Power supply control device and method for diagnosing failure in power supply control device

Abstract

A power supply control device according to the present invention comprises: a first power supply switch which is inserted in a first line of a power supply line that connects a power supply and a load drive circuit; a second power supply switch which is inserted in a second line of the power supply line; an inrush current prevention circuit which is inserted in the first line or the second line; and a control circuit. The inrush current prevention circuit has an inrush current prevention resistor and an inrush current prevention switch which is connected to the inrush current prevention resistor in parallel. The control circuit controls on / off of the first power supply switch, the second power supply switch, and the inrush current prevention switch. The inrush current prevention switch has a structure in which two semiconductor switching elements are inversely connected in series.

Description

Power supply control device and fault diagnosis method for power supply control device

[0001] The present invention relates to a power supply control device and a fault diagnosis method for the power supply control device.

[0002] In some cases, power is supplied from a power source to a load drive circuit that drives a load. In such cases, a power switch that switches the power line, which serves as a power path through which current flows between the power source and the load drive circuit, is inserted into the power line. For example, Patent Document 1 discloses a power cutoff circuit that constitutes a power supply control device in which multiple power switches are inserted into the power line. In a power supply control device in which multiple power switches are inserted into the power line, when it is necessary to stop driving the load, all of the power switches are cut off, thereby making it possible to reliably cut off the power line even if one of the switches is faulty.

[0003] At the beginning of a load drive, an inrush current exceeding a predetermined value may flow through a power supply line. This inrush current may cause damage to the load drive circuit or the power switch. To prevent this inrush current from flowing into the load drive circuit, etc., an inrush current prevention circuit, consisting of a resistor and a switch connected in parallel, must be inserted into the power supply line. However, if a mechanical relay such as an electromagnetic relay is used as the switch in the inrush current prevention circuit, the switch is likely to fail if it is turned on and off frequently in response to the frequent driving and stopping of the load. If a short circuit occurs in the switch of the inrush current prevention circuit, there is a problem in that it is not possible to prevent the inrush current from flowing into the load drive circuit, etc., at the beginning of the load drive.

[0004] JP 2023-46686 A

[0005] The object of the present invention is to provide a power supply control device that can accurately prevent inrush current from flowing into a load driving circuit even when the load is driven and stopped frequently, and a fault diagnosis method for the power supply control device.

[0006] A power supply control device according to one aspect of the present invention includes: a power supply line connecting a load drive circuit that drives a load to a power supply and having a first line and a second line through which a current flows; a first power switch inserted in the first line; a second power switch inserted in the second line; an inrush current prevention circuit inserted in the first line or the second line, the inrush current prevention circuit having an inrush current prevention resistor and an inrush current prevention switch connected in parallel to the inrush current prevention resistor; and a control circuit that controls the on / off of the first power switch, the second power switch, and the inrush current prevention switch. The inrush current prevention switch has a structure in which two semiconductor switching elements are connected in series in opposite directions.

[0007] The objects, features and advantages of the present invention will become more apparent from the following detailed description and the accompanying drawings.

[0008] Fig. 1 is a circuit diagram of a power supply control device according to a first embodiment of the present invention; Fig. 2 is a flowchart showing a processing flow of the power supply control device according to the first embodiment; Fig. 3 is a circuit diagram of a power supply control device according to a second embodiment of the present invention; Fig. 4 is a flowchart showing a processing flow of the power supply control device according to the second embodiment; Fig. 5 is a flowchart showing a processing flow of the power supply control device according to the second embodiment;

[0009] A power supply control device and a fault diagnosis method for a power supply control device according to an embodiment of the present invention will be described below with reference to the drawings.

[0010] 1 is a circuit diagram of a power supply control device 1 according to a first embodiment of the present invention. The power supply control device 1 is disposed between a power supply 11 and a load drive circuit 13 that drives a load 12, and controls the supply of power from the power supply 11 to the load drive circuit 13.

[0011] The power supply 11 may be either an AC power supply or a DC power supply, but in this embodiment, it is an AC power supply. The load 12 is, for example, an articulated robot driven by power supplied from the power supply 11 via a load drive circuit 13. The load drive circuit 13 is a circuit for driving the load 12, and is a circuit in which a diode bridge 131 having multiple diodes is electrically connected to multiple load-side capacitors 132. When the power supply 11 is an AC power supply, the load drive circuit 13 is a circuit that includes the diode bridge 131 and the multiple load-side capacitors 132. On the other hand, when the power supply 11 is a DC power supply, the load drive circuit 13 is a circuit that does not include the diode bridge 131 but includes the multiple load-side capacitors 132.

[0012] The power supply control device 1 comprises a power supply line 2 connecting a power supply 11 and a load drive circuit 13, a first power switch 3, a second power switch 4, an inrush current prevention circuit 5, a control circuit 6, a first detection circuit 7, and a second detection circuit 8.

[0013] The power supply line 2 connects the power supply 11 and the load drive circuit 13, and constitutes a power supply path through which a current flows between the power supply 11 and the load drive circuit 13. The power supply line 2 has a first line 21 and a second line 22 as paths through which a current flows in opposite directions.

[0014] The first power switch 3 is a switch inserted in the first line 21. The first power switch 3 is connected between a connection point L1 on the first line 21 and a connection point L2 located closer to the load drive circuit 13 than the connection point L1. The first power switch 3 can switch between conduction and interruption of the first line 21 by switching between on (ON) and off (OFF). The first power switch 3 conducts the first line 21 when in the on state and interrupts the first line 21 when in the off state. In this embodiment, the first power switch 3 is configured by an electromagnetic relay. In this case, the first power switch 3 is turned on when a predetermined voltage is applied to the first excitation coil 31, and is turned off when the application of voltage to the first excitation coil 31 is stopped. The on / off switching of the first power switch 3 is controlled by the control circuit 6.

