Patent ID: 7009828

Claim:
A semiconductor switching device comprising: self-quenching semiconductor switching elements connected in series, and snubber circuits connected in parallel to respective semiconductor switching elements, each snubber circuit comprising a diode and a capacitor connected in series, and a non-linear circuit connected in parallel with the capacitor, said non-linear circuit drawing current when an applied voltage exceeds a clamp voltage, wherein the clamp voltage is at least 1.27 times larger than a divided voltage normally applied to each of the semiconductor elements, and which is larger than a divided voltage applied to one of the semiconductor elements during a fault in a power system, wherein the non-linear circuit comprises an impedance element and at least one non-linear unit, each non-linear unit comprising a Zener diode having a cathode, an anode, and a Zener voltage, a resistor, and a controlling semiconductor element having a collector, an emitter, and a gate, the impedance element, the Zener diode, and the resistor are connected in series, the cathode and the anode of the Zener diode are connected to the collector and the gate of the controlling semiconductor element, respectively, the resistor is connected between the gate the emitter of the controlling semiconductor element, and the clamp voltage is a sum of the Zener voltages of each of the Zener diodes, and one of (i) impedance of the impedance element and (ii) number of the controlling semiconductor elements is adjusted so that loss in the controlling semiconductor element due to a current flowing through the controlling semiconductor element when the divided voltage applied to the semiconductor switching element due to a fault in a power system exceeds the clamp voltage, does not exceed power dissipation capacity of the controlling semiconductor element.