circuit breaker can interrupt the current by the specific circuit breaker when an overcurrent occurs during precharging of the capacitor.

[0032]

[12] An on-board circuit breaking device described in any one of [1] to

[11] , wherein the control unit switches the first circuit breaking unit to the first circuit breaking state and then returns the first circuit breaking unit to the first permissive state when a first return condition is satisfied.

[0033] Even when the first interrupting unit is switched to the first interrupting state, the above-described vehicle-mounted circuit breaking device can return the first interrupting unit to the first allowing state if the first return condition is satisfied.

[0034]

[13] The vehicle-mounted circuit breaking device according to any one of [1] to

[12] , wherein the specific circuit breaking unit is provided between the first power supply unit and the second power supply unit.

[0035] The above-described on-board circuit breaker device can more reliably interrupt the current flowing between the first power supply unit and the second power supply unit by means of the specific circuit breaker.

[0036] [Details of the embodiments of the present disclosure] 1. First embodiment 1-1. Overview of the on-vehicle system 100 Fig. 1 shows an on-vehicle system 100 including an on-vehicle circuit breaker 10. The on-vehicle system 100 is a system mounted on a vehicle. The on-vehicle system 100 includes a high-voltage battery 91, a low-voltage battery 92, a voltage conversion unit 93, a system main relay 94 (hereinafter also referred to as SMR 94), a capacitor 95, a load 96, a first conductive path 81, a second conductive path 82, and a third conductive path 83.

[0037] The output voltage of the high-voltage battery 91 is higher than the output voltage of the low-voltage battery 92. The high-voltage battery 91 is, for example, a lithium-ion battery or a sodium-ion battery. The low-voltage battery 92 is, for example, a lithium-ion battery or a lead battery. The low-voltage battery 92 corresponds to an example of a second power supply unit.

[0038] The voltage conversion unit 93 corresponds to an example of a first power supply unit. The voltage conversion unit 93 is provided between the high-voltage battery 91 and the low-voltage battery 92. The voltage conversion unit 93 performs a first conversion operation of stepping up or stepping down the voltage input from the high-voltage battery 91 side and outputting the voltage to the low-voltage battery 92 side. The voltage conversion unit 93 also performs a second conversion operation of stepping up or stepping down the voltage input from the low-voltage battery 92 side and outputting the voltage to the high-voltage battery 91 side. The voltage conversion unit 93 is configured by, for example, a DC-DC converter.

[0039] The SMR 94 is provided between the high-voltage battery 91 and the voltage conversion unit 93 .

[0040] The capacitor 95 is electrically connected to the electrical path between the SMR 94 and the voltage conversion unit 93 .

[0041] The first conductive path 81 corresponds to an example of a conductive path. The first conductive path 81 is provided between the voltage conversion unit 93 and the low-voltage battery 92. A load 96 is electrically connected to the first conductive path 81. The second conductive path 82 is provided between the voltage conversion unit 93 and the first conductive path 81. The third conductive path 83 is provided between the low-voltage battery 92 and the first conductive path 81.

[0042] When the start switch of the vehicle is turned ON, the in-vehicle system 100 causes the voltage conversion unit 93 to perform the second conversion operation while keeping the SMR 94 OFF, thereby precharging the capacitor 95. Then, the in-vehicle system 100 turns ON the SMR 94 after precharging the capacitor 95. The start switch is an ignition switch if the vehicle is an engine-equipped vehicle, and is a power switch if the vehicle is an electric vehicle.

[0043] 1-2. Configuration of the Vehicle-Mounted Circuit Breaker 10 The vehicle-mounted circuit breaker 10 is, for example, a junction box. The vehicle-mounted circuit breaker 10 is electrically connected to a voltage conversion unit 93, a low-voltage battery 92, and a load 96.

[0044] The vehicle-mounted circuit breaker 10 includes a first circuit breaker 21 , a second circuit breaker 22 , a current detector 23 , a controller 30 , and a thermal fuse 40 .

[0045] The first interrupter 21 is provided between the first conductive path 81 and the second conductive path 82. The first interrupter 21 is provided between the voltage converter 93 and the first conductive path 81. One end of the first interrupter 21 is electrically connected to the first conductive path 81. The other end of the first interrupter 21 is electrically connected to the voltage converter 93 via the second conductive path 82. The first interrupter 21 switches between a first permissive state in which it allows bidirectional current flow through itself, and a first blocked state in which it blocks current from flowing from the first conductive path 81 to the voltage converter 93. In this embodiment, when in the first blocked state, the first interrupter 21 allows current to flow from the voltage converter 93 to the first conductive path 81. The first interrupter 21 includes a MOSFET 21A. The first interrupter 21 enters the first permissive state when the MOSFET 21A is turned on. The first cutoff unit 21 is set to the first cutoff state when the MOSFET 21A is turned off. In this embodiment, the first cutoff unit 21 is configured by a normally-off switching element.

[0046] The second circuit breaker 22 is provided between the first conductive path 81 and the third conductive path 83. The second circuit breaker 22 is provided between the low-voltage battery 92 and the first conductive path 81. One end of the second circuit breaker 22 is electrically connected to the first conductive path 81. One end of the second circuit breaker 22 is electrically connected to one end of the first circuit breaker 21 via the first conductive path 81. The other end of the second circuit breaker 22 is electrically connected to the low-voltage battery 92 via the third conductive path 83. The second circuit breaker 22 switches between a second permissive state in which it allows bidirectional current flow through itself, and a second blocked state in which it blocks current from flowing from the first conductive path 81 to the low-voltage battery 92. In this embodiment, the second circuit breaker 22 allows current to flow from the low-voltage battery 92 to the first conductive path 81 when in the second blocked state. The second circuit breaker 22 includes a MOSFET 22A. The second cutoff unit 22 is in the second permissive state when the MOSFET 22A is turned ON. The second cutoff unit 22 is in the second cutoff state when the MOSFET 22A is turned OFF. In this embodiment, the second cutoff unit 22 is configured by a normally-off switching element.

