Control Circuit and Switching Device

Abstract

Provided are a control circuit which can be expected to suppress a surge voltage applied to a switching element while also suppressing a switching loss at the time of a turn-off of the switching element, and a switch device. A control circuit (10) controls a switching element (1) having a gate (G1) and a source (S1) corresponding to the gate (G1). The control circuit (10) is provided with an inductor (L1), a circuit element (5), and a resistor (R1). The inductor (L1) is connected between the gate (G1) and the source (S1) of the switching element (1). Between the gate (G1) and the source (S1) is connected in series to the inductor (L1). Current flows through the circuit element (5) when an electromotive force is generated in the inductor (L1). The resistor (R1) is connected in parallel to the inductor (L1) and the circuit element (5) between the gate (G1) and the source (S1).

Description

Technical Field

[0001] The present disclosure generally relates to a control circuit and a switch device, and more particularly to a control circuit for controlling a switching element and a switch device including the same.

Background Art

[0002] Patent Document 1 proposes a bidirectional switch circuit capable of suppressing an overvoltage applied to a switching transistor.

[0003] In an example of the bidirectional switch circuit described in Patent Document 1, a reactor is inserted between the sources of the two switching transistors. Also, a diode as an electromotive force supply element is connected between the gate and source of each switching transistor in a polarity that blocks the gate drive voltage to each switching transistor. A drive voltage of the gate drive circuit is supplied via a series resistor between a first control terminal connected to the common gate of the two switching transistors and a second control terminal connected to an intermediate tap of the reactor.

[0004] In a control circuit for controlling a semiconductor switch (switching element), it may be desirable to suppress a surge voltage applied to the semiconductor switch while suppressing switching loss at the turn-off of the semiconductor switch.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The present disclosure has been made in view of the above problems, and an object thereof is to provide a control circuit and a switch device that can suppress a surge voltage applied to a switching element while suppressing switching losses during turn-off of the switching element.

[0007] A control circuit according to an aspect of the present disclosure is a control circuit that controls a switching element having a gate and a source corresponding to the gate. The control circuit includes an inductor, a circuit element, and a resistor. A protection diode, and The inductor is connected between the gate and the source of the switching element. The circuit element is connected in series with the inductor between the gate and the source. When an electromotive force is generated in the inductor, a current flows through the circuit element. The resistor is connected in parallel with the inductor and the circuit element between the gate and the source. the protection diode has an anode and a cathode, the anode is connected to the connection point between the circuit element and the resistor, and the cathode is connected to the gate of the switching element. A control circuit according to an aspect of the present disclosure is a control circuit that controls a switching element having a gate and a source corresponding to the gate. The control circuit includes an inductor, a circuit element, a resistor, a first terminal, a second terminal, a second inductor, a voltage clamping element, and a third inductor. The inductor is connected between the gate and the source of the switching element. The circuit element is connected in series with the inductor between the gate and the source. When an electromotive force is generated in the inductor, a current flows through the circuit element. The resistor is connected in parallel with the inductor and the circuit element between the gate and the source. The first terminal is connected to the switching element on the side opposite to the source in the switching element. The second terminal is connected to the inductor on the side opposite to the switching element side in the inductor. The second inductor is connected between a first node between the first inductor, which is the inductor, and the second terminal and the circuit element. The voltage clamping element is connected in parallel with the switching element, the first inductor, and the second inductor. The third inductor is connected between a second node between the second inductor and the circuit element and the voltage clamping element. The control circuit does not allow current to flow through the third inductor in the on state of the switching element.

[0008] A switch device according to an aspect of the present disclosure includes the control circuit and the switching element. 。 A switching device according to an aspect of the present disclosure includes a control circuit that controls a switching element having a gate and a source corresponding to the gate, and the switching element. The control circuit includes an inductor, a circuit element, and a resistor. The inductor is connected between the gate and the source of the switching element. The circuit element is connected in series with the inductor between the gate and the source. When an electromotive force is generated in the inductor, a current flows through the circuit element. The resistor is connected in parallel with the inductor and the circuit element between the gate and the source. The switching element is a dual-gate type bidirectional switch having two gates and two sources respectively. The switching device includes two control circuits. One of the two control circuits is connected to a gate corresponding to the one control circuit among the two gates of the bidirectional switch, and the other control circuit is connected to a gate corresponding to the other control circuit among the two gates of the bidirectional switch.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0010] (Embodiment 1) Hereinafter, the control circuit 10 according to the present embodiment and the switch device 100 including the same will be described with reference to FIGS. 1 to 3.

[0011] (1) Outline As shown in Fig. 1, the control circuit 10 is a control circuit that controls the switching element 1 having the gate G1 and the source S1 corresponding to the gate G1. The switching element 1 has a drain D1 in addition to the gate G1 and the source S1. The control circuit 10 includes an inductor L1 connected between the gate G1 and the source S1 of the switching element 1, and a circuit element 5 connected in series with the inductor L1 between the gate G1 and the source S1 and conducting when an electromotive force is generated in the inductor L1. Here, regarding the circuit element 5, "conducting when an electromotive force is generated in the inductor L1" means that a current flows through the circuit element 5 when an electromotive force higher than the potential of the first end is generated at the second end of the inductor L1 opposite to the first end connected to the source S1 of the switching element 1. In other words, regarding the circuit element 5, "conducting when an electromotive force is generated in the inductor L1" means that a current flows through the circuit element 5 when a back electromotive force is generated in the inductor L1. Further, the control circuit 10 includes a resistor R1 connected in parallel to the inductor L1 and the circuit element 5 between the gate G1 and the source S1.

[0012] The inductor L1 generates an electromotive force (induced electromotive force) corresponding to the current change rate (di / dt = dIs / dt) of the source current Is, which is the main current of the switching element 1 when the switching element 1 is turned off. Here, the source current Is, which is the main current of the switching element 1, is the current flowing from the drain D1 to the source S1 of the switching element 1. That is, the source current Is is the same current as the drain current.

[0013] The circuit element 5 conducts when an electromotive force is generated in the inductor L1 according to the current change rate of the source current Is when the source current Is decreases. The circuit element 5 is, for example, a capacitor C1.

[0014] Resistor R1 is connected in parallel with inductor L1 and circuit element 5. That is, resistor R1 is connected in parallel with the series circuit including inductor L1 and circuit element 5. Since control circuit 10 includes resistor R1, it is possible to generate a potential difference between both ends of resistor R1, and to make the reference potential of the potential (gate potential) of gate G1 of switching element 1 different from the reference potential of the potential (source potential) of source S1.

[0015] Switching device 100 includes control circuit 10 and switching element 1. In switching device 100, for example, a load circuit including a series circuit of a load and a power supply is connected between drain D1 and source S1 of switching element 1. More specifically, in switching device 100, a load circuit including a load and a power supply is connected between the first terminal at one end and the second terminal at the other end of the series circuit of switching element 1 and inductor L1. The load and the power supply are not components of switching device 100.

[0016] (2) Configuration (2-1) Switching Element Switching element 1 is, for example, a switching element of a GaN-based semiconductor. More specifically, switching element 1 is a JFET (Junction Field Effect Transistor). The JFET constituting switching element 1 is, for example, a GaN-based GIT (Gate Injection Transistor).

[0017] The switching element 1 includes, for example, a substrate, a buffer layer, a first nitride semiconductor layer, a second nitride semiconductor layer, a source electrode, a gate electrode, a drain electrode, and a p-type layer. The buffer layer is formed on the substrate. The first nitride semiconductor layer is formed on the buffer layer. The second nitride semiconductor layer is formed on the first nitride semiconductor layer. The source electrode, the gate electrode, and the drain electrode are formed on the second nitride semiconductor layer. The p-type layer is interposed between the gate electrode and the second nitride semiconductor layer. In the switching element 1, the second nitride semiconductor layer and the p-type layer constitute a diode structure. The gate G1 in the switching element 1 includes the gate electrode and the p-type layer. The source S1 in the switching element 1 includes the source electrode. The drain D1 in the switching element 1 includes the drain electrode. The substrate is, for example, a silicon substrate. The buffer layer is, for example, an undoped GaN layer. The first nitride semiconductor layer is, for example, an undoped GaN layer. The second nitride semiconductor layer is, for example, an undoped AlGaN layer. The p-type layer is, for example, a p-type AlGaN layer. Each of the buffer layer, the first nitride semiconductor layer, and the second nitride semiconductor layer may contain impurities such as Mg, H, Si, C, and O that are inevitably mixed during growth by MOVPE (Metal Organic Vapor Phase Epitaxy) or the like.

[0018] (2-2) Switching device As shown in FIG. 1, the switching device 100 includes a switching element 1, a control circuit 10, a drive circuit 2, and a driver 3. The control circuit 10 according to Embodiment 1 includes an inductor L1, a capacitor C1 that is a circuit element 5, and a resistor R1, as described above.

[0019] The driver 3 has a high-potential side output terminal and a low-potential side output terminal. In the switching device 100, the high-potential side output terminal of the driver 3 is connected to the gate G1 of the switching element 1 via the drive circuit 2. The drive circuit 2 includes, for example, a gate resistor connected between the high-potential side output terminal of the driver 3 and the gate G1 of the switching element 1. The low-potential side output terminal of the driver 3 is connected to the source S1 of the switching element 1 via the resistor R1. The driver 3 is a driver capable of applying a positive bias voltage between the gate G1 and the source S1 of the switching element 1 and also capable of applying a negative bias voltage. The driver 3 includes, for example, a DC power supply and a CMOS (Complementary Metal-Oxide Semiconductor) inverter, and is a driver capable of changing the output voltage in the range of -12V to 18V.

[0020] The source S1 of the switching element 1 is connected to the first end of the inductor L1 and the first end of the resistor R1. The first end of the resistor R1 is connected to a node N1 on the path between the source S1 of the switching element 1 and the first end of the inductor L1. The gate G1 of the switching element 1 is connected to the high-potential side output terminal of the driver 3 via the drive circuit 2. The first end of the capacitor C1 is connected to the second end of the inductor L1. The capacitor C1 is connected to a node N2 on the path between the inductor L1 and the second terminal connected to the above-mentioned load circuit. The second end of the capacitor C1 is connected to a node N3 on the path between the resistor R1 and the gate G1 of the switching element 1. Here, more specifically, the second end of the capacitor C1 is connected to the second end of the resistor R1 and the low-potential side output terminal of the driver 3. The resistor R1 is connected in parallel with the inductor L1 and the capacitor C1. That is, the resistor R1 is connected in parallel with the series circuit of the inductor L1 and the capacitor C1. The above-mentioned node N3 can also be said to be the connection point between the resistor R1 and the circuit element 5. Hereinafter, for convenience of explanation, an arbitrary point on the path between the above-mentioned node N3 and the low-potential side output terminal of the driver 3 is referred to as a reference potential point P0, and the potential of the reference potential point P0 is referred to as a reference potential Vstd.

[0021] (3) Operation Next, the operation of the switch device 100 will be described with reference to FIGS. 1 to 3.

[0022] In the following description, the voltage between the gate G1 and the source S1 of the switching element 1 is referred to as the gate-source voltage Vgs, and the current flowing from the gate G1 of the switching element 1 to the drive circuit 2 is referred to as the discharge current Idis.

[0023] In the switch device 100, when a positive bias voltage is output from the driver 3 between the gate G1 and the source S1 of the switching element 1 and the gate-source voltage Vgs of the switching element 1 is equal to or higher than the threshold voltage of the switching element 1, the state of the switching element 1 is an on state. In the switch device 100, when turning off the switching element 1, the output voltage of the driver 3 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage). As a result, in the switch device 100, the source current Is, the electromotive force VL of the inductor L1, the gate-source voltage Vgs, the reference potential Vstd, and the discharge current Idis change as shown in FIG. 2. In FIG. 2, the time point when the output voltage of the driver 3 in the switch device 100 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage) is set as t0, the time point when the discharge current Ids1 starts to flow is set as t1, the time point when the change in the source current Is of the switching element 1 turns from an increase to a decrease is set as t2, and the time point when the source current Is becomes 0 is set as t3.

[0024] In the switch device 100, immediately after the start of turning off the switching element 1, the potential of the source S1 and the electromotive force of the inductor L1 are 0 V, and the reference potential Vstd is substantially equal to the source potential and is 0 V.

[0025] In the switch device 100, until the time point t2 when the change in the source current Is turns from increasing to decreasing, the charge of the gate G1 of the switching element 1 is discharged through the drive circuit 2, so that a discharge current Idis flows from the gate G1. At this time, in the switch device 100, the gate-source voltage Vgs of the switching element 1 rapidly decreases, and then the gate-source voltage Vgs becomes substantially constant.

[0026] In the switch device 100, when the source current Is starts to decrease at the time point t2, the current value of the discharge current Idis decreases, and the rate of decrease of the gate potential slows down, so that the rate of change (dIs / dt) of the source current Is slows down, and the surge voltage applied to the switching element 1 can be suppressed.

[0027] In the switch device 100, the induced electromotive force VL generated in the inductor L1 in response to the decrease in the source current Is raises the reference potential Vstd through the capacitor C1. More specifically, in the control circuit 10, due to the induced electromotive force generated in the inductor L1 in response to the decrease in the source current Is, the potential of the second end is higher than that of the first end of the inductor L1, so that the potential of the node N2 is higher than that of the source S1, and a current flows in the closed-loop circuit including the inductor L1, the capacitor C1, and the resistor R1. That is, in the control circuit 10, a current flows through the capacitor C1 which is the circuit element 5 (the capacitor C1 which is the circuit element 5 conducts). Thereby, in the switch device 100, the reference potential Vstd rises higher than the potential of the source S1, and the potential difference between the gate potential and the reference potential Vstd becomes smaller, so that the current value of the discharge current Idis from the gate G1 of the switching element 1 decreases, and the rate of decrease of the source current Is can be slowed down, and a gentle current interruption can be realized.

[0028] During the period from time point t1 to time point t2 (hereinafter also referred to as the first period), the control circuit 10 discharges the charge of the gate G1 at a higher speed than the period from time point t2 to time point t3 (hereinafter also referred to as the second period). During the second period, the charge of the gate G1 is discharged at a lower speed than the first period. Therefore, the switching device 100 can shorten the turn-off time by shortening the time from time point t1 to time point t2, and can reduce the absolute value of the current change rate of the source current Is from time point t2 to time point t3, thereby suppressing the surge voltage of the switching element 1.

[0029] As can be seen from the above description, in the control circuit 10, when the switching element 1 is turned off, an electromotive force is generated in the inductor L1 in response to the decrease in the source current Is flowing through the source S1, and a current corresponding to the electromotive force flows through the circuit element 5 (capacitor C1) and the resistor R1. Therefore, the potential of the reference potential point P0 included in the path between the node N3 to which the above-mentioned circuit element 5 is connected and the gate G1 of the switching element 1 increases. As a result, in the control circuit 10, the magnitude of the discharge current Idis from the gate G1 is determined by the potential difference between the potential of the gate G1 of the switching element 1 and the potential of the reference potential point P0.

