POWER SUPPLY CONTROL DEVICE AND FAILURE DETECTION PROCEDURES

Abstract

In a power supply control device, an upstream switch and a downstream switch are arranged before and after a load, respectively, in a current path for the current flowing through the load. One end of a first resistor is connected to a junction between the upstream switch and the load. One end of a series circuit, comprising a junction switch and a second resistor, is connected to a junction between the load and the downstream switch. A constant voltage is applied to the other end of the series circuit. A microcomputer detects faults in the upstream switch, the downstream switch, or the load based on one of the voltage values ​​at the two junctions.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a power supply control device and a fault detection method.

[0002] This application is based on Japanese Patent Application No. 2021-205402 filed on December 17, 2021, the entire contents of which are incorporated by reference. TECHNICAL BACKGROUND

[0003] Patent Document No. 1 discloses a vehicle power supply control device that controls the supply of power to a load from a DC power source. A switch is arranged in a current path through which a current flows from the DC power source to the load. By instructing the switch to turn on or off, the control device controls the supply of power to the load. PREVIOUSLY KNOWN TECHNICAL DOCUMENTSPATENT DOCUMENTS

[0004] Patent Document No. 1: JP 2019 - 41508 A OVERVIEW OF THE INVENTION

[0005] A power supply control device according to one aspect of the present disclosure is a power supply control device for controlling the supply of power to a load, comprising: an upstream switch arranged before the load in a current path for a current flowing through the load; a downstream switch arranged after the load in the current path; a first resistor having one end connected to a connection node between the upstream switch and the load; a series circuit having one end connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other;and a processing unit configured to perform processing, wherein a constant voltage relative to a potential of another end of the first resistor serving as a reference potential is applied to another end of the series circuit, and the processing unit configured to: acquire a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch, and detect a fault of the upstream switch, the downstream switch, or the load based on the acquired voltage value;

[0006] A fault detection method according to one aspect of the present disclosure is a fault detection method for detecting a fault of a circuit, the circuit comprising: an upstream switch disposed before a load in a current path for a current flowing through the load; a downstream switch disposed after the load in the current path; a first resistor having one end connected to a connection node between the upstream switch and the load;and a series circuit, one end of which is connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other, a constant voltage related to a potential of another end of the first resistor, which serves as a reference potential, is applied to another end of the series circuit, and the method comprises the following computer-executed steps: obtaining a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch; and detecting a fault of the upstream switch, the downstream switch, or the load based on the obtained voltage value.

[0007] Note that the present disclosure can be implemented not only as a power supply control device having such a characteristic processing unit, but also as a fault detection method including such characteristic processing as steps, or as a computer program for causing a computer to execute the steps. The present disclosure can also be implemented as a semiconductor integrated circuit partially or completely implementing the power supply control device, or as a power source system including the power supply control device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram illustrating a configuration of the main portion of a power source system according to Embodiment 1. Fig. 2 is a block diagram showing a configuration of the main portion of a microcomputer. Fig. Figure 3 is a diagram illustrating several thresholds. Fig. 4 is a table showing a fault diagnosis when a load is out of service. Fig. Figure 5 is a table showing fault diagnosis when the load is in operation. Fig. 6 is a flowchart illustrating a procedure of power supply control processing. Fig. 7 is a block diagram showing a configuration of the main portion of a power supply control device according to Embodiment 2. EMBODIMENTS OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] In the configuration of Patent Document No. 1, when a short-circuit fault occurs where the resistance value between the two ends of the switch is very small, the DC power source continues to supply power to the load even though the controller has issued an instruction to turn off the switch. In this case, the energy from the DC power source may be wasted.

[0009] The present disclosure has been made in consideration of such circumstances, and has as its object to provide a power supply control device capable of stopping the supply of power to a load upon occurrence of a short-circuit fault, and a fault detection method for detecting a fault of a circuit capable of stopping the supply of power to a load upon occurrence of a short-circuit fault. EFFECT OF THE INVENTION

[0010] With the power supply control device according to the above-described aspect, it is possible to stop supplying power to a load when a short-circuit fault occurs.

[0011] The fault detection method according to the above-described aspect detects a fault of a circuit capable of stopping the supply of power to a load upon the occurrence of a short-circuit fault. DESCRIPTION OF EMBODIMENTS

[0012] First, embodiments of the present disclosure will be listed and described. At least some of the embodiments described below can be suitably combined with one another.

[0013] (1) A power supply control device according to one aspect of the present disclosure is a power supply control device for controlling the supply of power to a load, comprising: an upstream switch arranged before the load in a current path for a current flowing through the load; a downstream switch arranged after the load in the current path; a first resistor having one end connected to a connection node between the upstream switch and the load; a series circuit having one end connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other;and a processing unit configured to perform processing, wherein a constant voltage relative to a potential of another end of the first resistor serving as a reference potential is applied to another end of the series circuit, and the processing unit configured to: acquire a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch, and detect a fault of the upstream switch, the downstream switch, or the load based on the acquired voltage value;

[0014] According to the aspect described above, a short-circuit fault of a switch is a phenomenon in which the resistance value between the two ends of the switch is very small even though an instruction to turn off the switch has been issued. When a short-circuit fault occurs in the upstream switch, power supply to the load is stopped by turning off the downstream switch. The processing unit detects a fault of the upstream switch, the downstream switch, or the load based on the voltage value of a voltage at the connection node between the upstream switch and the load or the voltage value of a voltage at the connection node between the load and the downstream switch.

[0015] (2) In the power supply control device according to one aspect of the present disclosure, when a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is configured to: issue an instruction to turn on the upstream switch, issue an instruction to turn off the downstream switch, and acquire a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is off, and detect an open-circuit fault of the upstream switch when the acquired voltage value is less than a voltage threshold,and the voltage threshold is greater than 0 V and less than or equal to a value of a voltage between one end and the other end of the DC power source.,

[0016] According to the aspect described above, when the upstream switch is turned on, the downstream switch is turned off, and the link switch is turned off, the voltage value acquired by the processing unit is equal to the voltage value of a voltage between the two ends of the DC power source and greater than or equal to the threshold value. A switch open circuit failure is a phenomenon in which the resistance value between the two ends of the switch is substantially high even though an instruction to turn on the switch has been given. When an instruction to turn on the upstream switch and an instruction to turn off the downstream switch have been given, and an open circuit failure has occurred in the upstream switch, the voltage value acquired by the processing unit while the link switch is turned off is 0 V and is less than the threshold value.

[0017] (3) In the power supply control device according to an aspect of the present disclosure, when a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is configured to: issue instructions to turn off the upstream switch and the downstream switch, acquire a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned off, and detect a short-circuit fault of the upstream switch when the acquired voltage value exceeds a second voltage threshold value, and the second voltage threshold value is 0 V or more and is smaller than a value of a voltage between one end and the other end of the DC power source.

[0018] According to the above-described aspect, when the upstream switch, the downstream switch, and the connecting switch are turned off, the voltage value obtained by the processing unit is 0 V and is less than or equal to the second voltage threshold. When instructions to turn off the upstream switch and the downstream switch have been issued and a short-circuit fault has occurred in the upstream switch, the voltage value obtained by the processing unit is equal to the voltage value of a voltage between the two ends of the DC power source and exceeds the second voltage threshold.

[0019] (4) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: issue an instruction to turn off the upstream switch; issue an instruction to turn on the downstream switch; obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is on;and detect an open circuit fault of the downstream switch when the acquired voltage value exceeds a third voltage threshold, and the third voltage threshold is 0 V or more and is smaller than a voltage value that the processing unit acquires when the upstream switch is turned off, the downstream switch is turned off, and the connecting switch is turned on;

[0020] According to the aspect described above, when the upstream switch is off, the downstream switch is on, and the link switch is on, the voltage value obtained by the processing unit is 0 V and is less than or equal to the third voltage threshold. When the upstream switch is off, the downstream switch is off, and the link switch is on, the first resistor, the second resistor, and the load divide the constant voltage. The voltage value obtained by the processing unit when the upstream switch is off, the downstream switch is off, and the link switch is on is referred to as the "divided voltage value."When an instruction to turn off the upstream switch and an instruction to turn on the downstream switch have been issued and an open circuit fault has occurred in the downstream switch, the voltage value obtained by the processing unit while the connecting switch is on is the divided voltage value and exceeds the third voltage threshold.

[0021] (5) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: issue instructions to turn off the upstream switch and the downstream switch, acquire a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is on; and detect a short-circuit fault of the downstream switch when the acquired voltage value is less than a fourth voltage threshold, and the fourth voltage threshold is greater than 0 V and less than or equal to a voltage value that the processing unit acquires when the upstream switch is off, the downstream switch is off, and the connection switch is on.

[0022] According to the aspect described above, when the upstream switch is off, the downstream switch is off, and the link switch is on, the voltage value obtained by the processing unit is a divided voltage value and greater than or equal to the fourth voltage threshold. When instructions to turn off the upstream switch and the downstream switch have been issued and a short-circuit fault has occurred in the downstream switch, the voltage value obtained by the processing unit while the link switch is on is 0 V and less than the fourth voltage threshold.

[0023] (6) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: issue instructions to turn off the upstream switch and the downstream switch; acquire a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is on; and detect an open-circuit fault of the load when the acquired voltage value exceeds a fifth voltage threshold, and the fifth voltage threshold is greater than a voltage value that the processing unit acquires when the upstream switch is off, the downstream switch is off, and the connection switch is on, and is less than a voltage value of the constant voltage.

