Design and Implementation of an Integrated Planar Transformer for High-Frequency LLC Resonant Converters

In this study, an LLC resonant converter equipped with an adjustable leakage inductance integrated transformer is proposed and applied to high-power adapters. To achieve high efficiency and power density, the magnetic circuit was increased by substituting the resonant inductor with an adjustable leakage inductance integrated transformer, and a novel core structure was designed to reduce copper loss. To further reduce the core loss and copper loss of the transformer, the core size was analyzed using a parametric technique. Finally, the total loss and physical footprint of the transformer were compared to select the most effective design point as the final design. The FEA 3D simulation was employed to verify the function of the transformer. An integrated transformer with adjustable leakage inductance replaced the resonant inductor in LLC resonant converters. Finally, a resonant converter was achieved with a switching frequency operating at 1 MHz, input voltage of 380 V, output voltage of 19 V, output power of 190 W, power density of 400 W/in3, and maximum efficiency of 94.3%.