[0015] A first detection circuit 7 is connected to the first line 21. In this embodiment, the first detection circuit 7 is connected in parallel to the first power switch 3. The first detection circuit 7 detects the on / off state of the first power switch 3 and outputs a first detection signal DS1. The first detection circuit 7 is connected in parallel to the first power switch 3 and detects the on / off state of the first power switch 3 by detecting a current flowing between connection points L1 and L2 on the first line 21 where the first power switch 3 is inserted. When a current flows between connection points L1 and L2 on the first line 21, the first detection circuit 7 detects that the first power switch 3 is on and outputs a first detection signal DS1 indicating the on state. On the other hand, when no current flows between connection points L1 and L2 on the first line 21, the first detection circuit 7 detects that the first power switch 3 is off and outputs a first detection signal DS1 indicating the off state. The first detection signal DS1 output from the first detection circuit 7 is input to the control circuit 6.

[0016] The first detection circuit 7 may be configured to detect the on / off state of the first power switch 3 by comparing the potential difference between the connection points L1 and L2 on the first line 21 with a predetermined threshold. In this case, when the potential difference between the connection points L1 and L2 on the first line 21 is equal to or smaller than the predetermined threshold, the first detection circuit 7 detects that the first power switch 3 is in the on state and outputs a first detection signal DS1 indicating the on state. On the other hand, when the potential difference between the connection points L1 and L2 on the first line 21 exceeds the predetermined threshold, the first detection circuit 7 detects that the first power switch 3 is in the off state and outputs a first detection signal DS1 indicating the off state.

[0017] The second power switch 4 is a switch inserted in the second line 22. The second power switch 4 is connected between a connection point N1 on the second line 22 and a connection point N2 located closer to the load drive circuit 13 than the connection point N1. The second power switch 4 can switch between conduction and interruption of the second line 22 by switching between on (ON) and off (OFF). The second power switch 4 conducts the second line 22 when in the on state and interrupts the second line 22 when in the off state. In this embodiment, the second power switch 4 is configured as an electromagnetic relay. In this case, the second power switch 4 is turned on when a predetermined voltage is applied to the second excitation coil 41, and is turned off when the application of voltage to the second excitation coil 41 is stopped. The second power switch 4 is switched on and off by the control circuit 6.

[0018] A second detection circuit 8 is connected to the second line 22. In this embodiment, the second detection circuit 8 is connected in parallel to the second power switch 4. The second detection circuit 8 detects the on / off state of the second power switch 4 and outputs a second detection signal DS2. The second detection circuit 8 is connected in parallel to the second power switch 4 and detects the on / off state of the second power switch 4 by detecting a current flowing between the connection points N1 and N2 on the second line 22 where the second power switch 4 is inserted. When a current flows between the connection points N1 and N2 on the second line 22, the second detection circuit 8 detects that the second power switch 4 is on and outputs a second detection signal DS2 indicating the on state. On the other hand, when no current flows between the connection points N1 and N2 on the second line 22, the second detection circuit 8 detects that the second power switch 4 is off and outputs a second detection signal DS2 indicating the off state. The second detection signal DS2 output from the second detection circuit 8 is input to the control circuit 6.

[0019] The second detection circuit 8 may be configured to detect the on / off state of the second power switch 4 by comparing the potential difference between the connection points N1 and N2 on the second line 22 with a predetermined threshold. In this case, when the potential difference between the connection points N1 and N2 on the second line 22 is equal to or less than the predetermined threshold, the second detection circuit 8 detects that the second power switch 4 is in the on state and outputs a second detection signal DS2 indicating the on state. On the other hand, when the potential difference between the connection points N1 and N2 on the second line 22 exceeds the predetermined threshold, the second detection circuit 8 detects that the second power switch 4 is in the off state and outputs a second detection signal DS2 indicating the off state.

[0020] The inrush current prevention circuit 5 is a circuit inserted in the first line 21 or the second line 22. In this embodiment, the inrush current prevention circuit 5 is a circuit inserted in the first line 21. More specifically, the inrush current prevention circuit 5 is inserted in the first line 21 on the load drive circuit 13 side of the first power switch 3. Note that when the inrush current prevention circuit 5 is inserted in the first line 21 of the first line 21 and the second line 22, the inrush current prevention circuit 5 may be inserted in the first line 21 on the power supply 11 side of the first power switch 3. The inrush current prevention circuit 5 prevents an inrush current equal to or greater than a predetermined value from flowing into the load drive circuit 13 at an early stage when the load drive circuit 13 starts driving the load 12. The inrush current prevention circuit 5 has an inrush current prevention resistor 51 and an inrush current prevention switch 52 connected in parallel with the inrush current prevention resistor 51.

[0021] When the inrush current prevention circuit 5 is inserted in the first line 21 on the load drive circuit 13 side of the first power switch 3, the inrush current prevention resistor 51 is connected between a connection point L3 located on the first line 21 closer to the load drive circuit 13 than the connection points L1 and L2 where the first power switch 3 is inserted, and a connection point L4 located on the load drive circuit 13 side than the connection point L3. The inrush current prevention resistor 51 has an electrical resistance set to, for example, about 15 ohms. When the load drive circuit 13 starts to drive the load 12, the inrush current prevention resistor 51 reduces the current flowing from the power supply 11 to the load drive circuit 13 via the first power switch 3 while the inrush current prevention switch 52 is off. This prevents an inrush current greater than a predetermined value from flowing into the load drive circuit 13.

[0022] The inrush current prevention switch 52 is a switch that can switch between conduction and interruption of the area between the connection points L3 and L4 on the first line 21 to which the inrush current prevention resistor 51 is connected, by switching between on (ON) and off (OFF). When the inrush current prevention switch 52 is in the on state, it makes the area between the connection points L3 and L4 on the first line 21 conductive, and when it is in the off state, it interrupts the area between the connection points L3 and L4 on the first line 21. A current flowing from the power supply 11 to the load drive circuit 13 via the first power switch 3 passes through the inrush current prevention switch 52 when the inrush current prevention switch 52 is in the on state, and passes through the inrush current prevention resistor 51 when the inrush current prevention switch 52 is in the off state.

