US Patent 7173290 Thyristor switch with turn-off current shunt, and operating method

A semiconductor switch includes a thyristor and a current shunt, preferably a transistor in parallel with and controlled by the thyristor, which shunts thyristor current at turn-off. The thyristor includes a portion of a bottom drift layer, with a p-n junction formed below a gate adjacent to the bottom drift layer to establish a depletion region with a high potential barrier to thyristor current flow at turn-off. The bottom drift layer also provides the transistor base, as well as a current path allowing the transistor base current to be controlled by the thyristor. The switch is voltage-controlled device using an insulated gate for turn-on and turn-off.