JP2013038555A - Two-wire ac switch - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve low power consumption for a two-wire AC switch.SOLUTION: The two-wire AC switch, inserted into a cable run for connecting an AC power supply with a load, includes: a main switch 3 having switch terminals S1, S2, gate terminals G1, G2 for controlling on-off operations between the switch terminals, a substrate terminal Sub, and a semiconductor switch in which electric current can be bidirectionally run between the switch terminals, the switch terminal S1 is connected with an AC power supply 1 and the switch terminal S2 is connected with a load 2; and a sub switch 9 which switches between grounding and floating the substrate terminal Sub of the main switch.

Description

  The present invention relates to a two-wire AC switch, and more particularly, to a two-wire AC switch including a semiconductor switch that can flow current in both directions.

  Conventionally, highly functional two-wire AC switches having a dimming function, a remote control function, a human sensor function, and the like have been commercialized. The switch used for this is required to be able to pass a current in both directions and to ensure a withstand voltage with both positive and negative polarities. In recent years, research and development for practical application of nitride-based semiconductors typified by gallium nitride (GaN) and wide band gap semiconductors such as silicon carbide (SiC) have been actively conducted as semiconductor device materials. Two-wire AC switches using a wide bandgap semiconductor bidirectional switch that can realize power consumption have been devised (references 1 and 2).

  FIG. 14 is a circuit diagram showing a two-wire AC switch using a group III nitride semiconductor bidirectional switch. The bidirectional switch 3 is a double-gate switching element made of a group III nitride semiconductor that has a configuration in which a current flows in both directions and turns on or off the current flow. Switching (conduction / non-conduction) The switch terminal S1 and the switch terminal S2 that are the targets of the current, the two gate terminals G1 and G2 for controlling the on and off of the current flow, and the substrate on which the bidirectional switch 3 is formed are electrically connected Board terminal Sub (hereinafter, also referred to as “Sub terminal”). Here, the commercial AC power source 1, the load 2, and the bidirectional switch 3 (its switch terminal S1 and switch terminal S2) are connected in series so as to form a closed circuit.

The full-wave rectifier 4 is a bridge diode or the like that is connected in parallel to the bidirectional switch 3 and that full-wave rectifies the AC power supplied from the commercial AC power supply 1.
The power supply circuit 5 is a circuit that smoothes the voltage after full-wave rectification output from the full-wave rectifier 4 and supplies DC power. Power necessary for the first gate drive circuit 7, the second gate drive circuit 8, and the control circuit 6 is supplied from the power supply circuit 5.

  The control circuit 6 is a circuit that controls the first gate drive circuit 7 and the second gate drive circuit 8. Specifically, when power is supplied from the commercial AC power supply 1 to the load 2, the gate terminal G1 and the gate of the bidirectional switch 3 are respectively connected to the first gate drive circuit 7 and the second gate drive circuit 8. When the bidirectional switch 3 is turned on by outputting a control signal having a voltage higher than the threshold voltage to the terminal G2, while the power supply from the commercial AC power supply 1 to the load 2 is cut off, Bidirectional switch by causing one gate drive circuit 7 and second gate drive circuit 8 to output a control signal having a voltage lower than the threshold voltage to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3, respectively. 3 is turned off.

More specifically, a signal indicating whether power is supplied from the commercial AC power supply 1 to the load 2 is transmitted from the external setting unit 11 to the control circuit 6. Based on the transmitted signal, the control circuit 6 outputs a control signal to the input terminal SIN1 of the first gate drive circuit 7 and the input terminal SIN2 of the second gate drive circuit 8.
The first gate drive circuit 7 and the second gate drive circuit 8 control signals from the output terminals OUT1 and OUT2 to the gate terminals G1 and G2 of the bidirectional switch 3, respectively, based on the control signal from the control circuit 6. Is output, the switching operation of the bidirectional switch 3 is controlled. Specifically, voltages higher than the threshold voltage of the bidirectional switch 3 (more specifically, its gate) from the first gate drive circuit 7 and the second gate drive circuit 8 respectively are gate terminals G1 and G2. Is applied between the switch terminal S1 and the switch terminal S2 of the bidirectional switch 3, and power is supplied to the load 2. On the other hand, voltages lower than the threshold voltage of the bidirectional switch 3 (more specifically, the gate) are supplied from at least one of the first gate driving circuit 7 and the second gate driving circuit 8 to the gate terminal G1 and the gate terminal G2, respectively. Is applied between the switch terminal S1 and the switch terminal S2 of the bidirectional switch 3, and the power supply to the load 2 is cut off. As a result, a two-wire AC switch using the bidirectional switch 3 made of a group III nitride semiconductor is realized.

