Abstract: The voltage stress of the power switch of the traditional isolated SEPIC power factor correction(PFC) converter is large, the efficiency of the traditional isolated SEPIC PFC converter is also limited because of the existence of the input rectifier bridge. An active clamped bridgeless isolated SEPIC PFC converter is proposed by using the bridgeless PFC technology and active clamp technology. Through the elimination of the rectifier bridge, the efficiency of the proposed converter is improved; through the use of active clamping technology, the soft switching of all switches is realized, the voltage stress of the power switch is reduced. Finally, a 70 W experimental prototype for aircraft in-seat power supply is built to achieve high power factor, high efficiency, and isolation between input and output, which verifies the correctness of the theoretical analysis.