[0030] The control circuit 10 can control the switching element 1 with the inductor L1, the resistor R1, and the capacitor C1. While a current is flowing in the closed-loop circuit including the inductor L1, the capacitor C1, and the resistor R1 due to the electromotive force of the inductor L1, the reference potential Vstd of the reference potential point P0 becomes higher than the source potential, and the potential difference between the potential of the gate G1 and the reference potential Vstd becomes smaller. Therefore, the discharge current Idis from the gate G1 becomes smaller. For this reason, in the control circuit 10, the current change rate of the source current Is in the second period (in other words, the cutoff speed of the source current Is) can be changed by changing at least one of the capacitance of the capacitor C1, the resistance value of the resistor R1, and the inductance of the inductor L1. For example, when the capacitance of the capacitor C1 in the control circuit 10 is changed, the characteristics in the first period are the same as each other, and the current change rates in the second period are different from each other. FIG. 3 shows the waveforms of the source current Is when the capacitance of the capacitor C1 is variously changed in the control circuit 10, and the characteristics in the second period are shown by different line types. In the example of FIG. 3, the capacitance of the capacitor C1 increases in the order of characteristic B1, characteristic B2, characteristic B3, and characteristic B4. From FIG. 3, it can be seen that as the capacitance of the capacitor C1 increases, the cutoff speed of the source current Is becomes slower. In the control circuit 10, even when the resistance value of the resistor R1 or the inductance of the inductor L1 is increased instead of the capacitance of the capacitor C1, the cutoff speed of the source current Is becomes slower. Here, in the control circuit 10, when the resistance value of the resistor R1 is increased, the switching speed at the turn-on of the switching element 1 decreases. That is, in the control circuit 10, the absolute value of the current change rate (di / dt) of the source current Is flowing through the switching element 1 decreases. Also, in the control circuit 10, when the inductance of the inductor L1 is increased, the size of the inductor L1 becomes larger, and the size of the control circuit 10 becomes larger. Therefore, from the viewpoint of suppressing the decrease in the switching speed at the turn-on of the switching element 1 and the increase in the size of the control circuit 10, it is preferable that the control circuit 10 determines the switching speed at the turn-off of the switching element 1 according to the capacitance of the capacitor C1.Note that in the control circuit 10, for example, the inductance of the inductor L1 is 50 nH, the resistance value of the resistor R1 is 1 Ω, and the capacitance of the capacitor C1 is 100 nF. However, these numerical values are just examples and are not limited to these values. Also, the resistance value of the gate resistor included in the drive circuit 2 is, for example, 50 Ω, but it is not limited to this value.

[0031] In a comparative example where the control circuit 10 does not include the circuit element 5, compared with the control circuit 10 including the circuit element 5, when the switching element 1 turns off, the discharge current Idis during the period from time point t2 to time point t3 can be increased, and the absolute value of the current change rate during the period from time point t2 to time point t3 can be increased. Therefore, the switching time can be shortened and the switching loss can be reduced. However, in the comparative example, a surge voltage is generated in the switching element 1, and there is a possibility that a problem may occur in the switching element 1. Also, in the comparative example, if the discharge current Idis during the period from time point t1 to time point t3 is reduced, the generation of the surge voltage can be suppressed, but the switching time becomes longer and the switching loss becomes larger. On the other hand, in the switch device 100 including the control circuit 10 of the present embodiment, the discharge current Idis from the gate G1 of the switching element 1 flows according to the potential difference between the gate potential and the reference potential Vstd. However, during the period from time point t2 to time point t3, the potential difference between the gate potential and the reference potential Vstd is reduced by the current flowing in the closed-loop circuit including the inductor L1, the circuit element 5, and the resistor R1, and the discharge current Idis becomes smaller, and the absolute value of the current change rate of the source current Is becomes smaller. Therefore, in the control circuit 10 of the present embodiment, when the switching element 1 turns off, the discharge current Idis is made different between the first period from time point t1 to time point t2 and the second period from time point t2 to time point t3. By increasing the discharge current in the first period, the switching loss can be suppressed, and by reducing the discharge current in the second period, it is possible to suppress the surge voltage. Here, the switching loss at turn-off means, for example, the power loss in the switching element 1 when the switching element 1, which is a semiconductor switch, turns off.

[0032] Further, in the switch device 100, when the switching element 1 is turned on, the current flowing through the resistor R1 of the control circuit 10 increases, so the reference potential Vstd rises, and the rising of the potential of the gate G1 becomes gentle.

[0033] (4) Advantages The control circuit 10 according to Embodiment 1 controls a switching element having a gate G1 and a source S1 corresponding to the gate G1. The control circuit 10 includes an inductor L1, a capacitor C1 as a circuit element 5, and a resistor R1. The inductor L1 is connected between the gate G1 and the source S1 of the switching element 1. The circuit element 5 is connected in series with the inductor L1 between the gate G1 and the source S1. When an electromotive force is generated in the inductor L1, a current flows through the circuit element 5. When an electromotive force is generated in the inductor L1, a current flows through the circuit element 5.

[0034] The control circuit 10 according to Embodiment 1 can suppress the switching loss when the switching element 1 is turned off and suppress the surge voltage applied to the switching element 1.

[0035] Further, since the switch device 100 according to Embodiment 1 includes the switching element 1 and the control circuit 10, it is possible to suppress the switching loss when the switching element 1 is turned off and suppress the surge voltage applied to the switching element 1.

[0036] (Modification Example of Embodiment 1) The modification examples of the control circuit 10 and the switch device 100 according to Embodiment 1 are listed below. Note that the modification examples described below can be applied in appropriate combination with the control circuit 10 and the switch device 100 according to Embodiment 1. For the components similar to those of the control circuit 10 and the switch device 100 according to Embodiment 1, the same reference numerals are given and the description is omitted.

[0037] (Modification Example 1 of Embodiment 1) Hereinafter, the control circuit 10a according to Modification 1 of Embodiment 1 and the switch device 100a including the same will be described with reference to FIG. 4.

[0038] The control circuit 10a is different from the control circuit 10a according to Embodiment 1 in that it includes a negative power supply V1. Here, the negative power supply V1 is connected between the above-described node N3 and the output terminal on the low-potential side of the driver 3 (hereinafter also referred to as the negative terminal). In the switch device 100a, the negative terminal of the negative power supply V1 is connected to the negative terminal of the driver 3. Other configurations of the control circuit 10a are the same as those of the control circuit 10 (see FIG. 1) according to Embodiment 1.

[0039] (Modification 2 of Embodiment 1) Hereinafter, the control circuit 10b according to Modification 2 of Embodiment 1 and the switch device 100b including the same will be described with reference to FIG. 5.

[0040] The control circuit 10b according to Modification 2 is different from the control circuit 10 according to Embodiment 1 in that the circuit element 5 is the diode Di1. The diode Di1 has an anode and a cathode. The anode of the diode Di1 is connected to the node N2. The cathode of the diode Di1 is connected to the above-described node N3. That is, in the control circuit 10b, the resistor R1 is connected between the first end of the inductor L1 and the cathode of the diode Di1.

[0041] The circuit operation of control circuit 10b, in which capacitor C1 of control circuit 10 is replaced with diode Di1, is the same as that of control circuit 10. In control circuit 10b, the electromotive force (back electromotive force) generated in inductor L1 is consumed by diode Di1 and resistor R1 in a closed-loop circuit including inductor L1, diode Di1, and resistor R1. In control circuit 10b, for example, by increasing the inductance of inductor L1, the cutoff speed of source current Is when switching element 1 turns off can be slowed down. FIG. 6 shows the waveforms of source current Is when the inductance of inductor L1 is varied variously in control circuit 10b, and the characteristics in the second period during which source current Is decreases are shown in different line types. In the example of FIG. 6, the inductance of inductor L1 increases in the order of characteristic B5, characteristic B6, characteristic B7, and characteristic B8. It can be seen from FIG. 6 that as the inductance of inductor L1 increases, the cutoff speed of source current Is becomes slower.

[0042] Also, in control circuit 10b, when the resistance value of resistor R1 is increased, the time constant of the series circuit of resistor R1 and inductor L1 becomes smaller. Therefore, increasing the resistance value of resistor R1 is one means of increasing the cutoff speed of source current Is when switching element 1 turns off. However, on the other hand, in control circuit 10b, when the resistance value of resistor R1 is increased, the resistance value of resistor R1 on the path through which discharge current Idis from gate G1 of switching element 1 flows through drive circuit 2 becomes larger. Therefore, increasing the resistance value of resistor R1 is also one means of slowing down the current cutoff speed of source current Is when switching element 1 turns off. In control circuit 10b, the relationship between the resistance value of resistor R1 and the cutoff speed of source current Is depends on the combination with other circuit parameters. Therefore, in control circuit 10b, it is easier to adjust the cutoff speed of source current Is by the inductance of inductor L1 than by the resistance value of resistor R1.

[0043] Also, in the switch device 100 including the control circuit 10 according to Embodiment 1, after the source current Is of the switching element 1 is cut off, a current that discharges the charge accumulated in the capacitor C1 flows, and the gate-source voltage Vgs of the switching element 1 becomes negative (that is, the potential of the source S1 becomes higher than the potential of the gate G1). On the other hand, in the switch device 100b including the control circuit 10b according to this modification, since the diode Di1 is provided as the circuit element 5 instead of the capacitor C1, the discharge current from the circuit element 5 after the source current Is is cut off becomes small, so even if the gate-source voltage Vgs of the switching element 1 becomes negative, it is possible to reduce its absolute value.

[0044] Note that the control circuit 10 according to Embodiment 1 may be combined with the control circuit 10b of this modification. Specifically, the control circuit adopting such a combination has a configuration in which the capacitor C1 is connected in series to the diode Di1 in the control circuit 10b of this modification, and the resistor R1 is connected in parallel to the inductor L1, the diode Di1, and the capacitor C1, and includes two circuit elements 5 connected in series to the inductor L1. If one of the two circuit elements 5 is called the first circuit element and the other is called the second circuit element, for example, the first circuit element is the diode Di1 and the second circuit element is the capacitor C1.

[0045] (Modification 3 of Embodiment 1) Hereinafter, the control circuit 10c according to Modification 3 of Embodiment 1 and the switch device 100c including the same will be described with reference to FIG. 7.

[0046] The control circuit 10c according to this modification is different from the control circuit 10 according to Embodiment 1 in that it further includes a protection diode Di2 in the control circuit 10 according to Embodiment 1. The protection diode Di2 has an anode and a cathode. The protection diode Di2 is, for example, a Schottky diode, but may be a diode different from the Schottky diode.

[0047] The protection diode Di2 is connected between the reference potential point P0 and the gate G1 so as to form a path different from the path connecting the node N3 and the gate G1. Specifically, in the control circuit 10c, the anode of the protection diode Di2 is connected to the node N7 on the path between the negative terminal of the driver and the node N3. The protection diode Di2 is connected to the connection point of the resistor R1 and the circuit element 5. Thereby, in the switch device 100c including the control circuit 10c, the anode of the protection diode Di2 is connected to the negative terminal of the driver 3, and has substantially the same potential as the potential of the reference potential point P0. The cathode of the protection diode Di2 is connected to the node N8 on the path between the drive circuit 2 and the gate G1 of the switching element 1, and has substantially the same potential as the potential of the gate G1 of the switching element 1.

[0048] In the switch device 100c including the control circuit 10c, after the source current Is of the switching element 1 is cut off, the charge accumulated in the capacitor C1 flows as the current I5 and is consumed in the closed-loop circuit including the capacitor C1, the inductor L1, and the resistor R1. When the interruption of the source current Is is completed, the potential of the gate G1 of the switching element 1 is substantially equal to the potential of the reference potential point P0. Therefore, in the switch device 100c, when the current I5 flows, the gate potential becomes lower than the source potential, and the gate-source voltage Vgs becomes negative. In the switch device 100c, when the gate-source voltage Vgs of the switching element 1 becomes negative, the protection diode Di2 acts to make the gate-source voltage Vgs constant. Thereby, in the switch device 100, the gate-source voltage Vgs becomes substantially equal to the conduction voltage of the protection diode Di2. Therefore, in the switch device 100, the switching element 1 is protected.

[0049] The control circuit 10c may include a resistor connected in series with the protection diode Di2 between the node N7 and the node N8, for example, for the purpose of preventing breakdown of the protection diode Di2.

[0050] The control circuit 10c may include a negative power supply with its positive terminal connected to node N7 between node N7 and the negative terminal of driver 3. In this case, it is preferable to configure protection diode Di2 as a series circuit of a plurality of diodes so that protection diode Di2 does not continue to conduct at the voltage of the negative power supply. Thereby, the forward voltage of protection diode Di2 becomes large, and it becomes possible to prevent protection diode Di2 from continuing to conduct due to the voltage of the negative power supply.

[0051] (Modification Example 4 of Embodiment 1) Hereinafter, the control circuit 10d according to Modification Example 4 of Embodiment 1 and the switch device 100d including the same will be described with reference to FIG. 8.

[0052] The control circuit 10d according to Modification Example 4 is different from the control circuit 10 according to Embodiment 1 in that it includes a protection diode Di3 connected between the gate G1 and the source S1 of the switching element 1. The protection diode Di3 has an anode and a cathode. The protection diode Di3 is, for example, a Schottky diode, but it may be a diode different from the Schottky diode. In the protection diode Di3, the anode of the protection diode Di3 is connected to the source S1 of the switching element 1, and the cathode of the protection diode Di3 is connected to the gate G1 of the switching element 1. In the switch device 100d including the control circuit 10d, the anode of the protection diode Di3 is connected to node N9 on the path between the source S1 of the switching element 1, the inductor L1, and the resistor R1, and the cathode of the protection diode Di3 is connected to node N10 on the path between the gate G1 of the switching element 1 and the drive circuit 2.

[0053] In the control circuit 10d according to Modification 4, since the protection diode Di3 is connected between the gate G1 and the source S1 of the switching element 1, after the source current Is of the switching element 1 is cut off, when the charge accumulated in the capacitor C1 flows as a current I5 (see FIG. 7) in a closed loop circuit including the capacitor C1, the inductor L1, and the resistor R1, the gate-source voltage Vgs can be kept constant (clamped) at the forward voltage of the protection diode Di3. As a result, the control circuit 10d can suppress the potential of the source S1 of the switching element 1 from becoming too large with respect to the potential of the gate G1, and can protect the switching element 1.

[0054] (Other Modifications of Embodiment 1) In the control circuit 10 according to Embodiment 1, the resistor R1 is an electronic component (resistor), but is not limited thereto. For example, the resistor R1 may be constituted by a conductive cable (wire cable). The resistance value of the resistor R1 may be smaller than 1 Ω, or may be a value closer to 0 Ω than 1 Ω.

[0055] In the control circuit 10 according to Embodiment 1, the inductor L1 is an electronic component (for example, a surface mount inductor), but is not limited to this configuration. For example, the inductor L1 may be constituted by a conductive cable (wire cable). That is, the inductor L1 may be a configuration that utilizes parasitic inductance.

[0056] (Embodiment 2) Hereinafter, the switch device 100e according to Embodiment 2 will be described with reference to FIG. 9.

[0057] If the configuration of the switch device 100 according to Embodiment 1 is taken as the basic circuit, the switch device 100e according to Embodiment 2 differs from Embodiment 1 in that it includes two basic circuits and a bidirectional switch formed by connecting the switching elements 1 of the two basic circuits. Regarding the switch device 100e according to Embodiment 2, the same components as those of the switch device 100 according to Embodiment 1 are denoted by the same reference numerals and the description thereof is omitted.

[0058] The bidirectional switch is an important device for replacing, for example, a power conversion circuit composed of an inverter circuit and a converter circuit with a matrix converter type power conversion circuit. In a matrix converter type power conversion circuit, by turning on and off the bidirectional switches arranged in a matrix at high speed, for example, AC power can be converted into AC power of an arbitrary frequency.

[0059] The switch device 100e differs from the switch device 100 according to Embodiment 1 in that it includes two switching elements 1 and two control circuits 10. Also, in the switch device 100e, the two switching elements 1 are connected in series, and the two control circuits 10 correspond one-to-one to the two switching elements 1.

