Efficiency Comparison of an Asymmetrical Half-Bridge PWM Converter with Schottky and Synchronous Rectification

Due to the high sales quantity and an ongoing miniaturization of notebook power supplies an improvement of efficiency is desirable. In order to achieve high power density, high switching frequency combined with low losses is necessary. The asymmetrical half-bridge PWM converter is suitable for these requirements, as it allows ZVS operation for the half-bridge MOSFETs. Simulations as well as practical setups reveal that the diode rectifier accounts for the largest share of losses within the converter. This calls for a replacement of the diode by a synchronous rectifier. Advantageously, the proposed converter minimizes the effort to implement synchronous rectification, because it only has one rectifier diode in comparison to other topologies like the LLC converter. This paper presents a comparison between an asymmetrical half-bridge PWM converter with Schottky and with a synchronous rectifier. For evaluating the performance the efficiency averaged for several operating points is utilized. Besides the efficiency of both converters the distribution of the power dissipation is investigated. Experimental results based on a 90 W adapter reveal an increase in efficiency of 1.3 % for the synchronous rectification compared to the Schottky diode.