Output characteristics of step-down (Buck) power converter

Abstract

Abstract. The output characteristics of switched-mode dc-dc buck power converter are discussed. The shape of output characteristics is especially important for converters used for supplying modern processors. An output impedance is usually used for description of output characteristics. Many efforts are described in the literature to obtain the satisfastory features of closed-loop output impedance. Another approach, presented in the paper, is based on the concept of the output voltage response corresponding to the load conductance change, and is expressed by hr transmittance. Simulations of output characteristics of the buck converter in frequency and in time-domain have been performed for the ideal case as well as for a more realistic situation, with the parasitic resistances of converter elements included. The measurement results differ substantially from characteristics calculated for an ideal converter and are in good consistency with simulations including parasitics.

Equivalent circuits for averaged description of DC-DC switch-mode power converters based on separation of variables approach

“…Large-signal and small-signal averaged models in widely used textbook of Erickson and Maksimovic [1] are valid only for ideal converters, without parasitic resistances. It is a very serious simplification, because parasitic resistances of converter components strongly influence converter behavior, as shown for example in [18] and [19]. Small-signal models of converters, useful in designing control circuits, may be found in application notes of controller manufacturers.…”

Small-signal transmittances of DC-DC step-down PWM converter in various operation modes

“…H g is known as input-to-output transmittance (or audio susceptibility) of converter and H d -as control-to-output transmittance. In some applications, other small-signal characteristics may be useful, for example input admittance or output impedance [17][18][19]20].…”

“…Parameters of general expression (10) obtained this way are the same as in [2], Ch. 10 with the exception of H dOCP that is described as: (18) where I O denotes D.C. value of the load current. .…”