Semiconductor switching element driver

Abstract

It suppresses overcurrent when the upper and lower arms are short-circuited, reducing damage to semiconductor switching elements such as IGBTs. [Solution] The inverter comprises a first gate driver that applies a voltage to the gate terminal of a first semiconductor switching element to turn the first semiconductor switching element on and off; a second gate driver that applies a voltage to the gate terminal of a second semiconductor switching element connected in series with the first semiconductor switching element to turn the second semiconductor switching element on and off; a first insulating transmission unit that detects the voltage of the gate terminal of the first semiconductor switching element on the primary side and generates a first on signal on the secondary side when the voltage exceeds a first reference value and the second semiconductor switching element is turned on; and a second insulating transmission unit that detects the voltage of the gate terminal of the second semiconductor switching element on the primary side and generates a second on signal on the secondary side when the voltage exceeds a second reference value and the first semiconductor switching element is turned on.

Description

[Technical Field]

[0001] The present disclosure relates to a semiconductor switching element driving device. [Background technology]

[0002] In a power conversion circuit such as an inverter, if a short circuit occurs between the upper arm and the lower arm, an overcurrent will flow. In Patent Document 1, after detecting the occurrence of a short circuit and the flow of an overcurrent, a protection circuit is activated to turn off the IGBT before a failure occurs in the IGBT. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2023 / 032024 Summary of the Invention [Problem to be solved by the invention]

[0004] In the device of Patent Document 1, when the upper and lower arms are short-circuited, there is a period when an overcurrent flows through the IGBT, which causes accumulated damage to the IGBT. In addition, when an overcurrent flows, the current flowing from the capacitance between the collector and gate of the IGBT increases the gate-emitter voltage, which increases the absolute maximum rating of the gate-emitter voltage of the IGBT, which may result in failure.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to suppress overcurrent when an upper or lower arm short circuit occurs and reduce damage to semiconductor switching elements such as IGBTs by activating a short-circuit protection circuit before a short circuit is detected. [Means for solving the problem]

[0006] The semiconductor switching element drive device of the present disclosure includes a first gate drive unit that applies a voltage to a gate terminal of a first semiconductor switching element to turn the first semiconductor switching element on and off, a second gate drive unit that applies a voltage to a gate terminal of a second semiconductor switching element connected in series with the first semiconductor switching element to turn the second semiconductor switching element on and off, and a secondary gate drive unit that detects the voltage of the gate terminal of the first semiconductor switching element on the primary side and turns the second semiconductor switching element on when the voltage exceeds a first reference value. the primary side detects the voltage of the gate terminal of the second semiconductor switching element, and when this voltage exceeds a second reference value and the first semiconductor switching element is turned on, a second insulating transmission unit generates a second on signal on the secondary side; a first gate voltage reducing unit reduces the voltage applied to the gate terminal of the first semiconductor switching element based on the second on signal; and a second gate voltage reducing unit reduces the voltage applied to the gate terminal of the second semiconductor switching element based on the first on signal. [Effects of the Invention]

[0007] The present disclosure makes it possible to suppress overcurrent when the upper and lower arms are short-circuited, thereby reducing damage to semiconductor switching elements. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing a schematic configuration of a semiconductor switching element driving device according to a first embodiment. [Figure 2] 3 is a time series diagram showing the state at each point in the semiconductor switching element driving device in the first embodiment. FIG. [Figure 3] 10 is a time series diagram showing the state at each point in a conventional semiconductor switching element driving device. [Figure 4] This is a superposition of the time series in Figure 2 and the time series in Figure 3. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present disclosure will be described with reference to the accompanying drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and redundant explanations will be appropriately simplified or omitted.

[0010] Embodiment 1 1 is a diagram showing a schematic configuration of a semiconductor switching element drive device according to a first embodiment. The drive device controls a first IGBT 101a, which is a semiconductor switching element forming an upper arm 100a, and a second IGBT 101b, which is a semiconductor switching element forming a lower arm 100b. Specifically, a gate voltage is applied to the gate terminal of the first IGBT 101a to control its on / off state. Also, a gate voltage is applied to the gate terminal of the second IGBT 101b to control its on / off state.

[0011] Incidentally, when the IGBT is on, the collector terminal C and the emitter terminal E are in a conductive state, and when it is off, the collector terminal C and the emitter terminal E are in a non-conductive state. The drive device is mainly composed of a gate drive circuit (gate drive unit) 1 and an RTC circuit (overcurrent protection circuit) 20.