[0060] Each of the two switching elements 1 has a source S1, a gate G1, and a drain D1. In the switching device 100e, the drains D1 of the two switching elements are connected to each other. In the switching device 100e, a bidirectional switch is constituted by the two switching elements 1. Hereinafter, for convenience of explanation, among the two switching elements 1, the lower switching element 1 in FIG. 9 may be referred to as the first switching element 1A, and the upper switching element 1 in FIG. 9 may be referred to as the second switching element 1B. Further, hereinafter, the source S1, the gate G1, and the drain D1 of the first switching element 1A may be referred to as the first source S11, the first gate G11, and the first drain D11, respectively, and the source S1, the gate G1, and the drain D1 of the second switching element 1B may be referred to as the second source S12, the second gate G12, and the second drain D12, respectively. Further, hereinafter, among the two control circuits 10, the control circuit 10 corresponding to the first switching element 1A may be referred to as the first control circuit 10e1, and the control circuit 10 corresponding to the second switching element 1B may be referred to as the second control circuit 10e2. Further, hereinafter, the inductor L1 of the first control circuit 10e1 may be referred to as the first inductor L11, and the inductor L1 of the second control circuit 10e2 may be referred to as the second inductor L12. Further, hereinafter, the driver 3 corresponding to the first switching element 1A may be referred to as the first driver 3A, and the driver 3 corresponding to the second switching element 1B may be referred to as the second driver 3B. Further, hereinafter, the potential of the reference potential point P0 between the node N3 of the first control circuit 10e1 and the output terminal on the low potential side of the first driver 3A may be referred to as the first reference potential Vstd1, and the potential of the reference potential point P0 between the node N3 of the second control circuit 10e2 and the output terminal on the low potential side of the second driver 3B may be referred to as the second reference potential Vstd2. Further, in the bidirectional switch including the two switching elements 1, the current flowing from the second source S12 to the first source S11 may be referred to as the source Is2s1, and the current flowing from the first source S11 to the second source S12 may be referred to as the source current Is1s2.In the switch device 100e, a load circuit including a load and a power supply is connected between a first terminal at one end and a second terminal at the other end of a series circuit of a first inductor L11, a first switching element 1A, a second switching element 1B, and a second inductor L12.

[0061] Next, the operation at the time of turning off the bidirectional switch will be described, starting from a state where a source current Is2s1 is flowing through the bidirectional switch including two switching elements 1 in the switch device 100e (that is, the two switching elements 1 are in the on state and the bidirectional switch is in the on state). Here, "turning off the bidirectional switch" means turning off the first switching element 1A and the second switching element 1B.

[0062] In the switch device 100e, after the start of turning off the bidirectional switch, when the change in the current of the source current Is1s2 changes from an increase to a decrease, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12. In the switch device 100e, when a back electromotive force is generated in the first inductor L11, the first reference potential Vstd1 becomes higher than the potential of the first source S11. As a result, in the switch device 100e, the potential difference between the potential of the first gate G11 of the first switching element 1A and the first reference potential Vstd1 becomes smaller, so the discharge current from the first gate G11 of the first switching element 1A becomes smaller, and the cutoff speed of the source current Is2s1 decreases.

[0063] On the other hand, in the switch device 100e, when a back electromotive force is generated in the second inductor L12, the second reference potential Vstd2 becomes lower than the source potential of the second switching element 1B. As a result, in the switch device 100e, the potential difference between the second gate G12 of the second switching element 1B and the second reference potential Vstd2 increases, and the second switching element 1B turns off before the first switching element 1A turns off. From the perspective of interrupting the source current Is2s1 of the bidirectional switch, since the source current Is2s1 flows through the second switching element 1B whether it is in the on state or the off state, the turn-off speed of the second switching element 1B does not affect the interruption of the main current (source current Is2s1) of the bidirectional switch.

[0064] In the first control circuit 10e1 corresponding to the first switching element 1A, after the source current Is2s1 of the bidirectional switch is interrupted, a current I7 flows to discharge the charge accumulated in the capacitor C1 in a closed-loop circuit including the capacitor C1, the resistor R1, and the first inductor L11. Also, in the second control circuit 10e2 corresponding to the second switching element 1B, after the source current Is2s1 is interrupted, a current I8 flows to discharge the charge accumulated in the capacitor C1 in a closed-loop circuit including the capacitor C1, the resistor R1, and the second inductor L12.

[0065] Next, the operation at the time of turning off the bidirectional switch will be described in the switch device 100e when the source current Is1s2 is flowing through the bidirectional switch including the two switching elements 1 (that is, the two switching elements 1 are in the on state and the bidirectional switch is in the on state).

[0066] In the switch device 100e, after the turn-off of the bidirectional switch starts and the change in the source current Is2s1 changes from increasing to decreasing, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12. In the switch device 100e, when a back electromotive force is generated in the first inductor L11, the first reference potential Vstd1 becomes lower than the source potential of the first switching element 1A, and the potential difference between the gate potential of the first switching element 1A and the first reference potential increases. Thus, the first switching element 1A turns off before the second switching element 1B turns off.

[0067] On the other hand, in the switch device 100e, when a back electromotive force is generated in the second inductor L12, the second reference potential Vstd2 becomes higher than the source potential of the second switching element 1B. As a result, in the switch device 100e, the potential difference between the potential of the second gate G12 of the second switching element 1B and the second reference potential Vstd2 becomes smaller, so the discharge current from the second gate G2 of the second switching element 1B becomes smaller, and the cutoff speed of the source current Is1s2 decreases.

[0068] The switch device 100e according to Embodiment 2 includes two switching elements 1 and two control circuits 10 that correspond one-to-one to the two switching elements 1. Therefore, for each of the two switching elements 1, it is possible to suppress the switching loss during turn-off and suppress the surge voltage applied to the switching element 1.

[0069] Also, in the switch device 100e according to Embodiment 2, it is possible to suppress the switching loss during the turn-off of the bidirectional switch and suppress the surge voltage applied to the bidirectional switch.

[0070] (Modification of Embodiment 2) The following lists modifications of the switch device 100e according to Embodiment 2. Note that the modifications described below can be applied in appropriate combination with Embodiments 1 and 2.

[0071] (Modification 1 of Embodiment 2) Hereinafter, the switch device 100f according to Modification 1 of Embodiment 2 will be described with reference to FIG. 10.

[0072] As described above, the switch device 100e according to Embodiment 2 includes a bidirectional switch configured by connecting the drains D1 of two switching elements 1 to each other. In contrast, the switch device 100f according to Modification 1 of Embodiment 2 is different from the switch device 100e according to Embodiment 2 in that it includes one switching element 1f instead of two switching elements 1. The switching element 1f is a dual-gate type bidirectional switch having two gates G1 and two sources S1 each.

[0073] In the switching element 1f, the two gates G1 and the two sources S1 correspond one-to-one. Hereinafter, for convenience of explanation, in the switching element 1f, one of the two gates G1 may be referred to as the first gate G11, and the other may be referred to as the second gate G12. Also, among the two sources S1, the source S1 corresponding to the first gate G111 may be referred to as the first source S11, and the source S1 corresponding to the second gate G12 may be referred to as the second source S12.

[0074] First, the switching element 1f will be briefly described, and then the switch device 100f will be described.

[0075] The switching element 1f is a type of GaN-based GIT. The switching element 1f includes, for example, a substrate, a buffer layer, a first nitride semiconductor layer, a second nitride semiconductor layer, a first source electrode, a first gate electrode, a second gate electrode, a second source electrode, a first p-type layer, and a second p-type layer. The buffer layer is formed on the substrate. The first nitride semiconductor layer is formed on the buffer layer. The second nitride semiconductor layer is formed on the first nitride semiconductor layer. The first source electrode, the first gate electrode, the second gate electrode, and the second source electrode are formed on the second nitride semiconductor layer. The first p-type layer is interposed between the first gate electrode and the second nitride semiconductor layer. The second p-type layer is interposed between the second gate electrode and the second nitride semiconductor layer. In the switching element 1f, the first source S11 includes the first source electrode. The first gate G11 includes the first gate electrode and the first p-type layer. The second gate G12 includes the second gate electrode and the second p-type layer. The second source S12 includes the second source electrode. The substrate is, for example, a silicon substrate. The buffer layer is, for example, an undoped GaN layer. The first nitride semiconductor layer is, for example, an undoped GaN layer. The second nitride semiconductor layer is, for example, an undoped AlGaN layer. Each of the first p-type layer and the second p-type layer is, for example, a p-type AlGaN layer. Each of the buffer layer, the first nitride semiconductor layer, and the second nitride semiconductor layer may have impurities such as Mg, H, Si, C, and O that are inevitably mixed during growth by MOVPE (Metal Organic Vapor Phase Epitaxy) or the like.

[0076] In the switching element 1f, the second nitride semiconductor layer forms a heterojunction with the first nitride semiconductor layer. In the first nitride semiconductor layer, a two-dimensional electron gas is generated in the vicinity of the heterojunction. The region containing the two-dimensional electron gas (hereinafter also referred to as the "two-dimensional electron gas layer") can function as an n-channel layer (electron conduction layer).

[0077] Hereinafter, for convenience of explanation, the control circuit 10 connected between the first gate G11 and the first source S11 of the switching element 1f among the two control circuits 10 is referred to as the first control circuit 10f1, and the control circuit 10 connected between the second gate G12 and the second source S12 of the switching element 1f may be referred to as the second control circuit 10f2. Further, hereinafter, the inductor L1 of the first control circuit 10f1 may be referred to as the first inductor L11, and the inductor L1 of the second control circuit 10f2 may be referred to as the second inductor L12. Further, hereinafter, the driver 3 corresponding to the first gate G11 of the switching element 1f may be referred to as the first driver 3A, and the driver 3 corresponding to the second gate G12 of the switching element 1f may be referred to as the second driver 3B. Further, hereinafter, the drive circuit 2 corresponding to the first gate G11 of the switching element 1f may be referred to as the first drive circuit 2A, and the drive circuit 2 corresponding to the second gate G12 of the switching element 1f may be referred to as the second drive circuit 2B. Further, the potential of the reference potential point P0 between the node N3 of the first control circuit 10f1 and the output terminal on the low potential side of the first driver 3A is referred to as the first reference potential Vstd1, and the potential of the reference potential point P0 between the node N3 of the second control circuit 10f2 and the output terminal on the low potential side of the second driver 3B may be referred to as the second reference potential Vstd2. Further, in the switching element 1f, the current flowing from the second source S12 to the first source S11 may be referred to as the source Is2s1, and the current flowing from the first source S11 to the second source S12 may be referred to as the source current Is1s2.

[0078] Also, hereinafter, a state where a voltage equal to or higher than a first threshold voltage (e.g., 1.3 V) is not applied between the first gate G11 and the first source S11 with the first gate G11 on the high potential side is also referred to as an off state of the first gate G11. Also, a state where a voltage equal to or higher than the first threshold voltage is applied between the first gate G11 and the first source S11 with the first gate G11 on the high potential side is also referred to as an on state of the first gate G11. Also, a state where a voltage equal to or higher than a second threshold voltage (e.g., 1.3 V) is not applied between the second gate G12 and the second source S12 with the second gate G12 on the high potential side is also referred to as an off state of the second gate G12. Also, a state where a voltage equal to or higher than the second threshold voltage is applied between the second gate G12 and the second source S12 with the second gate G12 on the high potential side is also referred to as an on state of the second gate 12G.

[0079] By including the above-described first p-type layer and second p-type layer, the switching element 1f realizes a normally-off type transistor.

[0080] The switching element 1f can switch between a bidirectional on state, a bidirectional off state, a first diode state, and a second diode state according to a combination of a first gate voltage and a second gate voltage applied to the first gate G11 and the second gate G12, respectively. The first gate voltage is a voltage applied between the first gate G11 and the first source S11. The second gate voltage is a voltage applied between the second gate G12 and the second source S12. The bidirectional on state is a state that allows a bidirectional current (a first direction and a second direction opposite to the first direction) to pass through. The bidirectional off state is a state that blocks a bidirectional current. The first diode state is a state that allows a current in the first direction to pass through. The second diode state is a state that allows a current in the second direction to pass through. The current in the first direction is the source current Is1s2, and the current in the second direction is the source current Is2s1.

[0081] In the switching element 1f, a bidirectional on-state is achieved when the first gate G11 is in the on-state and the second gate G12 is in the on-state. In the switching element 1f, a bidirectional off-state is achieved when the first gate G11 is in the off-state and the second gate G12 is in the off-state. In the switching element 1f, a first diode state is achieved when the first gate G11 is in the off-state and the second gate G12 is in the on-state. In the switching element 1f, a second diode state is achieved when the first gate G11 is in the on-state and the second gate G12 is in the off-state.

[0082] In the switch device 100f, a load circuit including a load and a power supply is connected between a first terminal at one end and a second terminal at the other end of a series circuit of the first inductor L11, the switching element 1f, and the second inductor L12. The operation at the time of turning off the switching element 1f from the state where the switching element 1f is in the on-state and the source current Is2s1 is flowing in the switch device 100f will be described. The operations of the first control circuit 10f1 and the second control circuit 10f2 are the same as those of the first control circuit 10e1 and the second control circuit 10e2, respectively.

[0083] In the switch device 100f, after the start of turning off the switching element 1f, when the change in the source current Is2s1 changes from an increase to a decrease, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12.

[0084] In the switch device 100f, when a back electromotive force is generated in the first inductor L11, the first reference potential Vstd1 becomes higher than the potential of the first source voltage S11. As a result, in the switch device 100f, the potential difference between the potential of the first gate G11 of the switching element 1f and the first reference potential Vstd1 decreases, so the discharge current from the first gate G11 becomes smaller and the cutoff speed of the source current Is2s1 decreases.

[0085] On the other hand, in the switch device 100f, when a back electromotive force is generated in the second inductor L12, the second reference potential Vstd2 becomes lower than the potential of the second source S12. As a result, in the switch device 100f, the potential difference between the potential of the second gate G12 and the reference potential Vstd2 increases, and the second gate G12 turns off.

[0086] In the switch device 100f, even when the second gate G12 is in the off state, as long as the first gate G11 is in the on state, the source current Is2s1 continues to flow, and when the first gate G11 turns off, the source current Is2s1 is cut off.

[0087] Next, the operation at the time of turning off the switching element 1f in the switch device 100f will be described, starting from the state where the source current Is1s2 is flowing through the switching element 1f.

[0088] In the switch device 100f, after the turn-off of the bidirectional switch starts and the change in the source current Is1s2 changes from an increase to a decrease, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12.

[0089] In the switch device 100f, when a back electromotive force is generated in the second inductor L12, the second reference potential Vstd2 becomes higher than the potential of the second source S12. As a result, in the switch device 100f, the potential difference between the potential of the second gate G12 and the second reference potential Vstd2 decreases, so the discharge current from the second gate G12 becomes smaller, and the cut-off speed of the source current Is1s2 decreases.

[0090] On the other hand, in the switch device 100f, when a back electromotive force is generated in the first inductor L11, the first reference potential Vstd1 becomes lower than the potential of the first source S11. As a result, in the switch device 100f, the potential difference between the potential of the first gate G11 and the first reference voltage Vstd1 increases, and the first gate G11 turns off.

[0091] In the switch device 100f, even when the first gate G11 is in the off state, as long as the second gate G12 is in the on state, the source current Is1s2 continues to flow, and when the second gate G12 becomes in the off state, the source current Is1s2 is cut off.

[0092] As can be understood from the above description, the switch device 100f can suppress the cut-off speed and suppress the surge voltage of the switching element 1f with respect to each of the bidirectional source currents Is2s1 and Is1s2.

[0093] The switch device 100f according to the first modification of the second embodiment can suppress the surge voltage applied to the switching element 1f while suppressing the switching loss at turn-off.

[0094] (Second modification of the second embodiment) Hereinafter, the switch device 100g according to the second modification of the second embodiment will be described with reference to FIG. 11.

[0095] The switch device 100e according to the second embodiment includes a bidirectional switch configured by connecting the drains D1 of the two switching elements 1 to each other. In contrast, the switch device 100g according to the second modification is different from the switch device 100e according to the second embodiment in that the sources S1 of the two switching elements 1 are connected to each other.

