A generalized DC model and low-frequency dynamic analysis for the Class-D converter at fixed frequency

A generalized DC model for constant frequency control of Class-D converters is presented. Based on the Class-D converter with a variable capacitance switch (VCS), a generalized DC model including some losses is found from its steady-state operation waveforms by Fourier analysis. The duty ratio of the power switches is retained as an explicit parameter in the model, which makes the model also useful for pulse width modulation (PWM) control. It is found that VCS control allows a much wider range of output voltage variation than PWM control. Moreover, by small-signal perturbation of the DC model, the AC models for low frequency control- and line-to-output responses can also be obtained. An experimental Class-D converter with a VCS operating at 350 kHz is implemented to verify the derived equations.