Protective circuit for power semiconductor element

Abstract

To provide a protective circuit for power semiconductor elements that can suppress the enlargement of semiconductor elements constituting the soft shutdown circuit even in a configuration in which a soft shutdown circuit and a precharge power supply share the same output terminal.SOLUTION: In a protective circuit 23, comparators 16 and 17 detect a short circuit between the collector and emitter of IGBT1 and an overcurrent flowing between the collector and emitter as abnormal, respectively. When the logic 10S determines that the abnormality has been detected, the soft shutdown section 7 operates to draw the charge charged on the gate of IGBT1 at a slower rate than during normal off. In the drive IC2, the terminal 6 connecting the gate of IGBT1 to the soft shutdown section 7 and the precharge power supply 8 is common, and logic 10 stops the supply of voltage by the precharge power supply 8 before the operation to lower the gate potential by the soft shutdown section 7 is started.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a circuit for protecting a power semiconductor element that constitutes a power conversion device. [Background technology]

[0002] Configurations for protecting power semiconductor elements are disclosed, for example, in Patent Documents 1 and 2. Patent Document 1 discloses a gate potential change circuit that can quickly cut off the current flowing through the power semiconductor element even when a short circuit occurs in the power semiconductor element and charge is injected into the gate by the feedback capacitance. Patent Document 2 discloses a soft cutoff circuit for turning off the power semiconductor element at a slower speed than normal and a precharge power supply as a gate potential control circuit that shares an IC output terminal. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2014-68071 A [Patent Document 2] Patent Publication No. 2021-176253 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the configuration of Patent Document 1 has a problem in that the inclusion of a gate potential changing circuit requires a separate terminal for that purpose, resulting in an increase in the size of the circuit. In addition, in Patent Document 2, the soft shutdown circuit and the precharge power supply share an output terminal, so that during soft shutdown operation, the current for discharging the charge stored in the gate capacitance of the power semiconductor element and the current flowing from the precharge power supply to the gate of the power semiconductor element are superimposed. This causes a problem in that the semiconductor element constituting the soft shutdown circuit must be increased in size.

[0005] The present invention has been made in consideration of the above circumstances, and has as its object to provide a protection circuit for a power semiconductor element that can suppress an increase in size of the semiconductor elements that make up the soft shutdown circuit, even in a configuration in which the output terminal is shared between the soft shutdown circuit and the precharge power supply. [Means for solving the problem]

[0006] According to the protection circuit for a power semiconductor element described in claim 1, the current abnormality detection unit (16, 17) detects either or both of a short circuit between the conductive terminals of the power semiconductor element (1) and an overcurrent flowing between the conductive terminals as an abnormality. Note that the power semiconductor element is a semiconductor element that constitutes a power conversion circuit such as an inverter and is capable of switching a relatively large amount of power. When the soft cutoff unit (7, 10S) determines that the abnormality has been detected, it operates to draw off the charge stored in the conduction control terminal of the power semiconductor element at a slower speed than during normal off-state.

[0007] The pre-charge power supply (8) suppresses a voltage rise at the conduction control terminal to protect against the short circuit. The conduction control terminal is connected to a common terminal (6) that connects the soft cutoff unit and the pre-charge power supply, and the power supply control unit (10) stops the supply of voltage from the pre-charge power supply before the soft cutoff unit completes the operation of lowering the voltage at the conduction control terminal.

[0008] With this configuration, the soft cutoff unit determines that an abnormality has been detected and stops outputting voltage from the pre-charge power supply before completing the operation of drawing off charge from the conduction control terminal of the power semiconductor element, so that the soft cutoff unit can somewhat suppress an increase in the power capacity of the circuit elements that form the path for drawing off charge, thereby making it possible to suppress an increase in the cost of constructing the protection circuit.

