Frederik wrote:
> I'm currently trying to build some Uplights/Spotlights for my Light
> Show. Therefore I need to control some High Power LEDs with an arduino.

A popular wish.


> It will act as the main
> power source for several other light effects. I want to step up this
> voltage to the required 34v for the LED.

Yes and no. A step up works, but it must use current control instead of 
voltage control, since LEDs need an external current limit.

> My question is how I
> can control/dimm the LED.

Via the enable pin of the step up controller.

> I think dimming could be archieved via a PWM
> signal. Are there any Problems I havent thought of?

As a rookie, there are plenty ;-)

> What transistors do
> I have to use? I never really learned anything about transistors and I
> dont know how to find a suitable one or what resistor to use at its
> base.

And you want to build a LED power supply? Good luck.
My advive. Buy some proper LED power supplies, they come with reasonable 
prices. Get some with the correct input voltage, so you can use you 
server PSU.

Hi,
I'm now ready to assemble one for testing. I bought a Dell L1100A-S0 
1100W for quite cheap. I'm now having a problem as the connector doesn't 
have 6 tiny pins but 8. It therefore isn't a normal common slot 
connector. This is why I don't know how to wire or bridge the contacts 
to turn it on. If anybody can help me I'd be happy.
Thanks a lot
Frederik

https://www.youtube.com/watch?v=syfrlyt9CO0

I already tried that but mine doesn't go into that false mode at the 
beginning. I connected the 4th pad with the other 4th pad. After 
connecting the 3rd and the 4th pad on its underside, the led turns 
yellow and I have to unplug the power supply as it doesn't do anything. 
Not shure what he did differnt.