Power supply control device and fault detection method

Abstract

To provide a power feeding control device capable of halting power feeding to a load in a case of short circuit failure, and a failure detection method for detecting circuit failure capable of halting power feeding to a load in a case of short circuit failure.SOLUTION: In a power feeding control device 10, an upstream switch 30 and a downstream switch 20 are arranged to an upstream side and a downstream side of a load 12 in a current path of a current flowing through the load 12. An end of a first resistor 23 is connected to a connection node between the upstream switch 30 and the load 12. An end of a series circuit 22 including a connection switch 40 and a second resistor 41 is connected to a connection node between the load 12 and the downstream switch 20. A constant voltage is applied to the other end of the series circuit 22. A microcontroller 26 detects failures of the upstream switch 30, the downstream switch 20, or the load 12 based on one of the voltages of the two connection nodes.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 discloses a power supply control device for a vehicle that controls power supply from a DC power source to a load. A switch is arranged in the current path of the current flowing from the DC power source to the load. The control device controls the power supply to the load by instructing the switch to switch on or off.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the configuration of Patent Document 1, even though the control device instructs the switch to switch off, when a short-circuit fault occurs where the resistance value between both ends of the switch is sufficiently small, the DC power source continues to supply power to the load. In this case, the power of the DC power source may be wasted.

[0005] The present disclosure has been made in view of such circumstances, and an object thereof is to provide a power supply control device capable of stopping power supply to a load when a short-circuit fault occurs, and a fault detection method for detecting a fault in a circuit capable of stopping power supply to a load when a short-circuit fault occurs.

Means for Solving the Problems

[0006] A power supply control device according to an aspect of the present disclosure is a power supply control device that controls power supply to a load. In a current path of a current flowing through the load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and one end of the series circuit is connected to a connection node between the load and the downstream switch, and a processing unit that executes processing. A constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit. The processing unit acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch, and detects a failure of the upstream switch, the downstream switch, or the load based on the acquired voltage value.

[0007] A failure detection method according to an aspect of the present disclosure is a failure detection method for detecting a failure of a circuit in which, in a current path of a current flowing through a load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and one end of the series circuit is connected to a connection node between the load and the downstream switch, and a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit. The method includes steps of: acquiring a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch; and detecting a failure of the upstream switch, the downstream switch, or the load based on the acquired voltage value, which are executed by a computer.

[0008] Note that the present disclosure can be implemented not only as a power supply control device including such a characteristic processing unit, but also as a fault detection method having such characteristic processing as steps, or as a computer program for causing a computer to execute such steps. Further, the present disclosure can be implemented as a semiconductor integrated circuit that implements part or all of the power supply control device, or as a power supply system including the power supply control device.

Advantages of the Invention

[0009] According to the power supply control device according to the above aspect, power supply to the load can be stopped when a short circuit fault occurs. According to the fault detection method according to the above aspect, a fault in a circuit that can stop power supply to the load when a short circuit fault occurs is detected.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Modes for Carrying Out the Invention

[0011] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. At least a part of the embodiments described below may be arbitrarily combined.

[0012] (1) The power supply control device according to one aspect of the present disclosure is a power supply control device that controls power supply to a load. In the current path of the current flowing through the load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and one end of the series circuit is connected to a connection node between the load and the downstream switch, and a processing unit that executes processing. A constant voltage with the potential of the other end of the first resistor as a reference voltage is applied to the other end of the series circuit. The processing unit acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch, and based on the acquired voltage value, detects a failure of the upstream switch, the downstream switch, or the load.

[0013] In the above aspect, a short - circuit failure of a switch is a phenomenon in which the resistance value between both ends of the switch is sufficiently small despite instructing the switch to switch to the off state. When a short - circuit failure of the upstream switch occurs, power supply to the load can be stopped by switching the downstream switch to the off state. The processing unit detects a failure of the upstream switch, the downstream switch, or the load based on the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch.

[0014] (2) In the power supply control device according to one aspect of the present disclosure, current flows from one end of a DC power supply through the current path to the other end of the DC power supply. The processing unit instructs the upstream switch to switch to the on state, instructs the downstream switch to switch to the off state, and in a state where the connection switch is off, acquires the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch. When the acquired voltage value is less than a voltage threshold value, an open - circuit failure of the upstream switch is detected. The voltage threshold value exceeds 0V and is less than or equal to the voltage value between both ends of the DC power supply.

[0015] In one aspect described above, when the upstream switch, the downstream switch, and the connection switch are on, off, and off respectively, the voltage value acquired by the processing unit is the voltage value between both ends of the DC power supply and is equal to or higher than the voltage threshold. An open failure of a switch is a phenomenon in which the resistance value between both ends of the switch is sufficiently high even though an instruction to switch the switch on has been given. When an instruction to switch the upstream switch on and to switch the downstream switch off is given, and an open failure of the upstream switch has occurred, the voltage value acquired by the processing unit with the connection switch off is 0V and is lower than the voltage threshold.

[0016] (3) In the power supply control device according to one aspect of the present disclosure, current flows from one end of the DC power supply to the other end of the DC power supply through the current path, and the processing unit instructs switching of the upstream switch and the downstream switch to off, and acquires the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, with the connection switch off. When the acquired voltage value exceeds a second voltage threshold, a short circuit failure of the upstream switch is detected. The second voltage threshold is equal to or higher than 0V and lower than the voltage value between both ends of the DC power supply.

[0017] In one aspect described above, when all of the upstream switch, the downstream switch, and the connection switch are off, the voltage value acquired by the processing unit is 0V and is equal to or lower than the second voltage threshold. When an instruction to switch the upstream switch and the downstream switch to off is given, and a short circuit failure of the upstream switch has occurred, the voltage value acquired by the processing unit is the voltage value between both ends of the DC power supply and exceeds the second voltage threshold.

[0018] (4) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs to switch the upstream switch to off, instructs to switch the downstream switch to on, and, with the connection switch being on, obtains the voltage value of the connection node between the upstream switch and the load or the voltage value of the connection node between the load and the downstream switch. When the obtained voltage value exceeds a third voltage threshold, a release failure of the downstream switch is detected. The third voltage threshold is equal to or higher than 0V and lower than the voltage value obtained by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively.

[0019] In the above aspect, when the upstream switch, the downstream switch, and the connection switch are off, on, and on, respectively, the voltage value obtained by the processing unit is 0V and is equal to or lower than the third voltage threshold. When the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, the first resistor, the second resistor, and the load divide a certain voltage. The voltage value obtained by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, is referred to as the divided voltage value. When instructing to switch the upstream switch to off and the downstream switch to on, when a release failure of the downstream switch has occurred, the voltage value obtained by the processing unit with the connection switch being on is the divided voltage value and exceeds the third voltage threshold.

[0020] (5) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs to switch the upstream switch and the downstream switch to off, and, with the connection switch being on, obtains the voltage value of the connection node between the upstream switch and the load or the voltage value of the connection node between the load and the downstream switch. When the obtained voltage value is less than a fourth voltage threshold, a short-circuit failure of the downstream switch is detected. The fourth voltage threshold is higher than 0V and lower than or equal to the voltage value obtained by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively.

[0021] In one aspect described above, when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, the voltage value acquired by the processing unit is a divided voltage value and is equal to or higher than a fourth voltage threshold. When instructing the upstream switch and the downstream switch to switch to off, if a short-circuit failure occurs in the downstream switch, the voltage value acquired by the processing unit with the connection switch on is 0V and is less than the fourth voltage threshold.

[0022] (6) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs the upstream switch and the downstream switch to switch to off, and acquires the voltage value of the connection node between the load and the downstream switch with the connection switch on. If the acquired voltage value exceeds a fifth voltage threshold, the processing unit detects an open failure of the load. The fifth voltage threshold exceeds the voltage value acquired by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, and is less than the voltage value of the constant voltage.

[0023] In one aspect described above, when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, and the load is normal, the voltage value acquired by the processing unit is a divided voltage value and is equal to or lower than a fifth voltage threshold. An open failure of the load is a phenomenon in which the resistance value between both ends of the load is extremely large. When an open failure of the load occurs with the upstream switch, the downstream switch, and the connection switch being off, off, and on, respectively, the voltage value acquired by the processing unit is the voltage value of a constant voltage and exceeds the fifth voltage threshold.

[0024] (7) In the power supply control device according to one aspect of the present disclosure, current flows from one end of the DC power supply to the other end of the DC power supply through the current path. The processing unit instructs the upstream switch and the downstream switch to switch to on, and acquires the voltage value of the connection node between the upstream switch and the load with the connection switch off. If the acquired voltage value is less than a sixth voltage threshold, the processing unit detects an open failure of the upstream switch. The sixth voltage threshold exceeds 0V and is less than or equal to the voltage value between both ends of the DC power supply.

[0025] In one aspect described above, when the upstream switch, the downstream switch, and the connection switch are on, on, and off respectively, the voltage value acquired by the processing unit is the voltage value between both ends of the DC power supply and is equal to or higher than the sixth voltage threshold. When instructing to switch the upstream switch and the downstream switch to on, when an open failure of the upstream switch occurs, the voltage value acquired by the processing unit with the connection switch off is 0V and is less than the sixth voltage threshold.

[0026] (8) In the power supply control device according to one aspect of the present disclosure, current flows from one end of the DC power supply to the other end of the DC power supply through the current path, the upstream switch is a semiconductor switch, the processing unit instructs to switch the upstream switch and the downstream switch to on, and acquires the voltage value of the connection node between the upstream switch and the load with the connection switch off. When the acquired voltage value is less than the seventh voltage threshold, a failure related to the resistance value of the upstream switch is detected, and the seventh voltage threshold is equal to or less than the voltage value between both ends of the DC power supply.

