Would like to know the difference between these two 4N35 optocouplers . They behave differently but cannot find what is related the "001Q" and "027Q" digit.

enter image description here

  • 1
    \$\begingroup\$ I would normally expect a date code in that position. Often in the form of a Year/Week. It is usually 4 digits though. \$\endgroup\$ Commented Sep 26, 2023 at 16:06
  • \$\begingroup\$ ...and behaving in a different way?? \$\endgroup\$
    – Ken90
    Commented Sep 26, 2023 at 16:13
  • 5
    \$\begingroup\$ behave differently is a vague, useless description of observed behavior ... how do the two components behave? ... please add the schematic of the test circuit \$\endgroup\$
    – jsotola
    Commented Sep 26, 2023 at 16:29
  • \$\begingroup\$ In what way are they behaving differently? There's a wide variation in CTR from part to part (esp. from different lots) so could be normal process variation. \$\endgroup\$
    – John D
    Commented Sep 26, 2023 at 16:30
  • \$\begingroup\$ @Ken90 - Just FYI (since other site members are suggesting you to add to the question): If you want to ask about the difference in behaviour you are seeing (whatever that is) and if you can provide schematics, measurements, analysis etc. that would be a reasonable question. However it would need to be asked as a new question, as it's too late to change this question from its original request to explain the different top codes. \$\endgroup\$
    – SamGibson
    Commented Sep 26, 2023 at 17:05

2 Answers 2


As commented, the different lines "001Q" and "027Q" are just date and assembly codes.

Top markings on OnSemi 4N35 opto-coupler

Image source: OnSemi 4N35 Optocoupler Datasheet

The two optocouplers should behave the same. If they don't, then either they are damaged, fake, being operated outside their specifications, or the difference is within specifications.

  • \$\begingroup\$ thanks. Will open another topic with different behavior problems eventually \$\endgroup\$
    – Ken90
    Commented Sep 27, 2023 at 5:18
  • \$\begingroup\$ /Should/ behave the same within the operational ranges specified by the datasheet. It's definitely not safe to measure the parameters of one and expect others- even assuming they're genuine- to behave the same to the last microamp. \$\endgroup\$ Commented Sep 27, 2023 at 9:34

the 4n35 to my knowledge has a few "edits" or versions since the first ed, from which it has been perfected. so the newer ones are likely more "linearized" in the optical current conversion. there's only a few "edits" of the old one 4n35. the newer ones are more linearized but also suffer a narrower slope.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.