Switch drive device

Abstract

A switch drive device (50) for driving a switch (SWH, SWL) comprises: a gate voltage determination unit (55) that determines whether or not the gate voltage of the switch is exceeding a gate voltage threshold; a voltage detection unit (42) that detects an inter-terminal voltage that is the voltage between a high-potential terminal and a low-potential terminal of the switch; an abnormality determination unit (53) that determines whether or not the detection value of the voltage detection unit is exceeding an abnormality threshold when a command to turn the switch on is issued; and a threshold change unit (57) that causes the abnormality threshold to be lower when the gate voltage is exceeding the gate voltage threshold than when the gate voltage is not exceeding the gate voltage threshold.

Description

Drive device for a switch Cross-reference to related applications

[0001] This application is based on Japanese Application No. 2024-226372 filed on December 23, 2024, the contents of which are incorporated herein by reference.

[0002] This disclosure relates to a drive device for a switch.

[0003] Conventionally, as described in, for example, Patent Document 1, a drive device for detecting a short-circuit current of a switch is known. The drive device sets an abnormal threshold value for detecting the short-circuit current of the switch, and when the current flowing through the switch exceeds the abnormal threshold value, it determines that a short-circuit current is flowing.

[0004] In the drive device described in Patent Document 1, considering the case where the current temporarily increases due to the inrush current, the abnormal threshold value is set to a value equal to or higher than the inrush current. The set abnormal threshold value is decreased after a certain period has elapsed since the ON command for the switch is issued.

[0005] Japanese Unexamined Patent Application Publication No. 2024-112369

[0006] If a short-circuit current flows before a certain period has elapsed since the ON command is issued, since the abnormal threshold value is set to a value equal to or higher than the inrush current, the determination that a short-circuit current is flowing will be delayed. As a result, there is a concern that the switch cannot be appropriately protected.

[0007] The main object of this disclosure is to provide a drive device that can quickly determine that a short-circuit current is flowing through a switch by changing an abnormal threshold value for detecting the short-circuit current of the switch at an appropriate timing.

[0008] This disclosure provides a switch drive device for driving a switch, comprising: a gate voltage determination unit that determines whether the gate voltage of the switch exceeds a gate voltage threshold; a voltage detection unit that detects a terminal voltage which is the voltage between the high-potential terminal and the low-potential terminal of the switch when an ON command for the switch is given; an abnormality determination unit that determines whether the value detected by the voltage detection unit exceeds an abnormality threshold; and a threshold changing unit that lowers the abnormality threshold when the gate voltage exceeds the gate voltage threshold compared to when the gate voltage does not exceed the gate voltage threshold.

[0009] The threshold adjustment unit lowers the abnormal threshold when the gate voltage exceeds the gate voltage threshold compared to when the gate voltage does not exceed the gate voltage threshold. In the event of an abnormal situation such as a short-circuit current flowing through the switch, the gate voltage continues to rise without a Miller period occurring. Therefore, the gate voltage reaches the gate voltage threshold faster than in normal conditions when no short-circuit current flows. As a result, the timing at which the abnormal threshold is lowered is also earlier than in normal conditions. Thus, the drive device can quickly determine that a short-circuit current is flowing.

[0010] The above-mentioned objectives and other objectives, features and advantages of this disclosure will become clearer from the following detailed description with reference to the attached drawings. The drawings are as follows: Figure 1 is an overall system configuration diagram of the first embodiment; Figure 2 is a configuration diagram of the drive unit and lower arm switch; Figure 3 is a flowchart showing the procedure for short-circuit current detection processing in the first embodiment; Figure 4 is a timing chart of drive signals etc. when no short-circuit current is flowing; Figure 5 is a timing chart of drive signals etc. when a short-circuit current is flowing; Figure 6 is a timing chart of drive signals etc. when an overcurrent is flowing; and Figure 7 is a flowchart showing the procedure for short-circuit current detection processing in the second embodiment.

[0011] <First Embodiment> Hereinafter, a first embodiment of the drive device according to the present disclosure will be described with reference to the drawings. In this embodiment, the system equipped with the drive device is mounted on a vehicle such as an electric vehicle or a hybrid vehicle. However, it is not limited to a vehicle, and the system may be mounted on a moving object such as an aircraft or a ship.