[0012] The upper arm 100a has a first IGBT 101a and a first freewheeling diode 102a connected in anti-parallel to it, and the lower arm 100b has a second IGBT 101b and a second freewheeling diode 102b connected in anti-parallel to it.

[0013] The gate drive circuit 1 comprises a first gate drive circuit 1a and a second gate drive circuit 1b. The first gate drive circuit 1a comprises an upper arm output stage circuit composed of a first power supply 2a, a second power supply 3a, a first MOSFET 4a, and a second MOSFET 5a. Here, the voltage of the first power supply 2a is set to +15V with respect to a reference potential VG1, and the voltage of the second power supply 3a is set to -10V with respect to the reference potential VG1.

[0014] Furthermore, the first gate drive circuit 1a includes a first control unit 6a that controls the first MOSFET 4a and the second MOSFET 5a, a first resistor 8a located between a terminal 7a of the upper arm output stage circuit and the gate terminal G of the first IGBT 101a, and a first protection operation detection unit 9a.

[0015] A connection point 103a on the emitter terminal side of the first IGBT 101a is connected to a reference potential VG1 of the first power supply 2a and the second power supply 3a. The first control unit 6a receives an on / off command signal SIN1 transmitted from a higher-level control device (not shown), and controls the first MOSFET 4a and the second MOSFET 5a based on a signal GSD from the first protection operation detection unit 9a.

[0016] That is, when the first MOSFET 4a is turned on and the second MOSFET 5a is turned off, the positive voltage of the first power supply 2a is applied to the gate terminal G of the first IGBT 101a from the terminal 7a of the upper arm output stage circuit, and the collector terminal C and the emitter terminal E become conductive, i.e., the first IGBT 101a is turned on.

[0017] Furthermore, with the first MOSFET 4a turned off and the second MOSFET 5a turned on, the negative voltage of the second power supply 3a is applied to the gate terminal G of the first IGBT 101a from the terminal 7a of the upper arm output stage circuit, and the collector terminal C and the emitter terminal E become non-conductive, i.e., enter the off state.

[0018] Similarly, the second gate drive circuit 1b includes a third power supply 2b, a fourth power supply 3b, and a lower arm output stage circuit configured with a third MOSFET 4b and a fourth MOSFET 5b. Here, the voltage of the third power supply 2b is set to +15 V with respect to the reference potential VG2, and the voltage of the fourth power supply 3b is set to -10 V with respect to the reference potential VG2.

[0019] Furthermore, the second gate drive circuit 1b includes a second control unit 6b that controls the third MOSFET 4b and the fourth MOSFET 5b, a second resistor 8b located between a terminal 7b of the lower arm output stage circuit and the gate terminal G of the second IGBT 101b, and a second protection operation detection unit 9b.

[0020] A connection point 103b on the emitter terminal side of the second IGBT 101b is connected to the reference potential VG2 of the third power supply 2b and the fourth power supply 3b. The second control unit 6b receives an on / off command signal SIN2 transmitted from a higher-level control device (not shown), and controls the third MOSFET 4b and the fourth MOSFET 5b based on a signal GSD from the second protection operation detection unit 9b.

[0021] That is, when the third MOSFET 4b is turned on and the fourth MOSFET 5b is turned off, the positive voltage of the third power supply 2b is applied to the gate terminal G of the second IGBT 101b from the terminal 7b of the lower arm output stage circuit, and the collector terminal C and the emitter terminal E become conductive, i.e., the second IGBT 101b enters the on state.

[0022] Furthermore, with the third MOSFET 4b turned off and the fourth MOSFET 5b turned on, the negative voltage of the fourth power supply 3b is applied from the terminal 7b of the lower arm output stage circuit to the gate terminal G of the second IGBT 101b, and the collector terminal C and the emitter terminal E become non-conductive, i.e., enter the off state.

[0023] The RTC circuit (overcurrent protection circuit) 20 is made up of a first RTC circuit 20a and a second RTC circuit 20b.

[0024] The first RTC circuit 20a includes a third resistor 21a located between the gate terminal G of the first IGBT 101a and the first resistor 8a.

[0025] The first RTC circuit 20a includes a branch circuit connected in parallel with the first IGBT 101a, which is connected from a node 104a on the collector terminal side of the first IGBT 101a to a node 103a on the emitter terminal side of the first IGBT 101a via a fourth resistor 22a and a fifth resistor 23a. The midpoint between the fourth resistor 22a and the fifth resistor 23a is connected to the base terminal of a transistor of the first overcurrent determination unit 24a.

