Detection circuit and power supply control device

Abstract

In the second detection circuit (25), a current outputter (50) outputs a current corresponding to a circuit voltage between an input terminal of the second FET (40) to which a current is input and a ground of the second drive circuit (42) that switches the second FET (40) to be on or off, to a circuit resistor (51). The second detection circuit (25) outputs a voltage between both ends of the circuit resistor (51). The voltage between the ground of the second drive circuit (42) and one end of the downstream side of the circuit resistor (51) exceeds 0 V.

Description

Technical Field

[0001] This disclosure relates to detection circuits and power supply control devices.

[0002] This application claims priority based on Japanese Application No. 2020-167159, filed on October 1, 2020, and invokes all the contents of that Japanese application. Background Technology

[0003] Patent Document 1 discloses a power supply system for a vehicle that supplies power from a DC power source to a load. In this power supply system, a semiconductor switch is arranged in the current path of the current flowing from the positive terminal of the DC power source to the load. The semiconductor switch is an N-channel FET (Field Effect Transistor). The input terminal, i.e., the drain, of the semiconductor switch receiving the input current is connected to the positive terminal of the DC power source. A switching circuit boosts the voltage at the input terminal of the semiconductor switch and applies the boosted voltage to the control terminal, i.e., the gate, of the semiconductor switch. This switches the semiconductor switch to ON.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-106624 Summary of the Invention

[0007] One aspect of the detection circuit disclosed herein includes: a current output device that outputs a current corresponding to the circuit voltage between the input terminal of a semiconductor switch to which the input current is applied and the ground of a switching circuit, the switching circuit switching the semiconductor switch to be on or off; a circuit resistor through which the current output by the current output device flows, the detection circuit outputting a voltage between the two ends of the circuit resistor, and the voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeding 0V.

[0008] One aspect of the power supply control device disclosed herein controls power supply via a semiconductor switch, comprising: a switching circuit for switching the semiconductor switch to on or off; a detection circuit for detecting the circuit voltage between the input terminal of the semiconductor switch receiving an input current and the ground of the switching circuit, and outputting a voltage representing the detected circuit voltage; and a processing unit for performing processing, wherein the processing unit instructs the switching circuit to switch the semiconductor switch to on or off based on the voltage output by the detection circuit, the detection circuit comprising: a current output device for outputting a current corresponding to the circuit voltage; and a circuit resistor, wherein the current output by the current output device flows through the circuit resistor, the detection circuit outputs a voltage between the two ends of the circuit resistor, and the voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeds 0V.

[0009] It should be noted that this disclosure can be implemented not only as a power supply control device for a processing unit with such characteristics, but also as a power supply control method that sets the aforementioned characteristic processing as steps, or as a computer program for causing a computer to execute the steps. Furthermore, this 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 that includes the power supply control device. Attached Figure Description

[0010] Figure 1 This is a block diagram showing the main structural components of the power supply system in Embodiment 1.

[0011] Figure 2 This is a circuit diagram of the first controller and the first detection circuit.

[0012] Figure 3 This is a circuit diagram of the second controller and the second detection circuit.

[0013] Figure 4 It is a block diagram showing the main structure of a microcomputer.

[0014] Figure 5 This is a flowchart showing the sequence of the second fault detection and processing.

[0015] Figure 6 This is a flowchart showing the sequence of the second power supply control process.

[0016] Figure 7 This is a flowchart showing the sequence of the second power supply control process in Implementation Method 2.

[0017] Figure 8 This is a circuit diagram of the second detection circuit in Implementation Method 3.

[0018] Figure 9 It is a block diagram showing the main structure of a microcomputer.

[0019] Figure 10 This is a flowchart showing the sequence of the second fault detection and processing.

[0020] Figure 11 This is a flowchart showing the sequence of the second power supply control process.

[0021] Figure 12 This is a flowchart illustrating the sequence of the second power supply control process in Implementation Method 4.

[0022] Figure 13 This is a block diagram showing the main structural components of the power supply system in Embodiment 5.

[0023] Figure 14 This is a block diagram showing the main structural components of the power supply system in Embodiment 6. Detailed Implementation

[0024] [The problem this disclosure aims to solve]

[0025] In a conventional power supply system as described in Patent Document 1, the switching circuit boosts the voltage between the switching circuit's ground and the input terminal of the semiconductor switch. The negative terminal of the DC power supply is grounded by connecting it to a grounding conductor, for example, to the body of a vehicle. The switching circuit is connected to the grounding conductor via a connecting wire. When power is supplied to the switching circuit, the current flows in the order of the switching circuit, the connecting wire, and the grounding conductor. The grounding of the switching circuit is the potential at one end of the upstream side of the connecting wire.

[0026] The resistance of the connecting wires is assumed to be a non-negligible value. In this case, the voltage between the ground of the switching circuit and the input terminal of the semiconductor switch is less than the voltage between the two ends of the DC power supply. The higher the voltage between the two ends of the connecting wires, the lower the voltage between the ground of the switching circuit and the input terminal of the semiconductor switch. If the switching circuit boosts the voltage when the voltage between the ground of the switching circuit and the input terminal of the semiconductor switch is less than a certain value, it may not be possible to apply an appropriate voltage from the switching circuit to the semiconductor switch. In this case, for example, in the semiconductor switch, the resistance between the input terminal and the output terminal of the output current may not drop to a sufficiently small resistance value.

[0027] When the resistance between the input and output terminals of a semiconductor switch is not sufficiently small, the switch generates a significant amount of heat when current flows through it. Therefore, there is a possibility that the semiconductor switch's temperature may rise abnormally and malfunction. To prevent this, the switching circuit should not indicate whether the semiconductor switch is on or off if the voltage between the ground of the switching circuit and the input terminal of the semiconductor switch is less than a certain value. To achieve this, it is necessary to detect the voltage between the ground of the switching circuit and the input terminal of the semiconductor switch, rather than the voltage across the DC power supply.

[0028] Therefore, the objective is to provide a detection circuit for detecting the voltage between the input terminal of a semiconductor switch receiving an input current and the ground of a switching circuit that switches the semiconductor switch to on or off, and a power supply control device having the detection circuit.

[0029] [The Effects of This Disclosure]

[0030] According to this disclosure, the voltage between the input terminal of the semiconductor switch that receives the input current and the ground of the switching circuit that switches the semiconductor switch to on or off is measured.

[0031] [Description of embodiments of this disclosure]

[0032] First, embodiments of this disclosure will be described. At least some of the embodiments described below may be combined arbitrarily.

[0033] (1) One aspect of the detection circuit disclosed herein includes: a current output device that outputs a current corresponding to the circuit voltage between the input terminal of a semiconductor switch to which the input current is applied and the ground of a switching circuit, the switching circuit switching the semiconductor switch to be on or off; and a circuit resistor through which the current output by the current output device flows, the detection circuit outputting a voltage between the two ends of the circuit resistor, and the voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeding 0V.

[0034] In the above configuration, the circuit voltage is detected by outputting a current corresponding to the circuit voltage. Given a constant circuit resistor, the voltage across the resistor is proportional to the current output to it. The current corresponding to the circuit voltage flows through the resistor. Therefore, the circuit voltage can be calculated based on the voltage across the resistor. Furthermore, since the circuit voltage is converted into a corresponding current, a microcomputer (hereinafter referred to as a microcomputer) with different grounding and switching circuit grounding can calculate the circuit voltage.

[0035] (2) In one embodiment of the detection circuit of this disclosure, the current output device has: a device resistor, to which current flows from the input terminal of the semiconductor switch; a PNP bipolar transistor, the emitter of which is connected to one end of the downstream side of the device resistor, the potential of the base of which is the ground of the switching circuit, and the current output from the collector of which flows to the circuit resistor.

[0036] In the configuration described above, the bipolar transistor adjusts the resistance between its emitter and collector in such a way that the current flowing through the device's resistance becomes a current proportional to the circuit voltage. As a result, the circuit voltage is converted into a current proportional to the circuit voltage.

[0037] (3) One aspect of the detection circuit of the present disclosure includes a connection switch connected between the input terminal of the semiconductor switch and the current output device, the current output device outputting the current introduced from the input terminal of the semiconductor switch to the circuit resistor.

[0038] In the above configuration, the detection circuit operates by switching the connection switch to the ON position. The detection circuit stops operating by switching the connection switch to the OFF position. The detection circuit operates only during periods when voltage detection is required. This suppresses unnecessary power consumption.

[0039] (4) One aspect of the power supply control device disclosed herein controls power supply via a semiconductor switch, comprising: a switching circuit that switches the semiconductor switch to on or off; a detection circuit that detects the circuit voltage between the input terminal of the semiconductor switch to which an input current is input and the ground of the switching circuit, and outputs a voltage representing the detected circuit voltage; and a processing unit that performs processing, wherein the processing unit instructs the switching circuit to switch the semiconductor switch to on or off based on the voltage output by the detection circuit, the detection circuit comprising: a current output device that outputs a current corresponding to the circuit voltage; and a circuit resistor, wherein the current output by the current output device flows through the circuit resistor, the detection circuit outputs a voltage between the two ends of the circuit resistor, and the voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeds 0V.

[0040] In the above configuration, the semiconductor switch is appropriately switched to be on or off based on the circuit voltage output by the detection circuit.

[0041] (5) One aspect of the power supply control device disclosed herein includes a current output section, which outputs a current corresponding to the current flowing through the semiconductor switch, wherein the voltage between the ground of the switching circuit and one end of the downstream side of the circuit resistor varies according to the current output by the current output section.

[0042] In the above configuration, the circuit voltage varies depending on the current output by the current output unit.

[0043] (6) In one embodiment of the power supply control device disclosed herein, the switching circuit boosts the circuit voltage and applies the boosted voltage to the control terminal of the semiconductor switch, thereby switching the semiconductor switch to ON.

[0044] In the above configuration, the semiconductor switch is, for example, an N-channel FET. In this case, the input and control terminals of the semiconductor switch are, for example, the drain and gate, respectively. The switching circuit boosts the circuit voltage and applies the boosted voltage to the control terminal. Thus, the semiconductor switch is switched on.

