A Method to Embed Resonant Inductor Into PCB Matrix Transformer for High-Density Resonant Converters

Magnetic integration of the passive transformer and inductor is a key to realizing a high-performance LLC resonant converter. With the advent of wide-bandgap devices, magnetics must cope with the increased switching frequency to maintain high efficiency and push for higher power density. This article presents a novel five-leg magnetic core structure that uses a printed circuit board to integrate a matrix of four transformers and a resonant inductor. The proposed design allows for controllable leakage inductance within the footprint of the original matrix transformer, resulting in excellent power density for the magnetics. The five-leg core structure operates by relocating the center-tapped secondary winding while maintaining the primary winding unchanged from the original transformer. This obviates the need for a stand-alone, lossy resonant inductor and offers a minimal increase in winding loss. The proposed magnetic structure is utilized to implement a regulated CLL resonant converter, demonstrated on a 3-kW 400 V/48 V dc–dc converter intended for data center applications. The converter, including magnetics, is implemented on a four-layer printed circuit board and offers a power density of $\text{550}\,\text{W}/\text{in}^{3}$ and a peak efficiency of $97.3 \%$ .