Relaxation of current filament due to RFC technology and ballast resistor for robust FWD operation

We have investigated the destruction mechanism of High Voltage (HV) Free Wheeling Diodes (FWD) during a reverse recovery operation. The most possible mode of the destruction phenomena originate in local heating due to current filament at the edge portion of the active area. To achieve a large reverse recovery Safe Operation Area (SOA), we focus on the boundary region between the active area and the termination area. To enforce our Relaxed Field of Cathode (RFC) concept, it is more effective for the wider SOA to place a ballast resistance for avoiding the current from crowding around the anode region in the top surface of the diode.