[0045] (7) In one embodiment of the power supply control device of this disclosure, the processing unit determines whether the circuit voltage is an on-state voltage based on the voltage output by the detection circuit when the semiconductor switch is off. The on-state voltage is a voltage that can boost the voltage that enables the switching of the semiconductor switch to on. When the processing unit determines that the circuit voltage is the on-state voltage, it instructs the switching circuit to switch the semiconductor switch to on. After instructing the switching of the semiconductor switch to on, the processing unit determines whether the semiconductor switch is on.

[0046] In the above configuration, when the circuit voltage is the on-state voltage, it is confirmed whether the semiconductor switch can be switched to on.

[0047] (8) In one embodiment of the power supply control device disclosed herein, current flows from the input terminal of the semiconductor switch in the order of the switching circuit and the grounding of the switching circuit, thereby supplying power to the switching circuit. The processing unit determines whether the circuit voltage is less than a threshold voltage based on the voltage output by the detection circuit when the semiconductor switch is off. If the processing unit determines that the circuit voltage is less than the threshold voltage, it determines whether the switching circuit is working.

[0048] In the above configuration, the switching circuit stops operating when the voltage applied to it is less than a certain threshold voltage. This threshold voltage is, for example, the certain voltage. The switching circuit's operation is independent of whether the voltage across the switching circuit is less than the threshold voltage; it indicates a fault in the detection circuit. By determining whether the switching circuit is operating, a fault in the detection circuit can be detected.

[0049] [Details of the embodiments of this disclosure]

[0050] Hereinafter, specific examples of power supply systems according to embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to these examples, but is disclosed in the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0051] (Implementation Method 1)

[0052] <Structure of Power Supply System>

[0053] Figure 1 This is a block diagram showing the main structural components of the power system 1 according to Embodiment 1. The power system 1 is mounted in a vehicle and includes a DC power supply 10, a first load 11, a second load 12, and a power supply control device 13. The DC power supply 10 is, for example, a battery. The power system 1 uses a first wire W1 and a second wire W2 with non-negligible resistance values ​​in its connections. The equivalent circuits of each of the first wire W1 and the second wire W2 are represented by the resistances Rw1 and Rw2 of the first wire and the second wire, respectively. As an example of the first wire W1 and the second wire W2, long wires can be cited. When the first wire W1 is long, the resistance value of the first wire Rw1 is non-negligible. When the second wire W2 is long, the resistance value of the second wire Rw2 is also non-negligible.

[0054] The negative terminal of the DC power supply 10 is connected to the grounding conductor G. Grounding is achieved through this connection to the grounding conductor G. The grounding conductor G is, for example, the body of a vehicle. The positive terminal of the DC power supply 10 is connected to the power supply control device 13 and one end of the first lead resistor Rw1. The other end of the first lead resistor Rw1 is connected to the power supply control device 13. The power supply control device 13 is also connected to one end of the first load 11, the second load 12, and the second lead resistor Rw2. The other ends of the power supply control device 13, the first load 11, the second load 12, and the second lead resistor Rw2 are connected to the grounding conductor G.

[0055] DC power supply 10 supplies power to power supply control device 13. At this time, current flows from the positive terminal of DC power supply 10 in the order of power supply control device 13 and grounding conductor G. DC power supply 10 also supplies power to the first load 11. At this time, current flows from the positive terminal of DC power supply 10 in the order of power supply control device 13, first load 11, and grounding conductor G. DC power supply 10 also supplies power to the second load 12. At this time, current flows from the positive terminal of DC power supply 10 in the order of first conductor resistance Rw1, power supply control device 13, second load 12, and grounding conductor G.

[0056] The power supply control device 13 controls the power supply from the DC power supply 10 to the first load 11 and the power supply from the DC power supply 10 to the second load 12. The first load 11 and the second load 12 are electrical devices mounted on the vehicle. The first load 11 and the second load 12 operate when power is supplied. The first load 11 and the second load 12 stop operating when the power supply is stopped.

[0057] <Structure of Power Supply Control Device 13>

[0058] The power supply control device 13 includes a first controller 21, a second controller 22, a regulator 23, a first detection circuit 24, a second detection circuit 25, and a microcomputer 26. Within the power supply control device 13, the first controller 21, regulator 23, and first detection circuit 24 are connected to the positive terminal of the DC power supply 10. The first controller 21 is also connected to one end of the upstream side of the first load 11 and the microcomputer 26. The regulator 23 and the first detection circuit 24 are also connected to the microcomputer 26. The first controller 21, first detection circuit 24, and microcomputer 26 are connected to the grounding conductor G.

[0059] The second controller 22 and the second detection circuit 25 are respectively connected to one end downstream of the first conductor resistor Rw1, the microcomputer 26, and one end of the second conductor resistor Rw2. The second controller 22 is also connected to one end upstream of the second load 12. The second detection circuit 25 is also connected to the grounding conductor G.

[0060] Current flows from the positive terminal of the DC power supply 10 in sequence to the first controller 21 and the grounding conductor G, supplying power to the first controller 21. The first controller 21 has a first FET 30 that functions as a semiconductor switch (see reference). Figure 2 DC power supply 10 supplies power to first load 11 via first FET 30. Microcomputer 26 outputs first indication signals representing high-level voltage and low-level voltage to first controller 21.

[0061] In the first controller 21, when the first load current flowing through the first load 11 is less than a certain first threshold current, and the voltage indicated by the first indication signal switches from a low level voltage to a high level voltage, the first FET 30 switches to the ON position. As a result, current flows from the positive terminal of the DC power supply 10 in the order of the first FET 30, the first load 11, and the ground conductor G, supplying power to the first load 11. When the voltage indicated by the first indication signal switches from a high level voltage to a low level voltage, or when the first load current rises to a current exceeding the first threshold current, the first FET 30 switches to the OFF position. As a result, power supply to the first load 11 stops, and the first load 11 ceases operation.

[0062] Hereinafter, the voltage at the positive terminal of the DC power supply 10 will be referred to as the power supply voltage. The reference potential of the power supply voltage is the potential of the ground conductor G. The ground of the microcomputer 26 is the potential of the ground conductor G. The power supply voltage varies due to various main reasons. The first detection circuit 24 detects the power supply voltage. The first detection circuit 24 outputs a voltage representing the detected power supply voltage as power supply voltage information to the microcomputer 26. Based on the power supply voltage represented by the power supply voltage information, the microcomputer 26 switches the voltage represented by the first indication signal to a high-level voltage or a low-level voltage. Thus, the switching of the first FET 30 corresponding to the power supply voltage is realized.

[0063] Regulator 23 steps down the power supply voltage to a certain level and applies the stepped-down voltage to the microcomputer 26. As a result, current flows from the positive terminal of the DC power supply 10 through regulator 23, microcomputer 26, and grounding conductor G, supplying power to the microcomputer 26. The reference potential of the stepped-down voltage by regulator 23 is the potential of the grounding conductor G.

[0064] Current flows from the positive terminal of the DC power supply 10 in the following order: first conductor resistor Rw1, second controller 22, second conductor resistor Rw2, and ground conductor G. The DC power supply 10 supplies power to the second controller 22. The second controller 22 has a second FET 40 that functions as a semiconductor switch (see reference). Figure 3 DC power supply 10 supplies power to second load 12 via second FET 40. Microcomputer 26 outputs a second indication signal, representing high-level voltage and low-level voltage, to second controller 22.

[0065] When the second load current flowing through the second load 12 is less than a certain second threshold current, and the voltage indicated by the second indicator signal switches from a low level to a high level, the second FET 40 switches on. As a result, current flows from the positive terminal of the DC power supply 10 in the order of the first wire resistor Rw1, the second FET 40, the second load 12, and the ground conductor G, supplying power to the second load 12. When the voltage indicated by the second indicator signal switches from a high level to a low level, or when the second load current rises to a current exceeding the second threshold current, the second FET 40 switches off. As a result, power supply to the second load 12 stops, and the second load 12 ceases operation.

[0066] As described above, in the power supply control device 13, the power supply via the first FET 30 is controlled by switching the first FET 30 on or off. Furthermore, the power supply via the second FET 40 is controlled by switching the second FET 40 on or off.

[0067] The first FET 30 and the second FET 40 are N-channel FETs. Current is input to the drain of the first FET 30 and the second FET 40, respectively, and current is output from the source. In the first FET 30 and the second FET 40, the drain functions as the input terminal for the input current, and the source functions as the output terminal for the output current.

[0068] The voltage at the drain of the second FET 40 will be described as the circuit voltage. The reference potential of the circuit voltage is the potential at one end of the upstream side of the second conductor resistor Rw2. The circuit voltage changes when the power supply voltage changes. The second detection circuit 25 detects the circuit voltage and outputs the voltage representing the detected circuit voltage as circuit voltage information to the microcomputer 26. The reference potential of the circuit voltage information is the ground of the microcomputer 26, i.e., the potential of the ground conductor G. Based on the circuit voltage information, the microcomputer 26 switches the voltage represented by the second indication signal to a high-level voltage or a low-level voltage. This achieves the switching of the second FET 40 corresponding to the circuit voltage.

[0069] <Structure of the first controller 21>

[0070] Figure 2 This is a circuit diagram of the first controller 21 and the first detection circuit 24. In addition to the first FET 30, the first controller 21 also includes a first output section 31, a first drive circuit 32, and a first voltage resistor 33. The drain of the first FET 30 is connected to the positive terminal of the DC power supply 10. The source of the first FET 30 is connected to the first output section 31. The first output section 31 is also connected to one end of the upstream side of the first load 11 and one end of the first voltage resistor 33. The drain and gate of the first FET 30 are connected to the first drive circuit 32. The first drive circuit 32 is also connected to the microcomputer 26. The connection node between the first output section 31 and the first voltage resistor 33 is connected to the microcomputer 26 and the first drive circuit 32. The other end of the first drive circuit 32 and the first voltage resistor 33 is connected to the ground conductor G.