[0023] The inrush current prevention switch 52 has a structure in which two semiconductor switching elements are connected in series in opposite directions. Examples of the semiconductor switching elements constituting the inrush current prevention switch 52 include a field effect transistor (FET) and an insulated gate bipolar transistor (IGBT). In this embodiment, the inrush current prevention switch 52 is configured as a semiconductor switching element in which two FETs 521 are connected in series in opposite directions. In other words, the inrush current prevention switch 52 is configured as a semiconductor switching element in which two FETs 521 are connected back-to-back. In this case, in the inrush current prevention switch 52, the gate terminals 521G of the two FETs 521 are electrically connected to each other and the source terminals 521S of the two FETs 521 are electrically connected to each other, the drain terminal 521D of one FET 521 is connected to a connection point L3, and the drain terminal 521D of the other FET 521 is connected to a connection point L4. In the off state of the inrush current prevention switch 52, in which no voltage is applied to the gate terminals 521G of the two FETs 521, the resistance between the drain terminal 521D and the source terminal 521S is, for example, about 1 megaohm. When a voltage is applied to the gate terminals 521G of the two FETs 521, the resistance between the drain terminal 521D and the source terminal 521S decreases to about 0 ohm, and the inrush current prevention switch 52 is turned on. That is, the inrush current prevention switch 52 is switched on and off by changing the resistance value between the drain terminal 521D and the source terminal 521S in response to application of voltage to each gate terminal 521G of the two FETs 521. The on and off switching of the inrush current prevention switch 52 is controlled by the control circuit 6.

[0024] The control circuit 6 is realized by, for example, a dual programmable controller in which two central processing unit (CPU) modules are communicatively connected. When the load drive circuit 13 drives the load 12, the control circuit 6 controls the on / off of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52. In this way, the control circuit 6 controls the current flowing through the first line 21 and the second line 22 that constitute the power line 2, thereby controlling the supply of power from the power supply 11 to the load drive circuit 13.

[0025] The control circuit 6 can accurately and quickly control the on / off of each of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52 by exchanging information between the two CPU modules. The control circuit 6 outputs a first control signal CS1 to the first excitation coil 31 to control the application of voltage to the first excitation coil 31, thereby controlling the on / off of the first power switch 3. The control circuit 6 also outputs a second control signal CS2 to the second excitation coil 41 to control the application of voltage to the second excitation coil 41, thereby controlling the on / off of the second power switch 4. The control circuit 6 also outputs a third control signal CS3 to each gate terminal 521G of the two FETs 521 to control the application of voltage to each gate terminal 521G, thereby controlling the on / off of the inrush current prevention switch 52.

[0026] The control circuit 6 controls the first power switch 3 and the second power switch 4 to turn on and the inrush current prevention switch 52 to turn off at an early stage when the load drive circuit 13 starts driving the load 12. As a result, between the power supply 11 and the load drive circuit 13, a current flows to the first line 21 via the first power switch 3, and a current flows to the second line 22 via the second power switch 4. At this time, because the inrush current prevention switch 52 is in the off state, the current flowing in the first line 21 passes through the inrush current prevention resistor 51. As a result, the current flowing in the first line 21 is reduced by the inrush current prevention resistor 51, and it is possible to prevent an inrush current equal to or greater than a predetermined value from flowing into the load drive circuit 13 at an early stage when the load 12 starts driving.

[0027] When charging of the load-side capacitor 132 of the load drive circuit 13 is completed and the current flowing through the power supply line 2 reaches a predetermined reference value, the control circuit 6 controls the inrush current prevention switch 52 to turn on while keeping the first power switch 3 and the second power switch 4 on. In this case, the current flowing through the first line 21 is restricted from passing through the inrush current prevention resistor 51 and instead passes through the inrush current prevention switch 52. This allows a current of the predetermined reference value to continue flowing through the power supply line 2 so that the load drive circuit 13 can continue driving the load 12.

[0028] The inrush current prevention switch 52 is repeatedly turned on and off in response to the load drive circuit 13 driving and stopping the load 12. If a mechanical relay such as an electromagnetic relay is used as the inrush current prevention switch 52, the mechanical relay has a relatively short lifespan and is prone to failure if the switch is repeatedly turned on and off frequently. Therefore, the inrush current prevention switch 52 is configured as a semiconductor switching element in which two FETs 521 are connected in series in reverse. The inrush current prevention switch 52 configured as such a semiconductor switching element is less likely to fail even when it is repeatedly turned on and off frequently and has a relatively long lifespan. This makes it possible to accurately prevent inrush current from flowing into the load drive circuit 13 at the initial stage of starting to drive the load 12, even when the load drive circuit 13 drives and stops the load 12 frequently.

[0029] In this embodiment, the control circuit 6 is configured to be able to diagnose faults in the first power switch 3 and the second power switch 4 while controlling the on / off of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52. The control circuit 6 diagnoses faults in the first power switch 3 based on the first detection signal DS1 output from the first detection circuit 7, and diagnoses faults in the second power switch 4 based on the second detection signal DS2 output from the second detection circuit 8. The control circuit 6 performs each step of the fault diagnosis method for the power supply control device 1 by performing a process to diagnose faults in the first power switch 3 and the second power switch 4. Each step of the fault diagnosis method performed by the control circuit 6 will be described with reference to the flowchart of FIG.

[0030] When the load drive circuit 13 drives the load 12, the control circuit 6 starts to control the on / off of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52. The control circuit 6 controls the first power switch 3, the second power switch 4, and the inrush current prevention switch 52 to turn off (step a1). In this case, the control circuit 6 outputs a first control signal CS1 to the first excitation coil 31 to turn off the first power switch 3, outputs a second control signal CS2 to the second excitation coil 41 to turn off the second power switch 4, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52.

[0031] The control circuit 6 diagnoses whether or not a short-circuit fault has occurred in the first power switch 3 by determining whether or not the first detection signal DS1 output from the first detection circuit 7 is a signal indicating an OFF state of the first power switch 3 (step a2). If the first detection signal DS1 is a signal indicating an ON state of the first power switch 3 in response to an output of the first control signal CS1 that turns the first power switch 3 OFF, the control circuit 6 diagnoses that a short-circuit fault has occurred in the first power switch 3 (step a21). On the other hand, if the first detection signal DS1 is a signal indicating an OFF state of the first power switch 3 in response to an output of the first control signal CS1 that turns the first power switch 3 OFF, the control circuit 6 diagnoses that a short-circuit fault has not occurred in the first power switch 3 (step a3).