[0012] As shown in Figure 1, the system comprises a rotating electric motor 10, an inverter 20, and a DC power supply 21. In this embodiment, the rotating electric motor 10 has three-phase windings 11 connected in a star configuration. The rotating electric motor 10 is, for example, a synchronous machine. When the system is applied to an automobile, the rotating electric motor 10 is an in-wheel motor installed on the drive wheels of the automobile, or an on-board motor installed on the body of the automobile.

[0013] The rotating electric machine 10 is connected to a DC power supply 21 via an inverter 20. The DC power supply 21 is, for example, a secondary battery. The rated voltage of the DC power supply 21 is, for example, 100V or higher. The inverter 20 is equipped with a smoothing capacitor 22. The smoothing capacitor 22 may be provided outside the inverter 20.

[0014] The inverter 20 is equipped with three phase upper and lower arm switches SWH and SWL. In this embodiment, each switch SWH and SWL is an N-channel MOSFET. In each switch SWH and SWL, the high-potential terminal is the drain and the low-potential terminal is the source. Each switch SWH and SWL has a body diode.

[0015] Note that the upper and lower arm switches SWH and SWL may be, for example, IGBTs. In this case, the high-potential terminal of each switch SWH and SWL is the collector, and the low-potential terminal is the emitter. A freewheeling diode is connected in antiparallel to each switch SWH and SWL.

[0016] The positive terminal of the DC power supply 21 is connected to the high-potential terminal of the upper arm switch SWH. The negative terminal of the DC power supply 21 is connected to the low-potential terminal of the lower arm switch SWL.

[0017] In each phase, the first end of the smoothing capacitor 22 is connected to the high-potential terminal of the upper arm switch SWH. In each phase, the high-potential terminal of the lower arm switch SWL is connected to the low-potential terminal of the upper arm switch SWH. In each phase, the second end of the smoothing capacitor 22 is connected to the low-potential terminal of the lower arm switch SWL. In each phase, the first end of the winding 11 of the rotating electric machine 10 is connected to the connection point between the low-potential terminal of the upper arm switch SWH and the high-potential terminal of the lower arm switch SWL. The second end of the winding 11 of each phase is connected at the neutral point.

[0018] The system includes a drive unit 50. In this embodiment, the drive unit 50 is provided individually for each switch SWH and SWL.

[0019] The system includes a control device 30. The control device 30 is an electronic control unit (ECU) that performs various controls on the system, and includes a processor 31 as hardware, a memory unit 32, and a communication bus 33 connecting the processor 31 and the memory unit 32. In order to control the drive of the rotating electric machine 10, the control device 30 controls the switching of the upper and lower arm switches SWH and SWL of each phase provided by the inverter 20 in order to control the control amount of the rotating electric machine 10 to a command value. The control device 30 outputs a drive signal MIN to the drive unit 50 that alternately turns on the upper and lower arm switches SWH and SWL of each phase, with a dead time in between. The drive signal MIN output by the control device 30 takes either an on command to turn on the switches SWH and SWL corresponding to the drive unit 50, or an off command to turn them off.

[0020] The memory unit 32 includes memory and storage as hardware. The memory is a storage device for storing data used in processing by the control device 30. The memory provides the processor 31 with a temporary workspace for use when the processor 31 performs processing. The memory includes, for example, ROM or RAM. The storage is a storage device that stores various programs and data for the processor 31 to read and execute, and is a non-transitory tangible storage medium. The storage includes, for example, an HDD or flash memory. The storage stores program information and the like for processing described later.

[0021] For example, program information stored on a non-transitional physical recording medium is installed in the storage unit 32. The recording medium is, for example, a USB memory stick, CD-ROM, or DVD. Also, for example, program information transmitted via a communication network, such as OTA (Over The Air), is installed in the storage unit 32.

[0022] Using Figure 2, we will explain the drive devices 50 that are individually provided for each switch SWH and SWL. Note that the drive devices 50 corresponding to each switch SWH and SWL have basically the same structure. Therefore, we will explain using the drive device 50 corresponding to the lower arm switch SWL as an example.

[0023] The drive unit 50 includes a drive circuit Dr, a first electrical path L1, a second electrical path L2, a power supply 40, a diode 41, and a capacitor 42 (corresponding to the "voltage detection unit").

