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Which LED do I need?

Discussion in 'Datasheets, Manuals and Component Identification' started by soul73, Jan 12, 2019.

  1. soul73

    soul73

    15
    2
    Oct 27, 2016
    Hey guys,
    My mixing desk needs a new 3mm power LED.

    Can you point me to a LED that will fit? I´ve read a lot about forward voltage and forward current but still can´t figure it out.

    Thanks!

    Cheers,
    Eno Unbenannt.jpg
     
  2. Alec_t

    Alec_t

    2,608
    686
    Jul 7, 2015
    If the 5k1 current-limiting resistor is external to the LED light itself then any 3mm diameter green LED will do. Most green LEDs have a forward voltage of about 2V, so in the circuit shown the current will be (16V-2V)/5k1 = ~2.7mA. That should be enough to give a reasonably bright indication that the power is on.
     
    soul73 likes this.
  3. soul73

    soul73

    15
    2
    Oct 27, 2016
    Thank you so much for your reply, Alec_t!

    Yes, the 5k1 resistor is external to the LED.
     
  4. dave9

    dave9

    674
    153
    Mar 5, 2017
    It seems unusual that a 3mm LED driven at 2.7mA would fail. Are you sure the LED is the fault? I'd sooner suspect a cracked solder joint or ???
     
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  5. soul73

    soul73

    15
    2
    Oct 27, 2016
    I´ve tested the circuit for continuity and couldn´t find a cracked joint.

    The desk is nearly 25 years old now so I suspect the LED simply died of old age.
     
  6. Alec_t

    Alec_t

    2,608
    686
    Jul 7, 2015
    Sounds about right. In my previous car I had to replace a LED which had dimmed considerably. I calculated it had been in use for ~50,000 hours.
     
    soul73 likes this.
  7. soul73

    soul73

    15
    2
    Oct 27, 2016
    After desoldering the old LED I´ve noticed that it had been installed the wrong way round. The new LED works great.

    Thanks again to you guys!
     
  8. dave9

    dave9

    674
    153
    Mar 5, 2017
    ^ ?? It can't have been installed the wrong way round (wrong polarity?) as it would have never worked, or did you mean that you put a replacement in and it didn't work, hence this topic exists?

    LEDs do dim over the years but this is usually when they're driven higher than a couple mA. I've never had any LEDs driven that slightly, fail. They might get a little dimmer, but even things like alarm clocks that have ran 24/7 for 30+ years, aren't noticeably dimmer... maybe I'd notice if they were side by side with a brand new one.
     
  9. soul73

    soul73

    15
    2
    Oct 27, 2016
    Well, I´ve bought the console second hand and I suspect the original LED indeed has never worked.
     
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