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Old 14th February 2007, 05:31 PM   #21
Wizard of Kelts
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Okay, I just saw your last post. I'll go look up the values for audio xformers.

Still the issue of how to do the AC source.

I do appreciate the advice I am getting very much.
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Old 14th February 2007, 05:39 PM   #22
kevinkr is offline kevinkr  United States
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To get an ac source go to the component library, click on voltage source and place it. Then click on the symbol in your schematic, click the advanced box, select sine, and then enter the values into the appropriate dialogs.

The program has a reasonably good help function. There is a users forum for SwitcherCad as well, I'd google for it.

You can't drag symbols from other programs into a spice schematic capture.

Once you get a little more familiar with the program and its quirks you'll quickly wonder how you did without. It is excellent..
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Old 14th February 2007, 05:50 PM   #23
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Quote:
Originally posted by kelticwizard
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?
To do this, first make sure you have your (maybe empty) schematic open. Now open up transformer.asc or transformer2.asc from the LTSpice educational directory. With the transformer schematic as the current schematic, press F6 to copy. Now drag the cursor over the transformer and its coupling spec. When you release the mouse, you'll see a "ghost" image of the transformer that you can drag around. Press Ctrl-tab to activate your schematic. Now press Ctrl-V to drag the transformer into place.
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Old 14th February 2007, 06:12 PM   #24
Wizard of Kelts
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Quote:
Originally posted by kevinkr
To get an ac source go to the component library, click on voltage source and place it. Then click on the symbol in your schematic, click the advanced box, select sine, and then enter the values into the appropriate dialogs.

Well, I go to the top "browser", click file-open swcadIII-lib, then get three folders: cmp, sub, sym. Opening "all files" to read, I see nothing which corresponds to ac voltage source. I go to power products, figuring that is where a power AC source would be, and I see a lot of numbers beginning with LT.

So where among these three folders do I find my voltage source and, once found, how do I get it up into the browser so I may click on it and then fill in how sine and voltage desired, (10 V).

I'm not actively trying to be thick, honest, but I am hearing how I can just draw this in, and wherever I go, except for the resistor and cap, I'm running into blockades.
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Old 14th February 2007, 06:15 PM   #25
andy_c is offline andy_c  United States
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Press F2 (same as Edit, Component), select "voltage" in the list and click OK.
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Old 14th February 2007, 06:56 PM   #26
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Oh, and just to make sure, you did start out by doing a "File, New Schematic" to give yourself an empty schematic to work with, right? If you don't do this, then many menu items will be missing or disabled.
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Old 14th February 2007, 09:25 PM   #27
kevinkr is offline kevinkr  United States
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Click the little AND gate symbol to get into the root level of the library where you will find the many components including all sorts of sources.
You have to have a file loaded or have selected new schematic from either the menu or toolbar.

The device you want is simply called "voltage" and is the second to last entry, scroll all the way to the right without clicking anything, then select it by clicking on it and you will see it is a voltage source. Then do as I instructed in a previous post to configure it.

Please read the program help section, it will answer most of your questions..

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Old 14th February 2007, 09:56 PM   #28
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Orcad, Microcap, Pspice, SWCAD and others are all merely front ends for spice, a time domain circuit solver developed at UC Berkeley. They all have some of their own enhancements to make them slightly different from the others.

The spice net list is a text file that is passed to the spice "engine". The schematic capture user interface translates your drawing into proper syntax spice statements. When you tell the simulation to run, you are telling the user interface to pass the net list to spice.

Back in the bad old days, before computing power was so high and cheap, the only way to enter a schematic into spice was to manually generate the netlist. I know because I used to do it. It was hard to do without making mistakes, so I spent a lot of time debugging my netlists.

In SWCAD, if you want to see the netlist, go to the view menu and select "spice netlist". Of course, there is only a netlist after you've entered a schematic...

There are numerous educational schematics packaged with SWCAD, including some basic transformers. Look through the folders...

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Old 14th February 2007, 11:57 PM   #29
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Okay, I'm getting a feel for this, but having just a bit of trouble with this inductor/transformer thing.

I tried drawing L1,then L2 according to the Kevin's formula, then putting in the K ratio, but it wouldn't fly.

So I got to the point where I was just ready to add the transformer, and hope I can be walked through on this. After this, I'll probably go to the support forum, but I want this one maiden voyage done here, if i can.

I figure 25H for the primary inductance, turns ratio 4:1, (if that means the secondary is higher).

I enclose a screenshot of where I am right now.

Just tell me what I do from here about the inductors and K coefficient, button by button if possible. Much thanks so far.
Attached Images
File Type: gif transformer inductor switchercad.gif (4.1 KB, 87 views)
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Old 15th February 2007, 01:38 AM   #30
Wizard of Kelts
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Well, I think I got it to work.

The circuit didn't work as I hoped, but at least I got a reading.

Turns out that it doesn't matter when you put in that directive for the SPICE directive to make the inductors into a transformer.

Circuit didn't work, but at least I can do a simple model now.

Much thanks to everyone for their patience.
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