[0071] In the first FET 30, when the gate voltage, which is at the source potential (reference potential), is above a certain first switching voltage, the resistance between the drain and source of the first FET 30 is very small. At this time, the first FET 30 is turned on, and current can flow through its drain and source. When the first FET 30 is turned on, current flows from the positive terminal of the DC power supply 10 in the order of the first FET 30, the first output section 31, the first load 11, and the ground conductor G. In the first FET 30, when the gate voltage, which is at the source potential (reference potential), is less than the first switching voltage, the resistance between the drain and source of the first FET 30 is very large. At this time, the first FET 30 is turned off, and current does not flow through its drain and source.

[0072] Current flows from the positive terminal of the DC power supply 10 in sequence through the first drive circuit 32 and the grounding conductor G, supplying power to the first drive circuit 32. The first drive circuit 32 operates when the power supply voltage rises above a certain first operating voltage. The first drive circuit 32 stops operating when the power supply voltage drops below the first operating voltage. The grounding of the first drive circuit 32 is the potential of the grounding conductor G.

[0073] The first driving circuit 32 boosts the power supply voltage and applies the boosted voltage to the gate of the first FET 30. As a result, the gate voltage of the first FET 30, which has a reference potential equal to the source potential, rises to a voltage above the first switching voltage. Consequently, the first FET 30 switches to ON. The reference potential of the boosted voltage is the potential of the ground conductor G. When the first driving circuit 32 stops boosting, the gate voltage of the first FET 30, which has a reference potential equal to the source potential, drops to a voltage below the first switching voltage. Consequently, the first FET 30 switches to OFF. As described above, the first driving circuit 32 switches the first FET 30 ON or OFF by adjusting the gate voltage of the first FET 30.

[0074] The first output unit 31, for example, is configured using a current mirror circuit, and outputs a current proportional to the first load current flowing through the first FET 30 to the first voltage resistor 33. The resistance value of the first voltage resistor 33 is constant. Therefore, the voltage across the first voltage resistor 33 is proportional to the current flowing through the first voltage resistor 33. Thus, the voltage across the first voltage resistor 33 is proportional to the first load current. The voltage across the first voltage resistor 33 is output to the microcomputer 26 and the first drive circuit 32 as first current information representing the first load current.

[0075] As previously described, the microcomputer 26 outputs a first indication signal to the first driving circuit 32. When the first load current indicated by the first current information is less than the first threshold current, and when the voltage indicated by the first indication signal switches from a low level to a high level, the first driving circuit 32 switches the first FET 30 to the ON position. When the voltage indicated by the first indication signal switches from a high level to a low level, or when the first load current indicated by the first current information becomes a current exceeding the first threshold current, the first driving circuit 32 switches the first FET 30 to the OFF position.

[0076] The microcomputer 26 communicates with the first driving circuit 32. By communicating with the first driving circuit 32, the microcomputer 26 can determine whether the first driving circuit 32 is operational. For example, the microcomputer 26 sends a request signal demanding the transmission of a response signal to the first driving circuit 32. The microcomputer 26 determines whether the first driving circuit 32 is operational based on whether it receives a response signal from the first driving circuit 32.

[0077] <Structure of the first detection circuit 24>

[0078] The first detection circuit 24 has two voltage divider resistors, Rd1 and Rd2. One end of voltage divider resistor Rd1 is connected to the positive terminal of DC power supply 10. The other end of voltage divider resistor Rd1 is connected to one end of voltage divider resistor Rd2. The other end of voltage divider resistor Rd2 is connected to the ground conductor G. The connection node between the two voltage divider resistors Rd1 and Rd2 is connected to the microcomputer 26.

[0079] The first detection circuit 24 divides the power supply voltage. The resistance values ​​of the two voltage divider resistors Rd1 and Rd2 are constant. Therefore, the voltage obtained by the first detection circuit 24 through voltage division of the power supply voltage is proportional to the power supply voltage. The first detection circuit 24 detects the power supply voltage by dividing the power supply voltage. The first detection circuit 24 outputs the voltage obtained by voltage division as power supply voltage information to the microcomputer 26. As mentioned above, the microcomputer 26 switches the voltage represented by the first indication signal to a high-level voltage or a low-level voltage according to the power supply voltage represented by the power supply voltage information.

[0080] <Structure of the second controller 22>

[0081] Figure 3 This is a circuit diagram of the second controller 22 and the second detection circuit 25. In addition to the second FET 40, the second controller 22 also includes a second output section 41, a second drive circuit 42, and a second voltage resistor 43. The drain of the second FET 40 is connected to one end downstream of the first lead resistor Rw1. One end upstream of the first lead resistor Rw1 is connected to the positive terminal of the DC power supply 10. The source of the second FET 40 is connected to the second output section 41. The second output section 41 is also connected to one end upstream of the second load 12 and one end of the second voltage resistor 43. The drain and gate of the second FET 40 are respectively connected to the second drive circuit 42. The second drive circuit 42 is also connected to the microcomputer 26. The connection node between the second output section 41 and the second voltage resistor 43 is connected to the microcomputer 26 and the second drive circuit 42. The other end of the second drive circuit 42 and the second voltage resistor 43 is connected to one end upstream of the second lead resistor Rw2. As mentioned above, one end downstream of the second lead resistor Rw2 is connected to the ground conductor G.

[0082] In the second FET 40, when the gate voltage at the source potential (reference potential) is above a certain second switching voltage, the resistance between the drain and source of the second FET 40 is very small. At this time, the second FET 40 is turned on, and current can flow through its drain and source. When the second FET 40 is turned on, current flows from the positive terminal of the DC power supply 10 in the order of the second FET 40, the second output section 41, the second load 12, and the ground conductor G. In the second FET 40, when the gate voltage at the source potential (reference potential) is less than the second switching voltage, the resistance between the drain and source of the second FET 40 is very large. At this time, the second FET 40 is turned off, and current does not flow through its drain and source.

[0083] Current flows from the positive terminal of the DC power supply 10 in the order of the first conductor resistor Rw1, the second drive circuit 42, the second conductor resistor Rw2, and the ground conductor G. This supplies power to the second drive circuit 42. The second drive circuit 42 operates when the circuit voltage rises to a level above the second operating voltage. The second drive circuit 42 stops operating when the circuit voltage drops below the second operating voltage. The ground of the second drive circuit 42 is the potential of one end upstream of the second conductor resistor Rw2. When power is supplied to the second drive circuit 42, current flows from the drain of the second FET 40 in the order of the second drive circuit 42 and its ground.

[0084] The second drive circuit 42 adjusts the reference potential to the voltage of its grounded gate. As mentioned earlier, the reference potential of the circuit voltage is the potential at one end of the upstream side of the second wire resistor Rw2, i.e., the ground of the second drive circuit 42. The second drive circuit 42 boosts the circuit voltage and applies the boosted voltage to the gate of the second FET 40. Thus, in the second FET 40, the gate voltage, where the reference potential is the source potential, rises to a voltage above the second switching voltage. As a result, the second FET 40 switches on. The reference potential of the boosted voltage is the ground of the second drive circuit 42.

[0085] The second drive circuit 42 stops the voltage boosting of the circuit. As a result, the voltage at the gate of the second drive circuit 42, which is grounded, drops. Consequently, in the second FET 40, the voltage at the gate of the source, which is the reference potential, drops to a level lower than the second switching voltage. Therefore, the second FET 40 switches off.

[0086] The second output section 41 is configured, for example, using a current mirror circuit, and outputs a current proportional to the second load current flowing through the second FET 40 to the second load 12. The second output section 41 functions as a current output section. The current output by the second output section 41 flows through the second voltage resistor 43 and the second wire resistor Rw2. The resistance value of the second voltage resistor 43 is constant. Therefore, the voltage across the second voltage resistor 43 is proportional to the current flowing through it. Thus, the voltage across the second voltage resistor 43 is proportional to the second load current. The voltage across the second voltage resistor 43 is output to the second drive circuit 42 as a second current information representing the second load current.

[0087] The resistance value of the second conductor resistor Rw2 is also constant. Therefore, the voltage across the series circuit connecting the second voltage resistor 43 and the second conductor resistor Rw2 is proportional to the current flowing through the second voltage resistor 43. Thus, the voltage across the series circuit is proportional to the second load current. The voltage across the series circuit is output to the microcomputer 26 as another piece of second current information representing the second load current.

[0088] As previously described, the microcomputer 26 outputs a second indication signal to the second driving circuit 42. When the second load current indicated by the second current information is less than the second threshold current, and when the voltage indicated by the second indication signal switches from a low level to a high level, the second driving circuit 42 switches the second FET 40 to the ON position. When the voltage indicated by the second indication signal switches from a high level to a low level, or when the second load current indicated by the second current information becomes a current exceeding the second threshold current, the second driving circuit 42 switches the second FET 40 to the OFF position.

[0089] Similar to the first driving circuit 32, the microcomputer 26 communicates with the second driving circuit 42. By communicating with the second driving circuit 42, the microcomputer 26 can determine whether the second driving circuit 42 is operational. For example, the microcomputer 26 sends a request signal demanding a response signal to the second driving circuit 42, and determines whether the second driving circuit 42 is operational based on whether a response signal is received from the second driving circuit 42.

[0090] <Structure of the second detection circuit 25>

[0091] The second detection circuit 25 has a current output device 50 and a circuit resistor 51. The current output device 50 has a device resistor Re and a transistor Te. The transistor Te is a PNP bipolar transistor.

[0092] One end of the device resistor Re is connected to the drain of the second FET 40. The other end of the device resistor Re is connected to the emitter of the transistor Te. The base of the transistor Te is connected to one end of the upstream side of the second wire resistor Rw2. Therefore, the potential of the base of the transistor Te is the ground of the second drive circuit 42. The collector of the transistor Te is connected to the microcomputer 26 and one end of the circuit resistor 51. The other end of the circuit resistor 51 is connected to the ground conductor G.

[0093] Current flows from the positive terminal of DC power supply 10 in the following order: first conductor resistor Rw1, device resistor Re, transistor Te, circuit resistor 51, and ground conductor G. Therefore, current flows from the downstream end of the first conductor resistor Rw1, i.e., the drain of the second FET 40, to the device resistor Re. In transistor Te, current flows in the order of emitter and collector. The emitter of transistor Te is connected to the downstream end of the device resistor Re.