[0024] According to the above-described aspect, when the upstream switch is turned off, the downstream switch is turned off, and the connecting switch is turned on, the voltage value obtained by the processing unit under normal load is a divided voltage value and is less than or equal to the fifth voltage threshold. An open-circuit fault of a load is a phenomenon in which the resistance value between the two ends of the load is extremely large. According to the above-described aspect, when the upstream switch is turned off, the downstream switch is turned off, and the connecting switch is turned on, the voltage value obtained by the processing unit is equal to the voltage value of a constant voltage and exceeds the fifth voltage threshold.

[0025] (7) In the power supply control device according to an aspect of the present disclosure, a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is configured to: issue instructions to turn on the upstream switch and the downstream switch; acquire a voltage value of a voltage at the connection node between the upstream switch and the load while the connection switch is turned off; and detect an open-circuit fault of the upstream switch when the acquired voltage value is less than a sixth voltage threshold value, and the sixth voltage threshold value is greater than 0 V and less than or equal to a value of a voltage between one end and the other end of the DC power source.

[0026] According to the above-described aspect, when the upstream switch is turned on, the downstream switch is turned on, and the link switch is turned off, the voltage value obtained by the processing unit is equal to the voltage value of a voltage between the two ends of the DC power source and greater than or equal to the sixth threshold. When instructions to turn on the upstream switch and the downstream switch have been issued and an open-circuit fault has occurred in the upstream switch, the voltage value obtained by the processing unit while the link switch is turned off is 0 V and is less than the sixth voltage threshold.

[0027] (8) In the power supply control device according to an aspect of the present disclosure, a current flows through the current path from one end of a DC power source to another end of the DC power source, the upstream switch is a semiconductor switch, the processing unit is configured to: issue instructions to turn on the upstream switch and the downstream switch; acquire a voltage value of a voltage at the connection node between the upstream switch and the load while the connection switch is off; and detect a fault in a resistance value of the upstream switch when the acquired voltage value is less than a seventh voltage threshold value, and the seventh voltage threshold value is less than or equal to a value of a voltage between one end and the other end of the DC power source.

[0028] According to the above-described aspect, a switch resistance error is a phenomenon in which the switch resistance is halfway between on and off, and is referred to as a "half-on error." According to the above-described aspect, when the upstream switch is on, the downstream switch is on, and the connecting switch is off, the voltage value obtained by the processing unit is equal to the voltage value of a voltage between the two ends of the DC power source and greater than or equal to the seventh threshold.When instructions to turn on the upstream switch and the downstream switch have been issued, and a half-on fault has occurred in the upstream switch, the voltage value obtained by the processing unit while the connecting switch is off is slightly lower than the voltage value of a voltage between the two ends of the DC power source. By setting the seventh voltage threshold to a value slightly lower than the voltage value of the voltage between the two ends of the DC power source and not greater than the voltage value of the voltage between the two ends of the DC power source, it is possible to detect a half-on fault of the upstream switch.

[0029] (9) In the power supply control device according to an aspect of the present disclosure, a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is configured to: issue instructions to turn on the upstream switch and the downstream switch; acquire a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned off; and detect an open-circuit fault of the downstream switch when the acquired voltage value exceeds an eighth voltage threshold value, and the eighth voltage threshold value is 0 V or more and is smaller than a value of a voltage between the one end and the other end of the DC power source.

[0030] According to the aspect described above, when the upstream switch is turned on, the downstream switch is turned on, and the link switch is turned off, the voltage value acquired by the processing unit is 0 V and is less than or equal to the eighth voltage threshold. When instructions to turn on the upstream switch and the downstream switch have been issued and an open circuit fault has occurred in the downstream switch, the voltage value acquired by the processing unit while the link switch is turned off is equal to the voltage value of a voltage between the two ends of the DC power source and exceeds the eighth voltage threshold.

[0031] (10) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: issue instructions to turn on the upstream switch and the downstream switch; acquire a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned off; and detect a fault in a resistance value of the downstream switch when the acquired voltage value exceeds a ninth voltage threshold value, and the ninth voltage threshold value is 0 V or more.

[0032] According to the aspect described above, when the upstream switch is turned on, the downstream switch is turned on, and the link switch is turned off, the voltage value acquired by the processing unit is 0 V and is less than or equal to the ninth voltage threshold. When instructions to turn on the upstream switch and the downstream switch have been issued and a half-on fault has occurred in the downstream switch, the voltage value acquired by the processing unit while the link switch is turned off is slightly higher than 0 V. By setting the ninth voltage threshold to a value equal to or greater than 0 V and less than a voltage value slightly higher than 0 V, it is possible to detect a half-on fault of the downstream switch.

[0033] (11) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: issue instructions to turn on the upstream switch and the downstream switch; obtain a current value of a current flowing through the upstream switch;and detect an open circuit fault of the load when the acquired current value is less than a current threshold, the current threshold is greater than a current value of a current flowing through the upstream switch when the upstream switch is turned on, the downstream switch is turned off, and the link switch is turned off, the current threshold is less than or equal to a current value of a current flowing through the upstream switch when the upstream switch and the downstream switch are turned on while the load is in a normal state, and a resistance value of the load is less than a resistance value of the first resistor;

[0034] According to the aspect described above, the current value of a current flowing through the upstream switch when the upstream switch and the downstream switch are turned on while the load is in a normal state is referred to as the "normal current value." The current value of a current flowing through the upstream switch when the upstream switch is turned on, the downstream switch is turned off, and the link switch is turned off is referred to as the "resistance current value." The resistance current value is the current value of a current flowing through the upstream switch and the first resistor, in that order. In addition, the resistance value of the load is smaller than the resistance value of the first resistor. Accordingly, the normal current value exceeds the resistance current value.

[0035] The current value obtained by the processing unit when the upstream switch and downstream switch are turned on while the load is in a normal state is equal to the normal current value and not less than the current threshold. In a case where the upstream switch and downstream switch are turned on, the current value obtained by the processing unit when an open-circuit fault has occurred in the load is equal to the resistance current value and less than the current threshold.

[0036] (12) In the power supply control device according to one aspect of the present disclosure, the processing unit is configured to: give instructions to turn on the upstream switch and the downstream switch; acquire a current value of a current flowing across the upstream switch; and detect a short-circuit fault of the load when the acquired current value exceeds a second current threshold value, and the second current threshold value is a current value of a current flowing across the upstream switch when the upstream switch and the downstream switch are turned on while the load is in a normal state.

[0037] According to the aspect described above, a short-circuit fault of a load is a phenomenon in which the resistance value between the two ends of the load is extremely small. When the upstream switch and the downstream switch are turned on while the load is in a normal state, the current value obtained by the processing unit is not greater than the second current threshold. When the upstream switch and the downstream switch are turned on and a short-circuit fault has occurred in the load, the current value obtained by the processing unit exceeds the second current threshold.

[0038] (13) In the power supply control device according to one aspect of the present disclosure, when a fault is detected in the upstream switch, the downstream switch, or the load, when instructions to turn on the upstream switch and the downstream switch have been given, the processing unit issues instructions to turn off the upstream switch and the downstream switch.

[0039] According to the aspect described above, upon detecting a fault in the upstream switch, the downstream switch, or the load, the processing unit issues instructions to turn off the upstream switch and the downstream switch. This makes it possible to stop current flow through the load.

[0040] (14) A fault detection method according to one aspect of the present disclosure is a fault detection method for detecting a fault of a circuit, the circuit comprising: an upstream switch disposed before a load in a current path for a current flowing through the load; a downstream switch disposed after the load in the current path; a first resistor having one end connected to a connection node between the upstream switch and the load;and a series circuit, one end of which is connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other, a constant voltage related to a potential of another end of the first resistor, which serves as a reference potential, is applied to another end of the series circuit, and the method comprises the following computer-executed steps: obtaining a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch; and detecting a fault of the upstream switch, the downstream switch, or the load based on the obtained voltage value.

[0041] According to the aspect described above, when a short-circuit fault occurs in the upstream switch, it is possible to stop the power supply to the load by turning off the downstream switch. The computer detects a fault in the upstream switch, the downstream switch, or the load based on the voltage value of a voltage at the connection node between the load and the downstream switch or the voltage value of a voltage at the connection node between the upstream switch and the load. DETAILED DESCRIPTION OF EMBODIMENTS

[0042] Hereinafter, specific examples of a power source system according to embodiments of the present disclosure will be described with reference to the drawings. It should be noted that the present disclosure is not limited to the examples but is defined by the claims, and all modifications equivalent in meaning and scope to the claims are intended to be embraced. Example 1Design of the power source system 1

[0043] Fig. 1 is a block diagram illustrating a configuration of the main portion of a power source system 1 according to Embodiment 1. The power source system 1 is installed in a vehicle C. The power source system 1 includes a power supply controller 10, a DC power source 11, and a load 12. The power supply controller 10 has a downstream switch 20 and an upstream switch 30. The upstream switch 30 and the downstream switch 20 are semiconductor switches, specifically, n-channel field-effect transistors (FETs). The DC power source 11 is, for example, a battery. The load 12 is an electrical device and has a load resistor 12a.

