High Frequency Active Clamp Flyback Converter with GaN Devices for Low Power AC-DC Adapter

摘要

With the amazing progress on microprocessors, integrating the voltage regulators module into internal CPU, more precise power control can be realized and power consumption can be decreased by more than 40%～60%. As a result, wall adaptor with 45W or below will power most laptop and notebook computers, and 45W adapter becomes the mainstream for the laptop power supply. This paper demonstrates a high frequency, high efficiency and high power density design of active clamp flyback converter for 45W adapter application. Both primary and secondary switches are gallium nitride (GaN) devices to reduce the conduction and switching loss. PCB winded transformer integrated with shielding layers are employed to improve the EMI performance and make the automation manufacture possible to reduce the labor cost. Close loop control is achieved by using microcontroller (MCU) from Texas Instruments. A prototype with 20V/2.25A output condition was built and can achieve 93% peak efficiency. Power density is 25W/in3 (including case), which is more than three times of the state-of-the-art product. Meanwhile, based on the same prototype, different output condition (15V/3A) with close loop control was tested under lower frequency range, and can also achieve very high efficiency.