Linear regulators are great for powering very low powered devices. They are easy to use and cheap, and therefore are very popular. However, due to the way they work, they are extremely inefficient.
A linear regulator works by taking the difference between the input and output voltages, and just burning it up as waste heat. The larger the difference between the input and output voltage, the more heat is produced. In most cases, a linear regulator wastes more power stepping down the voltage than it actually ends up delivering to the target device!
With typical efficiencies of 40%, and reaching as low as 14%, linear voltage regulation generates a lot of waste heat which must be dissipated with bulky and expensive heatsinks. This also means reduced battery life for your projects.
Even the new LDO (low drop-out) regulators are still inefficient linear regulators; They just give you more flexibility with input voltage drops.
A switching regulator works by taking small chunks of energy, bit by bit, from the input voltage source, and moving them to the output. This is accomplished with the help of an electrical switch and a controller which regulates the rate at which energy is transferred to the output (hence the term “switching regulator”). Switching regulators are complex circuits to design, and as a result they aren’t very popular with hobbyists.
With high input voltages, driving loads over 200mA with a linear regulator becomes extremely impractical. Most people use a separate battery pack in these situations, so they have one battery pack for high voltage devices and one for low voltage devices. This means you have twice as many batteries to remember to charge, and twice the hassle! A switching regulator can easily power heavy loads from a high voltage, and save you from splurging on an additional battery pack.
Where can you find more information on switching regulators?
Try searching for “buck converter”, “boost converter” or “dc-dc converter” and you should find some good tutorials.
I'm using LM2575-5 which have 5 pin T-220 only need 4 external components and supply 5V 1 Amp.
or you can use Hobbywing 5V/6V 3A Switch-Mode Ultimate BEC from dealextreme.com it cost USD$9.27 with Input: 5.5V-23V http://www.dealextreme.com/details.dx/sku.15149