Optimized Design of Integrated PCB-Winding Transformer for MHz LLC Converter

Intermediate bus architecture employing 48V Bus converters are widely used in power supply applications. With the rapid increase of demanded power by these load, higher efficiency and power density are driving for better performance power management solutions. In this paper, Gallium Nitride (GaN) based design of a two-stage solution is proposed. The first stage is a multi-phase buck for regulation. The second stage is an LLC converter with fixed switching frequency for isolation. The design and optimization of LLC matrix transformer are studied. A novel primary termination and via structure is proposed resulting in great loss reduction. In addition, to minimize the winding loss, an overlapped winding structure and a symmetrical winding layer scheme are proposed to reduce and balance the MMF. These efforts achieve much better current sharing and efficiency. The prototype for the two-stage converter is developed, with the peak efficiency of 96% and the power density of 680W/in3.