[0044] The negative terminal of the DC power source 11 is grounded. Grounding is achieved by connecting the negative terminal to the body of vehicle C. The positive terminal of the DC power source 11 is connected to the drain of the upstream switch 30. The source of the upstream switch 30 is connected to one end of the load resistor 12a of the load 12. Another end of the load resistor 12a is connected to the drain of the downstream switch 20. The source of the downstream switch 20 is grounded.

[0045] When the upstream switch 30 and the downstream switch 20 are turned on, the respective resistance between drain and source is sufficiently small. Therefore, a current can flow through the drain and source. When the upstream switch 30 and the downstream switch 20 are turned off, the respective resistance between drain and source is sufficiently large. Therefore, no current can flow through the drain and source.

[0046] The power supply control device 10 turns on the upstream switch 30 and the downstream switch 20. When the upstream switch 30 and the downstream switch 20 are turned on, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30, the load resistor 12a, the downstream switch 20, and the negative terminal of the DC power source 11, in this order, as indicated by arrows. Accordingly, in a current path E for a current flowing through the load resistor 12a of the load 12, the upstream switch 30 is arranged upstream of the load resistor 12a. In the current path E, the downstream switch 20 is arranged downstream of the load resistor 12a. A current flows from the positive terminal of the DC power source 11 via the current path E to the negative terminal of the DC power source 11.

[0047] When a current flows through the load resistor 12a, the load 12 is energized. When the electrical power of the current across the load 12 is greater than or equal to a predetermined power, the load 12 is in operation. When the electrical power of the current across the load 12 is less than the predetermined power, the load 12 is out of operation. When the power supply control device 10 turns on the upstream switch 30 and the downstream switch 20, the DC power source 11 supplies the load 12 with a current whose power is greater than or equal to the predetermined power. As a result, the load 12 is in operation.

[0048] If at least one of the upstream switch 30 and downstream switch 20 is turned off, the DC power source 11 does not supply power to the load 12. If at least one of the upstream switch 30 and downstream switch 20 is turned off, the current flowing through the load 12 is less than the predetermined power, and the load 12 is out of operation.

[0049] The power supply control device 10 turns off the upstream switch 30 and the downstream switch 20. This terminates the operation of the load 12.

[0050] As described above, the power supply control device 10 controls the supply of power from the DC power source 11 to the load 12 by turning the upstream switch 30 and the downstream switch 20 on or off. Design of the power supply control device 10

[0051] The power supply control device 10 includes, in addition to the downstream switch 20, an IPD 21, a series circuit 22, a first resistor 23, an upstream resistor 24, a downstream resistor 25, and a microcomputer 26. IPD stands for Intelligent Power Device. The upstream switch 30 is contained in the IPD 21. In addition to the upstream switch 30, the IPD 21 includes a drive circuit 31, a current detection circuit 32, and a temperature detection circuit 33. The series circuit 22 includes a connecting switch 40 and a second resistor 41.

[0052] In the series circuit 22, the connecting switch 40 is connected in series with the second resistor 41. Accordingly, one end of the connecting switch 40 is connected to one end of the second resistor 41. One end of the series circuit 22 is connected to a connection node between the load resistor 12a and the downstream switch 20. A constant voltage relative to a ground potential, which serves as a reference potential, is applied to the other end of the series circuit 22. Hereinafter, the voltage value of the constant voltage is referred to as the "constant voltage value." Fig. 1, the constant voltage value is denoted by Vc. The constant voltage is generated, for example, by a regulator that reduces the voltage between the two ends of the DC power source 11. The constant voltage value Vc is lower than the voltage value between the two ends of the DC power source 11.

[0053] In the example of Fig. 1, the constant voltage is applied to the other end of the connecting switch 40. The other end of the second resistor 41 is connected to the connection node between the load resistor 12a and the downstream switch 20. However, the constant voltage can also be applied to the other end of the second resistor 41. In this case, the other end of the connecting switch 40 is connected to the connection node between the load resistor 12a and the downstream switch 20.

[0054] In the IPD 21, the gate of the upstream switch 30 is connected to the drive circuit 31. The drive circuit 31 is further connected to the microcomputer 26. The drain of the upstream switch 30 is connected to the current detection circuit 32 in addition to the positive terminal of the DC power source 11. The current detection circuit 32 is grounded. The current detection circuit 32 is further connected to the microcomputer 26 and the drive circuit 31. The drive circuit 31 is further connected to the temperature detection circuit 33.

[0055] One end of the first resistor 23 and one end of the upstream resistor 24 are connected to a connection node between the upstream switch 30 of the IPD 21 and the load resistor 12a of the load 12. The other end of the first resistor 23 is grounded. The other end of the upstream resistor 24 is connected to the microcomputer 26. The connection node between the load resistor 12a and the downstream switch 20 is connected to the series circuit 22 and also to one end of the downstream resistor 25. The other end of the downstream resistor 25 is connected to the microcomputer 26.

[0056] If the gate voltage value of the upstream switch 30 or the downstream switch 20 relative to the source potential, which serves as a reference potential, is greater than or equal to a constant voltage value, the corresponding switch is turned on. If the gate voltage value of the upstream switch 30 or the downstream switch 20 relative to the source potential, which serves as a reference potential, is less than the constant voltage value, the corresponding switch is turned off.

[0057] The microcomputer 26 outputs a high-level voltage (high-level voltage) or a low-level voltage (low-level voltage) to the drive circuit 31. When the microcomputer 26 switches the voltage output to the drive circuit 31 from the low-level voltage to the high-level voltage, the drive circuit 31 increases the gate voltage of the upstream switch 30 with respect to the ground potential, which serves as a reference potential. As a result, the gate voltage of the upstream switch 30 with respect to the source potential, which serves as a reference potential, increases to a voltage value greater than or equal to the constant voltage value, and the upstream switch 30 is turned on.

[0058] When the microcomputer 26 switches the voltage output to the drive circuit 31 from the high-level voltage to the low-level voltage, the drive circuit 31 lowers the gate voltage of the upstream switch 30 relative to the ground potential serving as a reference potential. As a result, the gate voltage of the upstream switch 30 relative to the source potential serving as a reference potential decreases to a voltage value lower than the constant voltage value, and the upstream switch 30 is turned off.

[0059] In the manner described above, the control circuit 31 switches the upstream switch 30 on or off depending on the voltage 26 input from the microcomputer.

[0060] The microcomputer 26 also outputs a low-level voltage or a high-level voltage to the gate of the downstream switch 20. The source potential of the downstream switch 20 is the ground potential. When the microcomputer 26 outputs the low-level voltage to the gate of the downstream switch 20, the voltage value of the gate of the downstream switch 20 relative to the ground potential, which serves as a reference potential, is smaller than the constant voltage value, and the downstream switch 20 is turned off.

[0061] When the microcomputer 26 switches the voltage output to the downstream switch 20 from the low-level voltage to the high-level voltage, the voltage value of the gate of the downstream switch 20 increases to a voltage value greater than or equal to the constant voltage value with respect to the ground potential serving as a reference potential, and the downstream switch 20 is turned on. When the microcomputer 26 switches the voltage output to the downstream switch 20 from the high-level voltage to the low-level voltage, the voltage value of the gate of the downstream switch 20 decreases to a voltage value lower than the constant voltage value with respect to the ground potential serving as a reference potential, and the downstream switch 20 is turned off.

[0062] In the manner described above, the microcomputer 26 switches the voltage output to the gate of the downstream switch 20 to the low-level voltage or the high-level voltage to turn the downstream switch 20 on or off. The microcomputer 26 controls the state of the upstream switch 30 by switching the voltage to be output to the respective gate of the drive circuit 31 or the downstream switch 20 to the low-level voltage or the high-level voltage.

[0063] The microcomputer 26 turns on the upstream switch 30 and the downstream switch 20. When the upstream switch 30 and the downstream switch 20 are turned on, a current flows, as described above, from the positive terminal of the DC power source 11 to the upstream switch 30, the load resistor 12a, the downstream switch 20, and the negative terminal of the DC power source 11, in this order. When the upstream switch 30 is turned on, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30, the first resistor 23, and the negative terminal of the DC power source 11, in this order.

[0064] The resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a of the load 12. Accordingly, when the upstream switch 30 and the downstream switch 20 are turned on, almost all of the current that has flowed through the upstream switch 30 flows through the load resistor 12a.

[0065] The current detection circuit 32 detects the current value of a current flowing through the upstream switch 30. Hereinafter, the current value detected by the current detection circuit 32 is referred to as the "detected current value." The current detection circuit 32 outputs analog current information indicating the detected current value to the microcomputer 26 and the control circuit 31.

[0066] The temperature detection circuit 33 detects the temperature of the upstream switch 30. Hereinafter, the temperature detected by the temperature detection circuit 33 is referred to as the "detected temperature." The temperature detection circuit 33 outputs temperature information indicating the detected temperature to the control circuit 31.

[0067] As described above, when the detected current value is less than a certain reference current value and the detected temperature is lower than a certain reference temperature, the drive circuit 31 turns the upstream switch 30 on or off depending on the voltage input from the microcomputer 26. When the detected current value has increased to a current value greater than or equal to the reference current value, the drive circuit 31 forcibly turns the upstream switch 30 off regardless of the voltage input from the microcomputer 26. When the detected temperature has increased to a temperature higher than or equal to the reference temperature, the drive circuit 31 forcibly turns the upstream switch 30 off regardless of the voltage input from the microcomputer 26. When a predetermined condition is met, the drive circuit 31 cancels the forced off of the upstream switch 30.

