A measurement technique and algorithm for determining the NPN and PNP alphas of a thyristor

Abstract

A new method has been developed for accurately measuring the forward-blocking characteristics of gate-turn-off (GTO) thyristors, and for converting these characteristics into plots on npn and pnp gain as functions of anode current and anode voltage. Specifically, anode current and gate current are measured as function of gate-to-cathode voltage at a fixed anode voltage over several orders of magnitude of anode current. These data are used to determine the electron and hole components of anode current, which are, in turn, used to calculate αnprand αnpnover the entire range of anode current of interest. Examples are given that show how junction shorts, low minority-carrier lifetime in the n-base, and anomalously low npn gain are diagnosed in gate-turn-off thyristors. These new procedures have successfully diagnosed the causes of gate insensitivity in 95 percent of the devices to which they have been applied.