[0024] Power supply 40 is connected to power supply terminal Tom, which is provided in the drive circuit Dr. Power supply 40 is a constant voltage power supply with a power supply voltage of Vm. Furthermore, the power supply voltage Vm of power supply 40 is lower than the output voltage of the DC power supply 21.

[0025] The first end of the first electrical path L1 is connected to the detection terminal Tdesat provided in the drive circuit Dr. The second end of the first electrical path L1 is connected to the high-potential side terminal of the lower arm switch SWL.

[0026] The first end of the second electrical path L2 is connected to the ground terminal TGND provided in the drive circuit Dr. The second end of the second electrical path L2 is connected to the low-potential side terminal of the lower arm switch SWL.

[0027] The gate of the lower arm switch SWL is connected to the gate terminal Tgt provided in the drive circuit Dr.

[0028] Diode 41 is provided in the first electrical path L1. Specifically, diode 41 has its anode facing the detection terminal Tdesat and its cathode facing the high-potential side terminal of the lower arm switch SWL. The first end of capacitor 42 is connected to the anode side of diode 41 in the first electrical path L1. The second end of capacitor 42 is connected to the second electrical path L2. In other words, diode 41 is provided in the first electrical path L1 such that the forward direction is from the first end of capacitor 42 toward the high-potential side terminal of the lower arm switch SWL.

[0029] The drive circuit Dr includes a constant current power supply 51, a reset switch 52, a first comparator 53, a variable voltage source 54, and a drive control unit 57 (corresponding to the "threshold change unit"). In this embodiment, the reset switch 52 is a P-channel MOSFET.

[0030] The first end of the constant current power supply 51 is connected to the power supply terminal Tom. The second end of the constant current power supply 51 is connected to the detection terminal Tdesat. As a result, the constant current power supply 51 is powered by the power supply 40 and outputs a constant current to the capacitor 42. The source of the reset switch 52 is connected to the detection terminal Tdesat, and the drain of the reset switch 52 is connected to the ground terminal Tgnd.

[0031] The detection terminal Tdesat is connected to the non-inverting input terminal of the first comparator 53. As a result, the determination voltage Vdesat, which is the terminal voltage of capacitor 42, is input to the non-inverting input terminal of the first comparator 53. The positive terminal of the variable voltage source 54 is connected to the inverting input terminal of the first comparator 53. The ground terminal Tgnd is connected to the negative terminal of the variable voltage source 54. As a result, the abnormal threshold value VK, which is the output voltage of the variable voltage source 54, is input to the inverting input terminal of the first comparator 53. The first comparator 53 compares the terminal voltage of capacitor 42 with the abnormal threshold value VK, using the potential of the ground terminal Tgnd as the reference potential (0V). The output signal S1 of the first comparator 53 is input to the drive control unit 57.

[0032] The drive circuit Dr includes a charge switch SC and a discharge switch SD. In this embodiment, the charge switch SC is a P-channel MOSFET, and the discharge switch SD is an N-channel MOSFET. The power supply terminal Tom is connected to the source of the charge switch SC, and the gate terminal Tgt is connected to the drain of the charge switch SC. The drain of the discharge switch SD is connected to the gate terminal Tgt, and the ground terminal Tgnd is connected to the source of the discharge switch SD.

[0033] The drive control unit 57 is connected to a power terminal Tom and a ground terminal Tgnd. The drive control unit 57 acquires the drive signal MIN output from the control device 30 shown in Figure 1 via a signal terminal Tsg provided in the drive circuit Dr. If the acquired drive signal MIN is an ON command, the drive control unit 57 performs a charging process to turn on the lower arm switch SWL. The charging process is the process of turning on the charging switch SC and turning off the discharge switch SD. As a result of the charging process, the gate voltage Vgs of the lower arm switch SWL becomes greater than or equal to the threshold voltage Vth, and the lower arm switch SWL is switched from the OFF state to the ON state.

[0034] The drive control unit 57 performs a discharge process to turn off the lower arm switch SWL if the acquired drive signal MIN is an off command. The discharge process is the process of turning off the charge switch SC and turning on the discharge switch SD. As a result of the discharge process, the gate voltage Vgs of the lower arm switch SWL becomes less than the threshold voltage Vth, and the lower arm switch SWL is switched from the on state to the off state.

