Abstract
In papers are presented the structure and particularities of D.C. buck converter witch can be used in the electric system of automotive. The equivalent circuits of buck converter deduced by energetically reasons and analysis of the power transfer through this converter is presented. To the analysis of the power transfer are done considering three sort of load resistive, resistive inductive, and resistive capacitive load. Are analyzed the dependence of power transfer Vs switching frequency and duty factor. In the final part of the papers are presented graphics obtained by calculus.