This work presents a gate-driver-circuit which operates a LLC-half-bridge based on 650 V gallium-nitride transistors. The gate-driver-circuit reaches a switching frequency up to 20 MHz in no-load operation. Up to a switching frequency of 10 MHz, a HV-voltage of 200 V and an output-power of 70 W the function of the LLC-half-bridge can be proven. At a switching frequency of 1 MHz the converter is able to reach an output power of 500 W. Continuous operation is thermally limited at 10 MHz, because the switching losses (60 W per transistor) cannot be sufficiently dissipated despite zero-voltage-switching. In further development, the thermal path could be improved by heat spreading layer between the transistor-case and a water-cooled heat sink with the usage of ceramic substrates. For the gate-driver-circuit and the LLC-half-bridge only commercially components off the shelf were used.
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