A Sensorless Model-Based Digital Driving Scheme for Synchronous Rectification in 1-kV Input 1-MHz GaN LLC Converters

For 1-MHz GaN LLC converters with 1-kV input, the switching speed of eGaN high-electron mobility transistors (HEMTs) is as fast as 6 ns, which results in dv/dt up to 200 kV/mu s. It poses serious challenge for synchronous rectification (SR). A sensorless model-based SR driving scheme for high voltage applications is proposed to optimize the efficiency at steady state and the complementary control as an interlock mechanism is applied during the transients to ensure safety. A mathematic model is built to determine the turn-on instant and conduction time related to the switching frequency and load condition so that the driving signals are adjusted adaptively. The proposed method provides reliable gate driving signals without any detection circuits and is immune to high frequency noise. The transient response is analyzed and the tolerance effects of the resonant components are analyzed quantitatively. This control is fully transparent to design engineers compared to SR drive ICs, and is convenient to implement in high voltage and high frequency applications. A 1-MHz prototype with 1-kV input and 32 V/3 kW output is built, which achieves the power density of 103 W/in(3) and peak efficiency of 95.92% with an improvement of 2.0% at full load compared to the conventional SR driving scheme.