[0068] The microcomputer 26 switches the connecting switch 40 of the series circuit 22 on or off. When the connecting switch 40 is on, the resistance value between the two ends of the connecting switch 40 is sufficiently small. Therefore, a current can flow through the connecting switch 40. When the connecting switch 40 is off, the resistance value between the two ends of the connecting switch 40 is sufficiently large. Therefore, no current flows through the connecting switch 40.

[0069] Hereinafter, the voltage value at the connection node between the upstream switch 30 and the load resistor 12a is referred to as the "first voltage value." The voltage value at the connection node between the load resistor 12a and the downstream switch 20 is referred to as the "second voltage value." The reference potential for the first voltage value and the second voltage value is the ground potential. An analog first voltage value is input to the microcomputer 26 via the upstream resistor 24. An analog second voltage value is input to the microcomputer 26 via the downstream resistor 25. The microcomputer 26 detects faults of the upstream switch 30, the downstream switch 20, or the load 12 based on the first voltage value, the second voltage value, and the detected current value.

[0070] Fig. 2 is a block diagram illustrating a configuration of the main portion of the microcomputer 26. The microcomputer 26 includes a first output unit 50, a second output unit 51, three A / D converters 52, 53, and 54, a switching unit 55, a memory unit 56, and a control unit 57. These units are connected to an internal bus 58. The first output unit 50 is further connected to the drive circuit 31. The second output unit 51 is further connected to the gate of the downstream switch 20. The A / D converters 52, 53, and 54 are further connected to the current detection circuit 32, the other end of the upstream resistor 24, and the other end of the downstream resistor 25, respectively.

[0071] The first output unit 50 outputs the high-level voltage or the low-level voltage to the drive circuit 31. The voltage output from the microcomputer 26 to the drive circuit 31 is a voltage output from the first output unit 50 to the drive circuit 31. The control unit 57 instructs the first output unit 50 to turn on the upstream switch 30. In response, the first output unit 50 switches the voltage output to the drive circuit 31 from the low-level voltage to the high-level voltage. As a result, the drive circuit 31 turns on the upstream switch 30.

[0072] The control unit 57 instructs the first output unit 50 to turn off the upstream switch 30. In response, the first output unit 50 switches the voltage output to the drive circuit 31 from the high-level voltage to the low-level voltage. As a result, the drive circuit 31 turns off the upstream switch 30.

[0073] The second output unit 51 outputs the high-level voltage or the low-level voltage to the gate of the downstream switch 20. The voltage output from the microcomputer 26 to the gate of the downstream switch 20 is a voltage output from the first output unit 50 to the gate of the downstream switch 20. The control unit 57 instructs the second output unit 51 to turn on the downstream switch 20. In response, the second output unit 51 switches the voltage output to the gate of the downstream switch 20 from the low-level voltage to the high-level voltage. As a result, the downstream switch 20 is turned on.

[0074] The control unit 57 instructs the second output unit 51 to turn off the downstream switch 20. In response, the second output unit 51 switches the voltage output to the gate of the downstream switch 20 from the high-level voltage to the low-level voltage. As a result, the downstream switch 20 is turned off.

[0075] The current detection circuit 32 outputs analog current information indicating the detected current value to the A / D converter 52. The A / D converter 52 converts the analog current information into digital current information. The control unit 57 obtains the digital current information converted by the A / D converter 52. An analog first voltage value is input to the A / D converter 53 via the upstream resistor 24. The A / D converter 53 converts the analog first voltage value into a digital first voltage value. The control unit 57 obtains the digital first voltage value converted by the A / D converter 53.

[0076] An analog second voltage value is input to the A / D converter 54 via the downstream resistor 25. The A / D converter 54 converts the analog second voltage value into a digital second voltage value. The control unit 57 obtains the digital second voltage value converted by the A / D converter 54. The switching unit 55 turns the connection switch 40 on or off in accordance with an instruction from the control unit 57.

[0077] The storage unit 56 is, for example, a non-volatile memory. A computer program P is stored in the storage unit 56. The control unit 57 has a processing element for executing processing, for example, a central processing unit (CPU). The control unit 57 functions as a processing unit. By executing the computer program P, the processing element of the control unit 57 executes power supply control processing for controlling the supply of power from the DC power source 11 to the load 12.

[0078] It should be noted that the computer program P may be provided to the microcomputer 26 using a non-volatile storage medium A in which the computer program P is readably stored. The storage medium A is, for example, a portable memory. Examples of portable memory include a CD-ROM, a Universal Serial Bus (USB) memory, an SD card, a micro SD card, and a Compact Flash (registered trademark). If the storage medium A is a portable memory, the processing element of the control unit 57 may read the computer program P from the storage medium A using a reading device (not shown). The read computer program P is written into the storage unit 56. Furthermore, the computer program P may also be provided to the microcomputer 26 through a communication unit (not shown) of the microcomputer 26 that communicates with an external device.In this case, the processing element of the control unit 57 acquires the computer program P via the communication unit. The acquired computer program P is written into the storage unit 56.

[0079] The number of processing elements included in the control unit 57 is not limited to one, but may be two or more. If the control unit 57 includes multiple processing elements, the multiple processing elements can cooperate to perform power supply control processing.

[0080] In the power supply control processing, the control unit 57 diagnoses faults in the upstream switch 30, the downstream switch 20, or the load 12 using a plurality of preset thresholds. Description of the multiple thresholds

[0081] Fig. Figure 3 is a diagram illustrating several thresholds. Regarding voltage values, a high-voltage threshold Vh, a medium-voltage threshold Vm, and a low-voltage threshold Vw are predefined. Fig. 3, Vb denotes the value of a voltage between the two ends of the DC power source 11. Hereinafter, the value of a voltage between the two ends of the DC power source 11 is referred to as “power source voltage value”.

[0082] A possible fault of the upstream switch 30 and the downstream switch 20 is a half-on fault. When a half-on fault occurs in the upstream switch 30 or the downstream switch 20, the resistance value between drain and source is halfway between on and off, regardless of the gate voltage value. This value is neither a sufficiently large value nor a sufficiently small value. A half-on fault in the upstream switch 30 or the downstream switch 20 is a fault related to the resistance of the upstream switch 30 or the downstream switch 20, respectively.

[0083] As described above, the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a. Therefore, when a half-on fault occurs in the upstream switch 30 while the downstream switch 20 is on, the first voltage value substantially coincides with the voltage value of a voltage obtained by dividing the voltage between the two ends of the DC power source 11 by the upstream switch 30 and the load resistor 12a. The first voltage value when a half-on fault occurs in the upstream switch 30 while the downstream switch 20 is on is referred to as a "first fault voltage value." Vf1 denotes the first fault voltage value. The first fault voltage value Vf1 is smaller than the power source voltage value Vb.

[0084] As described above, Vc denotes the constant voltage value. The constant voltage value Vc is the voltage value of the constant voltage applied to the series circuit 22. The power source voltage value Vb is, for example, 12 V. The constant voltage value is, for example, 3.3 V, 5 V, or the like. The constant voltage value Vc is smaller than the first error voltage value Vf1.

[0085] When the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the connecting switch 40 is turned on, a second resistance circuit including the second resistor 41 and the load resistor 12a, and the first resistor 23 divide the constant voltage. The voltage value of a voltage obtained by dividing the constant voltage by the second resistance circuit and the first resistor 23 is referred to as the "first divided voltage value." Vd1 denotes the first divided voltage value. When the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the connecting switch 40 is turned on, the first divided voltage value Vd1 is equal to the first voltage value.

[0086] When the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the connecting switch 40 is turned on, the second resistor 41 and a first resistance circuit including the load resistor 12a and the first resistor 23 divide the constant voltage. The voltage value of a voltage obtained by dividing the constant voltage by the second resistor 41 and the first resistance circuit is referred to as a "second divided voltage value." Vd2 denotes the second divided voltage value. When the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the connecting switch 40 is turned on, the second divided voltage value Vd2 is equal to the second voltage value. The second divided voltage value Vd2 is smaller than the constant voltage value Vc. The first divided voltage value Vd1 is smaller than the second divided voltage value Vd2.

[0087] The resistance values ​​of the first resistor 23 and the second resistor 41 are sufficiently larger than the resistance value of the load resistor 12a. Accordingly, the first divided voltage value Vd1 and the second divided voltage value Vd2 substantially coincide with the voltage value of a voltage obtained by dividing the constant voltage by the second resistor 41 and the first resistor 23.

[0088] As described above, the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a. Therefore, when a half-on fault occurs in the downstream switch 20 while the upstream switch 30 is turned on, the second voltage value substantially coincides with the voltage value of a voltage obtained by dividing the voltage between the two ends of the DC power source 11 by the upstream switch 30 and the load resistor 12a. The second voltage value when a half-on fault occurs in the upstream switch 30 while the downstream switch 20 is turned on is referred to as a "second fault voltage value." Vf2 denotes the second fault voltage value. The second fault voltage value Vf2 is smaller than the first divided voltage value Vd1 and is greater than 0 V.

[0089] The high-voltage threshold Vh is a voltage value greater than the first fault voltage value Vf1 and less than the power source voltage value Vb. The medium-voltage threshold Vm is a voltage value greater than the second divided voltage value Vd2 and less than the constant voltage value Vc. The low-voltage threshold Vw is a voltage value greater than 0 V and less than the second fault voltage value Vf2.