[0047] The current detection unit 23 detects the current flowing from the first conductive path 81 to the voltage conversion unit 93, and also detects the current flowing from the voltage conversion unit 93 to the first conductive path 81. The current detection unit 23 is configured, for example, by a known current sensor. The current detection unit 23 outputs a detection value within a predetermined range (for example, a range of 0 to 5 V). For example, the current detection unit 23 outputs a reference voltage (for example, 2.5 V) when no current is flowing, outputs a voltage greater than the reference voltage when current is flowing from the first conductive path 81 to the voltage conversion unit 93, and outputs a voltage smaller than the reference voltage when current is flowing from the voltage conversion unit 93 to the first conductive path 81. For example, the current detection unit 23 outputs a higher voltage as the current flowing from the first conductive path 81 to the voltage conversion unit 93 increases, and outputs a lower voltage as the current flowing from the voltage conversion unit 93 to the first conductive path 81 increases.

[0048] The control unit 30 controls the first cutoff unit 21 and the second cutoff unit 22. The control unit 30 switches the first cutoff unit 21 to the first cutoff state based on the fact that a current exceeding a first threshold value TH1 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side only when the vehicle is in the first state out of the first and second states.

[0049] When the vehicle is in the first state, the control unit 30 may immediately switch the first cut-off unit 21 to the first cut-off state when a current exceeding the first threshold value TH1 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side, or may switch the first cut-off unit 21 to the first cut-off state when a current exceeding the first threshold value TH1 flows for a predetermined period of time, or may switch the first cut-off unit 21 to the first cut-off state when the average value over a predetermined period of time exceeds the first threshold value TH1.

[0050] The first state is a state in which power is supplied from the voltage conversion unit 93 to the first conductive path 81. In this embodiment, the first state is a state in which the start switch is ON and the SMR 94 is ON. The second state is a state in which power is supplied from the low-voltage battery 92 to the voltage conversion unit 93. In this embodiment, the second state is a state in which the start switch is ON and the SMR 94 is OFF. In other words, the vehicle enters the second state when the start switch is switched ON, and enters the first state when pre-charging is complete.

[0051] When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 22 is in the second permissive state, the control unit 30 switches the first cutoff unit 21 to the first cutoff state based on the fact that a current exceeding the first threshold value TH1 flows from the low-voltage battery 92 to the voltage conversion unit 93 when the vehicle is in the first state. When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 22 is in the second permissive state, power can be supplied to the load 96 from both the voltage conversion unit 93 and the low-voltage battery 92. When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 22 is in the second permissive state, it is preferable that power be supplied to the load 96 from the voltage conversion unit 93.

[0052] After switching the first blocking unit 21 to the first blocking state, the control unit 30 maintains the first blocking unit 21 in the first blocking state even if current no longer flows from the first conductive path 81 to the voltage conversion unit 93. After switching the first blocking unit 21 to the first blocking state, the control unit 30 restores the first blocking unit 21 to the first permissive state if a first restoration condition is satisfied. The first restoration condition may be, for example, a condition that is met every time a second time shorter than the first time elapses before the first time elapses. The first restoration condition may be that the output voltage of the voltage conversion unit 93 becomes equal to or greater than a first restoration voltage. The first restoration condition may be that the temperature of the first blocking unit 21 becomes equal to or greater than a first restoration temperature.

[0053] When a disconnection condition is satisfied while the first disconnection unit 21 is in the first permissive state and the second disconnection unit 22 is in the second permissive state, the control unit 30 switches the second disconnection unit 22 to the second disconnection state. The disconnection condition may be satisfied, for example, when the voltage at one end or the other end of the second disconnection unit 22 becomes equal to or lower than a threshold voltage, when a current flows from the first conductive path 81 to the low-voltage battery 92, or another condition. After switching the second disconnection unit 22 to the second disconnection state, the control unit 30 maintains the second disconnection unit 22 in the second disconnection state even if the disconnection condition is no longer satisfied. After switching the second disconnection unit 22 to the second disconnection state, the control unit 30 restores the second disconnection unit 22 to the second permissive state when a second restoration condition is satisfied. The second restoration condition may be satisfied, for example, every time a second time shorter than the first time elapses before the first time elapses. The second restoration condition may be satisfied when the output voltage of the low-voltage battery 92 becomes equal to or higher than a second restoration voltage. The second return condition may be that the temperature of the second interrupter 22 is equal to or higher than the second return temperature.

[0054] Control unit 30 includes a first shutoff circuit 31, a second shutoff circuit 32, and a circuit control unit 33. First shutoff circuit 31 and second shutoff circuit 32 are configured using discrete components. Circuit control unit 33 includes a microcomputer. Circuit control unit 33 controls first shutoff circuit 31 and second shutoff circuit 32.

[0055] The first blocking circuit 31 switches the first blocking unit 21 to the first blocking state based on the flow of current from the first conductive path 81 side to the voltage conversion unit 93 side when the first blocking unit 21 is in the first permissive state and the second blocking unit 22 is in the second permissive state.

[0056] The first shutoff circuit 31 switches the first shutoff unit 21 to the first shutoff state when the detection value of the current detection unit 23 exceeds the first threshold value TH1 in the first state.

[0057] First shutoff circuit 31 includes a comparator 31A, a NOT circuit 31B, and a latch circuit 31C.

[0058] The comparator 31A receives the detection value of the current detection unit 23 and a first threshold value TH1. The detection value of the current detection unit 23 is input to the non-inverting input terminal of the comparator 31A. The first threshold value TH1 is input to the inverting input terminal of the comparator 31A. The comparator 31A outputs a shutdown signal when the detection value of the current detection unit 23 exceeds the first threshold value TH1 in the first state. The shutdown signal is a high-level signal. The comparator 31A does not output a shutdown signal when the detection value of the current detection unit 23 does not exceed the first threshold value TH1 in the first state. In other words, the comparator 31A outputs a low-level signal. The comparator 31A is ON in the first state and OFF in the second state. In other words, the comparator 31A never outputs a shutdown signal in the second state, regardless of the detection value of the current detection unit 23.

