A duty cycle extension technique for single ended forward converters

A single-sided forward converter which operates at duty cycles above 50% is described. The circuit uses a simple LC dissipationless snubber to achieve a controlled resonant transformer reset without a clamp winding. The technique offers higher efficiency and lower stress than other passive extended duty cycle techniques. Formulas for choosing optimal L and C values for the snubber for this application are derived. Results of the technique applied to a low-power DC-to-DC converter are described