A high step-down non-isolated bus converter with partial power conversion based on synchronous LLC resonant converter

A novel DC/DC conversion architecture is proposed for a non-isolated front-end bus converter with wide input voltage range. A DC-DCX, which operates as a DC-DC converter with regulated output or as a DC-DC transformer with unregulated output, is adopted in the bus converter to provide an optimized intermediate DC-bus voltage for the down-stream converters. The input and output of the DC-DCX are in-series and connected to the total-input voltage. Therefore, part of the total input power is directly transferred to the intermediate bus without conversion, and the voltage and current stresses of the DC-DCX can be reduced. The DC-DCX is implemented with a synchronous-rectification LLC resonant converter. A hybrid synchronous driving scheme is presented for the LLC to further improve the conversion efficiency. In order to emphasize the superiority of the proposed driving scheme, the comparisons between the traditional and the newly proposed synchronous driving scheme are presented in this paper. Finally, a 36V~72V input, 10V~14V output and 100W-rated prototype is built and tested to verify the analysis, also help to demonstrate the effectiveness of the proposed control schemes.