International publication number WO2010-073092_A1 International publication number WO2010-146433_A1

  However, the bidirectional switch has a problem that when the Sub terminal is used in a floating state, the on-resistance increases, and the power consumption increases when the bidirectional switch is in the on state. Further, when the Sub terminal is grounded, the on-resistance can be reduced. However, since a leakage current flows from the gate terminal G1, the gate terminal G2, the switch terminal S1, and the switch terminal S2 to the Sub terminal, the bidirectional switch There is a problem that the leakage current at the time of turning off increases, and the power consumption when the bidirectional switch is turned off increases.

  Therefore, an object of the present invention is to realize low power consumption of a two-wire AC switch.

  A two-wire AC switch according to the present invention is a two-wire AC switch inserted in an electric circuit connecting an AC power source and a load, and includes first and second switch terminals, and the first and second switches. The first and second gate terminals for controlling on / off between the terminals and the substrate terminal, and a current can flow in both directions between the first and second switch terminals. A main switch composed of a semiconductor switch having a switch terminal connected to the AC power source and a second switch terminal connected to the load, and a sub-switch for switching between grounding or floating the substrate terminal of the main switch And comprising.

  According to the above configuration, the power consumption of the main switch, which is a semiconductor switch capable of flowing current in both directions, is switched by the sub switch according to the operation state of the main switch, thereby reducing the power consumption compared to the prior art. And can be used by connecting to a larger load.

Circuit diagram of a two-wire AC switch according to an embodiment of the present invention Sectional drawing which shows structure of bidirectional switch 3 Timing chart showing the operation of the two-wire AC switch of FIG. The figure which shows the characteristic of bidirectional switch 3 Timing chart showing a modification of the embodiment of the present invention The circuit diagram which shows the modification of embodiment of this invention The circuit diagram which shows the modification of embodiment of this invention The circuit diagram which shows the modification of embodiment of this invention Conceptual diagram of FIGS. 1 and 7 Conceptual diagram of FIGS. 6 and 8 The circuit diagram which shows the modification of embodiment of this invention Timing chart showing the operation of the two-wire AC switch of FIG. Timing chart showing a modification of the embodiment of the present invention Circuit diagram of conventional 2-wire AC switch

Hereinafter, embodiments of the two-wire AC switch of the present invention will be described with reference to the drawings.
<Circuit configuration>
FIG. 1 is a circuit diagram of a two-wire AC switch according to an embodiment of the present invention. The two-wire AC switch 10 is an AC switch inserted in an electric circuit connecting a commercial AC power source 1 and a load 2 such as a lighting fixture, and includes a bidirectional switch 3, a full-wave rectifier 4, a power circuit 5, A first gate drive circuit 7, a second gate drive circuit 8, a control circuit 6, and a semiconductor switch 9 are provided.

In this embodiment, the semiconductor switch 9 is inserted in an electric circuit connecting the Sub terminal and the ground terminal. Regarding the circuit configuration, the other points are the same as in FIG.
The semiconductor switch 9 is a sub-switch for switching whether the Sub terminal of the bidirectional switch 3 as the main switch is grounded or floating. When the semiconductor switch 9 is on, the Sub terminal of the bidirectional switch 3 is grounded, and when it is off, the Sub terminal of the bidirectional switch 3 is floating. Here, the term “floating” includes grounding through a high resistance of about several hundred MΩ to several thousand MΩ. In this embodiment, a field effect transistor is employed as an example of the semiconductor switch.