[0027] In one aspect described above, a failure related to the resistance value of the switch is a phenomenon in which the resistance value of the switch is an intermediate value, which is called a half-on failure. When the upstream switch, the downstream switch, and the connection switch are on, on, and off respectively, the voltage value acquired by the processing unit is the voltage value between both ends of the DC power supply and is equal to or higher than the seventh voltage threshold. When switching the upstream switch and the downstream switch to on is instructed, when a half-on failure of the upstream switch occurs, the voltage value acquired by the processing unit with the connection switch off is slightly lower than the voltage value between both ends of the DC power supply. By setting the seventh voltage threshold to a value that exceeds a voltage value slightly lower than the voltage value between both ends of the DC power supply and is equal to or less than the voltage value between both ends of the DC power supply, a half-on failure of the upstream switch can be detected.

[0028] (9) In the power supply control device according to one aspect of the present disclosure, current flows from one end of the DC power supply to the other end of the DC power supply via the current path. The processing unit instructs the switching of the upstream switch and the downstream switch to the on state, and acquires the voltage value of the connection node between the load and the downstream switch in a state where the connection switch is off. When the acquired voltage value exceeds the eighth voltage threshold, an open failure of the downstream switch is detected. The eighth voltage threshold is 0 V or more and less than the voltage value between both ends of the DC power supply.

[0029] In the above aspect, when the upstream switch, the downstream switch, and the connection switch are on, on, and off, respectively, the voltage value acquired by the processing unit is 0 V and is less than or equal to the eighth voltage threshold. When instructing the switching of the upstream switch and the downstream switch to the on state, when an open failure of the downstream switch occurs, the voltage value acquired by the processing unit in a state where the connection switch is off is the voltage value between both ends of the DC power supply and exceeds the eighth voltage threshold.

[0030] (10) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs the switching of the upstream switch and the downstream switch to the on state, and acquires the voltage value of the connection node between the load and the downstream switch in a state where the connection switch is off. When the acquired voltage value exceeds the ninth voltage threshold, a failure related to the resistance value of the downstream switch is detected. The ninth voltage threshold is 0 V or more.

[0031] In the above aspect, when the upstream switch, the downstream switch, and the connection switch are on, on, and off, respectively, the voltage value acquired by the processing unit is 0 V and is less than or equal to the ninth voltage threshold. When the switching of the upstream switch and the downstream switch to the on state is instructed, when a half-on failure of the downstream switch occurs, the voltage value acquired by the processing unit in a state where the connection switch is off is slightly higher than 0 V. By setting the ninth voltage threshold to a value that is 0 V or more and less than a voltage value slightly higher than 0 V, a half-on failure of the downstream switch can be detected.

[0032] (11) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs switching on of the upstream switch and the downstream switch, acquires a current value of the current flowing through the upstream switch, and when the acquired current value is less than the current threshold, detects an open failure of the load. The current threshold exceeds the current value of the current flowing through the upstream switch when the upstream switch, the downstream switch, and the connection switch are on, off, and off, respectively. The current threshold is less than or equal to the current value of the current flowing through the upstream switch when the upstream switch and the downstream switch are on in a state where the load is normal. The resistance value of the load is less than the resistance value of the first resistor.

[0033] In the above aspect, when the load is normal and the upstream switch and the downstream switch are on, the current value of the current flowing through the upstream switch is referred to as the normal current value. The current value of the current flowing through the upstream switch when the upstream switch, the downstream switch, and the connection switch are on, off, and off, respectively, is referred to as the resistance current value. The resistance current value is the current value of the current flowing through the upstream switch and the first resistor in this order. Also, the resistance value of the load is less than the resistance value of the first resistor. Therefore, the normal current value exceeds the resistance current value.

[0034] When the load is normal and the upstream switch and the downstream switch are on, the current value acquired by the processing unit is the normal current value and is greater than or equal to the current threshold. When an open failure of the load occurs while the upstream switch and the downstream switch are on, the current value acquired by the processing unit is the resistance current value and is less than the current threshold.

[0035] (12) In the power supply control device according to one aspect of the present disclosure, the processing unit instructs switching on of the upstream switch and the downstream switch, acquires a current value of the current flowing through the upstream switch, and when the acquired current value exceeds a second current threshold, detects a short-circuit failure of the load. The second current threshold is the current value of the current flowing through the upstream switch when the upstream switch and the downstream switch are on in a state where the load is normal.

[0036] In the above aspect, a short-circuit fault of the load is a phenomenon in which the resistance value between both ends of the load is extremely small. When the upstream switch and the downstream switch are on in a state where the load is normal, the current value acquired by the processing unit is equal to or less than a second current threshold value. When a short-circuit fault of the load occurs while the upstream switch and the downstream switch are on, the current value acquired by the processing unit exceeds the second current threshold value.

[0037] (13) In the power supply control device according to one aspect of the present disclosure, when the processing unit detects a failure of the upstream switch, the downstream switch, or the load while instructing the switching of the upstream switch and the downstream switch to on, the processing unit instructs the switching of the upstream switch and the downstream switch to off.

[0038] In the above aspect, when the processing unit detects a failure of the upstream switch, the downstream switch, or the load, the processing unit instructs the switching of the upstream switch and the downstream switch to off. Thereby, the flow of current through the load can be stopped.

[0039] (14) A fault detection method according to one aspect of the present disclosure includes an upstream switch disposed on the upstream side of the load in a current path of a current flowing through the load, a downstream switch disposed on the downstream side of 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 second resistor and a connection switch connected in series, and a series circuit having one end connected to a connection node between the load and the downstream switch, and detects a fault of a circuit in which a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit. The method includes a step of acquiring a voltage value of a connection node between the upstream switch and the load or a voltage value of a connection node between the load and the downstream switch, and a step of detecting a fault of the upstream switch, the downstream switch, or the load based on the acquired voltage value, which are executed by a computer.

[0040] In one aspect described above, when a short-circuit fault occurs in the upstream switch, power supply to the load can be stopped by switching the downstream switch off. The computer detects a fault in the upstream switch, the downstream switch, or the load based on the voltage value of the connection node between the load and the downstream switch, or the voltage value of the connection node between the upstream switch and the load.

[0041] [Details of Embodiments of the Present Disclosure] A specific example of a power supply system according to an embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, and is intended to be defined by the claims and to include all modifications within the meaning and scope equivalent to the claims.

[0042] (Embodiment 1) <Configuration of Power Supply System 1> FIG. 1 is a block diagram showing a main configuration of a power supply system 1 according to Embodiment 1. The power supply system 1 is mounted on a vehicle C. The power supply system 1 includes a power supply control device 10, a DC power supply 11, and a load 12. The power supply control device 10 has a downstream switch 20 and an upstream switch 30. Each of the upstream switch 30 and the downstream switch 20 is a semiconductor switch, specifically, an N-channel type FET (Field Effect Transistor). The DC power supply 11 is, for example, a battery. The load 12 is an electrical device and has a load resistor 12a.

[0043] The negative electrode of the DC power supply 11 is grounded. The grounding is realized, for example, by connection to the body of the vehicle C. The positive electrode of the DC power supply 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. The other 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.

[0044] For each of the upstream switch 30 and the downstream switch 20, when the state is on, the resistance value between the drain and the source is sufficiently small. Therefore, current can flow through the drain and the source. For each of the upstream switch 30 and the downstream switch 20, when the state is off, the resistance value between the drain and the source is sufficiently large. Therefore, no current flows through the drain and the source.

[0045] The power supply control device 10 switches the upstream switch 30 and the downstream switch 20 from off to on. When the upstream switch 30 and the downstream switch 20 are on, from the positive electrode of the DC power supply 11, current flows in the order of the upstream switch 30, the load resistor 12a, the downstream switch 20, and the negative electrode of the DC power supply 11 as indicated by the arrow. Therefore, in the current path E of the current flowing through the load resistor 12a of the load 12, the upstream switch 30 is arranged on the upstream side of the load resistor 12a. In the current path E, the downstream switch 20 is arranged on the downstream side of the load resistor 12a. The current flows from the positive electrode of the DC power supply 11 to the negative electrode of the DC power supply 11 through the current path E.

[0046] When current flows through the load resistor 12a, power is supplied to the load 12. When the power supplied to the load 12 is equal to or greater than a predetermined power, the load 12 operates. When the power supplied to the load 12 is less than the predetermined power, the load 12 stops operating. When the power supply control device 10 switches the upstream switch 30 and the downstream switch 20 from off to on, the DC power supply 11 supplies power equal to or greater than the predetermined power to the load 12. As a result, the load 12 operates.

[0047] When at least one of the upstream switch 30 and the downstream switch 20 is off, the DC power supply 11 does not supply power to the load 12. Therefore, when at least one of the upstream switch 30 and the downstream switch 20 is off, the power supplied to the load 12 is less than the predetermined power, and the load 12 stops operating.

[0048] The power supply control device 10 switches the upstream switch 30 and the downstream switch 20 from on to off. As a result, the load 12 stops operating. As described above, the power supply control device 10 controls the power supply from the DC power supply 11 to the load 12 by switching the upstream switch 30 and the downstream switch 20 on or off.

[0049] <Configuration of the power supply control device 10> In addition to the downstream switch 20, the power supply control device 10 includes an IPD 21, a series circuit 22, a first resistor 23, an upstream resistor 24, a downstream resistor 25, and a microcomputer (hereinafter referred to as a microcontroller) 26. IPD is an abbreviation for Intelligent Power Device. The upstream switch 30 is included in the IPD 21. The IPD 21 includes a drive circuit 31, a current detection circuit 32, and a temperature detection circuit 33 in addition to the upstream switch 30. The series circuit 22 includes a connection switch 40 and a second resistor 41.

