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
- posted
16 years ago
Blue LEDs
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- Vote on answer
- posted
16 years ago
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.
- Vote on answer
- posted
16 years ago
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
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- posted
16 years ago
I agree with UCLAN. Stick a 1K resistor in series with the LED and see what happens when you apply 5V to it.