Assessment of "Normally On" and "Quasi On" SiC VJFET's in Half-bridge Circuits

Mazzola, M., & Gafford, J. (2004). Assessment of "Normally On" and "Quasi On" SiC VJFET's in Half-bridge Circuits. Trans Tech Publications Ltd. 457-460(II), 1153-1156.

Abstract

The successful development of the silicon carbide vertical junction field effect transistor (VJFET) has provoked discussion about the role of "normally on" devices in modern power electronics. In this paper we report on the application of trench SiC VJFETs with blocking voltages up to 1000 V and saturated drain currents up to 4 A that have been engineered to exhibit "normally on," "normally off," and "quasi-on" operation. "Normally on" is defined as drain current saturation at, or close to, zero gate bias. "Quasi-on" is defined by a zero gate bias drain current significantly reduced from the final saturated value, but still well above the leakage current observed at pinch off. The quasi-on state can be exploited to manage abnormal operation of a pure VJFET-switched half-bridge circuit without resorting to normally off devices. The flexibility afforded by exploiting the safe operating area of the quasi-on VJFET is illustrated with a design example involving a half-bridge circuit.