Power supply control device

Abstract

In a power supply control device (10), power supply is controlled by switching a first semiconductor switch (20a) and a second semiconductor switch (20b) arranged in a current path to on or off. A first diode (21a) and a second diode (21b) are connected between the drain and the source of each of the first semiconductor switch (20a) and the second semiconductor switch (20b). The cathode of each of the first diode (21a) and the second diode (21b) is located on the downstream side and the upstream side of the anode in the current path. Although a microcomputer (26) instructs the first semiconductor switch (20a) and the second semiconductor switch (20b) to switch off, when current flows in the current path, a first drive circuit (22a) switches the first semiconductor switch (20a) to on.

Description

Technical Field

[0001] The present disclosure relates to a power supply control device.

[0002] This application claims the priority based on Japanese Application No. 2019-237424 filed on December 26, 2019, and cites all the contents described in the above Japanese Application. Background Art

[0003] Patent document 1 discloses a power supply control device for controlling power supply from a battery to a load. In the power supply control device, a first semiconductor switch and a second semiconductor switch are arranged in a current path of a current flowing from the battery to the load. A parasitic diode is connected to both ends of the first semiconductor switch and the second semiconductor switch. The cathode of the parasitic diode of each of the first semiconductor switch and the second semiconductor switch is located on the downstream side and the upstream side of the anode in the current path. The power supply from the battery to the load is controlled by switching the first semiconductor switch and the second semiconductor switch to be on or off.

[0004] The user may make an erroneous connection of the battery so that the current flows through the load before the first semiconductor switch and the second semiconductor switch. When the erroneous connection of the battery is made when the first semiconductor switch is not present and the second semiconductor switch is off, the current flows through the parasitic diode of the second semiconductor switch. When the current flows through the parasitic diode of the second semiconductor switch for a long time, the temperature of the second semiconductor switch rises to an abnormal temperature, which may cause a malfunction.

[0005] However, in the power supply control device described in Patent Document 1, since the first semiconductor switch is configured, when the first semiconductor switch and the second semiconductor switch are disconnected, regardless of whether the battery connection is normal, current will not flow in the parasitic diode of the first semiconductor switch or the second semiconductor switch.

[0006] Prior art literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2019-146414 Summary of the invention

[0008] A power supply control device of one embodiment of the present invention controls power supply by switching a first semiconductor switch and a second semiconductor switch, which are arranged in a current path and have parasitic diodes connected at both ends, to on or off. The power supply control device comprises: a processing unit, which executes processing to instruct the first semiconductor switch and the second semiconductor switch to switch to on or off; and a switching circuit, which switches the first semiconductor switch to on when current flows in the current path even though the processing unit instructs the first semiconductor switch and the second semiconductor switch to switch to off, and the cathodes of the parasitic diodes of each of the first semiconductor switch and the second semiconductor switch are located on the downstream side and upstream side of the anode in the current path. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a block diagram showing the configuration of a main portion of the power supply system in the first embodiment.

[0010] Figure 2 This is a timing chart for explaining the operation of the power supply control device.

[0011] Figure 3 It is a block diagram showing the structure of the main part of the microcomputer.

[0012] Figure 4 : is a flowchart showing the procedure of the power supply control process.

[0013] Figure 5 This is a block diagram showing the configuration of a main portion of a power supply system in the second embodiment.

[0014] Figure 6 This is a timing chart for explaining the operation of the voltage output circuit.

[0015] Figure 7 This is a block diagram showing the configuration of a main portion of a power supply system in the third embodiment.

[0016] Figure 8 This is a timing chart for explaining the operation of the voltage output circuit.

[0017] Fig. 9 This is a block diagram showing the configuration of a main portion of a power supply system in a fourth embodiment.

[0018] Fig.10 It is a block diagram showing the structure of the main part of the microcomputer.

[0019] Fig.11 : is a flowchart showing the procedure of the short circuit detection process.

[0020] Fig.12 This is a block diagram showing the configuration of a main portion of a power supply system in the fifth embodiment.

[0021] Fig.13 This is a block diagram showing the configuration of a main portion of a power supply system in the sixth embodiment.

[0022] Fig.14 This is a block diagram showing the configuration of a main portion of a power supply system in the seventh embodiment.

[0023] Fig.15 This is a block diagram showing the configuration of a main portion of a power supply system in the eighth embodiment.

[0024] Fig.16 This is a timing chart for explaining the operation of the voltage output circuit.

[0025] Fig.17 This is a block diagram showing the configuration of a main portion of a power supply system in the ninth embodiment.

[0026] Fig.18 This is a block diagram showing the configuration of a main portion of a power supply system in the tenth embodiment.

[0027] Fig.19 This is a block diagram showing the configuration of a main portion of a power supply system in the eleventh embodiment.

[0028] Fig. 20 This is a block diagram showing the configuration of a main portion of a power supply system in the twelfth embodiment. DETAILED DESCRIPTION

[0029] [Problems to be Solved by the Present Disclosure]

[0030] In the power supply control device described in Patent Document 1, it is assumed that both ends of the second semiconductor switch are short-circuited when the battery connection is normal and the first semiconductor switch is disconnected. In this case, the current flows from the battery through the parasitic diode of the first semiconductor switch, the second semiconductor switch, and the load in sequence. If the current flows through the parasitic diode of the first semiconductor switch for a long time, a fault may also occur in the first semiconductor switch.

[0031] Therefore, an object of the present invention is to provide a power supply control device that prevents a failure of one semiconductor switch from occurring due to a short circuit between both ends of the other semiconductor switch.

[0032] [Effects of the present disclosure]

[0033] According to the present disclosure, a malfunction of the first semiconductor switch will not occur due to a short circuit between both ends of the second semiconductor switch.

[0034] [Description of Embodiments of the Present Disclosure]

[0035] First, the embodiments of the present disclosure will be described by way of example. At least a portion of the embodiments described below may be combined arbitrarily.

[0036] (1) A power supply control device according to one embodiment of the present invention controls power supply by switching a first semiconductor switch and a second semiconductor switch, which are arranged in a current path and have parasitic diodes connected at both ends, to on or off. The power supply control device comprises: a processing unit that executes processing to instruct the first semiconductor switch and the second semiconductor switch to switch to on or off; and a switching circuit that switches the first semiconductor switch to on when current flows in the current path despite the processing unit instructing the first semiconductor switch and the second semiconductor switch to switch to off, and the cathodes of the parasitic diodes of the first semiconductor switch and the second semiconductor switch are located on the downstream side and upstream side of the anode in the current path.

[0037] In the above scheme, when the first semiconductor switch and the second semiconductor switch are instructed to be disconnected when the second semiconductor switch is short-circuited, only the first semiconductor switch is switched to be disconnected. At this time, the current flows in the parasitic diode of the first semiconductor switch. In the case where the current flows in the current path despite the instruction to switch the first semiconductor switch and the second semiconductor switch to be disconnected, the first semiconductor switch is switched to be connected as if both ends of the second semiconductor switch are short-circuited. As a result, the current does not flow in the parasitic diode of the first semiconductor switch for a long period of time, and therefore the failure of the first semiconductor switch does not occur due to the short circuit of both ends of the second semiconductor switch.

[0038] (2) In a power supply control device of one embodiment of the present invention, in the above-mentioned current path, the above-mentioned first semiconductor switch is arranged on the upstream side of the above-mentioned second semiconductor switch, and in the above-mentioned current path, a load is arranged on the downstream side of the above-mentioned second semiconductor switch. Although the above-mentioned processing unit instructs the above-mentioned first semiconductor switch and the above-mentioned second semiconductor switch to switch to disconnection, when the node voltage of the connection node between the above-mentioned second semiconductor switch and the above-mentioned load is greater than the threshold voltage, the above-mentioned switching circuit switches the above-mentioned first semiconductor switch to be connected.

[0039] In the above scheme, the current flows from the positive electrode of the DC power supply through the first semiconductor switch, the second semiconductor switch, and the load in sequence. When the two ends of the second semiconductor switch are short-circuited when the first semiconductor switch is disconnected, the current flows through the parasitic diode of the first semiconductor switch, the second semiconductor switch, and the load in sequence, and the node voltage is the voltage of the DC power supply or a value close to the voltage of the DC power supply. When the node voltage is high despite the instruction to disconnect the first semiconductor switch and the second semiconductor switch, it is considered that the two ends of the second semiconductor switch are short-circuited.

[0040] (3) In a power supply control device of one embodiment of the present invention, in the above-mentioned current path, the above-mentioned first semiconductor switch is arranged on the downstream side of the above-mentioned second semiconductor switch, and in the above-mentioned current path, a load is arranged on the downstream side of the above-mentioned first semiconductor switch, and even if the above-mentioned processing unit instructs the above-mentioned first semiconductor switch and the above-mentioned second semiconductor switch to switch to disconnection, when the node voltage of the connection node between the above-mentioned second semiconductor switch and the above-mentioned load is higher than the threshold voltage, the above-mentioned switching circuit switches the above-mentioned first semiconductor switch to be connected.

[0041] In the above scheme, the current flows from the positive electrode of the DC power supply through the second semiconductor switch, the first semiconductor switch, and the load in sequence. When the two ends of the second semiconductor switch are short-circuited when the first semiconductor switch is disconnected, the current flows through the second semiconductor switch, the parasitic diode of the first semiconductor switch, and the load in sequence, and the node voltage is the voltage of the DC power supply or a value close to the voltage of the DC power supply. When the node voltage is high despite the instruction to disconnect the first semiconductor switch and the second semiconductor switch, it is considered that the two ends of the second semiconductor switch are short-circuited.

[0042] (4) In a power supply control device of one embodiment of the present invention, the processing unit performs the following processing: when instructing the first semiconductor switch and the second semiconductor switch to switch to off, determining whether the node voltage is greater than the threshold voltage; when determining that the node voltage is greater than the threshold voltage, instructing the switching circuit to switch the first semiconductor switch to on.