<Bidirectional switch structure>
FIG. 2 is a sectional view showing the structure of the bidirectional switch 3. As shown in FIG. 2, the bidirectional switch 3 includes a buffer layer 127 having a thickness of about 1 μm formed on a conductive silicon (Si) substrate 126 and a semiconductor stacked layer formed on the buffer layer 127. Body (first semiconductor layer 128 and second semiconductor layer 129). The buffer layer 127 is made of aluminum nitride (AlN) having a thickness of about 10 nm and gallium nitride (GaN) having a thickness of about 10 nm, which are alternately stacked. The semiconductor stacked body includes a first semiconductor layer 128 and a second semiconductor layer 129 having a band gap larger than that of the first semiconductor layer 128, which are sequentially stacked from the substrate 126 side. In the present embodiment, the first semiconductor layer 128 is an undoped gallium nitride (GaN) layer having a thickness of about 2 μm. The second semiconductor layer 129 is an n-type aluminum gallium nitride (AlGaN) layer having a thickness of about 20 nm. This realizes a bidirectional switch with extremely low on-resistance.

In the vicinity of the heterointerface between the first semiconductor layer 128 made of GaN and the second semiconductor layer 129 made of AlGaN, charges are generated due to spontaneous polarization and piezoelectric polarization. Thereby, a channel region which is a two-dimensional electron gas (2DEG) layer having a sheet carrier concentration of 1 × 10 ¹³ cm ⁻² or more and a mobility of 1000 cm ² V / sec or more is generated.
A first ohmic electrode 123A and a second ohmic electrode 123B are formed on the semiconductor stacked body, that is, on the first semiconductor layer 128 and the second semiconductor layer 129, spaced apart from each other. Yes. In each of the first ohmic electrode 123A and the second ohmic electrode 123B, titanium (Ti) and aluminum (Al) are stacked, and are in ohmic contact with the above-described channel region. In FIG. 2, in order to reduce the contact resistance, a part of the second semiconductor layer 129 is removed and the first semiconductor layer 128 is dug down by about 40 nm so that the first ohmic electrode 123A and the second ohmic electrode are removed. An example is shown in which 123B is formed so as to be in contact with the interface between the first semiconductor layer 128 and the second semiconductor layer 129. Note that the first ohmic electrode 123 </ b> A and the second ohmic electrode 123 </ b> B may be formed over the second semiconductor layer 129.

  A first ohmic electrode wiring 122A made of Au and Ti is formed on the first ohmic electrode 123A, and is electrically connected to the first ohmic electrode 123A. Similarly, a second ohmic electrode wiring 122B made of Au and Ti is formed on the second ohmic electrode 123B, and is electrically connected to the second ohmic electrode 123B.

  In the region between the first ohmic electrode 123A and the second ohmic electrode 123B on the second semiconductor layer 129, the first p-type semiconductor layer 125A constituting the double gate of the bidirectional switch 103 and The second p-type semiconductor layer 125B is formed at a distance from each other. A first gate electrode 124A is formed on the first p-type semiconductor layer 125A, and a second gate electrode 124B is formed on the second p-type semiconductor layer 125B. Each of the first gate electrode 124A and the second gate electrode 124B is made of a stacked body of palladium (Pd) and gold (Au), and the first p-type semiconductor layer 125A and the second p-type semiconductor layer. It is in ohmic contact with 125B.

  The first ohmic electrode wiring 122A, the first ohmic electrode 123A, the second semiconductor layer 129, the first p-type semiconductor layer 125A, the first gate electrode 124A, the second p-type semiconductor layer 125B, the second A protective film 130 made of silicon nitride (SiN) is formed so as to cover the gate electrode 124B, the second ohmic electrode 123B, and the second ohmic electrode wiring 122B.