[0009] According to the protection circuit for a power semiconductor element described in claim 2, the soft cutoff unit (10S) waits for a judgment waiting time to elapse after the current abnormality detection unit detects an abnormality before making the judgment. This prevents erroneous judgment caused by, for example, noise being superimposed on a terminal that accepts an input from the current abnormality detection unit. Furthermore, the power supply control unit stops the output of voltage by the pre-charge power supply before the soft cutoff unit starts operating, so that an increase in the power capacity of the circuit elements that constitute the soft cutoff unit can be further suppressed.

[0010] According to the protection circuit for a power semiconductor device recited in claim 3, when the power supply control unit stops the output of voltage by the pre-charge power supply, the power supply control unit cuts off the tail current supplied to the differential input unit of the operational amplifier (12) constituting the pre-charge power supply. Therefore, it is possible to stop the operation of the pre-charge power supply simply by adding a configuration for cutting off the tail current inside the operational amplifier. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing a configuration of a protection circuit for an IGBT in a first embodiment; [Diagram 2] Circuit diagram showing the internal configuration of the operational amplifier that constitutes the precharge power supply [Diagram 3] Flowchart showing the logic processing [Figure 4] A diagram showing the voltage waveforms of each part when the output of the precharge power supply is not stopped and when it is stopped. [Diagram 5] A diagram showing the operation image corresponding to the upper case in Figure 4. [Figure 6] A diagram showing the operation image corresponding to the lower case in Figure 4. [Figure 7] FIG. 13 is a diagram showing a configuration of a protection circuit for an IGBT in a second embodiment; [Figure 8] FIG. 13 is a diagram showing a configuration of a protection circuit for an IGBT in a third embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (First embodiment) This embodiment is based on the configuration disclosed in Patent Document 2, and the configuration other than the part related to the gist is similar to that disclosed in, for example, Fig. 38 of Patent Document 2. As shown in Fig. 1, an IGBT (Insulated Gate Bipolar Transistor) 1, which is a power semiconductor element, constitutes a power conversion device such as an inverter, and is connected in series with another IGBT (not shown) between a power supply and ground. A sense emitter is provided in the IGBT 1, and a current detection resistor 1a is connected between the sense emitter and the emitter.

[0013] The gate of IGBT1, which is the conduction control terminal, is driven by driving IC2, but the configuration for driving IGBT1 to be normally turned on and off is not shown. The gate of IGBT1 is connected to ground via a series circuit of diode 3 and capacitor 4. The common connection point of diode 3 and capacitor 4 is connected to terminal 6 of driving IC2 via resistor element 5.

[0014] Inside the driver IC 2, a soft cutoff unit 7 and an output terminal of a precharge power supply 8 are connected to the terminal 6. The soft cutoff unit 7 includes an N-channel MOSFET 9 connected between the terminal 6 and ground, and the gate of the FET 9 is driven by a logic 10 via a driver 11. The resistance value of the resistor element 5 is set to be larger than the resistance value of a gate resistor provided in a discharge path when the IGBT 1 is turned off under normal control.

[0015] The pre-charge power supply 8 includes an operational amplifier 12. The output terminal of the operational amplifier 12 is connected to the terminal 6, and is also connected to ground via resistor elements 13 and 14. The common connection point of the resistor elements 13 and 14 is connected to the non-inverting input terminal of the operational amplifier 12, and a reference voltage Vref is applied to the inverting input terminal. The operation of the pre-charge power supply 8 is controlled by a logic 10 controlling the operational amplifier 12. The logic 10 corresponds to a power supply control unit.

[0016] The sense emitter of IGBT1 is connected to terminal 15 of driving IC2. Inside driving IC2, terminal 15 is connected to the non-inverting input terminal of comparator 16 for detecting overcurrent and comparator 17 for detecting short circuit, and the inverting input terminals are provided with threshold voltages Vth_oc and Vth_s for detecting overcurrent and short circuit, respectively. The output terminals of comparators 16 and 17 are connected to the input terminals of logic 10. Note that a "short circuit" refers to a short circuit between the collector and emitter, which are the conductive terminals of IGBT1. Comparators 16 and 17 correspond to a current abnormality detection unit.

