Design considerations of transformer DC bias of forward converter with active-clamp reset

In the forward converter with active-clamp reset circuit, the leakage inductance of the transformer and the parasitic capacitances of the switches produce a DC bias of the magnetizing current of the transformer. The DC bias of the magnetizing current could saturate the transformer core, cause diode reverse recovery problem, and make the active clamp switch lose zero voltage turn-on if the bias is not considered in the transformer design. This paper derives the explicit equation of the DC bias of the magnetizing current for the first time and provides the transformer design procedures according to the derived equations.