I have a few blue LEDs I want to use on a project. The LEDs operate at 5 volts nd my project also operates a 5 volts. Do I need a current limiting resistor in series with the LED.
Jimmie
Blue LEDs
Jan 30, 2008
3 Replies
Some LEDs have a current limiting resistor built in. Most don't. I would measure the forward drop with an ohmmeter if I were you. If no current limiting resistor is built in, add one. Helps to know the part number. If you are unsure, start with a 1K variable resistor. Decrease it slowly until the LED reaches your desired brightness. Measure what value of resistance you had, and use the closest value to that.
Raindrops on roses and whiskers on kittens.
All valid advice. I would add, measure the current at the same time. For most blue LEDs, as a general rule of thumb, don't exceed a forward current of 25 - 30 mA. The lower you can keep the current to get the brightness you need, the better when you are using DC rather than pulse drive. A lower forward current can extend the 50% life by several times.
Arfa
I agree with UCLAN. Stick a 1K resistor in series with the LED and see what happens when you apply 5V to it.
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