On 30/05/2024 04:22, zkf0100007@... wrote:
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?
The explanation has already been noted.
But did anyone look at the netlist of the original circuit with R4?
It's not there! Hovering the mouse over either end of R4 shows that
both ends are node N001. LTspice has already "silently" removed it.
Having done that, why does it then renumber node N004 to N003, when
R4 is removed from the schematic?
The details are interesting. In the first case, the netlist doesn't
have a node N002. It's clear that this would have been the node name
at the right end of R4 if it's value wasn't 0. But having removed it
from the netlist, both ends of R4 have become node N001, but the
rest of the netlist is left as-is without N002. When R4 is
physically removed from the schematic, all other lines apart from
those for V2 and C3 are renumbered, even though there was actually
no change to the circuit connectivity.
J1 N003 N006 N007 J310??? ???
??? ? ?? J1 N002 N005 N006 J310
R1 N006 0 470K??? ??? ??? ??? ??? ? ?? R1 N005 0 470K
C1 N006 N005 220p??? ??? ??? ???? ? ?? C1 N005 N004 220p
V1 N005 0 SINE(0 5m 7meg) AC 2??? ? ?? V1 N004 0 SINE(0 5m 7meg)
AC 2
L1 N001 N003 100? Rser=1m??? ???? ? ?? L1 N001 N002 100? Rser=1m
R2 N007 0 160??? ??? ??? ??? ???? ? ?? R2 N006 0 160
C2 N007 0 0.1???? ??? ??? ??? ??? ? ?? C2 N006 0 0.1?
C3 N001 0 0.1???? ??? ??? ??? ??? ?? ? C3 N001 0 0.1?
V2 N001 0 12??? ??? ??? ??? ??? ? ? ?? V2 N001 0 12
C4 N004 N003 0.01???? ??? ??? ??? ? ?? C4 N003 N002 0.01?
R3 N004 0 1K??? ??? ??? ??? ??? ? ? ?? R3 N003 0 1K
--
Regards,
Tony
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Re: opamp with offset pins
At 07:27 PM 2024-05-29, you wrote:
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
--
Carlos Delfino
Quem sou:?
Keybase (PGP):
ORCID:?
You can just add the two pins to a transistor-level model of the LM741.
If you can't find a decent transistor-level SPICE model, Sedra/Smith has
one in Chapter 10 of?
SPICE for for Microelectronic circuits, 3rd edition
You would connect the tops of the two 1k resistors R1 and R2 in Fig. 10.1
As others have said, using the offset null pins tends to introduce
excessive temperature dependence.
Best regards,
Spehro Pefhany
|
Re: opamp with offset pins
Roy wrote, "... I would suggest that you not teach it, because it was?a bad idea that did not catch on."
Then it might be useful for teaching an example of inferior circuit design, something that is usually best not done.
The other thing to remember is that "all" simulations with 741 op-amps are ideal and likely have zero (or nearly zero) input offset voltage.? The transistor matching in the SPICE model is perfect.
Andy
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Re: opamp with offset pins
Em qua., 29 de mai. de 2024 ¨¤s 21:15, Andy I via <AI.egrps+io= [email protected]> escreveu:
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
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Re: opamp with offset pins
Roy, I understand your point.
But at first, these are just small demonstrations of how to use OpAmp, I won't go too deep into this issue. I have other circuits that don't use this approach
Em qua., 29 de mai. de 2024 ¨¤s 23:35, Roy McCammon via <roymccammon= [email protected]> escreveu:
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.
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
|
I mean that remove R4, and connect with a wire.
|
Thank you very much!
?
I deleted V(N004) from the plots and click that node to plot it again, the output on R3 is still 100mvpp.
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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
|
It is not strange.
If you remove R4, you disconnect the power rail from the active
stage, which then does not work as expected.
toggle quoted message
Show quoted text
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!
|
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
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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.
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
|
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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
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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
|
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
--
Carlos Delfino Quem sou:?
Keybase (PGP): ORCID:?
Celular: ? ? ?(85)?985-205-490 (OI) - Aquiraz/CE ¡°Para o Triunfo do Mal, s¨® ¨¦ preciso que os homens de bem n?o fa?am nada¡± - Edmund Burke ¡°Ningu¨¦m comete erro maior do que n?o fazer nada porque s¨® pode fazer um pouco¡± - Edmund Burke
Conhe?a o Curso Maker (Arduino Minas): ? Arvore dos Saberes/Tecnologia no Social: ?
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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
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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.
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.
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.
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
|
Tony Casey
Roy McCammon