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Re: J310_AMP

 

Small typo correction.? I wrote: "Any name given a nodename stays put."? That should be "Any net or node given a nodename stays put" or does not change.

Andy
Re: J310_AMP

 

¿ªÔÆÌåÓý

It is not strange.
If you remove R4, you disconnect the power rail from the active stage, which then does not work as expected.

Le 30/05/2024 ¨¤ 04:22, zkf0100007@... a ¨¦crit?:

A simple J310 amlifier.
When I added R4, even the value is 0R, ?the output voltage on R3 is 50mvpp.
When I removed R4, the output voltage on R3 is only 5mvpp, same as the input voltage.
It is strange.
Could anyone tell me why?
Thanks!

Re: J310_AMP

 
Edited

zkf0100007, I see your uploaded file now.? Thank you.

When run as is, with R4 = 0, the output voltage across R3 is approx. 100 mVp-p.? Not 50 mV pp, but I understand that was probably what you really meant.

When R4 is simply removed, there is nearly no output across R3, but I'm sure that is not what you meant

When R4 is removed and replaced by a wire, the output voltage across R3 is still 100 mVpp.? It did not change.

HOWEVER, if you are still plotting V(N004), note that N004 is not the same circuit node anymore!? By removing R4 and replacing it by a wire, you have eliminated one unnamed node.? Because all of the nodes in your circuit (except for Ground) are not named, LTspice re-orders the unnamed nodenames so that they are sequential.? The result is that the top of R3 is now N003 instead of N004.? By plotting V(N004), you are looking at the input signal, not the output signal.

Two remedies:? Either delete V(N004) from the plots and click that node to plot it again, or - even better - add Labels (nodenames) to your circuit.? Any name node given a nodename stays put (does not change).? Any node without a name can and will change its name.? Avoid that by adding your own nodenames.

Andy
Re: opamp with offset pins

 

If it is for didactic?purposes, then I would suggest that you not teach it, because it was?a bad idea that did not catch on.? There are three sources of DC error: offset voltage, offset current, and bias current.? People tended to use the one knob to zero the error which generally left all three error terms uncorrected, but in a temporary?balance that would quickly drift away from zero.


On Wed, May 29, 2024 at 6:15?PM Andy I via <AI.egrps+io=[email protected]> wrote:
At this moment, I can't remember seeing a SPICE model for a 741-like op-amp that included those offset voltage pins, but they may exist.? They must be rather uncommon.

But there is a way to do it.? In your LTspice installation, there is an LTspice schematic for a full 741.? Find it on your computer's drive at examples\Educational\LM741.asc.? Near the lower left, the top ends of R1 and R3 come out to the IC pins for adjusting the offset voltage.? Note that the schematic shows the 741 wired-up in a complete circuit; don't forget to remove R11, R12, R14, and the voltage sources to get just the 741.

I would consider that OK as a teaching tool, but might not be good for serious work.? I don't know how accurate the schematic is, compared to a real LM741.? The schematic was literally lifted from the datasheet.? "For informational/educational purposes only."

LTspice doesn't come with a generic symbol for an op-amp with input offset pins, so you would need to make your own, if you want to use a symbol.

Andy

Re: J310_AMP

 

I have uploaded the file named ¡®J310_AMP.asc??¡¯
Thanks!
Re: J310_AMP

 

zkf0100007 wrote, "A simple J310 amlifier."

Where is it?? We can't read your mind.? Please, if you have a schematic, upload the schematic (.asc) file, plus any SPICE models that did not come with LTspice.? No pictures, please.? Upload to the Temp folder, by first navigating to Files > Temp, and then click the "New/Upload" button.

Then come back here and send a reply, telling us the file that you uploaded.

Andy
J310_AMP

 

A simple J310 amlifier.
When I added R4, even the value is 0R, ?the output voltage on R3 is 50mvpp.
When I removed R4, the output voltage on R3 is only 5mvpp, same as the input voltage.
It is strange.
Could anyone tell me why?
Thanks!
Re: opamp with offset pins

 

At this moment, I can't remember seeing a SPICE model for a 741-like op-amp that included those offset voltage pins, but they may exist.? They must be rather uncommon.

But there is a way to do it.? In your LTspice installation, there is an LTspice schematic for a full 741.? Find it on your computer's drive at examples\Educational\LM741.asc.? Near the lower left, the top ends of R1 and R3 come out to the IC pins for adjusting the offset voltage.? Note that the schematic shows the 741 wired-up in a complete circuit; don't forget to remove R11, R12, R14, and the voltage sources to get just the 741.

I would consider that OK as a teaching tool, but might not be good for serious work.? I don't know how accurate the schematic is, compared to a real LM741.? The schematic was literally lifted from the datasheet.? "For informational/educational purposes only."

LTspice doesn't come with a generic symbol for an op-amp with input offset pins, so you would need to make your own, if you want to use a symbol.