[0026] One end of a first gate voltage reducing unit 27a is connected to a connection point 25a between the first resistor 8a and the third resistor 21a via a first diode 26a on the line between the terminal 7a of the upper arm output stage circuit and the gate terminal of the first IGBT 101a, and the other end of the first gate voltage reducing unit 27a is connected to a reference potential VG1.

[0027] A line between the terminal 7a of the upper arm output stage circuit and the gate terminal of the first IGBT 101a branches from a connection point 28a between the third resistor 21a and the gate terminal of the first IGBT 101a, and is connected to a sixth resistor 29a, the primary side of a first insulation transmission unit, and one end of a first Zener diode 31a. The other end of the first Zener diode 31a is connected to a reference potential VG1. Note that the connection between the sixth resistor 29a and the first Zener diode 31a stabilizes this line at a predetermined voltage. Note that in this embodiment, a first photocoupler 30a is used as the first insulation transmission unit.

[0028] The first photocoupler 30a consists of a first light-emitting diode 30a1 on the primary side and a first phototransistor 30a2 on the secondary side. The first light-emitting diode 30a1 emits light when the detected voltage exceeds a first reference value. When the first phototransistor 30a2 receives this light, it turns on, i.e., the collector terminal and emitter terminal become conductive.

[0029] The collector terminal of the first phototransistor 30a2 is connected to Gun between the second resistor 8b and the connection point 25b in the second RTC circuit 20b, and the emitter terminal of the first phototransistor 30a2 is connected to the second gate voltage reducer 27b.

[0030] Similarly, the second RTC circuit 20b includes a seventh resistor 21b located between the gate terminal G of the second IGBT 101b and the second resistor 8b.

[0031] The second RTC circuit 20b includes a branch circuit connected in parallel with the second IGBT 101b from a node 104b on the collector terminal side of the second IGBT 101b to a node 103b on the emitter terminal side of the second IGBT 101b via an eighth resistor 22b and a ninth resistor 23b. The midpoint between the eighth resistor 22b and the ninth resistor 23b is connected to the base terminal of a transistor of the second overcurrent determination unit 24b.

[0032] One end of a second gate voltage reducer 27b is connected to a connection point 25b between the second resistor 8b and the seventh resistor 21b via a second diode 26b on the line between the terminal 7b of the lower arm output stage circuit and the gate terminal of the second IGBT 101b. The other end of the second gate voltage reducer 27b is connected to a reference potential VG2.

[0033] A line between the terminal 7b of the lower arm output stage circuit and the gate terminal of the second IGBT 101b branches from a connection point 28b between the seventh resistor 21b and the gate terminal of the second IGBT 101b, and is connected to a tenth resistor 29b, the primary side of a second insulation transmission unit, and one end of a second Zener diode 31b. The other end of the second Zener diode 31b is connected to a reference potential VG2. The connection between the tenth resistor 29b and the second Zener diode 31b stabilizes this line at a predetermined voltage. In this embodiment, a second photocoupler 30b is used as the second insulation transmission unit.

[0034] The second photocoupler 30b consists of a second light-emitting diode 30b1 on the primary side and a second phototransistor 30b2 on the secondary side. The second light-emitting diode 30b1 emits light when the detected voltage exceeds a second reference value. When the second phototransistor 30b2 receives this light, it enters the ON state, i.e., conduction occurs from the collector terminal to the emitter terminal. The second reference value is the same as the first reference value.

[0035] The collector terminal of the second phototransistor 30b2 is connected to Gup between the first resistor 8a and the connection point 25a in the first RTC circuit 20a, and the emitter terminal of the second phototransistor 30b2 is connected to the first gate voltage reducer 27a.

[0036] In this circuit configuration, the first IGBT 101a of the upper arm 100a and the second IGBT 101b of the lower arm 100b are normally controlled to alternately turn on. However, if an abnormality occurs in the gate drive circuit or an IGBT, causing a short circuit in which the first IGBT 101a and the second IGBT 101b are simultaneously turned on, an overcurrent flows through the first IGBT 101a and the second IGBT 101b. If this overcurrent continues to flow and exceeds the short-circuit resistance of the IGBT, the normal IGBT will also fail. Therefore, it is necessary to forcibly turn off the IGBT.

