In this paper, a novel simple single switch single stage ac/dc converter with high power factor correction (HPFC) and high efficiency on the flyback topology is presented. In this proposed converter, the bulk inductor of the conventional ac/dc converter is substituted for an auxiliary winding of a transformer. The voltage stress across the bulk capacitor can be clamped under the rectified line voltage. The efficiency of this converter can reach 90% and the maximum power factor (PF) of this converter is 0.99 at the power of 25W when the input voltage is 110 VAC. The major advantages of this converter are the high efficiency and high PFC. The circuit operation, analysis, and simulations are presented in the paper.