Abstract: A gate circuit for a thyristor is disclosed which includes a power supply for feeding gate-on current through a gate and cathode of the thyristor, a switching circuit connected in series with the power supply to turn the gate-on current on or off, and a diode connected between a gate ignition signal input terminal of said switching circuit and the anode of said thyristor with the cathode of said diode being coupled to said anode of said thyristor and the anode of said diode coupled to said switching circuit.

Abstract: A gate circuit for use with a gate turn-off thyristor comprises a capacitor to be charged by a power source supplying a gate turn-on current. The capacitor is connected in series with a power source supplying a gate turn-off current.

Abstract: A gate circuit for a gate turn-off (GTO) thyristor comprises current supply means for supplying a turn-off current to the GTO thyristor, and energy storing means for storing energy by receiving a current from the current supply means and supplying the stored energy to the GTO thyristor as the turn-on current therefor.

Abstract: The positive terminal of a series circuit consisting of two capacitors is connected with the cathode of a field controlled thyristor through a resistor and a transistor and the negative terminal thereof is connected with the gate of the field controlled thyristor. The junction of the series circuit is connected with the cathode of the field controlled thyristor through a thyristor. Each capacitor is charge by d.c. current. When the field controlled thyristor is intended to be turned off, the thyristor and the transistor are first made conductive and then the one capacitor is discharged through the thyristor. As a result, the field controlled thyristor is turned off. After the turn-off of the field controlled thyristor, the voltage of the other capacitor is applied to the gate of the field controlled thyristor to hold it in the blocking state.

Abstract: A noise control device which produces behind it an enlarged sound reducing region is disclosed. The device comprises a hollow structural body composed of a plurality of elongate hollow passages which are different in length and constructed such that the passage length is made the longest at a substantially center part in a vertical direction and is made gradually shorter from the center part toward upper and lower edges of the hollow structural body. The upper and lower edges allow direct propagation sound emitted from a noise source to pass thereover and therethrough.