Small-signal model of quasi-resonant converters in the presence of conduction losses

By extracting the switching part and resonant tank of the quasi-resonant converter circuit into a minimum separable switching configuration (MISSCO), an identifiable equivalent circuit model of the MISSCO can be obtained. By perturbing this model, separating the DC and AC components and including it in the converter structure to replace the MISSCO part, the DC and small-signal models of the converter are derived. The analysis includes the conduction losses of the switching devices and reactive elements to improve the model accuracy. The transfer functions of input to output, and control frequency to output are formulated. The model is suitable for frequency-domain analysis. Bode plots obtained by computer simulation are compared with the experimental results. A zero-current-switching buck quasi-resonant converter, operating in both half- and full-wave modes, is considered