A Design Method of Partially Interleaved Winding Structure With Low Leakage Inductance for Planar Transformer Application

For the planar transformer with turns ratio away from 1:1, the leakage inductance of fully interleaved winding structure is not the minimal and the structure should be optimized. In this article, a design method for partially interleaved winding structure is proposed to achieve the minimal leakage inductance at arbitrary turns ratio. According to the analysis of magnetomotive force, the tradeoff among the total number of layers, the number and the position of consecutive primary-side layers will be executed through the recursive design flow to minimize the leakage inductance. Based on this design method, the optimal partially interleaved structures for the transformers with 16:12 turns ratio and 25:3 turns ratio are “(P-S-P-S-P-S-P)₄” and “5P-S-5P-S-5P-5P-S-5P,” respectively, and the leakage inductances are verified by the finite element analysis and the experiment data. For the proposed structure, the measured leakage inductance drops 50%, and its dependence of frequency and the series resistance also decrease compared to the fully interleaved structure. Furthermore, the transformers with the proposed structures were tested in an LLC converter, where the loss of the converter and the change of resonant frequency are the smallest compared to other structures.