A zero voltage switching (ZVS) based on LLC resonant topology is proposed to implement a single-stage ac/dc converter which performs both input-current harmonics reduction and power factor correction (PFC). By integrating a boost-PFC cell and an LLC resonant dc/dc cell into a single power conversion stage, the power losses in the secondary rectifier diodes and the primary switches can be significantly reduced. The proposed architecture exhibits extreme simplicity and lower cost while providing nearly unity power factor and well-regulated output; hence, the proposed converter is very suitable for low power level applications. The operating principles and design procedures for the proposed converter are analyzed and discussed in this paper. Simulation and experimental results from a 125W laboratory prototype are provided to verify the feasibility.