LED's on 12v for computer applications

LED\'s on 12v for computer applications

I've recently been upgrading my computer and came across something that caught my eye. It's a LED that runs off a standard 12v power supply from your motherboard. It is connected to the same kind of 12v plug that plugs into your hard drive or cdrom. Check it out...

Now, as I recall, the power supply on a computer supplies 12v AND 5v. It looks to me like the LED is hooked up to the 5v supply. Would any resistance be necessary? The company who sells these LED lights also offers another one that's slightly different in green, orange, blue & red so I would hope there would be resistance for at least the orange & red on this item as well. Where would they put the resistance?

Anyone ever use anything like this? Would I be better off just buying something like this already assembled or try to do one myself?

Re: LED\'s on 12v for computer applications

Looks like the 12V side to me. For SURE they have a resistor in there, probably a tiny Surface Mount. Led color does not matter, with 12V, they need a resistor. If you have the tools, do it, otherwise buy /ubbthreads/images/graemlins/wink.gif

Re: LED\'s on 12v for computer applications

hmmm...I wonder if you hook up something like that on the Red (+5v) if it would work without a resistor...

LightBright, have you ever used anything like this?

Anyone seen anything like this on other sites?

Re: LED\'s on 12v for computer applications

LEDs run at different voltages, but never something like 5 or 12, there has to be a current limiting resistor

Re: LED\'s on 12v for computer applications

I've noticed 15 LED clusters in replacement tailight bulbs. I wondered if each bulb was wired with one resistor and 15 LEDs in parallel or 5 resistors and 5 parallel strings of 3 serial LEDs.

Re: LED\'s on 12v for computer applications

There are LEds out there with a resistor built into the casing itself for operation directly off 12V. Not sure how widely available they are, but I knwo for a fact that Maplin have them. I was thinking about getting some to light the heater controls in my car, and save me having to mess about with resistors - but I did anyway.

Re: LED\'s on 12v for computer applications

Yes, they make those - and do the calculation for you, but running a single LED off 12v wastes so much energy in the LED

Ohms law is very simple

Add up the voltages of the LEDs until it is right under your desired input voltage, and then put in a resistor to "get rid" of that left over voltage

Say you have 12v input, and you want to use 3.5v LEDs

3x3.5=10.5v, you need to "get rid of" 1.5v, if the LEDs are normal T1-3/4 (5mm) LEDs, you want to run them at 20ma

R=E/I
R=1.5/.020
R=75 Ohms