Inverter light triggered thyristor with unique arm-structure amplifying gate

A 1200-V 200-A directly light triggered thyristor suitable for inverter application has been developed. A new amplifying gate design with a second amplifying stage was used in achieving a factor of 15 to 50 increase in gate sensitivity without any loss in capability and only a small (less than a factor of two) reduction in device rating, despite a ten times smaller initial turn-on line length. In all, three versions were made with gate threshold currents down to 1 mA and capabilities to 1000 V/µs. All three types had 60-Hz di/dt capabilitLes of about 250 A/µs at 125 deg TJand turn-off times of approximately 25 µs. 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 just large enough to accommodate initial on-region spreading duriag the short on-time of the gate stage. The arms increase gate sensitivity while contributing very little to the overall current. The turn-on speed can be accounted for by most of the inner region being turned on by the photogate pulse. Like regular electrically fired thyristors, a gate overdrive factor is important. With these devices an overdrive factor of about 3 to 5 is needed for high turn-on whereas in an electrically triggered device this factor is closer to 10.