I'm working on a project to build usb car charger for my phone. The goal is to do it using only off the shelf parts (radio shack) and as cheap as possible. The size is also a bit of an issue but I'll deal with that later. I expect the phone to draw about 500mA and my car puts out a pretty steady 14.1V from the cigarette lighter.
I came up with the design below but I though of one big problem. IC1 is a 7805 5V regulator (sorry forgot to label it). It will give off somewhere around 4W, which is way too much and right on the edge of what it's rated for.
I set it up on the bread board and confirmed that it's very hot. Then I put the diode in to try and help distribute some of the heat but still way too hot. Any ideas? It seems like this will work as long as I can take care of the heat. There's not enough room in the case for a heat-sink either.