rugged or fast body diode

Most resonant circuits are half- or full-bridge topologies (2 or 4 transistors). As transistors are switched on and off, energy can be left in the transistor and this can cause failure.
Due to switching times if this only happens occasionally a rugged body diode is sufficient (CoolMOS™ C6/E6 series). If due to fast transition tomes it happens continually then a fast body diode is required to make sure all the energy will leave the transistor (CoolMOS™ CFD2 series).