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 [1]-[5]. However, there are two major problems in miniaturization: First, input capacitors miniaturization has not progressed. Second, the transformer miniaturization is still difficult especially planar transformer because the number of turns is limited usually which finally leads to large loss. To solve these two problems simultaneously, we propose a voltage-clamp circuit on the primary side followed by 150Vbus AHB (Asymmetric Half-Bridge Flyback) converter with 1MHz switching by Mid-voltage GaN-FET. This allows the input capacitor and the AHB transformer to reduce their size approximately 1/2. The AC input voltage-clamp circuit was implemented on universal board with AC90-264V, clamp voltage of 150V, and was confirmed it works properly. Also, the prototype of AHB board was implemented with 150Vin, 20Vout/2A, 1MHz. The AHB board was confirmed by simulation and will be tested experimentally soon.