[0032] The control circuit 6 diagnoses whether a short-circuit fault has occurred in the second power switch 4 by determining whether the second detection signal DS2 output from the second detection circuit 8 is a signal indicating an OFF state of the second power switch 4 (step a4). If the second detection signal DS2 is a signal indicating an ON state of the second power switch 4 in response to an output of the second control signal CS2 that turns the second power switch 4 OFF, the control circuit 6 diagnoses that a short-circuit fault has occurred in the second power switch 4 (step a41). On the other hand, if the second detection signal DS2 is a signal indicating an OFF state of the second power switch 4 in response to an output of the second control signal CS2 that turns the second power switch 4 OFF, the control circuit 6 diagnoses that a short-circuit fault has not occurred in the second power switch 4 (step a5).

[0033] The control circuit 6 may perform the process of step a2 and the process of step a4 simultaneously. That is, the control circuit 6 may simultaneously diagnose the first power switch 3 for a short-circuit fault and the second power switch 4 for a short-circuit fault.

[0034] If no short-circuit failure has occurred in the first power switch 3 and the second power switch 4, the control circuit 6 performs control to turn on the first power switch 3 while keeping the second power switch 4 and the inrush current prevention switch 52 off (step a6). In this case, the control circuit 6 outputs a second control signal CS2 to the second excitation coil 41 to turn off the second power switch 4, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52, and then outputs a first control signal CS1 to the first excitation coil 31 to turn on the first power switch 3.

[0035] The control circuit 6 diagnoses whether an open circuit fault has occurred in the first power switch 3 by determining whether the first detection signal DS1 output from the first detection circuit 7 is a signal indicating an ON state of the first power switch 3 (step a7). If the first detection signal DS1 is a signal indicating an OFF state of the first power switch 3 in response to the output of the first control signal CS1 that turns on the first power switch 3, the control circuit 6 diagnoses that an open circuit fault has occurred in the first power switch 3 (step a71). On the other hand, if the first detection signal DS1 is a signal indicating an ON state of the first power switch 3 in response to the output of the first control signal CS1 that turns on the first power switch 3, the control circuit 6 diagnoses that an open circuit fault has not occurred in the first power switch 3 (step a8).

[0036] If no open fault has occurred in the first power switch 3, the control circuit 6 turns on the first power switch 3 and performs control to turn on the second power switch 4 while keeping the inrush current prevention switch 52 off (step a9). In this case, the control circuit 6 outputs a first control signal CS1 to the first excitation coil 31 to turn on the first power switch 3, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52, and then outputs a second control signal CS2 to the second excitation coil 41 to turn on the second power switch 4.

[0037] The control circuit 6 diagnoses whether an open circuit fault has occurred in the second power switch 4 by determining whether the second detection signal DS2 output from the second detection circuit 8 is a signal indicating an ON state of the second power switch 4 (step a10). If the second detection signal DS2 is a signal indicating an OFF state of the second power switch 4 in response to an output of the second control signal CS2 that turns on the second power switch 4, the control circuit 6 diagnoses that an open circuit fault has occurred in the second power switch 4 (step a101). On the other hand, if the second detection signal DS2 is a signal indicating an ON state of the second power switch 4 in response to an output of the second control signal CS2 that turns on the second power switch 4, the control circuit 6 diagnoses that an open circuit fault has not occurred in the second power switch 4 (step a11).

[0038] When the control circuit 6 controls the first power switch 3 and the second power switch 4 to turn on and the inrush current prevention switch 52 to turn off, a current flows from the power supply 11 to the load drive circuit 13 via the first power switch 3 through the first line 21, and a return current flows from the load drive circuit 13 to the power supply 11 via the second power switch 4 through the second line 22. At this time, because the inrush current prevention switch 52 is in the off state, the current flowing in the first line 21 passes through the inrush current prevention resistor 51. As a result, the current flowing in the first line 21 is reduced by the inrush current prevention resistor 51, making it possible to prevent an inrush current equal to or greater than a predetermined value from flowing into the load drive circuit 13 at the initial stage of starting to drive the load 12.

[0039] The control circuit 6 determines whether charging of the load-side capacitor 132 of the load drive circuit 13 is complete (step a12). If charging of the load-side capacitor 132 is complete (YES in step a12), the control circuit 6 controls the inrush current prevention switch 52 to turn on (step a13). In this case, the control circuit 6 outputs a third control signal CS3 to each gate terminal 521G of the two FETs 521 to turn on the inrush current prevention switch 52. In this case, the current flowing through the first line 21 is restricted from passing through the inrush current prevention resistor 51 and passes through the inrush current prevention switch 52. This allows a current of a predetermined reference value to continue flowing through the power supply line 2 so that the load drive circuit 13 can continue driving the load 12.

[0040] 3 is a circuit diagram of a power supply control device 1 according to a second embodiment of the present invention. The power supply control device 1 according to the second embodiment is configured similarly to the first embodiment described above, except that it includes a third detection circuit 9, a detection resistor 91 connected in series to the third detection circuit 9, and a detection line 9L into which the third detection circuit 9 and the detection resistor 91 are inserted. Therefore, a description of the configuration of the power supply control device 1 according to the second embodiment that is similar to that of the first embodiment will be omitted.

[0041] The detection line 9L connects each source terminal 521S of the two FETs 521 serving as semiconductor switching elements in the inrush current prevention switch 52 to a connection point N0 located on the power supply 11 side of the second power switch 4 in the second line 22, which is not the first line 21 into which the inrush current prevention circuit 5 is inserted, of the first line 21 and the second line 22, thereby forming a path through which current flows.

[0042] The third detection circuit 9 is inserted into the detection line 9L, detects the on / off state of the inrush current prevention switch 52, and outputs a third detection signal DS3. As described above, the resistance value between the drain terminal 521D and the source terminal 521S of the inrush current prevention switch 52 changes significantly from approximately 1 megaohm to approximately 0 ohm depending on the voltage applied to each of the gate terminals 521G of the two FETs 521. The third detection circuit 9 detects the on / off state of the inrush current prevention switch 52 by utilizing this large change in the resistance value between the drain terminal 521D and the source terminal 521S.

