3w led driver and low battery indicator

408

05:15:10

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?

published 10 years ago

heritier

10 years ago

crazypz_pl

10 years ago

Interesting, but you still have a lot of mW when low battery indicator active, about 200mW in current controller, and 100mW for LED, and op amps supply currents. If your flashlight got switched on accidentally in your bag, it will discharged accu, and damage it. You can use relay as UVLO.

Awds95

10 years ago

Crazypz_pl I'm not sure what you mean. The op amps I'm intending to use have a supply current of less than 100uA. I know the current controller is not the most efficient possible, but I can't figure out a way to do it with a switch mode controller. If need be, the low battery indicator led could be driven at lower currents, I hadn't considered the impacts of that, so thank you for pointing that out. I don't know what a UVLO is, so I don't know what you're suggesting there, and I'm not sure what you mean by discharging the accu.

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