Current Detection and Control of Synchronous Rectifier in High-Frequency LLC Resonant Converter

The synchronous rectification technology is widely used to improve the efficiency of power converters in applications with low output voltage and large current. However, it is challenging to accurately control the synchronous rectifier (SR) for high-frequency and high-current LLC converters. This letter presents a method to detect the SR current for cycle-by-cycle SR control. The resonant current and the magnetizing current are detected through magnetic coupling, and then the SR current is obtained by subtracting the two. This method requires only a few passive components and has advantages, such as high bandwidth, strong anti-interference ability, and easy implementation. This letter illustrates the working principle and implementation of the proposed method in detail and then verifies the proposed method through experiments. The proposed method can be applied to SR control in an LLC circuit, suitable for high frequency and large current situations.