Experimental determination of turn-off time of high-voltage power thyristors

Silicon power thyristors were studied to determine the dependence of their turn-off time on the repetitive reverse voltage, on the rate of decrease of the forward current and on the lifetime of holes. Three groups of thyristors were tested corresponding to T630, T173-1250, T353-800 four-layer devices rated for 2400 to 2800 V, 2600 to 2800 V, 2800 to 3200 V respectively. The data are evaluated and the dynamics of charge buildup and dissipation during reversals of anode voltage polarity are considered. Significant differences in turn-off characteristics between the three groups of thyristors are shown. It decrease in the life of holes for minimum turn-off time and thus maximum switching speed involves a tradeoff with a higher blocking-state pulse voltage and larger leakage currents is indicated.