[0037] The control in the event of such a short circuit will be described below.

[0038] Possible causes of a short circuit include a failure in the gate drive circuit that causes a positive voltage to continue to be applied to the gate terminal of the IGBT, or a failure in the IGBT that causes the voltage applied to the gate terminal from the gate drive circuit to change from positive to negative, but does not break the continuity between the collector and emitter terminals.

[0039] FIG. 2 is a time series diagram showing the state at each point in the semiconductor switching element driving device of FIG. The state will be explained based on Figs. 1 and 2. Under normal conditions, an upper level control device (not shown) sends an on / off command signal SIN1 to the first control unit 6a. Also, an on / off command signal SIN2 is sent to the second control unit 6b. The on / off command signals SIN1 and SIN2 alternately turn on and off repeatedly with a dead time Td between them.

[0040] The first control unit 6a receives the ON command signal from SIN1, turns on the first MOSFET 4a, turns off the second MOSFET 5a, and applies a positive voltage to the gate terminal of the first IGBT 101a. This turns on the first IGBT 101a, causing a current to flow through the load. The current flowing through the collector and emitter terminals of the first IGBT 101a is Icp.

[0041] At this time, the voltage detected by the first light-emitting diode 30a1 exceeds the first reference value, but because no voltage is applied to Gun, no current flows through the first phototransistor 30a2 on the secondary side, and therefore the first on-signal Ip-n is not transmitted from the first phototransistor 30a2 to the second gate voltage reducer 27b.

[0042] Similarly, the second control unit 6b receives an ON command signal from SIN2, turns on the third MOSFET 4b, turns off the fourth MOSFET 5b, and applies a positive voltage to the gate terminal of the second IGBT 101b. This causes the collector and emitter terminals of the second IGBT 101b to become conductive, allowing current to flow from the load. The current flowing through the collector and emitter terminals of the second IGBT 101b is Icn.

[0043] At this time, the voltage detected by the second light-emitting diode 30b1 exceeds the second reference value, but because no voltage is applied to Gup, no current flows through the second phototransistor 30b2 on the secondary side, and therefore the second on-signal In-p is not transmitted from the second phototransistor 30b2 to the first gate voltage reducer 27a.

[0044] Next, in FIG. 2, it is assumed that at time t1, SIN2 issues an ON command signal while SIN1 continues to issue an ON command signal.

[0045] First, the gate driver 1b applies a positive voltage to the gate terminal of the second IGBT 101b, turning it on. During the rising process of this voltage, a voltage is also applied to Gun.

[0046] In the first photocoupler 30a, the first light-emitting diode 30a1 emits light. As a result, a current flows through the first phototransistor 30a2 on the secondary side, generating a first on-signal Ip-n. The first on-signal Ip-n is then transmitted to the second gate voltage reducer 27b. The second gate voltage reducer 27b is activated based on the first on-signal Ip-n, causing a current IB to flow from the connection point 25b. As a result, the voltage applied to the gate terminal of the second IGBT 101b is maintained at a lower value than during normal operation.

[0047] Furthermore, when the voltage detected by the second light-emitting diode 30b1 exceeds a second reference value during the rise of the voltage applied to the gate terminal of the second IGBT 101b, the second light-emitting diode 30b1 emits light. Because a voltage is applied to Gup, a current flows through the second phototransistor 30b2 on the secondary side, generating a second on-signal In-p. The second on-signal In-p is then transmitted to the first gate voltage reducer 27a. The first gate voltage reducer 27a is activated based on the second on-signal In-p, causing a current I A to flow from the connection point 25a. This reduces the voltage applied to the gate terminal of the second IGBT 101b and keeps it at a lower value than during normal operation.

[0048] In this state, the first IGBT 10a1 and the second IGBT 10b1 are short-circuited, but the voltage applied to the gate terminal is reduced, making it more difficult for current to flow between the collector terminal and the emitter terminal than in a normal state, thereby preventing overcurrent from flowing.

[0049] In the first gate drive circuit 1a, the first protection operation detector 9a detects that the first gate voltage reducer 27a has reduced the gate voltage, and generates a signal GSD at time t2 and sends it to the first controller 6a. Upon receiving the signal GSD, the first controller 6a ignores the command signal SIN1 and turns off the first MOSFET 4a, turns on the second MOSFET 5a, and turns off the first IGBT 101a. The same control is performed in the second gate drive circuit 1b.

