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How to run a simple AC sweep in a RC filter

+1 vote
I am trying to learn PLECS.  I have a simple RC low pass filter I want to measure the frequency response.  Please see the attachment.   I can not connect the AC source to the resistor.  The system doe snot allow it.  I think I am missing some kind of interface connector.   Can anybody please tell me how to correctly connect the source to the circuit?


Thank you so much


Victor Castrellon
asked Mar 23, 2018 by vichiker (13 points)

2 Answers

+1 vote

You're trying to connect a signal perturbation source to an electrical circuit.  The green arrow on the source and the open black circle cannot be connected, via any connector.  You need an electrical source from the electrical components.  In order to perturb said source, choose the appropriate controlled source (AC, DC, current, voltage, etc.) and connect your signal source to that.  You can see an example here.  The user manual has more information about small signal analysis.

answered Mar 24, 2018 by angrmgmt (43 points)

angrmgmt :  Thanks for your reply.  

I really try to do what you suggested me but I still can not run the simulation.   I connected the input as shown in the attached schematics but I am still unable to run the simulation.  I know for the experts is a very simple issue. For me, it is hard to implement the correct solution.  Is is possible somebody help me with a more detailed  explanation?  

Any help is very appreciated. 


0 votes

You should see the PLECS demo model "Frequency Response of Passive Circuit" that is included in the software. You will see that you shouldn't use a closed-loop configuration for the small-signal analysis, but a perturbation source and a response block, as shown in the attached schematic.

I hope this helps.

answered Mar 29, 2018 by Kris Eberle (1,575 points)
Thank you Kris,  I appreciate your help.

You know,  I can not find a file in the demo section of the software that runs AC response to a passive network.   I am sure is not there because I went trough all the files and I can not see it.

I put together an schematic using the perturbation source (see attachment)  but when I was ready to run the simulation, I got the error message shown in the picture.   

Any help is very appreciated


Victor Castrellon
Hi Victor,

You can access the Demo Models from the Window menu and you will find the model I mentioned in the Basic Topologies list. You are also able to search for the title in the inbuilt Help Viewer window. But I have attached the model here as well for your reference.