Turn-off failures in individual and paralleled MCT's

A turn-off failure mode in individual MOS-controlled thyristors (MCTs), initiated by a long gate voltage rise-time, is identified and analyzed. It is shown to be caused by turn-off current crowding in the MCT. In addition, a differential failure mode in paralleled devices is demonstrated in which the slower of the two MCTs fails to turn off. This is caused by the increase in anode current through the slower device and the decrease in gate voltage rise-time due to the MCTs Miller capacitance.