I'm building a simple temp PID controller for turning an SSR on and off (yes, I know I can buy them fairly cheap, but its a learning project) and I need DC to power my RBBB arduino and mains AC for the SSR. I'd like to do the AC to DC transformation in my project and I'm really clear on how to do it. Ideally, I have a small box that I'd like the project to fit in and the transformers of the circuits I keep seeing are way too big. Obviously you can do it very small - the Blackberry travel charger* is the size of a large gumball and does 5v @ 750mA.
Is there different technology used in such a small device or am I simply not sourcing a small transformer correctly?
*Worst case, these are like 5 dollars and I'll crack one open. It should be a sufficient current for me.