A study on maximum turn-off current of a high-power GTO

A 6 kV, 6 kA pnpn-type GTO was fabricated and its maximum turn-off current was investigated. Simulation uses three-segment device model together with an equivalent circuit model. Results of simulations with segments having di fferent on-state voltages showed current concentration to the lower on-stat e voltage segment in the fall period. By introducing a homogeneous fabricat ion process, the on-state voltage distribution band was decreased by a fact or of 2, The circuit model simulation results showed the maximum peak curre nt of the improved GTO with smaller on-state voltage band was reduced by a factor of 1.33 compared to that of the conventional GTO, A high-power GTO t urn-off limiting model was proposed from the measured 6 kA GTO turn-off loc us and the segment SOA's, This turn-off limiting model showed that the GTO would be destroyed when the segment current exceeds the SOA at the time a s pike voltage occurs in the fall period. it was demonstrated that the maximu m turn-off current estimated by this limiting model coincided well with the experimental results.