[0096] Hereinafter, for convenience of explanation, among the two switching elements 1, the upper switching element 1 in FIG. 11 may be referred to as the first switching element 1A, and the lower switching element 1 in FIG. 11 may be referred to as the second switching element 1B. Also, hereinafter, the source S1, gate G1, and drain D1 of the first switching element 1A may be referred to as the first source S11, the first gate G11, and the first drain D11, respectively, and the source S1, gate G1, and drain D1 of the second switching element 1B may be referred to as the second source S12, the second gate G12, and the second drain D12, respectively. Also, hereinafter, the control circuit 10 corresponding to the first switching element 1A among the two control circuits 10 may be referred to as the first control circuit 10g1, and the control circuit 10 corresponding to the second switching element 1B may be referred to as the second control circuit 10g2. Also, hereinafter, the inductor L1 of the first control circuit 10g1 may be referred to as the first inductor L11, and the inductor L1 of the second control circuit 10g2 may be referred to as the second inductor L12. Also, hereinafter, the drive circuit 2 corresponding to the first switching element 1A may be referred to as the first drive circuit 2A, and the drive circuit 2 corresponding to the second switching element 1B may be referred to as the second drive circuit 2B. Also, in the bidirectional switch including the two switching elements 1, the current flowing from the first drain D11 to the second drain D12 may be referred to as the drain current Id1d2, and the current flowing from the second drain D12 to the first drain D11 may be referred to as the drain current Id2d1.

[0097] The switch device 100g shares a capacitor C1, which is a circuit element 5, between a first control circuit 10g1 and a second control circuit 10g2, and a first inductor L11 and a second inductor L12 are connected in series. In the switch device 100g, a first end of the first inductor L11 is connected to a first source S11 of a first switching element 1A, a first end of the second inductor L12 is connected to a second source S12 of a second switching element 1B, and a second end of the first inductor L11 and a second end of the second inductor L12 are connected. In the switch device 100g, a capacitor C1 is connected between a node N15 on a path between the second ends of the first inductor L11 and the second inductor L12 and a node N3. A first drive circuit 2A is connected between an output terminal on the high potential side of a driver 3 and a first gate G11 of the first switching element 1A. Also, a second drive circuit 2B is connected between an output terminal on the high potential side of the driver 3 and a second gate G12 of the second switching element 1B. Here, the second drive circuit 2B is connected between a node N17 on a path between the output terminal on the high potential side of the driver 3 and the first drive circuit 2A and the second gate G12 of the second switching element 1B. Hereinafter, for convenience of explanation, an output terminal on the low potential side (negative terminal) of the driver 3 is defined as a reference potential point P0, and the potential of the reference potential point P0 is referred to as a reference potential Vstd.

[0098] Next, the operation at the time of turning off a bidirectional switch in a state where a drain current Id1d2 is flowing through the bidirectional switch including two switching elements 1 in the switch device 100g (that is, the two switching elements 1 are in an on state) will be described. Here, "turning off the bidirectional switch" means turning off the first switching element 1A and the second switching element 1B.

[0099] In the switch device 100g, after the turn-off of the bidirectional switch starts, when the change in the drain current Id1d2 changes from an increase to a decrease, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12. In the switch device 100g, when a back electromotive force is generated in the first inductor L11, the reference potential Vstd becomes higher than the potential of the first source S11 of the first switching element 1A, and the discharge current from the first gate G1 of the first switching element 1A becomes smaller. Therefore, the cut-off speed of the drain current Id1d2 becomes slower, and the surge voltage of the first switching element 1A is suppressed.

[0100] Also, in the switch device 100g, when a back electromotive force is generated in the second inductor L12, the reference potential Vstd becomes lower than the potential of the second source S12 of the second switching element 1B, and the discharge current from the second gate G12 of the second switching element 1B increases, and the second switching element 1B turns off earlier than the first switching element 1A. When the drain current Id1d2 is flowing in the switch device 100g, the second switching element 1B cannot cut off the drain current Id1d2 regardless of the on-state and off-state of the second switching element 1B, so it does not affect the cut-off speed of the drain current Id1d2.

[0101] In the switch device 100g, after the drain current Id1d2 is cut off, a current I9 flows through which the charge accumulated in the capacitor C1 is discharged in a first closed-loop circuit including the capacitor C1, the resistor R1, and the first inductor L11 in the first control circuit 10g1, and a current I10 flows through which the charge accumulated in the capacitor C1 is discharged in a second closed-loop circuit including the capacitor C1, the resistor R1, and the second inductor L12 in the second control circuit 10g2.

[0102] Next, the operation at the time of turning off the bidirectional switch will be described in a state where the drain current Id2d1 is flowing through the bidirectional switch including the two switching elements 1 in the switch device 100g (that is, the two switching elements 1 are in the on-state).

[0103] In the switch device 100g, after the turn-off of the bidirectional switch starts and the change in the drain current Id2d1 changes from an increase to a decrease, a back electromotive force (induced electromotive force) is generated in each of the first inductor L11 and the second inductor L12. In the switch device 100g, when a back electromotive force is generated in the second inductor L12, the reference potential Vstd becomes higher than the potential of the second source S12 of the second switching element 1B, and the discharge current from the second gate G12 of the second switching element 1B becomes smaller. Therefore, the cut-off speed of the drain current Id2d1 becomes slower, and the surge voltage is suppressed.

[0104] Also, in the switch device 100g, when a back electromotive force is generated in the first inductor L11, the reference potential Vstd becomes lower than the potential of the first source S11 of the first switching element 1A. Therefore, the discharge current from the first gate G11 of the first switching element 1A increases, and the first switching element 1A becomes off earlier than the second switching element 1B. When the drain current Id2d1 is flowing in the switch device 100g, the first switching element 1A cannot cut off the drain current Id2d1 regardless of the on-state and off-state of the first switching element 1A, so it does not affect the cut-off speed of the drain current Id2d1.

[0105] In the switch device 100g, after the drain current Id2d1 is cut off, a current I9 flows in which the charge accumulated in the capacitor C1 is discharged in a first closed-loop circuit including the capacitor C1, the resistor R1, and the first inductor L11 in the first control circuit 10g1, and a current I10 flows in which the charge accumulated in the capacitor C1 is discharged in a second closed-loop circuit including the capacitor C1, the resistor R1, and the second inductor L12 in the second control circuit 10g2.

[0106] From the above, even in the source-common type bidirectional switch device 100g, the cut-off speed can be suppressed for the bidirectionally flowing currents (Id1d2, Id2d1), and the surge voltage can be suppressed.

[0107] The switch device 100g according to Modification 2 of Embodiment 2 can suppress the surge voltage applied to each of the two switching elements 1 while suppressing the switching loss during turn-off.

[0108] (Other Modifications of Embodiment 2) In Embodiment 2, Modification 1, and Modification 2, the circuit element 5 is configured as the capacitor C1, but is not limited to this configuration. The circuit element 5 may be the diode Di1 as in the circuit element 5 in the control circuit 10b (see FIG. 5) according to Modification 1 of Embodiment 1.

[0109] Also, although the two basic circuits have the same configuration, it is not limited to this configuration. For example, the circuit element 5 of one of the two basic circuits may be the capacitor C1, and the circuit element 5 of the other basic circuit may be the diode Di1. Also, in the control circuit 10, two circuit elements 5 may be connected in series to the inductor L1, one circuit element 5 may be configured as the capacitor C1, and the other circuit element 5 may be configured as the diode Di1.

[0110] In Embodiment 2, Modification 1, and Modification 2, the protection diode Di2 (see FIG. 7) in the control circuit 10c according to Modification 3 of Embodiment 1 may be further provided.

[0111] Also, in Embodiment 2, Modification 1, and Modification 2, the protection diode Di3 in the control circuit 10d according to Modification 4 of Embodiment 1 may be further provided.

[0112] (Embodiment 3) Hereinafter, the control circuit 10h according to Embodiment 3 and the switch device 100h including the same will be described with reference to FIG. 12.

[0113] The control circuit 10h according to Embodiment 3 is different from the control circuit 10 according to Embodiment 1 in that, as the circuit element 5, it includes a resistor R1s instead of the capacitor C1 in the control circuit 10 according to Embodiment 1. The resistor R1s is connected between the inductor L1 and the output terminal (negative terminal) on the low-potential side of the driver 3. Hereinafter, for convenience of explanation, the resistor R1 may also be referred to as the first resistor R1, and the resistor Rs1 may also be referred to as the second resistor Rs1.

[0114] Next, the operation of the switch device 100h including the control circuit 10h will be described.

[0115] In the switch device 100h, when the change in the source current Is of the switching element 1 changes from increasing to decreasing, a back electromotive force (induced electromotive force) is generated in the inductor L1. When a back electromotive force is generated in the inductor L1, in the control circuit 10h, a current flows in a closed-loop circuit including the inductor L1, the second resistor R1s (circuit element 5), and the first resistor R1. As a result, in the switch device 100h, the reference potential Vstd of the reference potential point P0 becomes higher than the potential of the source S1 of the switching element 1. Therefore, the potential difference between the potential of the gate G1 of the switching element 1 and the reference potential Vstd becomes smaller, the discharge current Idis from the gate G1 of the switching element 1 becomes smaller, and gentle current interruption can be realized (the interruption speed of the source current Is can be slowed down).

[0116] When a capacitor C1 is adopted as the circuit element 5 as in the control circuit 10 according to Embodiment 1, the capacitor C1 is charged, so the change in the reference potential Vstd is large. On the other hand, when the second resistor R1s is adopted as the circuit element 5 as in the control circuit 10h according to Embodiment 3, compared with the case where the circuit element 5 is the capacitor C1, the change in the reference potential Vstd is small. Therefore, there is also an advantage that the operation of the control circuit 10h is easy to predict and the circuit design is facilitated.

[0117] Also, in the switch device 100h including the control circuit 10h according to Embodiment 3, since the current change rate of the main current (source current) of the switching element 1 can be adjusted by the ratio of the resistance value of the first resistor R1 and the resistance value of the second resistor R1s, the design of the current change rate is easy. Further, since the second resistor R1s has almost no capacitance component, it is possible to suppress the application of a negative bias to the gate G1 of the switching element 1 due to the discharge of the charge accumulated in the capacitance component.

[0118] Note that the control circuit 10h according to Embodiment 3 may be implemented in combination with the control circuit 10 according to Embodiment 1. That is, in the control circuit 10h according to Embodiment 3, in addition to the circuit element 5 (first circuit element) constituted by the first resistor Rs1, a circuit configuration including a second circuit element constituted by a capacitor C1 connected in series to the first circuit element may be employed.

[0119] (Modification Example of Embodiment 3) In Embodiment 3, the circuit element 5 is constituted by the resistor R1s, but the present invention is not limited to this configuration. Specifically, as shown in FIG. 13, the control circuit 10i according to the modification example of Embodiment 3 includes a circuit element 5 (second circuit element) constituted by a diode Dis in addition to the circuit element 5 (first circuit element) constituted by the resistor Rs1. For the control circuit 10i and the switch device 100i according to the modification example of Embodiment 3, the same components as those of the control circuit 10h and the switch device 100h according to Embodiment 3 are denoted by the same reference numerals and the description thereof is omitted as appropriate.

[0120] In the control circuit 10i included in the switch device 100i, the resistor R1s and the diode Dis are connected in series. Here, in the diode Dis, the cathode of the diode Dis is connected to the resistor R1s, and the anode of the diode Dis is connected to the node N2. Therefore, in the control circuit 10i, a resistor R1 is connected in parallel to a series circuit of a resistor Rs1 (first circuit element), a diode Dis (second circuit element), and an inductor L1. In the switch device 100i, similar to the switch device 100, the output terminal (positive terminal) on the high potential side of the driver 3 is connected to the gate G1 of the switching element 1 via the drive circuit 2.

[0121] Next, the operation of the switch device 100i including the control circuit 10i will be described.

[0122] When the control circuit 10i turns off the switching element 1, when the change in the source current Is of the switching element 1 changes from an increase to a decrease, an electromotive force (back electromotive force) is generated in the inductor L1. In the control circuit 10i, when a back electromotive force is generated in the inductor L1, a current flows through a closed circuit loop including the inductor L1, the diode Dis, the second resistor R1s, and the first resistor R1. As a result, in the switch device 100i, the reference potential Vstd of the reference potential point P0 becomes higher than the potential of the source S1. As a result, in the switch device 100i, the potential difference between the potential of the gate G1 of the switching element 1 and the reference potential Vstd becomes smaller, and the discharge current Idis from the gate G1 of the switching element 1 becomes smaller, so that a gentle current cutoff can be realized with respect to the cutoff of the source current Is of the switching element 1.

[0123] Also, in the switch device 100i including the control circuit 10i according to the modification of Embodiment 3, since the current change rate of the main current (source current) of the switching element 1 can be adjusted by the ratio of the first resistor R1 and the second resistor R1s, the design of the current change rate is easy. Further, since the second resistor R1s and the diode Dis have almost no capacitance component, it is possible to suppress the application of a negative bias to the gate G1 of the switching element 1 due to the discharge of the charge accumulated in the capacitance component.

[0124] The control circuit 10i according to the modification of Embodiment 3 may be implemented in combination with the control circuit 10 according to Embodiment 1. That is, the control circuit 10i may include a plurality of circuit elements 5 connected in series to each other between the node N2 and the node N3. For example, it may include a series circuit including a second resistor R1s (first circuit element), a diode Dis (second circuit element), and a capacitor C1 (third circuit element). When an electromotive force is generated in the inductor L1, a current flows through the first circuit element, the second circuit element, and the third circuit element.

[0125] (Embodiment 4) Hereinafter, the control circuit 10j according to Embodiment 4 and a switch device (switch system) 100j including the same will be described with reference to FIG. 14.

[0126] The control circuit 10j according to Embodiment 4 is substantially the same as the control circuit 10h (see FIG. 12) according to Embodiment 3, and is different from the control circuit 10h according to Embodiment 3 in that it further includes a voltage clamp element 9 connected in parallel to the switching element 1 and the inductor L1 (hereinafter, also referred to as a first inductor Ls1). Regarding the control circuit 10j and the switch device 100j according to Embodiment 4, the same components as those of the control circuit 10h and the switch device 100h according to Embodiment 3 are denoted by the same reference numerals and the description thereof is omitted.

[0127] The voltage clamp element 9 has a function of overvoltage protection that suppresses the surge voltage applied to the switching element 1 to a predetermined voltage (clamp voltage) when the switching element 1 is turned off. That is, the voltage clamp element 9 has a function of limiting the voltage between the drain D1 and the source S1 of the switching element 1 to a predetermined voltage when the switching element 1 is turned off. In the example of FIG. 14, the voltage clamp element 9 is a varistor, but it is not limited thereto and may be a Zener diode (for example, a TVS diode). When a voltage equal to or higher than a certain voltage is applied, the voltage clamp element 9 has a function of suppressing an increase in the voltage to a higher voltage, and a current flows through the voltage clamp element 9 at that time.

[0128] The control circuit 10j further includes a second inductor Ls2 and a third inductor Ls3. The second inductor Ls2 is connected between the first inductor Ls1 and the second resistor R1s which is the circuit element 5. The third inductor Ls3 is connected between the path between the second inductor Ls2 and the circuit element 5 and the voltage clamp element 9. Thereby, in the switching device 100j, a series circuit of the voltage clamp element 9, the third inductor Ls3, and the second inductor Ls2 is connected in parallel to the series circuit of the switching element 1 and the first inductor Ls1. In the control circuit 10j, the sum of the inductance of the first inductor Ls1 and the inductance of the second inductor Ls2 is larger than the inductance of the third inductor Ls3.

[0129] The switching device 100j further includes, for example, a first terminal T1 to which the drain D1 of the switching element 1 is connected, and a second terminal T2 to which the second end of the inductor L1 whose first end is connected to the source S1 of the switching element 1 is connected. That is, in the switching device 100j, a series circuit of the switching element 1 and the first inductor Ls1 is connected between the first terminal T1 and the second terminal T2. In the switching device 100j, for example, a load circuit including a series circuit of a load and a power supply is connected between the first terminal T1 and the second terminal T2, whereby the load circuit is connected to the series circuit of the switching element 1 and the first inductor Ls1. The load and the power supply are not components of the switching device 100j.

