Current regulators.

[Splunk_Au]

What are the key components to look for when designing a current regulator circuit? ie. Everything you need on the PCB?
I know traditional current regulators rely on a JFET, but I suppose regulators for flashlights have alot mor stuff on them from the pictures of the circuits sold on kaidomain/dealextreme.

 

[Mr Happy]

Can you clarify your question? Do you want to design a current regulator circuit, or do you want to know how to recognize one when you see it?

Neither question actually has an answer though. If you want to design one, you would already know more about the subject than your question implies. If you want to recognize one, there's no easy way to tell how a circuit will perform by looking at it. The only way is to subject it to tests.