[0017] As shown in FIG. 2, the differential input section of the operational amplifier 12 includes a mirror pair of P-channel MOSFETs 18a and 18b whose sources are connected to a power supply. The drains of the N-channel MOSFETs 19a and 19b are connected to the drains of the FETs 18a and 18b, respectively. The N-channel MOSFET 20b is connected between the sources of the FETs 19a and 19b and ground. The FET 20b forms a mirror pair with the N-channel MOSFET 20a, which is connected in series with a reference current source 21 between the power supply and ground. An N-channel MOSFET 22 is connected between the gates of the FETs 20a and 20b and ground, and the gate of the FET 22 is controlled by the logic 10.

[0018] If the logic 10 turns off the FET 22, a tail current flows to the differential input section via the mirror pair of FETs 20a and 20b. If the logic 10 turns on the FET 22, the supply of tail current to the differential input section is stopped, which stops the operation of the operational amplifier 12, stops the operation of the precharge power supply 8, and stops the output of voltage. The above constitutes the protection circuit 23.

[0019] Next, the operation of this embodiment will be described. As shown in Fig. 3, when the comparator 16 or 17 detects the occurrence of an overcurrent or a short circuit (S2a, S2b) from a normal state where no abnormality occurs (S1), the logic 10 sets a judgment waiting time corresponding to each detection (S3a, S3b). The judgment waiting time is set to avoid erroneous judgment due to, for example, noise being superimposed on the terminal of the logic 10 to which the signal output by the comparator 16, 17 is input. The judgment waiting time for a short circuit is set shorter than the judgment waiting time for an overcurrent.

[0020] If the detection state by comparators 16, 17 is resolved before the respective judgment wait times have elapsed, a transition to a normal state occurs. On the other hand, if the detection state by comparators 16, 17 is maintained even after the respective judgment wait times have elapsed, logic 10 determines that an overcurrent or short circuit has been detected (S4a, S4b). Then, logic 10 first stops the operation of precharge power supply 8 (S5), and then turns off FET 9 of soft cutoff unit 7, shown as the "soft cutoff element" in the figure (S6).

[0021] The upper part of FIG. 4 assumes that the logic 10 does not control the operation of the precharge power supply 8. It is assumed that a short circuit occurs between the collector and emitter of the IGBT1 while the driving IC 2 drives the gate of the IGBT1 to a high level. When the gate voltage rises through the mirror capacitance of the IGBT1 due to the occurrence of a short circuit and exceeds the threshold voltage Vth_s, the output signal of the comparator 17 becomes high level. When the logic 10 detects the occurrence of a short circuit, it waits for the judgment time Ts1 for short circuit judgment to elapse. If the state in which the occurrence of a short circuit is detected continues even after the judgment time Ts1 has elapsed, the logic 10 judges that a short circuit has occurred. Then, the logic 10 turns on the FET 9 of the soft cutoff unit 7. The drain potential of the FET 9 is a potential lower than the gate potential of the IGBT1 by the forward voltage of the diode 3, but when the FET 9 is turned on, it changes to a low level. The logic 10 also constitutes a soft cutoff unit, and the configuration of the functional part that judges the occurrence of a short circuit after waiting for the judgment time Ts1 to elapse is designated as 10S.

[0022] In contrast, the lower part of Fig. 4 shows the operation of this embodiment, in which the judgment time Ts2 for short circuit judgment is set shorter than the above judgment time Ts1. The logic 10 stops the operation of the pre-charge power supply 8 when the judgment time Ts2 has elapsed (S4b → S5). Then, the FET 9 of the soft cutoff unit 7 is turned on (S6). Although not reflected in the flowchart shown in Fig. 3, when the discharge of the gate of IGBT1 is completed and the gate potential becomes low level, the logic 10 resumes the operation of the pre-charge power supply 8.

