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Thread: Power budget for tiny LEDs

  1. #1

    Power budget for tiny LEDs

    Hi, thanks for taking the time to read this.

    I don't fully trust my measurement, and I don't have enough knowledge of an expected value.

    How much current would be expected to run two of these tiny LEDs on a ky-024 breakout?

    I want to run 13 boards, and I was assuming I would need a 3.3v regulator in addition to the one on my teensie 4.0. (I know the picture shows a 3.2)

    However, measuring the current drawn by the board when both LEDs are lit to full strength, I was only seeing draw of 6.5ma

    Click image for larger version. 

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    That would suggest I could easily run all x13 for just 85ma - which my gut says is implausible.

    I would normally budget 30ma for bright 3mm LEDs - so 30x2x13 > 0.8amp


    Any advice (before I change my design) would be very welcome.

  2. #2
    Senior Member
    Join Date
    Jul 2020
    Posts
    463
    Most 3mm LEDs will be rated 20mA maximum, so 30mA is possibly bad for them. Modern hyperbright LEDs need
    a lot less than 20mA to be bright enough for indoor use... Perhaps your 3mm LEDs are only superbright or ultrabright?
    (Actually I can't remember which of these meaningless marketing terms is supposed to be the brightest!).

    As LEDs evolved from the first primitive red GaAs LEDs the brightness was improved a 1000 times or more, so there
    are lots of different brightnesses available depending on the process used. The datasheet will normally say what
    the luminous intensity, beam angle and luminous flux are for a given forward current. Just beam angle can have
    massive effect on luminous intensity.

    These days properly bright LEDs use heterojunction/quantum well design similar to semiconductor lasers, and
    are getting pretty close to 100% quantum efficiency.

    1--5mA is normally plenty for a modern indicator LED. The smaller the LED the less current you need for it to
    hurt your eyes!

  3. #3
    Thank you very much @MarkT, for your interesting and helpful response.

    It does sound like I should have more than enough mA to go around.

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