Thyristors with overvoltage self-protection

Power thyristors which are immune to destructive triggering by overvoltage transients have been designed, fabricated, and tested. A 10- mil deep well was etched in the gate region prior to the final p-type diffusion. This modified the forward blocking junction so that it avalanched at 2800V. The avalanche current provided a gate signal which turned on the thyristor and avoided destructive edge firing. Measurements of the infrared recombination radiation verified that overvoltage turn-on occurred at the gate region. With overvoltage triggering,the thyristors withstood follow-on currents of 40A from snubber discharges. Standard thyristors with no self-protection were destroyed by 0.5A. The self-protected thyristors were light-triggered devices with VRRM= 2800V and IDRM= 900A. Incorporation of the overvoltage self-protection feature increases device reliability and eliminates the need for overrating of blocking voltages to allow for transients.