Theoretical and experimental comparison of light triggered and electrically triggered thyristor turn-on

As part of an EPRI funded reserach program on a directly light triggered thyristor for HVDC application, an existing 53mm, 2600V, 1000A electrically fired device was suitably modified to be turned on with an incident photopulse of 20nj, the basic problem being the retension of a 2000 volt per microsecond dV/dt capability. The price paid for high sensitivity and high dV/dt capability was found to be a device inherently more susceptible to di/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.