[0059] The NOT circuit 31B receives the signal output from the comparator 31A. If the comparator 31A does not output a cutoff signal, the NOT circuit 31B outputs a high-level signal. If the comparator 31A outputs a cutoff signal, the NOT circuit 31B outputs a low-level signal.

[0060] The latch circuit 31C receives the signal output from the NOT circuit 31B. The latch circuit 31C outputs a high-level signal (ON signal) until it receives a low-level signal from the NOT circuit 31B, thereby maintaining the first cutoff unit 21 in the first permissive state. When the latch circuit 31C receives a high-level signal from the NOT circuit 31B, it outputs a low-level signal (OFF signal) and switches the first cutoff unit 21 to the first cutoff state. After switching the first cutoff unit 21 to the first cutoff state, the latch circuit 31C maintains the first cutoff unit 21 in the first cutoff state even if the signal input from the NOT circuit 31B returns to a high-level signal. In other words, the latch circuit 31C maintains the first cutoff unit 21 in the first permissive state until a cutoff signal is output from the comparator 31A. Then, when a cutoff signal is output from the comparator 31A, the latch circuit 31C switches the first cutoff unit 21 to the first cutoff state.

[0061] When the shutoff condition is met, the second shutoff circuit 32 switches the second shutoff unit 22 to the second shutoff state. After switching the second shutoff unit 22 to the second shutoff state, the second shutoff circuit 32 maintains the second shutoff unit 22 in the second shutoff state even if the shutoff condition is no longer met.

[0062] When the first shutoff unit 21 switches to the first shutoff state, the circuit control unit 33 determines whether the first return condition is met. For example, when the circuit control unit 33 receives a shutoff signal output from the comparator 31A, the circuit control unit 33 starts determining whether the first return condition is met. When the circuit control unit 33 determines that the first return condition is met, the circuit control unit 33 controls the first shutoff circuit 31 to return the first shutoff unit 21 to the first permissive state. Specifically, the circuit control unit 33 releases the latched state of the latch circuit 31C and causes the latch circuit 31C to output an ON signal.

[0063] When second interrupter 22 switches to the second interrupted state, circuit control unit 33 determines whether the second return condition is met. If circuit control unit 33 determines that the second return condition is met, it controls second interrupter circuit 32 to return second interrupter 22 to the second permissive state.

[0064] The thermal fuse 40 corresponds to an example of a specific cutoff unit. The thermal fuse 40 is provided between the low-voltage battery 92 and the voltage conversion unit 93. The thermal fuse 40 is provided between the low-voltage battery 92 and a connection point CP where the load 96 is connected to the first conductive path 81. The thermal fuse 40 cuts off the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 when a current exceeding a second threshold value TH2, which is greater than the first threshold value TH1, flows from the low-voltage battery 92 to the voltage conversion unit 93. The thermal fuse 40 melts when its own temperature exceeds the threshold temperature.

[0065] 1-3. Example of Operation of the In-Vehicle System 100 In this example, the first cutoff unit 21 or the thermal fuse 40 cuts off the current, but the second cutoff unit 22 does not cut off the current.

[0066] When the vehicle start switch is switched ON, the SMR 94 remains OFF, the first shutoff unit 21 enters the first permissive state, the second shutoff unit 22 enters the second permissive state, and the voltage conversion unit 93 performs the second conversion operation. As a result, as shown in FIG. 2 , power from the low-voltage battery 92 is precharged to the capacitor 95. When the voltage of the capacitor 95 reaches a target voltage, precharging is completed and the SMR 94 is switched ON. Furthermore, as shown in FIG. 3 , the voltage conversion unit 93 performs the first conversion operation, thereby enabling power from the high-voltage battery 91 and power from the low-voltage battery 92 to be supplied to the load 96. As a result, while the vehicle is running, power from the high-voltage battery 91 and power from the low-voltage battery 92 can be supplied to the load 96.

[0067] During pre-charging, it is necessary to allow current to flow from the low-voltage battery 92 to the voltage conversion unit 93. For this reason, as shown in FIG. 2, the comparator 31A is turned OFF. In this state, if a ground fault occurs in the second conductive path 82 as shown in FIG. 4, for example, current from the low-voltage battery 92 flows to the ground-fault location in the second conductive path 82. If an overcurrent flows in the first conductive path 81, the thermal fuse 40 melts as shown in FIG. 5. This cuts off the current supplied from the low-voltage battery 92.

[0068] Furthermore, while the vehicle is traveling, it is necessary to maintain a state in which power can be supplied to the load 96 from both the voltage conversion unit 93 and the low-voltage battery 92, while quickly interrupting any backflow from the first conduction path 81 to the voltage conversion unit 93. For this reason, as shown in FIG. 3 , the comparator 31A is turned ON. In this state, if a ground fault occurs in the second conduction path 82, as shown in FIG. 6 , for example, current from the low-voltage battery 92 flows to the ground-fault location in the second conduction path 82. When the current flowing from the first conduction path 81 to the voltage conversion unit 93 exceeds a first threshold value TH1, the comparator 31A outputs a cutoff signal, and the first cutoff unit 21 is switched to the first cutoff state as shown in FIG. 7 . This allows the power supply source to be switched from the voltage conversion unit 93 to the low-voltage battery 92 so that the power supply to the load 96 is not interrupted.

[0069] 1-4. Example of Effects of the Vehicle Circuit Breaker 10 The vehicle circuit breaker 10 can switch the first circuit breaker 21 to the first circuit breaker state based on the flow of current exceeding the first threshold value TH1 from the low-voltage battery 92 to the voltage converter 93 in the first state. That is, the vehicle circuit breaker 10 can quickly switch the first circuit breaker 21 to the first circuit breaker state when current flows backward from the low-voltage battery 92 to the voltage converter 93 in the first state. Furthermore, the vehicle circuit breaker 10 can interrupt the current flowing from the low-voltage battery 92 to the voltage converter 93 using the thermal fuse 40 based on the flow of current exceeding the second threshold value TH2 from the low-voltage battery 92 to the voltage converter 93 in the second state. In this way, the vehicle circuit breaker 10 can easily interrupt the current appropriately depending on the state of the vehicle.