[0090] Regarding current values, an upper current threshold Ih and a lower current threshold Iw are predefined. The current value of a current flowing through the upstream switch 30 when the load 12 is in a normal state and the upstream switch 30 and the downstream switch 20 are turned on is referred to as the "normal current value." Fig. 3, In is a normal current value. The current value of a current flowing through the upstream switch 30 when the load 12 is in a normal state, the upstream switch 30 is turned on, the downstream switch 20 is turned off, and the connecting switch 40 is turned off, is called the "resistance current value." In Fig. 3 Ir is the resistance current value.

[0091] The resistance current value Ir is the current value of a current flowing from the positive terminal of the DC power source 11 to the upstream switch 30, the first resistor 23, and the negative terminal of the DC power source 11, in this order. As described above, the resistance value of the load resistor 12a is smaller than the resistance value of the first resistor 23. Therefore, the resistance current value Ir is smaller than the normal current value In. The upper current threshold value Ih is the normal current value In. The lower current threshold value Iw exceeds the resistance current value Ir and is less than or equal to the normal current value In. Fault diagnosis when load 12 is out of service

[0092] Fig. 4 is a table showing a fault diagnosis when load 12 is out of service. Fig. 4 shows instructions for the upstream switch 30, instructions for the downstream switch 20, states of the connecting switch 40, error conditions, and detection contents. The instructions for the upstream switch 30 are the instructions that the control unit 57 of the microcomputer 26 issues to the first output unit 50. The instructions for the downstream switch 20 are the instructions that the control unit 57 issues to the second output unit 51. "Turn-on instruction" refers to an instruction to turn on. "Turn-off instruction" refers to an instruction to turn off. Error conditions are conditions that exist when an error occurs. Detection contents indicate errors detected by the control unit 57.

[0093] V1 and V2 denote the first voltage value and the second voltage value, respectively. As described above, the first voltage value V1 is the value of a voltage at the connection node between the upstream switch 30 and the load resistor 12a. The second voltage value V2 is the value of a voltage at the connection node between the load resistor 12a and the downstream switch 20.

[0094] The control unit 57 performs a fault diagnosis when an instruction to turn off the upstream switch 30 and / or the downstream switch 20 has been issued. Therefore, the current through the load resistor 12a is not greater than or equal to the predetermined value, and the load 12 is out of operation.

[0095] The control unit 57 issues an instruction to turn on the upstream switch 30, issues an instruction to turn off the downstream switch 20, and acquires the first voltage value V1 from the A / D converter 53 while the connecting switch 40 is off. The control unit 57 detects an open circuit failure of the upstream switch 30 based on the acquired first voltage value V1. A switch open circuit failure is a phenomenon in which the resistance value between the two ends of the switch is sufficiently large even though an instruction to turn on the switch has been issued.

[0096] When the upstream switch 30 is turned on, the downstream switch 20 is turned off, and the link switch 40 is turned off, a current flows from the positive terminal of the DC power source 11 through the upstream switch 30 and through the first resistor 23, in that order. No current flows through the load resistor 12a. Accordingly, when the upstream switch 30 is turned on, the downstream switch 20 is turned off, and the link switch 40 is turned off, the first voltage value V1 and the second voltage value V2 are equal to the power source voltage value Vb and greater than or equal to the low-voltage threshold value Vw. When an open-circuit fault occurs in the upstream switch 30, no current flows through either the first resistor 23 or the load resistor 12a.Therefore, the first voltage value V1 and the second voltage value V2 are both 0 V, and they are smaller than the low voltage threshold value Vw.

[0097] As a result, the control unit 57 detects an open-circuit failure of the upstream switch 30 when the first voltage value V1 obtained from the A / D converter 53 is less than the low-voltage threshold value Vw. Note that the control unit 57 can also detect an open-circuit failure of the upstream switch 30 when the second voltage value V2 obtained from the A / D converter 54 is less than the low-voltage threshold value Vw. In this case, the control unit 57 issues an instruction to turn on the upstream switch 30 and an instruction to turn off the downstream switch 20, and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is off. A voltage threshold value for use in detecting an open-circuit failure of the upstream switch 30 only needs to be higher than 0 V and less than or equal to the power source voltage value Vb.

[0098] The control unit 57 issues an instruction to turn off the upstream switch 30 and the downstream switch 20 and acquires the first voltage value V1 from the A / D converter 53 while the connecting switch 40 is off. The control unit 57 detects a short-circuit fault of the upstream switch 30 based on the acquired first voltage value V1. A short-circuit fault of the switch is a phenomenon in which the resistance value between the two ends of the switch is very small even though an instruction to turn off the switch has been issued.

[0099] When the upstream switch 30, the downstream switch 20, and the connecting switch 40 are turned off, no current flows through either the first resistor 23 or the load resistor 12a. Accordingly, when the upstream switch 30, the downstream switch 20, and the connecting switch 40 are turned off, the first voltage value V1 and the second voltage value V2 are both 0 V and are less than or equal to the low-voltage threshold value Vw. When a short-circuit fault occurs in the upstream switch 30, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30 and the first resistor 23, in that order, and no current flows through the load resistor 12a. Therefore, the first voltage value V1 and the second voltage value V2 are equal to the power source voltage value Vb and are greater than the low-voltage threshold value Vw.

[0100] As a result, the control unit 57 detects a short-circuit fault of the upstream switch 30 when the first voltage value V1 obtained from the A / D converter 53 exceeds the low-voltage threshold Vw. Note that the control unit 57 can also detect a short-circuit fault of the upstream switch 30 when the second voltage value V2 obtained from the A / D converter 54 exceeds the low-voltage threshold Vw. In this case, the control unit 57 issues an instruction to turn off the upstream switch 30 and the downstream switch 20 and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is turned off. A second voltage threshold for use in detecting a short-circuit fault of the upstream switch 30 only needs to be 0 V or more and less than the power source voltage value Vb.

[0101] The control unit 57 issues an instruction to turn off the upstream switch 30 and an instruction to turn on the downstream switch 20, and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is on. The control unit 57 detects an open circuit fault of the downstream switch 20 based on the acquired second voltage value V2.

[0102] When the upstream switch 30 is turned off, the downstream switch 20 is turned on, and the link switch 40 is turned on, a current flows through the link switch 40, the second resistor 41, and the downstream switch 20, in this order, and no current flows through the first resistor 23. Accordingly, when the upstream switch 30 is turned off, the downstream switch 20 is turned on, and the link switch 40 is turned on, the first voltage value V1 and the second voltage value V2 are both 0 V and are less than the low-voltage threshold value Vw.

[0103] When an open-circuit fault occurs in the downstream switch 20, a current flows through the second resistor 41, the load resistor 12a, and the first resistor 23, in this order. The second resistor circuit and the first resistor 23 divide the constant voltage. The second resistor 41 and the first resistor circuit divide the constant voltage. Accordingly, the first voltage value V1 and the second voltage value V2 are equal to the first divided voltage value Vd1 and the second divided voltage value Vd2, respectively. Therefore, the first voltage value V1 and the second voltage value V2 exceed the low-voltage threshold value Vw.

[0104] As a result, the control unit 57 detects an open circuit fault of the downstream switch 20 when the second voltage value V2 obtained from the A / D converter 54 exceeds the low-voltage threshold Vw. Note that the control unit 57 can also detect an open circuit fault of the downstream switch 20 when the first voltage value V1 obtained from the A / D converter 53 exceeds the low-voltage threshold Vw. In this case, the control unit 57 issues an instruction to turn off the upstream switch 30 and an instruction to turn on the downstream switch 20, and acquires the first voltage value V1 from the A / D converter 53 while the connection switch 40 is on.As for the first voltage value V1, a third voltage threshold for use in detecting an open-circuit fault of the downstream switch 20 only needs to be 0 V or more and less than the first divided voltage value Vd1. As for the second voltage value V2, the third voltage threshold for use in detecting an open-circuit fault of the downstream switch 20 only needs to be 0 V or more and less than the second divided voltage value Vd2.

[0105] As described above, when the upstream switch 30 is off, the downstream switch 20 is off, and the connecting switch 40 is on, the first divided voltage value Vd1 is equal to the first voltage value V1 that the control unit 57 obtains from the A / D converter 53. When the upstream switch 30 is off, the downstream switch 20 is off, and the connecting switch 40 is on, the second divided voltage value Vd2 is equal to the first voltage value V2 that the control unit 57 obtains from the A / D converter 54.

[0106] When a current flows through the second resistor 41, the load resistor 12a, and the first resistor 23, in this order, the load 12 is energized. However, since the constant voltage value Vc is small, the current through the load 12 is less than a predetermined power. Accordingly, the load 12 is inoperative when a current flows through the second resistor 41, the load resistor 12a, and the first resistor 23, in this order.

[0107] The control unit 57 issues instructions to turn off the upstream switch 30 and the downstream switch 20 and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is on. The control unit 57 detects a short-circuit fault of the downstream switch 20 based on the acquired second voltage value V2.

[0108] As described above, when the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the link switch 40 is turned on, the first voltage value V1 and the second voltage value V2 are equal to the first divided voltage value Vd1 and the second divided voltage value Vd2, respectively. Accordingly, when the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the link switch 40 is turned on, the first voltage value V1 and the second voltage value V2 are greater than or equal to the low-voltage threshold value Vw. When a short-circuit fault occurs in the downstream switch 20, a current flows through the link switch 40, the second resistor 41, and the downstream switch 20, in this order, and no current flows through the load resistor 12a.Therefore, the first voltage value V1 and the second voltage value V2 are both 0 V and they are smaller than the low voltage threshold value Vw.