[0050] In the series circuit 22, the connection switch 40 is connected in series with the second resistor 41. Therefore, one end of the connection 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 with the ground potential as the 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. In FIG. 1, the constant voltage value is represented by Vc. The constant voltage is generated, for example, by a regulator stepping down the voltage between both ends of the DC power supply 11. The constant voltage value Vc is lower than the voltage value between both ends of the DC power supply 11.

[0051] In the example of FIG. 1, a constant voltage is applied to the other end of the connection switch 40. The other end of the second resistor 41 is connected to a connection node between the load resistor 12a and the downstream switch 20. However, a constant voltage may be applied to the other end of the second resistor 41. In this case, the other end of the connection switch 40 is connected to a connection node between the load resistor 12a and the downstream switch 20.

[0052] In IPD21, 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 electrode of the DC power supply 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.

[0053] One end of the first resistor 23 and one end of the upstream resistor 24 are connected to the connection node between the upstream switch 30 of IPD21 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 one end of the downstream resistor 25 in addition to the series circuit 22. The other end of the downstream resistor 25 is connected to the microcomputer 26.

[0054] For each of the upstream switch 30 and the downstream switch 20, when the voltage value of the gate with the source potential as the reference potential is equal to or higher than a certain voltage value, the state is on. For each of the upstream switch 30 and the downstream switch 20, when the voltage value of the gate with the source potential as the reference potential is less than a certain voltage value, the state is off.

[0055] The microcomputer 26 outputs a high-level voltage or a low-level voltage to the drive circuit 31. When the microcomputer 26 switches the voltage output to the drive circuit 31 from a low-level voltage to a high-level voltage, the drive circuit 31 increases the voltage of the gate of the upstream switch 30 with the ground potential as the reference potential. As a result, in the upstream switch 30, the voltage value of the gate with the source potential as the reference potential rises to a voltage value equal to or higher than a certain voltage value, and the upstream switch 30 switches from off to on.

[0056] 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 reduces the voltage of the gate with the ground potential as the reference potential in the upstream switch 30. As a result, in the upstream switch 30, the voltage value of the gate with the source potential as the reference potential drops below a certain voltage value, and the upstream switch 30 switches from on to off. As described above, the drive circuit 31 switches the upstream switch 30 on or off according to the voltage input from the microcomputer 26.

[0057] The microcomputer 26 also outputs a low-level voltage or a high-level voltage to the gate of the downstream switch 20. The potential of the source of the downstream switch 20 is the ground potential. When the microcomputer 26 outputs a low-level voltage to the gate of the downstream switch 20, in the downstream switch 20, the voltage value of the gate with the ground potential as the reference potential is less than a certain voltage value, and the downstream switch 20 is off.

[0058] When the microcomputer 26 switches the voltage output to the downstream switch 20 from the low-level voltage to the high-level voltage, in the downstream switch 20, the voltage value of the gate with the ground potential as the reference potential rises to a voltage value equal to or higher than a certain voltage value, and the downstream switch 20 switches from off to on. When the microcomputer 26 switches the voltage output to the downstream switch 20 from the high-level voltage to the low-level voltage, in the downstream switch 20, the voltage value of the gate with the ground potential as the reference potential drops below a certain voltage value, and the downstream switch 20 switches from on to off.

[0059] As described above, the microcomputer 26 switches the downstream switch 20 on or off by switching the voltage output to the gate of the downstream switch 20 between the low-level voltage and the high-level voltage. The microcomputer 26 controls the state of the upstream switch 30 by switching the voltages output to the gates of the drive circuit 31 and the downstream switch 20 between the low-level voltage and the high-level voltage.

[0060] The microcontroller 26 switches the upstream switch 30 and the downstream switch 20 from off to on. When the upstream switch 30 and the downstream switch 20 are on, as described above, from the positive electrode of the DC power supply 11, the current flows in the order of the upstream switch 30, the load resistor 12a, the downstream switch 20, and the negative electrode of the DC power supply 11. When the upstream switch 30 is on, from the positive electrode of the DC power supply 11, the current flows in the order of the upstream switch 30, the first resistor 23, and the negative electrode of the DC power supply 11.

[0061] The resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a of the load 12. Therefore, when the upstream switch 30 and the downstream switch 20 are on, most of the current passing through the upstream switch 30 flows through the load resistor 12a.

[0062] The current detection circuit 32 detects the current value of the 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 microcontroller 26 and the drive circuit 31.

[0063] 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 drive circuit 31.

[0064] When the detected current value is less than a certain reference current value and the detected temperature is less than a certain reference temperature, the drive circuit 31 switches the upstream switch 30 on or off according to the voltage input from the microcontroller 26 as described above. When the detected current value rises to a current value equal to or higher than the reference current value, the drive circuit 31 forcibly switches the upstream switch 30 from on to off regardless of the voltage input from the microcontroller 26. When the detected temperature rises to a temperature equal to or higher than the reference temperature, the drive circuit 31 forcibly switches the upstream switch 30 from on to off regardless of the voltage input from the microcontroller 26. When a predetermined condition is satisfied, the drive circuit 31 releases the forced off of the upstream switch 30.

[0065] The microcomputer 26 switches the connection switch 40 of the series circuit 22 between on and off. When the connection switch 40 is on, the resistance value between both ends of the connection switch 40 is sufficiently small. Therefore, current can flow through the connection switch 40. When the connection switch 40 is off, the resistance value between both ends of the connection switch 40 is sufficiently large. Therefore, no current flows through the connection switch 40.

[0066] Hereinafter, the voltage value of the connection node between the upstream switch 30 and the load resistor 12a is described as the first voltage value. The voltage value of the connection node between the load resistor 12a and the downstream switch 20 is described as the second voltage value. The reference potential of the first voltage value and the second voltage value is the ground potential. The analog first voltage value is input to the microcomputer 26 via the upstream resistor 24. The analog second voltage value is input to the microcomputer 26 via the downstream resistor 25. The microcomputer 26 detects failures of the upstream switch 30, the downstream switch 20, and the load 12 based on the first voltage value, the second voltage value, or the detected current value.

[0067] FIG. 2 is a block diagram showing the main configuration of the microcomputer 26. The microcomputer 26 includes a first output unit 50, a second output unit 51, three A / D conversion units 52, 53, 54, a switching unit 55, a storage unit 56, and a control unit 57. These 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. Each of the A / D conversion units 52, 53, 54 is 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.

[0068] The first output unit 50 outputs a high-level voltage or a low-level voltage to the drive circuit 31. The voltage that the microcomputer 26 outputs to the drive circuit 31 is the voltage that the first output unit 50 outputs to the drive circuit 31. The control unit 57 instructs the first output unit 50 to switch the upstream switch 30 on. As a result, the first output unit 50 switches the voltage output to the drive circuit 31 from a low-level voltage to a high-level voltage. Consequently, the drive circuit 31 switches the upstream switch 30 from off to on.

[0069] The control unit 57 instructs the upstream switch 30 to switch off to the first output unit 50. As a result, 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 switches the upstream switch 30 from on to off.

[0070] The second output unit 51 outputs a high-level voltage or a low-level voltage to the gate of the downstream switch 20. The voltage output by the microcomputer 26 to the gate of the downstream switch 20 is the voltage output by the first output unit 50 to the gate of the downstream switch 20. The control unit 57 instructs the second output unit 51 to switch the downstream switch 20 on. As a result, 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 switches from off to on.

[0071] The control unit 57 instructs the second output unit 51 to switch the downstream switch 20 off. As a result, 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 switches from on to off.

[0072] The current detection circuit 32 outputs analog current information indicating the detected current value to the A / D conversion unit 52. The A / D conversion unit 52 converts the analog current information into digital current information. The control unit 57 acquires the digital current information converted by the A / D conversion unit 52. The analog first voltage value is input to the A / D conversion unit 53 via the upstream resistor 24. The A / D conversion unit 53 converts the analog first voltage value into a digital first voltage value. The control unit 57 acquires the digital first voltage value converted by the A / D conversion unit 53.

[0073] The analog second voltage value is input to the A / D conversion unit 54 via the downstream resistor 25. The A / D conversion unit 54 converts the analog second voltage value into a digital second voltage value. The control unit 57 acquires the digital second voltage value converted by the A / D conversion unit 54. The switching unit 55 switches the connection switch 40 on or off according to the instruction of the control unit 57.

[0074] 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 that executes processing, for example, a CPU (Central Processing Unit). The control unit 57 functions as a processing unit. The processing element of the control unit 57 executes a power supply control process for controlling the power supply from the DC power supply 11 to the load 12 by executing the computer program P.

[0075] Note that the computer program P may be provided to the microcomputer 26 using a non-temporary storage medium A that stores the computer program P in a readable manner. The storage medium A is, for example, a portable memory. Examples of the portable memory include a CD-ROM, a USB (Universal Serial Bus) memory, an SD card, a micro SD card, or a compact flash (registered trademark), etc. When 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. Further, the computer program P may be provided to the microcomputer 26 by the communication unit (not shown) of the microcomputer 26 communicating with an external device. In this case, the processing element of the control unit 57 acquires the computer program P through the communication unit. The acquired computer program P is written into the storage unit 56.

[0076] The number of processing elements included in the control unit 57 is not limited to 1 and may be 2 or more. When the control unit 57 has a plurality of processing elements, the plurality of processing elements may execute the power supply control process in cooperation.

[0077] In the power supply control process, the control unit 57 diagnoses faults of the upstream switch 30, the downstream switch 20, and the load 12 using a plurality of preset threshold values.

