Optocoupler LED Aging

Discussion in 'General Electronics Chat' started by ¡MR.AWESOME!, Feb 8, 2011.

  1. ¡MR.AWESOME!

    Thread Starter Member

    Aug 15, 2010
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    After awhile, optocouplers get old and their Current Transfer Ratio becomes smaller meaning that the amount of current able to pass through the collector decreases for the same current put in to the emitter.

    How can one figure out what the forward current on the emitter should be for the longest optocoupler life but still be able to turn on the transistor enough after aging and the CTR decreases?

    Let's use the FODM124 as an example. Here's the datasheet
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Spacecraft do not use opto-couplers because of the aging problem.
    Maybe you can invent an auto-calibration circuit that works occasionally.
     
  3. ¡MR.AWESOME!

    Thread Starter Member

    Aug 15, 2010
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    Huh. That's an interesting piece of info.

    That's probably what I would have to do if I had no other choice.

    Is the end of life specified as when the CTR reaches 50% of it's original value for a consistent emitter forward current? Because then I could take that in to account and provide an emitter current that would still allow enough collector current to get the job done. Although, a higher emitter current will increase the rate of aging. Right?

    For example, the FODM124 has a CTR of a bit more than 100% at an emitter current of 1mA. If I need 1mA to pass through the collector for the whole lifespan, than I would use 2mA for the emitter.

    Do you think that's a decent, rough way to do it?
     
  4. blueroomelectronics

    AAC Fanatic!

    Jul 22, 2007
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    What are you trying to build?
     
  5. ¡MR.AWESOME!

    Thread Starter Member

    Aug 15, 2010
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    The design I'm currently working on only needs to ground a PIC pin so the aging effect doesn't really affect the design. I was just curious for future projects.
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    I have never seen a test of LED aging in an opto-coupler but maybe somebody has done one. But every manufacturer uses a different process so the results will vary amongst their products and different part numbers.

    I have a clock radio that is about 35 years old and its LED display has been lighted continuously for the entire time. Last year I decided that it is too dim in the daytime to see it but it is still working (I listen to it sometimes).
     
  7. ¡MR.AWESOME!

    Thread Starter Member

    Aug 15, 2010
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    I read this. It was barely informative.

    There is also this paper which may be more informative, but I don't have access to it.
     
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