A Synchronous Rectification Method for 6.78 MHz Applications

Synchronous rectification is routinely used in numerous applications below the megahertz range. However, with the rapid advancement of semiconductor technologies, particularly gallium nitride devices that support significantly higher switching frequencies, synchronous rectification becomes an attractive alternative for specific applications, such as inductive power transfer systems. Nevertheless, its operation at higher frequencies presents significant challenges due to the propagation delays of the control circuitry and the associated switching losses. This article presents a novel synchronous rectification method for 6.78 MHz inductive power transfer systems, in which a phase-locked loop is employed to compensate for all circuit delays, enabling zero-current switching. The adaptive dead-time capability of the method allows zero-voltage switching for a wide load range, minimizing not only the conduction losses of the rectifier but also the switching losses. The proposed method is implemented on a GaN-based half-bridge class DE rectifier using discrete and off-the-shelf components only.