MOSFET failure modes in the zero-voltage-switched full-bridge switching mode power supply applications

Phase-shifted zero-voltage-switching (ZVS) full bridge topologies are gaining popularity due to their extremely low switching losses in the power devices even at higher switching frequency. However the intrinsic body diode is required to conduct in order to create the ZVS turn-on rendition for the power MOSFET. Due to the extremely low reverse voltage, the reverse recovery charges might not be swept out before turning off the MOSFET. Therefore, the body diode might be subjected to the dv/dt stress when it is not yet capable of blocking reverse voltage. Also, not able to maintain the ZVS operation at low load will force the on-state MOSFET to turn off at hard-switching condition. Like in the hard-switched full bridge topology, the cdv/dt shoot-through current might produce a voltage spike at the gate of the off-state MOSFET on the same leg and cause devices failure. Several silicon technologies are presented to resolve the above-mentioned failure modes in the ZVS topology. Fast reverse recovery time and better dv/dt ruggedness make this new MOSFET technology suitable for higher frequency ZVS full-bridge applications. Inherent with extremely high silicon density and low gate charge, these new MOSFETs can reduce the component count with the same or better performance and will enable much higher power density for the next generation telecom/server SMPS designs.