[0109] As a result, the control unit 57 detects a short-circuit fault of the downstream switch 20 when the second voltage value V2 obtained from the A / D converter 54 is less than the low-voltage threshold Vw. Note that the control unit 57 can also detect a short-circuit fault of the downstream switch 20 when the first voltage value V1 obtained from the A / D converter 53 is less than the low-voltage threshold Vw. In this case, the control unit 57 issues instructions to turn off the upstream switch 30 and the downstream switch 20 and acquires the first voltage value V1 from the A / D converter 53 while the connection switch 40 is on.As for the first voltage value V1, a fourth voltage threshold for use in detecting a short-circuit fault of the downstream switch 20 only needs to be greater than 0 V and less than or equal to the first divided voltage value Vd1. As for the second voltage value V2, the fourth voltage threshold for use in detecting a short-circuit fault of the downstream switch 20 only needs to be greater than 0 V and less than or equal to the second divided voltage value Vd2.

[0110] The control unit 57 issues instructions to turn off the upstream switch 30 and the downstream switch 20, and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is on. The control unit 57 detects an open-circuit fault of the load 12 based on the acquired second voltage value V2. An open-circuit fault of the load 12 is a phenomenon in which the resistance value between the two ends of the load 12, that is, the resistance value between the two ends of the load resistor 12a, is extremely large.

[0111] As described above, when the upstream switch 30 is turned off, the downstream switch 20 is turned off, and the connecting switch 40 is turned on, and the load 12 is in a normal state, the second voltage value V2 is equal to the second divided voltage value Vd2 and less than or equal to the medium voltage threshold Vm. When an open-circuit fault occurs in the load 12, no current flows through the second resistor 41 while the connecting switch 40 is turned on. Therefore, the second voltage value V2 is equal to the constant voltage value Vc and exceeds the medium voltage threshold Vm.

[0112] As a result, the control unit 57 detects an open-circuit fault of the load 12 when the second voltage value V2 obtained from the A / D converter 54 exceeds the medium-voltage threshold Vm. Note that a fifth voltage threshold for use in detecting an open-circuit fault of the load 12 only needs to exceed the second divided voltage value Vd2 and be less than the constant-voltage value Vc. Fault diagnosis when load 12 is in operation

[0113] Fig. 5 is a table that shows a fault diagnosis when a load 12 is in operation. In a similar way to Fig. 4 shows Fig. 5 Instructions for upstream switch 30, instructions for downstream switch 20, states of connection switch 40, error conditions, and detection contents. Id denotes a detected current value. As described above, the detected current value is the current value of a current flowing through upstream switch 30.

[0114] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, and acquires the first voltage value V1 from the A / D converter 53 while the connection switch 40 is off. The control unit 57 detects an open circuit fault of the upstream switch 30 based on the acquired first voltage value V1.

[0115] As described above, when the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the connecting switch 40 is turned off, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30, the load resistor 12a, the downstream switch 20, and the negative terminal of the DC power source 11, in this order. In this situation, the DC power source 11 supplies the load resistor 12a with a current whose power is greater than or equal to the predetermined power, and thus the load 12 is operated. As described above, when the upstream switch 30 is turned on, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30, the first resistor 23, and the negative terminal of the DC power source 11, in this order.

[0116] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the connecting switch 40 is turned off, the first voltage value V1 is equal to the power source voltage value Vb and greater than or equal to the low-voltage threshold value Vw. When an open-circuit fault occurs in the upstream switch 30, no current flows through the first resistor 23. Therefore, the first voltage value V1 is 0 V and less than the low-voltage threshold value Vw. As a result, the control unit 57 detects an open-circuit fault of the upstream switch 30 when the first voltage value V1 obtained from the A / D converter 53 is less than the low-voltage threshold value Vw. Note that a sixth voltage threshold value for use in detecting an open-circuit fault of the upstream switch 30 only needs to be greater than 0 V and less than or equal to the power source voltage value Vb.

[0117] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, and acquires the first voltage value V1 from the A / D converter 53 while the connecting switch 40 is off. The control unit 57 detects a half-on fault of the upstream switch 30 based on the acquired first voltage value V1.

[0118] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the link switch 40 is turned off, the first voltage value V1 is equal to the power source voltage value Vb and greater than or equal to the high-voltage threshold value Vh. When a half-on fault has occurred in the upstream switch 30, the first voltage value V1 is equal to the first fault voltage value Vf1 and less than the high-voltage threshold value Vh. As a result, the control unit 57 detects a half-on fault of the upstream switch 30 when the first voltage value V1 obtained from the A / D converter 53 is less than the high-voltage threshold value Vh.It is noted that a seventh voltage threshold for use in detecting a half-on fault of the upstream switch 30 need only be greater than the first fault voltage value Vf1 and less than or equal to the power source voltage value Vb.

[0119] When a half-on fault occurs in the upstream switch 30 while the downstream switch 20 is on, the amount of heat generated by the upstream switch 30 per unit time increases rapidly. As a result, the temperature of the upstream switch 30 rises to a temperature higher than or equal to the reference temperature, and the drive circuit 31 forcibly turns off the upstream switch 30 regardless of a voltage input from the first output unit 50 of the microcomputer 26. A half-on fault of the upstream switch 30 is detected by the drive circuit 31 or the control unit 57.

[0120] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, and acquires the second voltage value V2 from the A / D converter 54 while the connection switch 40 is off. The control unit 57 detects an open circuit fault of the downstream switch 20 based on the acquired second voltage value V2.

[0121] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the link switch 40 is turned off, the second voltage value V2 is 0 V and is less than or equal to the high-voltage threshold value Vh. When an open-circuit fault occurs in the downstream switch 20, no current flows through the load resistor 12a. Therefore, the first voltage value V1 is equal to the power source voltage value Vb and exceeds the high-voltage threshold value Vh. As a result, the control unit 57 detects an open-circuit fault of the downstream switch 20 when the second voltage value V2 obtained by the A / D converter 54 exceeds the high-voltage threshold value Vh. Note that an eighth voltage threshold value for use in detecting an open-circuit fault of the downstream switch 20 only needs to be 0 V or more and less than the power source voltage value Vb.

[0122] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, and acquires the second voltage value V2 from the A / D converter 54 while the connecting switch 40 is off. The control unit 57 detects a half-on fault of the downstream switch 20 based on the acquired second voltage value V2.

[0123] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the link switch 40 is turned off, the second voltage value V2 is 0 V and is less than or equal to the low voltage threshold Vw. When a half-on fault has occurred in the downstream switch 20, the second voltage value V2 is equal to the second fault voltage value Vf2 and exceeds the low voltage threshold Vw, and is less than the high voltage threshold Vh. As a result, the control unit 57 detects a half-on fault of the downstream switch 20 when the second voltage value V2 exceeds the low voltage threshold Vw and is less than the high voltage threshold Vh.

[0124] It is noted that the lower voltage threshold for use in detecting a half-on fault of the downstream switch 20 only needs to be 0 V or more and less than the second fault voltage value Vf2. The lower voltage threshold corresponds to a ninth voltage threshold. It is noted that the upper voltage threshold for use in detecting a half-on fault of the downstream switch 20 only needs to be greater than or equal to the first fault voltage value Vf1 and less than the power source voltage value Vb.

[0125] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, and acquires current information from the A / D converter 52 while the connecting switch 40 is off. As described above, current information indicates the detected current value Id, that is, the current value of a current flowing through the upstream switch 30. Acquiring current information corresponds to acquiring the detected current value Id. The control unit 57 detects an open-circuit fault of the load 12 based on the detected current value Id indicated by the acquired current information.

[0126] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the link switch 40 is turned off while the load 12 is in a normal state, the detected current value Id is equal to the normal current value In and greater than or equal to the lower current threshold value Iw. When an open-circuit fault occurs in the load 12, the detected current value Id is equal to the resistance current value Ir and less than the lower current threshold value Iw. Accordingly, the control unit 57 detects an open-circuit fault of the load 12 when the detected current value Id, which the current information obtained from the A / D converter 52 indicates, is less than the lower current threshold value Iw.

[0127] The control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20 and acquires current information from the A / D converter 52 while the connecting switch 40 is off. The control unit 57 detects a short-circuit fault of the load 12 based on the detected current value Id indicated by the acquired current information. The short-circuit fault of the load 12 is a phenomenon in which the resistance value between the two ends of the load 12, that is, the resistance value between the two ends of the load resistor 12a, is extremely small.

[0128] When the upstream switch 30 is turned on, the downstream switch 20 is turned on, and the connecting switch 40 is turned off, while the load 12 is in a normal state, the detected current value Id is equal to the normal current value In and less than or equal to the upper current threshold Ih. When a short-circuit fault occurs in the load 12, the detected current value Id exceeds the upper current threshold Ih (the normal current value In). Accordingly, the control unit 57 detects a short-circuit fault of the load 12 when the detected current value Id, indicated by the current information acquired from the A / D converter 52, exceeds the upper current threshold Ih. The upper current threshold Ih refers to the second current threshold.