[0035] The drive unit 50 is equipped with a temperature sensor 43 that detects the temperature of the lower arm switch SWL. The temperature sensor 43 is, for example, a thermosensitive diode and is connected to a temperature terminal Tt provided in the drive circuit Dr. The temperature terminal Tt is connected to the drive control unit 57. As a result, the temperature of the lower arm switch SWL detected by the temperature sensor 43 is input to the drive control unit 57.

[0036] The drive circuit Dr includes a second comparator 55 and a constant voltage source 56. The gate terminal Tgt is connected to the non-inverting input terminal of the second comparator 55. As a result, the gate voltage Vgs of the lower arm switch SWL is input to the non-inverting input terminal of the first comparator 53. The positive terminal of the constant voltage source 56 is connected to the inverting input terminal of the second comparator 55. The ground terminal Tgnd is connected to the negative terminal of the constant voltage source 56. As a result, the gate voltage threshold Vref, which is the output voltage of the constant voltage source 56, is input to the inverting input terminal of the second comparator 55. The second comparator 55 compares the gate voltage Vgs of the lower arm switch SWL with the gate voltage threshold Vref, using the potential of the ground terminal Tgnd as a reference potential (0V). The output signal S2 of the second comparator 55 is input to the drive control unit 57.

[0037] Figure 3 shows the procedure for short-circuit current detection performed by the drive control unit 57. This process is repeated at a predetermined cycle. The drive control units 57 corresponding to the upper and lower arm switches SWH and SWL perform basically the same process. Therefore, these processes will be explained using the drive control unit 57 corresponding to the lower arm switch SWL as an example.

[0038] In step S10, it is determined whether the drive signal MIN input from the control device 30 is an ON command. If the determination in step S10 is positive, the charging process is performed and the process proceeds to step S11. On the other hand, if the determination in step S10 is negative, the discharge process is performed. During the execution period of the discharge process, the current output from the constant current power supply 51 is stopped. Also, during the execution period of the discharge process, the reset switch 52 is switched to the ON state.

[0039] In step S11, it is determined whether the logic of the output signal S2 input to the drive control unit 57 is L. If the determination in step S11 is positive, the process proceeds to step S12, and the abnormal threshold VK of the variable voltage source 54 is switched to the first threshold Vα. On the other hand, if the determination in step S12 is negative, the process proceeds to step S13, and the abnormal threshold VK of the variable voltage source 54 is switched to the second threshold Vβ. The second threshold Vβ is an abnormal threshold lower than the first threshold Vα.

[0040] In step S14, it is determined whether the logic of the output signal S1 input to the drive control unit 57 is H. If the determination in step S14 is positive, the process proceeds to step S15, where it is detected that a short-circuit current or overcurrent is flowing through the lower arm switch SWL. When the drive control unit 57 detects that a short-circuit current or overcurrent is flowing, it discharges the gate charge of the lower arm switch SWL to turn it off. In this case, the discharge switch SD may be turned on, or a well-known soft-shut-off switch different from the discharge switch SD may be turned on.

[0041] Using the drive control unit 57 corresponding to the lower arm switch SWL as an example, the process of detecting short-circuit current or overcurrent will be explained using the time charts in Figures 4 to 6.

[0042] Figure 4 shows the case where no overcurrent or short-circuit current flows through the lower arm switch SWL (hereinafter referred to as normal). Fig. 4(a) shows the transition of the drive signal MIN input to the drive control unit 57, Fig. 4(b) shows the transition of the gate voltage Vgs of the lower arm switch SWL, Fig. 4(c) shows the transition of the voltage Vds between the drain and source of the lower arm switch SWL, Fig. 4(d) shows the transition of the drain current Ids of the lower arm switch SWL, and Fig. 4(e) shows the transition of the determination voltage Vdesat.

[0043] At timing t1, the drive control unit 57 determines that the drive signal MIN input from the control device 30 has switched to an on command, and starts the charging process. As a result, the gate voltage Vgs begins to rise. When the gate voltage Vgs reaches the threshold voltage Vth, the lower arm switch SWL is turned on. Also, at timing t1, the drive control unit 57 turns off the reset switch 52 and starts the output of a constant current from the constant current source 51. As a result, current starts to be supplied from the constant current source 51 to the capacitor 42. As a result, the determination voltage Vdesat begins to rise from 0.

