This paper discusses the effect of an active-clamp circuit on the dynamic characteristics of a basic converter topology such as a buck-boost converter. The buck-boost converter has instability problems such as a jumping phenomenon and anoscillation of the output voltage. Recently we 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 thetransformer on the oscillatory instability is made clear through the analytical and experimental considerations. Then the effects of the other parameters are examined for designing sufficiently stable soft-switched converters.
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