A Digital PWM Controller of MHz Active Clamp Flyback with GaN Devices for AC-DC Adapter

Abstract

This paper presents a complete digital pulse-width modulation (PWM) controller for MHz active clamp flyback (ACF) converter with gallium nitride (GaN) devices. A proposed model based on state-space averaging is used to predict the dynamic behavior of ACF converter. With the model, a digital PID compensator is introduced to achieve high-speed dynamic response. Meanwhile, a high-resolution digital pulse-width modulator is employed to meet the requirement of tight output voltage regulation. The implementation techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of ACF converter based on FPGA. The proposed digital control scheme enables the system operates at the switching frequency of 1 MHz and obtains less than 200 us recovery time in case of load transient (2-0.2 A). The AC-DC adapter s prototype can achieve the maximum efficiency of 91.34% and power density (exclude case) of 18 W/in3.