[0130] In the switching device 100j, the first terminal T1 and the second terminal T2 are terminals through which the main current (source current Is) flowing through the switching element 1 flows when the switching element 1 is in the conductive state. One end of the second resistor Rs1 of the control circuit 10j is connected to a node N10 on the path between the voltage clamp element 9 and the second terminal T2. The node N10 is on the path through which the gate current of the switching element 1 flows when switching the switching element 1 in the switching device 100j. Also, the node N10 is on a path through which the source current Is does not flow when the switching element 1 is in the conductive state.

[0131] Next, the operation of the switch device 100j including the control circuit 10j will be described.

[0132] In the switch device 100j, when the change in the source current Is of the switching element 1 changes from an increase to a decrease at the turn-off of the switching element 1, an electromotive force (back electromotive force) is generated in the first inductor Ls1. At this time, an induced electromotive force is also generated in the parasitic inductor such as the wiring in the load circuit connected between the first terminal T1 and the second terminal T2. However, when the voltage exceeds the clamping voltage of the voltage clamp element 9, the voltage increase is suppressed by the voltage clamp element 9.

[0133] On the other hand, in the switch device 100j, when the voltage clamp element 9 operates, a current flows from the first terminal T1 to the second terminal T2 through the third inductor Ls3, the node N10, and the second inductor Ls2. Due to this current, induced electromotive forces are generated in the second inductor Ls2 and the third inductor Ls3, respectively. As a result, in the control circuit 10j, a current flows through a closed-loop circuit including the first inductor Ls1, the second inductor Ls2, the second resistor R1s, and the first resistor R1. Thereby, in the switch device 100j, the reference potential Vstd of the reference potential point P0 becomes higher than the potential of the source S1 of the switching element 1, the potential difference between the potential of the gate G1 of the switching element 1 and the reference potential Vstd becomes smaller, and the discharge current Idis from the gate G1 of the switching element 1 becomes smaller. Therefore, with respect to the source current Is, a gentle current cut-off can be realized.

[0134] The control circuit 10j according to Embodiment 4 includes a first inductor Ls1 and a second inductor Ls2 instead of the inductor L1 in the control circuit 0h (see FIG. 12) according to Embodiment 3. In the control circuit 10h, the induced electromotive force (back electromotive force) generated in the inductor L1 when the source current Is decreases increases as the inductance of the inductor L1 increases. In other words, if the inductance of the inductor L1 is large, even if the absolute value of the current change rate when the source current Is decreases is small, a large induced electromotive force is generated. Therefore, the control circuit 10j according to Embodiment 4 has an advantage that the operating range of the control circuit 10j is widened with respect to the current change rate of the source current Is. In the control circuit 10j according to Embodiment 4, there may be a case where it is easy to increase the inductance of the second inductor Ls2. In the control circuit 10j, since a current continues to flow through the first inductor Ls1 in the on state (conducting state) of the switching element 1, when heat generation becomes an issue, it is desirable to increase the width or diameter of the conductor portion constituting the first inductor Ls1. On the other hand, the second inductor Ls2 is a portion where a current flows only for a certain period when the switching element 1 turns off and the voltage clamp element 9 operates, and heat generation is less likely to be a problem. Therefore, the width or diameter of the conductor portion constituting the second inductor Ls2 can be reduced. Thus, when the inductance is increased, it is the second inductor Ls2 that is less likely to increase in size and cost. In the control circuit 10j according to Embodiment 4, by increasing the inductance of the second inductor Ls2, there is an advantage that it becomes easier to widen the operating range of the control circuit 10j with respect to the current change rate when the source current Is decreases.

[0135] Also, the induced electromotive force generated in the third inductor Ls3 in the control circuit 10j is superimposed on the clamp voltage of the voltage clamp element 9 and applied to the switching element 1. Therefore, in order to suppress the surge voltage applied to the switching element 1, it is desirable that the ratio of the inductance of the first inductor Ls1 to the sum of the inductances of the first inductor Ls1 and the second inductor Ls2 with respect to the third inductor Ls3 is larger.

[0136] The first inductor Ls1, the second inductor Ls2, and the third inductor L3 are not limited to electronic components, and for example, a conductor pattern (e.g., a copper pattern) on a substrate, a wire cable, a lead wire of the voltage clamp element 9, etc. may be used.

[0137] (Embodiment 5) Hereinafter, the switch device (switch system) 100k according to Embodiment 5 will be described with reference to FIG. 15.

[0138] The switch device 100k according to Embodiment 5 is different from the switch device 100j according to Embodiment 5 in that it includes a switching element 1k instead of the switching element 1 of the switch device 100j according to Embodiment 4 and includes two control circuits 10j. The switching element 1k is a dual-gate type bidirectional switch having two gates G1 and two sources S1 each.

[0139] In the switching element 1k, the two gates G1 and the two sources S1 correspond one-to-one. Hereinafter, for convenience of explanation, one of the two gates G1 may be referred to as the first gate G11 and the other as the second gate G12. Also, among the two sources S1, the source S1 corresponding to the first gate G11 may be referred to as the first source S11, and the source S1 corresponding to the second gate G12 may be referred to as the second source S12. The switching element 1k has the same configuration as the switching element 1f (see FIG. 10).

[0140] In the switch device 100k according to Embodiment 5, one of the two control circuits 10j is connected between the first gate G11 and the first source S11 of the switching element 1k, and the other control circuit 10j is connected between the second gate G12 and the second source S12 of the switching element 1k. Also, in the switch device 100k, the voltage clamp element 9 is shared by the two control circuits 10j, and the voltage clamp element 9 is connected between the two third inductors Ls3.

[0141] The switch device 100k according to Embodiment 5 can suppress the surge voltage applied to the switching element 1k while suppressing the switching loss when the switching element 1k is turned off.

[0142] The above-described Embodiments 1 to 5 and each modification are merely examples of the present disclosure. The above-described Embodiments 1 to 5 and each modification can be variously changed according to design and the like as long as the object of the present disclosure can be achieved.

[0143] For example, the control circuit 10 does not include the drive circuit 2 and the driver 3, but may include at least one of the drive circuit 2 and the driver 3. Further, in the switch device 100, the driver 3 may include the drive circuit 2.

[0144] The following aspects are disclosed in this specification from the above-described Embodiments 1 to 5 and each modification.

[0145] The control circuit (10; 10a; 10b; 10c; 10d; 10e1; 100e2; 10f1; 10f2; 10g1; 10g1; 10h; 10i; 10j) according to the first aspect is a control circuit that controls a switching element (1; 1f; 1k) having a gate (G1) and a source (S1) corresponding to the gate (G1). The control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i) includes an inductor (L1), a circuit element (5), and a resistor (R1). The inductor (L1) is connected between the gate (G1) and the source (S1) of the switching element (1; 1f; 1k). The circuit element (5) is connected in series with the inductor (L1) between the gate (G1) and the source (S1). When an electromotive force is generated in the inductor (L1), a current flows through the circuit element (5). The resistor (R1) is connected in parallel to the inductor (L1) and the circuit element (5) between the gate (G1) and the source (S1).

[0146] According to this configuration, it is possible to suppress the surge voltage applied to the switching element (1; 1f; 1k) while suppressing the switching loss at the turn-off of the switching element (1; 1f; 1k).

[0147] In the control circuit (10; 10a) according to the second aspect, in the first aspect, the circuit element (5) includes a capacitor (C1).

[0148] According to this configuration, by changing the circuit constant of the capacitance of the capacitor (C1), it becomes possible to change the current change rate of the main current (source current Is) flowing through the switching element (1).

[0149] In the control circuit (10b) according to the third aspect, in the first aspect, the circuit element (5) includes a diode (Di1).

[0150] According to this configuration, compared with the control circuit (10; 10a) according to the second aspect, it becomes possible to reduce the current discharged from the circuit element (5) after the interruption of the main current (source current Is).

[0151] In the control circuit (10h) according to the fourth aspect, in the first aspect, the circuit element (5) includes a resistor (R1s).

[0152] According to this configuration, compared with the control circuit (10; 10a) according to the second aspect and the control circuit (10b) according to the third aspect, the design of the current change rate of the main current (source current Is) flowing through the switching element (1; 1f; 1k) is easy, and the current change rate is determined by the ratio of the resistor (R1) and the resistor (R1s). Further, in the control circuit (10h) of the fourth aspect, since no discharge current flows from the circuit element (5) after the interruption of the main current of the switching element (1; 1f; 1k), the switching element (1; 1f; 1k) can be protected.

[0153] In the control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i; 10j) according to the fifth aspect, in any one of the first to fourth aspects, when the switching element (1; 1f; 1k) turns off, the current flowing through the source (S1) decreases, and an electromotive force is generated in the inductor (L1). When the current corresponding to the electromotive force flows through the circuit element (5) and the resistor (R1), the potential of the reference potential point (P0) included in the path between the connection point of the circuit element (5) and the resistor (R1) and the gate (G1) rises. The potential difference between the potential of the gate (G1) and the potential (Vstd) of the reference potential point (P0) of determines the discharge current (Idis) from the gate (G1).

[0154] According to this configuration, since the current (Idis) from the gate (G1) is determined by the potential difference between the potential of the gate (G1) and the potential (Vstd) of the reference potential point (P0), the discharge current (Idis) can be limited by increasing the potential (Vstd) of the reference potential point (P0).

[0155] In the control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i) according to the sixth aspect, in any one of the first to fifth aspects, a protection diode (Di2) is further provided. The protection diode (Di2) has an anode and a cathode, the anode is connected to the connection point (node N3) of the circuit element (5) and the resistor (R1), and the cathode is connected to the gate (G1) of the switching element (1; 1k).

[0156] According to this configuration, it is possible to protect the switching element (1; 1f; 1k).

[0157] In the control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i) according to the seventh aspect, in any one of the first to fifth aspects, a protection diode (Di3) is further provided. The protection diode (Di3) has an anode and a cathode, the anode is connected between the source (S1) of the switching element (1; 1f; 1k), the inductor (L1) and the resistor (R1), and the cathode is connected to the gate (G1) of the switching element (1; 1f; 1k).

[0158] According to this configuration, it becomes possible to protect the switching element (1; 1f; 1k).

[0159] The control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i; 10j) according to the eighth aspect further includes a first terminal (T1), a second terminal (T2), a second inductor (Ls2), and a third inductor (Ls3) in any one of the first to seventh aspects. The first terminal (T1) is connected to the switching element (1; 1f; 1k) on the side opposite to the source (S1) in the switching element (1; 1f; 1k). The second terminal (T2) is connected to the inductor (L1) on the side opposite to the switching element (1; 1f; 1k) side in the inductor (L1). The second inductor (Ls2) is connected between a first node (node N2) between the first inductor (Ls1) which is the inductor (L1) and the second terminal (T2) and the circuit element (5). The voltage clamp element (9) is connected in parallel to the switching element (1; 1f; 1k), the first inductor (Ls1), and the second inductor (Ls2). The third inductor (Ls3) is connected between a second node (node N10) between the second inductor (Ls2) and the circuit element (5) and the voltage clamp element (9). In the on state of the switching element (1; 1f; 1k), no current flows through the third inductor (Ls3) in the control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i; 10j).

[0160] According to this configuration, it becomes possible to protect the switching element (1; 1f; 1k), and it becomes easier to widen the operating range of the control circuit (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i; 10j) with respect to the current change rate when the current (source current Is) flowing through the source (S1) of the switching element (1; 1f; 1k) decreases.

[0161] The switching device (100; 100a; 100b; 100c; 100d; 100e1100e2; 100f1100f2; 100g1; 100g2; 100h; 100i; 100j) according to the ninth aspect includes any one of the control circuits (10; 10a; 10b; 10c; 10d; 10e1; 10e2; 10f1; 10f2; 10g1; 10g2; 10h; 10i; 10j) of the first to eighth aspects and a switching element (1; 1f; 1k).

[0162] According to this configuration, it can be expected to suppress the switching loss at the turn-off of the switching element (1; 1f; 1k) and suppress the surge voltage applied to the switching element (1; 1f; 1k).

[0163] The switching device (100; 100a; 100b; 100c; 100d; 100e; 100g; 100h; 100i) according to the tenth aspect includes two switching elements (1) and two control circuits (10; 10a; 10b; 10c; 10d;; 10h; 10i) in the ninth aspect. In the switching device (100; 100a; 100b; 100c; 100d; 100e; 100g; 100h; 100i), the two switching elements (1) are connected in series, and the two control circuits (10; 10a; 10b; 10c; 10d; 10h; 10i) correspond one-to-one to the two switching elements (1).

[0164] According to this configuration, it can be expected to suppress the switching loss at the turn-off of the two switching elements (1) and suppress the surge voltage applied to the switching element (1).

[0165] In the switching device (100; 100a; 100b; 100c; 100d; 100e; 100f; 100g) according to the 11th aspect, in the 10th aspect, each of the two switching elements (1) has a drain (D1) with respect to the gate (G1), and the drains (D1) of the two switching elements (1) are connected to each other.

[0166] According to this configuration, it can be expected to suppress the surge voltage applied to the two switching elements (1) while suppressing the switching loss at the turn-off of the two switching elements (1).

[0167] In the switching device (100f; 100k) according to the 12th aspect, in the 9th aspect, the switching element (1f; 1k) is a dual-gate type bidirectional switch having two gates (G1) and two sources (S1) respectively. The switching device (100f; 100k) includes two control circuits (10; 10j). One of the two control circuits is connected to the gate (G1) corresponding to one of the two gates (G1) of the bidirectional switch, and the other control circuit is connected to the gate (G1) corresponding to the other of the two gates (G1) of the bidirectional switch.

[0168] According to this configuration, it can be expected to suppress the surge voltage applied to the switching element (1f; 1k) while suppressing the switching loss at the turn-off of the switching element (1f; 1k) constituted by the dual-gate type bidirectional switch.

[0169] In the switching device (100g) according to the 13th aspect, in the 10th aspect, the sources (S1, S2) of the two switching elements (1) are connected to each other.

[0170] According to this configuration, it can be expected to suppress the surge voltage applied to the two switching elements (1) while suppressing the switching loss at the turn-off of the two switching elements (1).

[0171] In the present disclosure described below, an object is to provide a control circuit and a switch system capable of suppressing a surge voltage applied to a semiconductor switch while suppressing switching loss during turn-off of the semiconductor switch.

[0172] (Example 1) Hereinafter, the control circuit 12 according to Example 1 and the switch system 13 including the same will be described with reference to FIGS. 16 to 17.

[0173] (1) Outline The control circuit 12 is a control circuit that controls the semiconductor switch 11. The semiconductor switch 11 has a gate 11G and a source 11S corresponding to the gate 11G. The semiconductor switch 11 has a drain 11D in addition to the above-described gate 11G and source 11S. The control circuit 12 includes a first discharge path 21 and a second discharge path 22 that can discharge faster than the first discharge path 21 as a discharge path for discharging the charge of the gate 11G of the semiconductor switch 11. The control circuit 12 includes a first switch Q11 and a second switch Q12 provided in the second discharge path 22. The second switch Q12 is turned on based on the current change rate of the main current I DS (see FIG. 19). The main current I of the semiconductor switch 11 DS is the current flowing from the drain 11D to the source 11S of the semiconductor switch 11. The control circuit 12 includes, for example, an inductor Ls (see FIG. 17) connected to the source 11S of the semiconductor switch 11 as a current change rate detection unit 23 (see FIG. 16) that detects the current change rate.

