Hello,
I am trying to model a circuit for TRIAC firing that will use a DIAC and a potentiometer. But I can't find DIAC in my library.
Can anyone help with this? Also, I don't know how to vary the firing angle of the TRIAC to achieve variables for the output voltage.
Thanks
Copyright © 2020 Cadence Design Systems, Inc. All rights reserved.
Hello,
You can do it this way:
In the top menu, click Place->PSpice component->Search.
In the PSpice Component Search pane, go to Discrete->Thyristors->Triacs
Thank you, Idris.
I was able to design the circuit but another challenge came up, which is how to design subcircuits that will be used to trigger and control the TRIAC/Thyristors.
There are subcircuits that would be needed with a control a signal in form of the firing angle.
Any help regarding this will be appreciated.
Sorry, thought you were looking for TRIACs.
If you need a DIAC PSpice model, ST provides models for its DB30 and DB40 diacs, which are freely available. for download.
http://www.st.com/content/st_com/en/products/thyristors-scr-and-ac-switches/triacs/diacs/db3.html
This really worked for the diode, thank a lot.
If you can give a guide on how to design a subcircuit to fire the TRIAC/thyristor, I will appreciate it too.
Thanks again.
I don't have access to image hosting site from my work computer, so I'm posting the PSpice program in text format, and hopefully you may be able to recreate the circuit.
**** INCLUDING SCHEMATIC1.net ****
* source TRIAC_CIRCUIT
V_VMains VMAINS 0 AC 1
+SIN 0 311VAC 50 0 0 0
R_R1 N08903 VMAINS 450 TC=0,0
X_X3 N08903 N10881 0 MAC97A8
R_R3 N10642 VMAINS {Rpot} TC=0,0
C_C1 0 N10642 0.3u TC=0,0
X_X4 N10642 N10877 DB3TG
R_R4 N10877 N10881 1k TC=0,0
.PARAM rpot=120k
I've added R4 to limit the gate current during the triggering, some circuits do not have it.
And here's a nice video to explain the subject a bit more
http://www.pspice.com/resources/video-library/phase-control-triac
I appreciate your timely response.
I will like to attach a circuit but I don't know how to do that. Please check if the link I copied will work.
https://drive.google.com/open?id=18lnpS2eutAgIsGNXt2vE8zTtybhZlC6m
If I can understand how to design the trigger sub-circuit, my problem is solved.
Thank you Idris.
Hi again,
If I understand correctly, the blocks in your schematics accept a control voltage as input, and use it to determine when to trigger the SCR.
You should notice the {freq} parameter. That is the subcircuit is synchronized with the source (vs). In real life it's not as simple, you would need a Zero Crossing Detector circuit, which emits a high logic level when the mains voltage crosses zero, and using that signal, you can wait for an amount of time, for example 1/4 the period for a 90° angle, and then trigger the switch.
This is probably only useful when controlling the dimmer using a microcontroller, for instance in remotely controlled dimmers. Also, it requires additional circuitry.
If your circuit includes digital circuits and their power supplies, then tell me. We'll be able to elaborate on that.
Hi Idris,
I just feel like I don't understand the basis of how to fire an SCR/TRIACs in a circuit.
From this your post "I don't have access to image hosting site from my work computer, so I'm posting the PSpice program in text format, and hopefully you may be able to recreate the circuit." if there is a way you can use the google drive link to share the source TRIAC_CIRCUIT just as I did, maybe I will get it better.
I have many circuits (ZCS resonant buck converters, VAR control using Thyristor Controlled Inductor etc) to design and simulate that have TRIACs and SCRs in them and I need to fire each of them using different firing angles.
Okay here's an image of the circuit
https://drive.google.com/file/d/1ZQaUzklgnqOR1klh8eecEnGEd1xQx9xY/view?usp=sharing
The RC circuit provides a phase shifted image of the mains voltage. The DIAC starts conducting only at about 30V potential difference at its pins. This makes a sharp pulse at the TRIACs gate, thus triggering it. If the DIAC wasn't there, the input waveform would be a sinusoid and the TRIAC's gate would be "stealing" current from the weak voltage divider and you wouldn't be able to achieve all phase shifts without low resistance at the divider.
Here's an article that explains in detail and gives the circuit explanation:
https://www.electronics-tutorials.ws/power/diac.html
Oh o, now I understand your explanation better.
What if I want the TRIAC to fire after 130degrees, how will I design the circuit based on the circuit you attached here?
Thanks.
First thing you must note that the relationship between trigger angle and power delivered to the load is not linear. I remember reading the exact formula in a power electronics book, so I recommend you refer to one.
For my circuit (Frequency = 50 Hz, Mains = 230V RMS) Rpot at 140kOhm gives about 130° angle. I also recommend running a Parametric Sweep and see how the angle evolves with the pot resistance.
Thank you, you have been of great help.
I have been able to sort it out with your advice and help.
Can I model my resistor to work as a real power load? Like changing the resistor value from ohm to 5KW, 10KW etc.
Hello,
I'm not very well versed in Power Electronics, and I also know very little about your load.
In my circuit, I tried modelling a typical incadescent lamp. Typical power ranges from 40-100W. And usually lamps have a slightly higher resistance when they're initially offf (the filament is cold and more resistive). A resistor is a vey suitable model for the lamp, since it's practically a fixed resistance with very little inductance. So we have R=P/V^2 (I have V=230VRMS)
This probably won't hold for an inductive load such as a motor, and the voltage and current waveforms will be devinitely different.
It seems like all the methods you tried didn't solve the problem. Why not stop playing geometry dash 23 to refresh your thinking. Who knows, maybe you'll find something cool.