[0070] The thermal fuse 40 is provided between the connection point CP, where the load 96 is connected to the first conductive path 81, and the low-voltage battery 92. Therefore, even if the thermal fuse 40 is blown, the vehicle-mounted circuit breaker 10 can supply power to the load 96 from the voltage conversion unit 93 as long as the voltage conversion unit 93 is not malfunctioning.

[0071] The vehicle-mounted circuit breaker 10 can quickly switch the first circuit breaker 21 to the first circuit breaker state using the first circuit breaker circuit 31 when the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 exceeds the first threshold value TH1 in the first state.

[0072] First shutoff circuit 31 includes comparator 31A. Comparator 31A outputs a shutoff signal when the detection value of current detection unit 23 exceeds first threshold value TH1 in the first state. First shutoff unit 21 switches to the first shutoff state when the shutoff signal is output from comparator 31A. Comparator 31A is OFF in the second state. This configuration makes it easy to simplify the configuration of first shutoff circuit 31.

[0073] The vehicle-mounted circuit breaking device 10 switches the first circuit breaking unit 21 to the first circuit breaking state when the first circuit breaking unit 21 is in the first permissive state and the second circuit breaking unit 22 is in the second permissive state. Therefore, even when the first circuit breaking unit 21 is switched to the first circuit breaking state, the vehicle-mounted circuit breaking device 10 can supply power from the low-voltage battery 92 to the load 96 without interrupting the power supply to the load 96.

[0074] When power is supplied from the voltage conversion unit 93 to the first conductive path 81, the vehicle circuit breaker 10 can immediately switch the first circuit breaker 21 to the first circuit breaker state if a backflow occurs to the voltage conversion unit 93. Furthermore, when power is supplied from the low-voltage battery 92 to the voltage conversion unit 93, the vehicle circuit breaker 10 can cut off the current by the thermal fuse 40 if an overcurrent occurs.

[0075] The vehicle-mounted circuit breaker 10 can immediately switch the first circuit breaker 21 to the first circuit breaker state when a backflow to the voltage conversion unit 93 occurs while the vehicle is running. Furthermore, the vehicle-mounted circuit breaker 10 can cut off the current by the thermal fuse 40 when an overcurrent occurs during precharging of the capacitor 95.

[0076] Even when the first interrupting unit 21 is switched to the first interrupting state, the vehicle-mounted circuit breaking device 10 can return the first interrupting unit 21 to the first allowing state if the first return condition is satisfied.

[0077] 2. Second Embodiment In the first embodiment, a configuration in which the specific interrupter is the thermal fuse 40 is described. In the second embodiment, a configuration in which the specific interrupter is the second interrupter 22 is described. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0078] 2-1. Overview of the In-Vehicle System 200 As shown in FIG. 8 , the in-vehicle system 200 of the second embodiment includes a high-voltage battery 91, a low-voltage battery 92, a voltage conversion unit 93, an SMR 94, a capacitor 95, a load 96, a first conductive path 81, a second conductive path 82, and a third conductive path 83.

[0079] 2-2. Configuration of the Vehicle-Mounted Circuit Breaker 210 The vehicle-mounted system 200 includes the vehicle-mounted circuit breaker 210. The vehicle-mounted circuit breaker 210 has a first circuit breaker 21, a second circuit breaker 222, a current detector 23, and a controller 230.

[0080] The second cutoff unit 222 corresponds to an example of a specific cutoff unit. The second cutoff unit 222 includes MOSFETs 22A and 22B. MOSFETs 22A and 22B are connected in opposite directions. The second cutoff unit 222 differs from the second cutoff unit 22 described in the first embodiment in that it includes not only MOSFET 22A but also MOSFET 22B, but is otherwise common. The second cutoff unit 222 switches between a second permissive state in which bidirectional current flow is permitted through the second cutoff unit 222 and a second cutoff state in which current flow from the low-voltage battery 92 to the first conductive path 81 is blocked. In this embodiment, the second cutoff unit 222 blocks bidirectional current flow through the second cutoff unit 222 when in the second cutoff state. The second cutoff unit 222 enters the second permissive state when MOSFETs 22A and 22B are turned ON. The second cutoff unit 222 enters the second cutoff state when MOSFETs 22A and 22B are turned OFF. In this embodiment, the second cutoff unit 222 is configured by a normally-off switching element.

[0081] The control unit 230 controls the first cutoff unit 21 and the second cutoff unit 222. The control unit 230 switches the first cutoff unit 21 to the first cutoff state based on the fact that a current exceeding a first threshold value TH1 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side only when the vehicle is in the first state out of the first and second states.

[0082] When the vehicle is in the first state, the control unit 230 may immediately switch the first cut-off unit 21 to the first cut-off state when a current exceeding the first threshold value TH1 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side, or may switch the first cut-off unit 21 to the first cut-off state when a current exceeding the first threshold value TH1 flows for a predetermined period of time, or may switch the first cut-off unit 21 to the first cut-off state when the average value over a predetermined period of time exceeds the first threshold value TH1.

[0083] When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 222 is in the second permissive state, the control unit 230 switches the first cutoff unit 21 to the first cutoff state based on the fact that a current exceeding the first threshold value TH1 flows from the low-voltage battery 92 to the voltage conversion unit 93 when the vehicle is in the first state. When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 222 is in the second permissive state, power can be supplied to the load 96 from both the voltage conversion unit 93 and the low-voltage battery 92. When the first cutoff unit 21 is in the first permissive state and the second cutoff unit 222 is in the second permissive state, it is preferable that power be supplied to the load 96 from the voltage conversion unit 93.

