Abstract：This paper analyzes the winding loss of planar transformer with PCB windings in LLC resonant converter. Unlike conventional power transformer, the transformer in LLC is a combination of inductor and transformer. The primary side current and secondary side current is not in phase, which increases the power loss of the windings. In this paper, the effects of winding structure and air gap are analyzed respectively. Based on the loss analysis, some optimization method to design a planar transformer in LLC resonant converter are presented and discussed. Finite element analysis (FEA) simulation is used to aid the theoretical analysis. A prototype with 300-400V input and 12V/33A output is built to verify the analysis and FEA simulation.
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2012, Vol. 27 
