High-power-density high-efficiency LLC converter with an adjustable-leakage-inductance planar transformer for data centers

LLC converters can achieve high efficiency, high-power density, wide gain range, and galvanic isolation. This study presents a high-power-density and high-efficiency LLC converter with an adjustable-leakage-inductance planar transformer for the DC–DC conversion in data center power supplies. A planar transformer with adjustable leakage inductance is modelled and developed to provide an accurate design for resonant frequency and voltage gain. A detailed power loss analysis is performed. Furthermore, a thermal model is provided to aid in heat sink design. GaN devices are used in the converter to achieve high-switching frequency and low-switching loss. A 450 kHz, 360–400 V _DC input, 12 V _DC output, 750 W LLC converter prototype with an adjustable-leakage-inductance planar transformer is built and tested. The power density of the system is 15.4 W/cm ³ including an auxiliary power supply. The peak efficiency of the overall system is over 95%.