[0174] The switch system 13 includes the control circuit 12 and the semiconductor switch 11. In the switch system 13, for example, a series circuit of a load 15 and a power supply 16 is connected between the drain 11D and the source 11S of the semiconductor switch 11. In the switch system 13, a series circuit of a load 15 and a power supply 16 is connected to a series circuit of the semiconductor switch 11 and the inductor Ls. The load 15 and the power supply 16 are not components of the switch system 13.

[0175] (2) Components of the switch system (2.1) Semiconductor switch The semiconductor switch 11 is, for example, a GaN-based semiconductor switch. More specifically, the semiconductor switch 11 is a JFET (Junction Field Effect Transistor). The JFET constituting the semiconductor switch 11 is, for example, a GaN-based GIT (Gate Injection Transistor).

[0176] The semiconductor switch 11 includes, for example, a substrate, a buffer layer, a first nitride semiconductor layer, a second nitride semiconductor layer, a source electrode, a gate electrode, a drain electrode, and a p-type layer. The buffer layer is formed on the substrate. The first nitride semiconductor layer is formed on the buffer layer. The second nitride semiconductor layer is formed on the first nitride semiconductor layer. The source electrode, the gate electrode, and the drain electrode are formed on the second nitride semiconductor layer. The p-type layer is interposed between the gate electrode and the second nitride semiconductor layer. In the semiconductor switch 11, a diode structure is formed by the second nitride semiconductor layer and the p-type layer. The gate 11G in the semiconductor switch 11 includes the gate electrode and the p-type layer. The source 11S in the semiconductor switch 11 includes the source electrode. The drain 11D in the semiconductor switch 11 includes the drain electrode. The substrate is, for example, a silicon substrate. The buffer layer is, for example, an undoped GaN layer. The first nitride semiconductor layer is, for example, an undoped GaN layer. The second nitride semiconductor layer is, for example, an undoped AlGaN layer. The p-type layer is, for example, a p-type AlGaN layer. Each of the buffer layer, the first nitride semiconductor layer, and the second nitride semiconductor layer may contain impurities such as Mg, H, Si, C, and O that are inevitably mixed during growth by MOVPE (Metal Organic Vapor Phase Epitaxy) or the like.

[0177] (2.2) Control circuit (2.2.1) Configuration of the control circuit As shown in FIG. 17, the control circuit 12 according to Example 1 includes a first discharge path 21, a second discharge path 22, a first switch Q11, and a second switch Q12. The first discharge path 21 is connected to the gate 11G of the semiconductor switch 11. The second discharge path 22 is connected to the gate 11G of the semiconductor switch 11. The second discharge path 22 can discharge at a higher speed than the first discharge path 21. The second switch Q12 can be turned on and off separately from the first switch Q11. The second switch Q12 is provided on the second discharge path 22 and turns on based on the rate of change of the main current of the semiconductor switch 11. Here, in the control circuit 12 according to Example 1, the second switch Q12 turns on based on the electromotive force of the inductor Ls generated according to the rate of change of the current.

[0178] (2.2.2) Details of the control circuit As shown in FIG. 17, the control circuit 12 includes a first discharge path 21, a second discharge path 22, a first switch Q11, and a second switch Q12.

[0179] In the control circuit 12, the first discharge path 21 and the second discharge path 22 include a common discharge path 20 connected to the gate 11G of the semiconductor switch 11. The semiconductor switch 11 is a normally-off type semiconductor switch.

[0180] The first discharge path 21 has a gate resistor R G connected to the gate 11G of the semiconductor switch 11. The gate resistor R G is provided in a path of the first discharge path 21 other than the common discharge path 20. The first discharge path 21 is a path for reducing the absolute value of the rate of change of the main current I DS (-dI DS / dt) of the semiconductor switch 11 at turn-off.

[0181] The second discharge path 22 is connected to the gate 1G of the semiconductor switch 11 without passing through the gate resistor R G . The second discharge path 22 is a path for discharging the charge of the gate 11G of the semiconductor switch 11 at a higher speed than the first discharge path 21.

[0182] The first switch Q11 and the second switch Q12 are provided on the second discharge path 22.

[0183] The first switch Q11 is connected to a node N11 between the gate resistor R G and the gate 11G of the semiconductor switch 11. The first switch Q11 is a p-channel field effect transistor Tr1 provided on the second discharge path 22. Here, the p-channel field effect transistor Tr1 has a gate, a source, and a drain. In the illustrated example, the field effect transistor Tr1 is a normally-off p-channel MOSFET. Also, the second switch Q12 is a diode D2 provided on the second discharge path 22. The diode D2 has an anode and a cathode.

[0184] In the control circuit 12, the source of the p-channel field effect transistor Tr1 is connected to the gate 11G of the semiconductor switch 11, and the drain of the p-channel field effect transistor Tr1 is connected to the anode of the diode D2. Also, in the control circuit 12, a gate resistor R G is connected between the gate and the source of the p-channel field effect transistor Tr1.

[0185] The second discharge path 22 has an inductor Ls connected in series to the diode D2. Therefore, in the second discharge path 22, the p-channel field effect transistor Tr1, the diode D2, and the inductor Ls are connected in series. The inductor Ls has a first end and a second end. In the second discharge path 22, the first end of the inductor Ls is connected to the cathode of the diode D2. In the second discharge path 22, the second end of the inductor Ls is connected to the source 11S of the semiconductor switch 11. The second switch Q12 is provided on the second discharge path 22 as described above, and turns on based on the rate of change of the current of the main current I DS of the semiconductor switch 11. In the control circuit 12 according to Example 1, the second switch Q12 turns on based on the electromotive force generated in the inductor Ls in response to the change in the current of the main current I DS .

[0186] In the control circuit 12, a driver 14 is connected between the node N11 and the second end of the inductor Ls via a gate resistor Rg. The driver 14 is not a component of the control circuit 12 but a component of the switch system 13. The driver 14 has a high-potential side output terminal and a low-potential side output terminal. In the control circuit 12, the high-potential side output terminal of the driver 14 is connected to the gate resistor Rg, and the low-potential side output terminal of the driver 14 is connected to the second end of the inductor Ls. In the switch system 13, the low-potential side output terminal of the driver 14 is connected to a node N12 between the source 11S of the semiconductor switch 11 and the second end of the inductor Ls. The driver 14 is a driver capable of applying a positive bias voltage between the gate 11G and the source 11S of the semiconductor switch 11 and also capable of applying a negative bias voltage. The driver 14 includes, for example, a DC power supply and a CMOS (Complementary Metal-Oxide Semiconductor) inverter, and is a driver capable of changing the output voltage in the range of -12V to 18V.

[0187] (2.2.3) Operations of the control circuit and the switch system The operations of the control circuit 12 and the switch system 13 will be described with reference to FIGS. 18, 19A, 19B, 20A, 20B, 21A, and 21B. Note that in FIGS. 18, 19A, 20A, and 21A, in order to make the circuit portions where no current flows easier to understand, the line types of the circuit portions where no current flows are made different from those of the other circuit portions.

[0188] In the switch system 13, when a positive bias voltage is output from the driver 14 between the gate 11G and the source 11S of the semiconductor switch 11 (in FIG. 18, the driver 14 is represented by a DC power supply E4), the state of the semiconductor switch 11 is the on state. At this time, in the p-channel field effect transistor Tr1, since the potential of the gate is higher than the potential of the source, the p-channel field effect transistor Tr1 is not conducting.

[0189] In the switch system 13, when turning off the semiconductor switch 11, the output voltage of the driver 14 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage). As a result, the voltage V DS between the drain 11D and source 11S of the semiconductor switch 11, the main current I DS , and the voltage V GS between the gate 11G and source 11S change as shown in FIGS. 19B to 21B.

[0190] FIG. 19A is an operation explanatory diagram of the control circuit 12 and the switch system 13 during the period from time t0 to t2 in FIG. 19B (the period hatched in FIG. 19B). In FIG. 19B, the time point when the output voltage of the driver 14 in the switch system 13 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage) is set as t0, and the time point when the drain 11D-source 11S voltage V DS of the semiconductor switch 11 finishes rising is set as t2. During the period from time t0 to time t2 in FIG. 19B, since the first switch Q11 is on and the second switch Q12 is on, the gate current I G is discharged through the first switch Q11 and the second switch Q12. That is, the charge of the gate 11G of the semiconductor switch 11 is discharged through the second discharge path 22. Therefore, the gate current I G is dominated by the current I Q11 flowing through the first switch Q11. More specifically, during the period from time t0 to t1 before the voltage V DS between the drain 11D and source 11S of the semiconductor switch 11 starts to increase, the charge of the gate 11G of the semiconductor switch 11 is discharged at high speed, so the voltage V GS between the gate 11G and source 11S of the semiconductor switch 11 rapidly decreases. Then, when the voltage V DS between the drain 11D and source 11S of the semiconductor switch 11 starts to increase from time t1, the voltage V GS between the gate 11G and source 11S becomes substantially constant.

[0191] Figure 20A is an explanatory diagram of the operations of the control circuit 12 and the switch system 13 during the period from time t2 to t3 in Figure 20B (the period hatched in dot pattern in Figure 20B). In the switch system 13, as shown in Figure 20B, during the period from time t2 to t3, the voltage V DS between the drain 11D and the source 11S of the semiconductor switch 11 is substantially constant, and when the main current I DS starts to decrease from time t2, an electromotive force is generated between the first end and the second end of the inductor Ls due to the change in the main current I DS , and the diode D2 turns off. As a result, the current I Q11 flowing through the p-channel field effect transistor Tr1 decreases, so the gate current I G flows through the gate resistor R G . That is, the charge of the gate 11G of the semiconductor switch 11 is discharged through the first discharge path 21 instead of being discharged through the second discharge path 22. Thereby, the magnitude of the gate current I G is determined by the resistance value of the gate resistor R G . The resistance value of the gate resistor R G is, for example, 50 Ω to 5 kΩ. When the resistance value of the gate resistor R G is a relatively large value (for example, 3 kΩ or more), if the inductance of the inductor Ls is L1 and the threshold voltage at which the diode D2 turns on (conducts) is V thD2 , the current change rate dI DS / dt becomes a value derived from the following formula (1). L1 × dI DS / dt = V GS - V thD2 Formula (1) Figure 21A is an explanatory diagram of the operations of the control circuit 12 and the switch system 13 during the period from time t3 to t4 in Figure 21B (the period hatched in dot pattern in Figure 21B). In the switch system 13, as shown in Figure 21A, when the main current I DS of the semiconductor switch 11 becomes substantially zero at time t3, no electromotive force is generated in the inductor Ls, and the second switch Q12 turns on, so the gate current I Gflows through the second discharge path 22 instead of the first discharge path 21. That is, the gate current I G is dominated by the current I Q1 flowing through the first switch Q11. As a result, the gate charge of the semiconductor switch 11 is discharged at high speed through the second discharge path 22, so the voltage V GS between the gate 11G and the source 11S of the semiconductor switch 11 drops rapidly and becomes substantially zero at time t4.

[0192] (3) Characteristics of the semiconductor switch controlled by the control circuit FIG. 22 shows the characteristics of the semiconductor switch 11 when the resistance value of the gate resistor R G is changed in the range of 100 Ω to 5 kΩ in the control circuit 12. Here, the characteristics of the semiconductor switch 11 are the voltage V GS between the gate 11G and the source 11S of the semiconductor switch 11, the main current I DS , and the voltage V DS between the drain 11D and the source 11S, respectively, as characteristics of time change. In FIG. 22, five characteristics of the semiconductor switch 11 are shown, and notations A1, A2, A3, A4, and A5 are given in ascending order of the resistance value of the gate resistor R G . That is, in FIG. 22, A1 shows the characteristics when the resistance value of the gate resistor R G is the smallest, and A5 shows the characteristics when the resistance value of the gate resistor R G is the largest.

[0193] From FIG. 22, in the control circuit 12, by changing the resistance value of the gate resistor R G , the current change rate of the main current I DS of the semiconductor switch 11 can be changed, and it can be seen that by increasing the resistance value, the absolute value of the current change rate can be decreased. Also, from FIG. 22, in the control circuit 12, by increasing the resistance value of the gate resistor R G , the voltage V GS between the gate 11G and the source 11S of the semiconductor switch 11, the main current I DS , and the voltage V DSIt can be seen that each vibration can be suppressed. Also, from FIG. 22, in the control circuit 12, by applying a negative bias voltage between the gate 11G and the source 11S of the semiconductor switch 11, the voltage V GS between the gate 11G and the source 11S can be seen to be capable of suppressing the semiconductor switch 11 from erroneously arcing beyond the threshold voltage.

[0194] (4) Advantages The control circuit 12 according to Example 1 includes a first discharge path 21, a second discharge path 22, a first switch Q11, and a second switch Q12. The first discharge path 21 is connected to the gate 11G of the semiconductor switch 11. The second discharge path 22 is connected to the gate 11G of the semiconductor switch 11. The second discharge path 22 can discharge faster than the first discharge path 21. The second switch Q12 can be turned on and off separately from the first switch Q11. The second switch Q12 is provided on the second discharge path 22 and turns on based on the rate of change of the main current I DS of the semiconductor switch 11. Thereby, in the control circuit 12, it becomes possible to suppress the switching loss at the turn-off of the semiconductor switch 11 and suppress the surge voltage applied to the semiconductor switch 11.

[0195] When the semiconductor switch 11 is turned off, the control circuit 12 discharges the gate charge through the first discharge path 21 during the period from time point t2 to t3 when the main current I DS of the semiconductor switch 11 decreases. Therefore, it is possible to suppress the generation of a surge voltage caused by the parasitic inductance of the load circuit connected to the semiconductor switch 11 and the rate of change of the main current I DS . Also, when the semiconductor switch 11 is turned off, the control circuit 12 discharges the gate charge through the second discharge path 22 that can discharge faster than the first discharge path 21 during the periods other than the period from time point t2 to t3 (the period from time point t1 to t2, the period from time point t3 to t4). Thus, the turn-off time can be shortened. Thereby, in the control circuit 12 and the switch system 13, even if the surge voltage is suppressed by reducing the absolute value of the rate of change of the current of the semiconductor switch 11, it is possible to suppress the increase in the switching time and suppress the switching loss.

[0196] Also, in the control circuit 12, since the first discharge path 21 has the gate resistor R G when a part of the charge of the gate 11G of the semiconductor switch 11 is discharged by the second discharge path 22 and then the remaining charge of the gate 11G of the semiconductor switch 11 is discharged by the first discharge path 21, the absolute value of the current change rate of the main current I DS can also be reduced.

[0197] (Example 2) Hereinafter, the control circuit 12a according to Example 2 and the switch system 13a including the same will be described with reference to FIG. 23.

[0198] The control circuit 12a according to Example 2 is substantially the same as the control circuit 12 (see FIG. 17) according to Example 1, and is different from the control circuit 12 according to Example 1 in that an n-channel field effect transistor Tr11 is provided as the first switch Q11 instead of the p-channel field effect transistor Tr1. Regarding the control circuit 12a and the switch system 13a according to Example 2, the same components as those of the control circuit 12 and the switch system 13 according to Example 1 are denoted by the same reference numerals and the description thereof is omitted.

[0199] In the control circuit 12a according to Example 2, the first switch Q11 is the n-channel field effect transistor Tr11 provided on the second discharge path 22.

[0200] The n-channel field effect transistor Tr11 has a gate, a source, and a drain. The field effect transistor Tr11 (hereinafter also referred to as the first field effect transistor Tr11) is a normally-off type n-channel MOSFET in the illustrated example. Also, the second switch Q12 is the diode D2 provided on the second discharge path 22. The diode D2 has an anode and a cathode.

[0201] In the control circuit 12a, the drain of the first field-effect transistor Tr11 is connected to the gate 11G of the semiconductor switch 11, and the source of the first field-effect transistor Tr11 is connected to the anode of the diode D2. The second discharge path 22 has an inductor Ls connected in series to the diode D2. Therefore, in the second discharge path 22, the first field-effect transistor Tr11, the diode D2, and the inductor Ls are connected in series.