[0023] Figures 5 and 6 conceptually show the actions corresponding to the upper and lower parts of Figure 4, respectively. In the case shown in the upper part of Figure 4, when FET 9 of the soft cutoff unit 7 is turned on, the current (1) discharged from the gate of IGBT 1 and the current (2) supplied from the pre-charge power supply 8 join together and flow through FET 9. In contrast, in the case shown in the lower part of Figure 4, the pre-charge power supply 8 has stopped operating when FET 9 of the soft cutoff unit 7 is turned on, so only the current (1) flows through FET 9.

[0024] As described above, according to this embodiment, in the protection circuit 23, the comparators 16 and 17 detect a short circuit between the collector and emitter of the IGBT1 and an overcurrent flowing between the collector and emitter as abnormalities, respectively. When the logic 10S determines that the abnormality has been detected, the soft cutoff unit 7 operates to extract the charge stored in the gate of the IGBT1 at a slower speed than during normal off-state. In the driving IC 2, the terminal 6 connecting the gate of the IGBT1 to the soft cutoff unit 7 and the pre-charge power supply 8 is shared, and the logic 10 stops the output of voltage from the pre-charge power supply 8 before the soft cutoff unit 7 starts its operation to lower the gate potential.

[0025] With this configuration, the logic 10S determines that an abnormality has been detected and the pre-charge power supply 8 stops outputting voltage before the soft cutoff unit 7 starts the operation of extracting charge from the gate, so that the soft cutoff unit 7 can suppress an increase in the power capacity of the FET 9 that constitutes the path for extracting charge. Therefore, it becomes possible to suppress an increase in the cost of constructing the protection circuit 23.

[0026] Furthermore, the logic 10S waits for a judgment waiting time to elapse after the comparators 16 and 17 detect an abnormality before making a judgment. This prevents erroneous judgments caused by, for example, noise being superimposed on the terminals that accept inputs from the comparators 16 and 17. Furthermore, the logic 10 stops the output of voltage from the precharge power supply before the soft cutoff unit starts operating, so that an increase in the power capacity of the circuit elements that make up the soft cutoff unit can be significantly suppressed.

[0027] Furthermore, when the logic 10 stops the supply of voltage by the pre-charge power supply 8, it cuts off the tail current being supplied to the differential input section of the operational amplifier 12 constituting the pre-charge power supply 8. Therefore, it becomes possible to stop the operation of the pre-charge power supply 8 simply by adding an FET 22 for cutting off the tail current inside the operational amplifier 12.

[0028] Second embodiment Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted, and only the different parts will be described. As shown in FIG. 7, in the protection circuit 24 of the second embodiment, the precharge power supply 8 constituting the protection circuit 23 is replaced with a precharge power supply 25. The precharge power supply 25 includes an operational amplifier 26 instead of the operational amplifier 12. The operational amplifier 26 has a normal configuration without an internal FET 22, like the operational amplifier 12. A normally closed switch 27 is disposed between the output terminal of the operational amplifier 26 and the terminal 6 of the driving IC 2. When the logic 10 stops the supply of voltage by the precharge power supply 25, it switches the switch 27 from on to off.

[0029] Third embodiment 8, the third embodiment differs from the first embodiment in the external configuration of the driving IC 2. A resistor element 31 is connected in parallel to the capacitor 4. A series circuit of a resistor element 32 and a diode 33 is connected between the anode of the diode 3 and the terminal 6, and a series circuit of a diode 34 and a resistor element 35 is connected between the terminal 6 and the cathode of the diode 3.

[0030] (Other embodiments) The timing for stopping the operation of the precharge power supply 8 does not necessarily have to be before turning on the FET 9 of the soft cutoff unit 7, but may be any time after turning on and before the discharge of the charge stored in the gate of the IGBT 1 is completed. The power semiconductor element is not limited to an IGBT, but may be a power MOSFET or the like. It is also possible to perform only one of the detection of a short circuit and an overcurrent. The output signals of the comparators 16 and 17 may be directly input to the soft cutoff unit 7, so that the soft cutoff unit 7 can perform the waiting for the judgment waiting time to elapse when an abnormality occurs and the judgment after the time has elapsed. The configuration for stopping the supply of the tail current in the differential input section is not limited to that shown in FIG.

