moc3041 optocoupler life

i am using moc3041 in combination with bta16 triac to control a 230v relay coil, it is on for 24 x 7 all the time. my doubt is what is the led life time of moc3041 how much hours it will burn? are how much years moc will work good if it is on for 24 x7.

You are correct about your concern, the LED in the optocouplers does degrade over time.

Since a Triac, once that it latches, does not require additional triggering...................Something that you could do, is not to have the optocoupler on continuously, but pulsed.

In a 50 Hz powerline, each semicycle lasts 10 msecs. In an inductive load the current will lag, very worst case 90 degrees or 5 msecs after the voltage zero crosses. But most likely the current lag will be between 2 or 3 msecs after voltage zero cross.

So synchronize a delay with the voltage zero crossing, wait for 2 msecs, and then apply a 3 msec pulse. Then the Led will be on for just 3/10 = 30% of the total period.
The complete circuit can be done with half LM393 comparator, and the two monostables contained in a single CD4538.

If proper protective measures are adopted to prevent the Opto operate under harsh electric conditions ( avoiding surge current on LED, adding snubber on out ), the expected degradation of this component should be negligible if compared to other power devices on the circuit (Triac, Relay). As a thumb rule, with certain excuse, we could assume that lifespan of components decays radially from inner circuits ( TTL, CMOS levels ) to external circuits which interface with the "world" ( communication devices, power driving, etc...).

schmitt trigger said:

You are correct about your concern, the LED in the optocouplers does degrade over time..

Click to expand...

Of course every component decays over time and fails in an unpredictable way. I believe power components are more prone to failure but passive components like resistors and capacitors too fail in a circuit from time to time.

The life of any given component under specified conditions follows a normal distribution with a given "typical life" - MTBF and variance. We have another parameter widely called- accurately or not I do not know- "infant mortality". Some components die early but most survive and live a happy and productive life.

I have no specific detailed information but I know that LEDs are rather long living and other components, e.g., the triac or the diac or the capacitor (somewhere) will perhaps fail *before* the opto-coupler fails.

Unless it is a case of infant death.

I have heard that the light output of LEDs decays to 75% over 40K Hrs (~10years). Transistors do not decay, so it all depends on when your circuit thinks the light output of the LED is too low.
Frank

In power supplies with a phototransistor output and operate linearly, it is customary to use low (1 or 2 mA) in photocouplers to prevent aging.

However on a photo triac output, which must be driven hard, aging is a distinct possibility.

That is why I suggested the pulse method, as once that the Triac is triggered, it no longer requires gate current until the next semicycle.

schmitt trigger said:

You are correct about your concern, the LED in the optocouplers does degrade over time

Click to expand...

I would review my previous assumption, and now agree much more with your assertion. In fact, for some reason ( perhaps, intrinsically due to the GaAs substrate itself ), the failure rate of the Optocouplers are much larger than if compared to single LEDs, so that we could not see it as a standard low power device, but somehow as encapsulated "amplifiers". Optocouplers rather than Optoisolators are devices which has to have certain internal amount of energy enough to activate its output stage, and I would dare to say that increasing its insulation breakdown voltage ability would even require higher level of energy, somewhat aging few more the component.

Of course LEDs dim when operated continuously. You should see my clock radio that is about 30 years old and its LED display has been on the entire time. It can barely be seen in daylight now.
NASA has banned LED-opto products and LEDs from its spacecraft because they dim over time.