In those conventional arts, a DC/DC converter with secondary clamp circuit has a problem of voltage oscillation, and a DC/DC converter with primary clamp circuit has problems of heat and clamping losses due to larger forward and reverse currents passing the primary clamp circuit. The present invention applies a tapped inductor or a set of coupling inductors to a DC/DC converter with primary clamp circuit for reducing the voltage oscillation, and furthermore to decrease the forward and reverse current passing through the clamp circuit for reducing the clamping losses of the clamp circuit.