Miniaturization of AC-Adapter realized by Primary Voltage-Clamper with Mid-Voltage (150V) AHB Converter

There is a strong demand for miniaturization of AC adapters for mobile applications such as notebook PCs. Competition is intensifying with the advent of high voltage (650V class) GaN-FETs. However, there are two major problems in miniaturization: Firstly, the miniaturization of the input capacitors has not progressed because higher switching frequency does not contribute in this case. Secondly, the transformer miniaturization is still difficult especially for planar transformers because it is limited by the number of turns which finally leads to large core loss. To solve these two problems simultaneously, a combination of a voltage-clamper on the primary side and a 150Vbus AHB (Asymmetric Half-Bridge Flyback) converter with 1MHz GaN-FET is proposed. This allows the input capacitor and the AHB transformer to reduce their size approximately by half (1/2). The complete circuit including the AC input voltage-clamper with AHB converter board was implemented with an input of 90-264VAC, and output of 20Vo/3A. It is confirmed that the entire circuit works properly.