[0202] The control circuit 12a further includes a series circuit of a resistor R11 and a third switch Q13. The resistor R11 has a first end and a second end. The third switch Q13 is an n-channel field-effect transistor Tr3. The n-channel field-effect transistor Tr3 has a gate, a source, and a drain. The field-effect transistor Tr3 (hereinafter also referred to as the third field-effect transistor Tr3) is a normally-off type n-channel MOSFET in the illustrated example. In the control circuit 12a, the first end of the resistor R11 is connected to the drain of the first field transistor Tr11, and the second end of the resistor R11 is connected to the drain of the third field-effect transistor Tr3. The source of the third field-effect transistor Tr3 is connected to the low-potential side output terminal of the driver 14 and the source 11S of the semiconductor switch 11, and the gate of the third field-effect transistor Tr3 is connected to the high-potential side output terminal of the driver 14. The gate of the first transistor Tr11 is connected to a node between the second end of the resistor R11 and the drain of the third transistor Tr3.

[0203] In the switch system 13a, when a positive bias voltage is output from the driver 14 between the gate 11G and the source 11S of the semiconductor switch 11, the state of the semiconductor switch 11 is on. At this time, in the control circuit 12a, the third field-effect transistor Tr3 is on, and the first field-effect transistor Tr11 is off.

[0204] In the switch system 13a, when turning off the semiconductor switch 11, the output voltage of the driver 14 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage). As a result, in the control circuit 12a, the third field effect transistor Tr3 is turned off and the first field effect transistor Tr11 is turned on, so that the charge of the gate 11G of the semiconductor switch 11 is discharged through the second discharge path 22.

[0205] Thereafter, in the control circuit 12a, when the main current I DS of the semiconductor switch 11 starts to decrease, an electromotive force is generated between the first end and the second end of the inductor Ls due to the change in the main current I DS , and the diode D2 is turned off. As a result, the current flowing through the first switch Q11 (the first field effect transistor Tr11) decreases, so that the gate current I G (see FIG. 20) flows through the gate resistor R G . That is, the charge of the gate 11G of the semiconductor switch 11 is not discharged through the second discharge path 22, but is discharged through the first discharge path 21. As a result, the magnitude of the gate current I G is determined by the resistance value of the gate resistor R G .

[0206] Thereafter, in the control circuit 12a, when the main current I DS of the semiconductor switch 11 becomes substantially zero, no electromotive force is generated in the inductor Ls, and the second switch Q12 is turned on, so that the gate current I G flows through the second discharge path 22 instead of the first discharge path 21. That is, the gate current I G is dominated by the current I Q11 flowing through the first switch Q11 (see FIG. 21). As a result, the gate charge of the semiconductor switch 11 is rapidly discharged through the second discharge path 22, so that the voltage V GS between the gate 11G and the source 11S of the semiconductor switch 11 rapidly decreases and becomes substantially zero.

[0207] The control circuit 12a and the switch system 13a according to Example 2 can suppress the surge voltage applied to the semiconductor switch 11 while suppressing the switching loss at the turn-off of the semiconductor switch 11, similar to the control circuit 12 and the switch system 13 according to Example 1.

[0208] Also, in the switch system 13a according to Example 2, if each of the first field-effect transistor Tr11 and the third field-effect transistor Tr3 is configured by an n-channel GaN-based GIT, a monolithic integrated circuit in which the control circuit 12a including the first field-effect transistor Tr11 and the third field-effect transistor Tr3 and the semiconductor switch 11 are integrated can be easily realized.

[0209] (Example 3) Hereinafter, the control circuit 12b according to Example 3 and the switch system 13b including the same will be described with reference to FIG. 24.

[0210] The control circuit 12b according to Example 3 is substantially the same as the control circuit 12 (see FIG. 17) according to Example 1, and is different from the control circuit 12 according to Example 1 in that a normally-on type n-channel field-effect transistor Tr2 is provided as the second switch Q12 instead of the diode D2. Regarding the control circuit 12b and the switch system 13b according to Example 3, the same components as those of the control circuit 12 and the switch system 13 according to Example 1 are denoted by the same reference numerals and the description thereof is omitted.

[0211] In the control circuit 12b, the first switch Q11 is a p-channel field-effect transistor Tr1 provided on the second discharge path 22. The second switch Q12 is a normally-on type n-channel field-effect transistor Tr2 provided on the second discharge path 22. The second discharge path 22 has an inductor Ls connected in series to the n-channel field-effect transistor Tr2. In the second discharge path 22, the inductor Ls is connected to the source 11S of the semiconductor switch 11.

[0212] The normally-on type n-channel field effect transistor Tr2 has a gate, a source, and a drain. In the illustrated example, the field effect transistor Tr2 is a normally-on type n-channel GaN-based GIT.

[0213] The drain of the field effect transistor Tr2 is connected to the drain of the field effect transistor Tr1. Also, the source of the field effect transistor Tr2 is connected to the first end of the inductor Ls. The gate of the field effect transistor Tr2 is connected to the second end of the inductor Ls. Therefore, the gate of the field effect transistor Tr2 is connected to the low-potential side output terminal of the driver 14 and the source 11S of the semiconductor switch 11.

[0214] In the switch system 13b, when a positive bias voltage is output from the driver 14 between the gate 11G and the source 11S of the semiconductor switch 11, the state of the semiconductor switch 11 is an on state. At this time, in the control circuit 12b, the field effect transistor Tr1 is in an off state.

[0215] In the switch system 13b, when turning off the semiconductor switch 11, the output voltage of the driver 14 is changed from a positive bias voltage to, for example, 0 V (or a negative bias voltage). Thereby, in the control circuit 12b, since the field effect transistor Tr1 is turned on, the charge of the gate 11G of the semiconductor switch 11 is discharged through the second discharge path 22.

[0216] Thereafter, in the control circuit 12b, the main current I of the semiconductor switch 11 DS begins to decrease, and due to the change in the main current I DS , an electromotive force is generated between the first end and the second end of the inductor Ls, and the field effect transistor Tr2 is turned off. As a result, the current flowing through the field effect transistor Tr1 decreases, so the gate current I G (see FIG. 20) is the gate resistance R Gflows through. That is, the charge of the gate 11G of the semiconductor switch 11 is not discharged through the second discharge path 22, but is discharged through the first discharge path 21. As a result, the magnitude of the gate current I G is determined by the resistance value of the gate resistance R G .

[0217] After that, in the control circuit 12b, when the main current I DS of the semiconductor switch 11 becomes substantially zero, no electromotive force is generated in the inductor Ls, and the second switch Q12 turns on. Therefore, the gate current I G flows through the second discharge path 22 instead of the first discharge path 21. That is, the gate current I G is dominated by the current I Q1 flowing through the first switch Q11 (see FIG. 21). As a result, the gate charge of the semiconductor switch 11 is rapidly discharged through the second discharge path 22, so the voltage V GS between the gate 11G and the source 11S of the semiconductor switch 11 rapidly decreases and becomes substantially zero.

[0218] Similar to the control circuit 12 and the switch system 13 according to Example 1, the control circuit 12b and the switch system 13b according to Example 3 can suppress the switching loss when the semiconductor switch 11 is turned off and suppress the surge voltage applied to the semiconductor switch 11.

[0219] As described above, in the illustrated example, the field effect transistor Tr2 is a normally-on type n-channel GaN-based GIT, but is not limited thereto. For example, a normally-on type n-channel MOSFET may also be used.

[0220] (Example 4) Hereinafter, the switch system 13e according to Example 4 will be described with reference to FIG. 25.

[0221] The switch system 13e according to Example 4 differs from the switch system 13 according to Example 1 in that it includes two semiconductor switches 11 of the switch system 13 according to Example 1 and two control circuits 12. Regarding the switch system 13e according to Example 4, components similar to those of the switch system 13 according to Example 1 are denoted by the same reference numerals and the description thereof is omitted.

[0222] In the switch system 13e, two semiconductor switches 11 are connected in series. The two control circuits 12 correspond one-to-one to the two semiconductor switches 11.

[0223] In the switch system 13e according to Example 4, the drains 11D of the two semiconductor switches 11 are connected to each other.

[0224] In the switch system 13e, the polarities of the electromotive forces of the inductor Ls generated with respect to the current change are different between the two inductors Ls. In the inductor Ls connected to the source 11S of one of the two semiconductor switches 11, an electromotive force is generated in which the cathode side of the diode D2 becomes higher with respect to the source 11S, and in the inductor Ls connected to the source 11S of the other semiconductor switch 11, an electromotive force is generated in which the cathode side of the diode D2 becomes lower with respect to the source 11S. For this reason, in the switch system 13e, it is possible to suppress the surge voltage applied to the semiconductor switch 11 while suppressing the switching loss at the turn-off of the semiconductor switch 11 corresponding to the inductor Ls in which an electromotive force is generated in which the cathode side of the diode D2 becomes higher with respect to the source 11S.

[0225] Similar to the switch system 13 according to Example 1, the switch system 13e according to Example 4 can suppress the switching loss at the turn-off of the semiconductor switch 11 while suppressing the surge voltage applied to the semiconductor switch 11.

[0226] (Example 5) Hereinafter, the switch system 13f according to Example 5 will be described with reference to FIG. 26.

[0227] The switch system 13f according to Example 5 is different from the switch system 13 according to Example 1 in that it includes two semiconductor switches 11 and two control circuits 12. For the components similar to those of the switch system 13 according to Example 1 in the switch system 13f according to Example 5, the same reference numerals are used and the description thereof is omitted.

[0228] In the switch system 13f, two semiconductor switches 11 are connected in series. The two control circuits 12 correspond one-to-one to the two semiconductor switches 11.

[0229] In the switch system 13f, the sources 11S of the two semiconductor switches 11 are connected to each other via the inductors Ls of the two control circuits 12. Each diode D2 of the two control circuits 12 is connected to the inductor Ls of the corresponding control circuit 12 via the inductor Ls of a control circuit 12 different from the corresponding control circuit 12 among the two control circuits 12.

[0230] Similar to the switch system 13 according to Example 1, the switch system 13f according to Example 5 can suppress the switching loss when the semiconductor switch 11 is turned off and suppress the surge voltage applied to the semiconductor switch 11.

[0231] The switch system 13f according to Example 5 includes two drivers 14 for the two control circuits 12, and the output terminals on the low potential side of the two drivers 14 are connected to each other. However, it is not limited thereto, and one driver 14 may be shared for the two control circuits 12.

[0232] (Example 6) Hereinafter, the switch system 13g according to Example 6 will be described with reference to FIG. 27.

[0233] The switch system 13g according to Example 6 differs from the switch system 13 according to Example 1 in that it includes two semiconductor switches 11 and two control circuits 12. For the components similar to those of the switch system 13 according to Example 1 in the switch system 13g according to Example 6, the same reference numerals are used and the description thereof is omitted.

[0234] In the switch system 13g, two semiconductor switches 11 are connected in series, and two control circuits 12 correspond one-to-one to the two semiconductor switches 11.

[0235] In the switch system 13g, the sources 11S of the two semiconductor switches 11 are connected via the inductors Ls of the two control circuits 12. In the switch system 13g, the sources 11S of the two semiconductor switches 11 are connected. In the switch system 13g, a node N13 between the inductors Ls of the two control circuits 12 and a node N14 between the cathodes of the diodes D2 of the two control circuits 12 are connected.

[0236] Similar to the switch system 13 according to Example 1, the switch system 13g according to Example 6 can suppress the switching loss when the semiconductor switch 11 is turned off and suppress the surge voltage applied to the semiconductor switch 11.

[0237] (Example 7) Hereinafter, the switch system 13h according to Example 7 will be described with reference to FIG. 28.

[0238] The switch system 13h according to Example 7 differs from the switch system 13e according to Example 4 in that it includes a semiconductor switch 11h instead of the semiconductor switch 11 of the switch system 13e according to Example 4. The semiconductor switch 11h is a dual-gate type bidirectional switch having two gates 11G and two sources 11S respectively.

[0239] In the semiconductor switch 11h, the two gates 11G and the two sources 11S correspond one-to-one. Hereinafter, for convenience of explanation, one of the two gates 11G may be referred to as the first gate 111G, and the other may be referred to as the second gate 112G. Also, among the two sources 11S, the source 11S corresponding to the first gate 111G may be referred to as the first source 111S, and the source 11S corresponding to the second gate 112G may be referred to as the second source 112S.

[0240] Hereinafter, the semiconductor switch 11h will be briefly described, and then the switch system 13h will be described.

[0241] The semiconductor switch 11h is a type of GaN-based GIT. The semiconductor switch 11h includes, for example, a substrate, a buffer layer, a first nitride semiconductor layer, a second nitride semiconductor layer, a first source electrode, a first gate electrode, a second gate electrode, a second source electrode, a first p-type layer, and a second p-type layer. The buffer layer is formed on the substrate. The first nitride semiconductor layer is formed on the buffer layer. The second nitride semiconductor layer is formed on the first nitride semiconductor layer. The first source electrode, the first gate electrode, the second gate electrode, and the second source electrode are formed on the second nitride semiconductor layer. The first p-type layer is interposed between the first gate electrode and the second nitride semiconductor layer. The second p-type layer is interposed between the second gate electrode and the second nitride semiconductor layer. In the semiconductor switch 11h, the first source 111S includes the first source electrode. The first gate 111G includes the first gate electrode and the first p-type layer. The second gate 112G includes the second gate electrode and the second p-type layer. The second source 112S includes the second source electrode. The substrate is, for example, a silicon substrate. The buffer layer is, for example, an undoped GaN layer. The first nitride semiconductor layer is, for example, an undoped GaN layer. The second nitride semiconductor layer is, for example, an undoped AlGaN layer. Each of the first p-type layer and the second p-type layer is, for example, a p-type AlGaN layer. Each of the buffer layer, the first nitride semiconductor layer, and the second nitride semiconductor layer may have impurities such as Mg, H, Si, C, and O that are inevitably mixed during growth by MOVPE (Metal Organic Vapor Phase Epitaxy) or the like.

[0242] In the semiconductor switch 11h, the second nitride semiconductor layer forms a heterojunction with the first nitride semiconductor layer. In the first nitride semiconductor layer, a two-dimensional electron gas is generated in the vicinity of the heterojunction. The region containing the two-dimensional electron gas (hereinafter also referred to as the "two-dimensional electron gas layer") can function as an n-channel layer (electron conduction layer).

[0243] Hereinafter, for convenience of explanation, a state in which a voltage equal to or higher than a first threshold voltage (e.g., 1.3 V) is not applied with the first gate 111G on the high potential side between the first gate 111G and the first source 111S is also referred to as an off state of the first gate 111G. Further, a state in which a voltage equal to or higher than the first threshold voltage is applied with the first gate 111G on the high potential side between the first gate 111G and the first source 111S is also referred to as an on state of the first gate 111G. Also, a state in which a voltage equal to or higher than a second threshold voltage (e.g., 1.3 V) is not applied with the second gate 112G on the high potential side between the second gate 112G and the second source 112S is also referred to as an off state of the second gate 112G. Further, a state in which a voltage equal to or higher than the second threshold voltage is applied with the second gate 112G on the high potential side between the second gate 112G and the second source 112S is also referred to as an on state of the second gate 112G.

[0244] By including the above-described first p-type layer and second p-type layer, the semiconductor switch 11h realizes a normally-off type transistor.

[0245] The semiconductor switch 11h can switch between a bi-directional on state, a bi-directional off state, a first diode state, and a second diode state according to a combination of a first gate voltage and a second gate voltage applied to the first gate 111G and the second gate 112G, respectively. The first gate voltage is a voltage applied between the first gate 111G and the first source 111S. The second gate voltage is a voltage applied between the second gate 112G and the second source 112S. The bi-directional on state is a state that allows a bi-directional current (a first direction and a second direction opposite to the first direction) to pass through. The bi-directional off state is a state that blocks a bi-directional current. The first diode state is a state that allows a current in the first direction to pass through. The second diode state is a state that allows a current in the second direction to pass through.