[0044] At timing t1, the gate voltage Vgs has not reached the gate voltage threshold Vref. Therefore, the logic of the output signal S2 of the second comparator 55 becomes L. As a result, the drive control unit 57 switches the abnormal threshold VK to the first threshold Vα.

[0045] At timing t2, the gate voltage Vgs reaches the mirror voltage Vmil. The period from timing t2 to t3 is a mirror period during which the gate voltage Vgs is maintained at the mirror voltage Vmil.

[0046] At timing t3, the mirror period ends, and the gate voltage Vgs starts to rise again. During the period from timing t2 to t3, the voltage Vds between the drain and source decreases. As a result, at timing t3, the determination voltage Vdesat begins to decrease toward a certain determination voltage Vdesat.

[0047] At timing t4, the gate voltage Vgs reaches the gate voltage threshold Vref. Therefore, the logic of the output signal S2 of the second comparator 55 is inverted to H. As a result, the drive control unit 57 switches the abnormal threshold VK from the first threshold Vα to the second threshold Vβ.

[0048] At timing t5, the gate voltage Vgs reaches the power supply voltage Vom of the power supply 40.

[0049] At timing t6, the drive control unit 57 determines that the drive signal MIN input from the control device 30 has switched to an off command and starts the discharge process. Thereby, the gate voltage Vgs becomes less than the threshold voltage Vth, and the lower arm switch SWL is turned off. Also, the drive control unit 57 stops the output of the constant current from the constant current power supply 51 at timing t6. Further, the drive control unit 57 turns on the reset switch 52 after timing t6. Thereby, the determination voltage Vdesat in the capacitor 42 is reset to 0. Note that during the period when the drive signal MIN acquired from the control device 30 is an off command, the detection processing of overcurrent and short-circuit current is not executed.

[0050] FIG. 5 shows the case where a short-circuit current flows through the lower arm switch SWL (hereinafter, at the time of short circuit). Note that FIGS. 5(a) to (e) correspond to FIGS. 4(a) to (e) above. The short-circuit current is a current that flows when an upper and lower arm short circuit occurs in which the upper and lower arm switches SWH and SWL are simultaneously turned on.

[0051] At timing t1, the drive control unit 57 determines that the drive signal MIN input from the control device 30 has switched to an on command and starts the charging process. Thereby, the gate voltage Vgs starts to rise. When the gate voltage Vgs reaches the threshold voltage Vth, the lower arm switch SWL is turned on. Also, the drive control unit 57 turns off the reset switch 52 at timing t1 and starts the output of the constant current from the constant current power supply 51. As a result, current starts to be supplied from the constant current power supply 51 to the capacitor 42. As a result, the determination voltage Vdesat starts to rise from 0.

[0052] At timing t1, the gate voltage Vgs has not reached the gate voltage threshold Vref. Therefore, the logic of the output signal S2 of the second comparator 55 becomes L. As a result, the drive control unit 57 switches the abnormal threshold VK to the first threshold Vα.

[0053] In the example shown in Figure 5, since a short-circuit current is flowing, the gate voltage Vgs rises without the Miller period appearing. Also, the judgment voltage Vdesat continues to rise without decreasing.

[0054] At timing t2, the gate voltage Vgs reaches the gate voltage threshold Vref. Therefore, the logic of the output signal S2 of the second comparator 55 inverts to H. In this case, the drive control unit 57 switches the abnormal threshold VK from the first threshold Vα to the second threshold Vβ. Also at timing t2, the determination voltage Vdesat reaches the second threshold Vβ. In this case, the first comparator 53 inputs the logic H output signal S1 to the drive control unit 57. The drive control unit 57, having received the logic H output signal S1, determines that a short-circuit current is flowing through the lower arm switch SWL.

