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Blue LEDs

Discussion in 'Electronic Repair' started by Jimmie D, Jan 30, 2008.

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  1. Jimmie D

    Jimmie D Guest

    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.

  2. UCLAN

    UCLAN Guest

    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.
  3. Arfa Daily

    Arfa Daily Guest

    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.

  4. 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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