[0246] In the semiconductor switch 11h, a bi-directional on-state is achieved when the first gate 111G is in the on-state and the second gate 112G is in the on-state. In the semiconductor switch 11h, a bi-directional off-state is achieved when the first gate 111G is in the off-state and the second gate 112G is in the off-state. In the semiconductor switch 11h, a first diode state is achieved when the first gate 111G is in the off-state and the second gate 112G is in the on-state. In the semiconductor switch 11h, a second diode state is achieved when the first gate 111G is in the on-state and the second gate 112G is in the off-state.

[0247] In the switch system 13h, the first discharge path 21 and the second discharge path 22 of one of the two control circuits 12 are connected to the first gate 111G, which is one of the two gates 11G. The first discharge path 21 and the second discharge path 22 of the remaining one of the two control circuits 12 are connected to the second gate 112G, which is the other gate of the two gates 11G. In the switch system 13h, the inductor Ls of one of the two control circuits 12 is connected to the first source 111S corresponding to the first gate 111G among the two sources 11S, and the inductor Ls of the remaining one of the two control circuits 12 is connected to the second source 112S corresponding to the second gate 112G among the two sources 11S.

[0248] Similar to the switch system 13 according to Example 1, the switch system 13h according to Example 7 can suppress the switching loss when turning off the semiconductor switch 11h and suppress the surge voltage applied to the semiconductor switch 11h.

[0249] The above Examples 1 to 7 are merely one of various examples of the present disclosure. The above Examples 1 to 7 can be variously modified according to design and the like as long as the object of the present disclosure can be achieved.

[0250] Also, the p-type layer in the semiconductor switch 11 of the switch system 13h is not limited to a p-type AlGaN layer, and may be, for example, a p-type GaN layer or a p-type metal oxide semiconductor layer. The p-type metal oxide semiconductor layer is, for example, a NiO layer. The NiO layer may contain, for example, at least one alkali metal selected from the group consisting of lithium, sodium, potassium, rubidium, and cesium as an impurity. Further, the NiO layer may contain, for example, transition metals such as silver and copper that become monovalent when added as an impurity. The same applies to each of the first p-type layer and the second p-type layer in the semiconductor switch 11h of the switch system 13h as the p-type layer in the semiconductor switch 11.

[0251] Each of the semiconductor switch 11 and the semiconductor switch 11h may include one or more nitride semiconductor layers between the buffer layer and the first nitride semiconductor layer. Also, the buffer layer is not limited to a single-layer structure and may have, for example, a superlattice structure.

[0252] Also, the substrate in each of the semiconductor switch 11 and the semiconductor switch 11h is not limited to a silicon substrate and may be, for example, a GaN substrate, an SiC substrate, a sapphire substrate, or the like.

[0253] (Aspect) The following aspects are disclosed in this specification from Examples 1 to 7 and the like described above.

[0254] The control circuit (12; 12a; 12b) according to the first aspect is a control circuit that controls a semiconductor switch (11; 11h) having a gate (11G) and a source (11S) corresponding to the gate (11G). The control circuit (12; 12a; 12b) includes a first discharge path (21), a second discharge path (22), a first switch (Q11), and a second switch (Q12). The first discharge path (21) is connected to the gate (11G) of the semiconductor switch (11; 11h). The second discharge path (22) is connected to the gate (11G) of the semiconductor switch (11; 11h). The second discharge path (22) can discharge faster than the first discharge path (21). The second switch (Q12) can be turned on and off separately from the first switch (Q11). The second switch (Q12) is provided on the second discharge path (22) and turns on based on the rate of change of current.

[0255] In the control circuit (12; 12a; 12b) according to the first aspect, it is possible to suppress the surge voltage applied to the semiconductor switch (11; 11h) while suppressing the switching loss when the semiconductor switch (11; 11h) is turned off.

[0256] In the control circuit (12; 12a; 12b) according to the second aspect, in the first aspect, the first switch (Q11) is provided on the second discharge path (22).

[0257] In the control circuit (12; 12a; 12b) according to the second aspect, the presence or absence of discharge through the second discharge path (22) is switched according to the state of the first switch (Q11).

[0258] In the control circuit (12; 12a; 12b) according to the third aspect, in the first or second aspect, the first switch (Q11) turns on when the semiconductor switch (11; 11h) is turned off.

[0259] In the control circuit (12; 12a; 12b) according to the third aspect, it is possible to discharge the charge of the gate (11G) of the semiconductor switch (11; 11h) through the first switch (Q11) when the semiconductor switch (11; 11h) is turned off.

[0260] In the control circuit (12) according to the fourth aspect, in any one of the first to third aspects, the first switch (Q11) is a p-channel field effect transistor (Tr1) provided on the second discharge path (22). The second switch (Q12) is a diode (D2) provided on the second discharge path (22). The second discharge path (22) has an inductor (Ls) connected in series to the diode (D2). In the second discharge path (22), the inductor (Ls) is connected to the source (1S) of the semiconductor switch (11; 11h).

[0261] In the control circuit (12) according to the fourth aspect, it is possible to suppress the voltage drop in each of the first switch (Q11) and the second switch (Q12).

[0262] In the control circuit (12a) according to the fifth aspect, in any one of the first to third aspects, the first switch (Q11) is an n-channel field effect transistor (Tr11) provided on the second discharge path (22). The second switch (Q12) is a diode (D2) provided on the second discharge path (22). The second discharge path (22) has an inductor (Ls) connected in series to the diode (D2). In the second discharge path (22), the inductor (Ls) is connected to the source (11S) of the semiconductor switch (11).

[0263] In the control circuit (12a) according to the fifth aspect, it is possible to suppress the voltage drop in each of the first switch (Q11) and the second switch (Q12).

[0264] In the control circuit (12b) according to the sixth aspect, in any one of the first to third aspects, the first switch (Q11) is a p-channel field effect transistor (Tr1) provided on the second discharge path (22). The second switch (Q12) is a normally-on n-channel field effect transistor (Tr2) provided on the second discharge path (22). The second discharge path (22) has an inductor (Ls) connected in series to the n-channel field effect transistor (Tr2). In the second discharge path (22), the inductor (Ls) is connected to the source (11S) of the semiconductor switch (11).

[0265] In the control circuit (12b) according to the sixth aspect, it is possible to suppress the voltage drop in each of the first switch (Q11) and the second switch (Q12).

[0266] In the control circuit (12) according to the seventh aspect, in the first or second aspect, the first switch (Q11) turns on when the semiconductor switch (11) turns on.

[0267] In the control circuit (12; 12a; 12b) according to the eighth aspect, in any one of the first to seventh aspects, the first discharge path (21) has a gate resistor (R G ) connected to the gate (11G) of the semiconductor switch (11; 11h). The second discharge path (22) is connected to the gate (11G) of the semiconductor switch (11; 11h) without passing through the gate resistor (R G ).

[0268] In the control circuit (12; 12a; 12b) according to the eighth aspect, by changing the resistance value of the gate resistor (R G ), the rate of change of the current of the main current (I DS ) of the semiconductor switch (11; 11h) can be changed.

[0269] The switch system (13; 13a; 13b; 13e; 13g; 13g; 13h) according to the ninth aspect includes a control circuit (12; 12a; 12b) according to any one of the first to eighth aspects and a semiconductor switch (11; 11h).

[0270] In the switch system (13; 13a; 13b; 13e; 13g; 13g; 13h) according to the ninth aspect, it is possible to suppress the surge voltage applied to the semiconductor switch (11; 11h) while suppressing the switching loss at the turn-off of the semiconductor switch (11; 11h).

[0271] The switch system (13e; 13f; 13g) according to the tenth aspect includes two semiconductor switches (11) and two control circuits (12) in the ninth aspect. In the switch system (13e; 13f; 13g), the two semiconductor switches (11) are connected in series. The two control circuits (12) correspond one-to-one to the two semiconductor switches (11).

[0272] In the switch system (13e; 13f; 13g) according to the tenth aspect, for each of the two semiconductor switches (11), by changing the resistance value of the gate resistor (R G ), the rate of change of the main current (I DS ) of the semiconductor switch (11) can be changed.

[0273] In the switch system (13e) according to the eleventh aspect, in the tenth aspect, each of the two semiconductor switches (11) has a drain (11D) corresponding to the gate (11G). In the switch system (13), the drains (11D) of the two semiconductor switches (11) are connected to each other.

[0274] The switch system (13f) according to the 12th aspect is based on the 10th aspect. In each of the two control circuits (12), the first switch (Q11) is a p-channel field effect transistor (Tr1) provided on the second discharge path (22). In each of the two control circuits (12), the second switch (Q12) is a diode (D2) provided on the second discharge path (22). In each of the two control circuits (12), the second discharge path (22) has an inductor (Ls) connected in series with the diode (D2). The inductor (Ls) is connected to the source (11S) of the semiconductor switch (11). In the switch system (13f), the sources (11S) of the two semiconductor switches (11) are connected to each other via the inductors (Ls) of the two control circuits (12). The diode (D2) of each of the two control circuits (12) is connected to the inductor (Ls) of the corresponding control circuit (12) via the inductor (Ls) of a control circuit (12) different from the corresponding control circuit (12) among the two control circuits (12).

[0275] The switch system (13g) according to the 13th aspect is based on the 10th aspect. In each of the two control circuits (12), the first switch (Q11) is a p-channel field effect transistor (Tr1) provided on the second discharge path (22). In each of the two control circuits (12), the second switch (Q12) is a diode (D2) provided on the second discharge path (22). In each of the two control circuits (12), the second discharge path (22) has an inductor (Ls) connected in series with the diode (D2). The inductor (Ls) is connected to the source (11S) of the semiconductor switch (11). In the switch system (13g), the sources (11S) of the two semiconductor switches (11) are connected to each other via the inductors (Ls) of the two control circuits (12). In the switch system (13g), the sources (11S) of the two semiconductor switches (11) are connected to each other. In the switch system (13g), a node (N13) between the inductors (Ls) of the two control circuits (12) and a node (N14) between the cathodes of the diodes (D2) of the two control circuits (12) are connected to each other.

[0276] In the switch system (13g) according to the 13th aspect, it is possible to share one driver (14) for two control circuits (12).

[0277] In the switch system (13h) according to the 14th aspect, in the 9th aspect, the semiconductor switch (11) is a dual-gate type bidirectional switch having two gates (11G) and two sources (11S) respectively. The switch system (13h) includes two control circuits (12). In the switch system (13h), one of the two control circuits (12) is connected to a first gate (111G) which is one of the two gates (11G), and the remaining one control circuit (12) is connected to a second gate (112G) which is the other of the two gates (11G).

Explanation of symbols

[0278] 1, 1k switching element 5 circuit element 10, 10a, 10b, 10c, 10d, 10e1, 10e2, 10f1, 10f2, 10g1, 10g2, 10h, 10i, 10j control circuit 100, 100a, 100b, 100c, 100d, 100e, 100f, 100g, 100h, 100i, 100j, 100k switch device D1 drain Di1 diode Di2 protection diode Di3 protection diode Dis diode G1 gate L1 inductor P0 reference potential point R1 resistor S1, S2 source 11 semiconductor switch 11D drain 11G gate 111G first gate 112G second gate 11S source 111S First source 112S Second source 12, 12a, 12b Control circuit 21 First discharge path 22 Second discharge path 13, 13a, 13b, 13e, 13f, 13g, 13h Switch system 14 Driver N11 Node N12 Node N13 Node N14 Node D2 Diode Ls Inductor R G Gate resistance Tr1 p-channel field-effect transistor Tr11 Field-effect transistor Tr2 Normally-on n-channel field-effect transistor

Claims

1. A control circuit for controlling a switching element having a gate and a source corresponding to the gate, an inductor connected between the gate and the source of the switching element, a circuit element connected in series with the inductor between the gate and the source, and through which current flows when an electromotive force is generated in the inductor, a resistor connected in parallel with the inductor and the circuit element between the gate and the source, a protection diode having an anode and a cathode, the anode being connected to the connection point between the circuit element and the resistor, and the cathode being connected to the gate of the switching element, the control circuit.

2. A control circuit for controlling a switching element having a gate and a source corresponding to the gate, an inductor connected between the gate and the source of the switching element, a circuit element connected in series with the inductor between the gate and the source, and through which current flows when an electromotive force is generated in the inductor, a resistor connected in parallel with the inductor and the circuit element between the gate and the source, a first terminal connected to the switching element on the side opposite to the source in the switching element, a second terminal connected to the inductor on the side opposite to the switching element side in the inductor, a second inductor connected between a first node between the first inductor, which is the inductor, and the second terminal and the circuit element, a voltage clamping element connected in parallel with the switching element, the first inductor, and the second inductor, a third inductor connected between a second node between the second inductor and the circuit element and the voltage clamping element, wherein no current flows through the third inductor in the on state of the switching element, the control circuit.

3. The circuit element includes a capacitor, The control circuit according to claim 1 or 2.

4. The circuit element includes a diode, The control circuit according to claim 1 or 2.

5. The circuit element includes a resistor, The control circuit according to claim 1 or 2. Claim 6. When the switching element turns off, the current flowing through the source of the switching element decreases, an electromotive force is generated in the inductor, and a current corresponding to the electromotive force flows through the circuit element and the resistor, so that the potential of the reference potential point included in the path between the connection point of the circuit element and the resistor and the gate rises. The magnitude of the current flowing from the gate to the path changes due to the potential difference between the potential of the gate and the potential of the reference potential point. The control circuit according to any one of claims 1 to 5. Claim 7. Further comprising a protection diode having an anode and a cathode, the anode being connected between the source of the switching element and the inductor and the resistor, and the cathode being connected to the gate of the switching element. The control circuit according to claim 2. Claim 8. A first terminal connected to the switching element on the side opposite to the source in the switching element, A second terminal connected to the inductor on the side opposite to the switching element side in the inductor, A second inductor connected between a first node between the first inductor, which is the inductor, and the second terminal and the circuit element, A voltage clamp element connected in parallel to the switching element, the first inductor, and the second inductor, Further comprising a third inductor connected between a second node between the second inductor and the circuit element and the voltage clamp element. In the on state of the switching element, no current flows through the third inductor. In the on state of the switching element, no current flows through the third inductor. The control circuit according to claim 1. Claim 9. A control circuit according to any one of claims 1 to 8, And the switching element. A switch device. Claim 10. Comprising two switching elements, Comprising two control circuits, The two switching elements are connected in series, The two control circuits correspond one-to-one to the two switching elements. The switch device according to claim 9. Claim 11. Each of the two switching elements has a drain corresponding to the gate, The drains of the two switching elements are connected to each other. The switch device according to claim 10. Claim 12. The switching element is a dual-gate type bidirectional switch having two gates and two sources respectively, Comprising two control circuits. One of the two control circuits is connected to the gate corresponding to the one control circuit among the two gates of the bidirectional switch, and the other control circuit is connected to the gate corresponding to the other control circuit among the two gates of the bidirectional switch. The switch device according to claim 9.

13. The sources of the two switching elements are connected to each other. The switch device according to claim 10.

14. A control circuit for controlling a switching element having a gate and a source corresponding to the gate, The switching element, and comprising: The control circuit is An inductor connected between the gate and the source of the switching element, A circuit element connected in series with the inductor between the gate and the source, and through which a current flows when an electromotive force is generated in the inductor, A resistor connected in parallel to the inductor and the circuit element between the gate and the source, The switching element is a dual-gate type bidirectional switch having two gates and two sources respectively, Two of the control circuits are provided, One of the two control circuits is connected to the gate corresponding to the one control circuit among the two gates of the bidirectional switch, and the other control circuit is connected to the gate corresponding to the other control circuit among the two gates of the bidirectional switch. Switch device.

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