[0094] In transistor Te, a very small portion of the current input from the device resistor Re to the emitter flows from the base in the order of the second conductor resistor Rw2 and the ground conductor G. Almost all of the current input to the emitter exits from the collector. Therefore, the current exiting from the base is negligible, and the current input to the emitter is essentially the same as the current exiting from the collector.

[0095] The voltage at the drain of the second FET40 is denoted as Vd. The voltage at one end of the upstream side of the second conductor resistor Rw2 is denoted as Vg. The reference potentials for voltages Vd and Vg are the potentials of the ground conductor G. (Vd-Vg) is the circuit voltage. The resistance value of the device resistor Re is denoted as re. The absolute value of the voltage between the base and emitter of transistor Te is denoted as Vf. The current flowing through the device resistor Re is denoted as Iv.

[0096] The transistor Te adjusts the resistance between its emitter and collector such that the voltage across its emitter, which is the reference potential of the ground conductor G, is (Vg + Vf). As a result, the transistor Te adjusts the resistance between its emitter and collector such that the current Iv satisfies the following equation (1).

[0097] Iv=(Vd-(Vg+Vf)) / re…(1)

[0098] As mentioned earlier, almost all of the current input to the emitter is output from the collector. Therefore, the current flowing through circuit resistor 51 is essentially the same as the current Iv.

[0099] By expanding equation (1), we can obtain equation (2) below.

[0100] Iv=((Vd-Vg)-Vf) / re…(2)

[0101] As mentioned earlier, (Vd-Vg) is the circuit voltage. The voltage Vf and resistance re are essentially constant, therefore the current Iv is proportional to the circuit voltage. Thus, the current output device 50 converts the circuit voltage into a current Iv proportional to the circuit voltage and outputs the converted current Iv to the circuit resistor 51. The current Iv is introduced from the drain of the second FET 40. The current Iv output from the collector of the transistor Te in the current output device 50 flows through the circuit resistor 51. The current output device 50 detects the circuit voltage by outputting the current Iv.

[0102] The resistance value of circuit resistor 51 is recorded as rc. The voltage between the two ends of circuit resistor 51 is recorded as Vc. The voltage Vc is expressed by the following equation (3).

[0103] Vc=rc·Iv…(3)

[0104] "·" indicates product. When the current Iv is eliminated using equations (2) and (3), the voltage Vc satisfies the following equation (4).

[0105] Vc=((Vd-Vg)-Vf)·rc / re…(4)

[0106] As mentioned earlier, (Vd-Vg) is the circuit voltage. Not only are the voltage Vf and the resistance value re, but the resistance value rc is also essentially a constant value. Therefore, the voltage Vc is proportional to the circuit voltage. Since the voltage Vf and the resistance values ​​rc and re are essentially constant values, substituting the voltage Vc into equation (4) allows us to calculate the circuit voltage, i.e., (Vd-Vg).

[0107] As described above, the second detection circuit 25 detects the circuit voltage and outputs a voltage Vc proportional to the detected circuit voltage as circuit voltage information to the microcomputer 26. The microcomputer 26 calculates the circuit voltage based on the circuit voltage information, i.e., voltage Vc and equation (4). The grounding of the microcomputer 26, as previously described, is the potential of the grounding conductor G, which is different from the grounding of the second drive circuit 42. However, in the second detection circuit 25, the current output device 50 converts the circuit voltage into a current Iv, thus enabling the microcomputer 26 to calculate the circuit voltage.

[0108] When power is supplied to the second drive circuit 42, current flows from the positive terminal of the DC power supply 10 in the following order: first conductor resistor Rw1, second drive circuit 42, second conductor resistor Rw2, and ground conductor G. One downstream end of the circuit resistor 51 is connected to the ground conductor G. As previously mentioned, the potential of one upstream end of the second conductor resistor Rw2 is the ground of the second drive circuit 42. When power is supplied to the second drive circuit 42, current flows through the second conductor resistor Rw2, therefore the voltage between the ground of the second drive circuit 42 and one downstream end of the circuit resistor 51 exceeds 0V.

[0109] As previously stated, the current output from the second output unit 41 is proportional to the second load current and flows through the second lead resistor Rw2. Therefore, when the second FET 40 is off, the current output from the second output unit 41 is 0A. When the second FET 40 is switched on, the current output from the second output unit 41 increases. Consequently, the current flowing through the second lead resistor Rw2 also increases. Furthermore, when the second FET 40 is off, the current flowing through the first lead resistor Rw1 is only the current flowing through the second drive circuit 42, which is relatively small. When the second FET 40 is switched on, the current flowing through the first lead resistor Rw1 is the sum of the current flowing through the second drive circuit 42 and the current flowing through the second FET 40. Based on the above, the circuit voltage when the second FET 40 is off is higher than the circuit voltage when the second FET 40 is on.

[0110] As mentioned above, the current output by the second output unit 41 flows through the second wire resistor Rw2. Therefore, the voltage between the two ends of the second wire resistor Rw2, that is, the voltage between the ground of the second drive circuit 42 and one end downstream of the circuit resistor 51, varies according to the current output by the second output unit 41.

[0111] <Structure of Microcomputer 26>

[0112] Figure 4 This is a block diagram showing the main structural components of the microcomputer 26. The microcomputer 26 includes A / D conversion units 60, 61, 62, and 63; signal output units 64 and 65; communication units 66 and 67; notification units 68; storage units 69; and control units 70. The A / D conversion units 60, 61, 62, and 63, signal output units 64 and 65, communication units 66 and 67, notification units 68, storage units 69, and control units 70 are connected to an internal bus 71.

[0113] The A / D converter 60 is also connected to the connection node between the voltage divider resistors Rd1 and Rd2 in the first detection circuit 24. The signal output unit 64 and the communication unit 66 are also connected to the first drive circuit 32. The A / D converter 61 is also connected to the connection node between the first output unit 31 and the first voltage resistor 33 in the first controller 21. The A / D converter 62 is also connected to one end of the upstream side of the circuit resistor 51 in the second detection circuit 25. The signal output unit 65 and the communication unit 67 are also connected to the second drive circuit 42. The A / D converter 63 is connected to the connection node between the second output unit 41 and the second voltage resistor 43 in the second controller 22.

[0114] The first detection circuit 24 inputs analog power supply voltage information to the A / D converter 60. The A / D converter 60 converts the input analog power supply voltage information into digital power supply voltage information. The control unit 70 obtains the digital power supply voltage information from the A / D converter 60.

[0115] The signal output unit 64 outputs a first indication signal to the first drive circuit 32. According to the instructions of the control unit 70, the signal output unit 64 converts the voltage represented by the first indication signal into a high-level voltage or a low-level voltage.

[0116] The communication unit 66 sends signals to the first drive circuit 32 according to the instructions of the control unit 70. The communication unit 66 also receives signals from the first drive circuit 32.

[0117] The first controller 21 inputs analog first current information to the A / D converter 61. The A / D converter 61 converts the input analog first current information into digital first current information. The control unit 70 obtains the digital first current information from the A / D converter 61.

[0118] The analog circuit voltage information is input from the second detection circuit 25 to the A / D conversion unit 62. The A / D conversion unit 62 converts the input analog circuit voltage information into digital circuit voltage information. The control unit 70 obtains the digital circuit voltage information from the A / D conversion unit 62.

[0119] The signal output unit 65 outputs the second indication signal to the second drive circuit 42. According to the instructions of the control unit 70, the signal output unit 65 switches the voltage represented by the second indication signal to a high-level voltage or a low-level voltage.

[0120] The communication unit 67 sends signals to the second drive circuit 42 according to the instructions of the control unit 70. The communication unit 67 also receives signals from the second drive circuit 42.

[0121] Analog second current information is input from the second controller 22 to the A / D converter 63. The A / D converter 63 converts the input analog second current information into digital second current information. The control unit 70 obtains the digital second current information from the A / D converter 63.

[0122] Notification unit 68 issues notifications according to the instructions of control unit 70. Notifications are made through signal transmission, light activation, or message display.

[0123] Storage unit 69 is, for example, non-volatile memory. Computer program P is stored in storage unit 69. Control unit 70 has a processing element that performs the processing, such as a CPU (Central Processing Unit). The processing element of control unit 70 performs first fault detection processing, first power supply control processing, second fault detection processing, and second power supply control processing, etc., by executing computer program P. Control unit 70 functions as a processing unit.

[0124] The first fault detection process is the processing of faults related to the first controller 21 or the first detection circuit 24. The first power supply control process is the processing of controlling the power supply to the first load 11. The second fault detection process is the processing of faults related to the second controller 22 or the second detection circuit 25. The second power supply control process is the processing of controlling the power supply to the second load 12.

[0125] It should be noted that the computer program P can also be stored on the storage medium A in a manner readable by the processing element of the control unit 70. In this case, the computer program P, read from the storage medium A by a read device (not shown), is written to the storage unit 69. The storage medium A is an optical disc, floppy disk, magnetic disk, magneto-optical disk, or semiconductor memory, etc. The optical disc is a CD (CompactDisc)-ROM (Read Only Memory), DVD (Digital Versatile Disc)-ROM, or BD (Blu-ray Disc), etc. The magnetic disk is, for example, a hard disk. Furthermore, the computer program P can also be downloaded from a device (not shown) connected to a communication network (not shown), and the downloaded computer program P can be written to the storage unit 69.

[0126] The number of processing elements in the control unit 70 is not limited to one; it can also be two or more. In this case, multiple processing elements can also collaboratively execute the first fault detection processing, the first power supply control processing, the second fault detection processing, the second power supply control processing, etc., according to the computer program P.

[0127] When comparing the technology of this disclosure with the prior art, the main differences lie in the second fault detection process and the second power supply control process. Therefore, the second fault detection process and the second power supply control process will be explained first below. Then, the first fault detection process will be explained by describing the differences between the first fault detection process and the second fault detection process. The first power supply control process will be explained by describing the differences between the first power supply control process and the second power supply control process. These processes will be explained based on the assumption that the first load current does not rise above the first threshold current and the second load current does not rise above the second threshold current.

