A novel control circuit model for designing a current-mode controlled forward converter

Current-mode controlled (CMC) converters, which have a wide band with a sufficient phase margin and an excellent conducted susceptibility, are becoming widely used in power supplies. We propose a novel control circuit model for a CMC forward converter. This control circuit model is derived from the small-signal model, which incorporates a magnetizing current of a transformer and voltage drops of secondary rectifier diodes. By employing this control circuit model, circuit parameters can be easily designed without making trial-and-error experiments. The stability condition of the CMC forward converter is analyzed and the control characteristics, such as voltage-open loop characteristics, are calculated by making use of the proposed control circuit model. The validity of this control circuit model is confirmed by an experimental result