Directly light-fired thyristors with high di/dt capability

A 1200V 100A directly light triggered thyristor suitable for invertor application has been developed. A new amplifying gate design with a second amplifying stage was used in achieving a factor of 50 increase in gate sensitivity without any loss in dV/dt capability and only a small (less than a factor of two) reduction in device di/dt rating, despite a ten times smaller initial turn-on line length. In all, three versions were made with gate threshold currents down to 2ma and dV/dt capabilities to 1000V/µ second. All three types had 60Hz di/dt capabilities of about 250A/µsecond at 125° TJand turn-off times of approximately 25µ seconds. The new light sensitive amplifying gate stage design features a gate thyristor region with extending arms for high gate sensitivity, the inner portion of which is only large enough to accomodate initial on-region spreading during the short on time of the gate stage. The arms increase gate sensitivity while contributing very little to the overall dV/dt current. The turn-on speed can be accounted for by most of the inner region being turned on by the photo-gate pulse. Like regular electrically fired thyristors, a gate over-drive factor is important. With these devices an over-drive factor of about 10 is needed for high di/dt turn-on.