A GaN-based MHz active clamp flyback converter with adaptive dual edge dead time modulation for AC-DC adapters

Abstract

The Active Clamp Flyback (ACF) converter utilizing Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT) is expected to achieve high switching frequency and high efficiency for system miniaturization in AC-DC adapter applications. Due to high switching speed and large reverse conduction loss of GaN devices, the improper dead time length in a high-frequency ACF converter can lead to severe oscillation and efficiency decrease. This paper presents a high-frequency and high-efficiency ACF converter with an adaptive dual edge dead time modulation which can realize ideal Zero Voltage Switching (ZVS) ON for primary GaN FETs and Zero Current Switching (ZCS) for GaN synchronous rectifier. Designed by a high voltage 0.18um BCD process, the controller IC can enable a 65 W (19.5V/3.3A) ACF converter to operate at 1 MHz and automatically adjust the dead-time length under universal input (100VAC-260VAC) as well as wide load condition (0.33A-3.33A). With the proposed adaptive dual edge dead time control, the ACF converter can achieve the maximum efficiency of 94.3% and around 80% efficiency at the worst case. In addition, the converter based on this analog IC solution excludes any external active sampling devices, which will bring lower system cost.