PWM switch model of a buck-boost converter operated under discontinuous conduction mode

A small-signal circuit model for PWM dc-dc converters operated in discontinuous conduction mode DCM is presented. The model is composed of controlled current sources, and resistances. The principle of energy conservation approach is utilized to take into account parasitic resistances of the transistor and diode and the diode threshold voltage. The proposed model is suitable for small-signal, frequency-domain representation of the converters. This model is used to derive the expressions for a buck-boost converter control-to-output transfer function, input-to-output voltage transfer function, input impedance, and the output impedance. Bode plots are also given for these transfer functions