why is this amp clipping?

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https://www.dropbox.com/s/bud5t07msshhldz/Clipping.jpg?raw=1

This is universalopamp2, level.2, and the current limit should be 1
amp. It's behaving like it has internal resistance in series with its
output, or a soft current limit.  

If I use the level.1 amp, which presumably ignores the current limit
parameter, it swings to the rails.  


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Sunday, September 23, 2018 at 8:22:07 PM UTC-4, John Larkin wrote:
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I wish you would post the ASC file so we can confirm your results. Otherwise we are just guessing in the dark.

Re: why is this amp clipping?
mandag den 24. september 2018 kl. 02.22.07 UTC+2 skrev John Larkin:
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maybe it doesn't have rail-to-rail output ?

try upping the supply a few volt and see if it goes away on the high side







Re: why is this amp clipping?
On Sun, 23 Sep 2018 17:33:44 -0700 (PDT), Lasse Langwadt Christensen

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One param is rail=0, which should make it rro. Another is ilimit=1.
Something else is going on.

Making rail=1 or so makes it worse.

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Nope, the waveform doesn't change.

I guess I'll just run at level.1, which ignores the ilimit and rail
params. It's just strange.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Sunday, September 23, 2018 at 8:47:12 PM UTC-4, John Larkin wrote:
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There are 4 levels in universalopamp2. Here are the first two

Op Amp In SPICE terms an op amp is not really a model it is a
sub-circuit (ie it is made up of combination of the basic model
elements). However LTSpice has a handy universal op amp sub-circuit
with 4 levels of complexity. To use it select the UniversalOpamp
component from the op amp library (it's the very last one).

You can select the level by Right Clicking on the component (NB not
CTRL right clicking) Level 1 is a basic 1 pole op amp that doesn't
even use supply rails Level 2 is my favourite. It has supply rails,
voltage, current and slew rate limits.

For more info on the parameters of the universal op-amp look at the file
C:\Program Files\LTC\SwCADIII\examples\Educational\UniversalOpamp.asc

http://eleceng.dit.ie/kgaughan/notes/FT220pe/Common%20Spice%20Problems%20rev%202.pdf

Here are the 4 levels

This demonstrates the use of the symbol UniversalOpamp2(improved
version to the UniversalOpamp). You set the SpiceModel to be higher
to simulate more aspects of opamp behavior. Level1 is merely a
transconductance working into an R||C and doesn't use power from the
supplies. Level2 adds slewrate, current and voltage limits. Level3a
adds a second pole. Level3b adds a delay to the dominate pole
response. Noise is modeled at all levels.

https://www.diyaudio.com/forums/software-tools/244043-741-ltspice-model.html


Your circuit will behave differently as you select different levels.


Re: why is this amp clipping?
On Sunday, September 23, 2018 at 9:22:45 PM UTC-4, Steve Wilson wrote:
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You can save a lot of wasted thrshing about. Just go directly to

C:\Program Files\LTC\SwCADIII\examples\Educational\UniversalOpamp.asc  

There is a lot of useful information you should know. Thanks to JL for raising the issue.

Re: why is this amp clipping?
On Sun, 23 Sep 2018 18:50:33 -0700 (PDT), Steve Wilson

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I've tried all the opamp levels, and I have seen the example.  

I'm simulating a circuit that uses the TCA0372 power opamp, which can
output a full amp at about 1 volt off the rails, and UniversalOpamp2
can't model it. Level.1 ignores the power supplies, so clearly can't
simulate clipping or calculate power dissipation.






--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Sunday, September 23, 2018 at 10:23:38 PM UTC-4, John Larkin wrote:

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Why not post your ASC?

If none of the levels do what you want. then make your own model.

Re: why is this amp clipping?
On Sun, 23 Sep 2018 20:05:14 -0700 (PDT), Steve Wilson

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I managed to plug the old Motorola TCA0372 macromodel into LT Spice
but it doesn't want to converge. It does the startup stuff forever.

grrrrr.

I guess I'll have to design this product the old-fashioned way, with
math and stuff.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Sunday, September 23, 2018 at 11:22:06 PM UTC-4, John Larkin wrote:
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That's no fun. Try this

Version 4
SHEET 1 1288 680
WIRE 1008 -160 448 -160
WIRE 880 -128 528 -128
WIRE 1184 -128 880 -128
WIRE 880 -112 880 -128
WIRE 1184 -112 1184 -128
WIRE 528 -96 528 -128
WIRE 448 -80 448 -160
WIRE 496 -80 448 -80
WIRE 688 -64 560 -64
WIRE 768 -64 688 -64
WIRE 816 -64 768 -64
WIRE 352 -48 336 -48
WIRE 496 -48 352 -48
WIRE 336 -32 336 -48
WIRE 1184 -16 1184 -32
WIRE 880 32 880 -16
WIRE 1008 32 1008 -160
WIRE 1008 32 880 32
WIRE 1088 32 1008 32
WIRE 1104 32 1088 32
WIRE 1104 48 1104 32
WIRE 336 64 336 48
WIRE 880 80 880 32
WIRE 768 128 768 -64
WIRE 816 128 768 128
WIRE 1104 144 1104 128
WIRE 528 192 528 -32
WIRE 880 192 880 176
WIRE 880 192 528 192
WIRE 528 224 528 192
WIRE 528 320 528 304
FLAG 1184 -16 0
FLAG 528 320 0
FLAG 336 64 0
FLAG 1088 32 Vout
FLAG 352 -48 Vin
FLAG 1104 144 0
FLAG 688 -64 U1O
SYMBOL voltage 336 -48 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value SINE(0 20 1kHz)
SYMBOL voltage 528 208 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value -15.53
SYMBOL voltage 1184 -128 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value +15.53
SYMBOL res 1088 32 R0
SYMATTR InstName R1
SYMATTR Value 14
SYMBOL opampspole 528 -64 R0
SYMATTR InstName U1
SYMATTR SpiceLine ilimit=1 rail=0 Vos=0
SYMBOL npn 816 -112 R0
SYMATTR InstName Q1
SYMATTR Value TIP31C
SYMBOL pnp 816 176 M180
SYMATTR InstName Q2
SYMATTR Value TIP32C
TEXT 384 -216 Left 2 !.tran 0 1m 0 1u
TEXT 384 -248 Left 2 ;'Larkin RRO OpAmp