[0128] <Second Fault Detection and Handling>

[0129] Figure 5 This is a flowchart illustrating the sequence of the second fault detection processing. The control unit 70 performs the second fault detection processing before activating the second load 12. For example, the control unit 70 performs the second fault detection processing when the vehicle's engine is started while the second load 12 is stopped. Therefore, the second fault detection processing is performed with the second FET 40 disconnected. If no fault is detected during the second fault detection processing, the control unit 70 performs the second power supply control processing.

[0130] In the second fault detection process, the control unit 70 obtains circuit voltage information from the A / D conversion unit 62 (step S1). The circuit voltage information obtained in step S1 is the voltage output by the second detection circuit 25 when the second FET 40 is off. The circuit voltage indicated by the circuit voltage information obtained in step S1 is higher than the circuit voltage when the second FET 40 is on. Next, the control unit 70 determines whether the circuit voltage indicated by the circuit voltage information obtained in step S1 is less than the second operating voltage (step S2). If the circuit voltage is less than the second operating voltage, the second drive circuit 42 stops operating. The second operating voltage functions as a threshold voltage.

[0131] If the control unit 70 determines that the circuit voltage indicated by the circuit voltage information is less than the second operating voltage (S2: Yes), it determines whether the second drive circuit 42 is operating (step S3). If the second drive circuit 42 is operating at the point where step S3 is executed, it indicates that the second detection circuit 25 is not outputting an appropriate voltage, i.e., a fault has occurred in the second detection circuit 25. The control unit 70 can detect the fault in the second detection circuit 25 by executing step S2.

[0132] As a method for determining whether the second drive circuit 42 is working, a communication method can be used. In this method, the control unit 70, for example, causes the communication unit 66 to send a request signal requesting the transmission of a response signal to the second drive circuit 42. If the communication unit 66 receives a response signal within a predetermined period from the time the request signal was sent, the control unit 70 determines that the second drive circuit 42 is working. If the communication unit 66 does not receive a response signal within the predetermined period from the time the request signal was sent, the control unit 70 determines that the second drive circuit 42 is not working.

[0133] As another method for determining whether the second drive circuit 42 is working, a method for confirming the state of the second FET 40 can be listed. In this method, the control unit 70, for example, instructs the signal output unit 65 to switch the voltage represented by the second indication signal from a low level voltage to a high level voltage. When the second indication signal represents a high level voltage, the control unit 70 obtains second current information from the A / D conversion unit 63 and instructs the signal output unit 65 to return the voltage represented by the second indication signal to a low level voltage. If the second load current represented by the second current information is above a certain value, it indicates that the second FET 40 is turned on. If the second load current represented by the second current information is below a certain value, it indicates that the second FET 40 is turned off. If the second load current represented by the second current information is above a certain value, the control unit 70 determines that the second drive circuit 42 is working. If the second load current represented by the second current information is below a certain value, the control unit 70 determines that the second drive circuit 42 is not working.

[0134] If the control unit 70 determines that the second drive circuit 42 is operating (S3: Yes), it fixes the second FET 40 to either be on or off as if a fault has occurred in the second detection circuit 25 (step S4). The control unit 70 instructs the signal output unit 65 to fix the voltage represented by the second indication signal to a high level, thereby fixing the second FET 40 to be on. Alternatively, the control unit 70 instructs the signal output unit 65 to fix the voltage represented by the second indication signal to a low level, thereby fixing the second FET 40 to be off.

[0135] The second load 12 is fixed to be on or off based on its characteristics. A load that would not cause a malfunction if it were to operate without a function, such as an indoor light, is assumed to be the second load 12. In this case, in step S4, the control unit 70 fixes the second FET 40 to be off. A load that would cause a malfunction if it were to operate without a function, such as a headlight, is assumed to be the second load 12. In this case, in step S4, the control unit 70 fixes the second FET 40 to be on.

[0136] If the control unit 70 determines that the circuit voltage indicated by the circuit voltage information is above the second operating voltage (S2: No), it determines whether the circuit voltage indicated by the circuit voltage information obtained in step S1 is an on-state voltage (step S5). When the circuit voltage is low, the second drive circuit 42 cannot boost the circuit voltage to the voltage required to switch the second FET 40 to on. The on-state voltage is a voltage that can boost the voltage required to switch the second FET 40 to on, and it is a voltage within a preset voltage range. Even when the circuit voltage is on when the second FET 40 is off, the circuit voltage is high, and the second drive circuit 42 can switch the second FET 40 to on.

[0137] When the control unit 70 determines that the circuit voltage is the on-state voltage (S5: Yes), it instructs the signal output unit 65 to switch the second FET 40 to on (step S6). Specifically, the control unit 70 instructs the signal output unit 65 to switch the voltage represented by the second instruction signal from a low level voltage to a high level voltage. As a result, the second drive circuit 42 switches the second FET 40 to on.

[0138] Next, the control unit 70 determines whether the second FET 40 is turned on based on the second load current represented by the second current information obtained from the A / D conversion unit 63 (step S7). In step S7, the control unit 70 determines that the second FET 40 is turned on if the second load current is above a certain value. The control unit 70 determines that the second FET 40 is not turned on if the second load current is below a certain value. The control unit 70 confirms whether the second FET 40 can be switched on by executing steps S6 and S7.

[0139] When the control unit 70 determines that the second FET 40 is turned on (S7: Yes), it instructs the signal output unit 65 to switch the second FET 40 to turn off (step S8). Specifically, the control unit 70 instructs the signal output unit 65 to switch the voltage represented by the second instruction signal to a low-level voltage. As a result, the second drive circuit 42 switches the second FET 40 off. After executing step S8, the control unit 70 ends the second fault detection process. After executing step S8 and ending the second fault detection process, the control unit 70 executes the second power supply control process.

[0140] If the control unit 70 determines that the second drive circuit is not working (S3: No), or after executing step S4, determines that the circuit voltage is not the on-state voltage (S5: No), or determines that the second FET 40 is not turned on (S7: No), it causes the notification unit 68 to issue a notification (step S9). If the control unit 70 determines that the second drive circuit is not working or that the circuit voltage is not the on-state voltage, it instructs the notification unit 68 to output a signal indicating a low circuit voltage to a device (not shown). In the notification issued after executing step S4, a signal indicating a fault in the second detection circuit 25 is output to the device. If the control unit 70 determines that the second FET 40 is not turned on, it instructs the notification unit 68 to output a signal indicating a fault in the second detection circuit 25 or the second drive circuit 42 to the device.

[0141] After executing step S9, the control unit 70 terminates the second fault detection process. If the control unit 70 terminates the second fault detection process after executing step S9, it does not execute the second power supply control process.

[0142] <Second Power Supply Control Process>

[0143] Figure 6 This is a flowchart illustrating the sequence of the second power supply control process. The second power supply control process is executed with the second FET 40 disconnected. In the second power supply control process, the control unit 70 determines whether to activate the second load 12 (step S11). If, for example, a receiving device (not shown) receives an instruction to activate the second load 12, the control unit 70 determines that the second load 12 should be activated. If the receiving device does not receive an instruction to activate the second load 12, the control unit 70 determines that the second load 12 should not be activated.

[0144] If the control unit 70 determines that the second load 12 should not be operated (S11: No), it terminates the second power supply control process and restarts the second power supply control process. Therefore, if the control unit 70 determines in step S11 that the second load 12 should not be operated, it executes step S11 again.

[0145] When the control unit 70 determines that the second load 12 should be activated (S11: Yes), it obtains circuit voltage information from the A / D conversion unit 62 (step S12). The circuit voltage represented by the circuit voltage information obtained in step S12 is the circuit voltage when the second FET 40 is off. Next, the control unit 70 determines whether the circuit voltage represented by the circuit voltage information obtained in step S12 is within the normal range (step S13). The normal range is the range of circuit voltages within which the second drive circuit 42 can appropriately switch the second FET 40 to be on or off.

[0146] If the control unit 70 determines that the circuit voltage is within the normal range (S13: Yes), it instructs the signal output unit 65 to switch the second FET 40 to turn on, similar to step S6 of the second fault detection process (step S14). Power is then supplied to the second load 12, and the second load 12 operates. After executing step S14, the control unit 70 obtains circuit voltage information from the A / D conversion unit 62 (step S15). The circuit voltage represented by the circuit voltage information obtained in step S15 is the circuit voltage when the second FET 40 is turned on.

[0147] Next, the control unit 70 determines whether the circuit voltage indicated by the circuit voltage information obtained in step S15 is within the normal range (step S16). If the control unit 70 determines that the circuit voltage is within the normal range (S16: Yes), it determines whether to stop the operation of the second load 12 (step S17). For example, if the receiving device receives a stop instruction from the second load 12, the control unit 70 determines to stop the operation of the second load 12. If the receiving device does not receive a stop instruction from the second load 12, the control unit 70 determines not to stop the operation of the second load 12.

[0148] If the control unit 70 determines that the operation of the second load 12 should not be stopped (S17: No), it executes step S15 again, repeatedly executing steps S16 and S17 until the circuit voltage becomes outside the normal range or the operation of the second load 12 is stopped. If the control unit 70 determines that the circuit voltage is not within the normal range (S16: No) or determines that the operation of the second load 12 should be stopped (S17: Yes), it instructs the signal output unit 65 to switch the second FET 40 to disconnect (step S18), similar to step S8 of the second fault detection process, and ends the second power supply control process. After ending the second power supply control process, the control unit 70 executes the second power supply control process again. For example, if the engine stops operating, the control unit 70 stops the repetition of the second power supply control process.

[0149] As described above, in the second power supply control process, based on the circuit voltage information output by the second detection circuit 25, the control unit 70 instructs the signal output unit 65 to switch the second FET 40 to either be on or off. The second drive circuit 42 switches the second FET 40 to be on or off according to the instruction of the control unit 70. Therefore, based on the circuit voltage detected by the second detection circuit 25, the second FET 40 is appropriately switched to be on or off by the second drive circuit 42. The power supply to the second load 12 is appropriately controlled. The second drive circuit 42 functions as a switching circuit.