[0043] In the above aspect, when the node voltage is high despite the instruction to switch the first semiconductor switch and the second semiconductor switch to OFF, the switching circuit is instructed to switch the first semiconductor switch to ON.

[0044] (5) In a power supply control device of one embodiment of the present invention, in the above-mentioned current path, the above-mentioned first semiconductor switch is arranged on the upstream side of the above-mentioned second semiconductor switch, and in the above-mentioned current path, a load is arranged on the upstream side of the above-mentioned first semiconductor switch. Although the above-mentioned processing unit instructs the above-mentioned first semiconductor switch and the above-mentioned second semiconductor switch to switch to disconnection, when the node voltage of the connection node between the above-mentioned load and the above-mentioned second semiconductor switch is less than the threshold voltage, the above-mentioned switching circuit switches the above-mentioned first semiconductor switch to be connected.

[0045] In the above scheme, the current flows from the positive electrode of the DC power supply to the load, the first semiconductor switch, and the second semiconductor switch in sequence. When the two ends of the second semiconductor switch are short-circuited when the first semiconductor switch is turned off, the current flows through the load, the parasitic diode of the first semiconductor switch, and the second semiconductor switch in sequence, and the node voltage is zero V or a value close to zero V. When the node voltage is low despite the instruction to turn off the first semiconductor switch and the second semiconductor switch, it is considered that the two ends of the second semiconductor switch are short-circuited.

[0046] (6) In a power supply control device of one embodiment of the present invention, in the above-mentioned current path, the above-mentioned first semiconductor switch is arranged on the downstream side of the above-mentioned second semiconductor switch, and in the above-mentioned current path, a load is arranged on the upstream side of the above-mentioned second semiconductor switch. Although the above-mentioned processing unit instructs the above-mentioned first semiconductor switch and the above-mentioned second semiconductor switch to switch to disconnection, when the node voltage of the connection node between the above-mentioned load and the above-mentioned second semiconductor switch is less than the threshold voltage, the above-mentioned switching circuit switches the above-mentioned first semiconductor switch to disconnection.

[0047] In the above scheme, the current flows from the positive electrode of the DC power supply to the load, the second semiconductor switch, and the first semiconductor switch in sequence. When the two ends of the second semiconductor switch are short-circuited when the first semiconductor switch is turned off, the current flows through the load, the second semiconductor switch, and the parasitic diode of the first semiconductor switch in sequence, and the node voltage is zero V or a value close to zero V. When the node voltage is low despite the instruction to turn off the first semiconductor switch and the second semiconductor switch, it is considered that the two ends of the second semiconductor switch are short-circuited.

[0048] (7) In a power supply control device of one embodiment of the present invention, the processing unit performs the following processing: when instructing the first semiconductor switch and the second semiconductor switch to switch to off, determining whether the node voltage is less than the threshold voltage; when determining that the node voltage is less than the threshold voltage, instructing the switching circuit to switch the first semiconductor switch to on.

[0049] In the above aspect, when the node voltage is low despite the instruction to switch the first semiconductor switch and the second semiconductor switch to OFF, the switching circuit is instructed to switch the first semiconductor switch to ON.

[0050] [Details of the embodiments of the present disclosure]

[0051] Below, while referring to the attached Figure 1 The present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0052] (Implementation Method 1)

[0053] <Structure of Power Supply System 1>

[0054] Figure 1 1 is a block diagram showing the structure of the main part of the power supply system 1 in Embodiment 1. The power supply system 1 is suitably mounted on a vehicle and includes: a power supply control device 10, a load 11, a battery 12, a positive terminal Tp, and a negative terminal Tn. The power supply control device 10 is connected to one end of the load 11 and the positive terminal Tp. The other end of the load 11 and the negative terminal Tn are grounded. The battery 12 is connected between the positive terminal Tp and the negative terminal Tn by the user in a detachable manner.

[0055] Usually, if Figure 1 As shown, the user connects the positive and negative electrodes of the battery 12 to the positive terminal Tp and the negative terminal Tn, respectively. This connection is a normal connection. The power supply control device 10 controls the power supply from the battery 12 to the load 11 by electrically connecting the positive terminal Tp to the load 11 and disconnecting the electrical connection. When the power supply control device 10 electrically connects the positive terminal Tp to the load 11 when the connection of the battery 12 is a normal connection, the battery 12 supplies power to the load 11. When the power supply control device 10 disconnects the electrical connection under the same circumstances, the power supply from the battery 12 to the load 11 stops.

[0056] The user may mistakenly connect the positive and negative electrodes of the battery 12 to the negative terminal Tn and the positive terminal Tp, respectively. This connection is reverse connection. The power supply control device 10 can stop the power supply from the battery 12 to the load 11 when the connection of the battery 12 is reverse connection.

[0057] The load 11 is an electrical device mounted on the vehicle, such as a motor that drives a fan. When power is supplied from the battery 12 to the load 11, the load 11 operates. When power supply from the battery 12 to the load 11 stops, the load 11 stops operating.

[0058] <Structure of Power Supply Control Device 10>

[0059] The power supply control device 10 includes: a first semiconductor switch 20a, a second semiconductor switch 20b, a first diode 21a, a second diode 21b, a first drive circuit 22a, a second drive circuit 22b, an OR circuit 23, a voltage output circuit 24, a device resistor 25, and a microcomputer (hereinafter referred to as a microcomputer) 26. The first semiconductor switch 20a and the second semiconductor switch 20b are N-channel FETs (Field Effect Transistors). The OR circuit 23 has two input terminals and one output terminal. The voltage output circuit 24 has circuit resistors 30 and 31.

[0060] The first diode 21a and the second diode 21b are parasitic diodes of the first semiconductor switch 20a and the second semiconductor switch 20b, respectively. Therefore, the first diode 21a and the second diode 21b are formed in the first semiconductor switch 20a and the second semiconductor switch 20b, respectively, when the first semiconductor switch 20a and the second semiconductor switch 20b are manufactured. The cathode and anode of the first diode 21a are connected to the drain and source of the first semiconductor switch 20a, respectively. The cathode and anode of the second diode 21b are connected to the drain and source of the second semiconductor switch 20b, respectively.

[0061] The source of the first semiconductor switch 20a is connected to the positive terminal Tp. The drain of the first semiconductor switch 20a is connected to the drain of the second semiconductor switch 20b. The source of the second semiconductor switch 20b is connected to one end of the load 11. The gates of the first semiconductor switch 20a and the second semiconductor switch 20b are connected to the first drive circuit 22a and the second drive circuit 22b, respectively. The first drive circuit 22a is further connected to the output end of the OR circuit 23.

[0062] A connection node between the source of the second semiconductor switch 20b and one end of the load 11 is connected to one end of a circuit resistor 30 of the voltage output circuit 24. The other end of the circuit resistor 30 is connected to one end of a circuit resistor 31. The other end of the circuit resistor 31 is grounded. A connection node between the circuit resistors 30 and 31 is connected to one input end of the OR circuit 23. The second drive circuit 22b and the other input end of the OR circuit 23 are connected to one end of a device resistor 25. The other end of the device resistor 25 is connected to a microcomputer 26.

[0063] For each of the first semiconductor switch 20a and the second semiconductor switch 20b, when the voltage of the gate based on the potential of the source is above a certain voltage, the resistance value between the drain and the source is sufficiently small. At this time, the first semiconductor switch 20a and the second semiconductor switch 20b are respectively turned on, and the current can flow through the drain and the source. For each of the first semiconductor switch 20a and the second semiconductor switch 20b, when the voltage of the gate based on the potential of the source is less than a certain voltage, the resistance value between the drain and the source is sufficiently large. At this time, the first semiconductor switch 20a and the second semiconductor switch 20b are respectively turned off, and the current does not flow through the drain and the source.

[0064] The OR circuit 23 outputs a high level voltage or a low level voltage to the first drive circuit 22a. When the voltage input from the OR circuit 23 is switched from a low level voltage to a high level voltage, the first drive circuit 22a increases the voltage of the gate of the first semiconductor switch 20a with respect to the ground potential. As a result, in the first semiconductor switch 20a, the voltage of the gate with respect to the potential of the source increases to a voltage higher than a certain voltage, and the first semiconductor switch 20a is switched on.

[0065] The first drive circuit 22a reduces the gate voltage of the first semiconductor switch 20a with respect to the ground potential when the voltage input from the OR circuit 23 is switched from a high level voltage to a low level voltage. As a result, the gate voltage with respect to the source potential of the first semiconductor switch 20a is reduced to a voltage lower than a certain voltage, and the first semiconductor switch 20a is switched off.

[0066] As described above, the first drive circuit 22 a switches the first semiconductor switch 20 a on or off according to the voltage input from the OR circuit 23 .

[0067] The microcomputer 26 outputs a high level voltage or a low level voltage to the OR circuit 23 and the second drive circuit 22b via the device resistor 25. When the voltage input from the microcomputer 26 is switched from a low level voltage to a high level voltage, the second drive circuit 22b switches the second semiconductor switch 20b on in the same manner as the first drive circuit 22a. When the voltage input from the microcomputer 26 is switched from a high level voltage to a low level voltage, the second drive circuit 22b switches the second semiconductor switch 20b off in the same manner as the first drive circuit 22a.

[0068] Hereinafter, the voltage of the connection node connected to the voltage output circuit 24 is recorded as the node voltage. In Embodiment 1, the node voltage is a voltage applied to the connection node between the source of the second semiconductor switch 20b and one end of the load 11 with the ground potential as a reference. The circuit resistors 30 and 31 of the voltage output circuit 24 divide the node voltage. The voltage obtained by dividing the circuit resistors 30 and 31 is input to the OR circuit 23 as the output voltage of the voltage output circuit 24. The output voltage is determined according to the ratio of the resistance values ​​of the circuit resistors 30 and 31. The resistance values ​​of the circuit resistors 30 and 31 are constant values. In the case where the resistance value of the circuit resistor 30 is twice the resistance value of the circuit resistor 31, the output voltage of the voltage output circuit 24 is a voltage obtained by dividing the node voltage by 3.

