How to find led forward voltage?

[rvk2]

Hey guys, I just got a blue led from an old dvd player. I am sorta a newb at electronics, wanted to know how I'd be able to find out the voltage and current of the LED?

 

[Russlk]

The voltage should be around 3 volts. Put a 1k resistor in series and connect to a voltage higher than 3 volts but not higher than 20 volts and measure the voltage drop. The current rating will depend on the size and heat sinking, if any. Typical for a T 1 3/4 size is 20 mA.

 

[John Sorensen]

old dvd player

How old could it possible be :shock: ?! As Russel suggested, blue LEDs forward voltages run relatively high, in the neighborhood of 3V. They also require less current for a reasonable brightness than red or green LEDs. In fact, for indication in the lab, when I'm just looking for an on or off, and I don't want to load my circuit, I'll just use a blue LED with microamps through it. But, also, the forward voltage will depend on current, but it won't vary widely. For government work, 3V will get you far.

Be aware, though, blue LEDs are static sensitive, for real.

j.

 

[Exo]

Just measure it. Most DMM's have a diode test feature wich also displays the diode's forward voltage.

if you don't have such a DMM just put a 1K resistor in series with it, put it on a 9V battery and measure the voltage across the diode.

 

[evandude]

a DMM might work, but a lot of DMMs won't measure forward voltage over a volt or so. for instance i have a reasonably nice craftsman dmm and it won't do a lot of LEDs, presumably because their forward voltage is over 1.5 volts or so...