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.
An externally hosted image should be here but it was not working when we last tested it.
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 😀
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.
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.
Attachments
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)
1) Macromodel subcircuit (TL431_a)
2) Device-level subcircuit (TL431A)
3) LTSpice symbol file for the above (TL431.asy)
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:
both cross over at the same frequency.
and here's a Bode plot for a real Texas Instruments TL431:
An externally hosted image should be here but it was not working when we last tested it.
both cross over at the same frequency.
and here's a Bode plot for a real Texas Instruments TL431:
An externally hosted image should be here but it was not working when we last tested it.
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:
Looks like there's some other good material related to LTSpice on that web site.
Dale
- "Realistic SPICE model for TL431: stability, noise, impedance and performance simulation of TL431 shunt regulator" at http://www.audio-perfection.com/vol...ance-simulation-of-tl431-shunt-regulator.html
- "Accurate TL431 model development, analysis and evaluation" at http://www.audio-perfection.com/voltage-regulators/linear-regulators/accurate-tl431-model-development-analysis-and-evaluation.html
Looks like there's some other good material related to LTSpice on that web site.
Dale
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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Christophe Basso linked to this Audio Perfection series of notes on the TL431 from his website-- interesting to read, analysis of impedance and noise
Realistic SPICE model for TL431: stability, noise, impedance and performance simulation of TL431 shunt regulator | Audio Perfection
Realistic SPICE model for TL431: stability, noise, impedance and performance simulation of TL431 shunt regulator | Audio Perfection
An impressive and helpful job for simulation and understanding.
For those of us using the TL431 on a whim, I understand Figures 16 and 18 (Stability Boundary Conditions) of the datasheet such that the capacitive loading for safe operation should be either up to 1nF (capacitor tolerances taken into account) or above 10uF. Making sure that the parallel loading circuit remains below 1nF may be difficult, so, in practice the advice for DIYs is to give it 10uF between Anode and Cathode as a minimum?
Am I right here?
For those of us using the TL431 on a whim, I understand Figures 16 and 18 (Stability Boundary Conditions) of the datasheet such that the capacitive loading for safe operation should be either up to 1nF (capacitor tolerances taken into account) or above 10uF. Making sure that the parallel loading circuit remains below 1nF may be difficult, so, in practice the advice for DIYs is to give it 10uF between Anode and Cathode as a minimum?
Am I right here?
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