[0069] When the output voltage of the voltage output circuit 24 or the microcomputer 26 is greater than the reference voltage, the OR circuit 23 outputs a high level voltage to the first drive circuit 22a. When the output voltage of the voltage output circuit 24 and the microcomputer 26 is less than the reference voltage, the OR circuit 23 outputs a low level voltage to the first drive circuit 22a. The reference voltage is a certain value exceeding zero V and is set in advance. The high level voltage output by the microcomputer 26 is greater than the reference voltage. The low level voltage output by the microcomputer 26 is less than the reference voltage.

[0070] The output voltage of the voltage output circuit 24 is proportional to the node voltage. The node voltage when the output voltage of the voltage output circuit 24 is the reference voltage is recorded as the threshold voltage. Because the reference voltage exceeds zero V, the threshold voltage also exceeds zero V. When the node voltage is less than the threshold voltage, the voltage output circuit 24 outputs a voltage less than the reference voltage to the OR circuit 23. When the node voltage is greater than the threshold voltage, the voltage output circuit 24 outputs a voltage greater than the reference voltage to the OR circuit 23.

[0071] <Operation of Power Supply Control Device 10>

[0072] Figure 2 1 is a timing chart for explaining the operation of the power supply control device 10. Figure 2 , the output voltage of the microcomputer 26, the node voltage, the output voltage of the voltage output circuit 24, the output voltage of the OR circuit 23, and the transition of the states of the first semiconductor switch 20a and the second semiconductor switch 20b are shown. In these transitions, time is shown on the horizontal axis. The voltage of the positive electrode of the battery 12 based on the potential of the negative electrode is recorded as the battery voltage. The battery voltage exceeds the threshold voltage. Figure 2 In , the high level voltage, low level voltage, reference voltage, battery voltage and threshold voltage are represented by H, L, Vr, Vb and Vth respectively. Figure 2In other figures, the high-level voltage, the low-level voltage, the reference voltage, the battery voltage, and the threshold voltage are also shown in the same manner.

[0073] In the following, it is assumed that the connection of the storage battery 12 is a normal connection. Figure 2 As shown, when there is no fault in the power supply control device 10, when the output voltage of the microcomputer 26 is a low level voltage, the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. The node voltage and the output voltage of the voltage output circuit are zero V. The output voltage of the OR circuit 23 is a low level voltage.

[0074] When the microcomputer 26 switches the output voltage from a low level voltage to a high level voltage, the OR circuit 23 switches the output voltage to the first drive circuit 22a to a high level voltage, and the first drive circuit 22a switches the first semiconductor switch 20a to on. In addition, because the output voltage to the second drive circuit 22b is switched from a low level voltage to a high level voltage, the second drive circuit 22b switches the second semiconductor switch 20b to on. Therefore, when the microcomputer 26 switches the output voltage to a high level voltage, the first semiconductor switch 20a and the second semiconductor switch 20b are switched on.

[0075] When the first semiconductor switch 20a and the second semiconductor switch 20b are switched on, the node voltage rises to the battery voltage Vb. As a result, the output voltage of the voltage output circuit 24 rises to a voltage higher than the reference voltage Vr. When the first semiconductor switch 20a and the second semiconductor switch 20b are switched on, the positive terminal Tp and one end of the load 11 are electrically connected, and the battery 12 supplies power to the load 11 via the first semiconductor switch 20a and the second semiconductor switch 20b.

[0076] At this time, the current flows from the positive terminal Tp to the first semiconductor switch 20a, the second semiconductor switch 20b, the load 11, and the negative terminal Tn in sequence. In this way, the first semiconductor switch 20a, the second semiconductor switch 20b, and the load 11 are sequentially arranged in the current path of the current flowing from the positive terminal Tp to the negative terminal Tn. The cathodes of the first diode 21a and the second diode 21b are located on the downstream side and the upstream side of the anode in the current path.

[0077] When the first semiconductor switch 20a is on, the voltage between the drain and the source is substantially zero V, so current does not flow through the first diode 21a. Similarly, when the second semiconductor switch 20b is on, current does not flow through the second diode 21b.

[0078] When the microcomputer 26 switches the output voltage from a high level voltage to a low level voltage, the second drive circuit 22b switches the second semiconductor switch 20b to off. When the second semiconductor switch 20b is switched to off, the flow of current through the load 11 and the flow of current through the circuit resistors 30 and 31 are stopped, so the node voltage and the output voltage of the voltage output circuit 24 drop to zero V. As a result, the two voltages input to the OR circuit 23 are lower than the reference voltage Vr, so the output voltage of the OR circuit 23 is switched to a low level voltage, and the first drive circuit 22a switches the first semiconductor switch 20a to off.

[0079] As described above, when no failure occurs in the power supply control device 10, when the microcomputer 26 switches the output voltage from the high level voltage to the low level voltage, the first semiconductor switch 20a and the second semiconductor switch 20b are switched to be off. When the first semiconductor switch 20a and the second semiconductor switch 20b are switched to be off, the electrical connection between the positive terminal Tp and one end of the load 11 is cut off, and the power supply from the battery 12 to the load 11 is stopped.

[0080] When the drain and source of the second semiconductor switch 20b are short-circuited while the microcomputer 26 is outputting a low-level voltage, a current flows from the positive electrode of the battery 12 through the first diode 21a of the first semiconductor switch 20a, the second semiconductor switch 20b, and the load 11 in sequence, and the node voltage rises to a value near the battery voltage Vb, exceeding the threshold voltage Vth. As a result, the output voltage of the voltage output circuit 24 becomes higher than the reference voltage Vr, and the output voltage of the OR circuit 23 switches from a low-level voltage to a high-level voltage. As a result, the first drive circuit 22a switches the first semiconductor switch 20a on, and the flow of current through the first diode 21a stops.

[0081] As described above, when the microcomputer 26 instructs the first semiconductor switch 20a and the second semiconductor switch 20b to switch off, if the drain and source of the second semiconductor switch 20b are short-circuited, the first drive circuit 22a switches the first semiconductor switch 20a on.

[0082] Short circuiting of the drain and source of the second semiconductor switch 20b means a failure in which the resistance value between the drain and the source is fixed to a small value regardless of the gate voltage in the second semiconductor switch 20b. When a short circuit occurs, current can flow through the drain and the source.

[0083] When the drain and source of the second semiconductor switch 20b are short-circuited while the microcomputer 26 is outputting a high-level voltage, even if the microcomputer 26 switches the output voltage to a low-level voltage, the node voltage does not drop to a voltage lower than the threshold voltage Vth. Therefore, even if the output voltage of the microcomputer 26 is switched to a low-level voltage, the OR circuit 23 continues to output a high-level voltage, and the first drive circuit 22a maintains the first semiconductor switch 20a in the on state.

[0084] Normally, the battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected. At this time, even if the connection of the battery 12 is reversed, the node voltage and the output voltage of the voltage output circuit 24 are maintained at zero V, and the output voltage of the OR circuit 23 does not switch from a low-level voltage to a high-level voltage. Therefore, when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected, regardless of whether the connection of the battery 12 is normally connected, current does not flow from the battery 12.

[0085] <Structure of Microcomputer 26>

[0086] Figure 3 2 is a block diagram showing the configuration of the main part of the microcomputer 26. The microcomputer 26 includes an output unit 40, a storage unit 41, and a control unit 42. These are connected to an internal bus 43. The output unit 40 is further connected to the OR circuit 23 and the second drive circuit 22b via the device resistor 25.

[0087] The output unit 40 outputs a low voltage or a high voltage to the OR circuit 23 and the second drive circuit 22b via the device resistor 25. The output unit 40 switches the output voltage to the OR circuit 23 and the second drive circuit 22b to a low voltage or a high voltage according to the instruction of the control unit 42.

[0088] The storage unit 41 is a nonvolatile memory. The storage unit 41 stores a computer program P. The control unit 42 includes a processing element, such as a CPU (Central Processing Unit) for executing processing. The processing element of the control unit 42 executes the computer program P to execute a power supply control process for controlling power supply to the load 11 .

[0089] In addition, the computer program P can also be stored in the storage medium A in a manner that can be read by the processing element of the control unit 42. In this case, the computer program P read from the storage medium A by the reading device not shown in the figure is written to the storage unit 41. The storage medium A is an optical disk, a floppy disk, a magnetic disk, a magneto-optical disk, or a semiconductor memory, etc. The optical disk is a CD (Compact Disc: Optical Disk)-ROM (Read Only Memory: Read Only Memory), a DVD (Digital Versatile Disc: Digital Versatile Disc)-ROM or a BD (Blu-ray (registered trademark) Disc: Blu-ray Disc), etc. The magnetic disk is, for example, a hard disk. In addition, the computer program P can also be downloaded from an external device not shown in the figure that is connected to a communication network not shown in the figure, and the downloaded computer program P can be written to the storage unit 41.

[0090] The number of processing elements included in the control unit 42 is not limited to one, and may be two or more. In this case, the plurality of processing elements may cooperatively execute the temperature calculation process and the power supply control process according to the computer program P.

[0091] <Power supply control processing>

[0092] Figure 4 is a flowchart showing the process of power supply control processing. In the following, it is assumed that the connection of the storage battery 12 is normally connected. In the power supply control processing, first, the control unit 42 determines whether to supply power to the load 11 (step S1). For example, when an operation signal indicating the operation of the load 11 is input to an input unit not shown, the control unit 42 determines that power is supplied to the load 11. When the operation signal is not input to the input unit, the control unit 42 determines that power is not supplied to the load 11.

[0093] When the control unit 42 determines that power is not supplied (S1: No), it determines whether to stop the power supply to the load 11 (step S2). For example, when a stop signal indicating the stop of the power supply to the load 11 is input to an input unit not shown in the figure, the control unit 42 determines that the power supply to the load 11 is stopped. When the stop signal is not input to the input unit, the control unit 42 determines that the power supply to the load 11 is not stopped. When the control unit 42 determines that the power supply is not stopped (S2: No), the power supply control process is terminated. After terminating the power supply control process, the control unit 42 executes the power supply control process again. Therefore, the control unit 42 waits until the power supply to the load 11 needs to be supplied or the power supply to the load 11 needs to be stopped.