[0078] <Explanation of a plurality of threshold values> FIG. 3 is an explanatory diagram of a plurality of threshold values. Regarding the voltage value, a high voltage threshold value Vh, a medium voltage threshold value Vm, and a low voltage threshold value Vw are preset. In FIG. 3, Vb indicates the voltage value between both ends of the DC power supply 11. Hereinafter, the voltage value between both ends of the DC power supply 11 is referred to as the power supply voltage value.

[0079] One of the faults of each of the upstream switch 30 and the downstream switch 20 is a half-on fault. When a half-on fault occurs in each of the upstream switch 30 and the downstream switch 20, the resistance value between the drain and the source is maintained at an intermediate value regardless of the gate voltage value. The intermediate value is not a sufficiently large value nor a sufficiently small value. The half-on fault of each of the upstream switch 30 and the downstream switch 20 is a fault related to the resistance of the upstream switch 30 and the downstream switch 20.

[0080] 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 the downstream switch 20 is on and a half-on fault of the upstream switch 30 occurs, the first voltage value substantially coincides with the voltage value of the voltage obtained by dividing the voltage between both ends of the upstream switch 30 and the load resistor 12a by the DC power supply 11. The first voltage value when a half-on fault of the upstream switch 30 occurs while the downstream switch 20 is on is referred to as the first fault voltage value. Vf1 is the first fault voltage value. The first fault voltage value Vf1 is less than the power supply voltage value Vb.

[0081] As described above, Vc is a constant voltage value. The constant voltage value Vc is the voltage value of a constant voltage applied to the series circuit 22. The power supply voltage value Vb is, for example, 12V. The constant voltage value is 3.3V or 5V, etc. The constant voltage value Vc is less than the first fault voltage value Vf1.

[0082] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on respectively, the second resistor 41 and the second resistor circuit including the load resistor 12a and the first resistor 23 divide a constant voltage. The voltage value of the voltage obtained by the second resistor circuit and the first resistor 23 dividing the constant voltage is referred to as the first divided voltage value. Vd1 is the first divided voltage value. The first divided voltage value Vd1 is the first voltage value when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on respectively.

[0083] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on respectively, the second resistor 41 and the first resistor circuit including the load resistor 12a and the first resistor 23 divide a constant voltage. The voltage value of the voltage obtained by the second resistor 41 and the first resistor circuit dividing the constant voltage is referred to as the second divided voltage value. Vd2 is the second divided voltage value. The second divided voltage value Vd2 is the second voltage value when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on respectively. The second divided voltage value Vd2 is less than the constant voltage value Vc. The first divided voltage value Vd1 is less than the second divided voltage value Vd2.

[0084] 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. Therefore, each of the first divided voltage value Vd1 and the second divided voltage value Vd2 substantially coincides with the voltage value of the voltage obtained by the second resistor 41 and the first resistor 23 dividing the constant voltage.

[0085] 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 the upstream switch 30 is on and a half-on failure of the downstream switch 20 occurs, the second voltage value substantially coincides with the voltage value of the voltage obtained by the upstream switch 30 and the load resistor 12a dividing the voltage across both ends of the DC power supply 11. The second voltage value when a half-on failure of the upstream switch 30 occurs with the downstream switch 20 being on is referred to as the second failure voltage value. Vf2 is the second failure voltage value. The second failure voltage value Vf2 is less than the first divided voltage value Vd1 and exceeds 0V.

[0086] The high voltage threshold Vh is a voltage value that exceeds the first failure voltage value Vf1 and is less than the power supply voltage value Vb. The medium voltage threshold Vm is a voltage value that exceeds the second divided voltage value Vd2 and is less than a constant voltage value Vc. The low voltage threshold Vw is a voltage value that exceeds 0V and is less than the second failure voltage value Vf2.

[0087] Regarding the current value, an upper current threshold Ih and a lower current threshold Iw are preset. The current value of the current flowing through the upstream switch 30 when the upstream switch 30 and the downstream switch 20 are on with the load 12 being normal is referred to as the normal current value. In in FIG. 3 is the normal current value. The current value of the current flowing through the upstream switch 30 when the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, off, and off respectively with the load 12 being normal is referred to as the resistance current value. Ir in FIG. 3 is the resistance current value.

[0088] The resistance current value Ir is the current value of the current flowing in the order of the positive electrode of the DC power supply 11, the upstream switch 30, the first resistor 23, and the negative electrode of the DC power supply 11. As described above, the resistance value of the load resistor 12a is less than the resistance value of the first resistor 23. Therefore, the resistance current value Ir is less than the normal current value In. The upper current threshold Ih is the normal current value In. The lower current threshold Iw exceeds the resistance current value Ir and is less than or equal to the normal current value In.

[0089] <Fault diagnosis when load 12 has stopped operating> FIG. 4 is a chart for explaining fault diagnosis when load 12 has stopped operating. In FIG. 4, the instructions of upstream switch 30, the instructions of downstream switch 20, the state of connection switch 40, fault conditions, and detected content are shown. The instruction of upstream switch 30 is the instruction given by control unit 57 of microcomputer 26 to first output unit 50. The instruction of downstream switch 20 is the instruction given by control unit 57 to second output unit 51. The on instruction is an instruction to switch to on. The off instruction is an instruction to switch to off. The fault condition is a condition satisfied when a fault has occurred. The detected content indicates the fault detected by control unit 57.

[0090] V1 and V2 are the first voltage value and the second voltage value respectively. As described above, the first voltage value V1 is the voltage value of the connection node between upstream switch 30 and load resistor 12a. The second voltage value V2 is the voltage value of the connection node between load resistor 12a and downstream switch 20.

[0091] Control unit 57 performs fault diagnosis when at least one of upstream switch 30 and downstream switch 20 is instructed to turn off. For this reason, power of a predetermined power or more is not supplied to load resistor 12a, and load 12 has stopped operating.

[0092] Control unit 57 instructs upstream switch 30 to switch to on, instructs downstream switch 20 to switch to off, and acquires the first voltage value V1 from A / D conversion unit 53 in a state where connection switch 40 is off. Control unit 57 detects an open fault of upstream switch 30 based on the acquired first voltage value V1. An open fault of a switch is a phenomenon in which the resistance value between both ends of the switch is sufficiently large even though an instruction to switch to on of the switch is given.

[0093] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, off, and off respectively, current flows from the positive electrode of the DC power supply 11 in the order of the upstream switch 30 and the first resistor 23. No current flows through the load resistor 12a. Therefore, when the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, off, and off respectively, the first voltage value V1 and the second voltage value V2 are the power supply voltage value Vb and are equal to or higher than the low voltage threshold value Vw. When an open failure occurs in the upstream switch 30, no current flows through the first resistor 23 and no current flows through the load resistor 12a. For this reason, the first voltage value V1 and the second voltage value V2 are 0V and are less than the low voltage threshold value Vw.

[0094] As a result, when the first voltage value V1 acquired by the A / D conversion unit 53 is less than the low voltage threshold value Vw, the control unit 57 detects an open failure of the upstream switch 30. Note that the control unit 57 may detect an open failure of the upstream switch 30 when the second voltage value V2 acquired by the A / D conversion unit 54 is less than the low voltage threshold value Vw. In this case, the control unit 57 instructs the upstream switch 30 to be switched on, instructs the downstream switch 20 to be switched off, and acquires the second voltage value V2 from the A / D conversion unit 54 with the connection switch 40 off. There is no problem as long as the voltage threshold for detecting an open failure of the upstream switch 30 exceeds 0V and is equal to or lower than the power supply voltage value Vb.

[0095] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to be switched off, and acquires the first voltage value V1 from the A / D conversion unit 53 with the connection switch 40 off. The control unit 57 detects a short circuit failure of the upstream switch 30 based on the acquired first voltage value V1. A short circuit failure of a switch is a phenomenon in which the resistance value between both ends of the switch is sufficiently small despite an instruction to switch the switch off.

[0096] When all of the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, current does not flow through the first resistor 23, and current does not flow through the load resistor 12a. Therefore, when all of the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, the first voltage value V1 and the second voltage value V2 are 0 V, which is equal to or lower than the low voltage threshold value Vw. When a short circuit fault occurs in the upstream switch 30, current flows from the positive electrode of the DC power supply 11 through the upstream switch 30 and the first resistor 23 in sequence, and current does not flow through the load resistor 12a. For this reason, the first voltage value V1 and the second voltage value V2 are equal to the power supply voltage value Vb, which exceeds the low voltage threshold value Vw.

[0097] As a result, when the first voltage value V1 acquired by the A / D conversion unit 53 by the control unit 57 exceeds the low voltage threshold value Vw, the control unit 57 detects a short circuit fault in the upstream switch 30. Note that the control unit 57 may detect a short circuit fault in the upstream switch 30 when the second voltage value V2 acquired from the A / D conversion unit 54 exceeds the low voltage threshold value Vw. In this case, the control unit 57 instructs switching of the upstream switch 30 and the downstream switch 20 to off, and acquires the second voltage value V2 from the A / D conversion unit 54 while the connection switch 40 is off. The second voltage threshold value for detecting a short circuit fault in the upstream switch 30 is 0 V or higher and less than the power supply voltage value Vb, which is not a problem.

[0098] The control unit 57 instructs switching of the upstream switch 30 to off, instructs switching of the downstream switch 20 to on, and acquires the second voltage value V2 from the A / D conversion unit 54 while the connection switch 40 is on. The control unit 57 detects an open fault in the downstream switch 20 based on the acquired second voltage value V2.

[0099] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, on, and on respectively, current flows through the connection switch 40, the second resistor 41, and the downstream switch 20 in sequence, and current does not flow through the first resistor 23. Therefore, when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, on, and on respectively, the first voltage value V1 and the second voltage value V2 are 0 V, which is equal to or lower than the low voltage threshold value Vw.

