2-Phase Series Capacitor Synchronous Rectifier in Active Clamp Forward Converter

A 2-phase series capacitor synchronous rectifier (SC-SR) in active clamp forward (ACF) converters is proposed to solve the inductor cooling problems caused by the recent trend of increasing the output current. The proposed 2-phase SC-SR can achieve the interleaved operation by adding only one flying capacitor to the 2-parallel conventional SRs without increasing the number of the primary circuit elements and transformer. Furthermore, the proposed 2-phase SC-SR can achieve the automatic inductor current balancing, which helps distribute the heat evenly in the two inductors. In the measurement at 140 V-to-5 V conversion, the peak efficiency of the ACF converters with the proposed 2-phase SC-SR and conventional SR was 90.3 % and 85.9 % at 28 AOUT, respectively, resulting in the improvement in efficiency by 4.4 %. In addition, the interleaved operation of the proposed 2-phase SC-SR reduced the output current ripple from 10.8 A to 6.4 A compared to the conventional SR at 40 AOUT. The current imbalance between the two output inductors of the proposed 2-phase SC-SR was less than 10% under heavy load even without any control or compensation, demonstrating the practicability of the proposed 2-phase SC-SR in ACF converters.