The topology of LLC half bridge resonant converter provides ZVS characteristic. The voltage stress and current stress are smaller than that of the general resonant converters. So the LLC HB resonant converter can be considered as a optimal circuit for the notebook computer adapter. In the adapter design, we should consider the weight, the size and the overheat of the adapter. Thus the higher efficiency is an essential particular. First of all, the optimal design of transformer is the most important facts. Some parameters should be considered in order to get the highest efficiency. The adapter is designed through the considering of these parameters including the PFC circuit as the pre-regulator. It converts AC line input into about DC 390V link voltage of the LLC HB converter input and the converter has 16V/90W ratings. The efficiency measured is about up to 93%.