[0094] When the control unit 42 determines that power is to be supplied (S1: Yes), it instructs the output unit 40 to switch the output voltage to a high-level voltage (step S3). As a result, the output unit 40 switches the output voltage to the OR circuit 23 and the second drive circuit 22b to a high-level voltage. As a result, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned on, and the battery 12 supplies power to the load 11. The control unit 42 instructs the first drive circuit 22a and the second drive circuit 22b to switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned on by executing step S3.

[0095] When the control unit 42 determines that the power supply is stopped (S2: Yes), it instructs the output unit 40 to switch the output voltage to a low-level voltage (step S4). As a result, the output unit 40 switches the output voltage to the OR circuit 23 and the second drive circuit 22b to a low-level voltage. When the two ends of the second semiconductor switch 20b are not short-circuited, when the output unit 40 switches the output voltage to a low-level voltage, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be disconnected, and the power supply from the battery 12 to the load 11 is stopped.

[0096] The control unit 42 executes step S4 to instruct the first drive circuit 22a and the second drive circuit 22b to switch the first semiconductor switch 20a and the second semiconductor switch 20b to OFF. The control unit 42 functions as a processing unit.

[0097] After executing one of steps S3 and S4, the control unit 42 ends the power supply control process. As described above, after ending the power supply control process, the control unit 42 executes the power supply control process again.

[0098] <Effects of the Power Supply Control Device 10>

[0099] As described above, the control unit 42 of the microcomputer 26 instructs the first semiconductor switch 20a and the second semiconductor switch 20b to switch to off by instructing the output unit 40 to switch the output voltage to a low level voltage. Although the control unit 42 instructs the first semiconductor switch 20a and the second semiconductor switch 20b to switch to off, when the node voltage is above the threshold voltage, it is considered that the drain and source of the second semiconductor switch 20b are short-circuited, and the OR circuit 23 switches the output voltage to a high level voltage. As a result, the first drive circuit 22a switches the first semiconductor switch 20a to on. The node voltage being above the threshold voltage means that the current is flowing in the current path from the positive terminal Tp to the negative terminal Tn.

[0100] Since the first drive circuit 22a operates as described above, the current does not flow through the first diode 21a for a long time, and the temperature of the first semiconductor switch 20a does not rise to an abnormal temperature. The first semiconductor switch 20a does not fail due to a short circuit between the drain and the source of the second semiconductor switch 20b. The first drive circuit 22a functions as a switching unit.

[0101] (Implementation Method 2)

[0102] The configuration of the voltage output circuit 24 is not limited to the configuration described in the first embodiment.

[0103] Hereinafter, the differences between Embodiment 2 and Embodiment 1 will be described. The other configurations except for the configuration described below are common to Embodiment 1. Therefore, the same reference numerals as those in Embodiment 1 are given to the configurations common to Embodiment 1, and the description thereof will be omitted.

[0104] <Structure of Voltage Output Circuit 24>

[0105] Figure 5 1 is a block diagram showing the structure of the main part of the power supply system 1 in Embodiment 2. When Embodiment 2 is compared with Embodiment 1, the structure of the voltage output circuit 24 is different. In Embodiment 2, the voltage output circuit 24 includes circuit resistors 50, 51, ..., 54, a first circuit switch 55, and a second circuit switch 56. The first circuit switch 55 is an NPN type bipolar transistor. The second circuit switch 56 is a PNP type bipolar transistor.

[0106] One end of the circuit resistor 50 is connected to a connection node between the source of the second semiconductor switch 20b and one end of the load 11. The other end of the circuit resistor 50 is connected to the base of the first circuit switch 55. A circuit resistor 51 is connected between the base and the emitter of the first circuit switch 55. The emitter of the first circuit switch 55 is grounded. The collector of the first circuit switch 55 is connected to one end of the circuit resistor 52. The other end of the circuit resistor 52 is connected to the base of the second circuit switch 56.

[0107] A circuit resistor 53 is connected between the base and the emitter of the second circuit switch 56. A certain voltage Vc is applied to the emitter of the second circuit switch 56. The certain voltage Vc is a voltage based on the ground potential. The collector of the second circuit switch 56 is connected to one end of the circuit resistor 54. The other end of the circuit resistor 54 is grounded. The connection node between the collector of the second circuit switch 56 and one end of the circuit resistor 54 is connected to one input end of the OR circuit 23.

[0108] In the first circuit switch 55, when the voltage of the base electrode based on the potential of the emitter electrode is greater than a certain positive voltage, the resistance value between the collector and the emitter electrode is sufficiently small. At this time, the first circuit switch 55 is turned on, and the current can flow through the collector and the emitter electrode. In the first circuit switch 55, when the voltage of the base electrode based on the potential of the emitter electrode is less than a certain positive voltage, the resistance value between the collector and the emitter electrode is sufficiently large. At this time, the first circuit switch 55 is turned off, and the current does not flow through the collector and the emitter electrode.

[0109] In the second circuit switch 56, when the voltage of the base electrode based on the potential of the emitter electrode is less than a negative certain voltage, the resistance value between the collector and the emitter electrode is sufficiently small. At this time, the second circuit switch 56 is turned on, and the current can flow through the emitter and the collector. In the second circuit switch 56, when the voltage of the base electrode based on the potential of the emitter electrode is more than a negative certain voltage, the resistance value between the collector and the emitter electrode is sufficiently large. At this time, the second circuit switch 56 is turned off, and the current does not flow through the collector and the emitter electrode.

[0110] <Operation of Voltage Output Circuit 24>

[0111] Figure 6 2 is a timing chart for explaining the operation of the voltage output circuit 24. Figure 6 2 shows the transition of the node voltage, the state of the first circuit switch 55, the state of the second circuit switch 56, and the output voltage of the voltage output circuit 24. The horizontal axis shows the time for these transitions.

[0112] When the node voltage exceeds zero, the current flows through the circuit resistors 50 and 51 in sequence. A voltage drop occurs in the circuit resistor 51. In the first circuit switch 55, the voltage of the base electrode based on the potential of the emitter electrode is consistent with the amplitude of the voltage drop in the circuit resistor 51. The higher the node voltage is, the greater the current flowing in the circuit resistor 51 is, and therefore the amplitude of the voltage drop is greater. The threshold voltage Vth is the node voltage when the voltage of the base electrode based on the potential of the emitter electrode in the first circuit switch 55 is a positive constant voltage of the first circuit switch 55. The threshold voltage Vth exceeds zero V and is less than the battery voltage Vb.

[0113] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned off, the node voltage is zero V, which is less than the threshold voltage Vth. When the node voltage is less than the threshold voltage Vth, the voltage of the base based on the potential of the emitter is less than a positive constant voltage in the first circuit switch 55. Therefore, the first circuit switch 55 is turned off.

[0114] When the first circuit switch 55 is off, the current does not flow through the circuit resistors 53 and 52, so in the second circuit switch 56, the voltage of the base based on the potential of the emitter is zero V, which is a positive voltage or more. Therefore, the second circuit switch 56 is also off. When the second circuit switch 56 is off, the current does not flow through the circuit resistor 54, so the voltage output circuit 24 outputs zero V to the OR circuit 23. Zero V is smaller than the reference voltage Vr. Therefore, when the node voltage is zero V, the voltage output circuit 24 outputs a voltage smaller than the reference voltage Vr, similar to the first embodiment.

[0115] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on or the first semiconductor switch 20a is turned off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is the battery voltage Vb or a value near the battery voltage Vb, which is greater than the threshold voltage Vth. At this time, in the first circuit switch 55, the voltage of the base electrode based on the emitter electrode is greater than a certain positive voltage, and the first circuit switch 55 is turned on. When the first circuit switch 55 is turned on, current flows through the circuit resistors 53 and 52 in sequence, and a voltage drop occurs in the circuit resistor 53.

[0116] At this time, in the second circuit switch 56, the voltage of the base with the emitter as the reference is less than the negative constant voltage, and the second circuit switch 56 is turned on. When the second circuit switch 56 is turned on, the voltage output circuit 24 outputs the constant voltage Vc to the OR circuit 23. The constant voltage Vc is greater than or equal to the reference voltage Vr of the OR circuit 23. Therefore, when the node voltage is the battery voltage Vb or a value close to the battery voltage Vb, the voltage output circuit 24 outputs a voltage greater than or equal to the reference voltage, similar to the first embodiment.

[0117] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is zero V, which is less than the threshold voltage Vth, so the first circuit switch 55 and the second circuit switch 56 are disconnected, and the voltage output circuit 24 outputs zero V. Therefore, when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected, regardless of whether the connection of the battery 12 is normally connected, current does not flow from the battery 12.

[0118] As described above, the voltage output circuit 24 in the second embodiment functions in the same manner as the voltage output circuit 24 in the first embodiment. Therefore, the power supply control device 10 in the second embodiment achieves the same effects as the power supply control device 10 in the first embodiment.

[0119] (Implementation method 3)

[0120] The configuration of the voltage output circuit 24 is not limited to the configurations described in the first and second embodiments.

[0121] Hereinafter, Embodiment 3 will be described with respect to points different from Embodiment 1. The other structures except the structure described below are common to Embodiment 1. Therefore, the same reference numerals as those in Embodiment 1 are attached to the components common to Embodiment 1, and the description thereof will be omitted.

[0122] <Structure of Voltage Output Circuit 24>

[0123] Figure 7 1 is a block diagram showing the structure of the main part of the power supply system 1 in Embodiment 3. When Embodiment 3 is compared with Embodiment 1, the structure of the voltage output circuit 24 is different. In Embodiment 3, the voltage output circuit 24 has a comparator 60, a circuit resistor 61, and a DC power supply 62. The comparator 60 has a positive terminal, a negative terminal, and an output terminal.

