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Old 28th April 2007, 03:08 PM   #1
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Default What's really going on in that TL431

I thought I would post this -- it's just a simulation -- the standard TL431 model doesn't incorporate all of the reactive componenets in the device -- but does have the temperature dependent resistances fitted in -- some of the TI folks had pointed this out in 2005, so here's what the bode plot should look like -- note I put in 6dB gain block to lift the x-axis -- the graph on the left is the usual TI model, that on the left mirrors reality a bit more.

Click the image to open in full size.
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Old 5th May 2007, 01:37 AM   #2
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Don't ya hate it when you post something cool and nobody says anything? Anyway, I don't use the 431 much, but do have a little bag of 'em to play with, and thought your improved model was more enlightening than the factory version
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Old 6th May 2007, 02:19 AM   #3
andy_c is offline andy_c  United States
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Hi Jack,

This forum tends to be a little sleepy sometimes, partly because it's not linked from the main page I think. I missed your post earlier.

Anyway, here's the schematic of another TL431 macromodel, by analogspiceman of the LTSpice user's group. Also, Helmut Sennewald has done a device-level subcircuit based on the schematics from the datasheet (which have component values). I'll post the subcircuit files of those next.

I originally had a bunch of convergence problems with the primitive TI macromodel. I've had good success with convergence using the macromodel from analogspiceman. I've also compared the frequency domain data of open-loop gain and so forth, and the macromodel seems a bit closer to the datasheet than the device-level model. If you use these along with the LTSpice loop gain probe, you can see stability issues with various capacitive loads. Kind of neat. I've found them useful anyway.
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Old 6th May 2007, 02:22 AM   #4
andy_c is offline andy_c  United States
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Okay, here are the models themselves. Included in the attached zip file are:

1) Macromodel subcircuit (TL431_a)
2) Device-level subcircuit (TL431A)
3) LTSpice symbol file for the above (TL431.asy)
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File Type: zip tl431.zip (1.4 KB, 82 views)
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Old 28th November 2012, 06:14 PM   #5
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Here's a comparison of Christophe Basso's model (from his book "Switch Mode Power Supplies") with Thompson - recently posted to the LTSpice Group over there on Yahoo:

Click the image to open in full size.

both cross over at the same frequency.

and here's a Bode plot for a real Texas Instruments TL431:

Click the image to open in full size.
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Old 30th November 2012, 04:34 AM   #6
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I don't know if this will add new insight, or if it's just old news but I stumbled across discussions (and additional examples) of TL431 macromodels in the "Audio Perfection" web pages:
and:
(Sorry, I didn't try to run the models or verify their accuracy - you'll have to do that yourself if you have particular interest in the TL431. I came across the pages as I was looking for something else, noticed that they seemed to have substantial technical content, and recalled Jack's recent post.)

Looks like there's some other good material related to LTSpice on that web site.

Dale
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Old 1st December 2012, 11:53 AM   #7
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by jackinnj View Post
I thought I would post this -- it's just a simulation -- ...................
Quote:
Originally Posted by Conrad Hoffman View Post
Don't ya hate it when you post something cool and nobody says anything? ...............
But post1 has no sim and no schematic.
What is there to comment on?

Edit:
post5 similarly has no pics.
Post3, 4 & 6 have pics, or attachments/links.
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regards Andrew T.

Last edited by AndrewT; 1st December 2012 at 11:57 AM.
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