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Old 3rd August 2013, 09:14 AM   #1161
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Default Doubly Inscrutable.

Quote:
Originally Posted by jcx View Post
takes tables of data... in examples\Educational\FRA folder
inscrutable directions - but I got it to work
could be an approach to answer David's interest in Nichols plotting?
It is certainly obscure, as is your own response, since it's in a different thread in a different forum You do like to hide your lamp under a bushel.
But thanks for the idea, I will see if it works.

Best wishes
David
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Old 4th August 2013, 03:43 PM   #1162
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Quote:
Originally Posted by jcx View Post
in examples\Educational\FRA folder

inscrutable directions - but I got it to work
I tried it as per instructions - run the ASC, view the error log, R. click and select "Plot Measured data", When window pops up then choose yes to combine Real and Im. data.
A new plot window appears, but no plotted data.
What's the secret trick?

Best wishes
David
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Old 4th August 2013, 04:17 PM   #1163
jcx is offline jcx  United States
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in any plot window you can see what data it can plot by right clicking, selecting Add Trace or select from tool bar View>Add Trace

there is a ReadMe.txt in the FRA folder too - doesn't add much but you may not see it if you navigate there inside LTspice with .asc default
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Old 4th August 2013, 05:04 PM   #1164
jcx is offline jcx  United States
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and of course you need a solution for Vista and later file/folder permissions defaults - I just "save as" any .asc from Program Files/LTspice/Examples... in a subfolder in My Documents before running
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Old 5th August 2013, 12:55 AM   #1165
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Quote:
Originally Posted by jcx View Post
in any plot window you can see what data it can plot by right clicking, selecting Add Trace or select from tool bar View>Add Trace

there is a ReadMe.txt in the FRA folder too - doesn't add much but you may not see it if you navigate there inside LTspice with .asc default
Thanks for the reminder. I don't update LTSpice very often and I had only read the old txt. RTFM and it works.

Best wishes
David
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Old 19th August 2013, 11:40 AM   #1166
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Question ISC and NC?

I have asked about this in Solid-State without response, so perhaps there is an expert here?
Any comments on the ISC and respective NC parameters?
It is the Base/Collector version of ISE and NE which control low current Beta fall off.
As far as I can see it should be mostly irrelevant in typical audio circuits.
But some of the "reverse" parameters have an impact on normal operation because of the way the Ebers-Moll and Spice models handle all quadrants with one set of equations.
So, any tricks or recommendations?

David
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Old 18th September 2013, 12:28 PM   #1167
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I've been searching all afternoon to try and work out what is a reasonable series resistance to put in a voltage source for an AC voltage in a PS simulation. (I use a sine wave to simulate the AC voltage).

All I have been able to find is "Voltage sources are ideal you should add some realistic parasitics for resistance and capacitance" The problem is I have no idea what is realistic!!

I was seeing RMS current in the first caps in my PS of around 5.5A Which is a lot. I figured this was unlikely as the transformer in reality would not be a perfect voltage source. I added in 0.1 ohms of series resistance and the current in the caps dropped quite significantly (along with the rectified voltage).

The thing is I don't know of 0.1 ohms is a reasonable number to put in. It may be too high or too low. The main reason I was simming was to try and get a feel for whether the caps I was looking at would be up to the task.

Anyone able to make some suggestions?

Tony.
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Last edited by wintermute; 18th September 2013 at 12:29 PM. Reason: add sine wave.
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Old 18th September 2013, 05:07 PM   #1168
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Quote:
Originally Posted by wintermute View Post
I've been searching all afternoon to try and work out what is a reasonable series resistance to put in a voltage source for an AC voltage in a PS simulation. (I use a sine wave to simulate the AC voltage).

All I have been able to find is "Voltage sources are ideal you should add some realistic parasitics for resistance and capacitance" The problem is I have no idea what is realistic!!

I was seeing RMS current in the first caps in my PS of around 5.5A Which is a lot. I figured this was unlikely as the transformer in reality would not be a perfect voltage source. I added in 0.1 ohms of series resistance and the current in the caps dropped quite significantly (along with the rectified voltage).

The thing is I don't know of 0.1 ohms is a reasonable number to put in. It may be too high or too low. The main reason I was simming was to try and get a feel for whether the caps I was looking at would be up to the task.

Anyone able to make some suggestions?

Tony.
Connect a 100-watt light bulb to your mains and measure how much the mains voltage falls. Then measure the current being drawn by the light bulb (you can put a 0.1 ohm resistor in series with it and measure the drop to see what the bulb current actually is). Then simply divide the observed mains voltage drop by the measured current of the light bulb. If the mains drops 0.2V and the bulb draws 0.8A, then the mains resistance is on the order of 0.25 ohms. Try to do this at a time when the mains voltage is not moving all over the place.

Cheers,
Bob
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Old 18th September 2013, 11:03 PM   #1169
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ah thanks Bob. I probably should have specified I'm not using a transformer in this model (being a bit lazy) I was just setting a voltage source up with a 50Hz sine wave and 1.414 X the expected rms transformer secondary voltage. But what you have just told me makes me think it would be best to actually make a transformer in spice Time to go read those spice chapters in your book me thinks

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Old 19th September 2013, 12:32 AM   #1170
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You can get a good Transformer resistance from its regulation spec.

eg 500VA 50V 10A transformer with 10% regulation means the output voltage will drop 10% at full load of 10A. ie 5V at 10A which give you 0R5 series resistance. All calculations with AC

For da nitpickers, there is a difference between da rebel colonies (US of A) and da old world over whether the voltage spec is at full load, no load or something in between.

But if you want to sim charging currents in a conventional PSU, you need the leakage inductance of the transformer too. I think I saw a page with typical inductances of big toroids somewhere.

I think this is enough to simulate a transformer. No need to do a full model.
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