Digitally controlled GaN‐based MHz active clamp flyback converter with dynamic dead time optimisation for AC–DC adapter

Abstract

The active clamp flyback (ACF) converter utilising gallium nitride (GaN) devices with high-switching frequency and high efficiency is impressive in system miniaturisation for AC–DC adapters. Owing to poor reverse conduction of GaN devices, the improper dead time between two switches can cause large power consumption in high frequency. This study proposes a dynamic dead time optimisation technique for GaNs ideal zero-voltage switching (ZVS) to address the issue. It adjusts the clamp switch on time to avoid large reverse conduction voltage stress on the main switch in different loads conditions. In addition, a new control scheme for clamp switch is introduced for enhancing efficiency in light to medium load. These techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of an ACF converter with a field-programmable gate array. The controller enables the system to operate at 1 MHz and dynamically modulates the dead-time under universal input and full load. With the light load ZVS control scheme, the system can achieve a maximum efficiency of 94.12 and 80.23% in the worst case. The prototyped converter can achieve power density (exclude case and controller) of 18 W/in3.