Abstract: A semiconductor switch is provided with a main element having reverse conductivity and serving as a voltage-driven switching element having a high withstand voltage, an auxiliary element serving as a voltage-driven switching element having a withstand voltage lower than that of the main element, and a high-speed freewheel diode having a withstand voltage equal to that of the main element, wherein a negative pole of the main element is connected to a negative pole of the auxiliary element to define the positive pole of the main element as a positive pole terminal and the positive pole of the auxiliary element as a negative pole terminal, and the high-speed freewheel diode is parallel-connected between the positive pole terminal and the negative pole terminal so that a direction from the negative pole terminal toward the positive pole terminal constitutes a forward direction.

Abstract: An electric power conversion system includes a DC power supply, plural main circuit switching devices bridge-connected to carry out DC/AC convert, having freewheeling diodes connected in reverse parallel thereto, respectively, and a reverse voltage application circuit for applying a reverse voltage smaller than the DC power supply to each freewheeling diode, upon a cutoff of back-flow current of the freewheeling diode, the reverse voltage application circuit being composed of a series connection of a low-voltage DC power supply, a reverse voltage application switching device having a lower withstand voltage than the main circuit switching devices and adapted to turn on upon a reverse recovery of the freewheeling diode, and an auxiliary diode having a shorter reverse recovery time than the freewheeling diode, the reverse voltage application switch being a device having holes as a majority carrier.

Abstract: A semiconductor switch is provided with a main element having reverse conductivity and serving as a voltage-driven switching element having a high withstand voltage, an auxiliary element serving as a voltage-driven switching element having a withstand voltage lower than that of the main element, and a high-speed freewheel diode having a withstand voltage equal to that of the main element, wherein a negative pole of the main element is connected to a negative pole of the auxiliary element to define the positive pole of the main element as a positive pole terminal and the positive pole of the auxiliary element as a negative pole terminal, and the high-speed freewheel diode is parallel-connected between the positive pole terminal and the negative pole terminal so that a direction from the negative pole terminal toward the positive pole terminal constitutes a forward direction.

Abstract: There are provided: sets of pairs of main circuit switching elements (4u), (4x) that supply power to a load, connected in series with a DC power source; free-wheel diodes (5u), (5x) connected in anti-parallel with these main circuit switching elements; and a reverse voltage application circuit (8) that applies reverse voltage smaller than the DC voltage source to the free-wheel diodes when these free-wheel diodes cut off. The reverse voltage application circuit includes a current suppression circuit (10) that suppresses the main circuit current flowing in the low-voltage DC voltage power source on reverse recovery of the free-wheel diodes.

Abstract: An electric power conversion system including a direct current power supply, plural main circuit switching devices bridge-connected to convert the direct current to alternating current, including free wheeling diodes connected in reverse parallel thereto, respectively, and a reverse voltage application circuit applying a reverse voltage smaller than the direct current power supply to each free wheeling diode, upon cutoff of back-flow current of the free wheeling diode. The reverse voltage application circuit includes in series connection a low-voltage direct current power supply having a voltage lower than the direct current power supply, a reverse voltage application switching device having holes as a majority current and a lower withstand voltage than the main circuit switching devices and adapted to turn on upon reverse recovery of the free wheeling diode, and an auxiliary diode having a shorter reverse recovery time than the free wheeling diode.

Abstract: There are provided: sets of pairs of main circuit switching elements (4u), (4x) that supply power to a load, connected in series with a DC power source; free-wheel diodes (5u), (5x) connected in anti-parallel with these main circuit switching elements; and a reverse voltage application circuit (8) that applies reverse voltage smaller than the DC voltage source to the free-wheel diodes when these free-wheel diodes cut off. The reverse voltage application circuit includes a current suppression circuit (10) that suppresses the main circuit current flowing in the low-voltage DC voltage power source on reverse recovery of the free-wheel diodes.

Abstract: A gate control circuit for turning on and off an insulated gate semiconductor device having gate, emitter and collector terminals, including a first DC power source coupled to the gate terminal via a first switch and configured to apply a positive voltage to the gate terminal in order to turn on the insulated gate semiconductor device when the first switch is turned on and the second switch is turned off; a second DC power source coupled to the gate terminal via a second switch and configured to apply a negative voltage to the gate terminal in order to turn off the insulated gate semiconductor device when the second switch is turned on and the first switch is turned off; a parallel circuit of a diode and a capacitor coupled in series to the second switch; and a turn off assist circuit configured to produce a negative charge on the capacitor to assist in turning off the insulated gate semiconductor device.