[0043] The third detection circuit 9 detects the on / off state of the inrush current prevention switch 52 by detecting the current flowing through the detection line 9L. When a current flows through the detection line 9L, the third detection circuit 9 detects that the inrush current prevention switch 52 is on and outputs a third detection signal DS3 indicating the on state. On the other hand, when no current flows through the detection line 9L, the third detection circuit 9 detects that the inrush current prevention switch 52 is off and outputs a third detection signal DS3 indicating the off state. The third detection signal DS3 output from the third detection circuit 9 is input to the control circuit 6.

[0044] The detection resistor 91 is a resistor connected in series to the detection line 9L on the connection point N0 side of the third detection circuit 9. The detection resistor 91 reduces the current flowing through the detection line 9L.

[0045] In this embodiment, the control circuit 6 is configured to be able to diagnose faults in the first power switch 3, the second power switch 4, and the inrush current prevention switch 52 while controlling the on / off of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52. The control circuit 6 diagnoses faults in the first power switch 3 based on the first detection signal DS1 output from the first detection circuit 7, diagnoses faults in the second power switch 4 based on the second detection signal DS2 output from the second detection circuit 8, and diagnoses faults in the inrush current prevention switch 52 based on the third detection signal DS3 output from the third detection circuit 9. The control circuit 6 performs processes to diagnose faults in the first power switch 3, the second power switch 4, and the inrush current prevention switch 52, thereby performing each process of the fault diagnosis method for the power supply control device 1. Each process of the fault diagnosis method performed by the control circuit 6 will be described with reference to the flowcharts of FIGS. 4 and 5 . Note that, in describing each process of the fault diagnosis method for the power supply control device 1 according to the second embodiment, processes similar to those in the first embodiment will be described in a simplified manner.

[0046] When the load drive circuit 13 drives the load 12, the control circuit 6 starts to control the on / off of the first power switch 3, the second power switch 4, and the inrush current prevention switch 52. The control circuit 6 controls the first power switch 3, the second power switch 4, and the inrush current prevention switch 52 to turn off (step b1). In this case, the control circuit 6 outputs a first control signal CS1 to the first excitation coil 31 to turn off the first power switch 3, outputs a second control signal CS2 to the second excitation coil 41 to turn off the second power switch 4, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52.

[0047] The control circuit 6 determines whether the first detection signal DS1 output from the first detection circuit 7 is a signal indicating the OFF state of the first power switch 3 (step b2). If the first detection signal DS1 is a signal indicating the ON state of the first power switch 3 in response to the output of the first control signal CS1 that turns the first power switch 3 OFF, the control circuit 6 diagnoses that a short-circuit fault has occurred in the first power switch 3 (step b21). On the other hand, if the first detection signal DS1 is a signal indicating the OFF state of the first power switch 3 in response to the output of the first control signal CS1 that turns the first power switch 3 OFF, the control circuit 6 diagnoses that a short-circuit fault has not occurred in the first power switch 3 (step b3).

[0048] The control circuit 6 determines whether the second detection signal DS2 output from the second detection circuit 8 is a signal indicating that the second power switch 4 is in an OFF state (step b4). If the second detection signal DS2 is a signal indicating that the second power switch 4 is in an ON state, in response to the output of the second control signal CS2 that turns the second power switch 4 OFF, the control circuit 6 diagnoses that a short-circuit fault has occurred in the second power switch 4 (step b41). On the other hand, if the second detection signal DS2 is a signal indicating that the second power switch 4 is in an OFF state, in response to the output of the second control signal CS2 that turns the second power switch 4 OFF, the control circuit 6 diagnoses that a short-circuit fault has not occurred in the second power switch 4 (step b5).

[0049] If no short-circuit failure has occurred in the first power switch 3 and the second power switch 4, the control circuit 6 performs control to turn on the first power switch 3 while keeping the second power switch 4 and the inrush current prevention switch 52 off (step b6). In this case, the control circuit 6 outputs a second control signal CS2 to the second excitation coil 41 to turn off the second power switch 4, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52, and then outputs a first control signal CS1 to the first excitation coil 31 to turn on the first power switch 3.

[0050] The control circuit 6 determines whether the first detection signal DS1 output from the first detection circuit 7 is a signal indicating the ON state of the first power switch 3 (step b7). If the first detection signal DS1 is a signal indicating the OFF state of the first power switch 3 in response to the output of the first control signal CS1 that turns on the first power switch 3, the control circuit 6 diagnoses that an open circuit fault has occurred in the first power switch 3 (step b71). On the other hand, if the first detection signal DS1 is a signal indicating the ON state of the first power switch 3 in response to the output of the first control signal CS1 that turns on the first power switch 3, the control circuit 6 diagnoses that an open circuit fault has not occurred in the first power switch 3 (step b8).

[0051] If there is no open circuit fault in the first power switch 3, the control circuit 6 diagnoses whether there is a short circuit fault in the inrush current prevention switch 52 by determining whether the third detection signal DS3 output from the third detection circuit 9 is a signal indicating that the inrush current prevention switch 52 is in an off state (step b9).

[0052] If the third detection signal DS3 indicates that the inrush current prevention switch 52 is on, in response to the output of the third control signal CS3 that turns off the inrush current prevention switch 52, the control circuit 6 diagnoses that the inrush current prevention switch 52 has a short-circuit fault (step b91). If the inrush current prevention switch 52 has a short-circuit fault while the first power switch 3 is on and the second power switch 4 is off, the current from the power supply 11 passes through the first power switch 3 and the inrush current prevention switch 52, then flows through the detection line 9L without flowing toward the load drive circuit 13, and returns to the power supply 11 in a state reduced by the detection resistor 91. This makes it possible to reliably prevent inrush current from flowing into the load drive circuit 13, even if the inrush current prevention switch 52 has a short-circuit fault.