[0124] The positive terminal of the comparator 60 is connected to a connection node between the source of the second semiconductor switch 20b and one end of the load 11 and one end of the circuit resistor 61. The negative terminal of the comparator 60 is connected to the positive electrode of the DC power supply 62. The other end of the circuit resistor 61 and the negative electrode of the DC power supply 62 are grounded. The output terminal of the comparator 60 is connected to one input terminal of the OR circuit 23.

[0125] The voltage of the positive electrode of the DC power supply 62 based on the ground potential is a constant value, and functions as a threshold voltage Vth. When the voltage of the positive terminal based on the ground potential, that is, the node voltage, is greater than the threshold voltage Vth, the comparator 60 outputs a high-level voltage to the OR circuit 23. The high-level voltage output by the comparator 60 is greater than the reference voltage of the OR circuit 23. When the node voltage is less than the threshold voltage, the comparator 60 outputs a low-level voltage to the OR circuit 23. The low-level voltage output by the comparator 60 is less than the reference voltage of the OR circuit 23.

[0126] <Operation of Voltage Output Circuit 24>

[0127] Figure 8 2 is a timing chart for explaining the operation of the voltage output circuit 24. Figure 8 2 shows the transition of the node voltage and the output voltage of the voltage output circuit 24. The horizontal axis shows the time for these transitions.

[0128] When the first semiconductor switch 20 a and the second semiconductor switch 20 b are off, the node voltage is zero V. When the node voltage is zero V, the comparator 60 , ie, the voltage output circuit 24 , outputs a voltage lower than the reference voltage Vr similarly to the first embodiment.

[0129] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on or the first semiconductor switch 20a is turned off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is the battery voltage Vb or a value close to the battery voltage Vb. At this time, the comparator 60 outputs a high-level voltage. Therefore, when the node voltage is the battery voltage Vb or a value close to the battery voltage Vb, the voltage output circuit 24 outputs a voltage higher than the reference voltage, similar to the first embodiment.

[0130] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, since the other end of the circuit resistor 61 is grounded, the node voltage is zero V. When the node voltage is zero V, the comparator 60, that is, the voltage output circuit 24 outputs a low level voltage. Therefore, when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected, regardless of whether the connection of the battery 12 is normally connected, current does not flow from the battery 12.

[0131] As described above, the voltage output circuit 24 in the third embodiment functions in the same manner as the voltage output circuit 24 in the first embodiment. Therefore, the power supply control device 10 in the third embodiment achieves the same effects as the power supply control device 10 in the first embodiment.

[0132] (Implementation 4)

[0133] In the first embodiment, the determination of whether the node voltage is equal to or higher than the threshold voltage is performed by the OR circuit 23. However, the device that performs this determination is not limited to the OR circuit 23.

[0134] Hereinafter, Embodiment 4 will be described with respect to points different from Embodiment 1. The other structures except the structure described below are the same as those of Embodiment 1. Therefore, the same reference numerals as those of Embodiment 1 are attached to the structural parts common to Embodiment 1, and the description thereof is omitted.

[0135] Fig. 9 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 4. The power supply control device 10 in Embodiment 4 has a configuration part other than the OR circuit 23 in the configuration part of the power supply control device 10 in Embodiment 1. In Embodiment 4, the connection node between the circuit resistors 30 and 31 of the voltage output circuit 24 is connected to the microcomputer 26. The microcomputer 26 is connected to the first drive circuit 22a and the second drive circuit 22b via the device resistor 25.

[0136] The output voltage of the voltage output circuit 24 is input to the microcomputer 26. The microcomputer 26 outputs a high level voltage or a low level voltage to the first drive circuit 22a and the second drive circuit 22b. When the voltage input from the microcomputer 26 is switched from a low level voltage to a high level voltage, the first drive circuit 22a switches the first semiconductor switch 20a on. When the voltage input from the microcomputer 26 is switched from a high level voltage to a low level voltage, the first drive circuit 22a switches the first semiconductor switch 20a off.

[0137] When the output voltage of the microcomputer 26 is switched to a high level voltage, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned on, similarly to Embodiment 1. When the output voltage of the microcomputer 26 is switched to a low level voltage, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned off, regardless of the output voltage of the voltage output circuit 24.

[0138] <Structure of Microcomputer 26>

[0139] Fig.10 2 is a block diagram showing the structure of the main part of the microcomputer 26. The microcomputer 26 in the fourth embodiment has an input unit 44 and an A / D conversion unit 45 in addition to the components of the microcomputer 26 in the first embodiment. The output unit 40 is connected to the internal bus 43 and is connected to the first drive circuit 22a and the second drive circuit 22b via the device resistor 25. The A / D conversion unit 45 is connected to the internal bus 43 and the input unit 44. The input unit 44 is further connected to the connection node between the circuit resistors 30 and 31 of the voltage output circuit 24.

[0140] The output unit 40 outputs a high voltage or a low voltage to the first drive circuit 22a and the second drive circuit 22b via the device resistor 25. The output unit 40 switches the output voltage to the first drive circuit 22a and the second drive circuit 22b to a high voltage or a low voltage according to the instruction of the control unit 42.

[0141] The voltage output circuit 24 outputs an analog voltage to the input unit 44. When the analog voltage is input, the input unit 44 outputs the input analog voltage to the A / D conversion unit 45. The A / D conversion unit 45 converts the analog voltage input from the input unit 44 into a digital voltage. The control unit 42 obtains the digital voltage converted by the A / D conversion unit 45 from the A / D conversion unit 45. The voltage obtained by the control unit 42 is substantially consistent with the voltage output by the voltage output circuit 24 at the time of acquisition.

[0142] The processing element of the control unit 42 executes the computer program P to perform, in addition to the power supply control process, a short-circuit detection process for detecting a short circuit between the drain and the source of the second semiconductor switch 20 b .

[0143] <Short Circuit Detection Processing>

[0144] Fig.11 2 is a flowchart showing the process of short circuit detection processing. The control unit 42 determines whether the output voltage of the output unit 40 is a low level voltage (step S11). As described in the description of the first embodiment, the output voltage of the output unit 40 is a low level voltage, which means that the control unit 42 instructs the first semiconductor switch 20a and the second semiconductor switch 20b to be disconnected.

[0145] When the control unit 42 determines that the output voltage is a low-level voltage (S11: Yes), it determines whether the node voltage is greater than the threshold voltage (step S12). In step S12, the control unit 42 determines that the node voltage is greater than the threshold voltage when the output voltage of the voltage output circuit 24 is greater than the reference voltage Vr. When the output voltage of the voltage output circuit 24 is less than the reference voltage Vr, it determines that the node voltage is less than the threshold voltage.

[0146] The control unit 42 terminates the short-circuit detection process when it is determined that the output voltage is not a low-level voltage (S11: No) or when it is determined that the node voltage is less than the threshold voltage (S12: No). After the short-circuit detection process is terminated, the control unit 42 performs the short-circuit detection process again. Therefore, the control unit 42 waits until the node voltage becomes greater than the threshold voltage when the output voltage is a low-level voltage.

[0147] When the control unit 42 determines that the node voltage is greater than the threshold voltage (S12: Yes), it assumes that the drain and source of the second semiconductor switch 20b are short-circuited, and instructs the output unit 40 to switch the output voltage to the first drive circuit 22a and the second drive circuit 22b to a high-level voltage (step S13). As a result, the first drive circuit 22a switches the first semiconductor switch 20a on. The control unit 42 instructs the first drive circuit 22a to switch the first semiconductor switch 20a on by executing step S13.

[0148] After executing step S13 , the control unit 42 ends the short-circuit detection process and executes the short-circuit detection process again.

[0149] As described above, in the power supply control device 10 in the fourth embodiment, similarly to the first embodiment, when the node voltage is equal to or higher than the threshold voltage, the first drive circuit 22a switches the first semiconductor switch 20a to be turned on even though the control unit 42 instructs the first semiconductor switch 20a and the second semiconductor switch 20b to be turned off. The power supply control device in the fourth embodiment has the same effect as the power supply control device 10 in the first embodiment.

[0150] (Implementation 5)

[0151] In Embodiment 1, the first semiconductor switch 20a is arranged on the upstream side of the second semiconductor switch 20b. The arrangement of the first semiconductor switch 20a and the second semiconductor switch 20b is not limited to this arrangement.

[0152] Hereinafter, Embodiment 5 will be described with respect to points different from Embodiment 1. The other structures except the structure described later are the same as those of Embodiment 1. Therefore, the same reference numerals as those of Embodiment 1 are attached to the structural parts common to Embodiment 1, and the description thereof is omitted.

[0153] <Structure of Power Supply Control Device 10>

[0154] Fig.12 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 5. When Embodiment 5 is compared with Embodiment 1, the configuration of the first semiconductor switch 20a and the second semiconductor switch 20b is different. In the power supply control device 10 in Embodiment 5, the drain of the second semiconductor switch 20b is connected to the positive terminal Tp. The source of the second semiconductor switch 20b is connected to the source of the first semiconductor switch 20a. The drain of the first semiconductor switch 20a is connected to one end of the load 11.

[0155] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on when the connection of the battery 12 is normally connected, the current flows sequentially through the positive terminal Tp, the second semiconductor switch 20b, the first semiconductor switch 20a, the load 11, and the negative terminal Tn. The second semiconductor switch 20b, the first semiconductor switch 20a, and the load 11 are sequentially arranged on the current path of the current flowing from the positive terminal Tp to the negative terminal Tn.

[0156] One end of the circuit resistor 30 of the voltage output circuit 24 is connected to the connection node between the sources of the first semiconductor switch 20a and the second semiconductor switch 20b. The node voltage in the fifth embodiment is a voltage applied to the connection node between the sources of the first semiconductor switch 20a and the second semiconductor switch 20b with reference to the ground potential.

