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Novel active auxiliary circuits that allow the power switch in single-switch, pulse-width-modulated (PWM) converters to operate with zero-voltage switching (ZVS) are proposed in this paper. The main feature of these circuits is that the auxiliary switch can operate with a zero-current switching turn-on and turn-off without increasing the peak current stresses of the main switch. In this paper, the operation of active auxiliary circuits in general is reviewed, and a systematic method for synthesizing auxiliary circuits belonging to the new family is presented and demonstrated with several examples. Several new auxiliary circuits are presented, and the operation of one of the new circuits is briefly explained. A general set of guidelines for the design of auxiliary circuits belonging to the new family is presented. The feasibility of the new family of circuits is confirmed by experimental results obtained from a 500 W, 100 kHz zero-voltage-transition (ZVT)-PWM boost converter prototype implemented with an example auxiliary circuit.