A CLL Resonant Asymmetrical Pulsewidth-Modulated Converter With Improved Efficiency

In this paper, a CLL resonant tank fed by an asymmetrical pulsewidth-modulated (APWM) drive train is presented as an attractive option for low-power point-of-use power supplies used in telecom applications. This configuration can guarantee zero-voltage switching (ZVS) for an extended input voltage range of 35-75 V, while significantly reducing the associated conduction loss present in existing topologies. Proper resonant tank design will ensure efficient operation over the entire working range by maintaining ZVS for all line and load conditions, as well as minimizing the conduction loss by decreasing the circulating-current commensurate with load. Analysis of the converter topology is conducted, and a design procedure is presented. Experimental results from a 25-W 48-V/2.5-V proof-of-concept prototype are presented to validate the analysis and simulation results and to highlight the merits of the proposed topology. The proposed converter is shown to provide a 7%-14% efficiency improvement over a reference topology.