Effects of parasitic components on diode duty cycle and small-signal model of PWM DC-DC buck converter in DCM

A procedure to derive corrected values of diode duty cycle is introduced taking into account converter power losses. The proposed D₁ adjustment increases the accuracy of a small-signal converter model presented in a previous paper. The control-to-output transfer function T_p(s) of a PWM DC-DC buck converter operated in discontinuous conduction mode (DCM) is derived by utilizing an equivalent circuit of the switching-cell, where the circuit components are calculated using a corrected value D_1C of the diode duty-cycle. The expression for the transfer function is obtained in a closed form by using a symbolic circuit simulator, SapWin, which has been developed by the same authors. This program also allows the Bode plots of the transfer function to be automatically derived. The experimental results confirm the accuracy of the proposed modelling technique.