simple question with 3w leds

HI!
I've got 4x ''3w'' leds (not really 3w) ripped from cheap MXDL flashlights. I wanted to make a headlight for my RC.
So, led need 3.4v at 300-400ma, I connected 4 in parallel and the ouput of my RC's ESC is 5v. How do I regulated voltage and current?
I'm still a bit confused about how led driver works. Does this one could fit?
Would that be simpler with a resistor or would they burn if they were plugged directly to the 5v output?

Thanks!

Nobody?

That driver you posted should be good for what you described and much better than using resistors.
connect your LEDs in parallel and give them supply through the red and black wires that come out of the driver, and also solder 2 other wires to the "blank" side of the driver - one at the centre, and one on the edge ring and supply 5V to those wires where +ve goes to the centre

Thanks dude! I'll buy it.
I'm trying to understand how driver work. Correct me if I am wrong: so the driver regulate the amperage (in this case, 1250ma,) and the led decide what is the voltage? This led is rated 3.4v, so no matter what is the input voltage in the driver, the output would be 3.4v?

Think of your typical ohms law triangle with
V
I R

You can think of the led as "R"

VegasF6 said:

Think of your typical ohms law triangle with
V
I R


You can think of the led as "R"

Click to expand...

OK!!! I totally forgot about that!! So the voltage would be the resistance of the led X the rated amperage...


thanks guys, that's all I wanted to know!

Just remember that the LEDs.resistance changes with current. Ohm's law can't be used to analyze and predict nonlinear component behavior. In other words, don't take it too far.

emmanhello, the LED voltage varies depending on current, heat, etc. Some datasheets show how this varies. However, you don't need to worry much when using a driver.

What happens really is that the LED sort of "decides" how much current to use depending on the voltage, however that doesn't mean that if you give a constant voltage the current will be constant, and a small variation in voltage can have a huge impact on current. What that driver does is that it adjusts the voltage so that the current remains constant all the time.

Oh yeah, I also realized that, while measuring amperage from a flashlight. As the led warm up, the amp decreased (in the tail of the flashlight.)
I saw the graph where you can see the non-linear relation between voltage and amperage of a XM-L T6.
That makes so much sense. I think that you guys helped to understand many things. Thanks again!!!!