Andy
opamp with offset pins

 

Greetings everyone, I need a 741 model or it could be another op amp that has offset correction pins, the need for these pins is because I'm making some circuits for teaching purposes, such as the full wave rectifier precision, these circuits are didactic and reinforcement in nature.

grateful
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Re: Al Dutcher's forgotten message

 

Most 'real' circuits have enough other stuff going on, so that the timestep stays more limited.? A smaller timestep leads to less difference between the unfiltered and filtered node voltages from the Modified Trap's filter.

Sometimes it is the "simple" circuits (the ones that don't actually do anything) that lead to visible artifacts.

Andy
Re: Al Dutcher's forgotten message

 

I tried this with my original ckt and
alls well.
Btw that ckt is a mosfet motor run relay replacement.
Thanx again.


On Wed, May 29, 2024 at 1:20?PM Al Dutcher <alziedood@...> wrote:
I tried Gear and Trap and alls well.
Mod Trap is a mess.
Didnt need to mess with max time step at all.
Wow, Nice, Thanx again!
Learn something new every day.

OK, back to my original skizzy.

On Tue, May 28, 2024 at 11:29?PM Andy I via <AI.egrps+io=[email protected]> wrote:
Hmm, I tried something different, and now I see badly distorted waveforms.? They are nothing like sinewaves, but maybe this is what you were talking about.

One of LTspice's interesting "features" is the "Modified Trap" algorithm.? It does a very good job of removing Trap Ringing when it happens.? But there was a change in about 2019, and since then it is not applied uniformly to all waveforms.? (Grrr!)? A consequence is that SOME differential plots do not look right, when plotting small differential signals in the presence of larger signals.? Yes, it is very much like the common-mode problem.

In this circuit, I think the Modified Trap filter gets applied only to V(N002) but not to V(N001) or V(N003) because they are driven directly by voltage sources.? So,
  • If you use Modified Trap, and plot either V(N002,N001) or V(N002,N003), it looks bad.
  • If you plot V(N003,N001), it looks good.
  • If you plot any signal by itself, it looks normal.
  • If you change from Modified Trap to either Trapezoidal or Gear and re-run the simulation, everything looks good.

LTspice's Help page for LTspice? > Integration Methods talks about this.

I almost forgot about this because I stopped using Modified Trap a while ago.? Trap Ringing happens infrequently so I rarely need Modified Trap, and I think I can spot Trap Ringing when it happens and then re-enable Modified Trap.? YMMV.

Andy



--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla


--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla
Re: Al Dutcher's forgotten message

 

I tried Gear and Trap and alls well.
Mod Trap is a mess.
Didnt need to mess with max time step at all.
Wow, Nice, Thanx again!
Learn something new every day.

OK, back to my original skizzy.


On Tue, May 28, 2024 at 11:29?PM Andy I via <AI.egrps+io=[email protected]> wrote:
Hmm, I tried something different, and now I see badly distorted waveforms.? They are nothing like sinewaves, but maybe this is what you were talking about.

One of LTspice's interesting "features" is the "Modified Trap" algorithm.? It does a very good job of removing Trap Ringing when it happens.? But there was a change in about 2019, and since then it is not applied uniformly to all waveforms.? (Grrr!)? A consequence is that SOME differential plots do not look right, when plotting small differential signals in the presence of larger signals.? Yes, it is very much like the common-mode problem.

In this circuit, I think the Modified Trap filter gets applied only to V(N002) but not to V(N001) or V(N003) because they are driven directly by voltage sources.? So,
  • If you use Modified Trap, and plot either V(N002,N001) or V(N002,N003), it looks bad.
  • If you plot V(N003,N001), it looks good.
  • If you plot any signal by itself, it looks normal.
  • If you change from Modified Trap to either Trapezoidal or Gear and re-run the simulation, everything looks good.

LTspice's Help page for LTspice? > Integration Methods talks about this.

I almost forgot about this because I stopped using Modified Trap a while ago.? Trap Ringing happens infrequently so I rarely need Modified Trap, and I think I can spot Trap Ringing when it happens and then re-enable Modified Trap.? YMMV.

Andy



--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla
Re: Al Dutcher's forgotten message

 

Thanx so much Andy and peeps

I will give these a try.
Makes a lot of sense.
So many places to get trapped.
Pun intended.


On Wed, May 29, 2024 at 12:39?AM Andy I via <AI.egrps+io=[email protected]> wrote:
Al,

By the way, this error is considerably reduced by using a smaller timestep.? There was almost nothing in the simple circuit to force the timestep smaller.? Setting a Maximum Timestep of 10? us essentially eliminates it.

Andy



--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla
Re: Al Dutcher's forgotten message

 

Al,

By the way, this error is considerably reduced by using a smaller timestep.? There was almost nothing in the simple circuit to force the timestep smaller.? Setting a Maximum Timestep of 10? us essentially eliminates it.

Andy
Re: Al Dutcher's forgotten message

 

Hmm, I tried something different, and now I see badly distorted waveforms.? They are nothing like sinewaves, but maybe this is what you were talking about.

