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This paper presents analysis and design of an active-clamp buck converter with coupled inductors. The active switch in the converter can sustain a long enough duty cycle while it operates with a high step-down voltage ratio, reducing current stress significantly. In the converter, the active-clamp circuit is used to eliminate voltage spike induced from the leakage inductor of the coupled inductors. Moreover, since both main and auxiliary switches can be turned on with zero voltage switching, switching loss can be reduced and conversion efficiency therefore can be improved significantly. A 120 W prototype of the proposed buck converter was built and experimental results have shown that efficiency can reach as high as 95% (power stage only) and surge can be suppressed effectively. It is relatively feasible for applications to hybrid electric vehicle on-board chargers.