Re: why is this amp clipping?
On Sun, 23 Sep 2018 20:40:29 -0700 (PDT), Steve Wilson

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That stalls on not finding 1pole, but something like that would work.
It works if I drop in most any rrio opamp from the library.  

Where does opampspole  come from?


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Monday, September 24, 2018 at 10:38:12 AM UTC-4, John Larkin wrote:
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I can't believe it. I use IV, since it runs in XP. In XVII, it can't find the opamp symbol. But if you go to Educational/opamp.asc, which also uses opamp, it has no trouble finding the symbol and running.

I am becoming convinced that Mike E. did not write XVII. There are too many glitches and aberrations like this. I recommend returning to IV to avoid these problems.

Anyway, thanks for taking a look.
  
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Probably from the beginning. Maybe PSpice.

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Re: why is this amp clipping?
On Monday, September 24, 2018 at 11:31:59 AM UTC-4, Steve Wilson wrote:

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I also find that IV on XP runs about twice as fast as XVII on Win7. I haven't tried IV on Win7, but I find everything runs slower on W7.

Re: why is this amp clipping?
On Mon, 24 Sep 2018 08:31:54 -0700 (PDT), Steve Wilson

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XVII runs fine under Win7. Sims seem to run a bit faster than IV under
Win7, maybe 25% or so.  

XVII really screwed up the simulation editors. I complained directly
to Mike, and he likes them the new way they are. He is still involved.

Since IV is not supported, and updates don't seeem to work any more,
XVII is the way to go. It's 64 bit code, so probably won't run under
XP.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: why is this amp clipping?
On Monday, September 24, 2018 at 12:11:34 PM UTC-4, John Larkin wrote:
  
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You still run IV? Then I don't need to waste time trying to convert my IV files to XVII.
  
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But he doesn't write the kind of crap that's in XVII.

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XVII 32 bit won't run in XP either. It makes a call that doesn't exist in XP.

You don't need updates for IV. It runs fine with none of the snags, aberrations, gotchas and quirks of XVII.
  
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Re: why is this amp clipping?
On Mon, 24 Sep 2018 10:49:02 -0700 (PDT), Steve Wilson

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Not any more. As far as I can tell, old .asc files run fine on the new
version.

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Seems fine to me. What problems are you seeing?

I suspect that other people wrote the Analog Devices models. They look
rushed.

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Again, XVII seems fine to me.

XP is ancient and I remember it being very flakey. Win7 is very solid.
Every 5 or 10 years, you've got to upgrade your hardware and OS.


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

We've slightly trimmed the long signature. Click to see the full one.
Re: why is this amp clipping?
On Tuesday, September 25, 2018 at 12:38:12 AM UTC+10, John Larkin wrote:
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Feedback theory - if you roll off the gain of an op amp linearly with frequency, it doesn't oscillate in negative feedback circuits.

Bob Widlar had to use two compensation capacitors on the uA709 to get enough gain roll-off to keep it stable (and a resistor in series with one of the compensating capacitors to keep the total roll-off linear with frequency).

With the LM301 he'd worked out how to do it with one capacitor, and one that was small enough to realise on the chip (though the uA741 was the version of that that hit the market first).

--  
Bill Sloman, Sydney

Re: why is this amp clipping?
John Larkin
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it is spice, nothing to do with reality.


probably need tweeking a little pappa mama ra meter in its model.

Re: why is this amp clipping?
On Monday, September 24, 2018 at 2:14:12 AM UTC-4, snipped-for-privacy@nospam.org wrote:

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Tell me when you can get two identical 'real' circuits to behave exactly the same. Which one is 'real'?

Or three circuits? Or four?

You can easily get any number of identical circuits to behave exactly the same in Spice, to within the limits of numerical accuracy.

Over the decades, Spice has been taught to millions of engineers. It is an invaluable tool, if you know how to use it.

Re: why is this amp clipping?
Steve Wilson thought

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Strawman

A _real_ circuit is one that you can power up,
and does whatever.
Spice is no more than the like of NASA's 'artist impressions of alien planets'.


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To the limits that model fits reality, and it never 100% will.
Especially in the RF field you would need a lot more than that simple spice to get anything working.
Or experience.

Interesting in this context is that sort of recently (last year or a year ago IIRC)
somebody started a research into 'make a neural net say WHY it makes a decision'.
You see AI (alias neural nets) more and more make decisions,
even life supporting decisions (medical diagnosis, controlling cars, trains, and planes, etc).
Just like somebody who has experience designing some circuit will make decisions that spice does no have, and never will have, a clue about.
It is called 'experience' in common language.

Much more important than a simple mathematical construct,

The difference between going to the moon and returning (they had no spice)
and string theory (mamamatical babble).

  

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Earth was flat was also toucht to the scientists of those days.
When people come from uni-verse-city who never held a soldering iron in their front legs, and never did see a real transistor
in their life, I'd say the writing on the wall (or graffiti in plain language) announces the end that was predicted by all the prophets ..
LOL

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