Effects of nonlinear resonant inductor on the behavior of zero-voltage switching quasi-resonant converters

A simple technique for overcoming the difficulties found in ZVS-QRCs (zero-voltage switching quasi-resonant power converters), such as voltage stress, limited load range, and large switching frequency range is presented. The technique consists of replacing the linear resonant inductor with a nonlinear one, so that the inductance value decreases with increasing load current. The nonlinear resonant inductor is constructed with an ungapped ferrite core. The principle of operation, analysis, and extensive experimental results are presented, and a comparison is made with a buck-ZVS-QRC with linear inductor. It is demonstrated that the output voltage and the peak voltage across the MOSFET become nearly independent of the load current while the load range is extended, without sacrificing the commutation under zero-voltage.<>