[0100] When an open failure of the downstream switch 20 occurs, the current flows in the order of the second resistor 41, the load resistor 12a, and the first resistor 23. The second resistor circuit and the first resistor 23 divide a constant voltage. The second resistor 41 and the first resistor circuit divide a constant voltage. Therefore, the first voltage value V1 and the second voltage value V2 are respectively the first divided voltage value Vd1 and the second divided voltage value Vd2. Accordingly, the first voltage value V1 and the second voltage value V2 exceed the low voltage threshold Vw.

[0101] As a result, when the second voltage value V2 acquired from the A / D conversion unit 54 by the control unit 57 exceeds the low voltage threshold Vw, the control unit 57 detects an open failure of the downstream switch 20. Note that the control unit 57 may detect an open failure of the downstream switch 20 when the first voltage value V1 acquired from the A / D conversion unit 53 exceeds the low voltage threshold Vw. In this case, the control unit 57 instructs the upstream switch 30 to be switched off, instructs the downstream switch 20 to be switched on, and acquires the first voltage value V1 from the A / D conversion unit 53 while the connection switch 40 is on. Regarding the first voltage value V1, there is no problem as long as the third voltage threshold for detecting an open failure of the downstream switch 20 is 0V or more and less than the first divided voltage value Vd1. Regarding the second voltage value V2, there is no problem as long as the third voltage threshold for detecting an open failure of the downstream switch 20 is 0V or more and less than the second divided voltage value Vd2.

[0102] As described above, the first divided voltage value Vd1 is the first voltage value V1 that the control unit 57 acquires from the A / D conversion unit 53 when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on, respectively. The second divided voltage value Vd2 is the second voltage value V2 that the control unit 57 acquires from the A / D conversion unit 54 when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on, respectively.

[0103] When current flows in the order of the second resistor 41, the load resistor 12a, and the first resistor 23, power is supplied to the load 12. However, since the constant voltage value Vc is small, the power supplied to the load 12 is less than the predetermined power. Therefore, when current flows in the order of the second resistor 41, the load resistor 12a, and the first resistor 23, the load 12 does not operate.

[0104] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to switch off, and acquires the second voltage value V2 from the A / D conversion unit 54 while the connection switch 40 is on. The control unit 57 detects a short-circuit failure of the downstream switch 20 based on the acquired second voltage value V2.

[0105] As described above, when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on, respectively, the first voltage value V1 and the second voltage value V2 are the first divided voltage value Vd1 and the second divided voltage value Vd2, respectively. Therefore, when the upstream switch 30, the downstream switch 20, and the connection switch 40 are off, off, and on, respectively, the first voltage value V1 and the second voltage value V2 are equal to or higher than the low voltage threshold value Vw. When a short-circuit failure of the downstream switch 20 has occurred, current flows in the order of the connection switch 40, the second resistor 41, and the downstream switch 20, and no current flows through the load resistor 12a. For this reason, the first voltage value V1 and the second voltage value V2 are 0 V and are less than the low voltage threshold value Vw.

[0106] As a result, when the second voltage value V2 acquired from the A / D conversion unit 54 is less than the low voltage threshold value Vw, the control unit 57 detects a short-circuit failure of the downstream switch 20. Note that the control unit 57 may detect a short-circuit failure of the downstream switch 20 when the first voltage value V1 acquired from the A / D conversion unit 53 is less than the low voltage threshold value Vw. In this case, the control unit 57 instructs switching of the upstream switch 30 and the downstream switch 20 to OFF, and acquires the first voltage value V1 from the A / D conversion unit 53 with the connection switch 40 being ON. Regarding the first voltage value V1, there is no problem as long as the fourth voltage threshold value for detecting a short-circuit failure of the downstream switch 20 exceeds 0V and is equal to or less than the first divided voltage value Vd1. Regarding the second voltage value V2, there is no problem as long as the fourth voltage threshold value for detecting a short-circuit failure of the downstream switch 20 exceeds 0V and is equal to or less than the second divided voltage value Vd2.

[0107] The control unit 57 instructs switching of the upstream switch 30 and the downstream switch 20 to OFF, and acquires the second voltage value V2 from the A / D conversion unit 54 with the connection switch 40 being ON. The control unit 57 detects an open failure of the load 12 based on the acquired second voltage value V2. The open failure of the load 12 is a phenomenon in which the resistance value between both ends of the load 12, that is, the resistance value between both ends of the load resistor 12a, is extremely large.

[0108] As described above, when the upstream switch 30, the downstream switch 20, and the connection switch 40 are OFF, OFF, and ON, respectively, and the load 12 is normal, the second voltage value V2 is the second divided voltage value Vd2 and is equal to or less than the middle voltage threshold value Vm. When an open failure of the load 12 has occurred, no current flows through the second resistor 41 with the connection switch 40 being ON. For this reason, the second voltage value V2 is a constant voltage value Vc and exceeds the middle voltage threshold value Vm.

[0109] As a result, when the second voltage value V2 acquired from the A / D conversion unit 54 exceeds the middle voltage threshold value Vm, the control unit 57 detects an open failure of the load 12. Note that there is no problem as long as the fifth voltage threshold value for detecting an open failure of the load 12 exceeds the second divided voltage value Vd2 and is less than the constant voltage value Vc.

[0110] <Fault diagnosis when load 12 is operating> FIG. 5 is a chart for explaining fault diagnosis when load 12 is operating. In FIG. 5, similar to FIG. 4, the instruction of upstream switch 30, the instruction of downstream switch 20, the state of connection switch 40, fault conditions, and detected contents are shown. Id is the detected current value. As described above, the detected current value is the current value of the current flowing through upstream switch 30.

[0111] The control unit 57 instructs the switching of upstream switch 30 and downstream switch 20 to on, and acquires the first voltage value V1 from the A / D conversion unit 53 in a state where connection switch 40 is off. The control unit 57 detects an open fault of upstream switch 30 based on the acquired first voltage value V1.

[0112] As described above, when upstream switch 30, downstream switch 20, and connection switch 40 are on, on, and off respectively, from the positive electrode of DC power supply 11, the current flows in the order of upstream switch 30, load resistor 12a, downstream switch 20, and the negative electrode of DC power supply 11. At this time, since DC power supply 11 supplies power of a predetermined power or more to load resistor 12a, load 12 is operating. As described above, when upstream switch 30 is on, from the positive electrode of DC power supply 11, the current flows through upstream switch 30, first resistor 23, and the negative electrode of DC power supply 11.

[0113] When upstream switch 30, downstream switch 20, and connection switch 40 are on, on, and off respectively, the first voltage value V1 is the power supply voltage value Vb and is equal to or higher than the low voltage threshold value Vw. When an open fault of upstream switch 30 occurs, no current flows through first resistor 23. For this reason, the first voltage value V1 is 0 V and is less than the low voltage threshold value Vw. As a result, the control unit 57 detects an open fault of upstream switch 30 when the first voltage value V1 acquired from the A / D conversion unit 53 is less than the low voltage threshold value Vw. Note that the sixth voltage threshold value for detecting an open fault of upstream switch 30 exceeds 0 V and is not a problem as long as it is equal to or lower than the power supply voltage value Vb.

[0114] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to switch on, and acquires the first voltage value V1 from the A / D conversion unit 53 in a state where the connection switch 40 is off. The control unit 57 detects a half-on failure of the upstream switch 30 based on the acquired first voltage value V1.

[0115] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, on, and off respectively, the first voltage value V1 is the power supply voltage value Vb and is equal to or higher than the high voltage threshold value Vh. When a half-on failure of the upstream switch 30 occurs, the first voltage value V1 is the first failure voltage value Vf1 and is less than the high voltage threshold value Vh. As a result, the control unit 57 detects a half-on failure of the upstream switch 30 when the first voltage value V1 acquired from the A / D conversion unit 53 is less than the high voltage threshold value Vh. Note that the seventh voltage threshold value for detecting a half-on failure of the upstream switch 30 may exceed the first failure voltage value Vf1 and be equal to or less than the power supply voltage value Vb without any problem.

[0116] When a half-on failure of the upstream switch 30 occurs while the downstream switch 20 is on, the amount of heat generated by the upstream switch 30 per unit time rapidly increases. As a result, the temperature of the upstream switch 30 rises to a temperature equal to or higher than the reference temperature, and the drive circuit 31 forcibly switches the upstream switch 30 off regardless of the voltage input from the first output unit 50 of the microcomputer 26. The half-on failure of the upstream switch 30 is detected by the drive circuit 31 or the control unit 57.

[0117] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to switch on, and acquires the second voltage value V2 from the A / D conversion unit 54 in a state where the connection switch 40 is off. The control unit 57 detects an open failure of the downstream switch 20 based on the acquired second voltage value V2.

[0118] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are all on, on, and off respectively, the second voltage value V2 is 0V and is below the high voltage threshold Vh. When an open failure of the downstream switch 20 occurs, no current flows through the load resistor 12a. Therefore, the first voltage value V1 is the power supply voltage value Vb and exceeds the high voltage threshold Vh. As a result, when the second voltage value V2 acquired from the A / D conversion unit 54 by the control unit 57 exceeds the high voltage threshold Vh, the control unit 57 detects an open failure of the downstream switch 20. Note that there is no problem as long as the eighth voltage threshold for detecting an open failure of the downstream switch 20 is 0V or higher and less than the power supply voltage value Vb.

[0119] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to be switched on, and acquires the second voltage value V2 from the A / D conversion unit 54 with the connection switch 40 off. The control unit 57 detects a half-on failure of the downstream switch 20 based on the acquired second voltage value V2.

