Analysis of an LLC Converter with Planar Inverse Coupled Current Doubler Rectifier using Silicon and GaN devices

In this paper a 2 kW 400 V/36 V LLC converter with an inverse coupled planar current doubler rectifier with minimized stray inductance is presented and assessed in conjunction with state of the art 100 V silicon and gallium nitride power semiconductors. First, the general impact of the current doubler on ZVS behaviour and turn-off overvoltage without a snubber circuit is discussed. Afterwards, two low inductance planar coupled inductor designs are presented and their impact on performance and efficiency is evaluated. The proposed LLC converter with a multi-stack planar coupled inductor is able to reach an efficiency of more than 98% at a switching frequency of 290 kHz and can be operated without snubber circuit, when the right combination of coupled inductor and transistor is chosen.