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triac help - triac seems to latch and not want to "unla

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asdfghjkl1

asdfghjkl1

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triac help

Hey,

I am trying to put together an ac switch using a triac and a MOC3020. I've tried simulating it with the circuit given in the MOC302x datasheet, but the triac seems to latch and not want to "unlatch". (for sim purposes I used Q4015L5 triac...couldn't find IT415 lib)

I can reduce the gate current so it doesnt' latch and it works fine when I take away the gate it stops conducting...the problem is I don't want to supply the gate current the whole time since I'd be wasting massive amounts of power compared to the latching technique.

Anyways, I was wondering if anyone had any experience with triacs and could tell me a little by about this latching thing. I've found pdf's on it, but they only concern having the right amount of gate current and pulse width to make it latch, not unlatch. Thanks in advance.

edit:
Er don't mind the diode before the MOC, I was trying to trigger it directly before and forgot to take it out :oops:
 

triac help

You're talking of a simulation. How can we know, that you are using suitable simulation models and that
the simulation timestep is low enough to model the zerocrossing behaviour correctly?

The real circuit, at least with a resistive load, won't latch.
 

Re: triac help - triac seems to latch and not want to "

Yes, it seems as though you are correct...I'm not sure what was happening there with the latching. I'm attaching an updated sim. The step is 0.1ms, and I'm not sure where else to get spice models...these were on a yahoo group for LTspice. If you've got some more appropriate ones I'd be happy to use them.
So anyways, back to the latching...do I need to add in an inductor and a snubber network for it to latch? How do I make it turn off again after it latches?
 

Re: triac help

asdfghjkl1 said:
Hey,

I am trying to put together an ac switch using a triac and a MOC3020. I've tried simulating it with the circuit given in the MOC302x datasheet, but the triac seems to latch and not want to "unlatch". (for sim purposes I used Q4015L5 triac...couldn't find IT415 lib)

I can reduce the gate current so it doesnt' latch and it works fine when I take away the gate it stops conducting...the problem is I don't want to supply the gate current the whole time since I'd be wasting massive amounts of power compared to the latching technique.

Anyways, I was wondering if anyone had any experience with triacs and could tell me a little by about this latching thing. I've found pdf's on it, but they only concern having the right amount of gate current and pulse width to make it latch, not unlatch. Thanks in advance.

edit:
Er don't mind the diode before the MOC, I was trying to trigger it directly before and forgot to take it out :oops:
Click to expand...

..It me gairhe.
its been very long time so u must have solved this problem....
i need moc3021 for my final year project. I'm also facing the same problem of latching. Even if i remove the VCC supply at pin 1 of Moc3021 the triac seems to be conducting. How can i switch off the triac...
i'll be very thankful if u help me...

>>gairhe
 

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