[0120] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are all on, on, and off respectively, the second voltage value V2 is 0V and is below the low voltage threshold Vw. When a half-on failure of the downstream switch 20 occurs, the second voltage value V2 is the second failure voltage value Vf2, exceeds the low voltage threshold Vw, and is less than the high voltage threshold Vh. As a result, when the second voltage value V2 exceeds the low voltage threshold Vw and is less than the high voltage threshold Vh, the control unit 57 detects a half-on failure of the downstream switch 20.

[0121] Note that there is no problem as long as the lower voltage threshold for detecting a half-on failure of the downstream switch 20 is 0V or higher and less than the second failure voltage value Vf2. The lower voltage threshold corresponds to the ninth voltage threshold. There is no problem as long as the upper voltage threshold for detecting a half-on failure of the downstream switch 20 is equal to or higher than the first failure voltage value Vf1 and less than the power supply voltage value Vb.

[0122] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to be switched on, and acquires current information from the A / D conversion unit 52 in a state where the connection switch 40 is off. As described above, the current information indicates the detected current value Id, that is, the current value of the current flowing through the upstream switch 30. The acquisition of the current information corresponds to the acquisition of the detected current value Id. The control unit 57 detects an open failure of the load 12 based on the detected current value Id indicated by the acquired current information.

[0123] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, on, and off, respectively, in a state where the load 12 is normal, the detected current value Id is the normal current value In and is equal to or greater than the lower current threshold value Iw. When an open failure of the load 12 has occurred, the detected current value Id is the resistance current value Ir and is less than the lower current threshold value Iw. Therefore, when the detected current value Id indicated by the current information acquired from the A / D conversion unit 52 is less than the lower current threshold value Iw, the control unit 57 detects an open failure of the load 12.

[0124] The control unit 57 instructs the upstream switch 30 and the downstream switch 20 to be switched on, and acquires current information from the A / D conversion unit 52 in a state where the connection switch 40 is off. The control unit 57 detects a short-circuit failure of the load 12 based on the detected current value Id indicated by the acquired current information. The short-circuit failure of the load 12 is a phenomenon in which the resistance value between both ends of the load 12, that is, the resistance value between both ends of the load resistor 12a, is extremely small.

[0125] When the upstream switch 30, the downstream switch 20, and the connection switch 40 are on, on, and off, respectively, in a state where the load 12 is normal, the detected current value Id is the normal current value In and is equal to or less than the upper current threshold value Ih. When a short-circuit failure of the load 12 has occurred, the detected current value Id exceeds the upper current threshold value Ih (normal current value In). Therefore, when the detected current value Id indicated by the current information acquired from the A / D conversion unit 52 exceeds the upper current threshold value Ih, the control unit 57 detects a short-circuit failure of the load 12. The upper current threshold value Ih is the second current threshold value.

[0126] When a short - circuit fault occurs in the load 12 with the upstream switch 30 and the downstream switch 20 being on, the detected current value Id indicates a current equal to or greater than the reference current value, and the drive circuit 31 forcibly switches the upstream switch 30 to off regardless of the voltage input from the first output section 50 of the microcomputer 26. The short - circuit fault of the load 12 is detected by the drive circuit 31 or the control section 57.

[0127] <Power - supply control process> FIG. 6 is a flowchart showing the procedure of the power - supply control process. Hereinafter, the fault diagnosis when the load 12 is stopped will be referred to as the fault diagnosis during stop. The fault diagnosis when the load 12 is operating will be referred to as the fault diagnosis during operation. The control section 57 of the microcomputer 26 executes the power - supply control process in a state where switching off of the upstream switch 30, the downstream switch 20, and the connection switch 40 is instructed.

[0128] In the power - supply control process, the control section 57 determines whether to operate the load 12 (step S1). If the control section 57 determines not to operate the load 12 (S1: NO), it executes step S1 again. The control section 57 waits until the timing to operate the load 12 arrives. If the control section 57 determines to operate the load 12 (S1: YES), it executes the fault diagnosis during stop according to the content of FIG. 4 (step S2).

[0129] The control section 57 realizes the turning - on of the connection switch 40 by instructing the switching section 55 to switch the connection switch 40 to on. The control section 57 realizes the turning - off of the connection switch 40 by instructing the switching section 55 to switch the connection switch 40 to off. The control section 57 determines 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 has occurred by performing the fault diagnosis during stop. The control section 57 ends the fault diagnosis during stop in a state where switching off of the upstream switch 30, the downstream switch 20, and the connection switch 40 is instructed.

[0130] After executing step S2, the control unit 57 determines whether a failure has been detected in the stopped fault diagnosis (step S3). If the control unit 57 determines that no failure has been detected in the stopped fault diagnosis (S3: NO), it instructs the first output unit 50 and the second output unit 51 to switch the upstream switch 30 and the downstream switch 20 to on (step S4). When the upstream switch 30 and the downstream switch 20 are switched to on with the load 12 being normal, the DC power supply 11 supplies power of a predetermined power or more to the load resistor 12a. Thereby, the load 12 operates.

[0131] After executing step S4, the control unit 57 performs an operating fault diagnosis according to the content of FIG. 5 (step S5). By performing the operating fault diagnosis, the control unit 57 determines whether an open fault of the upstream switch 30, a half-on fault of the upstream switch 30, an open fault of the downstream switch 20, a half-on fault of the downstream switch 20, an open fault of the load 12, or a short-circuit fault of the load 12 has occurred. The control unit 57 ends the operating fault diagnosis in a state where the upstream switch 30 and the downstream switch 20 are instructed to be switched to on and the connection switch 40 is instructed to be switched to off.

[0132] After executing step S5, the control unit 57 determines whether a failure has been detected in the operating fault diagnosis (step S6). If the control unit 57 determines that no failure has been detected in the operating fault diagnosis (S6: NO), it determines whether to stop the operation of the load 12 (step S7). If the control unit 57 determines not to stop the operation of the load 12 (S7: NO), it executes step S5 again. The control unit 57 waits until a timing to detect a failure or stop the operation of the load 12 arrives.

[0133] When the control unit 57 determines that a failure has been detected during the operation diagnosis (S6: YES), or when it determines to stop the operation of the load 12 (S7: YES), it instructs each of the first output unit 50 and the second output unit 51 to switch the upstream switch 30 and the downstream switch 20 to OFF (step S8). When the upstream switch 30 and the downstream switch 20 are switched to OFF, the power supply from the DC power supply 11 to the load resistor 12a stops, and the load 12 stops operating.

[0134] When the control unit 57 determines that a failure has been detected during the stop diagnosis (S3: YES), or after executing step S8, it ends the power supply control process. When the power supply control process ends and no failure is detected, the control unit 57 executes the power supply control process again. Note that the control unit 57 may execute the stop diagnosis again after executing step S8. In this case, the control unit 57 ends the power supply control process after executing the stop diagnosis.

[0135] As described above, in the power supply control process, when a failure is detected during the operation diagnosis, the control unit 57 instructs the switching of the upstream switch 30 and the downstream switch 20 to OFF. Therefore, when a short - circuit failure occurs in the upstream switch 30, the downstream switch 20 is switched to OFF, and the power supply to the load 12 stops. Also, the control unit 57 detects failures of the upstream switch 30, the downstream switch 20, and the load 12 based on the first voltage value V1 or the second voltage value V2.

[0136] (Embodiment 2) In Embodiment 1, the drive circuit 31 detects the half - on failure of the upstream switch 30 and the short - circuit failure of the load 12. However, the drive circuit 31 may not have the function of detecting failures. Hereinafter, the differences between Embodiment 2 and Embodiment 1 will be described. For other configurations except the configurations described later, they are common to Embodiment 1. Therefore, the same reference numerals as those in Embodiment 1 are assigned to the constituent parts common to Embodiment 1, and the description of those constituent parts is omitted.

[0137] <Configuration of the power supply control device 10> FIG. 7 is a block diagram showing a main configuration of the power supply control device 10 in Embodiment 2. The power supply control device 10 in Embodiment 2 includes a downstream switch 20, a series circuit 22, a first resistor 23, an upstream resistor 24, a downstream resistor 25, an upstream switch 30, a drive circuit 31, and a current detection circuit 32. The power supply control device 10 further includes a shunt resistor 34. The power supply control device 10 does not have an IPD 21.

[0138] The connection of the load resistor 12a, the downstream switch 20, the series circuit 22, the downstream resistor 25, and the drive circuit 31 is the same as that in Embodiment 1. Similar to Embodiment 1, a constant voltage is applied to the series circuit 22. The connection of the drain and gate of the upstream switch 30 is the same as that in Embodiment 1.

[0139] 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 ends of the first resistor 23 and the upstream resistor 24 are connected to the 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 the 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 conversion unit 53 of the microcomputer 26. One end and the other end of the shunt resistor 34 are separately connected to the current detection circuit 32. The current detection circuit 32 is further connected to the A / D conversion unit 52 of the microcomputer 26.

[0140] When the upstream switch 30 and the downstream switch 20 are on, the current flows from the positive electrode of the DC power supply 11 to the negative electrode of the DC power supply 11 through the current path E in the same manner as in Embodiment 1. In the current path E, the current flows in the order of the upstream switch 30, the shunt resistor 34, the load resistor 12a, the downstream switch 20, and the negative electrode of the DC power supply 11 as indicated by the arrow. When the upstream switch 30 is on, the current flows from the positive electrode of the DC power supply 11 in the order of the upstream switch 30, the shunt resistor 34, and the load resistor 12a.

