Evaluation of the need for SiC SBD in parallel with SiC MOSFETs in a module phase leg configuration

Abstract:
This paper presents the characterization of Full SiC MOSFET phase leg modules and compares the performance of “SiC MOSFET only” and SiC MOSFETs with SiC Schottky Barrier (SBD) parallel diodes. SiC MOSFET exhibit body diodes that feature a reverse recovery behavior almost as good as true parallel SiC SBDs even if reverse recovery time and recovery energy is a little higher and show some slight dependency on temperature. But this body diode presents significantly high VF. This VF becomes higher as the gate voltage become more negative. In this case it makes great sense implementing external SiC parallel diodes to lower the losses in reverse conduction and transfer those diode conduction losses from the SiC MOSFET body diode to the SiC diode. Biasing the SiC MOSFET with a positive gate voltage helps eliminating the need for parallel SiC diode in the third quadrant of operation.This paper will detail the performance of those SiC MOSFET phase leg options at different temperatures, gate voltages over the full range of current to help system designers optimize the use of SiC MOSFETs and carefully determine the need for parallel SiC SBDs.