[0055] In this embodiment, the gate voltage threshold Vref is set to be higher than the Miller voltage Vmil and lower than the power supply voltage Vm. In other words, the gate voltage threshold Vref is set to a value such that the timing at which the gate voltage Vgs reaches the gate voltage threshold Vref changes depending on whether a Miller period occurs, such as in normal operation, or whether a Miller period does not occur, such as in a short circuit. When a Miller period does not occur, such as in a short circuit, the gate voltage Vgs reaches the gate voltage threshold Vref at an earlier timing compared to normal operation. Therefore, in the event of a short circuit, the abnormal threshold VK is switched from the first threshold Vα to the second threshold Vβ at an earlier timing compared to normal operation. As a result, the short-circuit current can be detected quickly.

[0056] Figure 6 shows the case where an overcurrent other than a short-circuit current is flowing through the lower arm switch SWL (hereinafter referred to as "overcurrent"). Figures 6(a) to 6(e) correspond to Figures 4(a) to 6(e). An overcurrent is a current that is larger than the rated current of the lower arm switch SWL, and can flow even when there is no short circuit between the upper and lower arms.

[0057] At timing t1, the drive control unit 57 determines that the drive signal MIN input from the control device 30 has switched to an ON command and starts the charging process. As a result, the gate voltage Vgs starts to rise. When the gate voltage Vgs reaches the threshold voltage Vth, the lower arm switch SWL is turned ON. Also at timing t1, the drive control unit 57 turns the reset switch 52 OFF and starts outputting a constant current from the constant current power supply 51. As a result, current is supplied from the constant current power supply 51 to the capacitor 42. Consequently, the determination voltage Vdesat starts to rise from 0.

[0058] At timing t1, the gate voltage Vgs has not reached the gate voltage threshold Vref. Therefore, the logic of the output signal S2 of the second comparator 55 becomes L. As a result, the drive control unit 57 switches the abnormal threshold VK to the first threshold Vα.

[0059] At timing t2, the gate voltage Vgs reaches the Miller voltage Vmil. The period from timing t2 to t3 is the Miller period, during which the gate voltage Vgs is maintained at the Miller voltage Vmil.

[0060] At timing t3, the Miller period ends, and the gate voltage Vgs begins to rise again. Also, because an overcurrent is flowing through the lower arm switch SWL, the drain-source voltage Vds rises instead of remaining constant as it would under normal conditions. As a result, the judgment voltage Vdesat rises again without decreasing to a certain judgment voltage Vdesat.

[0061] At timing t4, the gate voltage Vgs reaches the gate voltage threshold Vref. In this case, the logic of the output signal S2 of the second comparator 55 is inverted to H. As a result, the drive control unit 57 switches the abnormal threshold VK from the first threshold Vα to the second threshold Vβ.

[0062] At timing t5, the continuously rising determination voltage Vdesat reaches the second threshold Vβ. In this case, the first comparator 53 inputs the logic H output signal S1 to the drive control unit 57. Upon receiving the logic H output signal S1, the drive control unit 57 determines that an overcurrent is flowing through the lower arm switch SWL. The drive control unit 57 may also perform the following processing, for example: When the drive control unit 57 determines that the logic of the output signal S1 has inverted to H, it determines whether or not a Miller period has occurred based on the acquired gate voltage Vgs. The drive control unit 57 may determine that a short-circuit current has flowed if it determines that a Miller period has occurred, and determine that an overcurrent has flowed if it determines that a Miller period has occurred.

[0063] According to the embodiment described above, the following effects can be obtained.

[0064] The abnormal threshold VK is switched from a first threshold Vα to a second threshold Vβ based on the gate voltage Vgs. In the case of a short circuit as shown in Figure 5, the gate voltage Vgs continues to rise without a Miller period occurring. Therefore, the gate voltage Vgs during a short circuit reaches the gate voltage threshold Vref faster than during a normal operation as shown in Figure 4. As a result, the timing of the switch from the first threshold Vα to the second threshold Vβ based on the gate voltage threshold Vref is also faster. Thus, the drive control unit 57 can quickly determine if an overcurrent is flowing through each switch SWH, SWL.

[0065] Under normal conditions, after an ON command is issued to each switch SWH and SWL, a Miller period occurs before the gate voltage Vgs reaches the power supply voltage Vom. Therefore, if the gate voltage threshold Vref is set to a value less than the Miller voltage Vmil, the drive control unit 57 may mistakenly determine that a short-circuit current is flowing when no short-circuit current is actually flowing.

