Analysis and Implementation of Low-side Active Clamp Forward Converters with Synchronous Rectification

This paper analyzes low-side active clamp forward converter with synchronous rectification (LACFC-SR) in detailed. Due to the additional clamp circuit composed of an auxiliary switch and clamp capacitor, the power transformer can be reset without the conventional tertiary winding. Moreover, the clamp circuit not only replaces the traditional RCD snubber circuit to mend spike current but also offers the main and auxiliary switches of the converter to achieve zero-voltage switching (ZVS). It reduces switching losses of the main and auxiliary switches. To deal with low voltage and high current output, the synchronous rectification is used to reduce conduction losses. A prototype of LACFC-SR with 30 ~ 60 V input and 5 V/ 20 A output has been implemented to verify the theoretical analysis. The power transfer efficiency is improved by the achievement of ZVS and synchronous rectification.