Forward-flyback converter with current-doubler rectifier: analysis, design, and evaluation results

Authors:
  • LHL. Huber
    L. Huber
  • MJM.H. Jovanovic
    M.H. Jovanovic
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Abstract
Complete design-oriented steady-state analysis of the forward-flyback converter with the current-doubler rectifier is provided. Advantages and disadvantages of this topology com- pared to the conventional forward converter are discussed. In particular, the transformer-secondary copper losses are eval- uated. In addition, a step-by-step design procedure is given. Finally, experimental evaluation results obtained on a 3.3-V/50- A dc/dc converter prototype for the 40-60-V input-voltage range are presented. N A CONTINUING effort to decrease power consump- tion and increase the speed of data-processing circuits, their power-supply-voltage requirements are continuously be- ing reduced. Currently, 3.3-V integrated circuits (IC's) are gradually replacing the standard 5-V IC's due to their bet- ter speed/power-consumption performance and higher inte- gration densities. However, the transition to lower supply voltages usually requires higher output currents as well as lower output-voltage ripples. As a result, the design of an efficient secondary-side circuit is an extremely challenging task. The efficiency of the secondary-side circuit in a converter with a high-output current may be improved by employ- ing the current-doubler-rectifier (CDR), also called hybridge, technique. The idea was first described in (1), while imple- mentations of the CDR in the half-bridge, full-bridge, and forward converters were reported in (2)-(7). Since the forward converter with CDR operates in a forward-flyback fashion, this topology is more appropriately called forward-flyback converter with CDR. The CDR offers the following advantages compared to the conventional secondary-side rectifier topolo- gies such as the full-wave diode bridge, full-wave rectifier with center-tapped transformer secondary, and conventional forward:

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