An increasing percentage of modern electronic systems are designed for portable operation. Until a more exotic power source is developed, this means that they must be powered by batteries, either single use or rechargeable. It would be nice if we could simply replace the lab power supply with a battery of the same voltage. In some cases this will work, but in others the realities of battery chemistry require more complex solutions. These realities include:
To overcome these limitations, most battery powered designs incorporate a power converter between the battery and the rest of the system. This converter will adjust the battery voltage (up, down, or both), providing a low-impedance, regulated output. To maximize battery life, high efficiency is required, so this conversion almost always utilizes switching circuits and reactive components (inductors and capacitors), rather than linear dissipative regulators.
There are literaly hundreds of chips available for this job. Terms to use in your search include "dc-dc converter," "switching regulator," and "buck regulator." A couple of examples to start with would be the National LM2575 or the Micrel MIC4690.