Simple synchronous rectifier (SR) control method for improving light load efficiency in asymmetrical half-bridge converter

Abstract

An asymmetric half-bridge (AHB) converter with a series capacitor rectifier (SCR) was proposed. It has various advantages such as the zero dc-offset current in the transformer and balanced average current of diodes. Hence, the AHB converter with SCR has small conduction loss under heavy load conditions. However, it suffers from high snubber loss and weakened energy for zero-voltage switching (ZVS) under light load conditions. To improve this drawback, simple synchronous rectifier (SR) switch control method is proposed in this paper. Under heavy load conditions, the proposed converter operates identically to the AHB converter with SCR by turning on SR switches synchronized with the main switch. Consequently, it has the benefits of the AHB converter with SCR under heavy load conditions. Furthermore, the proposed converter reduces the switching loss and snubber loss under light load conditions by normally turning on SR switches. Therefore, the proposed converter can achieve high efficiency compared to the AHB converter with SCR under light load conditions. The validity of the proposed converter is verified with a 300–400 V input and 48 V/400 W output.