Triac Simulation Question

Thread Starter

ppkpatrick

Joined Nov 20, 2020
4
Hello all,

New to the forum and came here to get some more information about simulating mains voltage Triac circuits.
My issue is the following;

I have an opto-isolated TRIAC control circuit for a resistive load (water boiler). I know that Triacs generally have a junction voltage drop of ~1-3V however, in my simulations I am observing a drop of anywhere from 30-40Vac. Can anyone explain what the reason for this is? Part of me is thinking that there is some Gate-to-Main Terminal interaction that I am not aware of.

I am using triac models from ST and have tried a few different models but they all have more or less the same behaviour.
Here is the circuit:

1605909031482.png

Here is the simulated voltage of Vmt2 - Vmt1 (both referenced to ground):

1605909171807.png

Thanks in advance!


1605909031482.png1605909149188.png1605909171807.png
 

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Thread Starter

ppkpatrick

Joined Nov 20, 2020
4
Thanks for this. I have attempted to replicate this circuit exactly in my simulation. However, I am seeing the same as before. Would you mind uploading the .asc file so I can analyze it please?
 

Thread Starter

ppkpatrick

Joined Nov 20, 2020
4
Thanks for this. This is interesting. I can replicate your plots using your symbols and models. But no matter what, I can not replicate the data using LTSPice's default triac symbol, even if I use one of your working models.

i compared one of your symbol files to the default. I am not familiar enough with with this stuff to make any comments though...
Left = bordodynov symbol. Right = default
1605965841611.png

It would be good to know why the default symbol will not work but the main thing is that I can continue to simulate now that this is working as expected.
 

Bordodynov

Joined May 20, 2015
2,733
In my element symbols there is a link to the spice model file. In the standard symbol there is no such a link to the file. To function, you need a link to the model file using the directives ".lib ...." or ".inc ....". For all the other things I use a specially configured symbol for several elements. When you open such a symbol, you can call up a pop-up menu and then select the desired item from the list.
Why do you look inside the symbol file and not open it with LTspice? Use cntrl+right mouse button.
 

Thread Starter

ppkpatrick

Joined Nov 20, 2020
4
In my element symbols there is a link to the spice model file. In the standard symbol there is no such a link to the file. To function, you need a link to the model file using the directives ".lib ...." or ".inc ....". For all the other things I use a specially configured symbol for several elements. When you open such a symbol, you can call up a pop-up menu and then select the desired item from the list.
Why do you look inside the symbol file and not open it with LTspice? Use cntrl+right mouse button.
Yes, normally i add the model i want to use as the "spice model" or "value" parameter in the symbol properties in the schematic editor but it does not seem to work for the default LTSpice triac symbol. I wanted to see the symbol file as text to see if there was anything which explain why it does not work.
 
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