[0053] On the other hand, if the third detection signal DS3 is a signal indicating that the inrush current prevention switch 52 is in an off state in response to the output of the third control signal CS3 that turns off the inrush current prevention switch 52, the control circuit 6 diagnoses that there is no short-circuit fault in the inrush current prevention switch 52 (step b10).

[0054] If there is no short-circuit failure in the inrush current prevention switch 52, the control circuit 6 turns on the first power switch 3 and turns on the second power switch 4 while keeping the inrush current prevention switch 52 off (step b11). In this case, the control circuit 6 outputs a first control signal CS1 to the first excitation coil 31 to turn on the first power switch 3, and outputs a third control signal CS3 to the gate terminals 521G of the two FETs 521 to turn off the inrush current prevention switch 52, and then outputs a second control signal CS2 to the second excitation coil 41 to turn on the second power switch 4.

[0055] When the second power switch 4 is turned on while the first power switch 3 is on, there is no short-circuit failure in the inrush current prevention switch 52, and control is performed to turn off the inrush current prevention switch 52. In this case, the current from the power supply 11 passes through the first power switch 3 and the inrush current prevention resistor 51, and returns to the power supply 11 via the load drive circuit 13 in a state where it is reduced by the inrush current prevention resistor 51. This makes it possible to reliably prevent inrush current from flowing into the load drive circuit 13.

[0056] The control circuit 6 determines whether the second detection signal DS2 output from the second detection circuit 8 is a signal indicating the ON state of the second power switch 4 (step b12). If the second detection signal DS2 is a signal indicating the OFF state of the second power switch 4 in response to the output of the second control signal CS2 that turns the second power switch 4 ON, the control circuit 6 diagnoses that an open circuit fault has occurred in the second power switch 4 (step b121). On the other hand, if the second detection signal DS2 is a signal indicating the ON state of the second power switch 4 in response to the output of the second control signal CS2 that turns the second power switch 4 ON, the control circuit 6 diagnoses that an open circuit fault has not occurred in the second power switch 4 (step b13).

[0057] When there is no open fault in the second power switch 4, when the control circuit 6 controls the first power switch 3 and the second power switch 4 to turn on and controls the inrush current prevention switch 52 to turn off, current flows from the power supply 11 to the first line 21 via the first power switch 3 toward the load drive circuit 13, and a return current flows from the load drive circuit 13 to the power supply 11 via the second power switch 4 toward the second line 22.

[0058] The control circuit 6 determines whether charging of the load-side capacitor 132 of the load drive circuit 13 is complete (step b14). If charging of the load-side capacitor 132 is complete (YES in step b14), the control circuit 6 performs control to turn on the inrush current prevention switch 52 while keeping the first power switch 3 and the second power switch 4 on (step b15). In this case, the control circuit 6 outputs a third control signal CS3 to each gate terminal 521G of the two FETs 521 to turn on the inrush current prevention switch 52.

[0059] The control circuit 6 determines whether the third detection signal DS3 output from the third detection circuit 9 is a signal indicating the ON state of the inrush current prevention switch 52 (step b16). If the third detection signal DS3 is a signal indicating the OFF state of the inrush current prevention switch 52 in response to the output of the third control signal CS3 that turns the inrush current prevention switch 52 ON, the control circuit 6 diagnoses that an open fault has occurred in the inrush current prevention switch 52 (step b161). On the other hand, if the third detection signal DS3 is a signal indicating the ON state of the inrush current prevention switch 52 in response to the output of the third control signal CS3 that turns the inrush current prevention switch 52 ON, the control circuit 6 diagnoses that an open fault has not occurred in the inrush current prevention switch 52 (step b17).

[0060] If the inrush current prevention switch 52 does not have an open fault, the current flowing in the first line 21 is restricted from passing through the inrush current prevention resistor 51 and passes through the inrush current prevention switch 52. This allows a current of a predetermined reference value to continue flowing in the power supply line 2 so that the load drive circuit 13 can continue to drive the load 12.

[0061] Although the embodiment of the present invention has been described above, the present invention is not limited to this and may take the following modified embodiments, for example.

[0062] In the above embodiment, the first power switch 3 and the second power switch 4 are each an electromagnetic relay, but the present invention is not limited to this. Each of the first power switch 3 and the second power switch 4 may be configured with a semiconductor switching element. For example, each of the first power switch 3 and the second power switch 4 may be configured with a semiconductor switching element in which two FETs are connected in series in reverse, similar to the inrush current prevention switch 52.

[0063] In the above embodiment, the inrush current prevention circuit 5 is inserted in the first line 21 of the first line 21 and the second line 22, but the present invention is not limited to this. The inrush current prevention circuit 5 may be inserted in the second line 22. In this case, the detection line 9L connects the source terminals 521S of the two FETs 521 in the inrush current prevention switch 52 to a connection point located on the power supply 11 side of the first power switch 3 in the first line 21 other than the second line 22 in which the inrush current prevention circuit 5 is inserted. A third detection circuit 9 is inserted in this detection line 9L.

[0064] In the above embodiment, the control circuit 6 is configured as a dual programmable controller equipped with two CPU modules, but the present invention is not limited to this. The control circuit 6 may be configured as a single CPU module, or as three or more CPU modules.

[0065] The above-described specific embodiments mainly include inventions having the following configurations.

[0066] A power supply control device according to one aspect of the present invention includes: a power supply line connecting a load drive circuit that drives a load to a power supply and having a first line and a second line through which a current flows; a first power switch inserted in the first line; a second power switch inserted in the second line; an inrush current prevention circuit inserted in the first line or the second line, the inrush current prevention circuit having an inrush current prevention resistor and an inrush current prevention switch connected in parallel to the inrush current prevention resistor; and a control circuit that controls the on / off of the first power switch, the second power switch, and the inrush current prevention switch. The inrush current prevention switch has a structure in which two semiconductor switching elements are connected in series in opposite directions.

[0067] According to this power supply control device, the control circuit controls the on / off of the first power switch, the second power switch, and the inrush current prevention switch when the load drive circuit drives the load, thereby controlling the current flowing through the first line and the second line that make up the power supply line, thereby controlling the supply of power from the power supply to the load drive circuit.

