Multi-Megahertz Load Independent Synchronous Rectifier for Resonant Wireless Power Transfer Applications

Abstract

This paper presents a load-independent class-E synchronous rectifier (SR) design for resonant wireless power transfer (WPT) applications at multi-megahertz switching frequencies. Load independence alleviates synchronization requirements and yields a relatively stable rectified voltage, only rising by approximately 18% when the load is removed. A flexible and largely passive trigger circuit design is introduced to ensure precise and reliable switch timing under highly dynamic loading conditions. Prototypes based on the proposed design were built and tested as part of resonant capacitive power transfer (RCPT) systems operating at 13.56 and 27.12 MHz. Enhancement-mode gallium nitride (eGaN) switches were used to achieve load power levels exceeding 75 W at 13.56 MHz (70 W nominal) and 40 W at 27.12 MHz (35 W nominal), with estimated rectifier efficiencies of 93% and 86%, respectively. Experimental results illustrate the strongly load-independent behaviour of the proposed SR design, thus enabling the WPT system to accommodate wider coupling variations. Finally, options for improving SR efficiency are discussed for each operating frequency.