A buck converter or step-down converter is a DC-to-DC converter which decreases voltage, while increasing current, from its input to its output. It is a class of switched-mode power supply. Switching
Fig. 10: Closeup picture of a multiphase CPU power supply for an AMD Socket 939 processor. The three phases of this supply can be recognized by the three black toroidal inductors in the foreground. The smaller inductor below the heat sink is part of an input filter.