A 1-MHz GaN Converter with 4X Voltage Range^*

Wide input wide output converters are popular for their versatility in different bus systems. The voltage variation is four times as both input and output voltage vary two times. At the same time, high input voltage can effectively reduce bus loss and the volume and weight. When the input voltage is up to 800 V, current 650 V GaN devices cannot be directly used. A stacked bridge structure is used, ensuring the application of 650 V GaN devices and reducing dv/dt to 20 kV/μs, even when the input voltage is 800 V. The LLC resonant converters are well-known for its high efficiency, compact and wide range of ZVS. However, on the occasion when input voltage is 400-800V and output voltage is 22-40 V whose voltage range varieties four times, a single stage LLC converter is hardly suitable to maintain high efficiency and high power density because the switching frequency variation has to be considerably large and the magnetics cannot be optimally designed. A two-stage solution consisting of a LLC-DCX and three-phase interleaving synchronous buck converters are proposed to maintain high efficiency. All GaN HEMTS are applied and the converter can run up to 1MHz to achieve high power density. The analysis of the influence of parasitic junction capacitance of the rectifier diodes on the primary-side ZVS realization is given. A 2-kW GaN-based prototype with 400-800 V input and 22-40 V output was built to verify the theoretical analysis. The converter can achieve power density of 130 W/in ³ and peak efficiency of 93.8%.