op amp - does op amp exceed the source of voltage that i supply it

crutschow

Joined Mar 14, 2008
34,280
It's not that bad. Every once in a while, one of us humans will reach a tipping point and unload on a random passerby. I know I have. That one person then receives the accumulated aggravation built up from the ten before him. When you've been here a while and seen some crazy requests for yourself, you'll see why it takes great patience. It wouldn't surprise me if half or more of the posts in this forum are to ask basic questions of the thread starter, so that we can understand what they are doing or what they want. It grows old.
Yes, after the umpteenth question along the lines of "My circuit doesn't work, what's wrong with it" with no schematic or little other information, it's hard not to blow a (figurative) fuse.
Somehow they seem to think we're all technically clairvoyant. :rolleyes:
 

WBahn

Joined Mar 31, 2012
29,976
He may have only 37 posts, but I was told the same thing. It doesn't make sense. I'm pretty sure most biggener's questions have been asked and discussed many times. So if your not allowed to ask questions that have been asked unless you do all kinds of search ing first, then this site should be an information site only, and no questions allowed. I got scream at a couple of times for asking something or adding to the site. Again, to be clear, as new people, we are asked to read everything first before participating. I think he was just passing that on and meant nothing otherwise. I like what you posted.
If you think it's bad here, check out most of the StackExchange sites. Supposedly if someone asks a question that has been answered before, someone is supposed to post a link to where the answer is before blocking the thread. But I've seen many posts there where the only response is that the question has been asked and answered before. Period. Go away. Here we are generally willing to answer the same questions over and over -- in part because most of us don't want to take the time to refer the poster to a prior post. But, especially in the Homework Help, we want to see effort put forth by the poster for a number of reasons: (1) the goal is to get the person closer to being able to work problems for themselves. In most cases they have seen similar examples worked out in the text and in class, so just seeing one more problem worked out is unlikely to make a huge difference -- they need to fight with it in order to break through the specific problems they are having; (2) we need to see what they are trying to do so that we can better figure out what the mistake is that they are making; (3) the poster often needs some serious practice in communicating ideas and what they have done, a skill that is getting rarer and rarer.
 

hp1729

Joined Nov 23, 2015
2,304
does op amp exceed the source of voltage that i supply it
Is it really proper to say an op amp "amplifies a signal"? It recreates an input signal up to the limits of applied power and the limits of the op amp. What comes out is not really the signal coming in made larger. Just an image of the signal.
 

WBahn

Joined Mar 31, 2012
29,976
I think that's a distinction without a significant difference. What is a "signal"? In many regards it is an abstract concept to begin with that is more concerned with the representation of information, in which case it is completely reasonable to talk about the output signal being a modification to the input signal. To insist on formally treating them as separate in all respects just has the potential to cause all kinds of needless descriptive difficulties. For instance, by that same reasoning, the current entering a resistor isn't really the current entering the resistor, or the voltage across one resistor is not really the same as the voltage across a parallel resistor (even assuming resistanceless connections). Very arguably both of these statements are true and, in some contexts, the distinction IS significant, in almost all meaningful contexts the distinctions are insignificant significant.
 

Whatashame

Joined Nov 30, 2015
88
If you think it's bad here, check out most of the StackExchange sites. Supposedly if someone asks a question that has been answered before, someone is supposed to post a link to where the answer is before blocking the thread. But I've seen many posts there where the only response is that the question has been asked and answered before. Period. Go away. Here we are generally willing to answer the same questions over and over -- in part because most of us don't want to take the time to refer the poster to a prior post. But, especially in the Homework Help, we want to see effort put forth by the poster for a number of reasons: (1) the goal is to get the person closer to being able to work problems for themselves. In most cases they have seen similar examples worked out in the text and in class, so just seeing one more problem worked out is unlikely to make a huge difference -- they need to fight with it in order to break through the specific problems they are having; (2) we need to see what they are trying to do so that we can better figure out what the mistake is that they are making; (3) the poster often needs some serious practice in communicating ideas and what they have done, a skill that is getting rarer and rarer.
Very good explanation. It makes perfect sense. I will learn and people are now explaining this well. I just tried hooking up a Flip-flop setup someone directed me to and nothing worked. I don't have an exact caps. at 0.01uf the schematic shows. That's probably all it takes to make it fail. That's an example where one might rather ask than reading or surfing the Internet for hours. But anyhow, I posted something I would like to say to you again. Passing on your knowledge to us with less knowledge , is very commendable, and I for one know it is alot of hard work n time, on your part and others to do this sharing. I thank you. If you could see my house and see all the time I spend trying to learn n tinkering I do, you would know I just not trying to use anyone for easy answers. I'm 63 and it tires my brain. My father wanted me to learn this stuff years ago. Had no interest then. I love this stuff now n it gives me something to do now that I'm retired. Thanks for your sharing. Giving of yourself is better than throwing money at people. Whatashame out.
 

wayneh

Joined Sep 9, 2010
17,496
Is it really proper to say an op amp "amplifies a signal"? It recreates an input signal up to the limits of applied power and the limits of the op amp. What comes out is not really the signal coming in made larger. Just an image of the signal.
It is proper, because the output of the op-amp can be, compared to the input, greater voltage, greater current, or both. It's important to note that the power at the output comes from the power supply rails of the op-amp, not the input signal.

