Design and Optimization of 1-MHz 48-12 V LLC Resonant Converter with GaN Devices and FPCB Planar Transformer

The PCB planar transformer is a high-efficiency transformer commonly used in server power sup-plies. To reduce the manufacturing complexity and cost associated with multi-layer board coils, a flexible printed circuit board (FPCB) planar transformer structure using a foldable circuit board is proposed. However, the design methods for minimizing losses in this configuration are not well-established. This paper introduces a low-loss design approach by parameterizing the core diameter of the FPCB planar transformer, conducting experimental loss testing, and validating the feasibility of the method. Based on the parameters of the FPCB planar transformer, this paper also designs and optimizes a 12 V bus architecture LLC resonant converter using GaN devices, with simulation con-firming a reduction in circuit losses.