The Topology of a High-Power Compound Transistor and Its Blocking Ability during Commutation

Abstract

This article considers the problem of maintaining the blocking ability of high-power compound transistors in dynamic (commutation) modes. A compound transistor is an electrostatically controlled high-voltage induction thyristor serially connected to a low-voltage metal-oxide-semiconductor field effect transistor (MOSFET) that provides control along an isolated gate circuit. In addition, a major component of the compound circuit is a key threshold switch that supports floating potential mode in the gate circuit of the induction thyristor, when it is open, and fixes the gate to the common bus at locking. Emergency situations that render the compound transistor inoperable occur in the transient shutdown process and are associated with two main causes. The first one is the reduction in the negative locking voltage in the gate-source circuit of the induction thyristors below the level that ensures the closure of the space charge regions in its base region. The second cause is the rising voltage in the output circuit of the low-voltage MOSFET above the maximum permissible level. Mathematical criteria of maintaining the blocking ability of the high-power compound transistor are derived. It is shown that the reliable operation of the compound circuit requires reducing the reverse current amplitude in the gate circuit of the induction thyristor and parasitic inductance in the commutation loop, and harmonizing the parasitic capacitance values in the compound circuit elements. The suggested analytical model is used to consider methods of ensuring the blocking ability of compound thyristors for a number of practical circuit configurations with various threshold elements.