Study and implementation of a low conduction loss zero-current resonant switch

Zero-current (ZC) resonant switches allow one to reduce the switching losses in high-frequency DC/DC switched mode power supplies. ZC resonant switches can be either unidirectional (half-wave) or bidirectional (full-wave). If a conventional power MOSFET is chosen to implement the ZC resonant switch, the turn-on of the slow intrinsic diode has to be avoided. This is usually done with a fast blocking diode, which is connected in series with the MOSFET. Furthermore, an antiparallel fast diode is added when a FW ZC resonant switch is required. The conduction losses are relevant in this implementation, owing to the threshold voltage and to the series resistances of the two diodes. In this paper, a low-conduction-loss FW ZC resonant switch has been proposed. Its implementation is based on a power MOSFET and a single antiparallel Schottky diode. The possibility of an implementation with a power MOSFET alone is also discussed. A control circuit suitable for the proposed ZC resonant switch has been described. The experimental results obtained from a ZCS-QR buck converter are discussed.