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A novel auxiliary switch dc-dc converter with coupled inductor is presented in this paper. The proposed circuit achieves loss-less switching for both the main and auxiliary switches without increasing the main device current/voltage rating. A tapping in the pole inductor is added for the purpose of commutation. The proposed circuit is capable of operation at elevated switching frequencies of several hundreds of kHz, in a range of line and load variations. The proposed circuit is applicable to all isolated and non-isolated dc-dc converters. The performance and the design equations of the ZVS are identical for all types of dc-dc converters when the throw voltage and the pole current are properly defined. In the sections that follow, operating principle and theoretical analysis of the proposed circuit is outlined through the example of buck converter. Simulation and experimental results of 33 W,400 kHz boost converter are presented. Index Terms--Auxiliary switch converters, coupled inductor, resonant converters, zero current switching (ZCS), zero voltage switching (ZVS).