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Life time of an optocoupler

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neilhao:

--- Quote from: ali_asadzadeh on December 08, 2019, 06:14:56 am ---Thanks neilhao, I managed to lower the input led to a lower level, Now it can work with 2ma! does it mean I should bother about aging?

--- End quote ---

Actually you will get the reasonable aging life when the current is about 5mA to 10mA. The concept had been well explained by Kleinstein. Of course, the optocoupler temperature may be rosen by the 5ma current about 1C to 5C, but compares to the affection of other heat sources in your system, the affection to the aging life may be omitted.

According to my experience, the major factor which affects the aging life of optocoupler is the environmental temperature near the optocoupler. This temp can be roughly measured by attaching a thermocouple to the optocoupler case. Low temp = long aging life, however for my design, a ACDC, the major heat source is not the optocoupler, but mosfet. The optocoupler temp is risen up by the heat exchange between the optocoupler and the heat sources. Therefore, try to keep the sufficient  clearance from  the optocouplers and the heat sources. The heat sink may also necessary.

I used EL817 in a ACDC design. The high temperature aging life was more than 11.4 years when the current was 5ma.  You will notice the major heat source is the Switcher IC which contains the Mosfet.

coppice:
The ageing of LEDs in a pain. I did a couple of things where pulses from a LED along a fibre were used to report measurement results. These designs had to operate for at least 25 years. The only way to keep the LED output reasonably consistent for that long was to use a high lifetime LED, a variable current drive for it, a light sensor, and some MCU software to use the sensor to steadily adapt the LED current over the years.

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