On the back surface of the silicon substrate 126, a back electrode 131 having a thickness of about 800 nm in which nickel (Ni), chromium (Cr), and silver (Ag) are stacked is formed. The back electrode 131 is in ohmic contact with the silicon substrate 126. It is joined.
The first p-type semiconductor layer 125A and the second p-type semiconductor layer 125B each have a thickness of about 300 nm and are made of p-type GaN doped with magnesium (Mg). The first p-type semiconductor layer 125A, the second p-type semiconductor layer 125B, and the second semiconductor layer 129 form pn junctions. As a result, when the voltage between the first ohmic electrode 123A and the first gate electrode 124A is, for example, 0 V or less, a depletion layer spreads from the first p-type semiconductor layer 125A into the channel region. It is possible to cut off the current flowing through the. Similarly, when the voltage between the second ohmic electrode 123B and the second gate electrode 124B is, for example, 0 V or less, a depletion layer spreads from the second p-type semiconductor layer 125B into the channel region. The current flowing through the channel can be cut off. Therefore, it is possible to realize a double-gate switching element that performs a so-called normally-off operation. Further, the distance between the first p-type semiconductor layer 125A and the second p-type semiconductor layer 125B can withstand the maximum voltage applied to the first ohmic electrode 123A and the second ohmic electrode 123B. design.

  Note that the terminal S1 connected to the first ohmic electrode 123A, the terminal G1 connected to the first gate electrode 124A, the terminal G2 connected to the second gate electrode 124B, and the second ohmic electrode 123B are connected. The terminal S2 corresponds to the switch terminal S1, the gate terminal G1, the gate terminal G2, and the switch terminal S2 of FIG. Further, the terminal Sub connected to the back electrode 131 corresponds to the substrate terminal Sub in FIG.

<Operation>
FIG. 3 is a timing chart showing the operation of the two-wire AC switch of FIG. In FIG. 3, VAC is the voltage of the commercial AC power supply 1, VS2S1 is a voltage between the switch terminals of the bidirectional switch 3, IS2S1 is a current flowing between the switch terminals of the bidirectional switch 3, and VG1 is a gate terminal G1 of the bidirectional switch 3. , VG 2 is a control signal input to the gate terminal G 2 of the bidirectional switch 3, and Sub terminal connection changeover switch signal is a control signal input to the gate terminal of the semiconductor switch 9. In the present embodiment, the power supplied from the commercial AC power supply 1 to the load 2 is adjusted by phase control. The reason why the control signals VG1 and VG2 repeat pulses in FIG. 3 is because the phase is controlled.

  In the timing chart shown in FIG. 3, the control circuit 6 is connected to the semiconductor switch 9 while the repetitive pulse is applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3 (while the bidirectional switch 3 is in the ON state). Control is performed so that the Sub terminal is grounded by applying an ON signal. On the other hand, while the repetitive pulse is not applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3 (while the bidirectional switch 3 is in the OFF state), the control circuit 6 applies the OFF signal to the semiconductor switch 9 and applies the Sub terminal. Is controlled to float.

<Effect>
As shown in FIG. 4, when the bidirectional switch 3 is used with the Sub terminal in a floating state, the on-resistance becomes large, and the power consumption increases when the bidirectional switch is on. Further, when the Sub terminal is grounded, the on-resistance can be reduced. However, since a leakage current flows from the gate terminal G1, the gate terminal G2, the switch terminal S1, and the switch terminal S2 to the Sub terminal, the bidirectional switch The leakage current when the switch 3 is turned off increases, and the power consumption when the bidirectional switch 3 is turned off increases.

  In this embodiment, by switching on / off of the semiconductor switch 9 according to the on / off state of the bidirectional switch 3, the Sub terminal is grounded when the bidirectional switch 3 is on, and when the bidirectional switch 3 is off. Can float the Sub terminal. As a result, the on-resistance can be reduced when the bidirectional switch 3 is on, and the leakage current can be reduced when the bidirectional switch 3 is off. Therefore, the power consumption of the bidirectional switch 3 and thus the power consumption of the two-wire AC switch 10 can be reduced. Further, since the Sub terminal is floated when the bidirectional switch 3 is off, the bidirectional switch 3 can be protected against a surge from the Sub terminal.

