A DC—DC converter is disclosed comprising an active clamp topology, including an active clamp resonant transition system to provide substantially zero or reduced voltage for turn-on of the primary switch. The resonant transition system includes an inductor in series with the primary winding of the power transformer and a clamp diode that operate cooperatively to turn on the primary switch with reduced voltage. The addition of these circuit components provides lower switching losses and lower component stresses in the overall design.