Sequential Parallel Switching for Drain-Source Synchronous Rectification Efficiency Boost in Parallel Switch Rectifiers

Abstract

Drain-source voltage-sensed synchronous rectification (SR) is a technique that can be used to reduce the secondary-side diode conduction loss of an LLC converter. In drain-source SR, an early SR-switch turn off issue is observed due to parasitics present in the path of the SR drain-source sensing loop. In rectifiers with parallel switches which is common in higher current applications, a new sequential turn-off method named “sequential parallel switching” (SPS) is proposed to extend the SR conduction period. By increasing the drain-source voltage signal near the turn-off moment, the effect of the parasitic inductance on the SR signal can be minimized, extending the total SR conduction time. This results in a net increase in total converter efficiency, despite a small increase in the SR switch channel conduction. A SPS-based rectifier is built with an FPGA based on a commercial SR controller and tested on a 300-V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</sub> , 1-kW LLC converter.