Having played a central role in the modernization of power electronics in the 1960s, large-capacity thyristors are now handling higher voltages and currents. They evolved from the reverse-blocking thyristors with no self arc extinction capability to the self arc extinction type GTO (Gate Turn Off) thyristors that switch from on to off when negative current is applied to the gate, even in a DC circuit. However, as this requires a drive circuit whose negative current has to be a fifth of the main current, we tried to achieve faster operation by developing the GCT (Gate Commutated Turn-off) thyristor that brings low impedance to the GTO's gate.
