Novel gate concept improves performance of light fired thyristor

A high voltage pilot-thyristor (4000 V) with amplifying gate, exhibiting light sensitivities of 1...2 mW under worst case condition is discussed. Since it must deliver large narrow base width pulses (e.g.50 A, 1...5 µs), differential turn-on delay between the two stages must be minimized. As shown by an infra-red recombination experiment, low enough a turn-on ratio is required. This can be achieved by a locally diffused p-base structure designed such as to yield a good ratio of light triggering level to dV/dt in addition. Initial tests in the power circuit of a broadcast transmitter have been highly successful.