Improving SiC JFET Switching Behavior Under Influence of Circuit Parasitics

Abstract

This paper investigates the switching behavior of normally OFF silicon carbide (SiC) JFETs in an inverter for a motor drive. The parasitic ringing caused by different parasitic effects is analyzed. Two different methods, the use of an RC snubber and the use of suppression ferrite component, are investigated for dampening the parasitic oscillations. It is found that applying a ferrite bead not only dampens the parasitic oscillations, but also results in significantly lower switching losses. Furthermore, it is shown that the capacitive coupling between SiC devices in the bridge leg and heat sinks significantly deteriorates the JFETs’ switching performance. The effect of two substrates, an insulated metal substrate and a printed circuit board, on the capacitive coupling is investigated. A method in which the use of two separate heat spreaders minimizes the capacitive coupling, thus, exploiting the full potential of fast SiC JFETs is proposed.