In recent years, in order to overcome the material limit and reduce conduction loss, the introduction of semiconductor elements using a wide gap semiconductor such as a group III nitride semiconductor represented by GaN or silicon carbide (SiC) has been studied. Yes. A wide gap semiconductor has a dielectric breakdown electric field about an order of magnitude higher than that of silicon (Si). Electric charges are generated at the heterojunction interface between aluminum gallium nitride (AlGaN) and gallium nitride (GaN) due to spontaneous polarization and piezoelectric polarization. As a result, a two-dimensional electron gas (2DEG) layer having a sheet carrier concentration of 1 × 10 ¹³ cm ⁻² or more and a high mobility of 1000 cm ² V / sec or more is formed even when undoped. For this reason, the AlGaN / GaN heterojunction field effect transistor (AlGaN / GaN-HFET) is expected as a power switching transistor that realizes low on-resistance and high breakdown voltage.

  In particular, a bidirectional switch can be formed with one semiconductor element by using a structure having two gate electrodes using an AlGaN / GaN heterojunction. The bidirectional switch having this structure is equivalent in circuit to two transistors connected in series in opposite directions, and can be reduced in on-resistance compared to the conventional triac, and the first ohmic electrode side Both the current flowing from the second ohmic electrode side to the second ohmic electrode side and the current flowing from the second ohmic electrode side to the first ohmic electrode side can be controlled. Therefore, a bidirectional switch composed of a group III nitride semiconductor and having two gate electrodes can be a triac simple substance, a power MOSFET (metal oxide semiconductor field effect transistor), or an IGBT (insulated gate bipolar transistor). It has been attracting attention as an element that can be reduced in size and save power as compared with a conventional bidirectional switch in which a plurality of power transistors are combined.

In this embodiment, since the bidirectional switch composed of such a group III nitride semiconductor is employed, a small-sized and power-saving two-wire AC switch can be realized.
<Modification>
(1) Control In the above embodiment, the semiconductor switch 9 is switched on and off depending on whether or not a repetitive pulse is applied to the gate terminals G1 and G2 of the bidirectional switch 3. However, the present invention is not limited to this. When a pulse is repeatedly applied to the gate terminals G1 and G2 of the bidirectional switch 3, it can be said that the bidirectional switch 3 is in an on state because electric power is supplied to the load 2, but microscopically both The direction switch 3 is repeatedly turned on and off. Therefore, as shown in FIG. 5, the semiconductor switch 9 may be turned on / off in accordance with the on / off of the bidirectional switch 3.

  In the timing chart shown in FIG. 5, while the ON signal is applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3, the control circuit 6 applies the ON signal to the semiconductor switch 9 so that the Sub terminal is grounded. Is controlling. On the other hand, while the off signal is applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3, the control circuit 6 applies the off signal to the semiconductor switch 9 to control the Sub terminal to be in a floating state.

(2) Grounding via a resistor In the above embodiment, the Sub terminal of the bidirectional switch 3 is grounded without a resistor, but the present invention is not limited to this. In the two-wire AC switch 10 a shown in FIG. 6, a resistor 12 is inserted in series with the semiconductor switch 9 in the electric path connecting the Sub terminal and the ground terminal of the bidirectional switch 3. The resistance value of the resistor 12 is about several tens of Ω to several MΩ. When the Sub terminal is grounded, the on-resistance decreases, but the leakage current may increase. As shown in FIG. 6, it is possible to balance both by using a ground via a resistor. Note that either the operation shown in FIG. 3 or FIG. 5 may be adopted for the operation.

