High-Speed Body-Diode Conduction Detection Circuit for 6.78 MHz WPT Systems with Adaptive Synchronous Rectification Control

Wireless power transfer (WPT) systems operating at megahertz (MHz) frequencies have gained considerable attention due to their potential for enhanced efficiency and reduced component size. To further improve system efficiency, synchronous rectification (SR) is often adopted to minimize conduction losses associated with passive rectifiers. However, implementing SR in MHz-range WPT systems remains challenging due to limited detection bandwidth, propagation delays, and high-frequency voltage oscillations. This paper proposes a high-speed body-diode-conduction (BDC) detection circuit and an adaptive cycle-by-cycle synchronous rectification control (ACSRC) strategy tailored for 6.78 MHz WPT systems. The proposed BDC detection circuit integrates a blocking diode, anti-series Zener diodes, and a fast-recovery branch to accelerate detection and suppress voltage spikes. Additionally, a softwaredefined sampling window is introduced to reliably extract BDC signals despite high-frequency oscillations. These BDC signals are employed in the ACSRC algorithm to dynamically adjust the GaN HEMT’s turn-on instant and conduction duration, ensuring both zero-voltage switching (ZVS) and zero-current switching (ZCS) operation. A 120.53 W, 6.78 MHz WPT prototype validates the proposed approach, demonstrating efficiency improvements of 8.72% under light load and 2.25% under heavy load compared to conventional passive rectification.