Active clamp forward converters (ACFC) are widely used for low-voltage and high-current applications. Despite their extensive usage, the open-loop power stage characteristics of the converter have not been fully investigated and require further analyses. This paper will show that the clamping-capacitor voltage could develop an overly large overshoot, which could trigger the saturation of the transformer if the feedback compensation is not properly designed. This paper presents a new small-signal model of the converter and provides the power stage transfer functions in factorized form, which carries the whole information about the origin and remedy of the clamping-capacitor voltage overshoot.