[0084] After switching the first blocking unit 21 to the first blocking state, the control unit 230 maintains the first blocking state even if current stops flowing from the first conductive path 81 to the voltage conversion unit 93. After switching the first blocking unit 21 to the first blocking state, the control unit 230 restores the first blocking unit 21 to the first permissive state when a first restoration condition is satisfied.

[0085] When the vehicle is at least in the second state, the control unit 230 cuts off the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 based on the fact that a current exceeding a second threshold value TH2, which is larger than the first threshold value TH1, flows from the low-voltage battery 92 to the voltage conversion unit 93. In other words, when the vehicle is at least in the second state, the control unit 230 switches the second cutoff unit 222 to the second cutoff state based on the fact that a current exceeding a second threshold value TH2, which is larger than the first threshold value TH1, flows from the low-voltage battery 92 to the voltage conversion unit 93.

[0086] When the vehicle is in the second state, the control unit 230 may immediately switch the second cut-off unit 222 to the second cut-off state when a current exceeding the second threshold value TH2 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side, or may switch the second cut-off unit 222 to the second cut-off state when a current exceeding the second threshold value TH2 flows for a predetermined period of time, or may switch the second cut-off unit 222 to the second cut-off state when the average value over a predetermined period of time exceeds the second threshold value TH2.

[0087] When the first cut-off unit 21 is in the first permissive state and the second cut-off unit 222 is in the second permissive state and the vehicle is in the second state, the control unit 230 switches the second cut-off unit 222 to the second cut-off state based on the fact that a current exceeding the second threshold value TH2 flows from the low-voltage battery 92 side to the voltage conversion unit 93 side.

[0088] When the vehicle is in the second state with first cutoff unit 21 in the first permissive state and second cutoff unit 222 in the second permissive state, control unit 230 switches second cutoff unit 222 to the second cutoff state based on a current flowing from voltage conversion unit 93 to low-voltage battery 92. Control unit 230 may switch second cutoff unit 222 to the second cutoff state based on a current flowing from voltage conversion unit 93 to low-voltage battery 92 exceeding 0 A, or may switch second cutoff unit 222 to the second cutoff state based on a current flowing from voltage conversion unit 93 to low-voltage battery 92 exceeding a threshold current greater than 0 A.

[0089] After switching second cutoff unit 222 to the second cutoff state, control unit 230 maintains second cutoff unit 222 in the second cutoff state even if a current exceeding second threshold TH2 no longer flows from low-voltage battery 92 to voltage conversion unit 93. After switching second cutoff unit 222 to the second cutoff state, control unit 230 restores second cutoff unit 222 to the second permissive state when a second restoration condition is satisfied.

[0090] Control unit 230 includes a first shutoff circuit 231, a second shutoff circuit 232, and a circuit control unit 233. First shutoff circuit 231 and second shutoff circuit 232 are configured using discrete components. Circuit control unit 233 includes a microcomputer. Circuit control unit 233 controls first shutoff circuit 231 and second shutoff circuit 232.

[0091] The first shutoff circuit 231 has the same configuration as the first shutoff circuit 31 described in the first embodiment. The first shutoff circuit 231 includes a first comparator 231A, a NOT circuit 31B, and a latch circuit 31C. The first comparator 231A has the same configuration as the comparator 31A described in the first embodiment. The first comparator 231A outputs a first shutoff signal in place of the shutoff signal of the comparator 31A.

[0092] The second cut-off circuit 232 switches the second cut-off unit 222 to the second cut-off state based on the flow of current from the low-voltage battery 92 side to the voltage conversion unit 93 side when the first cut-off unit 21 is in the first permissive state and the second cut-off unit 222 is in the second permissive state.

[0093] The second cutoff circuit 232 switches the second cutoff unit 222 to the second cutoff state when the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 exceeds the second threshold value TH2 in the second state. The second cutoff circuit 232 switches the second cutoff unit 222 to the second cutoff state when the detection value of the current detection unit 23 exceeds the second threshold value TH2 in the second state.

[0094] The second shutoff circuit 232 includes a second comparator 232A, a NOT circuit 232B, and a latch circuit 232C.

[0095] The second comparator 232A receives the detection value of the current detection unit 23 and a second threshold value TH2. The detection value of the current detection unit 23 is input to the non-inverting input terminal of the second comparator 232A. The second threshold value TH2 is input to the inverting input terminal of the second comparator 232A. The second comparator 232A outputs a second shutdown signal when the detection value of the current detection unit 23 exceeds the second threshold value TH2 in the second state. The second shutdown signal is a high-level signal. The second comparator 232A does not output the second shutdown signal when the detection value of the current detection unit 23 does not exceed the second threshold value TH2 in the second state. In other words, the second comparator 232A outputs a low-level signal. The second comparator 232A is OFF in the first state and ON in the second state. That is, in the second state, the second comparator 232A never outputs the second cutoff signal regardless of the detection value of the current detection unit 23 .

[0096] The NOT circuit 232B receives the signal output from the second comparator 232A. The NOT circuit 232B outputs a high-level signal when the second comparator 232A does not output a second cutoff signal. The NOT circuit 232B outputs a low-level signal when the second comparator 232A outputs a second cutoff signal.

[0097] The latch circuit 232C receives the signal output from the NOT circuit 232B. The latch circuit 232C outputs a high-level signal (ON signal) until it receives a low-level signal from the NOT circuit 232B, thereby maintaining the second cutoff unit 222 in the second permissive state. When the latch circuit 232C receives a low-level signal from the NOT circuit 232B, it outputs a low-level signal (OFF signal) and switches the second cutoff unit 222 to the second cutoff state. After switching the second cutoff unit 222 to the second cutoff state, the latch circuit 232C maintains the second cutoff unit 222 in the second cutoff state even if the signal input from the NOT circuit 232B returns to a high-level signal. In other words, the latch circuit 232C maintains the second cutoff unit 222 in the second permissive state until the second cutoff signal is output from the second comparator 232A. When the second comparator 232A outputs a second cutoff signal, the latch circuit 232C switches the second cutoff unit 222 to the second cutoff state.