[0150] <First Fault Detection and Handling and First Power Supply Control Processing>

[0151] The control unit 70 performs the first fault detection process in the same way as the second fault detection process. The control unit 70 performs the first power supply control process in the same way as the second power supply control process. The second FET 40, the second drive circuit 42, the circuit voltage information, the second operating voltage, and the second current information described in the description of the second fault detection process and the second power supply control process correspond to the first FET 30, the first drive circuit 32, the power supply voltage information, the first operating voltage, and the first current information in the first fault detection process and the first power supply control process, respectively.

[0152] Furthermore, the A / D conversion units 62 and 63, the signal output unit 65, and the communication unit 67 described in the description of the second fault detection processing and the second power supply control processing correspond to the A / D conversion units 60 and 61, the signal output unit 64, and the communication unit 66, respectively, in the first fault detection processing and the first power supply control processing. The normal range of the first power supply control processing is the range within which the first drive circuit 32 can appropriately switch the first FET 30 to the power supply voltage for on or off.

[0153] (Implementation Method 2)

[0154] In the second power supply control process of Embodiment 1, the second drive circuit 42 switches the second FET 40 to be turned on or off based on whether the circuit voltage is within the normal range. However, the switching of the second FET 40 is not limited to a switching that corresponds to whether the circuit voltage is within the normal range.

[0155] Hereinafter, regarding Embodiment 2, the differences from Embodiment 1 will be explained. All other structures besides those described later are common to Embodiment 1. Therefore, for structural parts common to Embodiment 1, the same reference numerals as in Embodiment 1 will be used, and the description of these structural parts will be omitted.

[0156] <Structure of Microcomputer 26>

[0157] In implementation method 2, Figure 4 The signal output unit 65 shown outputs a second PWM signal to the second drive circuit 42 instead of the second indicator signal. The second PWM signal, like the second indicator signal, represents a high-level voltage and a low-level voltage. Similar to Embodiment 1, the second drive circuit 42 switches the second FET 40 to ON when the voltage represented by the second PWM signal switches from a low-level voltage to a high-level voltage. The second drive circuit 42 switches the second FET 40 to OFF when the voltage represented by the second PWM signal switches from a high-level voltage to a low-level voltage. The second drive circuit 42 keeps the second FET 40 OFF when the output of the second PWM signal stops.

[0158] In the second PWM signal, the switching from a low-level voltage to a high-level voltage occurs periodically. The duty cycle of the second PWM signal is adjusted by changing the timing of the high-level voltage transition. The duty cycle is the proportion of the period in one cycle during which the second PWM signal represents a high-level voltage.

[0159] It should be noted that in the second PWM signal, the switching from a high-level voltage to a low-level voltage can also be performed periodically. In this case, the duty cycle of the second PWM signal is adjusted by changing the timing of the switching from a low-level voltage to a high-level voltage.

[0160] The signal output unit 65 outputs and stops the second PWM signal according to the instruction of the control unit 70. The control unit 70 sets the duty cycle of the second PWM signal in the signal output unit 65. When outputting the second PWM signal, the signal output unit 65 adjusts the duty cycle of the second PWM signal to the set value.

[0161] <Second Power Supply Control Process>

[0162] Figure 7 This is a flowchart illustrating the sequence of the second power supply control process in Embodiment 2. Regarding the second power supply control process in Embodiment 2, steps common to the steps in the second power supply control process of Embodiment 1 are labeled with the same reference numerals, and their descriptions are omitted. The common steps are steps S11, S12, S15, and S17.

[0163] The second power supply control process in Embodiment 2 is the same as in Embodiment 1, and is executed with the second FET 40 disconnected. In the second power supply control process, the control unit 70 first executes step S11. If the control unit 70 determines that the second load 12 should not be operated (S11: No), the second power supply control process ends and starts again. Therefore, if the control unit 70 determines in step S11 that the second load 12 should not be operated, it executes step S11 again.

[0164] If the control unit 70 determines that the second load 12 should be activated (S11: Yes), it executes step S12. After obtaining circuit voltage information from the A / D converter 62 in step S12, the control unit 70 sets the duty cycle of the second PWM signal in the signal output unit 65 to a value corresponding to the circuit voltage represented by the obtained circuit voltage information (step S21). The circuit voltage represented by the circuit voltage information obtained in step S12 is the circuit voltage when the second FET 40 is turned off.

[0165] Next, the control unit 70 instructs the signal output unit 65 to output the second PWM signal to the second drive circuit 42 (step S22). As a result, the second drive circuit 42 alternately switches the second FET 40 on and off repeatedly according to the voltage represented by the second PWM signal. Consequently, current flows in the order of the first wire resistor Rw1, the second FET 40, the second output unit 41, the second load 12, and the ground conductor G, supplying power to the second load 12. The average value of the voltage applied to the second load 12 is adjusted to a value corresponding to the duty cycle of the second PWM signal.

[0166] After executing step S22, control unit 70 executes step S15. In step S15, control unit 70 acquires circuit voltage information during the period when the second FET 40 is turned on, i.e., during the period when the second PWM signal represents a high-level voltage. After acquiring the circuit voltage information in step S15, control unit 70 changes the duty cycle of the second PWM signal to a value corresponding to the circuit voltage represented by the acquired circuit voltage information (step S23). Thus, the duty cycle of the second PWM signal is changed. After executing step S23, control unit 70 executes step S17.

[0167] If the control unit 70 determines that the operation of the second load 12 should not be stopped (S17: No), it executes step S15. The control unit 70 repeatedly changes the duty cycle corresponding to the circuit voltage until it determines that the operation of the second load 12 should be stopped. If the control unit 70 determines that the operation of the second load 12 should be stopped (S17: Yes), it instructs the signal output unit 65 to stop the output of the second PWM signal (step S24), thus ending the second power supply control process. After ending the second power supply control process, the control unit 70 executes the second power supply control process again. For example, the control unit 70 stops the repetition of the second power supply control process when the engine stops operating.

[0168] As described above, in the second power supply control process, the control unit 70 changes the duty cycle of the second PWM signal based on the circuit voltage information output by the second detection circuit 25. The second drive circuit 42 switches the second FET 40 to on or off based on the voltage represented by the second PWM signal. Therefore, the average value of the voltage applied to the second load 12 is adjusted to an appropriate value, and the power supply to the second load 12 is appropriately controlled. In Embodiment 2, the second load 12 is, for example, a lamp.

[0169] The power supply control device 13 and the second detection circuit 25 of Embodiment 2 perform the same functions as the power supply control device 13 and the second detection circuit 25 of Embodiment 1.

[0170] <Note>

[0171] In embodiment 2, the signal output unit 64 can also be configured in the same way as the signal output unit 65. In this case, the signal output unit 64 outputs a first PWM signal that is the same as the second PWM signal, and the first drive circuit 32 switches the first FET 30 to be turned on or off according to the voltage represented by the first PWM signal. The control unit 70 executes the first power supply control process in the same way as the second power supply control process.

[0172] The second FET 40, the second drive circuit 42, and the circuit voltage information described in the description of the second power supply control process correspond to the first FET 30, the first drive circuit 32, and the power supply voltage information in the first power supply control process, respectively. Furthermore, the A / D conversion units 62 and 63 and the signal output unit 65 described in the description of the second power supply control process correspond to the A / D conversion units 60 and 61 and the signal output unit 64, respectively, in the first power supply control process.

[0173] (Implementation Method 3)

[0174] In embodiment 1, current flows continuously through the second detection circuit 25, which continuously detects the circuit voltage. However, the second detection circuit 25 may not always detect the circuit voltage.

[0175] Hereinafter, regarding Embodiment 3, the differences from Embodiment 1 will be explained. All other structures besides those described later are common to Embodiment 1. Therefore, for structural parts common to Embodiment 1, the same reference numerals as in Embodiment 1 will be used, and the description of these structural parts will be omitted.

[0176] <Structure of the second detection circuit 25>

[0177] Figure 8 This is a circuit diagram of the second detection circuit 25 in Embodiment 3. The second detection circuit 25 in Embodiment 3, like in Embodiment 1, includes a current output device 50 and a circuit resistor 51. The connections of the current output device 50 and the circuit resistor 51 are the same as in Embodiment 1, except for the connection at one end upstream of the device resistor Re.

[0178] The second detection circuit 25 in embodiment 3 further includes a first circuit switch 52, a second circuit switch 53, and switching resistors 54, 55, 56, and 57. The first circuit switch 52 is a PNP type bipolar transistor. The second circuit switch 53 is an NPN type bipolar transistor.

[0179] The emitter of the first circuit switch 52 is connected to the drain of the second FET 40. The collector of the first circuit switch 52 is connected to one end of the upstream side of the device resistor Re. A switching resistor 54 is connected between the emitter and base of the first circuit switch 52. The base of the first circuit switch 52 is connected to one end of the switching resistor 55. The first circuit switch 52 functions as a connection switch.

[0180] The other end of the switching resistor 55 is connected to the collector of the second circuit switch 53. The emitter of the second circuit switch 53 is connected to the ground conductor G. A switching resistor 56 is connected between the emitter and base of the second circuit switch 53. The base of the second circuit switch 53 is connected to the microcomputer 26 via a switching resistor 57.

[0181] Regarding the second circuit switch 53, the microcomputer 26 adjusts the voltage at the base of the reference potential (the potential of the ground conductor G) to a high-level voltage or a low-level voltage. When the microcomputer 26 adjusts the voltage at the base of the second circuit switch 53 to a high-level voltage, the second circuit switch 53 is switched on. When the second circuit switch 53 is on, the resistance between the collector and emitter of the second circuit switch 53 is very small, allowing current to flow through both the collector and emitter.

[0182] When the second circuit switch 53 is turned on, current flows from one end of the upstream side of the second controller 22 to the switching resistors 54 and 55, the second circuit switch 53, and the ground conductor G. This causes the first circuit switch 52 to turn on. When the first circuit switch 52 is turned on, the resistance between the emitter and collector of the first circuit switch 52 is very small, allowing current to flow through both the emitter and collector. When the first circuit switch 52 is turned on, the current output device 50 draws current from the drain of the second FET 40 through the first circuit switch 52, and the second detection circuit 25 detects the circuit voltage. As described above, the second detection circuit 25 operates when the first circuit switch 52 is turned on.

