# SCR/Thyristor LTSpice simulation

Discussion in 'The Projects Forum' started by ville_91, Jun 19, 2014.

1. ### ville_91 Thread Starter New Member

Jun 19, 2014
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Hello

I'm not very experienced in LTSpice yet, and I'm stuck with my problem. I'm trying simulate the two transistor and two resistor thyristor and I'm trying to get the typical voltage-current curves. In other words, I'm trying to draw a graph anode-cathode voltage vs. anode current. I simulated it by DC-sweeping the the anode voltage. It seems that I get the correct graph up to the breakdown voltage (except voltage is in the y-axis and current in the x-axis). The question is, how will I get the full graph, that is, also the graph when the thyristor in triggered in the forward-conduction mode?
I would appreciate some clear step-by-step instructions. Thanks in advance!
Sorry that I don't have any pictures.

2. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Welcome to the forum!
Can you post your .asc file?

3. ### ville_91 Thread Starter New Member

Jun 19, 2014
3
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Oh yes, of course, here it is.
So, I do the DC-sweep, measure the voltage in the "anode" node and set I(R4) as the x-axis. Now there's also a picture of the graph that I get.

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4. ### Alec_t AAC Fanatic!

Sep 17, 2013
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I don't understand. What you have is the full graph of anode current v anode voltage. If you want to inspect the trigger point you can zoom in on the waveform (click and drag the area of interest); but first reduce the DC increment size to, say, 1mV. You could also do a DC analysis where V1 is swept instead of V2.

5. ### ville_91 Thread Starter New Member

Jun 19, 2014
3
0
The problem is that I also want to talso get the voltage-current characteristics once the thyristor has been triggered into forward-conduction mode. So the curve should look like the picture below. I'd like to get a curve that also shows how the anode current depends on the anode-cathode voltage when the thyristor is in forward-conduction mode. So the problem is that LTSpice does the sweep only once, and that's why it doesn't show what happens after the triggering.

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6. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Ah, I see now what you're after. You can get LTS to do a DC sweep through a list of values, but when I tried that I couldn't get a voltage or current plot at all . Like you, I'm still getting to grips with LTS, so perhaps someone else here can advise.
That curve involves reverse-voltage breakdown, which LTS doesn't model directly. You would probably need to add zener diodes at strategic points to model breakdown.