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I have a simple circuit with a MOC and Snubberless TRIAC.

I am using the ST Snubberless Library for my simulation.

I cannot understand why the TRIAC does not turn on in the negative half cycle, even though there is a negative gate current and negative terminal voltage.

Perhaps I am burnt out of thinking about this problem for too long, a second eye would be appreciated. The model file itself could be the problem, but again, I am not sure. enter image description here

The green graph is the gate current. The orange graph is the voltage across the load. The cyan graph is the voltage over MT2 and MT1 (VAC and Vload).

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    \$\begingroup\$ Note that snubberless TRIACs are 3 quadrant devices designed to NOT fire in 4th quadrant. You are not describing 4th quadrant problem but it may relate. \$\endgroup\$ – Russell McMahon Aug 14 '14 at 14:49
  • \$\begingroup\$ Yes I am aware of the 4th quadrant. That is where there is a positive I_G and negative I_T, correct me if I am wrong, and here in this simulation that case does not occur. The library has snubberless and standard models in it, using the standard model, there are no issues. There is a strong possibility that the model file itself has an error. I am going to sit and try to make sense of the model file \$\endgroup\$ – Armandt Aug 15 '14 at 6:38
  • \$\begingroup\$ Your text:"There is a strong possibility that the model file itself has an error. I am going to sit and try to make sense of the model file" I am seeing same thing. I have a PCB using snubberless ST:"T410-600B-TR". ST model shows the operaton seen in your graph above. PCB shows the TRIAC triggers in 3rd quadrant as expected. I have not noodled through the model to find why model does not work like PCB. \$\endgroup\$ – Curt Sep 30 '18 at 16:13
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This is a mistake on Lib file. Open lib in a text editor like notepad. Find your part number. change "Standard=0" to "Standard=1"

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