[0068] The control circuit can control the first power switch and the second power switch to be on and the inrush current prevention switch to be off at an early stage when the load drive circuit starts driving the load. In this case, between the power supply and the load drive circuit, current flows to the first line via the first power switch and to the second line via the second power switch. At this time, because the inrush current prevention switch is off, the current flowing in the first line passes through the inrush current prevention resistor. As a result, the current flowing in the first line is reduced by the inrush current prevention resistor, preventing an inrush current greater than a predetermined value from flowing into the load drive circuit at an early stage when the load drive circuit starts driving. Note that when the current flowing through the power supply line reaches a predetermined reference value, the control circuit controls the inrush current prevention switch to be on while keeping the first power switch and the second power switch on. In this case, the current flowing in the first line is restricted from passing through the inrush current prevention resistor and passes through the inrush current prevention switch.

[0069] Here, the inrush current prevention switch is repeatedly turned on and off in response to the load drive circuit driving and stopping the load. If a mechanical relay such as an electromagnetic relay is used as the inrush current prevention switch, the mechanical relay has a relatively short lifespan, and therefore the switch is prone to failure if the switch is repeatedly turned on and off frequently. Therefore, the inrush current prevention switch has a structure in which two semiconductor switching elements are connected in series in reverse. An inrush current prevention switch formed by such semiconductor switching elements is less likely to fail even when the switch is repeatedly turned on and off frequently, and has a relatively long lifespan. This makes it possible to accurately prevent inrush current from flowing into the load drive circuit at the initial stage of load drive, even when the load drive circuit drives and stops the load frequently.

[0070] The power supply control device further includes a first detection circuit that detects the on / off state of the first power switch and outputs a first detection signal, a second detection circuit that detects the on / off state of the second power switch and outputs a second detection signal, a third detection circuit inserted in a detection line connecting a source terminal of a field-effect transistor serving as the semiconductor switching element in the inrush current prevention switch and a connection point located on the power supply side of the first power switch or the second power switch in one of the first and second lines other than the line in which the inrush current prevention circuit is inserted, the third detection circuit detecting the on / off state of the inrush current prevention switch and outputting a third detection signal, and a resistor connected in series with the third detection circuit on the detection line. In this case, the control circuit diagnoses a fault of the first power switch based on the first detection signal, a fault of the second power switch based on the second detection signal, and a fault of the inrush current prevention switch based on the third detection signal while controlling the on / off of the first power switch, the second power switch, and the inrush current prevention switch.

[0071] According to this power supply control device, the control circuit is configured to be able to diagnose failures in the first power switch, the second power switch, and the inrush current prevention switch while controlling the on / off of the first power switch, the second power switch, and the inrush current prevention switch. The control circuit can diagnose failures in the first power switch based on a first detection signal output from the first detection circuit, diagnose failures in the second power switch based on a second detection signal output from the second detection circuit, and diagnose failures in the inrush current prevention switch based on a third detection signal output from the third detection circuit.

[0072] In the above-described power supply control device and fault diagnosis method for the power supply control device, the inrush current prevention circuit is inserted in the first line of the first line and the second line. In this case, the control circuit, while controlling the first power switch, the second power switch, and the inrush current prevention switch to be turned off, diagnoses whether or not a short-circuit fault has occurred in the first power switch based on the first detection signal, and diagnoses whether or not a short-circuit fault has occurred in the second power switch based on the second detection signal. When the first power switch and the second power switch do not have a short-circuit fault, the control circuit, while controlling the first power switch to be turned on while keeping the second power switch and the inrush current prevention switch off, diagnoses whether or not an open-circuit fault has occurred in the first power switch based on the first detection signal, and when the first power switch does not have an open-circuit fault, diagnoses whether or not a short-circuit fault has occurred in the inrush current prevention switch based on the third detection signal.

[0073] In this aspect, when there is no short-circuit failure in the first power switch and the second power switch, and the first power switch is on and the second power switch is off, the control circuit diagnoses whether there is a short-circuit failure in the inrush current prevention switch. If there is a short-circuit failure in the inrush current prevention switch, the current from the power supply passes through the first power switch and the inrush current prevention switch, then flows through the detection line without flowing toward the load drive circuit, and returns to the power supply in a state reduced by the detection resistor. This makes it possible to accurately prevent inrush current from flowing into the load drive circuit even if there is a short-circuit failure in the inrush current prevention switch.

[0074] In the above power supply control device and fault diagnosis method for the power supply control device, when a short-circuit fault does not occur in the inrush current prevention switch, the control circuit diagnoses whether or not an open-circuit fault has occurred in the second power supply switch based on the second detection signal while controlling the first power supply switch and the second power supply switch to be turned on while keeping the inrush current prevention switch off.And when an open-circuit fault does not occur in the second power supply switch, the control circuit diagnoses whether or not an open-circuit fault has occurred in the second power supply switch based on the third detection signal while controlling the first power supply switch, the second power supply switch, and the inrush current prevention switch to be turned on.

[0075] In this aspect, when there is no short-circuit failure in the inrush current prevention switch, the control circuit turns on the first power switch and controls the second power switch to turn on while keeping the inrush current prevention switch off. When the second power switch is turned on while the first power switch is on, there is no short-circuit failure in the inrush current prevention switch, and control is performed to turn off the inrush current prevention switch. In this case, the current from the power supply passes through the first power switch and the inrush current prevention resistor, and returns to the power supply via the load drive circuit in a state where it is reduced by the inrush current prevention resistor. This makes it possible to reliably prevent inrush current from flowing into the load drive circuit.

[0076] As described above, the present invention provides a power supply control device that can accurately prevent inrush current from flowing into a load drive circuit even when the load is driven and stopped frequently. Also, it provides a power supply control device and a fault diagnosis method for the power supply control device that can accurately prevent inrush current from flowing into a load drive circuit even when a short-circuit fault occurs in at least one of the first power switch, the second power switch, and the inrush current prevention switch.

