Small-Signal Equivalent Circuit Model of Quasi-Square-Wave Flyback Converter

One benefit of switching a converter at very high frequencies-even to the multimegahertz range-is that the loop bandwidth can be increased so that the transient performance is significantly improved. However, using the conventional small-signal model of continuous conduction mode (CCM) for quasi-square-wave (QSW) converters introduces a huge mismatch for the placement of the dominant poles when compared to the experiment results. The double poles in high-frequency QSW converters are split widely which cannot be predicted by the conventional model. A modified small-signal model of the QSW flyback converter is proposed to predict the double-pole splitting phenomenon and to analytically quantify the damping effect. The impacts of deadtime on control-to-output transfer function have been investigated in detail. The conventional CCM model turns out to be a special case of the proposed model. The theoretical analyses were eventually verified by Simplis simulation and experimental results on a 5-MHz QSW flyback converter.