Characteristics and Application of Normally-Off SiC-JFETs in Converters Without Antiparallel Diodes

In this paper, reverse characteristics of vertical-channel SiC-JFETs similar to an equivalent diode are discussed and compared with an actual SiC-SBD. The relationship between the reverse conduction voltage and the applied gate-to-source voltage is extracted along with channel structure of JFETs. Experiments involving operation of normally-off SiC-JFETs in actual converters are then conducted with and without antiparallel SiC-SBDs at different temperatures. The issue of JFET channel mistriggering is observed and evaluated by introducing extra negative gate bias during the switch-off state. Excellent dynamic performance can be obtained with minimal reverse-recovery charge when the SiC-JFET is driven properly. The dynamic losses are then calculated in different conditions. The results indicate that SiC-JFETs can perform the function of antiparallel diodes with minimal performance sacrifice in converters. Furthermore, an actual SiC-JFET-based dc-dc converter with/without antiparallel SiC-SBDs is built to verify the influence of eliminating the external diodes. It is concluded that with slight modification in the gate driver circuit to maintain safety, antiparallel diodes could be eliminated in vertical-channel SiC-JFET-based applications.