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Life time of an optocoupler
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ali_asadzadeh:
Hi,
I want to isolate a digital IO, So I used EL817 as the main optocoupler, due to speed requirements, I have drived the input of the opto @ 10mA and the output transistor also is driven @ 10mA, so my question is, Does this affect the life of the input LED? how many hours or years of work should I expect? generally what's the life of an optocoupler?
Cliff Matthews:
MTBF is the term you are looking for. Google gives PDF's and about 40K results on "MTBF optocoupler"
David Hess:
For whatever reason, optocouplers are not as reliable as other common parts.  They all seem to degrade over a period of decades with a loss of current transfer ratio.  I suspect this has to do with loss of output from the GaAs LED.

DBecker:
The MTBF number isn't directly useful here.  You aren't concerned with failure, but rather the transfer ratio dropping below your specific threshold.

The light output of the LED decreases over time due to several factors.  The dominant one is high LED current.  To compensate you can increase the LED current.  Which obviously becomes counterproductive.  The alternative is to select parts with a higher CTR and run them as gently as you can, or use a digital isolator.

SiliconWizard:
A typical LED's operating time is in the order of thousands of hours; they rarely die suddenly (unless the conditions are very severe), but they will lose brightness over time.

I would expect something similar for optocouplers. Thousands of hours may sound like a lot, but if your device is operating 24/7, it's really not. 10000 hours, for instance, is just a bit more than 1 year of continuous operation. Of course, in practice, even under 24/7 operation, the opto's LED won't be ON at all times, thus the operating life will be a multiple of this.

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