[0066] On the other hand, in the case of a short circuit, after an ON command is issued to each switch SWH and SWL, no Miller period occurs before the gate voltage Vgs reaches the power supply voltage Vom, and the gate voltage Vgs continues to rise toward the power supply voltage Vom. Furthermore, since the gate voltage Vgs continues to rise toward the power supply voltage Vom, if the gate voltage threshold Vref is set to a voltage higher than the power supply voltage Vom, the gate voltage Vgs will not reach the gate voltage threshold Vref.

[0067] Therefore, the gate voltage threshold Vref is set to a voltage that is higher than the Miller voltage Vmil and lower than the power supply voltage Vm. This allows the drive control unit 57 to quickly determine whether a short-circuit current is flowing through each switch SWH, SWL, while reducing the risk of the above-mentioned erroneous determination.

[0068] <Second Embodiment> The second embodiment will be described below, focusing on the differences from the first embodiment, with reference to the drawings. In this embodiment, the first and second threshold values ​​Vα and Vβ are made variable based on the temperature of the switch.

[0069] In this embodiment, the drive control unit 57 adjusts the abnormal threshold VK in the variable voltage source 54 based on the temperature of each switch SWH, SWL input from the temperature sensor 43. In this embodiment, the drive control unit 57 lowers the abnormal threshold VK when the temperature of each switch SWH, SWL is high compared to when the temperature of each switch SWH, SWL is low.

[0070] Next, Figure 7 shows the procedure for the short-circuit current detection process performed by the drive control unit 57. In Figure 7, for convenience, the same step numbers are used for processes that are the same as those in Figure 3.

[0071] If the processing in step S10 is completed, the process proceeds to step S20. In step S20, the drive control unit 57 obtains the temperature of the switch detected by the temperature sensor 43 and proceeds to step S11.

[0072] If a positive determination is made in step S11, the process proceeds to step S21. In step S21, the drive control unit 57 sets the abnormal threshold VK of the variable voltage source 54 to a first threshold Vα. The higher the temperature obtained in step S20, the lower the first threshold Vα is set by the drive control unit 57. For example, the drive control unit 57 may continuously lower the first threshold Vα or set the first threshold Vα to be lower in stages as the obtained temperature increases.

[0073] If a negative determination is made in step S11, the process proceeds to step S22. In step S22, the drive control unit 57 sets the abnormal threshold VK of the variable voltage source 54 to the second threshold Vβ. The drive control unit 57 lowers the second threshold Vβ as the temperature obtained in step S20 increases. For example, the drive control unit 57 may continuously lower the second threshold Vβ as the obtained temperature increases, or set the second threshold Vβ to be lower in stages. Note that when the switch temperature is the same, the second threshold Vβ is lower than the first threshold Vα.

[0074] According to the embodiment described above, the following effects can be obtained.

[0075] Each switch SWH and SWL has the characteristic that its short-circuit withstand capability decreases as its temperature increases. In other words, when the temperature of each switch SWH and SWL is high and a short-circuit current is flowing, the drive control unit 57 must determine that a short-circuit current is flowing more quickly. Therefore, when the temperature of each switch SWH and SWL is high, the drive control unit 57 lowers the abnormal threshold than when the temperature of each switch SWH and SWL is low. This allows for a quicker determination of whether a short-circuit current is flowing.

[0076] <Modification of the second embodiment> The process in step S20 may be performed after the determination in step S11 and before the processes in steps S21 and S22.

[0077] <Other Embodiments> The above embodiments may be modified and implemented as follows.

[0078] The gate voltage threshold Vref may be set to a value less than or equal to the Miller voltage Vmil.

[0079] The abnormal threshold VK is not limited to being switchable in two stages, such as a first threshold Vα or a second threshold Vβ, but may be switchable in three or more stages as the gate voltage Vgs increases. Furthermore, the abnormal threshold VK is not limited to being switched in steps, but may be continuously changed so as the gate voltage Vgs increases.

[0080] The control devices and methods described herein may be implemented by a dedicated computer provided by configuring a processor and memory programmed to perform one or more functions embodied by a computer program. Alternatively, the control devices and methods described herein may be implemented by a dedicated computer provided by configuring a processor by one or more dedicated hardware logic circuits. Alternatively, the control devices and methods described herein may be implemented by one or more dedicated computers configured by a combination of a processor and memory programmed to perform one or more functions and a processor configured by one or more hardware logic circuits. Furthermore, the computer program may be stored as instructions executed by the computer on a computer-readable non-transitional tangible recording medium.

