A New Physical Model for Calculating Storage

In this paper, we propose a new two-dimensional analytical model, developed from first principles, to substantiate, for the first time, the dependence of storage time on the nature of the gate current ramp, anode current, and device geometry, as observed in our and other experimental studies on single-element gate turn-off thyristors (GTO's). Our model originates in the solution of the continuity equation in the p base for evaluation of the plasma squeezing rate. It addresses realistic issues such as high injection effects, variation in the base transport factors, and the physical basis for the minimum ON region dimension that are not considered in any previous treatment. I. INTRODUCTION ATE turn-off thyristors (GTO's) have assumed a very sig- G nificant status in high-power switching applications, in large part due to their capability of turning off large currents with a gate signal. Very briefly, for turn-off, a negative voltage pulse is applied to the gate terminal, causing a current ramp, arising from the gate circuit inductance. This leads to a progressive shrinking of the conduction region plasma that continues until the end of the storage time (l). The anode current remains practically unchanged in this time since part of the cathode junction is still in forward bias and the impedance of the GTO is small compared with the load. This is followed by the fall time during which the center junction of the p-n-p-n structure recov- ers, causing the anode current to drop to practically zero.