[0183] When the microcomputer 26 adjusts the voltage at the base of the second circuit switch 53 to a low level, the second circuit switch 53 switches to open. When the second circuit switch 53 is open, the resistance between the collector and emitter of the second circuit switch 53 is very high, and current cannot flow through the collector and emitter.

[0184] When the second circuit switch 53 is switched off, the current flow through the switching resistor 54 stops, therefore the first circuit switch 52 is switched off. When the first circuit switch 52 is off, the resistance between the emitter and collector of the first circuit switch 52 is very high, and current cannot flow through the emitter and collector. When the first circuit switch 52 is off, the current output device 50 stops introducing current through the first circuit switch 52, and the second detection circuit 25 stops operating.

[0185] As described above, the microcomputer 26 switches the first circuit switch 52 to be on or off by adjusting the voltage of the base of the second circuit switch 53 to a high level voltage or a low level voltage.

[0186] <Structure of the first detection circuit 24>

[0187] In Embodiment 3, the first detection circuit 24, in addition to the voltage divider resistors Rd1 and Rd2, similarly includes a first circuit switch 52, a second circuit switch 53, and switching resistors 54, 55, 56, and 57, as in the second detection circuit 25. The first circuit switch 52, the second circuit switch 53, and the switching resistors 54, 55, 56, and 57 are connected in the same way as in the second detection circuit 25. Therefore, the first circuit switch 52 is connected between the first controller 21 and one end upstream of the voltage divider resistor Rd1. The emitter of the second circuit switch 53 is connected to one end downstream of the voltage divider resistor Rd2. The base of the second circuit switch 53 is connected to the microcomputer 26 via the switching resistor 57.

[0188] The microcomputer 26 switches the first circuit switch 52 to either be on or off by adjusting the base voltage of the second circuit switch 53 (which has a reference potential of ground conductor G) to a high or low level. When the base of the second circuit switch 53 is switched to a high level, the first circuit switch 52 is on, and the first detection circuit 24 operates. When the base of the second circuit switch 53 is switched to a low level, the first circuit switch 52 is off, and the first detection circuit 24 stops operating.

[0189] <Structure of Microcomputer 26>

[0190] Figure 9 This is a block diagram showing the main structural components of the microcomputer 26. In addition to the structural components of the microcomputer 26 in Embodiment 1, the microcomputer 26 of Embodiment 3 includes switching units 72 and 73. Switching units 72 and 73 are connected to the internal bus 71. Switching unit 72 is also connected to the second circuit switch 53 via a switching resistor 57 within the first detection circuit 24. Switching unit 73 is also connected to the second circuit switch 53 via a switching resistor 57 within the second detection circuit 25.

[0191] The switching unit 72 adjusts the voltage at the base of the second circuit switch 53, whose reference potential is the potential of the ground conductor G, to a high-level voltage or a low-level voltage within the first detection circuit 24. The switching unit 72 switches the first circuit switch 52 to on or off according to the instruction of the control unit 70. Specifically, the switching unit 72 switches the second circuit switch 53 to on by adjusting the voltage at its base to a high-level voltage. Thus, the first circuit switch 52 is switched to on. The switching unit 72 switches the second circuit switch 53 to off by adjusting the voltage at its base to a low-level voltage. Thus, the first circuit switch 52 is switched to off.

[0192] Similarly, within the second detection circuit 25, the switching unit 73 adjusts the voltage at the base of the second circuit switch 53, whose reference potential is the potential of the ground conductor G, to a high-level voltage or a low-level voltage. The switching unit 73 switches the first circuit switch 52 to on or off according to the instruction of the control unit 70. Specifically, the switching unit 73 switches the second circuit switch 53 to on by adjusting the voltage at its base to a high-level voltage. Thus, the first circuit switch 52 is switched to on. The switching unit 73 switches the second circuit switch 53 to off by adjusting the voltage at its base to a low-level voltage. Thus, the first circuit switch 52 is switched to off.

[0193] <Second Fault Detection and Handling>

[0194] Figure 10 This is a flowchart illustrating the sequence of the second fault detection process. Similar to Embodiment 1, the control unit 70 performs the second fault detection process before activating the second load 12. Therefore, the second fault detection process is performed with the second FET 40 disconnected. If no fault is detected during the second fault detection process, the control unit 70 performs the second power supply control process.

[0195] In the second fault detection process of Embodiment 3, all the steps performed by the second fault detection process of Embodiment 1 are executed. These steps are labeled with the same reference numerals, and their descriptions are omitted. The steps performed by the second fault detection process of Embodiment 1 are steps S1 to S9.

[0196] In the second fault detection process, the control unit 70 first causes the switching unit 72 to switch the first circuit switch 52 of the second detection circuit 25 to the on position, thereby enabling the second detection circuit 25 to operate (step S31). After executing step S31, the control unit 70 executes step S1 to obtain circuit voltage information from the A / D conversion unit 62.

[0197] After executing step S1, the control unit 70 causes the switching unit 72 to switch the first circuit switch 52 of the second detection circuit 25 to open, thereby stopping the operation of the second detection circuit 25 (step S32). After executing step S32, the control unit 70 executes step S2.

[0198] <Second Power Supply Control Process>

[0199] Figure 11 This is a flowchart illustrating the sequence of the second power supply control process. Similar to Embodiment 1, the second power supply control process is executed with the second FET40 disconnected.

[0200] In the second power supply control process of Embodiment 3, all the steps executed by the second power supply control process of Embodiment 1 are performed. These steps are labeled with the same reference numerals, and their descriptions are omitted. The steps executed by the second power supply control process of Embodiment 1 are steps S11 to S18.

[0201] In the second power supply control process, when the control unit 70 determines that the second load 12 should be operated (S11: Yes), the switching unit 72 switches the first circuit switch 52 of the second detection circuit 25 to be turned on, thereby enabling the second detection circuit 25 to operate (step S41). After executing step S41, the control unit 70 executes step S12.

[0202] After executing step S18, or if the control unit 70 determines that the circuit voltage indicated by the circuit voltage information obtained in step S12 is not within the normal range (S13: No), it causes the switching unit 72 to switch the first circuit switch 52 of the second detection circuit 25 to open, thereby stopping the operation of the second detection circuit 25 (step S42). After executing step S42, the control unit 70 ends the second power supply control process.

[0203] <First Fault Detection and Handling and First Power Supply Control Processing>

[0204] The control unit 70 performs the first fault detection process in the same way as the second fault detection process. The control unit 70 also performs the first power supply control process in the same way as the second power supply control process. When power supply voltage information is needed, the control unit 70 instructs the switching unit 72 to turn on the first circuit switch 52 of the first detection circuit 24. As a result, the first detection circuit 24 operates. When power supply voltage information is not needed, the control unit 70 instructs the switching unit 72 to turn off the first circuit switch 52 of the first detection circuit 24. As a result, the first detection circuit 24 stops operating.

[0205] As described above, in the power supply control device 13 of Embodiment 3, the first detection circuit 24 operates only during periods when it is necessary to detect the power supply voltage. The second detection circuit 25 operates only during periods when it is necessary to detect the circuit voltage. This suppresses unnecessary power consumption.

[0206] The power supply control device 13 of Embodiment 3 has the same effect as the power supply control device 13 of Embodiment 1.

[0207] (Implementation Method 4)

[0208] In embodiment 2, the microcomputer 26, the first detection circuit 24, and the second detection circuit 25 can also be configured in the same way as in embodiment 3.

[0209] Hereinafter, regarding Embodiment 4, the differences from Embodiment 2 will be explained. All other structures besides those described later are common to Embodiment 2. Therefore, for structural parts common to Embodiment 2, the same reference numerals as in Embodiment 2 will be used, and the description of these structural parts will be omitted.

[0210] <First Fault Detection and Handling and Second Fault Detection and Handling>

[0211] In the power supply control device 13 of Embodiment 4, the microcomputer 26, the first detection circuit 24, and the second detection circuit 25 are configured in the same manner as in Embodiment 3. The control unit 70 of the microcomputer 26 performs the first fault detection process and the second fault detection process in the same manner as in Embodiment 3.

[0212] <Second Power Supply Control Process>

[0213] Figure 12 This is a flowchart illustrating the sequence of the second power supply control process in Embodiment 4. Similar to Embodiment 2, the second power supply control process is executed with the second FET40 disconnected.

[0214] In the second power supply control process of Embodiment 4, all the steps executed by the second power supply control process of Embodiment 2 are performed. These steps are labeled with the same reference numerals, and the description of these steps is omitted. The steps executed by the second power supply control process of Embodiment 2 are steps S11, S12, S15, S17, and S21 to S24.

[0215] In the second power supply control process, when the control unit 70 determines that the second load 12 should be operated (S11: Yes), the switching unit 72 switches the first circuit switch 52 of the second detection circuit 25 to be turned on, thereby enabling the second detection circuit 25 to operate (step S51). After executing step S51, the control unit 70 executes step S12.

[0216] After executing step S24, the control unit 70 causes the switching unit 72 to switch the first circuit switch 52 of the second detection circuit 25 to the off position, thereby stopping the operation of the second detection circuit 25 (step S52). After executing step S52, the control unit 70 ends the second power supply control process.

[0217] <First Power Supply Control Process>

[0218] The control unit 70 performs the first power supply control process in the same way as the second power supply control process. The control unit 70 activates the first detection circuit 24 when power supply voltage information is needed. The control unit 70 deactivates the first detection circuit 24 when power supply voltage information is not needed.

[0219] As described above, in the power supply control device 13 of Embodiment 4, the first detection circuit 24 operates only during periods when it is necessary to detect the power supply voltage. The second detection circuit 25 operates only during periods when it is necessary to detect the circuit voltage. This suppresses unnecessary power consumption.

[0220] The power supply control device 13 of Embodiment 4 has the same effect as the power supply control device 13 of Embodiment 2.

[0221] <Note>

[0222] In embodiments 3 and 4, the first circuit switch 52 is not limited to a PNP type bipolar transistor, and can also be a P-channel FET. The second circuit switch 53 is not limited to an NPN type bipolar transistor, and can also be an N-channel FET. Furthermore, the first circuit switch 52 is not limited to a semiconductor switch, and can also be a relay contact. The circuit that switches the first circuit switch 52 to on or off is not limited to a circuit that uses the second circuit switch 53.

