|
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: ?
|
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
|
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
|
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
|
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
|
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
|
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
|
Without a doubt, showing the bad way and the good way is a way of teaching. The title of the article where I read about this project that uses correction ports is: "Perverting OP AMP" and I see this proposal in it, too bad it's very old.
Em qui., 30 de mai. de 2024 ¨¤s 00:02, Andy I via <AI.egrps+io= [email protected]> escreveu:
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
|
Here's another book that I would love to have in my library, but the time is not right for shopping.
Em qui., 30 de mai. de 2024 ¨¤s 00:56, Spehro Pefhany via <speff= [email protected]> escreveu:
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
|
Hello Carlos.
I think that PSpice has the LM741 with the offset null pins (1 and 5).?
In this link you can see it:
Hyu
On Friday, May 31, 2024 at 12:51:05 AM GMT-3, Carlos Delfino <consultoria@...> wrote:
Here's another book that I would love to have in my library, but the time is not right for shopping.
Em qui., 30 de mai. de 2024 ¨¤s 00:56, Spehro Pefhany via <speff= [email protected]> escreveu:
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
|
Hyu wrote, "I think that PSpice has the LM741 with the offset null pins (1 and 5).?"
I guess you would need to install PSpice to get that model.
That reddit page is somewhat confusing.? The Netlist code below the picture shows that the two LM741's have only 5 pins, not 7, so they did not include the offset pins.? It's not clear what is going on.
I've checked T.I.'s LM741 SPICE (PSpice) models, and theirs do not have the offset pins.? In fact I think they do not have that portion of the on-chip circuitry at all, so you can't just dig into the model and find the two resistors where the pins would go.? They are not there at all in the SPICE model (from T.I.).? That's not saying that ALL (LM)741 models from T.I. are like that.? Sometimes T.I. has several web pages for minor versions of the same basic part, some with and some without SPICE models.
Andy
|
If it is just for didactic purposes, just add the resisters externally to the inputs.? For extra credit, buffer them with a common base stage.
Hyu wrote, "I think that PSpice has the LM741 with the offset null pins (1 and 5).?"
I guess you would need to install PSpice to get that model.
That reddit page is somewhat confusing.? The Netlist code below the picture shows that the two LM741's have only 5 pins, not 7, so they did not include the offset pins.? It's not clear what is going on.
I've checked T.I.'s LM741 SPICE (PSpice) models, and theirs do not have the offset pins.? In fact I think they do not have that portion of the on-chip circuitry at all, so you can't just dig into the model and find the two resistors where the pins would go.? They are not there at all in the SPICE model (from T.I.).? That's not saying that ALL (LM)741 models from T.I. are like that.? Sometimes T.I. has several web pages for minor versions of the same basic part, some with and some without SPICE models.
Andy
|
The diagram appears to have the pins, but the posts do not have concrete information on the topic. The link to github is invalid and there is no repository with a similar name in the author's account.
The post is very old too.
Em sex., 31 de mai. de 2024 ¨¤s 17:47, hyu hyu via <hyu2123= [email protected]> escreveu:
Hello Carlos.
I think that PSpice has the LM741 with the offset null pins (1 and 5).?
In this link you can see it:
Hyu
On Friday, May 31, 2024 at 12:51:05 AM GMT-3, Carlos Delfino < consultoria@...> wrote:
Here's another book that I would love to have in my library, but the time is not right for shopping.
Em qui., 30 de mai. de 2024 ¨¤s 00:56, Spehro Pefhany via <speff= [email protected]> escreveu:
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
|
I found the first edition of the book Replicated on a website, by Professor Gordon W. Roberts, follows the link below if someone else may need.
--
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: ?
Em qui., 30 de mai. de 2024 ¨¤s 00:56, Spehro Pefhany via <speff= [email protected]> escreveu:
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
|
Carlos wrote: ? ? That looks maybe not quite exactly, but very nearly identical to the LM741.asc that is already on your computer, in the folder examples > Educational.? (See message #153898.)? It's from the LM741/uA741 datasheets from decades ago. Andy
|
I haven't read the book yet, I imagine that when it comes to the models there isn't much to change, more due to the theme and how it is dealt with.
Em sex., 31 de mai. de 2024 ¨¤s 23:21, Andy I via <AI.egrps+io= [email protected]> escreveu:
Carlos wrote:
? ?
That looks maybe not quite exactly, but very nearly identical to the LM741.asc that is already on your computer, in the folder examples > Educational.? (See message #153898.)? It's from the LM741/uA741 datasheets from decades ago.
Andy
|
Roy McCammon