[0129] If a short-circuit fault occurs in load 12 while upstream switch 30 and downstream switch 20 are turned on, the detected current value Id increases to a current greater than or equal to a reference current value, and drive circuit 31 forcibly turns off upstream switch 30 regardless of a voltage output from first output unit 50 of microcomputer 26. A short-circuit fault of load 12 is detected by drive circuit 31 or control unit 57. Power supply control processing

[0130] Fig. 6 is a flowchart illustrating a procedure of power supply control processing. Hereinafter, fault diagnosis when the load 12 is out of operation is referred to as "non-operation fault diagnosis." Fault diagnosis when the load 12 is in operation is referred to as "operation fault diagnosis." The control unit 57 of the microcomputer 26 executes power supply control processing in a state where instructions have been issued to turn off the upstream switch 30, the downstream switch 20, and the link switch 40.

[0131] During power supply control processing, the control unit 57 determines whether the load 12 should be operated (step S1). If it is determined not to operate the load 12 (NO in step S1), the control unit 57 executes step S1 again. The control unit 57 waits until the time for operating the load 12 arrives. If it is determined to operate the load 12 (YES in step S1), the control unit 57 performs a non-operational fault diagnosis in accordance with the contents in Fig. 4 (step S2).

[0132] By instructing the switching unit 55 to turn on the connecting switch 40, the control unit 57 turns on the connecting switch 40. By instructing the switching unit 55 to turn off the connecting switch 40, the control unit 57 turns off the connecting switch 40. The control unit 57 performs the non-operation fault diagnosis to determine whether an open circuit fault of the upstream switch 30, a short circuit fault of the upstream switch 30, an open circuit fault of the downstream switch 20, a short circuit fault of the downstream switch 20, or an open circuit fault of the load 12 occurs. The control unit 57 ends the non-operation fault diagnosis in a state in which instructions to turn off the upstream switch 30, the downstream switch 20, and the connecting switch 40 have been issued.

[0133] After executing step S2, the control unit 57 determines whether a fault was detected during the non-operational fault diagnosis (step S3). If it is determined that no fault was detected during the non-operational fault diagnosis (NO in step S3), the control unit 57 issues instructions to turn on the upstream switch 30 and the downstream switch 20, respectively, to the first output unit 50 and the second output unit 51 (step S4). When the upstream switch 30 and the downstream switch 20 are turned on while the load 12 is in a normal state, the DC power source 11 supplies the load resistor 12a with a current whose power is greater than or equal to the predetermined power. Therefore, the load 12 is in operation.

[0134] After the execution of step S4, the control unit 57 performs an error diagnosis in operation in accordance with the contents in Fig. 5 (step S5). The control unit 57 performs the in-operation fault diagnosis to determine whether an open-circuit fault of the upstream switch 30, a half-closed fault of the upstream switch 30, an open-circuit fault of the downstream switch 20, a half-closed fault of the downstream switch 20, an open-circuit fault of the load 12, or a short-circuit fault of the load 12 occurs. The control unit 57 ends the in-operation fault diagnosis in a state in which instructions to turn on the upstream switch 30 and the downstream switch 20 have been issued, and an instruction to turn off the connecting switch 40 has been issued.

[0135] After executing step S5, the control unit 57 determines whether an error was detected during the in-operation error diagnosis (step S6). If it is determined that no error was detected during the in-operation error diagnosis (NO in step S6), the control unit 57 determines whether to stop the operation of the load 12 (step S7). If it is decided not to stop the operation of the load 12 (NO in step S7), the control unit 57 executes step S5 again. The control unit 57 waits until an error is detected or the time to stop the operation of the load 12 arrives.

[0136] If it is determined that a fault has been detected during the operation fault diagnosis (YES in step S6) or it is determined to stop the operation of the load 12 (YES in step S7), the control unit 57 issues instructions to turn off the upstream switch 30 and the downstream switch 20, respectively, to the first output unit 50 and the second output unit 51 (step S8). When the upstream switch 30 and the downstream switch 20 are turned off, the power supply from the DC power source 11 to the load resistor 12a is stopped, and the load 12 is out of operation.

[0137] If it is determined that a fault was detected during the non-operational fault diagnosis (YES in step S3), or after step S8 is executed, the control unit 57 ends the power supply control processing. If the power supply control processing is completed and no fault is detected, the control unit 57 executes the power supply control processing again. Note that the control unit 57 may also execute the non-operational fault diagnosis after executing step S8. In this case, the control unit 57 executes the non-operational fault diagnosis and then ends the power supply control processing.

[0138] As described above, in the power supply control processing, when a fault is detected during fault diagnosis in operation, the control unit 57 issues instructions to turn off the upstream switch 30 and the downstream switch 20. Accordingly, when a short-circuit fault occurs in the upstream switch 30, the downstream switch 20 is turned off, and the power supply to the load 12 is stopped. Furthermore, the control unit 57 detects faults in the upstream switch 30, the downstream switch 20, or the load 12 based on the first voltage value V1 or the second voltage value V2. Example 2

[0139] In Embodiment 1, the control circuit 31 detects a half-on fault of the upstream switch 30 and a short-circuit fault of the load 12. However, the control circuit 31 does not need to have such a fault detection function.

[0140] The following describes the configurations of Embodiment 2 that are different from those of Embodiment 1. Configurations not mentioned below are the same as those of Embodiment 1. Accordingly, configurations similar to those of Embodiment 1 are given the same reference numerals as those of Embodiment 1, and their description is omitted. Design of the power supply control device 10

[0141] Fig.7 is a block diagram illustrating a configuration of the main portion of the power supply control device 10 according to Embodiment 2. The power supply control device 10 of Embodiment 2 includes the downstream switch 20, the series circuit 22, the first resistor 23, the upstream resistor 24, the downstream resistor 25, the upstream switch 30, the drive circuit 31, and the current detection circuit 32. The power supply control device 10 further includes a shunt resistor 34. The power supply control device 10 does not include the IPD 21.

[0142] The connections between the load resistor 12a, the downstream switch 20, the series circuit 22, the downstream resistor 25, and the drive circuit 31 are the same as in Embodiment 1. A constant voltage is applied to the series circuit 22 in a similar manner to Embodiment 1. The connection between the drain and gate of the upstream switch 30 is the same as in Embodiment 1.

[0143] The source of the upstream switch 30 is connected to one end of the shunt resistor 34. The other end of the shunt resistor 34 is connected to one end of the load resistor 12a. One end of the first resistor 23 and one end of the upstream resistor 24 are connected to a connection node between the shunt resistor 34 and the load resistor 12a. The connection node between the shunt resistor 34 and the load resistor 12a is a connection node between the upstream switch 30 and the load resistor 12a. One end of the first resistor 23 is grounded. The other end of the upstream resistor 24 is connected to the A / D converter 53 of the microcomputer 26. One end and the other end of the shunt resistor 34 are individually connected to the current detection circuit 32. The current detection circuit 32 is further connected to the A / D converter 52 of the microcomputer 26.

[0144] As in Embodiment 1, when the upstream switch 30 and the downstream switch 20 are turned on, a current flows through the current path E from the positive terminal of the DC power source 11 to the negative terminal of the DC power source 11. In the current path E, a current flows to the upstream switch 30, the shunt resistor 34, the load resistor 12a, the downstream switch 20, and the negative terminal of the DC power source 11, in this order, as indicated by arrows. When the upstream switch 30 is turned on, a current flows from the positive terminal of the DC power source 11 to the upstream switch 30, the shunt resistor 34, and the load resistor 12a, in this order.

[0145] All the current flowing from the upstream switch 30 flows into the shunt resistor 34. Accordingly, the current value flowing through the shunt resistor 34 matches the current value flowing through the upstream switch 30. The resistance value of the shunt resistor 34 is a fixed value. Accordingly, the voltage value between the two ends of the shunt resistor 34 is proportional to the current value flowing through the upstream switch 30. By detecting the voltage value between the two ends of the shunt resistor 34, the current detection circuit 32 detects the current value flowing through the upstream switch 30. The current detection circuit 32 outputs the voltage value between the two ends of the shunt resistor 34 as analog current information to the A / D converter 52 of the microcomputer 26.

[0146] By dividing the voltage value between the two ends of the shunt resistor 34 by the resistance value of the shunt resistor 34, the current value flowing through the shunt resistor 34 is calculated. Therefore, the current information indicates a detected current value Id detected by the current detection circuit 32. In a similar manner to Embodiment 1, the A / D converter 52 converts the analog current information into digital current information. The control unit 57 of the microcomputer 26 acquires the digital current information converted by the A / D converter 52. In Embodiment 2, the drive circuit 31 does not turn off the upstream switch 30 based on the detected current value Id or the temperature of the upstream switch 30. First error voltage value Vf1 and second error voltage value Vf2

[0147] As mentioned above in the description of Embodiment 1, the first error voltage value Vf1 is equal to the first voltage value V1 when a half-on fault has occurred in the upstream switch 30 and the downstream switch 20 is turned on. Since the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a, the first error voltage value Vf1 substantially coincides with the voltage value of a voltage obtained by dividing the power source voltage value Vb by a circuit including the upstream switch 30 and the shunt resistor 34, and the load resistor 12a.