[0050] Thereafter, at time t3, the result becomes Fail, and the upper control device (not shown) stops sending SIN1 and SIN2.

[0051] For reference, the control when a short circuit occurs in a conventional semiconductor switching element driver will be described. The conventional driver does not include the sixth resistor 29a, the first photocoupler 30a, or the first Zener diode 31a. The tenth resistor 29b, the second photocoupler 30b, or the second Zener diode 31b are also not included.

[0052] 3 is a time series diagram showing the state of each point in a conventional semiconductor switching element drive device. In FIG. 3, at time t1, it is assumed that SIN2 issues an ON command signal while SIN1 continues to issue an ON command signal.

[0053] First, the second gate drive circuit 1b applies a positive voltage to the gate terminal of the second IGBT 101b, turning it on. This brings the collector and emitter terminals of the second IGBT 101b into conduction. This causes a short circuit between the first IGBT 101a and the second IGBT 101b, causing an overcurrent to flow.

[0054] When this overcurrent causes the voltage divided by the fourth resistor 22a and the fifth resistor 23a to exceed the voltage Vbe applied to the base terminal of the transistor of the first overcurrent determination unit 24a, which is required to drive the transistor, the transistor turns on. In other words, an overcurrent is determined to be present. Then, a first determination signal is sent from the first overcurrent determination unit 24a to the first gate voltage reduction unit 27a. The first gate voltage reduction unit 27a is activated based on the first determination signal, and a current IA flows from the connection point 25a.

[0055] Similarly, the transistor of the second overcurrent determination unit 24b is turned on. Then, the second determination signal is sent from the second overcurrent determination unit 24b to the second gate voltage reduction unit 27b. The second gate voltage reduction unit 27b is activated, and a current IB flows from the connection point 25b.

[0056] Figure 4 shows the time series of Figure 2 superimposed on the time series of Figure 3. The solid lines are based on FIG. 2, and the dashed lines are based on FIG. Comparing Gup, the rise in gate-emitter voltage after time t1 is suppressed in Figure 2. Also, comparing Icp and Icn, the steepness of the current is suppressed in Figure 2.

[0057] In some cases, even if an IGBT fails and the voltage applied to the gate terminal from the gate drive circuit changes from positive to negative, the continuity between the collector terminal and the emitter terminal may not be broken. In this case, the first photocoupler 30a does not generate the first on-signal Ip-n. Similarly, the second photocoupler 30b does not generate the second on-signal In-p.

[0058] Therefore, a first determination signal is sent from the first overcurrent determination unit 24a to the first gate voltage reduction unit 27a. Also, a second determination signal is sent from the second overcurrent determination unit 24b to the second gate voltage reduction unit 27b. This suppresses conduction between the collector terminal and the emitter terminal of the normal IGBT, preventing a failure of the normal IGBT.

[0059] In this manner, in this embodiment, by operating the gate voltage reducing unit before detecting a short circuit, it is possible to suppress overcurrent when the upper and lower arms are short-circuited, and reduce damage to semiconductor switching elements such as IGBTs.

[0060] In FIG. 1, IGBTs are used as the upper arm and lower arm switching elements, but other semiconductor switching elements such as MOFSETs having a gate terminal may also be used.

[0061] In addition, although a photocoupler is used as the insulating transmission section in FIG. 1, anything that can perform insulating transmission, such as an isolator, may be used.

[0062] Although the first and second reference values ​​are set to the same value, they may be different values. By adjusting them to different values, it becomes possible to select whether both arms or only one arm are operated in the event of a short circuit, and it becomes possible to use them to select the location of the shorted arm.

[0063] Although the preferred embodiments have been described in detail above, the present invention is not limited to these embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the disclosure.

[0064] Furthermore, when the number, quantity, amount, range, etc. of each element is mentioned in the embodiments, the device of this disclosure is not limited to the mentioned number unless otherwise specified or clearly specified in principle. Furthermore, the structures, etc. described in the embodiments are not necessarily essential unless otherwise specified or clearly specified in principle. [Explanation of symbols]