Claims

1. A power supply line having a first line and a second line through which current flows, which connects a load drive circuit that drives a load and a power supply, A first power switch inserted into the first line, The second power switch inserted into the second line, An inrush current prevention circuit inserted into the first line or the second line, comprising an inrush current prevention resistor and an inrush current prevention switch connected in parallel to the inrush current prevention resistor, The system includes a control circuit that controls the on and off states of the first power switch, the second power switch, and the inrush current prevention switch, The inrush current prevention switch is a power control device having a structure in which two semiconductor switching elements are connected in series in opposite directions.

2. A first detection circuit that detects the on and off state of the first power switch and outputs a first detection signal, A second detection circuit detects the on and off state of the second power switch and outputs a second detection signal, A third detection circuit is inserted into a detection line connecting the source terminal of the field-effect transistor, which serves as the semiconductor switching element in the inrush current prevention switch, and the connection point located on the power supply side of the first power switch or the second power switch in the line that is not the line in which the inrush current prevention circuit is inserted, and detects the on and off state of the inrush current prevention switch and outputs a third detection signal. The detection line further comprises a resistor connected in series with the third detection circuit, The power control device according to claim 1, wherein the control circuit controls the on and off states of the first power switch, the second power switch, and the inrush current prevention switch, diagnoses a malfunction of the first power switch based on the first detection signal, diagnoses a malfunction of the second power switch based on the second detection signal, and diagnoses a malfunction of the inrush current prevention switch based on the third detection signal.

3. The inrush current prevention circuit is inserted into the first line of the first line and the second line, The aforementioned control circuit is With the first power switch, the second power switch, and the inrush current prevention switch in an OFF state, the system diagnoses whether a short-circuit fault has occurred in the first power switch based on the first detection signal, and diagnoses whether a short-circuit fault has occurred in the second power switch based on the second detection signal. The power control device according to claim 2, wherein, when no short-circuit fault occurs in the first power switch and the second power switch, the first power switch is turned on while the second power switch and the inrush current prevention switch remain off, and a diagnosis is made based on the first detection signal to determine whether or not an open circuit fault has occurred in the first power switch, and when no open circuit fault has occurred in the first power switch, a diagnosis is made based on the third detection signal to determine whether or not a short-circuit fault has occurred in the inrush current prevention switch.

4. The aforementioned control circuit is If no short-circuit failure has occurred in the inrush current prevention switch, the first power switch and the second power switch are turned on while the inrush current prevention switch remains off, and a diagnosis is made based on the second detection signal to determine whether or not an open circuit failure has occurred in the second power switch. The power control device according to claim 3, wherein, when no open fault has occurred in the second power switch, the first power switch, the second power switch, and the inrush current prevention switch are turned ON, and a diagnosis is made based on the third detection signal whether or not an open fault has occurred in the inrush current prevention switch.

5. A method for diagnosing a fault in a power supply control device according to claim 2, The inrush current prevention circuit is inserted into the first line of the first line and the second line, The aforementioned control circuit is With the first power switch, the second power switch, and the inrush current prevention switch in an OFF state, the system diagnoses whether a short-circuit fault has occurred in the first power switch based on the first detection signal, and diagnoses whether a short-circuit fault has occurred in the second power switch based on the second detection signal. A method for diagnosing a fault in a power control device, wherein, when no short-circuit fault has occurred in the first power switch and the second power switch, the first power switch is turned on while the second power switch and the inrush current prevention switch remain off, and the device diagnoses whether or not an open circuit fault has occurred in the first power switch based on the first detection signal, and when no open circuit fault has occurred in the first power switch, the device diagnoses whether or not a short-circuit fault has occurred in the inrush current prevention switch based on the third detection signal.

6. The aforementioned control circuit is If no short-circuit failure has occurred in the inrush current prevention switch, the first power switch and the second power switch are turned on while the inrush current prevention switch remains off, and a diagnosis is made based on the second detection signal to determine whether or not an open circuit failure has occurred in the second power switch. A fault diagnosis method for a power supply control device according to claim 5, wherein, when no open fault has occurred in the second power supply switch, the first power supply switch, the second power supply switch, and the inrush current prevention switch are turned ON, and a diagnosis is made based on the third detection signal to determine whether or not an open fault has occurred in the inrush current prevention switch.

7. A power supply line having a first line and a second line through which current flows, which connects a load drive circuit that drives a load and a power supply, A first power switch inserted into the first line, The second power switch inserted into the second line, An inrush current prevention circuit inserted into the first line or the second line, comprising: an inrush current prevention resistor; and an inrush current prevention switch connected in parallel to the inrush current prevention resistor, having a structure in which two semiconductor switching elements are connected in series in opposite directions; A detection circuit is inserted into a detection line connecting the source terminal of the semiconductor switching element in the inrush current prevention switch and the connection point located on the power supply side of the first power switch or the second power switch in the line that is not the line in which the inrush current prevention circuit is inserted, and detects the on and off state of the inrush current prevention switch and outputs a detection signal. The system includes a control circuit that controls the on and off states of the first power switch, the second power switch, and the inrush current prevention switch, The control circuit is a power control device that diagnoses a malfunction of the inrush current prevention switch based on the detection signal while controlling the on and off states of the first power switch, the second power switch, and the inrush current prevention switch.

8. The inrush current prevention circuit is inserted into the first line of the first line and the second line, The aforementioned control circuit is With the second power switch and the inrush current prevention switch in the OFF state, control is performed to turn on the first power switch, and based on the detection signal, it is diagnosed whether or not a short circuit failure has occurred in the inrush current prevention switch. The power control device according to claim 7, wherein, while controlling the first power switch, the second power switch, and the inrush current prevention switch to be turned ON, the device diagnoses whether or not an open fault has occurred in the inrush current prevention switch based on the detection signal.

9. A method for diagnosing a fault in a power supply control device according to claim 7, The inrush current prevention circuit is inserted into the first line of the first line and the second line, The aforementioned control circuit is With the second power switch and the inrush current prevention switch in the OFF state, control is performed to turn on the first power switch, and based on the detection signal, it is diagnosed whether or not a short circuit failure has occurred in the inrush current prevention switch. A method for diagnosing a fault in a power control device, comprising: performing control to turn on the first power switch, the second power switch, and the inrush current prevention switch, and then diagnosing whether or not an open fault has occurred in the inrush current prevention switch based on the detection signal.