MHz High Power Density Converters With GaN Hemts

This paper proposes an air-core transformer integration method,which mounts the transformer straightly into the multi-layer PCB,and maintains the proper distance between the inner transformer and other components on the top layer.The integration method reduces the PCB area significantly,ensuring higher power density.The design of the complete structure is accomplished with Finite Element Analysis?FEA?to ensure that the unconstrained transformer magnetic field does not affect other components.It is applied to three resonant flyback converters operating at 20 MHz with Si MOSFETs,30-MHz and 50-MHz with eGaN HEMTs respectively.The 30-MHz eGaN prototype achieves the full load efficiency of 80.1%?an increase of 1.1%compared with the 20-MHz Si prototype?and power density of 32 W/in³ at 5 V input and 5V/2 W output.The 50-MHz eGaN prototype achieves the power density of 39.4 W/in³,which is 41%higher than the 20-MHz Si prototype.With the similar efficiency,the overall height of the converters in this paper is less than half of the commercial products,very suitable for low thickness and profile applications.A modular multilevel LLC converter suitable for high voltage and high power applications is proposed to reduce the voltage stress of the primary devices by half.The 650 V eGaN HEMTs with much lower R_ds?on?can be applied instead of 1700 V SiC MOSFETs at 1 kV input voltage and 1 MHz frequency.With lower Q_g,the eGaN HEMTs produces less switching loss and drive loss.The split resonant inductor solution is proposed to reduce the distortion of the resonant current to maintain ZVS realization.The matrix transformer is also employed to realize high step-down ratio conversion with the secondary-side current sharing and even thermal capability.To reduce the transformer parasitic capacitance,the non-interleaving type windings are proposed to minimize the displacement current from the primary-side to secondary-side.A prototype with 1 kV input and 32 V/3 kW output at 1MHz was built.It achieves the full load efficiency of 95.9%?1.8%higher than the diode prototype and 1.5%higher than the 300-kHz SiC counterpart?and power density of 107 W/in³,a size reduction of 69%compared to the 300-kHz SiC counterpart.