I have a question regarding the MOC30XX series opto-couplers. What is the real difference in their operation? So far I know only that the forward current of the input driving diode is 15, 10 and 5 mA respectively. Is there any difference in their theory of operation, ie. auto turn-off at 0 cross etc? I would appreciate all info.


These all have triac outputs. Triacs have the intrinsic feature to turn off at currents below the holding current. The control circuit takes care not to turn on immediately when the voltage isn't near zero. That makes it safe to use that part as a on/off switch in a simplyfied circuit for inductive and capacitive load. You cannot control phase-angle that way, though.

The MOC3041/42/43 are binned for manufacturing tolerances of the optocouple. That's it.

  • \$\begingroup\$ Thank you for answer. Let me ask a followup question. If I supply the current for the input LED constantly (no switching, LED is ON all the time), should the connected triac fire itself after zero cross automatically (Assuming resistive load)? I am asking this, because I wonder either zero cross detector is necessary here for the MCU just to turn the load ON/OFF. \$\endgroup\$ – Bremen Oct 10 '17 at 9:42
  • \$\begingroup\$ Do you mean "Yes it will turn on" or "yes you need zero cross detector"? Sorry, just want to make sure. \$\endgroup\$ – Bremen Oct 10 '17 at 9:48
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    \$\begingroup\$ It turns on automatically after first zero-cross then. The zero-cross dectector is an add-on which helps you simplyfying your output circuit for inductive loads. \$\endgroup\$ – Janka Oct 10 '17 at 9:51

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