I recall we had a discussion here quite a while ago about what is an amplifier, and that latter point was a big part of it. You can, for instance, have an amplifier with a gain less than one, with no increase in voltage, current or power. I would say it could still technically be called an amplifier if the output power is not coming from the input. This distinguishes an amplifier from a passive device like a resistor. A single transistor can be considered an amplifier by this definition.
 

WBahn

Joined Mar 31, 2012
29,976
Rail-to-rail op amps seldom give rail-to-rail performance.
Certainly not if you want to pull any more than just-short-of-negligible current from them.

Actually, I think "rail-to-rail" is more of a near-marketing term that really only implies that they can get significantly closer to the rails than their traditional predecessors. It was probably a very impressive advancement at first and probably no one quipped about them not being truly rail-to-rail because it was such a huge improvement over what was then available.
 

DerStrom8

Joined Feb 20, 2011
2,390
Rail-to-rail op amps seldom give rail-to-rail performance.
Certainly not if you want to pull any more than just-short-of-negligible current from them.

Actually, I think "rail-to-rail" is more of a near-marketing term that really only implies that they can get significantly closer to the rails than their traditional predecessors. It was probably a very impressive advancement at first and probably no one quipped about them not being truly rail-to-rail because it was such a huge improvement over what was then available.
Exactly. The output can swing much closer to the supply voltages than other types of op-amps available, which is why I brought it up. Obviously we do not live in a perfect world, so there will be losses and voltage drops.
 

Whatashame

Joined Nov 30, 2015
88
Yes, after the umpteenth question along the lines of "My circuit doesn't work, what's wrong with it" with no schematic or little other information, it's hard not to blow a (figurative) fuse.
Somehow they seem to think we're all technically clairvoyant. :rolleyes:
You made me laugh. I see said the blind man.
Certainly not if you want to pull any more than just-short-of-negligible current from them.

Actually, I think "rail-to-rail" is more of a near-marketing term that really only implies that they can get significantly closer to the rails than their traditional predecessors. It was probably a very impressive advancement at first and probably no one quipped about them not being truly rail-to-rail because it was such a huge improvement over what was then available.
Could you fill me in . What is rail-to-rail?
 

WBahn

Joined Mar 31, 2012
29,976
You made me laugh. I see said the blind man.

Could you fill me in . What is rail-to-rail?
A "rail" refers to the power supply. The output of "traditional" opamps can only get within a volt or two of the power supply voltages (sometimes worse). So if you are running an opamp from ±15 V supplies, the output might only be able to go between ±13 V. But a "rail-to-rail" can get much closer to the supply voltages under typical operating currents, perhaps ±14.8 V.
 

Whatashame

Joined Nov 30, 2015
88
Thanks, I thought it meant power supply. They probably got that term from railroad tracks that supplies the train. I was also thinking of the electrical buse of large electrical cabinets. Also the rails of a breadboard. Very good.
 

WBahn

Joined Mar 31, 2012
29,976
Thanks, I thought it meant power supply. They probably got that term from railroad tracks that supplies the train. I was also thinking of the electrical buse of large electrical cabinets. Also the rails of a breadboard. Very good.
The source of why the term "rail" is used for the power supply is probably not known for sure. I'm pretty sure the use of the term predates electric trains, but not positive of that.

But consider where "bread board" comes from. To prototype circuit you would literally take a bread board (or other piece of wood, but bread boards were a convenient size and readily available) and drive nails or screws into them and wire up components between the posts. As part of this, you often strung thick wire along the edges of the board to make power connections readily available and these were known as the power rails.
 

wayneh

Joined Sep 9, 2010
17,496
My working definitions of op-amp descriptions are that "regular" cannot get within 1-3V of either rail, a "single-supply" amp cannot get any closer to one rail, but can get within 0.1V of one rail, usually the lower, and a "rail-to-rail" can get to within 0.1V of both rails. Applies to inputs and outputs.

You have to read datahseets carefully and consider your application to hone it any closer.

[edit] I'll add that failing to consider the operating range limits is what drives most noobs to come here seeking help with their op-amp circuit that doesn't work. Op-amps have many non-ideal behaviors but this one is the most relevant.
 
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Whatashame

Joined Nov 30, 2015
88
The source of why the term "rail" is used for the power supply is probably not known for sure. I'm pretty sure the use of the term predates electric trains, but not positive of that.

But consider where "bread board" comes from. To prototype circuit you would literally take a bread board (or other piece of wood, but bread boards were a convenient size and readily available) and drive nails or screws into them and wire up components between the posts. As part of this, you often strung thick wire along the edges of the board to make power connections readily available and these were known as the power rails.
Thats funny. But how else. My book from Radio Shack by Forest Minns, shows breadboards out of wood and nail. He shows how to wrap the wires. The book and he is very good but when I saw those drawings ,I said, What? "Are you kidding me?". I thought I just bought a book of ancient history of electronics. As it turns out, I like the book and author. Just scared for a moment. Electronics are now smaller but the atoms or electrons act the same as way back when. Fill me in more or add or correct my statements would be nice. You write like an author. Whatashame out. Tumbs up.
 
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