One of LTspice's interesting "features" is the "Modified Trap" algorithm.? It does a very good job of removing Trap Ringing when it happens.? But there was a change in about 2019, and since then it is not applied uniformly to all waveforms.? (Grrr!)? A consequence is that SOME differential plots do not look right, when plotting small differential signals in the presence of larger signals.? Yes, it is very much like the common-mode problem.

In this circuit, I think the Modified Trap filter gets applied only to V(N002) but not to V(N001) or V(N003) because they are driven directly by voltage sources.? So,
  • If you use Modified Trap, and plot either V(N002,N001) or V(N002,N003), it looks bad.
  • If you plot V(N003,N001), it looks good.
  • If you plot any signal by itself, it looks normal.
  • If you change from Modified Trap to either Trapezoidal or Gear and re-run the simulation, everything looks good.

LTspice's Help page for LTspice? > Integration Methods talks about this.

I almost forgot about this because I stopped using Modified Trap a while ago.? Trap Ringing happens infrequently so I rarely need Modified Trap, and I think I can spot Trap Ringing when it happens and then re-enable Modified Trap.? YMMV.

Andy
Re: Al Dutcher's forgotten message

 

Al wrote, "The only place with the square wave is the pulse source."

So if you plot the differential voltage across "the res and BE junction", that is exactly the pulse voltage source.? There is no difference.? They are connected by wires.

re: "The res and jctn have this strange distorted 4V sine wave."

That makes it sound a little like waveform compression.? But your simulation has it turned off.? Anyway, 3 V out of 170 V is not enough to cause much if any visible inaccuracy.? (Small waveforms riding on top of larger signals can suffer from waveform compression, but there has to be a greater difference in their amplitudes.)

Andy
Re: Al Dutcher's forgotten message

 

Hmph!
I wonder whats different?
You have exactly the same ckt.
The only place with the square wave
is the pulse source.
The res and jctn have this strange distorted 4V sine wave.
Its like its having trouble cancelling the common mode voltage
Very strange

On Tue, May 28, 2024 at 8:51?PM Andy I via <AI.egrps+io=[email protected]> wrote:
Al wrote, "If you look differentially across Either the res Or the Vbe jctn alone youll see the 4V"

I do not see 4 V.

Across R1, I see 2.645 V or 0 V (alternating).

Across the Vbe junction, I see 0.655 V or 0 V.

I think you did something wrong, but I can't tell what.

Do you see square waves?

Andy



--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla
Re: Al Dutcher's forgotten message

 

Al wrote, "If you look differentially across Either the res Or the Vbe jctn alone youll see the 4V"

I do not see 4 V.

Across R1, I see 2.645 V or 0 V (alternating).

Across the Vbe junction, I see 0.655 V or 0 V.

I think you did something wrong, but I can't tell what.

Do you see square waves?

Andy
Re: Al Dutcher's forgotten message

 

Didnt see a place to send a message.
Uploading generates an announcement.
I thought the text included with the upload was the message
I used LTspice 24.

If you look differentially across Either the res Or the Vbe jctn alone
youll see the 4V
The jctn cant do that in fwd bias!
This is a snippet from another project that does use the 120Vrms
I didnt want to confuse the situation with extra stuff


On Tue, May 28, 2024 at 4:38?PM Andy I via <AI.egrps+io=[email protected]> wrote:
Group member Al Dutcher uploaded a file (PecoCMp.asc) but then he forgot to send any message about it.

Al, please re-read the instructions on the group's main webpage, especially the part that tells you to always send a Message about what you uploaded.

The Description attached to your file is:

Heres a strange one thats making no sense
Its a snippet from something that I m working on
120Vrms with a small ckt on the top
If you use the diff prob,
youll get ~4V across the res and BE junction
from 3V source
especially in fwd bias, huh?!
The current is ok
What am i doing wrong?
Its in Temp

What program did you use to simulate it?? I used LTspice, and the simulated differential voltage V(N003,N001) = the voltage across R1 + the Vbe junction, alternates between 0 and 3.3 V.

I saw no ~4 V.

The source is a square wave with 3.3 V amplitude (not "3V" but close).

So my question is, what were you looking at?? Did you upload the wrong circuit?

There are many problems with your circuit.? The 120 Vrms source does nothing, so I don't know why you mentioned it.

Andy



--
AC2CL

I do not think there is any thrill that
can go through the human heart like that felt by the inventor as
he sees some creation of the brain unfolding to success...
Such emotions make a man forget food, sleep, friends, love, everything.

- Nikola Tesla
Re: Oscillator stops oscillating

 

Tony wrote, "By default, this has a tanh transfer function, ..."

That is true, but only partly so.? The tanh curvature applies only when the op-amp's output would be operating between the supply voltages.? With a more typical Avol and supply voltages, then the transfer curve clips first before the tanh has much effect.? I think you are right that the tanh curve is to mimic the input diff. amp.

Whether it is curved or straight linear, I think the "problem" in this case (Ethan's oscillator) is that the transfer function is idealized and the component does not seem to give feedback to the timestep control algorithm.

Andy
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