Instructables

Power LED Help

I'm looking to make some home lighting with LEDs, but I'm not sure how to regulate the current properly. I've really only used resistors up until now for led projects. I have a couple ATX pc power supplies, and I've used it to power an ebay led with no problems. I just touched the led directly to the 3.3v line and ground and it lit up fine. What I'm wondering is, is does the psu automatically adjust the current to what you need? Or is there something else I would need to worry about? (I figured it would be okay to power something off the 3.3V line if they were 3.7V leds, say several P4s)

Gjdj35 years ago
Try these links below for LED info. Essentially though, LED's are more current dependent, not as much voltage dependent. The current drop across the diode (LED) is what creates the light, and the resistive value is what provides the current drop. Diodes inherently don't have much resistive value, therefore, if you put most (not all, but most) LED's straight up to a supply, they will either not light at all, or burn momentarily, as the resistive value is so low that all of the current flows through them and then they fail. You can get LED drivers http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=525265&keywords=led%20driver that should work, or you can add resistors individually, to each LED. Sparkfun also sells LED light bulbs pre-made, with heat sinks attached for the really bright ones, but then again, where's the fun in that?
Hope this helps.
http://www.superbrightleds.com/led_info.htm
http://led.linear1.org/why-do-i-need-a-resistor-with-an-led/