Comparison between two single-switch isolated flyback and forward high-quality rectifiers for low power applications

In this paper, two isolated single-switch high-quality rectifiers are compared: one is based on the forward topology with secondary side resonant reset, the other is a flyback rectifier with a lossless passive snubber. These rectifiers were both designed for universal input voltage range (90-260 V/sub RMS/) and 200 W nominal output power. The adopted control technique is a modified nonlinear carrier control based on the integration of the switch current signal, which does not require any input voltage sensing, analog multiplier and current error amplifier. The comparison is based both on theoretical analysis and measurements on fully developed prototypes and takes into account the following aspects: basic design guidelines, voltage and current rating of active devices, power losses on the main devices, overall efficiency and conducted EMI generation. This work, highlighting advantages and drawbacks of both the selected topologies, will allow designers to make a proper choice for a given application in the low power range (below 300 W).