Buck/half-bridge input-series two-stage converter

This study presents a concept of connecting two-stage DC-DC converters in an input-series connection. An application example is discussed in detail where the first stage utilises two series connected buck converters that have reduced voltage stress. A single second stage is a half-bridge converter and is able to regulate the charge balance of the first stage. The benefits of the topology include: reduced primary switch voltage stress, simple self-driven synchronous rectification for wide input voltage range, self-voltage balancing on intermediate bus capacitors and simple housekeeping power supply. Further, the topology exhibits an unusual ripple match concept that can be utilised to suppress the current ripple of the second stage. Based on the detailed analysis, prototypes with 500-700-V input and 5-V/30-A output are built. Experimental results verify the principle and performance of the new topology.