# PSPICE - where to discuss best in these forums?

Discussion in 'General Electronics Chat' started by Krischu, Jul 11, 2014.

1. ### Krischu Thread Starter New Member

Jul 11, 2014
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Hi, I'm new to "allaboutcircuits". In searching the web for "pspice forum" I came across this site. It looks to me quite well visited, so I jumped in. I'm from Germany, so bear with me if I express myself strangely sometimes

Ok, now for my question: I'm a senior electronics engineer with little experience in Pspice. Got a bit acqainted to Pspice by Orcad Pspice student and now LT Pspice. Anyway underlying them all seem to be PSPICE and my question is where to discuss PSPICE problems or questions best here.

My particular problem is to define and simulate a variable capacitor (rotary capacitor) The angle of the rotary arm is the input value, the output value is the capacity.

Any help much appreciated,

--
Christoph

EDIT: I thought I'd add another diagram showing the equivalent circuit for the capacitor. The plates of the stator od rotor are formed as segments of a circle (like a pie slice), and as the rotor moves toward covering the stator plates the area increases linearly and thus the capacitance.

So maybe the PSPICE problem reduces to me to define three variable capacitors, each with a value defined by function in the angle.

Still difficult enough to me PSPICE beginner

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2. ### MrChips Moderator

Oct 2, 2009
12,636
3,454
Welcome to AAC.
This is the correct forum to discuss general Pspice issues. There are many users who would be more than happy to help you.

3. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,504
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I am looking though Spice For Circuits And Electronics Using PSpice, Second Edition, by Muhammad H. Rashid, and I don't see anything about variable capacitors.

I know I saw a symbol for variable capacitor in Multisim.

Jan 31, 2014
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5. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,975
1,135
The LTspice Help (at LTspice/CircuitElements/Capacitor) explains the non-linear cap syntax.
Below is an example of its use.
What you've drawn looks like a differential cap. Is that what you want to simulate?

Edit:
Attached is a spice model of a variable cap I've just made. It has minimum and maximum values which you can right-click to edit. A voltage (representing rotor angle) in the range 0 to 1 volt applied to its adjust terminal will vary the capacitance from Cmin to Cmax. Hope that's useful.
Delete the .txt extension from the uploaded .asy.txt file.

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• ###### VariableCap.asy.txt
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Last edited: Jul 12, 2014