Generic LED question

[Jimmy Yakapucci]

Is there a way to measure the voltage that is feeding an LED that is currently mounted on a PC board? The reason that I ask is that I want to replace an LED that is currently in one of my video game systems, but I would like to make sure that I have the correct voltage for the one that I would like to put in. Thanks.

JY

[crazzywolfie]

the ones that are usually in pc's are 3volt.

[jb143]

What color is it? That's going to be the main determining factor.

There's a chart showing voltage drops for LED's here...
http://en.wikipedia.org/wiki/LED

There's always going to be a current limiting resistor in the circuit that will keep the LED from popping. So your probally safe to replace it with whatever you like (unless it's a high power LED or something, which I doubt)

--EDIT
Also, when you replace it, make sure you get the polarity correct. For a normal LED the leg nearest the flat part of the base is negative.

I should also add that "voltage rating" for an LED doesn't really mean the same thing as say, with a light bulb. If an LED says 3.3V Max that doesn't mean you can just hook it up to 3V. It means that anythign over that will probally destroy it. You'll want to know it's forward voltage(voltage drop). The current rating is a bit more important, and the resistor in series. Lets say that the circuit is 5V and your replacing a red LED (probaly about 20mA). This means that the resistor in series is probally around 150 ohms. If you're replacing it with a blue LED (probally around 30mA) you'll want a smaller resistor to allow more curent to the LED or else it will be dim. Probally around 68 ohms.

[Jimmy Yakapucci]

After looking at everything again, I may have a problem. Here is what I am planning on doing. I have added a region mod switch to my X'Eye and I would like to replace the red power indicator LED with a multi-color LED using one color for US and another color for Japanese. I was planning on using green and blue since based on the specs on the package, they will operate in the same voltage range and have the same current draw. ( 3.5V typical, 4.0V max and 30mA ) But looking at the specs for the red portion, ( 2.0V typical and 2.6V max) I am wondering if it will supply enough power to run the green/blue portion. I guess I could always tap from some other 5V source in the unit and add a resistor in-line to drop the voltage. Any ideas whether or not this would work? Thanks.

JY

[jb143]

I'd probally just tap the 5V elsewhere. I'm not exactly sure what the mod looks like so I can't really provide a schematic. It should be simple enough though. Is there a switch to select the region?

By the way, here's the equation I was using before for selecting the resistor...
R = (Vs-Vd)/I

Vs = Source voltage (5V)
Vd = Forward voltage of diode (If you don't have a better spec you'll probally want to use use typical voltage)
I = Current rating in Amps (30mA = 0.3A)
R = Resistance in Ohms - It doesn't need to be exact, just get the next biggest one available.

[Jimmy Yakapucci]

I'd probally just tap the 5V elsewhere. I'm not exactly sure what the mod looks like so I can't really provide a schematic. It should be simple enough though. Is there a switch to select the region?

By the way, here's the equation I was using before for selecting the resistor...
R = (Vs-Vd)/I

Vs = Source voltage (5V)
Vd = Forward voltage of diode (If you don't have a better spec you'll probally want to use use typical voltage)
I = Current rating in Amps (30mA = 0.3A)
R = Resistance in Ohms - It doesn't need to be exact, just get the next biggest one available.

I will probably wind up find a +5 somewhere in there. It shouldn't be to hard. I just figured that it would be easiest to take it from the current location. Silly me. As for calculating the resistor, I was using some on-line calculator, but the equation is probably the same. Thanks.

JY