Free Spice Or Cheap Spice Simulator-Where To Start?

[richie00boy]

Pete you draw the schematic in the schematic editor of the software (SWcad or Microcap or whatever), so unfortunately you have wasted the effort of doing it in paint

It's pretty easy to draw the schematic once you get going. There's usually a button along the top somewhere for you to select components like passives and semiconductors.

I use an ancient version of Microsim. I tried SWcad for a brief moment, but I found it a little harder to use and I couldn't be bothered at the time.

I might have a look at Microcap.

[phase_accurate]

The demo version of ORCAD/P-SPICE can be had for free but it is limited to 50 elements. The circuit capture function is quite easy to do. If you can't get it from ORCAD themselves I can send you a copy of the CD (it actually says: "Copying of this software is welcomed and encouraged !").

Regards

Charles

[kelticwizard]

Richie:

Pete you draw the schematic in the schematic editor of the software (SWcad or Microcap or whatever), so unfortunately you have wasted the effort of doing it in paint

No biggie. If using schematic draw is as easy as using Paint, I will have learned a valuable thing. I'll be starting the schematic draw later today to see what happens.

[kelticwizard]

Charles:

Thank you for the offer. I'm off to the Orcad website to see about obtaining the demo. I'll definitely be in touch if I can't get it from them.

[richie00boy]

Using the schematic draw is even easier then Paint! There is a grid to help align things and the components are already drawn, you just pick them and drop them where you want them. Then link them with the wire tool.

[kelticwizard]

Unfortunately, I am still having trouble.

I got the AC source by opening audioamp and starting a new schematic above it, then dragging the AC source from audioamp to that separate space.

I wanted to avoid getting the transformer by making two inductors, because then I would have to go to coupling coefficients and would complicate things. So I went to another file with transformers in it, but cannot move the transformer to the "audioamp" file where I am building the new schematic, above and separate from the already existing audioamp file. After my new schematic was complete, I planned to copy it to a new file.

How do I capture an existing tranformer in a separate file and import it-just the transformer, not the rest of the circuit-to a different file?

[kevinkr]

Linear Tech Spice AKA Switchercad is free and has an unlimited number of nodes. Best of all there are lots of tube libraries available for it. Most competing op-amps models can be easily plugged into it as well.
I've used MCAP in the past, but now exclusively use LTspice.

[kelticwizard]

I am using switchercad, but they have a limited number of things to plug into the draw from the top "browser" line. A transformer is not among them, so I need to know how to import a transformer from another file in switchercad to avoid using a double inductor and coupling coefficient.

[kevinkr]

Originally posted by kelticwizard
I am using switchercad, but they have a limited number of things to plug into the draw from the top "browser" line. A transformer is not among them, so I need to know how to import a transformer from another file in switchercad to avoid using a double inductor and coupling coefficient.

I don't understand the issue, this is how transformers are done in spice.. To get the transformation ratio right select a reasonable inductance for the primary (say 25H - 50H for a 3K primary) and to get the secondary inductance divide this by the square of the turns ratio. Set K=1 (coupling coefficient) and if you want to simulate leakage inductance add an inductor in series with the primary of an appropriate number of mH.. (This generally is easier to manage and results in less calculation overhead.) This should suffice for most applications.

[kelticwizard]

Let me spell out the problems I am having on this maiden voyage, because they might not be clear from my previous posts.

I go to swither cad. I want to analyze the circuit on the previous page drawn in Paint.

A) Where do I get the AC source-how do I draw, or from where do I import? I would like it to be 10 V, 1.25 amps.

B) I don't think I'll have trouble entering the resistor and capacitor

C) Where do I get the audio transformer to put into the drawing. Do I draw it, or do I import it from the Educational circuits. How do I import it-I tried drag, I tried move, I can put a dotted box around the Xformer and move it around it's own circuit-but cannot move it to the file which contains the circuit I am building.

I have gotten advice that it is easy to draw a circuit, but with this simple circuit I see no way to get an AC source or a transformer, and that is half the circuit.