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A widely observed phenomenon is investigated where a dc-to-dc converter operating in the discontinuous MMF mode with a constant-frequency control law can exhibit wide variations in dynamic performance over a narrow range of input voltage or output load. This behavior is related to the sinusoidal energy exchange between the parasitic capacitances of the power stage and the energy-storage reactor during the discontinuous MMF mode of operation. The resulting ringing can cause dramatic variations in the apparent gain of the power train, thereby affecting the dynamic performance of the power supply. The objective is to provide the power-supply designer with insight into this phenomenon. In this endeavor, a new large-signal computer simulation technique is employed to compare theoretical results with actual measurements.