[0065] 1 gate drive circuit, 1a first gate drive circuit, 1b second gate drive circuit, 2a first power supply; 3a second power supply; 4a first MOSFET; 5a second MOFSET, 6a first control unit, 7a upper arm output stage circuit terminal, 8a first resistor 8a, 9a first protection operation detection unit, 2b third power supply, 3b fourth power supply, 4b third MOSFET, 5b fourth MOFSET, 6b second control unit, 7b terminal of lower arm output stage circuit, 8b second resistor, 9b second protection operation detection unit, 20 RTC circuit, 20a first RTC circuit, 20b second RTC circuit, 21a third resistor, 22a fourth resistor, 23a fifth resistor, 24a first overcurrent determination unit, 25a connection point, 26a first diode, 27a first gate voltage reducing portion, 28a connection point, 29a Sixth Resistance, 30a first photocoupler, 30a1: first light-emitting diode; 30a2: first phototransistor; 31a: first Zener diode; 21b 7th resistor, 22b 8th resistor, 23b 9th resistor, 24b second overcurrent determination unit, 25b connection point, 26b second diode, 27b second gate voltage reducing portion, 28a connection point, 29b The Tenth Resistance, 30b a second optocoupler; 30b1: second light-emitting diode; 30b2: second phototransistor; 31b second Zener diode; 100a upper arm, 100b lower arm, 101a first IGBT, 101b: second IGBT; 102a: first freewheeling diode; 102b second freewheeling diode, 103a node, 103b node, 104a connection point, 104b connection point

Claims

1. a first gate driver that applies a voltage to a gate terminal of a first semiconductor switching element to turn the first semiconductor switching element on and off; a second gate driver that applies a voltage to a gate terminal of a second semiconductor switching element connected in series with the first semiconductor switching element to turn on and off the second semiconductor switching element; a first insulating transmission unit that detects a voltage of a gate terminal of the first semiconductor switching element on the primary side, and generates a first on signal on the secondary side when the voltage exceeds a first reference value and the second semiconductor switching element is turned on; a second insulating transmission unit that detects a voltage of a gate terminal of the second semiconductor switching element on the primary side, and generates a second on signal on the secondary side when the voltage exceeds a second reference value and the first semiconductor switching element is turned on; a first gate voltage reducing unit that reduces a voltage applied to a gate terminal of the first semiconductor switching element based on the second on signal; a second gate voltage reducing section that reduces the voltage applied to the gate terminal of the second semiconductor switching element based on the first on signal.

2. a first gate driver that applies a voltage to a gate terminal of a first semiconductor switching element that forms an upper arm to turn the first semiconductor switching element on and off; a second gate driver that applies a voltage to a gate terminal of a second semiconductor switching element that forms a lower arm connected in series to the upper arm, thereby turning on and off the second semiconductor switching element; a first overcurrent determination unit that determines an overcurrent flowing through the first semiconductor switching element; a second overcurrent determination unit that determines whether the overcurrent flows through the second semiconductor switching element; a first gate voltage reducing unit that reduces a voltage applied to a gate terminal of the first semiconductor switching element based on a first determination signal that is output when the first overcurrent determining unit determines that an overcurrent exists; a second gate voltage reducing unit that reduces a voltage applied to a gate terminal of the second semiconductor switching element based on a second determination signal that is output when the second overcurrent determining unit determines that the overcurrent exists; a first insulating transmission unit configured to detect a voltage of a gate terminal of the first semiconductor switching element on a primary side, and to transmit a first ON signal to the second gate voltage reducing unit on a secondary side when the voltage exceeds a first reference value and the second semiconductor switching element is turned ON; a second insulating transmission unit configured to detect a voltage of a gate terminal of the second semiconductor switching element on a primary side, and to transmit a second ON signal to the first gate voltage reducing unit on a secondary side when the voltage exceeds a second reference value and the first semiconductor switching element is turned ON; a first gate voltage reducing unit that reduces a voltage applied to a gate terminal of the first semiconductor switching element based on the second on signal, and a second gate voltage reducing unit that reduces a voltage applied to a gate terminal of the second semiconductor switching element based on the first on signal.

3. 3. The semiconductor switching element drive device according to claim 1, wherein the first gate drive unit includes a first protection operation detection unit that detects a voltage at a gate terminal of the first semiconductor switching element, and when the first protection operation detection unit detects a voltage reduction by the first gate voltage reduction unit, the semiconductor switching element is turned off.

4. 4. The semiconductor switching element drive device according to claim 3, wherein the second gate drive unit includes a second protection operation detection unit that detects a voltage at a gate terminal of the second semiconductor switching element, and when the second protection operation detection unit detects a voltage reduction by the second gate voltage reduction unit, the second semiconductor switching element is turned off.

5. 3. The semiconductor switching element driving device according to claim 1, wherein the first reference value and the second reference value are different values.

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