Originally Posted by
mmeiser
For example Radioshack sells a 5-volt [regulator] for $1.47. This resistor with theoretically knock anything up to 35 volts down to 5-volts which is the USB standard for power. Therefore it's theoretically possible to create a little black box or battery pack that you can connect anyting from a 4AA battery pack, to a 9-volt or a 6-volt to and get clean consistent power to your light, camera, mp3 player or smartphone. Been meaning to build one, but haven't had the time yet. I guess I've been to busy reading / writing on special topics on forums and mailing lists passive aggressively.
That's a linear regulator. You don't want to use a linear regulator unless you don't care about carrying a big chunk of battery around.
Linear regulators DO act like an intelligent resistor. If you have a 9 volt battery and you're regulating down to 5 volts, a linear regulator does it by turning 9/5, or nearly half, of the output of the battery into heat, and delivering the rest to the device.
It's OK for quick-and-dirty but what you really want to do is to use a switching power regulator. They're certainly more complex than a linear regulator, but not horribly so. You can easily get 80% efficiencies with switchers, and probably higher. Google "simple switcher" - the manufacturer has a web page that will calculate all the parts you need.