Synchronous Rectifier for High-Power Wireless Transfer Applications

Abstract

The appliance of wireless power transfer based on inductive coupling, nowadays, is a state-of-the-art approach and widely used in the industry. Different kinds of standards have been established in the past years, e.g. Qi or WPC (Wireless Power Consortium)to name but a few. Regardless of the development, the rectification of the alternative current (AC)itself is, in general, not part of the standard. Up to now, low-cost devices such as smartphone chargers use standard half- or full-wave passive rectifiers. This might give acceptable results for low-power and/or low-cost devices but the achievable efficiency is limited by this approach. The dissipated heat itself is for low-power devices, in most cases, neglectable as the charger itself is mostly connected to the power grid. In this paper, a straightforward solution is proposed which has been successfully implemented for < 600 W wireless-power application. The solution is not limited to sinusoidal waveforms and prohibits reverse-current flow automatically. The approach automatically switches to passive rectification, when running idle or if a low-load is present, to maximize the efficiency without the requirement to know the waveform for adjustment in advance.