[0098] When the first shutoff unit 21 switches to the first shutoff state, the circuit control unit 233 determines whether the first restoration condition is satisfied. For example, when the circuit control unit 233 receives a first shutoff signal output from the first comparator 231A, the circuit control unit 233 starts determining whether the first restoration condition is satisfied. When the circuit control unit 233 determines that the first restoration condition is satisfied, the circuit control unit 233 controls the first shutoff circuit 231 to restore the first shutoff unit 21 to the first permissive state. Specifically, the circuit control unit 233 releases the latched state of the latch circuit 31C and causes the latch circuit 31C to output an ON signal.

[0099] When the second shutoff unit 222 switches to the second shutoff state, the circuit control unit 233 determines whether the second return condition is satisfied. For example, when the circuit control unit 233 receives a second shutoff signal output from the second comparator 232A, the circuit control unit 233 starts determining whether the second return condition is satisfied. When the circuit control unit 233 determines that the second return condition is satisfied, the circuit control unit 233 controls the second shutoff circuit 232 to return the second shutoff unit 222 to the second permissive state. Specifically, the circuit control unit 233 releases the latched state of the latch circuit 232C and causes the latch circuit 232C to output an ON signal.

[0100] 2-3. Operation Example of the In-Vehicle System 200 When the start switch is switched ON, the SMR 94 remains OFF, the first shutoff unit 21 enters the first permissive state, the second shutoff unit 222 enters the second permissive state, and the voltage conversion unit 93 performs the second conversion operation. As a result, as shown in FIG. 9 , power from the low-voltage battery 92 is precharged to the capacitor 95. When the voltage of the capacitor 95 reaches the target voltage, precharge is completed and the SMR 94 is switched ON. Furthermore, as shown in FIG. 10 , the voltage conversion unit 93 performs the first conversion operation, and power from the high-voltage battery 91 and the low-voltage battery 92 is able to be supplied to the load 96. As a result, power from the high-voltage battery 91 and the low-voltage battery 92 is able to be supplied to the load 96 while the vehicle is running.

[0101] During precharge, it is necessary to allow current to flow from the low-voltage battery 92 to the voltage conversion unit 93. For this reason, as shown in FIG. 9 , the first comparator 231A is turned OFF. However, if an overcurrent flows, the second comparator 232A is turned ON so that the current can be cut off. In this state, if a ground fault occurs in the second conductive path 82, as shown in FIG. 11 , for example, current from the low-voltage battery 92 flows to the ground-fault location in the second conductive path 82. When a current exceeding the second threshold TH2 flows through the first conductive path 81, the second comparator 232A outputs a second cutoff signal, and the second cutoff unit 222 is switched to the second cutoff state as shown in FIG. 12 . This cuts off the current supplied from the low-voltage battery 92.

[0102] Furthermore, while the vehicle is traveling, it is necessary to maintain a state in which power can be supplied to the load 96 from both the voltage conversion unit 93 and the low-voltage battery 92, while quickly interrupting the reverse current flow from the first conduction path 81 to the voltage conversion unit 93. Therefore, as shown in FIG. 10 , the first comparator 231A is turned ON, and the second comparator 232A is turned OFF. In this state, if a ground fault occurs in the second conduction path 82, as shown in FIG. 13 , for example, current from the low-voltage battery 92 flows to the ground-fault location in the second conduction path 82. When the current flowing from the first conduction path 81 to the voltage conversion unit 93 exceeds a first threshold value TH1, the first comparator 231A outputs a first interruption signal, and the first interruption unit 21 is switched to the first interruption state, as shown in FIG. 14 . This allows the power supply source to be switched from the voltage conversion unit 93 to the low-voltage battery 92 so that the power supply to the load 96 is not interrupted.

[0103] 2-4. Example of Effects of the Vehicle Cutoff Device 210 The vehicle cutoff device 210 can switch the first cutoff unit 21 to the first cutoff state based on the flow of current exceeding the first threshold value TH1 from the low-voltage battery 92 to the voltage conversion unit 93 in the first state. That is, the vehicle cutoff device 210 can quickly switch the first cutoff unit 21 to the first cutoff state when current flows backward from the low-voltage battery 92 to the voltage conversion unit 93 in the first state. Furthermore, the vehicle cutoff device 210 can interrupt the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 by using the second cutoff unit 222 based on the flow of current exceeding the second threshold value TH2 from the low-voltage battery 92 to the voltage conversion unit 93 in the second state. In this way, the vehicle cutoff device 210 can easily interrupt the current appropriately depending on the state of the vehicle.

[0104] The second cutoff unit 222 is provided between the connection point CP at which the load 96 is connected to the first conductive path 81 and the low-voltage battery 92. When the vehicle is at least in the second state, the control unit 230 cuts off the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 and cuts off the current flowing from the voltage conversion unit 93 to the low-voltage battery 92 based on the current exceeding the second threshold value TH2 flowing from the low-voltage battery 92 to the voltage conversion unit 93. Therefore, even when the second cutoff unit 222 has switched to the second cutoff state, the onboard cutoff device 10 can supply power from the voltage conversion unit 93 to the load 96 as long as the voltage conversion unit 93 is not malfunctioning.

[0105] When the current flowing from the low-voltage battery 92 side to the voltage conversion unit 93 side exceeds a first threshold value TH1 in the first state, the on-board cutoff device 210 can quickly switch the first cutoff unit 21 to the first cutoff state by the first cutoff circuit 231. Furthermore, when the current flowing from the low-voltage battery 92 side to the voltage conversion unit 93 side exceeds a second threshold value TH2 in the second state, the on-board cutoff device 210 can quickly switch the second cutoff unit 222 to the second cutoff state by the second cutoff circuit 232.

