This tutorial article shows how the widely used analysis techniques of averaging and linearisation ave applied to the buch or step-down DC-DC converter to obtain. simple equations which may then be used for control design. Three common control methods are described. Their principal characteristics are illustrated using Matlab and the Simulink block diagram system along with experimental results. The analysis procedures described may be applied directly to other DC-DC converters and the principles may be extended to move complex power electronic systems.