(3) Type of switch Although the semiconductor switch is employed in the above embodiment, the present invention is not limited to this. The two-wire AC switches 10b and 10c shown in FIGS. 7 and 8 employ a mechanical relay 13 instead of the semiconductor switch 9. 9 is a conceptual diagram of FIGS. 1 and 7, and FIG. 10 is a conceptual diagram of FIGS. 6 and 8. Here, the switch 14 is inserted in the electric circuit connecting the Sub terminal and the ground terminal.

(4) Switching of three states In the above embodiment, the Sub terminal of the bidirectional switch 3 is switched between two states of floating and ground, but the present invention is not limited to this. In the two-wire AC switch 10f shown in FIG. 11, a switch 15 that can select one of the following three states (a) to (c) is inserted in the electric path connecting the Sub terminal and the ground terminal of the bidirectional switch 3. Has been.

(A) Sub terminal is floating (b) Sub terminal is grounded via a resistor (c) Sub terminal is grounded not via a resistor FIG. 12 is a timing chart showing the operation of the two-wire AC switch of FIG. . In the timing chart shown in FIG. 12, while the repetitive pulse is applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3 (while the bidirectional switch 3 is on), the control circuit 6 is connected to the semiconductor switch 9. Control is performed so that the Sub terminal is grounded by applying an ON signal. However, from the time when the bidirectional switch 3 is turned on until the predetermined period elapses, the Sub terminal is grounded without a resistor, and when the predetermined period elapses, the Sub terminal is grounded via the resistor 12. . On the other hand, while the repetitive pulse is not applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3 (while the bidirectional switch 3 is in the OFF state), the control circuit 6 applies the OFF signal to the semiconductor switch 9 and applies the Sub terminal. Is controlled to float. The length of the predetermined period is determined in advance according to the type of load.

(5) Switching timing In the above embodiment, the timing at which the bidirectional switch 3 is switched from OFF to ON coincides with the timing at which the Sub terminal of the bidirectional switch 3 is switched from floating to ground. Not limited to.
FIG. 13 is a diagram showing detailed timings of a control signal applied to the gate terminal G1 and the gate terminal G2 of the bidirectional switch 3 and a control signal applied to the semiconductor switch 9 connected in series to the Sub terminal. In the operation of FIG. 13, when the bidirectional switch 3 is switched from OFF to ON (the two-wire AC switch is turned ON), the Sub terminal is switched to the Sub terminal at a timing earlier than the control signal applied to the gate terminal G1 and the gate terminal G2. An ON signal is applied to the semiconductor switches 9 connected in series. As a result, the on-resistance of the bidirectional switch 3 can be further reduced, and a large current can flow through the load.

(6) Others Although the two-wire AC switch according to the present invention has been described above using the embodiments and modifications thereof, the present invention is not limited to these embodiments and modifications. . Without departing from the spirit of the present invention, these embodiments and modifications can be obtained by various modifications conceived by those skilled in the art, and any combination of these embodiments and modifications can be obtained. Forms that can be used are also included in the present invention.

  For example, in the above embodiment, the bidirectional switch 3 has a normally-off gate electrode formed on the p-type semiconductor layer (the first p-type semiconductor layer 125A and the second p-type semiconductor layer 125B). It was a double gate semiconductor device of the type. However, the gate of the bidirectional switch according to the present invention is not limited to such a structure. For example, normally-off characteristics may be realized by forming a gate recess or reducing the thickness of the second semiconductor layer 129.

Further, as the gate structure of the bidirectional switch according to the present invention, an insulating layer is provided in place of the p-type semiconductor under the gate electrode to form an insulating gate, or the gate is not provided with the p-type semiconductor under the gate electrode. A junction-type gate in which the electrode and the semiconductor stacked body are in Schottky junction may be used.
Further, depending on the circuit configuration, the bidirectional switch 3 can be realized as a normally-on double gate semiconductor element.

  Moreover, although the example which is a silicon substrate about the board | substrate of the bidirectional switch 3 was shown, this invention is not limited to a silicon substrate. Any substrate that can form a nitride semiconductor may be used, and a silicon carbide (SiC) substrate, a sapphire substrate, or another substrate may be used instead of the Si substrate.