[0141] All the current output from the upstream switch 30 is input to the shunt resistor 34. Therefore, the current value of the current flowing through the shunt resistor 34 matches the current value of the current flowing through the upstream switch 30. The resistance value of the shunt resistor 34 is a constant value. For this reason, the voltage value across both ends of the shunt resistor 34 is proportional to the current value of the current flowing through the upstream switch 30. The current detection circuit 32 detects the current value of the current flowing through the upstream switch 30 by detecting the voltage value across both ends of the shunt resistor 34. The current detection circuit 32 outputs the voltage value across both ends of the shunt resistor 34 to the A / D conversion unit 52 of the microcomputer 26 as analog current information.

[0142] By dividing the voltage value across both ends of the shunt resistor 34 by the resistance value of the shunt resistor 34, the current value of the current flowing through the shunt resistor 34 is calculated. For this reason, the current information indicates the detected current value Id detected by the current detection circuit 32. Similar to Embodiment 1, the A / D conversion unit 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 conversion unit 52. The drive circuit 31 in Embodiment 2 does not switch the upstream switch 30 off according to the detected current value Id or the temperature of the upstream switch 30.

[0143] <First failure voltage value Vf1 and second failure voltage value Vf2> As described in the explanation of Embodiment 1, the first failure voltage value Vf1 is the first voltage value V1 when the downstream switch 20 is on in the case where a half-on failure of the upstream switch 30 has occurred. Since the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a, the first failure voltage value Vf1 substantially matches the voltage value of the voltage obtained by dividing the power supply voltage value Vb between the circuit including the upstream switch 30 and the shunt resistor 34 and the load resistor 12a.

[0144] As described in the description of Embodiment 1, the second failure voltage value Vf2 is the second voltage value V2 when the upstream switch 30 is on in the case where a half-on failure of the downstream switch 20 has occurred. Since the resistance value of the first resistor 23 is sufficiently larger than the resistance value of the load resistor 12a, the second failure voltage value Vf2 substantially coincides with the voltage value of the voltage obtained by dividing the power supply voltage value Vb by the circuit including the shunt resistor 34 and the load resistor 12a and the downstream switch 20.

[0145] <Fault diagnosis> In Embodiment 1, when the upstream switch 30 is on or a short-circuit failure of the upstream switch 30 has occurred, the first voltage value V1 is the power supply voltage value Vb. In Embodiment 2, when the upstream switch 30 is on or a short-circuit failure of the upstream switch 30 has occurred and the downstream switch 20 is off or an open failure of the downstream switch 20 has occurred, the first voltage value V1 is the voltage value of the voltage obtained by dividing the power supply 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 supply voltage value Vb.

[0146] 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 the upstream switch 30 is on or a short-circuit failure of the upstream switch 30 has occurred and the downstream switch 20 is on or a short-circuit failure of the downstream switch 20 has occurred, the first voltage value V1 is the voltage value of the 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, this voltage value substantially coincides with the power supply voltage value Vb.

[0147] <Effect> The power supply control device 10 in Embodiment 2 exhibits the same effects as the other effects obtained by the power supply control device 10 in Embodiment 1 excluding the effect obtained by the drive circuit 31 detecting a failure.

[0148] <Modification Example> In Embodiments 1 and 2, there is no problem as long as each of the upstream switch 30 and the downstream switch 20 is a semiconductor switch. Therefore, each of the upstream switch 30 and the downstream switch 20 is not limited to an N-channel type FET, and may be a P-channel type FET, a bipolar transistor, or the like.

[0149] The technical features (constituent elements) described in Embodiments 1 and 2 can be combined with each other, and new technical features can be formed by the combination. The disclosed Embodiments 1 and 2 should be considered as illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Description of Reference Numerals

[0150] 1 Power supply system 10 Power supply control device 11 DC power supply 12 Load 12a Load resistor 20 Downstream switch 21 IPD 22 Series circuit 23 First resistor 24 Upstream resistor 25 Downstream resistor 26 Microcomputer 30 Upstream switch 31 Drive circuit 32 Current detection circuit 33 Temperature detection circuit 34 Shunt resistor 40 Connection switch 41 Second resistor 50 First output section 51 Second output section 52, 53, 54 A / D conversion section 55 Switching section 56 Storage section 57 Control section (processing section) 58 Internal bus A Memory medium C Vehicle E Current path P Computer program

Claims

1. A power supply control device for controlling power supply to a load, an upstream switch disposed on the upstream side of the load in the current path of the current flowing through the load; a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and having one end connected to a connection node between the load and the downstream switch; a processing unit that executes processing and is provided with a constant voltage with the potential of the other end of the first resistor as a reference voltage is applied to the other end of the series circuit, the processing unit acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch, based on the acquired voltage value, detects a failure of the upstream switch, downstream switch or load, the current flows from one end of the DC power supply through the current path to the other end of the DC power supply, the processing unit instructs switching on of the upstream switch, instructs switching off of the downstream switch, in a state where the connection switch is off, acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch, when the acquired voltage value is less than a voltage threshold, detects an open failure of the upstream switch, the voltage threshold exceeds 0 V and is less than or equal to the voltage value between both ends of the DC power supply A power supply control device.

2. A power supply control device for controlling power supply to a load, an upstream switch disposed on the upstream side of the load in the current path of the current flowing through the load; In the current path, a downstream switch disposed on the downstream side of the load; A first resistor having one end connected to a connection node between the upstream switch and the load; A series circuit including a second resistor and a connection switch connected in series, and having one end connected to a connection node between the load and the downstream switch; A processing unit that executes processing; and comprising: A constant voltage with the potential of the other end of the first resistor as a reference voltage is applied to the other end of the series circuit; The processing unit: Acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch; Based on the acquired voltage value, detects a failure of the upstream switch, the downstream switch, or the load; Instructs switching of the upstream switch to off; Instructs switching of the downstream switch to on; With the connection switch being on, acquires a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch; When the acquired voltage value exceeds a third voltage threshold, detects an open failure of the downstream switch; The third voltage threshold is 0 V or more and less than the voltage value acquired by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively; A power supply control device.

3. A power supply control device for controlling power supply to a load, comprising: An upstream switch disposed on the upstream side of the load in a current path through which current flows through the load; A downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, with one end connected to a connection node between the load and the downstream switch, A processing unit that executes processing And is provided with A constant voltage with the potential at the other end of the first resistor as the reference potential is applied to the other end of the series circuit, The processing unit Obtains the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, Based on the obtained voltage value, detects a failure of the upstream switch, the downstream switch, or the load, Instructs switching off of the upstream switch and the downstream switch, With the connection switch being on, obtains the voltage value of the connection node between the load and the downstream switch, When the obtained voltage value exceeds a fifth voltage threshold, detects an open failure of the load, The fifth voltage threshold exceeds the voltage value obtained by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively, and is less than the voltage value of the constant voltage. Power supply control device.

4. A power supply control device for controlling power supply to a load, An upstream switch disposed on the upstream side of the load in the current path of the current flowing through the load, A downstream switch disposed on the downstream side of the load in the current path, A first resistor having one end connected to the connection node between the upstream switch and the load, A series circuit including a second resistor and a connection switch connected in series, with one end connected to the connection node between the load and the downstream switch, A processing unit that executes processing And is provided with A constant voltage with the potential at the other end of the first resistor as the reference potential is applied to the other end of the series circuit, The processing unit Obtain the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, Based on the obtained voltage value, detect a failure of the upstream switch, downstream switch or load, The current flows from one end of the DC power supply through the current path to the other end of the DC power supply, The processing unit, Instruct the upstream switch and the downstream switch to switch on, With the connection switch off, obtain the voltage value of the connection node between the upstream switch and the load, If the obtained voltage value is less than the sixth voltage threshold, detect an open failure of the upstream switch, The sixth voltage threshold is greater than 0V and less than or equal to the voltage value between both ends of the DC power supply Power supply control device.

5. A power supply control device for controlling power supply to a load, comprising: An upstream switch disposed on the upstream side of the load in the current path of the current flowing through the load; A downstream switch disposed on the downstream side of the load in the current path; A first resistor having one end connected to the connection node between the upstream switch and the load; A series circuit including a second resistor and a connection switch connected in series, and having one end connected to the connection node between the load and the downstream switch; A processing unit that executes processing; And A constant voltage with the potential of the other end of the first resistor as the reference potential is applied to the other end of the series circuit, The processing unit, Obtain the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, Based on the obtained voltage value, detect a failure of the upstream switch, downstream switch or load, The current flows from one end of the DC power supply through the current path to the other end of the DC power supply, The upstream switch is a semiconductor switch, The processing unit, instructs switching on of the upstream switch and the downstream switch, obtains a voltage value of a connection node between the upstream switch and the load while the connection switch is off, when the obtained voltage value is less than a seventh voltage threshold, detects a failure related to a resistance value of the upstream switch, The seventh voltage threshold is equal to or less than a voltage value between both ends of the DC power supply Power supply control device.

6. A power supply control device that controls power supply to a load, an upstream switch disposed on the upstream side of the load in a current path of a current flowing through the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and having one end connected to a connection node between the load and the downstream switch, a processing unit that executes processing, and a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit, The processing unit, obtains a voltage value of a connection node between the upstream switch and the load, or a voltage value of a connection node between the load and the downstream switch, based on the obtained voltage value, detects a failure of the upstream switch, the downstream switch, or the load, instructs switching on of the upstream switch and the downstream switch, obtains a voltage value of a connection node between the load and the downstream switch while the connection switch is off, when the obtained voltage value exceeds a ninth voltage threshold, detects a failure related to a resistance value of the downstream switch, The ninth voltage threshold value is 0 V or more. Power supply control device.

