A Transformer-Less Quadruple Active Half-Bridge Converter for the Two-Stage 48V VRM Application

A high power density transformer-less quadruple active half-bridge DC-DC converter suitable for the input-stage of a two-stage 48 V VRM is proposed in this paper. The converter consists of four half-bridge circuits and three small AC link power transfer inductors connected strategically among them. In the absence of the transformer, the voltage matching among the half-bridge circuits is achieved by stacking all of them together in series. The converter achieves high efficiency since all of its switches undergo inherent zero-voltage switching. It also needs to handle reduced power as a significant portion of the total load power flows directly to the output. It has several other advantages like reduced switch voltage and current stresses, efficient voltage regulation ability (and hence scalability), and a wide range variable switching frequency operation. These features allow the converter to achieve a flat high-efficiency curve. Topological evolution of the converter from its isolated version is explained and the concept is generalised to obtain the transformer-less multiple active half-bridge converters. Thereafter, the circuit operation of the quadruple active half-bridge configuration is analysed and a capacitor voltage control scheme is proposed. Finally, experimental results from a 48 V-12 V, 8 A laboratory prototype show that the converter achieves a peak efficiency of 98.1% and a full load efficiency of 97.23%.