Optocoupler Current Requirement Confusion

Other Hardware General Electronics
1

Hello,

I am looking at using a MOC3033M in a project and have got myself a little bit confused about the current requirement for the LED.

Datasheet: https://docs-emea.rs-online.com/webdocs/12cf/0900766b812cfe58.pdf

Reading that for the MOC3033M, it states that maximum current for switching the LED (IFT) is 5mA so to me that would suggest if I'm using an ESP8266-01 with a voltage of 3V and the MOC3033M having a forward voltage of 1.25 that I would need a 430ohm resistor to limit the current to below 5mA?

(3.3v - 1.25v) / 0.005 = 410ohm

However, there is then a line underneath that really confuses me:

"All devices are guaranteed to trigger at at an If value less than or equal to max IFT. Recommended operating IF lies between 5mA for MOC3033M and absolute max IF (60mA).

So that first sentence is saying to me that it the LED will light for any current that is less than 5mA... so the 430ohm resistor would work fine... however, the second part of that block then goes on to say the recommended value is between 5mA and 60mA which contradicts the first sentence and would suggest to me that I could put anything up to 60mA through it and it'd be fine.

Can someone shed some light on my confusion please as it's bugging me and I don't want to kill either my ESP8266 or the MOC3033M.

Thanks

2

The absolute maximum section shows that the LED has a maximum of 60mA.

The trigger current maximum means that for all devices measured, all will trigger at 5mA or less - ie
that is the maximum needed for triggering, not the maximum it can take.

3

So in short, you should aim to be above 5mA to be absolutely sure that your output is triggered!

If you apply less than 5mA it might not trigger.

So maybe rather a 390 ohm resistor.

4

Use 220 ohms, you have to allow for the voltage rail being a bit low, the LED forward voltage being a bit high
and the series resistance of the output drivers (which will be 50 ohms or more anyway)