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Single-stage power-factor-corrected AC-DC converters (S2PFCCs) usually suffer from high current and voltage stresses due to the repeated process of input power through the power switch and power imbalance between the input and output, respectively. The paper presents a detailed analysis of an improved single-switch S2PFCC with an auxiliary transformer, which provides a direct linkage between the input and output stages of the converter. The auxiliary transformer is the key to reducing the voltage stress across the storage capacitor on decreasing load, to reduce the current stress on the power switch and to obtain a high power factor through elimination of input-current dead angle. Detailed analyses of the component stresses and the input current relating to the circuit parameters are presented. The theoretical analysis and effectiveness of the proposed approach are confirmed experimentally with a 15 V 60 W hardware prototype.