In this paper, a direct current (DC) to DC full-bridge (FB) converter is studied and developed to have the benefits of (1) less switching loss at light load, (2) wide hold up time when input power is OFF, (3) less circulating current loss, and (4) less output filter inductance. A half-bridge (HB) resonant circuit is connected to the lagging-leg of conventional FB converter to improve soft switching range of lagging-leg switches. The output voltage of HB circuit is connected to the rectified side of FB circuit with a clamp diode. At the commutated state of FB circuit, the output voltage of HB circuit can force the primary current of FB circuit to zero and also reduce inductor voltage. Therefore, the circulating current loss is removed and the output inductance is reduced. To prolong hold-up time without using large size of input electrolytic capacitor under input power is OFF, an auxiliary windings are employed to realize high voltage gain and keep load voltage at the chosen voltage value. A laboratory prototype with 1440 W rated power of the studied converter with wide hold-up time is built and test under 280 $V\sim 400V$ input and 48 V output. The feasibility and practicability of the proposed topology are conducted and verified from experimental results.
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