[0148] As mentioned above in the description of Embodiment 1, the second error voltage value Vf2 is equal to the second voltage value V2 when a half-on fault has occurred in the downstream switch 20 and the upstream switch 30 is turned on. Since the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a, the second error voltage value Vf2 substantially coincides with the voltage value of a voltage obtained by dividing the power source voltage value Vb by a circuit including the shunt resistor 34 and the load resistor 12a and the downstream switch 20. Troubleshooting

[0149] In Embodiment 1, when the upstream switch 30 is turned on or a short-circuit fault has occurred in the upstream switch 30, the first voltage value V1 is equal to the power source voltage value Vb. In Embodiment 2, when the upstream switch 30 is turned on or a short-circuit fault has occurred in the upstream switch 30, and when the downstream switch 20 is turned off or an open-circuit fault has occurred in the downstream switch 20, the first voltage value V1 is equal to the voltage value of a voltage obtained by dividing the power source voltage value Vb by the shunt resistor 34 and the first resistor 23. Since the first resistor 23 is sufficiently larger than the shunt resistor 34, this voltage value substantially coincides with the power source voltage value Vb.

[0150] As described above, the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a. Accordingly, when the upstream switch 30 is turned on or a short-circuit fault has occurred in the upstream switch 30, and when the downstream switch 20 is turned on or a short-circuit fault has occurred in the downstream switch 20, the first voltage value V1 is equal to the voltage value of a voltage obtained by dividing the shunt resistor 34 and the load resistor 12a. Since the resistance value of the load resistor 12a is sufficiently larger than the resistance value of the shunt resistor 34, the voltage value substantially coincides with the power source voltage value Vb. Effects

[0151] The power supply control device 10 of Embodiment 2 achieves the same effects as the power supply control device 10 of Embodiment 1, except for the effects achieved by the error detection performed by the drive circuit 31. Variations

[0152] In Embodiments 1 and 2, it is sufficient that the upstream switch 30 and the downstream switch 20 are semiconductor switches. Therefore, the upstream switch 30 and the downstream switch 20 are not limited to n-channel FETs, but may also be p-channel FETs, bipolar transistors, or the like.

[0153] Technical features (components) described in embodiments 1 and 2 can be combined with each other and new technical features can be formed by their combination.

[0154] The disclosed embodiments 1 and 2 are to be considered in all respects as illustrative and not restrictive. The scope of the invention is defined by the claims, not in the sense described above, and all modifications equivalent in meaning and scope to the claims are intended to be embraced. LIST OF REFERENCE SYMBOLS 1 power source system 10 Power supply control device 11 DC power source 12 Last 12a load resistance 20 downstream switch 21 IPD 22 series connection 23 first resistance 24 upstream resistor 25 downstream resistor 26 microcomputers 30 upstream switch 31 Control circuit 32 Current detection circuit 33 Temperature detection circuit 34 Shunt resistance 40 connection switches 41 second resistance 50 first output unit 51 second output unit 52, 53, 54 A / D converters 55 switching unit 56 storage unit 57 Control unit (processing unit) 58 internal bus A storage medium C vehicle E current path P computer program QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2021 - 205402

[0002] JP 2019 - 41508 A

[0004]

Claims

[1] A power supply control device for controlling the supply of power to a load, comprising: an upstream switch arranged upstream of the load in a current path for a current flowing through the load; a downstream switch arranged after the load in the current path; a first resistor having one end connected to a connection node between the upstream switch and the load; a series circuit having one end connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other; and a processing unit configured to carry out processing operations, wherein a constant voltage related to a potential of another end of the first resistor, which serves as a reference potential, is applied to another end of the series circuit and the processing unit is set up to: to obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch and to detect a fault in the upstream switch, the downstream switch or the load based on the voltage value obtained. [2] Power supply control device according to claim 1, wherein a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is set up to: to give an instruction to switch on the upstream switch, to give an instruction to switch off the downstream switch, and to obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned off, and to detect an open circuit fault of the upstream switch if the obtained voltage value is less than a voltage threshold, and the voltage threshold is greater than 0 V and less than or equal to a value of a voltage between one end and the other end of the DC power source. [3] Power supply control device according to claim 1 or 2, wherein a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is set up to: to give instructions to switch off the upstream switch and the downstream switch, to obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned off, and to detect a short-circuit fault of the upstream switch if the obtained voltage value exceeds a second voltage threshold, and the second voltage threshold value is 0 V or more and is less than a value of a voltage between one end and the other end of the DC power source. [4] Power supply control device according to one of claims 1 to 3, wherein the processing unit is arranged to: to give an instruction to switch off the upstream switch; to give an instruction to switch on the downstream switch; to obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned on; and detect an open circuit fault of the downstream switch when the acquired voltage value exceeds a third voltage threshold, and the third voltage threshold is 0 V or more and is less than a voltage value that the processing unit acquires when the upstream switch is turned off, the downstream switch is turned off, and the connecting switch is turned on. [5] Power supply control device according to one of claims 1 to 4, wherein the processing unit is arranged to: to give instructions to switch off the upstream switch and the downstream switch, to obtain a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is turned on; and to detect a short-circuit fault of the downstream switch when the acquired voltage value is less than a fourth voltage threshold and the fourth voltage threshold is greater than 0 V and less than or equal to a voltage value that the processing unit acquires when the upstream switch is turned off, the downstream switch is turned off, and the connecting switch is turned on. [6] Power supply control device according to one of claims 1 to 5, wherein the processing unit is arranged to: to give instructions to switch off the upstream switch and the downstream switch; obtain a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is on; and to detect an open circuit fault of the load when the acquired voltage value exceeds a fifth voltage threshold and the fifth voltage threshold is greater than a voltage value that the processing unit acquires when the upstream switch is off, the downstream switch is off, and the connecting switch is on, and is less than a voltage value of the constant voltage. [7] Power supply control device according to one of claims 1 to 6, wherein a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is set up to: to give instructions to switch on the upstream switch and the downstream switch; obtain a voltage value of a voltage at the connection node between the upstream switch and the load while the connection switch is off; and detect an open circuit fault of the upstream switch if the obtained voltage value is less than a sixth voltage threshold, and the sixth voltage threshold value is greater than 0 V and less than or equal to a value of a voltage between one end and the other end of the DC power source. [8] Power supply control device according to one of claims 1 to 7, wherein a current flows through the current path from one end of a DC power source to another end of the DC power source, the upstream switch is a semiconductor switch, the processing unit is set up to: to give instructions to switch on the upstream switch and the downstream switch; obtain a voltage value of a voltage at the connection node between the upstream switch and the load while the connection switch is off; and detect an error in a resistance value of the upstream switch if the obtained voltage value is less than a seventh voltage threshold, and the seventh voltage threshold is less than or equal to a value of a voltage between one end and the other end of the DC power source. [9] Power supply control device according to one of claims 1 to 8, wherein a current flows through the current path from one end of a DC power source to another end of the DC power source, the processing unit is set up to: to give instructions to switch on the upstream switch and the downstream switch; to obtain a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is off; and to detect an open circuit fault of the downstream switch if the obtained voltage value exceeds an eighth voltage threshold, and the eighth voltage threshold value is 0 V or more and is less than a value of a voltage between one end and the other end of the DC power source. [10] Power supply control device according to one of claims 1 to 9, wherein the processing unit is arranged to: to give instructions to switch on the upstream switch and the downstream switch; to obtain a voltage value of a voltage at the connection node between the load and the downstream switch while the connection switch is off; and to detect an error in a resistance value of the downstream switch when the obtained voltage value exceeds a ninth voltage threshold and the ninth voltage threshold is 0 V or more. [11] Power supply control device according to one of claims 1 to 10, wherein the processing unit is configured to: to give instructions to switch on the upstream switch and the downstream switch; to obtain a current value of a current flowing through the upstream switch; and to detect a load interruption fault if the current value obtained is less than a current threshold, the current threshold is greater than a current value of a current flowing through the upstream switch when the upstream switch is turned on, the downstream switch is turned off, and the connecting switch is turned off, the current threshold is less than or equal to a current value of a current flowing through the upstream switch when the upstream switch and the downstream switch are turned on while the load is in a normal state, and a resistance value of the load is smaller than a resistance value of the first resistor. [12] Power supply control device according to one of claims 1 to 11, wherein the processing unit is configured to: to give instructions to switch on the upstream switch and the downstream switch; to obtain a current value of a current flowing through the upstream switch; and detect a short-circuit fault of the load when the acquired current value exceeds a second current threshold, and the second current threshold is a current value of a current flowing through the upstream switch when the upstream switch and the downstream switch are turned on while the load is in a normal state. [13] The power supply control device according to any one of claims 1 to 12, wherein the processing unit, upon detecting a fault in the upstream switch, the downstream switch, or the load when instructions to turn on the upstream switch and the downstream switch have been given, gives instructions to turn off the upstream switch and the downstream switch. [14] A fault detection method for detecting a fault in a circuit, the circuit comprising: an upstream switch arranged before a load in a current path for a current flowing through the load; a downstream switch arranged after the load in the current path; a first resistor, one end of which is connected to a connection node between the upstream switch and the load; and a series circuit, one end of which is connected to a connection node between the load and the downstream switch, the series circuit comprising a second resistor and a connection switch connected in series with each other, a constant voltage related to a potential of another end of the first resistor, which serves as a reference potential, is applied to another end of the series circuit, and the method comprises the following steps carried out by a computer: Obtaining a voltage value of a voltage at the connection node between the upstream switch and the load or a voltage value of a voltage at the connection node between the load and the downstream switch; and Detect a fault of the upstream switch, the downstream switch or the load based on the voltage value obtained.

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