SINGLE-STAGE (SS) ac/dc converters have received much attention in the past decades because of its cost effective- ness, compact size, and simple control mechanism. Among ex- isting SS converters, most of them are comprised of a boost power-factor correction (PFC) cell followed by a dc/dc cell for output voltage regulation [1]–[7]. Their intermediate bus voltage is usually greater than the line input voltage and easily goes be- yond 450 V at high-line application [8]. Although there are a lot of efforts to limit this bus voltage, it is still near or above the peak of the line voltage due to the nature of boost-type PFC cell. For application with low output voltage (e.g., ≤48V), this high inter- mediate bus voltage increases components stresses on the dc/dc cell. With a simple step-down dc/dc cell (i.e. buck or buck–boost converter), extremely narrow duty cycle is needed for the con- version. This leads to poor circuit efficiency and limits the input voltage range for getting better performance [9], [10]. Therefore, a high step-down transformer is usually employed even when galvanic isolation is not mandatory. For example, LED drivers without isolation may satisfy safety requirement [11]. Also, in