[0223] (Implementation Method 5)

[0224] The power supply system 1 in Embodiment 1 has one DC power source. However, the number of DC power sources in the power supply system 1 is not limited to one.

[0225] Hereinafter, regarding Embodiment 5, the differences from Embodiment 1 will be explained. All other structures besides those described later are common to Embodiment 1. Therefore, structural parts common to Embodiment 1 will be labeled with the same reference numerals as in Embodiment 1, and descriptions of these structural parts will be omitted.

[0226] <Structure of Power System 1>

[0227] Figure 13This is a block diagram showing the main structural components of the power supply system 1 in Embodiment 5. In addition to the structural components present in the power supply system 1 of Embodiment 1, the power supply system 1 of Embodiment 5 also includes a second DC power supply 14. The second DC power supply 14 is, for example, a battery. The negative terminal of the second DC power supply 14 is connected to the grounding conductor G. The positive terminal of the second DC power supply 14 is connected to one end of the first conductor resistor Rw1. The other end of the first conductor resistor Rw1 is connected in the same manner as in Embodiment 1. In Embodiment 5, it is not the DC power supply 10 but the second DC power supply 14 that functions as the power source for the second load 12, the second controller 22, and the second detection circuit 25.

[0228] The power supply control device 13, the first detection circuit 24 and the second detection circuit 25 of Embodiment 5 respectively perform the same effects as the power supply control device 13, the first detection circuit 24 and the second detection circuit 25 of Embodiment 1.

[0229] (Implementation Method 6)

[0230] In Embodiment 1, the connection object at one downstream end of the second load 12 is the grounding conductor G. However, the connection object at one downstream end of the second load 12 is not limited to the grounding conductor G. Hereinafter, regarding Embodiment 6, the differences from Embodiment 1 will be explained. All other structures besides those described later are common to Embodiment 1. Therefore, for structural parts common to Embodiment 1, the same reference numerals as in Embodiment 1 will be used, and the description of these structural parts will be omitted.

[0231] <Structure of Power System 1>

[0232] Figure 14 This is a block diagram showing the main structure of the power supply system 1 according to Embodiment 6. In the power supply system 1 of Embodiment 6, one downstream end of the second load 12 is connected to one upstream end of the second lead resistor Rw2. In the power supply system 1 of Embodiment 6, when the second FET 40 of the second controller 22 is turned on, current flows from the positive terminal of the DC power supply 10 in the following order: first lead resistor Rw1, second FET 40, second output section 41, second load 12, second lead resistor Rw2, and ground conductor G. In this case, the circuit voltage is the same as the voltage of the drain of the second FET 40, which is a reference potential at the downstream end of the second load 12.

[0233] The power supply control device 13, the first detection circuit 24, and the second detection circuit 25 of Embodiment 6 respectively achieve the same effect as the power supply control device 13, the first detection circuit 24, and the second detection circuit 25 of Embodiment 1.

[0234] <Note>

[0235] In embodiments 2 to 4 and 6, similar to embodiment 5, the power supply system 1 may also include a DC power supply 10 and a second DC power supply 14.

[0236] In embodiments 2 to 5, similar to embodiment 6, the connection object of one end of the downstream side of the second load 12 can also be one end of the upstream side of the second wire resistor Rw2.

[0237] In embodiments 1 to 6, whenever the second wire W2 is used, it is necessary to detect the circuit voltage, and the second detection circuit 25 functions effectively. Therefore, the first wire W1 can also be a wire whose resistance value is negligible.

[0238] In embodiments 1 to 6, the downstream end of the second voltage resistor 43 of the second controller 22 is not limited to the upstream end of the second wire resistor Rw2; it can also be a ground conductor G. In this case, the current output by the second output unit 41 does not flow in the second wire resistor Rw2, so the voltage across the two ends of the second wire resistor Rw2 will not change depending on the current output by the second output unit 41.

[0239] In embodiments 1 to 6, it is acceptable for the component connected between the positive terminal of the DC power supply 10 and the drain of the second FET 40 to be a resistive component. Therefore, a circuit element with a non-negligible resistance value can be configured instead of the first wire W1. This circuit element is, for example, a semiconductor switch with a non-negligible switching resistance value. Similarly, in embodiments 1 to 6, it is acceptable for the component connected between the second drive circuit 42 and the ground conductor G to be a resistive component. Therefore, a circuit element with a non-negligible resistance value can be configured instead of the second wire W2.

[0240] In embodiments 1 to 6, any semiconductor switch used to control the power supply to the first load 11 and the second load 12 that results in a smaller resistance between the current input and current output terminals when the voltage applied to the control terminal is higher is acceptable. Therefore, an IGBT (Insulated Gate Bipolar Transistor) can be used instead of the first FET 30. Similarly, an IGBT can be used instead of the second FET 40.

[0241] It should be considered that the disclosed embodiments 1 to 6 are illustrative in all respects and not restrictive. The scope of the invention is defined not by the foregoing but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0242] Label Explanation

[0243] 1 Power System

[0244] 10 DC power supply

[0245] 11 First Load

[0246] 12 Second Load

[0247] 13 Power supply control device

[0248] 14 Second DC power supply

[0249] 21 First Controller

[0250] 22 Second Controller

[0251] 23 Regulator

[0252] 24 First Detection Circuit

[0253] 25 Second Detection Circuit

[0254] 26 Microcomputers

[0255] 30 First FET

[0256] 31 First Output Section

[0257] 32 First driving circuit

[0258] 33 First Voltage Resistance

[0259] 40. Second FET (Semiconductor Switch)

[0260] 41 Second Output Section (Current Output Section)

[0261] 42 Second drive circuit (switching circuit)

[0262] 43 Second Voltage Resistor

[0263] 50 Current Output Device

[0264] 51 Circuit Resistor

[0265] 52 First circuit switch (connection switch)

[0266] 53 Second Circuit Switch

[0267] 54, 55, 56, 57 Switching resistors

[0268] A / D conversion sections 60, 61, 62, and 63

[0269] Signal output sections 64 and 65

[0270] 66, 67 Ministry of Communications

[0271] 68 Notification Department

[0272] 69 Storage Department

[0273] 70. Control Department (Processing Department)

[0274] 71 Internal Bus

[0275] Switching sections 72 and 73

[0276] A storage medium

[0277] G Grounding conductor

[0278] P Computer Program

[0279] Rd1 and Rd2 voltage divider resistors

[0280] Re Device Resistance

[0281] Rw1 First wire resistance

[0282] Rw2 Second wire resistance

[0283] Te transistor (bipolar transistor)

[0284] W1 First Conductor

[0285] W2 is the second conductor.

Claims

1. A detection circuit, wherein, have: A current output device outputs a current corresponding to the circuit voltage between the input terminal of a semiconductor switch to which the input current is applied and the ground of a switching circuit, wherein the switching circuit switches the semiconductor switch to be on or off. and The circuit resistor, through which the current output from the current output device flows. The detection circuit outputs the voltage between the two ends of the circuit resistor. The voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeds 0V. The current output device has: The device resistor, from which current flows from the input terminal of the semiconductor switch to the device resistor; A PNP bipolar transistor, wherein the emitter of the bipolar transistor is connected to one end of the downstream side of the device resistor. The base potential of the bipolar transistor is the ground of the switching circuit. The current output from the collector of the bipolar transistor flows to the circuit resistor.

2. The detection circuit according to claim 1, wherein, The detection circuit includes a connection switch, which is connected between the input terminal of the semiconductor switch and the current output device. The current output device outputs the current introduced from the input terminal of the semiconductor switch to the circuit resistor.

3. A power supply control device for controlling power supply via a semiconductor switch, wherein, have: A switching circuit switches the semiconductor switch to either on or off. A detection circuit detects the circuit voltage between the input terminal of the semiconductor switch receiving the input current and the ground of the switching circuit, and outputs a voltage representing the detected circuit voltage; and Processing Department, Execute Processing The processing unit instructs the switching circuit to switch the semiconductor switch to either on or off based on the voltage output by the detection circuit. The detection circuit has the following features: A current output device that outputs a current corresponding to the voltage of the circuit; and The circuit resistor, through which the current output from the current output device flows. The detection circuit outputs the voltage between the two ends of the circuit resistor. The voltage between the ground of the switching circuit and one downstream end of the circuit resistor exceeds 0V. The current output device has: The device resistor, from which current flows from the input terminal of the semiconductor switch to the device resistor; A PNP bipolar transistor, wherein the emitter of the bipolar transistor is connected to one end of the downstream side of the device resistor. The base potential of the bipolar transistor is the ground of the switching circuit. The current output from the collector of the bipolar transistor flows to the circuit resistor.

4. The power supply control device according to claim 3, wherein, The power supply control device includes a current output section, which outputs a current corresponding to the current flowing through the semiconductor switch. The voltage between the ground of the switching circuit and one end of the downstream side of the circuit resistor varies according to the current output by the current output unit.

5. The power supply control device according to claim 3 or 4, wherein, The switching circuit boosts the circuit voltage and applies the boosted voltage to the control terminal of the semiconductor switch, thereby switching the semiconductor switch to ON.

6. The power supply control device according to claim 5, wherein, The processing unit determines whether the circuit voltage is an on-state voltage based on the voltage output by the detection circuit when the semiconductor switch is off. The on-state voltage is a voltage that can boost the voltage that switches the semiconductor switch to on state. When the processing unit determines that the circuit voltage is the on-state voltage, it instructs the switching circuit to switch the semiconductor switch to on. After instructing the semiconductor switch to switch to on, the processing unit determines whether the semiconductor switch is on.

7. The power supply control device according to claim 3 or 4, wherein, Current flows from the input terminal of the semiconductor switch in the order of the switching circuit and the grounding of the switching circuit, thereby supplying power to the switching circuit. The processing unit determines whether the circuit voltage is less than a threshold voltage based on the voltage output by the detection circuit when the semiconductor switch is off. If the processing unit determines that the circuit voltage is less than the threshold voltage, it determines whether the switching circuit is working.

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