This is a circuit I created to use in a powerful flashlight. It uses a single 3w led (3.4v @ 700mA) and is powered by two lithium ion batteries in series (8.4v nominal) represented here by a 10F capacitor. It has two brightness modes, one drives the led at 680mA and the other at 340mA. There is a low battery indicator that lights a small red led (~10mA) when the battery voltage drops below 7.2v (3.6v per cell or roughly 20% battery level). As an added protection the load is cut off at 6v (3v per cell or the minimum safe level for lithium ion batteries).
A couple of notes; The capacitor obviously represents the two lithium ion batteries in series. The 8.4v voltage source is simply for demonstration purposes. The relay and the transistor would both actually be logic level mosfets, but mosfets are strange on everycircuit.
I have space on here for another op amp circuit, and I plan to use a quad op amp in the actual application, but I don't know what to do with the fourth op amp. Anyone have any ideas for extra features I could add?