  The two-wire AC switch according to the present invention is useful, for example, as a two-wire AC switch for controlling a house lighting lamp or a ventilation fan having a dimming function.

DESCRIPTION OF SYMBOLS 1 Commercial AC power supply 2 Load 3 Bidirectional switch 4 Full wave rectifier 5 Power supply circuit 6 Control circuit 7 Gate drive circuit 8 Gate drive circuit 9 Semiconductor switch 10, 10a, 10b, 10c, 10d, 10e, 10f Two-wire AC switch 11 External setting unit 12 Resistor 13 Relay 14 Switch 15 Switch 103 Bidirectional switch 122A, 122B Ohmic electrode wiring 123A, 123B Ohmic electrode 124A, 124B Gate electrode 125A, 125B P-type semiconductor layer 126 Substrate 127 Buffer layer 128 First semiconductor layer 129 Second semiconductor layer 130 Protective film 131 Back electrode

Claims (15)

A two-wire AC switch inserted in an electric circuit connecting an AC power source and a load,
The first and second switch terminals, first and second gate terminals for controlling on / off between the first and second switch terminals, and a substrate terminal, and the first and second switch terminals. A main switch composed of a semiconductor switch in which a current can flow in both directions between the switch terminals, the first switch terminal is connected to the AC power supply, and the second switch terminal is connected to the load;
A sub switch that switches between grounding or floating the board terminal of the main switch;
2-wire AC switch.   2. The control circuit according to claim 1, further comprising: a control circuit that controls the sub switch so that the board terminal is floated when the main switch is off and the board terminal is grounded when the main switch is on. The two-wire AC switch described. The grounding of the substrate terminal can be selected between grounding via a resistance element and grounding not via a resistance element,
The control circuit includes:
The grounding not through the resistance element is selected until a predetermined period elapses after the main switch is turned on, and the grounding through the resistance element is selected when the predetermined period elapses. A two-wire AC switch described in 1.   2. The two-wire AC switch according to claim 1, further comprising a control circuit that controls the sub switch so that the state of the substrate terminal is switched from floating to ground before the main switch is switched from OFF to ON.   The two-wire AC switch according to claim 1, wherein the main switch is a normally-off type switch.   The two-wire AC switch according to claim 1, wherein the main switch is a normally-on type switch. The main switch is
A substrate,
A semiconductor laminate formed on the substrate and composed of a group III nitride semiconductor;
First and second ohmic electrodes formed on the semiconductor laminate and constituting the first and second switch terminals, respectively.
The first and second gate terminals are formed in order from the first ohmic electrode side between the first and second ohmic electrodes on the semiconductor stacked body and constitute the first and second gate terminals, respectively. Two gate electrodes;
A substrate electrode that is formed on the substrate opposite to the first and second gate electrodes and constitutes the substrate terminal;
A two-wire AC switch according to claim 1, comprising: The main switch further includes:
A first semiconductor layer formed between the first gate electrode and the semiconductor stacked body and forming a pn junction with the semiconductor stacked body;
A second semiconductor layer formed between the second gate electrode and the semiconductor stacked body and forming a pn junction with the semiconductor stacked body;
A two-wire AC switch according to claim 7.   The two-wire AC switch according to claim 7, wherein the first and second gate electrodes are electrodes for insulated gates.   The two-wire AC switch according to claim 7, wherein the first and second gate electrodes form a Schottky junction with the semiconductor stacked body. The main switch further includes:
The two-wire AC switch according to claim 7, further comprising a gate made of a p-type group III nitride semiconductor in ohmic contact with each of the first and second gate electrodes.   The two-wire AC switch according to claim 7, wherein the substrate is a silicon substrate.   The two-wire AC switch according to claim 7, wherein the substrate is a silicon carbide substrate.   The two-wire AC switch according to claim 7, wherein the substrate is a sapphire substrate. The AC power source is a commercial AC power source,
The load is a lighting fixture;
The two-wire AC switch according to claim 1.

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