Volume switch for Cree's?

[fireofenergy]

Hi,
Just wondering what kind of transistor or FET to use for controlling the input current to 4 XML's in series from a 12.8v battery. I assume that 2A is too much for a potentiometer, so want to connect a potentiometer to the base (or gate) of the transistor (or FET) where, in my limited understanding, a small current controls the much larger current of about 2A. I hear that they drop about 0.7v, so enough voltage should be present from 4 LiFePO4's (which are safe li-ion type of battery) in series to drive each XML at about 3v which, should be about 1.1A at full power, which I know is nowhere close to max rating for the XML, but is good enough for the light I want to make.
My problem is trying to figure out WHICH transistor or FET is the best for this setup as there are so many different kinds to choose from...
Thanks

 

[Preamp]

Hi, that won't work. You'll need a driver that keeps the current to the LEDs constant. You won't be able to set the current with a poti, and should you manage to do so, you'd need to correct it while the LEDs are heating up. I wouldn't even try it, 'cause you'll surely kill your LEDs in no time.
Look for a driver which can handle your 2A and is dimmable via PWM or - even better - via poti.

Regards,
Lasse

 

[abhi555]

I agree with Lasse, I fried couple of LEDs with wrong resistor. cheap DX driver is mcuh better than potentiometer ( or poti :-) never used that shortform)

 

[Preamp]

( or poti :-) never used that shortform)

Very common here in Germany ;)