[0081] The following describes characteristic configurations extracted from each of the embodiments described above. [Configuration 1] A switch drive device (50) for driving switches (SWH, SWL), comprising: a gate voltage determination unit (55) that determines whether the gate voltage of the switch exceeds a gate voltage threshold; a voltage detection unit (42) that detects the terminal voltage, which is the voltage between the high-potential side terminal and the low-potential side terminal of the switch; an abnormality determination unit (53) that determines whether the value detected by the voltage detection unit exceeds an abnormality threshold when an ON command for the switch is given; and a threshold changing unit (57) that lowers the abnormality threshold when the gate voltage exceeds the gate voltage threshold than when the gate voltage does not exceed the gate voltage threshold. [Configuration 2] The switch drive device according to Configuration 1, wherein the gate voltage threshold is higher than the Miller voltage of the switch and lower than the power supply voltage supplied to the gate of the switch. [Configuration 3] The drive device is equipped with a temperature sensor (43) for detecting the temperature of the switch, and the threshold changing unit lowers the abnormal threshold when the temperature detected by the temperature sensor is high compared to when the temperature detected by the temperature sensor is low, as described in Configuration 1 or 2. [Configuration 4] The drive device comprises a first electrical path (L1), a second electrical path (L2), and a diode (41) provided in the first electrical path with its anode facing the first end of the first electrical path and its cathode facing the second end of the first electrical path, and the voltage detection unit comprises a capacitor (42) connected to the first end of the first electrical path and the first end of the second electrical path, the second end of the first electrical path is connected to the high-potential side terminal of the switch, the second end of the second electrical path is connected to the low-potential side terminal of the switch, and the abnormality determination unit determines that a short-circuit current is flowing through the switch when an ON command for the switch has been issued and the detected value of the voltage detection unit exceeds the abnormality threshold, wherein the drive device for a switch according to any one of Configurations 1 to 3.

[0082] This disclosure is described in accordance with the embodiments, but it is understood that this disclosure is not limited to such embodiments or structures. This disclosure also includes various modifications and variations within the equivalence. In addition, various combinations and forms, as well as other combinations and forms that include only one, more, or fewer of those elements, fall within the scope and concept of this disclosure.

Claims

1. A switch drive device (50) for driving switches (SWH, SWL), comprising: a gate voltage determination unit (55) for determining whether the gate voltage of the switch exceeds a gate voltage threshold; a voltage detection unit (42) for detecting the terminal voltage, which is the voltage between the high-potential terminal and the low-potential terminal of the switch; an abnormality determination unit (53) for determining whether the value detected by the voltage detection unit exceeds an abnormality threshold when an ON command for the switch has been issued; and a threshold changing unit (57) for lowering the abnormality threshold when the gate voltage exceeds the gate voltage threshold than when the gate voltage does not exceed the gate voltage threshold.

2. The switch drive device according to claim 1, wherein the gate voltage threshold is higher than the Miller voltage of the switch and lower than the power supply voltage supplied to the gate of the switch.

3. The drive device for a switch according to claim 1 or 2, wherein the drive device comprises a temperature sensor (43) for detecting the temperature of the switch, and the threshold changing unit lowers the abnormal threshold when the temperature detected by the temperature sensor is high compared to when the temperature detected by the temperature sensor is low.

4. The drive device for a switch according to claim 1 or 2, comprising: a first electrical path (L1); a second electrical path (L2); and a diode (41) provided in the first electrical path with its anode facing the first end of the first electrical path and its cathode facing the second end of the first electrical path; the voltage detection unit comprising a capacitor (42) connected to the first end of the first electrical path and the first end of the second electrical path; the second end of the first electrical path being connected to the high-potential side terminal of the switch; the second end of the second electrical path being connected to the low-potential side terminal of the switch; and the abnormality determination unit determining that a short-circuit current is flowing through the switch when an ON command for the switch has been issued and the detected value of the voltage detection unit exceeds the abnormality threshold.

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