This paper discusses the effect of an active-clamp circuit on the dynamic characteristics of a basic converter topology such as a buck-boost power converter. The buck-boost converter has instability problems such as a jumping phenomenon and an oscillation of the output voltage. Recently, the authors have found an unstable phenomenon due to inserting an active-clamp circuit in the buck-boost converter with a large conversion ratio. The effect of the clamp capacitance and the leakage inductance of the transformer on the oscillatory instability is made clear through both analytical and experimental considerations. Then the effects of the other parameters are examined for designing sufficiently stable soft-switched converters.
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