Comparison of light triggered and electrically triggered thyristor turn-on

As part of an EPRI (Electric Power Research Institute) funded research program on a directly light triggered (LT) thyristor for HV dc application, an existing 53-mm 2600-V 1000-A electrically fired device was suitably modified to be turned on with an incident photo-pulse of 20 nJ, the basic problem being the retention of a 2000 V/µs dV/dt capability. The price paid for high sensitivity and high dV/dt capability was found to be a device inherently more susceptible to dV/dt failure. In the efforts to cope with this problem a number of computer-type models were developed to assist in predicting turn-on in both electrically and light fired devices with one or more amplifying stages. At the same time, devices were fabricated which could be either light or electrically fired. Both the model and experiment point to faster turn-on of the light fired device and an increased requirement for careful design.