[0106] The first shutoff circuit 231 includes a first comparator 231A. The second shutoff circuit 232 includes a second comparator 232A. The first comparator 231A outputs a first shutoff signal when, in the first state, the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 exceeds a first threshold value TH1. The second comparator 232A outputs a second shutoff signal when, in the second state, the current flowing from the low-voltage battery 92 to the voltage conversion unit 93 exceeds a second threshold value TH2. The first shutoff unit 221 switches to the first shutoff state when the first comparator 231A outputs the first shutoff signal. The second shutoff unit 222 switches to the second shutoff state when the second comparator 232A outputs the second shutoff signal. The first comparator 231A is OFF in the second state. This configuration makes it easy to simplify the configurations of the first shutoff circuit 231 and the second shutoff circuit 232.

[0107] The vehicle-mounted cutoff device 210 switches the first cutoff unit 21 to the first cutoff state when the first cutoff unit 21 is in the first permissive state and the second cutoff unit 222 is in the second permissive state. Therefore, even when the first cutoff unit 21 is switched to the first cutoff state, the vehicle-mounted cutoff device 210 can supply power from the low-voltage battery 92 to the load 96 without interrupting the power supply to the load 96.

[0108] In a state where power is supplied from the voltage conversion unit 93 to the first conductive path 81, the vehicle-mounted circuit breaker 210 can immediately switch the first circuit breaker 21 to the first circuit breaker state if a backflow occurs to the voltage conversion unit 93. In addition, in a state where power is supplied from the low-voltage battery 92 to the voltage conversion unit 93, the vehicle-mounted circuit breaker 210 can cut off the current by the second circuit breaker 222 if an overcurrent occurs.

[0109] The on-board circuit breaker device 210 can immediately switch the first circuit breaker unit 21 to the first circuit breaker state when a backflow to the voltage conversion unit 93 occurs while the vehicle is running. Also, the on-board circuit breaker device 210 can switch the second circuit breaker unit 222 to the second circuit breaker state when an overcurrent occurs during precharging of the capacitor 95.

[0110] Even if the on-board cutoff device 210 switches the first cutoff unit 21 to the first cutoff state, it can return the first cutoff unit 21 to the first permissive state if the first return condition is satisfied.

[0111] <Other Embodiments> The present disclosure is not limited to the embodiments described above and in the drawings. For example, any combination of features of the above-described or below-described embodiments is possible within a range that does not contradict. Furthermore, any feature of the above-described or below-described embodiments may be omitted unless explicitly stated as essential. Furthermore, the above-described embodiments may be modified as follows.

[0112] In each of the above embodiments, the first cutoff unit 21 is configured only by the MOSFET 21A. However, the first cutoff unit 21 may be configured by a pair of MOSFETs connected in opposite directions. In this case, the first cutoff unit 21 cuts off the flow of current in both directions through itself when in the first cutoff state. Furthermore, the first cutoff unit 21 may be configured by a switch other than a MOSFET.

[0113] In the first embodiment, the second cutoff unit 22 is configured by a MOSFET 22A. However, the second cutoff unit 22 may be configured by a pair of MOSFETs connected in opposite directions. In this case, the second cutoff unit 22 cuts off the flow of current in both directions through itself when in the second cutoff state. Furthermore, the second cutoff unit 22 may be configured by a switch other than a MOSFET.

[0114] In the second embodiment, the second cutoff unit 222 is configured with MOSFETs 22A and 22B. However, the second cutoff unit 222 may be configured with only MOSFET 22A. In this case, in the second cutoff state, the second cutoff unit 222 cuts off current flow from the low-voltage battery 92 to the voltage conversion unit 93 and allows current flow from the voltage conversion unit 93 to the low-voltage battery 92. The second cutoff unit 222 may also be configured with a switch other than a MOSFET.

[0115] In the first embodiment, the vehicle-mounted circuit breaking device 10 does not necessarily have to have the second circuit breaking portion 22 .

[0116] In the first embodiment, the thermal fuse 40 is arranged between the connection point CP and the low-voltage battery 92. However, the thermal fuse 40 may be arranged between the connection point CP and the voltage conversion unit 93. Furthermore, the thermal fuse 40 may be arranged at a position other than between the low-voltage battery 92 and the voltage conversion unit 93, as long as it can interrupt the current flowing between the low-voltage battery 92 and the voltage conversion unit 93.

[0117] It should be noted that the embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is not limited to the embodiments disclosed herein, and is intended to include all modifications within the scope indicated by the claims or within the scope equivalent to the claims.

[0118] DESCRIPTION OF SYMBOLS 10...In-vehicle circuit breaker 21...First circuit breaker section 21A...MOSFET 22...Second circuit breaker section 22A, 22B...MOSFET 23...Current detection section 30...Control section 31...First circuit breaker circuit 31A...Comparator 31B...NOT circuit 31C...Latch circuit 32...Second circuit breaker circuit 33...Circuit control section 40...Thermal fuse (specific circuit breaker section) 81...First conductive path (conductive path) 82...Second conductive path 83...Third conductive path 91...High voltage battery 92...Low voltage battery (second power supply section) 93...Voltage conversion section (first power supply section) 94...System main relay 95...Capacitor 96...Load 100...In-vehicle system 200...In-vehicle system 210...In-vehicle circuit breaker 222...Second circuit breaker section (specific circuit breaker section) 230...Control section 231...First circuit breaker circuit 231A...First comparator 232...Second cutoff circuit 232A...Second comparator 232B...NOT circuit 232C...Latch circuit 233...Circuit control section CP...Connection point TH1...First threshold value TH2...Second threshold value

Claims

1. An on-board circuit breaker included in an on-board system having: a first power supply unit; a second power supply unit; a conductive path provided between the first power supply unit and the second power supply unit; and a load electrically connected to the conductive path, the on-board circuit breaker having a first circuit breaker provided between the first power supply unit and the conductive path, a control unit for controlling the first circuit breaker, and a specific circuit breaker, the first circuit breaker switching between a first permissive state that allows a current to flow from the second power supply unit side to the first power supply unit side and a first circuit breaker state that blocks a current from flowing from the second power supply unit side to the first power supply unit side, the control unit switching the first circuit breaker to the first circuit breaker state based on a current exceeding a first threshold value flowing from the second power supply unit side to the first power supply unit side only when the vehicle is in the first state out of a first state and a second state, The specific cut-off unit cuts off the current flowing from the second power supply unit to the first power supply unit when the vehicle is in at least the second state, based on a current flowing from the second power supply unit to the first power supply unit that exceeds a second threshold value that is greater than the first threshold value.