[0031] In addition to the inventions described in the claims, this case includes the following inventions: [1] a current abnormality detection unit (16, 17) that detects, as an abnormality, either or both of a short circuit between conductive terminals of the power semiconductor element (1) and an overcurrent flowing between the conductive terminals; a soft cutoff unit (7, 10S) that operates to extract the charge stored in the conduction control terminal of the power semiconductor element at a speed slower than that during normal off-state when it is determined that the abnormality has been detected; a precharge power supply (8) for suppressing a voltage rise at the conduction control terminal in order to protect against the short circuit; The conduction control terminal is a common terminal (6) that connects the soft cutoff unit and the precharge power supply, The protection circuit for a power semiconductor element further includes a power supply control unit (10) that stops the supply of voltage from the pre-charge power supply before the soft cutoff unit completes the operation of reducing the voltage of the conduction control terminal. [2] The soft cutoff unit (10S) waits for a judgment waiting time to elapse after the current abnormality detection unit detects an abnormality before making the judgment, The power supply control unit stops the supply of the voltage before the soft shutdown unit starts operation. [3] The precharge power supply includes an operational amplifier (12); The protection circuit for a power semiconductor element according to [1] or [2], wherein the power supply control unit cuts off a tail current being supplied to the differential input unit of the operational amplifier when the supply of the voltage is stopped. [4] a normally-closed switch (27) disposed between the precharge power source and the conduction control terminal; The protection circuit for a power semiconductor element according to [1] or [2], wherein the power supply control unit opens the switch when stopping the supply of the voltage. [5] a series circuit of a diode (3) and a capacitor (4) connected between the conduction control terminal and a low potential reference point; The protection circuit for a power semiconductor element according to any one of [1] to [4], wherein an output terminal of the precharge power supply is connected to a common connection point between the diode and the capacitor.

[0032] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0033] In the drawing, 1 indicates an IGBT, 2 indicates a driving IC, 3 indicates a diode, 4 indicates a capacitor, 6 indicates a terminal, 7 indicates a soft cutoff section, 8 indicates a precharge power supply, 9 indicates an N-channel MOSFET, 10 indicates logic, 12 indicates an operational amplifier, 16 and 17 indicate comparators, 18a and 18b indicate MOSFETs, and 23 indicates a protection circuit.

Claims

1. A current anomaly detection unit (16, 17) that detects either one or both of a short circuit between the conduction terminals of the power semiconductor device (1) or an overcurrent flowing between the conduction terminals as an anomaly, When the detection of the anomaly is determined, a soft cut-off unit (7, 10S) that operates to extract the charge charged on the conduction control terminal of the power semiconductor device at a slower speed than during normal off state, A precharge power supply (8) that suppresses the voltage rise of the conduction control terminal for protection against the short circuit, and is provided with, The terminal (6) connecting the conduction control terminal, the soft cut-off unit, and the precharge power supply is shared, Before the operation of reducing the voltage of the conduction control terminal by the soft cut-off unit is completed, a power supply control unit (10) that stops the supply of voltage by the precharge power supply is further provided, The precharge power supply includes an operational amplifier (12), The power supply control unit is a protection circuit for a power semiconductor device that cuts off the tail current supplied to the differential input part of the operational amplifier when stopping the supply of the voltage.

2. The soft cut-off unit (10S) waits for the elapse of a determination standby time from when the current anomaly detection unit detects an anomaly until the determination is made, The power supply control unit stops the supply of the voltage before the soft cut-off unit starts operating. The protection circuit for a power semiconductor device according to Claim 1.

3. A series circuit of a diode (3) and a capacitor (4) connected between the conduction control terminal and a low potential reference point is provided, The output terminal of the precharge power supply is connected to the common connection point of the diode and the capacitor. The protection circuit for a power semiconductor device according to Claim 1 or 2.

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