A Digital Adaptive Control Method for Optimizing Valley Current of Active Clamp Flyback Converter

In an active clamp flyback (ACF) converter working in critical mode (CRM), the zero-voltage switching (ZVS) of the main power switch can be realized by the negative valley current, which is related to conduction loss and switching loss. Therefore, how to control the negative valley current will affect the overall efficiency of the system. This article investigates and compares the three existing technologies and summarizes their limitations in practical applications. Therefore, a digital adaptive control method is proposed to regulate the valley current according to different working conditions. Meanwhile, small-signal analysis is performed to ensure the stability of the proposed control method. The proposed control method is verified by a field-programmable gate array (FPGA)-based 12-V, 3-A ACF, and experimental results show that the proposed theoretical model should be accurate and practical and there is an average efficiency improvement of 1.34% compared to conventional control.