2. The vehicle-mounted circuit breaker device described in claim 1, wherein the specific circuit breaker is provided between the second power supply unit and a connection point where the load is connected to the conductive path, and when the vehicle is in at least the second state, cuts off the current flowing from the second power supply unit to the first power supply unit and cuts off the current flowing from the first power supply unit to the second power supply unit based on a current exceeding the second threshold value flowing from the second power supply unit to the first power supply unit when the vehicle is in at least the second state.

3. The vehicle-mounted cutoff device according to claim 1 or 2, wherein the specific cutoff portion is a thermal fuse that melts when a threshold temperature is exceeded.

4. An on-board circuit breaker as described in claim 3, further comprising a current detection unit that detects a current flowing from the conductive path side to the first power supply unit side, the control unit including a first cut-off circuit, and the first cut-off circuit switching the first cut-off unit to the first cut-off state when the detection value of the current detection unit exceeds the first threshold value in the first state.

5. The vehicle-mounted cut-off device according to claim 4, wherein the first cut-off circuit includes a comparator, the comparator outputs a cut-off signal when the detection value of the current detection unit exceeds the first threshold value in the first state, the first cut-off unit switches to the first cut-off state when the cut-off signal is output from the comparator, and the comparator is OFF in the second state.

6. An on-board circuit breaker as described in claim 3, further comprising a second circuit breaker provided between the second power supply unit and the conductive path, the second circuit breaker being controlled by the control unit and switching between a second permissive state that allows current to flow from the second power supply unit to the first power supply unit and a second circuit breaker state that blocks current from flowing from the second power supply unit to the first power supply unit, and the control unit switching the first circuit breaker to the first circuit breaker state when the vehicle is in the first state and the first circuit breaker is in the second permissive state, based on the fact that a current exceeding the first threshold has flowed from the second power supply unit to the first power supply unit.

7. The vehicle-mounted circuit breaker device according to claim 1 or claim 2, wherein the specific circuit breaker is a second circuit breaker provided between the second power supply unit and the conductive path, the second circuit breaker being controlled by the control unit and switching between a second permissive state that allows current to flow from the second power supply unit side to the first power supply unit side and a second circuit breaker state that blocks current from flowing from the second power supply unit side to the first power supply unit side, and the control unit, when the vehicle is in the first state, switches the first circuit breaker to the first circuit breaker state based on a current exceeding the first threshold value flowing from the second power supply unit side to the first power supply unit side, and when the vehicle is in the second state, switches the second circuit breaker to the second circuit breaker state based on a current exceeding the second threshold value flowing from the second power supply unit side to the first power supply unit side.

8. The vehicle-mounted cut-off device according to claim 7, wherein the control unit includes a first cut-off circuit and a second cut-off circuit, the first cut-off circuit switches the first cut-off unit to the first cut-off state when the current flowing from the second power supply unit side to the first power supply unit side in the first state exceeds the first threshold, and the second cut-off circuit switches the second cut-off unit to the second cut-off state when the current flowing from the second power supply unit side to the first power supply unit side in the second state exceeds the second threshold.

9. The vehicle-mounted cut-off device according to claim 8, wherein the first cut-off circuit includes a first comparator, the second cut-off circuit includes a second comparator, the first comparator outputs a first cut-off signal when a current flowing from the second power supply unit side to the first power supply unit side in the first state exceeds the first threshold, the second comparator outputs a second cut-off signal when a current flowing from the second power supply unit side to the first power supply unit side in the second state exceeds the second threshold, the first cut-off unit switches to the first cut-off state when the first cut-off signal is output from the first comparator, the second cut-off unit switches to the second cut-off state when the second cut-off signal is output from the second comparator, and the first comparator is OFF in the second state.

10. An on-board circuit breaker device as described in claim 1 or claim 2, wherein the first state is a state in which power is supplied from the first power supply unit to the conductive path side, and the second state is a state in which power is supplied from the second power supply unit to the first power supply unit.

11. The vehicle-mounted system includes a high-voltage battery, a system main relay, and a capacitor, the second power supply unit is a low-voltage battery, the first power supply unit is a voltage conversion unit provided between the high-voltage battery and the low-voltage battery, the voltage conversion unit performs a first conversion operation of stepping up or stepping down a voltage input from the high-voltage battery side and outputting the voltage to the low-voltage battery side, and a second conversion operation of stepping up or stepping down a voltage input from the low-voltage battery side and outputting the voltage to the high-voltage battery side, the system main relay is provided between the high-voltage battery and the voltage conversion unit, and the capacitor is electrically connected to a power path between the system main relay and the voltage conversion unit, and when a start switch of the vehicle is switched ON, the vehicle-mounted system causes the voltage conversion unit to perform the second conversion operation while keeping the system main relay OFF to pre-charge the capacitor, and switches the system main relay ON after pre-charging the capacitor, 11. The vehicle-mounted shutoff device according to claim 10, wherein the first state is a state in which the starter switch is ON and the system main relay is ON, and the second state is a state in which the starter switch is ON and the system main relay is OFF.

12. An on-board cutoff device as described in claim 1 or claim 2, wherein the control unit, after switching the first cutoff unit to the first cutoff state, returns the first cutoff unit to the first permissive state when a first return condition is satisfied.

13. An on-vehicle circuit breaking device according to claim 1 or 2, wherein the specific circuit breaking unit is provided between the first power supply unit and the second power supply unit.

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