Characterizing the turn-off performance of multi-cathode GTO thyristors using thermal imaging

The thermal imaging of a switching gate-turn-off thyristor (GTO) is described. Using this method, the extent of redistribution occurring at turn-off under various gate drive and anode circuit conditions is determined. The effect of redistribution on the device rating and performance is discussed. Any redistribution in the current will be accompanied by an increase in the losses in the region to turn off last, and a reduction in the losses elsewhere. The experimental procedure for making the switching losses dominant is described. Results show that, under certain gate drive and anode-cathode voltage conditions at turn-off, the anode current redistributes between cathode islands, greatly stressing some islands. From this, conclusions are made concerning GTO rating and circuit design