Totally light controlled switch and new means for electrical turn-off of thyristors

Due to the development of thyristors with turn-off times below 10µs it has become possible to use an antiparallel diode for turn-off, After "charging" the diode to a high carrier concentration by irradiation of infrared light or by a forward biased current puls, it can carry the load current at nearly zero voltage drop. If this period lasts for a time of at least one turn-off time, the thyristor switches off. The following completion of the diode recovery process causes a moderate rate of rise of the blocking voltage. "Charging" of the diode by light irradiation is more elegant, but the requirement to use high power laser may be prohibitive. "Charging" by a current puls on the other hand has proofed to allow for a less expensive turn-off circuit compared to the usual forced commutation arrangement.