High-dv/dt-Immune Fine-Controlled Parameter-Adaptive Synchronous Gate Driving for GaN-Based Secondary Rectifier in EV Onboard Charger

LLC and CLLC resonant converters are good candidates for the isolated dc-dc stage in electric vehicle (EV) onboard chargers (OBCs) due to their capability of achieving zero-voltage-switching (ZVS) at full load range. The synchronous rectifier (SR) is usually utilized to reduce the conduction loss and improve the system efficiency compared with the conventional diode bridge rectifier. In this article, a high-dv/dt-immune, fine-controlled, and parameter-adaptive gate driving scheme is presented for GaN-based SR in EV OBCs. A novel self-driven SR drain-to-source voltage sensing circuit is proposed. The circuit provides a low-impedance bypassing path for the displacement current induced by the high dv/dt, which addresses the overvoltage and oscillation issues for the controller input. The detailed operating principles and the design considerations of the novel sensing circuit are discussed as well. Moreover, the adaptive SR ON-time tuning algorithm is implemented, which avoids the influence from the loop stray inductance and the propagation delay in the path and reaches the SR zero-current turn-off moment with fine accuracy. A 3.3-kW, 500-kHz CLLC resonant converter prototype is built to validate the proposed SR gate driving scheme. With the employment of the proposed gate driving scheme, the SR almost achieves zero-current turn-off for the whole operating frequency range. The prototype demonstrates the peak efficiency of 97.6% and the power density of 130 W/in3.