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In this paper, a two-stage AC/DC converter is presented for a low-profile laptop adaptor. The system consists of a boost power factor preregulator and LLC resonant converter. The preregulator features high PF and high-efficiency, while secondary LLC converter features zero voltage switching (ZVS). The transformer in LLC converter is splited in two to reduce current stress and converter height. The proposed circuit operates at high switching frequency to increase power density. A thermal analysis of the proposed converter is discussed and analyzed. The proposed system is verified by a 40W experimental prototype for a 6.3mm-thick laptop adaptor.