7. A power supply control device for controlling power supply to a load, an upstream switch disposed upstream of the load in a current path of a current flowing through the load; a downstream switch disposed downstream of 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 including a second resistor and a connection switch connected in series, and having one end connected to a connection node between the load and the downstream switch; a processing unit that executes processing; and a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit, The processing unit acquires a voltage value of a connection node between the upstream switch and the load or a voltage value of a connection node between the load and the downstream switch, detects a failure of the upstream switch, the downstream switch, or the load based on the acquired voltage value, instructs switching on of the upstream switch and the downstream switch, acquires a current value of a current flowing through the upstream switch, when the acquired current value is less than a current threshold value, detects an open failure of the load, The current threshold value exceeds a current value of a current flowing through the upstream switch when the upstream switch, the downstream switch, and the connection switch are on, off, and off, The current threshold value is equal to or less than a current value of a current flowing through the upstream switch when the upstream switch and the downstream switch are on and the load is normal, The resistance value of the load is less than the resistance value of the first resistor. Power supply control device.

8. The current flows from one end of the DC power supply through the current path to the other end of the DC power supply. The processing unit instructs to switch the upstream switch and the downstream switch to off, acquires the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, with the connection switch being off, when the acquired voltage value exceeds a second voltage threshold, detects a short - circuit fault of the upstream switch, wherein the second voltage threshold is equal to or greater than 0V and less than the voltage value between both ends of the DC power supply. The power - supply control device according to any one of claims 1 to 7.

9. The processing unit instructs to switch the upstream switch and the downstream switch to off, acquires the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch, with the connection switch being on, when the acquired voltage value is less than a fourth voltage threshold, detects a short - circuit fault of the downstream switch, wherein the fourth voltage threshold exceeds 0V and is less than or equal to the voltage value acquired by the processing unit when the upstream switch, the downstream switch, and the connection switch are off, off, and on, respectively. The power - supply control device according to any one of claims 1 to 8.

10. The current flows from one end of the DC power supply through the current path to the other end of the DC power supply. The processing unit instructs to switch the upstream switch and the downstream switch to on, acquires the voltage value of the connection node between the load and the downstream switch, with the connection switch being off, when the acquired voltage value exceeds an eighth voltage threshold, detects an open - circuit fault of the downstream switch, The eighth voltage threshold is equal to or greater than 0 V and less than the voltage value across both ends of the DC power supply. The power supply control device according to any one of claims 1 to 9.

11. The processing unit instructs switching on of the upstream switch and the downstream switch, acquires the current value of the current flowing through the upstream switch, when the acquired current value exceeds a second current threshold, detects a short circuit fault of the load, wherein the second current threshold is the current value of the current flowing through the upstream switch when the upstream switch and the downstream switch are on in a state where the load is normal. The power supply control device according to any one of claims 1 to 10.

12. When the processing unit detects a fault in the upstream switch, the downstream switch, or the load while instructing switching on of the upstream switch and the downstream switch, the processing unit instructs switching off of the upstream switch and the downstream switch. The power supply control device according to any one of claims 1 to 11.

13. A fault detection method for detecting a fault in a circuit including an upstream switch disposed on the upstream side of a load in a current path of a current flowing through the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and having a constant voltage with the potential of the other end of the first resistor as a reference potential applied to the other end of the series circuit, the method comprising: acquiring a voltage value of a connection node between the upstream switch and the load or a voltage value of a connection node between the load and the downstream switch; and detecting a fault in the upstream switch, the downstream switch, or the load based on the acquired voltage value, which is executed by a computer. The current flows from one end of the DC power supply through the current path to the other end of the DC power supply. The computer instructs to switch the upstream switch on. instructs to switch the downstream switch off. With the connection switch off, obtain the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch. If the obtained voltage value is less than the voltage threshold, detect an open fault of the upstream switch. The voltage threshold exceeds 0 V and is less than or equal to the voltage value between both ends of the DC power supply. Fault detection method.

14. In a current path of a current flowing through a load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of 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 including a second resistor and a connection switch connected in series, and one end of the series circuit is connected to a connection node between the load and the downstream switch. A fault detection method for detecting a fault in a circuit in which a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit, comprising: obtaining the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch; The computer executes steps of detecting a fault in the upstream switch, the downstream switch, or the load based on the obtained voltage value. The computer instructs to switch the upstream switch off. instructs to switch the downstream switch on. With the connection switch on, obtain the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch. If the obtained voltage value exceeds a third voltage threshold, detect an open fault of the downstream switch. The third voltage threshold is 0 V or higher and less than the voltage value obtained by the computer when the upstream switch, the downstream switch, and the connection switch are off, off, and on. Fault detection method.

15. A fault detection method for detecting a fault in a circuit including an upstream switch disposed on the upstream side of a load in a current path of a current flowing through the load, a downstream switch disposed on the downstream side of 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 second resistor and a connection switch connected in series, and a series circuit having one end connected to a connection node between the load and the downstream switch, and a constant voltage with the potential of the other end of the first resistor as a reference potential being applied to the other end of the series circuit, the method comprising: obtaining a voltage value of a connection node between the upstream switch and the load or a voltage value of a connection node between the load and the downstream switch; the computer executing a step of detecting a fault in the upstream switch, the downstream switch, or the load based on the obtained voltage value; the computer: instructing switching of the upstream switch and the downstream switch to off; obtaining a voltage value of a connection node between the load and the downstream switch with the connection switch on; when the obtained voltage value exceeds a fifth voltage threshold, detecting an open fault in the load; the fifth voltage threshold exceeding the voltage value obtained by the computer when the upstream switch, the downstream switch, and the connection switch are off, off, and on and being less than the voltage value of the constant voltage; Fault detection method. **Claim 16**: In the current path of the current flowing through the load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of the load in the current path, a first resistor having one end connected to the connection node between the upstream switch and the load, and a second resistor and a connection switch connected in series, and a series circuit having one end connected to the connection node between the load and the downstream switch, and a failure detection method for detecting a failure of a circuit in which a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit, a step of obtaining a voltage value of the connection node between the upstream switch and the load, or a voltage value of the connection node between the load and the downstream switch; a step of the computer detecting a failure of the upstream switch, the downstream switch, or the load based on the obtained voltage value; The current flows from one end of the DC power supply through the current path to the other end of the DC power supply. The computer instructs the switching on of the upstream switch and the downstream switch, obtains the voltage value of the connection node between the upstream switch and the load with the connection switch off, when the obtained voltage value is less than a sixth voltage threshold, detects an open failure of the upstream switch, The sixth voltage threshold exceeds 0V and is less than or equal to the voltage value between both ends of the DC power supply. Failure detection method. **Claim 17**: In the current path of the current flowing through the load, an upstream switch disposed on the upstream side of the load, a downstream switch disposed on the downstream side of the load in the current path, a first resistor having one end connected to the connection node between the upstream switch and the load, and a second resistor and a connection switch connected in series, and a series circuit having one end connected to the connection node between the load and the downstream switch, and a failure detection method for detecting a failure of a circuit in which a constant voltage with the potential of the other end of the first resistor as a reference potential is applied to the other end of the series circuit, The step of obtaining the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch; The computer executes the step of detecting a failure of the upstream switch, the downstream switch, or the load based on the obtained voltage value; The current flows from one end of the DC power supply through the current path to the other end of the DC power supply; The upstream switch is a semiconductor switch; The computer; Instructs the switching-on of the upstream switch and the downstream switch; With the connection switch off, obtains the voltage value of the connection node between the upstream switch and the load; When the obtained voltage value is less than the seventh voltage threshold, detects a failure related to the resistance value of the upstream switch; The seventh voltage threshold is less than or equal to the voltage value between both ends of the DC power supply; A failure detection method.

18. A failure detection method for detecting a failure of a circuit including an upstream switch disposed on the upstream side of a load in a current path of a current flowing through the load, a downstream switch disposed on the downstream side of 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 second resistor and a connection switch connected in series, and a series circuit having one end connected to a connection node between the load and the downstream switch, and a constant voltage with the potential of the other end of the first resistor as a reference potential being applied to the other end of the series circuit, the method comprising: The step of obtaining the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch; The computer executes the step of detecting a failure of the upstream switch, the downstream switch, or the load based on the obtained voltage value; The computer; Instructs the switching-on of the upstream switch and the downstream switch; In a state where the connection switch is off, obtain the voltage value of the connection node between the load and the downstream switch, When the obtained voltage value exceeds the ninth voltage threshold, detect a failure related to the resistance value of the downstream switch, The ninth voltage threshold is 0 V or more Fault detection method.

19. In the current path of the current flowing through the load, an upstream switch arranged on the upstream side of the load, a downstream switch arranged on the downstream side of the load in the current path, a first resistor having one end connected to the connection node between the upstream switch and the load, a second resistor and a connection switch connected in series, and a series circuit having one end connected to the connection node between the load and the downstream switch, and a fault detection method for detecting a fault in a circuit in which a constant voltage with the potential of the other end of the first resistor as the reference potential is applied to the other end of the series circuit, comprising: Obtaining the voltage value of the connection node between the upstream switch and the load, or the voltage value of the connection node between the load and the downstream switch; The computer executes steps of detecting a fault in the upstream switch, the downstream switch or the load based on the obtained voltage value, The computer is Instructing the switching on of the upstream switch and the downstream switch, Obtaining the current value of the current flowing through the upstream switch, When the obtained current value is less than the current threshold, detecting an open fault of the load, The current threshold exceeds the current value of the current flowing through the upstream switch when the upstream switch, the downstream switch and the connection switch are on, off and off, The current threshold is less than or equal to the current value of the current flowing through the upstream switch when the upstream switch and the downstream switch are on and the load is normal, The resistance value of the load is less than the resistance value of the first resistor Fault detection method.

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