The characterisation of snubber diodes for use with high voltage GTO thyristors

In a GTO (gate turn-off) thyristor the rate of rise of reapplied voltage during turn-off is limited by a snubber capacitor to avoid a refire. The capacitor stored energy is dissipated during turn-on by a resistor, which is then `shorted´ out by a snubber diode during turn-off. Thus during normal GTO operation the snubber diode is subjected to a successive sequence of forward and reverse voltage bias. The reverse bias results in reverse current being drawn through the diode as the stored charge accumulated during the on-state is extracted. The author characterises various snubber diodes for use in the protection of HV GTO-thyristors