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    Is a snubber circuit required with zero-cross optocoupler

    I am a newbie to power electronics but can understand the basics. My very specific question is, whether a snubber circuit is needed for a triac that is driven by an optocoupler that is based on zero-crossing, like MOC3043?

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    Re: Is a snubber circuit required with zero-cross optocoupler

    I think it depends on the application. If you've got an inductive load, where current and voltage are 90 degrees out of phase, you might still need a snubber.


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    Re: Is a snubber circuit required with zero-cross optocoupler

    Quote Originally Posted by barry View Post
    I think it depends on the application. If you've got an inductive load, where current and voltage are 90 degrees out of phase, you might still need a snubber.
    Hi Barry, thank you for response. So, if I understood you correctly, since it is zero cross voltage, current might still not be zero which can cause undesirable effect. in this case, what type of capacitor is ideal. should I go for capacitors at some rated AC voltage of like 275VAC or a smaller one will do as we only deal with current?



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    Re: Is a snubber circuit required with zero-cross optocoupler

    A snubber is a good idea if the load is unknown, these drivers switch the triac on soon after zero crossing, so the load current will start from zero too ( although will go up quickly for some loads ) when the opto led drive is removed the triac will turn off as the load current goes through zero - as long as the re-applied dv/dt does not trigger it back on - some inductive or motor loads can provide a back emf which can trigger the triac back on - the snubber is to prevent this ... ( the dv/dt at turn off being too high )



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    Re: Is a snubber circuit required with zero-cross optocoupler

    I experienced a case where a MOC3040 plus triac combination was periodically self triggered even with pure resistive load by power supply dV/dt. A 220 ohm/47 nF snubber and filter was added to the MOC3040 circuit.



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