[0157] Assuming that the first semiconductor switch 20a is disconnected and the drain and source of the second semiconductor switch 20b are short-circuited when the connection of the battery 12 is normal, the current flows through the positive terminal Tp, the second semiconductor switch 20b, the first diode 21a of the first semiconductor switch 20a, the load 11, and the negative terminal Tn in sequence.

[0158] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is zero V, similar to the first embodiment. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is the battery voltage Vb or a value close to the battery voltage Vb, similar to the first embodiment.

[0159] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is zero V as in the first embodiment.

[0160] Therefore, the power supply control device 10 in the fifth embodiment achieves the same effects as achieved by the power supply control device 10 in the first embodiment.

[0161] In the fifth embodiment, the configuration of the voltage output circuit 24 is not limited to the configuration using the circuit resistors 30 and 31 , and may be the configuration of the voltage output circuit 24 in the second and third embodiments.

[0162] (Implementation method 6)

[0163] In the fifth embodiment, the node voltage is based on the ground potential, but is not limited to the voltage applied to the connection node between the sources of the first semiconductor switch 20 a and the second semiconductor switch 20 b based on the ground potential.

[0164] Hereinafter, the differences from Embodiment 5 will be described with respect to Embodiment 6. The configuration other than the configuration described below is common to Embodiment 5. Therefore, the same reference numerals as those in Embodiment 5 are given to the configuration portions common to Embodiment 5, and the description thereof will be omitted.

[0165] <Structure of Power Supply Control Device 10>

[0166] Fig.131 is a block diagram showing the structure of the main part of the power supply system 1 in Embodiment 6. When Embodiment 6 is compared with Embodiment 5, the connection node to which the voltage output circuit 24 is connected is different. As described in the description of Embodiment 5, the structure of the voltage output circuit 24 is not limited to the structure using the circuit resistors 30 and 31, and may be the structure of one of the voltage output circuits 24 in Embodiments 2 and 3.

[0167] exist Fig.13 , the configuration of the voltage output circuit 24 is an example of the configuration of the first embodiment using the circuit resistors 30 and 31. In this case, one end of the circuit resistor 30 is connected to the connection node between the drain of the first semiconductor switch 20a and one end of the load 11. In the sixth embodiment, the node voltage is a voltage applied to the connection node between the drain of the first semiconductor switch 20a and one end of the load 11 with reference to the ground potential.

[0168] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is zero V, similarly to Embodiment 5. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is the battery voltage Vb or a value close to the battery voltage Vb, similarly to Embodiment 5.

[0169] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is zero V as in the fifth embodiment.

[0170] Therefore, the power supply control device 10 in the sixth embodiment achieves the same effects as achieved by the power supply control device 10 in the fifth embodiment.

[0171] (Implementation 7)

[0172] In Embodiment 4, the first semiconductor switch 20a is arranged on the upstream side of the second semiconductor switch 20b. The arrangement of the first semiconductor switch 20a and the second semiconductor switch 20b is not limited to this arrangement.

[0173] Hereinafter, Embodiment 7 will be described with respect to points different from Embodiment 4. The other structures except the structure described later are common to Embodiment 4. Therefore, the same reference numerals as those in Embodiment 4 are attached to the structural parts common to Embodiment 4, and the description thereof is omitted.

[0174] <Structure of Power Supply Control Device 10>

[0175] Fig.14 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 7. When Embodiment 7 is compared with Embodiment 4, the configuration of the first semiconductor switch 20a and the second semiconductor switch 20b is different. In the power supply control device 10 in Embodiment 7, the drain of the second semiconductor switch 20b is connected to the positive terminal Tp. The source of the second semiconductor switch 20b is connected to the source of the first semiconductor switch 20a. The drain of the first semiconductor switch 20a is connected to one end of the load 11.

[0176] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on when the connection of the battery 12 is normally connected, the current flows sequentially through the positive terminal Tp, the second semiconductor switch 20b, the first semiconductor switch 20a, the load 11, and the negative terminal Tn. The second semiconductor switch 20b, the first semiconductor switch 20a, and the load 11 are sequentially arranged on the current path of the current flowing from the positive terminal Tp to the negative terminal Tn.

[0177] As described in the description of the fourth embodiment, the configuration of the voltage output circuit 24 is not limited to the configuration using the circuit resistors 30 and 31, and may be the configuration of the voltage output circuit 24 in the second and third embodiments. Fig.14 , an example is shown in which the configuration of the voltage output circuit 24 is the configuration of the first embodiment using the circuit resistors 30 and 31. In this example, one end of the circuit resistor 30 is connected to the connection node between the sources of the first semiconductor switch 20a and the second semiconductor switch 20b. The node voltage in the seventh embodiment is a voltage applied to the connection node between the sources of the first semiconductor switch 20a and the second semiconductor switch 20b with reference to the ground potential.

[0178] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is zero V, similarly to Embodiment 4. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is the battery voltage Vb or a value close to the battery voltage Vb, similarly to Embodiment 4.

[0179] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is zero V as in the fourth embodiment. Therefore, the power supply control device 10 in the seventh embodiment has the same effect as the power supply control device 10 in the fourth embodiment.

[0180] <Attachment>

[0181] The connection node to which the voltage output circuit 24 is connected may be the connection node between the drain of the first semiconductor switch 20a and one end of the load 11 as in Embodiment 6. In this case, the node voltage is a voltage applied to the connection node between the drain of the first semiconductor switch 20a and one end of the load 11 with reference to the ground potential.

[0182] (Implementation 8)

[0183] In the second embodiment, the load 11 is arranged on the downstream side of the power supply control device 10. However, the arrangement of the load 11 is not limited to this arrangement.

[0184] Hereinafter, the differences between Embodiment 8 and Embodiment 2 will be described. The other structures except the structures described below are the same as those of Embodiment 2. Therefore, the same reference numerals as those of Embodiment 2 are attached to the structural parts common to Embodiment 2, and the description thereof will be omitted.

[0185] <Structure of Power Supply System 1>

[0186] Fig.15 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 8. In the power supply system 1 in Embodiment 8, the positive terminal Tp is connected to one end of the load 11. The other end of the load 11 is connected to the source of the first semiconductor switch 20a included in the power supply control device 10. The source of the second semiconductor switch 20b is grounded.

[0187] In Embodiment 8, the power supply control device 10 switches the first semiconductor switch 20a and the second semiconductor switch 20b to ON. As a result, the other end of the load 11 and the negative terminal Tn are electrically connected, and power is supplied from the battery 12 to the load 11. The power supply control device 10 switches the first semiconductor switch 20a and the second semiconductor switch 20b to OFF. As a result, the electrical connection between the other end of the load 11 and the negative terminal Tn is cut off, and the power supply from the battery 12 to the load 11 is stopped.

[0188] <Structure of Power Supply Control Device 10>

[0189] The power supply control device 10 in the eighth embodiment has all the components of the power supply control device 10 in the second embodiment. The first semiconductor switch 20a, the second semiconductor switch 20b, the first drive circuit 22a, the second drive circuit 22b, the OR circuit 23, the device resistor 25, and the microcomputer 26 are connected in the same manner as in the second embodiment. The voltage output circuit 24 in the eighth embodiment has the circuit resistors 52, 53, 54 and the second circuit switch 56 in the same manner as in the second embodiment. These are connected in the same manner as in the second embodiment.

[0190] One end of the circuit resistor 52 is connected to the connection node between the drains of the first semiconductor switch 20a and the second semiconductor switch 20b. A certain voltage Vc is applied to the emitter of the second circuit switch 56. The connection node between the collector of the second circuit switch 56 and one end of the circuit resistor 54 is connected to one input terminal of the OR circuit 23. The node voltage in the eighth embodiment is a voltage applied to the connection node between the drains of the first semiconductor switch 20a and the second semiconductor switch 20b with reference to the ground potential.

[0191] When the connection of the battery 12 is normally connected, when the first semiconductor switch 20a and the second semiconductor switch 20b are turned on, the current flows from the positive terminal Tp to the load 11, the first semiconductor switch 20a, the second semiconductor switch 20b, and the negative terminal Tn in sequence. In this way, the load 11, the first semiconductor switch 20a, and the second semiconductor switch 20b are sequentially arranged in the current path of the current flowing from the positive terminal Tp to the negative terminal Tn. Assume that the first semiconductor switch 20a is turned off and the drain and source of the second semiconductor switch 20b are short-circuited under the same circumstances. In this case, the current flows through the positive terminal Tp, the load 11, the first diode 21a of the first semiconductor switch 20a, the second semiconductor switch 20b, and the negative terminal Tn in sequence.

[0192] <Operation of Voltage Output Circuit 24>

[0193] Fig.16 2 is a timing chart for explaining the operation of the voltage output circuit 24. Fig.16 2 shows the transition of the node voltage and the output voltage of the voltage output circuit 24. The horizontal axis shows the time for these transitions.

[0194] When the node voltage is less than the certain voltage Vc, the current flows through the circuit resistors 53 and 52 in sequence, and a voltage drop occurs in the circuit resistor 53. At this time, in the second circuit switch 56, the voltage of the base based on the potential of the emitter is a negative voltage. The absolute value of the negative voltage is consistent with the amplitude of the voltage drop. The lower the node voltage, the greater the current flowing in the circuit resistor 53, and therefore the greater the amplitude of the voltage drop. The threshold voltage Vth is the node voltage when the voltage of the base based on the potential of the emitter in the second circuit switch 56 is a negative certain voltage of the second circuit switch 56. The threshold voltage Vth exceeds zero V and is less than the certain voltage Vc.

[0195] In the eighth embodiment, when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off, the current does not flow through the circuit resistors 52 and 53, so the node voltage is a constant voltage Vc, which is greater than the threshold voltage Vth. In this case, the second circuit switch 56 is turned off, and the voltage output circuit 24 outputs zero V, which is less than the reference voltage Vr, to the OR circuit 23. When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on or the first semiconductor switch 20a is turned off in a state where the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is zero V, which is less than the threshold voltage Vth. In this case, the second circuit switch 56 is turned on, and the voltage output circuit 24 outputs a constant voltage Vc, which is greater than the reference voltage Vr, to the OR circuit 23.

