High-Efficiency Stacked Half-Bridge Sigma Topology for Wide Input Range and High Step-Down Application

In wide input range and high step-down application, conventional Sigma converter suffers from the problem of small duty cycle and low efficiency of the internal Buck converter. A stacked half-bridge (SHB)-based Sigma-type topology has been proposed by integrating an LLC resonant converter and a Buck converter with an SHB structure, which inherently halves the input voltage for the LLC and Buck converter. Compared with the conventional Sigma topology, the proposed topology achieves higher efficiency under the same gain and power distribution conditions, due to the optimized duty cycle range of the Buck converter. Besides, all switches in the SHB achieve ZVS through phase-shift control, effectively reducing switching losses. An experimental prototype with 42-55V input and 5V/80W output is built, demonstrating a peak efficiency of 95.1%.