A non-isolated DC-DC converter topology which outputs a voltage less than or equal to the input voltage.
A buck converter is a non-isolated DC-DC converter topology used to step down voltage. It is one of the most fundamental converter topologies in existence.
The basic buck converter power train is comprised of a switch (usually a MOSFET or transistor), an inductor, a diode, and a capacitor.
The duty cycle of the switch determines the ratio of load voltage to supply voltage:
$$ \frac{V_{out}}{V_{in}} \mbox = D $$
An improvement on the buck converter is the synchronous buck converter, where the diode is replaced with another switch. This increases the efficiency of the converter but requires more complicated control.