[0196] Therefore, even though the control unit 42 of the microcomputer 26 causes the output unit 40 to output a low-level voltage, when the node voltage is less than the threshold voltage, the drain and source of the second semiconductor switch 20b are considered to be short-circuited, and the OR circuit 23 switches the output voltage to a high-level voltage. As a result, the first drive circuit 22a switches the first semiconductor switch 20a on. The node voltage being less than the threshold voltage Vth means that current is flowing in the current path from the positive terminal Tp to the negative terminal Tn.

[0197] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is a certain voltage Vc, which is greater than the threshold voltage Vth, so the second circuit switch 56 is disconnected, and the voltage output circuit 24 outputs zero V. Therefore, when the first semiconductor switch 20a and the second semiconductor switch 20b are disconnected, regardless of whether the connection of the battery 12 is normally connected, current does not flow from the battery 12.

[0198] The power supply control device 10 in the eighth embodiment functions in the same manner as the power supply control device 10 in the second embodiment, and achieves the same effects as achieved by the power supply control device 10 in the second embodiment.

[0199] (Implementation method 9)

[0200] In the eighth embodiment, the node voltage is not limited to the voltage applied to the connection node between the drains of the first semiconductor switch 20 a and the second semiconductor switch 20 b with reference to the ground potential.

[0201] Hereinafter, the differences between Embodiment 9 and Embodiment 8 will be described. The configuration other than the configuration described below is common to Embodiment 8. Therefore, the same reference numerals as those in Embodiment 8 are given to the configuration portions common to Embodiment 8, and the description thereof will be omitted.

[0202] <Structure of Power Supply Control Device 10>

[0203] Fig.17 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 9. When Embodiment 9 is compared with Embodiment 8, the connection node to which one end of the circuit resistor 52 of the voltage output circuit 24 is connected is different. One end of the circuit resistor 52 is connected to the connection node between the other end of the load 11 and the source of the first semiconductor switch 20a. In Embodiment 9, the node voltage is a voltage applied to the connection node between the other end of the load 11 and the source of the first semiconductor switch 20a with reference to the ground potential.

[0204] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is a certain voltage Vc, which is equal to or greater than the threshold voltage Vth as in Embodiment 8. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is zero V or a value close to zero V, which is lower than the threshold voltage Vth as in Embodiment 8.

[0205] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is a constant voltage Vc, which is equal to or higher than the threshold voltage Vth as in the eighth embodiment.

[0206] Therefore, the power supply control device 10 in the ninth embodiment achieves the same effects as achieved by the power supply control device 10 in the eighth embodiment.

[0207] (Implementation 10)

[0208] In the eighth embodiment, the determination of whether the node voltage is equal to or higher than the threshold voltage is performed by the OR circuit 23. However, the device that performs this determination is not limited to the OR circuit 23. Hereinafter, the differences from the eighth embodiment will be described with respect to the tenth embodiment. The other structures except for the structure described later are common to the eighth embodiment. Therefore, the same reference numerals as those in the eighth embodiment are marked on the structural parts common to the eighth embodiment, and the description thereof is omitted.

[0209] Fig.181 is a block diagram showing the structure of the main part of the power supply system 1 in the tenth embodiment. The power supply control device 10 in the tenth embodiment has a structure other than the OR circuit 23 in the structure of the power supply control device 10 in the eighth embodiment. The microcomputer 26 in the tenth embodiment is configured in the same manner as the microcomputer 26 in the fourth embodiment. In the tenth embodiment, the connection node between the collector of the second circuit switch 56 of the voltage output circuit 24 and the circuit resistor 54 is connected to the input section 44 of the microcomputer 26. The output section 40 of the microcomputer 26 is connected to the first drive circuit 22a and the second drive circuit 22b via the device resistor 25.

[0210] The output voltage of the voltage output circuit 24 is input to the input unit 44 of the microcomputer 26. The output unit 40 of the microcomputer 26 outputs a high level voltage or a low level voltage to the first drive circuit 22a and the second drive circuit 22b. When the voltage input from the output unit 40 is switched from a low level voltage to a high level voltage, the first drive circuit 22a switches the first semiconductor switch 20a on. When the voltage input from the output unit 40 of the microcomputer 26 is switched from a high level voltage to a low level voltage, the first drive circuit 22a switches the first semiconductor switch 20a off.

[0211] When the output voltage of the output unit 40 is switched to a high level voltage, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned on, similarly to Embodiment 8. When the output voltage of the output unit 40 is switched to a low level voltage, the first drive circuit 22a and the second drive circuit 22b switch the first semiconductor switch 20a and the second semiconductor switch 20b to be turned off, regardless of the output voltage of the voltage output circuit 24.

[0212] In the tenth embodiment, similarly to the fourth embodiment, the voltage output circuit 24 outputs a voltage lower than the reference voltage Vr when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. The voltage output circuit 24 outputs a voltage higher than the reference voltage Vr when the first semiconductor switch 20a and the second semiconductor switch 20b are turned on or when the first semiconductor switch 20a is turned off in a state where the drain and the source of the second semiconductor switch 20b are short-circuited.

[0213] Since the control unit 42 of the microcomputer 26 performs the short-circuit detection process similar to that of the fourth embodiment, the power supply control device 10 in the tenth embodiment can achieve the same effects as those achieved by the power supply control device 10 in the fourth embodiment.

[0214] In step S12 of the short-circuit detection process in the tenth embodiment, the control unit 42 determines that the node voltage is equal to or greater than the threshold voltage when the output voltage of the voltage output circuit 24 is less than the reference voltage Vr. The control unit 42 determines that the node voltage is less than the threshold voltage when the output voltage of the voltage output circuit 24 is greater than the reference voltage Vr. When the control unit 42 determines that the node voltage is less than the threshold voltage (S12: No), it assumes that the drain and source of the second semiconductor switch 20b are short-circuited and executes step S13. When the control unit 42 determines that the node voltage is equal to or greater than the threshold voltage (S12: Yes), the short-circuit detection process ends.

[0215] <Attachment>

[0216] One end of the circuit resistor 52 of the voltage output circuit 24 may be connected to the connection node between the other end of the load 11 and the source of the first semiconductor switch 20a, as in Embodiment 9. In this case, the node voltage is a voltage applied to the connection node between the other end of the load 11 and the source of the first semiconductor switch 20a with reference to the ground potential, as in Embodiment 9.

[0217] (Implementation 11)

[0218] In Embodiment 8, the first semiconductor switch 20a is arranged on the upstream side of the second semiconductor switch 20b. The arrangement of the first semiconductor switch 20a and the second semiconductor switch 20b is not limited to this arrangement.

[0219] Hereinafter, the differences from Embodiment 8 will be described with respect to Embodiment 11. The configuration other than the configuration described below is common to Embodiment 8. Therefore, the same reference numerals as those in Embodiment 8 are given to the configuration portions common to Embodiment 8, and the description thereof is omitted.

[0220] <Structure of Power Supply Control Device 10>

[0221] Fig.19 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 11. When Embodiment 11 is compared with Embodiment 8, the configuration of the first semiconductor switch 20a and the second semiconductor switch 20b is different. In the power supply control device 10 in Embodiment 11, the drain of the second semiconductor switch 20b is connected to the other end of the load 11. The source of the second semiconductor switch 20b is connected to the source of the first semiconductor switch 20a. The drain of the first semiconductor switch 20a is grounded.

[0222] When the connection of the battery 12 is normally connected, when the first semiconductor switch 20a and the second semiconductor switch 20b are turned on, the current flows through the positive terminal Tp, the load 11, the second semiconductor switch 20b, the first semiconductor switch 20a, and the negative terminal Tn in sequence. The load 11, the second semiconductor switch 20b, and the first semiconductor switch 20a are sequentially arranged on the current path of the current flowing from the positive terminal Tp to the negative terminal Tn. Assume that the first semiconductor switch 20a is turned off and the drain and source of the second semiconductor switch 20b are short-circuited under the same circumstances. In this case, the current flows through the positive terminal Tp, the load 11, the second semiconductor switch 20b, the first diode 21a of the first semiconductor switch 20a, and the negative terminal Tn in sequence.

[0223] One end of the circuit resistor 52 of the voltage output circuit 24 is connected to the connection node between the other end of the load 11 and the drain of the first semiconductor switch 20a. The node voltage in the eleventh embodiment is a voltage applied to the connection node between the other end of the load 11 and the drain of the first semiconductor switch 20a with reference to the ground potential.

[0224] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is a certain voltage Vc, which is equal to or greater than the threshold voltage Vth as in Embodiment 8. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is zero V or a value close to zero V, which is lower than the threshold voltage Vth as in Embodiment 8.

[0225] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is a constant voltage Vc, which is equal to or higher than the threshold voltage Vth as in the eighth embodiment.

[0226] Therefore, the power supply control device 10 in the eleventh embodiment achieves the same effects as achieved by the power supply control device 10 in the eighth embodiment.

[0227] (Implementation 12)

[0228] In Embodiment 10, the first semiconductor switch 20a is arranged on the upstream side of the second semiconductor switch 20b. The arrangement of the first semiconductor switch 20a and the second semiconductor switch 20b is not limited to this arrangement.

[0229] Hereinafter, the differences from Embodiment 10 will be described with respect to Embodiment 12. The other structures except the structure described later are common to Embodiment 10. Therefore, the same reference numerals as those in Embodiment 10 are attached to the structural parts common to Embodiment 10, and the description thereof is omitted.

[0230] <Structure of Power Supply Control Device 10>

[0231] Fig. 20 1 is a block diagram showing the configuration of the main part of the power supply system 1 in Embodiment 12. When Embodiment 12 is compared with Embodiment 10, the configuration of the first semiconductor switch 20a and the second semiconductor switch 20b is different. In the power supply control device 10 in Embodiment 12, the drain of the second semiconductor switch 20b is connected to the other end of the load 11. The source of the second semiconductor switch 20b is connected to the source of the first semiconductor switch 20a. The drain of the first semiconductor switch 20a is grounded.

