Analysis of Synchronous-Rectification Switch Control for Active Class-E Rectifier

Recently, a rectification stage plays an important role in MHz resonant power conversion. Besides the traditional role of converting AC to DC power, synchronous rectification is beneficial to increase the efficiency of the system. Also, active rectification can optimize the system under various operating conditions. In previous works, most active rectifications were achieved by adding dedicated circuits while maintaining the passive rectification. Therefore, additional losses, increases in complexity and size are inevitable. No attempt has been made to provide an in-depth analysis of an active synchronous Class E rectifier without additional circuits. In this paper, active Class-E rectification for resonant power conversion system is proposed. By utilizing a synchronous rectification switch and a small output inductor, the proposed active rectifier regulates output power to a certain level under various load conditions. With mode analysis, the shunt capacitor voltage and inductor current equation are derived, and an analytical model for rectifier characteristics is studied. To verify the proposed circuit, a prototype board is implemented for a 40 W resonant DC-DC conversion system with 1 MHz of operating frequency. The experimental result confirms the validity of the analysis and shows that the proposed rectifier regulates its output voltage over a wide range of loads with 84 % of the rectification efficiency.