Getting the best out of a PC PSU

[Steviecuk]

Hi and happy new year.

I wish to illuminate some SMD LED's using an old PC PSU. It is rated at 500w.

I aim to be using CREE XML LEDS and need to have two runs.

One run comprising of 8 LEDs and one with 4. Each LED has a forward voltage of 3v @ 1000mA which should deliver 3w/444 Lumens.

A. How would/could I power these from the PSU that I already have?

Secondly, I need to add some sort of dimmer in order to dim each run of LEDs independently. How and what can I use to do this?

Thanks all.

 

[monjoor]

I'm sure you are going to need a constant current driver to power the LEDs up properly.

An LM317 adjustable voltage regulator can be configured to provide this function.

As for the dimming you need to adjust the current of the LED.

Some LED drivers come with built in PWM and analogue dimming features.

 

[Steviecuk]

Hi. Thanks for your reply. Someone else has mentioned co start current drivers, however I have been told that a friends of a friend has done the same thing but using the PC PSU. I have tried asking how but he hasn't got back. Is there a way that anyone knows of?

 

[shanky887614]

its not advisable to use a pc psu, for a start you would need to either chop the 24pin connector and put a switch in or use a paperclip everytime you wanted to start it.

it will tell you the outputs for the psu on the side, look carefully as it might be split between different rails and you could damage the psu if your not careful.

most of the connections on a modern psu will be 12/5v

(carefully read google)

they usually name the leads on pincount (the 24pin is motherboard cable)

 

[Steviecuk]

Cheers Shanky. What about the voltage and current side? I imagine that the 4x leds (12v total) could run off of one of the 12v wires. But how could I run the string of 8? I suppose I could run them from two of the other 12v wires but then again I need them to be dimmable together? Any ideas?