[0232] When the first semiconductor switch 20a and the second semiconductor switch 20b are turned on when the connection of the battery 12 is normally connected, the current flows sequentially through the positive terminal Tp, the load 11, the second semiconductor switch 20b, the first semiconductor switch 20a, and the negative terminal Tn. The load 11, the second semiconductor switch 20b, and the first semiconductor switch 20a are sequentially arranged in the current path of the current flowing from the positive terminal Tp to the negative terminal Tn.

[0233] Assuming that the first semiconductor switch 20a is disconnected and the drain and source of the second semiconductor switch 20b are short-circuited when the battery 12 is normally connected, electricity flows sequentially to the positive terminal Tp, the load 11, the second semiconductor switch 20b, the first diode 21a of the first semiconductor switch 20a, and the negative terminal Tn.

[0234] One end of the circuit resistor 52 is connected to the connection node between the other end of the load 11 and the drain of the first semiconductor switch 20a. The node voltage in the twelfth embodiment is a voltage applied to the connection node between the other end of the load 11 and the drain of the first semiconductor switch 20a with reference to the ground potential.

[0235] When the first semiconductor switch 20a and the second semiconductor switch 20b are off, the node voltage is a certain voltage Vc, which is equal to or greater than the threshold voltage Vth as in Embodiment 10. When the first semiconductor switch 20a and the second semiconductor switch 20b are on, or when the first semiconductor switch 20a is off and the drain and source of the second semiconductor switch 20b are short-circuited, the node voltage is zero V or a value close to zero V, which is lower than the threshold voltage Vth as in Embodiment 10.

[0236] The battery 12 is connected between the positive terminal Tp and the negative terminal Tn when the first semiconductor switch 20a and the second semiconductor switch 20b are turned off. At this time, it is assumed that the connection of the battery 12 is reverse connection. In this case, the node voltage is a constant voltage Vc, which is equal to or higher than the threshold voltage Vth as in the tenth embodiment.

[0237] Therefore, the power supply control device 10 in the twelfth embodiment achieves the same effects as achieved by the power supply control device 10 in the tenth embodiment.

[0238] <Modification>

[0239] In Embodiments 1 to 12, the first semiconductor switch 20a and the second semiconductor switch 20b are not limited to N-channel FETs as long as they have parasitic diodes. The first semiconductor switch 20a may also be a P-channel FET. In this case, the cathode and anode of the first diode 21a are connected to the source and drain of the first semiconductor switch 20a.

[0240] When the first semiconductor switch 20a is a P-channel FET, the connection destinations of the drain and source of the first semiconductor switch 20a are changed to the connection destinations of the source and drain of the first semiconductor switch 20a when the first semiconductor switch 20a is an N-channel FET. The first drive circuit 22a switches the first semiconductor switch 20a on by decreasing the voltage of the gate of the first semiconductor switch 20a. The first drive circuit 22a switches the first semiconductor switch 20a off by increasing the voltage of the gate of the first semiconductor switch 20a.

[0241] Similarly, the second semiconductor switch 20b may be a P-channel FET. In this case, the cathode and anode of the second diode 21b are also connected to the source and drain of the second semiconductor switch 20b. When the second semiconductor switch 20b is a P-channel FET, the connection destinations of the drain and source of the second semiconductor switch 20b are changed to the connection destinations of the source and drain of the second semiconductor switch 20b when the second semiconductor switch 20b is an N-channel FET. The second drive circuit 22b switches the second semiconductor switch 20b on by decreasing the voltage of the gate of the second semiconductor switch 20b. The second drive circuit 22b switches the second semiconductor switch 20b off by increasing the voltage of the gate of the second semiconductor switch 20b.

[0242] In embodiments 1 to 12, the microcomputer 26 is connected to the OR circuit 23 and the second drive circuit 22b or the first drive circuit 22a and the second drive circuit 22b via the device resistor 25. In the case where the power supply control device 10 has two device resistors 25, the microcomputer 26 may be connected to the OR circuit 23 or the first drive circuit 22a via one device resistor 25, and connected to the second drive circuit 22b via the other device resistor 25. In this case, the microcomputer 26 outputs a high level voltage or a low level voltage to the OR circuit 23 or the first drive circuit 22a, and outputs a high level voltage or a low level voltage to the second drive circuit 22b. In the structure in which the microcomputer 26 directly outputs a high level voltage or a low level voltage to the first drive circuit 22a, when the output voltage of the voltage output circuit 24 is greater than the reference voltage Vr, the microcomputer 26 switches the voltage output to the first drive circuit 22a to a high level voltage.

[0243] In embodiments 1 to 3, 5, and 6, one input terminal of the OR circuit 23 may be directly connected to a connection node on the current path without passing through the voltage output circuit 24. In this case, the reference voltage of the voltage input to one input terminal of the OR circuit 23 is consistent with the threshold voltage. Similarly, in embodiments 1 to 3, 5, and 6, one input terminal of the OR circuit 23 may be connected to a connection node on the current path via a diode instead of the voltage output circuit 24. In this case, the reference voltage of the voltage input to one input terminal of the OR circuit 23 is also consistent with the threshold voltage. The cathode of the diode is arranged on the OR circuit 23 side.

[0244] In Embodiments 2, 5 to 7, the first circuit switch 55 is not limited to an NPN bipolar transistor, and may be, for example, an N-channel FET, as long as it is a switch that switches on when the voltage at the control terminal becomes equal to or higher than a certain voltage.

[0245] In Embodiments 2, 5 to 12, the second circuit switch 56 may be any switch that switches on when the voltage at the control terminal becomes lower than a certain voltage, and is not limited to a PNP bipolar transistor, but may be, for example, a P-channel FET.

[0246] The disclosed embodiments 1 to 12 are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is indicated by the claims rather than the above meaning, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0247] Description of Reference Numerals

[0248] 1 Power System

[0249] 10 Power supply control device

[0250] 11 Load

[0251] 12. Battery

[0252] 20a First semiconductor switch

[0253] 20b Second semiconductor switch

[0254] 21a First diode

[0255] 21b Second diode

[0256] 22a First drive circuit (switching unit)

[0257] 22b Second driving circuit

[0258] 23 OR circuit

[0259] 24 Voltage output circuit

[0260] 25 Device resistance

[0261] 26 Microcomputer

[0262] 30, 31, 50, 51, 52, 53, 54, 61 circuit resistance

[0263] 40 Output section

[0264] 41 Storage

[0265] 42 Control unit (processing unit)

[0266] 43 Internal bus

[0267] 44 Input section

[0268] 45 A / D conversion unit

[0269] 55 First circuit switch

[0270] 56 Second circuit switch

[0271] 60 Comparator

[0272] 62 DC power supply

[0273] A Storage Media

[0274] P Computer Program

[0275] Tn Negative terminal

[0276] Tp positive terminal.

Claims

1. A power supply control device that controls power supply by switching on or off a first semiconductor switch and a second semiconductor switch that are arranged in a current path and have parasitic diodes connected at both ends. The power supply control device comprises: a processing unit that executes processing for instructing the first semiconductor switch and the second semiconductor switch to switch on or off; and a switching circuit that switches the first semiconductor switch to on when current flows in the current path even though the processing unit instructs the first semiconductor switch and the second semiconductor switch to switch to off, The cathode of each parasitic diode of the first semiconductor switch and the second semiconductor switch is located on the downstream side and the upstream side of the anode in the current path.

2. The power supply control device according to claim 1, wherein: In the current path, the first semiconductor switch is arranged on the upstream side of the second semiconductor switch, In the current path, a load is arranged on the downstream side of the second semiconductor switch, The switching circuit switches the first semiconductor switch on when a node voltage at a connection node between the second semiconductor switch and the load is equal to or higher than a threshold voltage even though the processing unit instructs the first semiconductor switch and the second semiconductor switch to switch off.

3. The power supply control device according to claim 1, wherein: In the current path, the first semiconductor switch is arranged on the downstream side of the second semiconductor switch, In the current path, a load is arranged on the downstream side of the first semiconductor switch, The switching circuit switches the first semiconductor switch on when a node voltage at a connection node between the second semiconductor switch and the load is equal to or higher than a threshold voltage even though the processing unit instructs the first semiconductor switch and the second semiconductor switch to switch off.

4. The power supply control device according to claim 2 or 3, wherein: The processing unit performs the following processing: When the first semiconductor switch and the second semiconductor switch are instructed to switch off, determining whether the node voltage is equal to or higher than the threshold voltage, When it is determined that the node voltage is equal to or higher than the threshold voltage, the switching circuit is instructed to switch the first semiconductor switch to on.

5. The power supply control device according to claim 1, wherein: In the current path, the first semiconductor switch is arranged on the upstream side of the second semiconductor switch, In the current path, a load is arranged on the upstream side of the first semiconductor switch, When a node voltage at a connection node between the load and the second semiconductor switch is lower than a threshold voltage despite the processing unit instructing the first semiconductor switch and the second semiconductor switch to switch off, the switching circuit switches the first semiconductor switch on.

6. The power supply control device according to claim 1, wherein: In the current path, the first semiconductor switch is arranged on the downstream side of the second semiconductor switch, In the current path, a load is arranged on the upstream side of the second semiconductor switch, When a node voltage at a connection node between the load and the second semiconductor switch is lower than a threshold voltage despite the processing unit instructing the first semiconductor switch and the second semiconductor switch to switch off, the switching circuit switches the first semiconductor switch on.

7. The power supply control device according to claim 5 or 6, wherein: The processing unit performs the following processing: When the first semiconductor switch and the second semiconductor switch are instructed to switch off, determining whether the node voltage is less than the threshold voltage, When it is determined that the node voltage is lower than the threshold voltage, the switching circuit is instructed to switch the first semiconductor switch to on.

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