A high-efficiency high-power-density 1MHz LLC converter with GaN devices and integrated transformer

This paper presents a design of a high-efficiency LLC converter with power density >140W/in³. Gallium Nitride (GaN) FETs are adopted in this design to minimize the required transformer size for 1MHz operation. To further reduce the magnetic losses and size, a new integrated transformer is proposed in this paper. The proposed integrated transformer uses “∞” winding structure to reduce the required magnetic effect area. Synchronous rectifier (SR) FETs and output capacitors are integrated with output windings in order to minimize the AC termination losses. The parasitic effect for high frequency LLC converter design is also analyzed in details. An unregulated 1kW LLC resonant converter prototype is designed and tested with a peak efficiency of 97.6%.