OpAmp Diagram

[Zero999]

I think there's some confusion.

1st, I added the batts for illustrative purposes only. What those batts are, their voltage, is not relevant here.
2nd, the ckt in 1st post is from a TI PDF, I did not create the ckt illustration.
3rd, if the TI illustration indicates "-2.5v" for the OA "V-" connection, then the batt symbol used, along with the "+" sign should indicate neg voltage on OA V- pin.

Like this.

No, that won't work, because voltages are relative. The op-amp'a power supply pins will  both see 2.5V. If all the inputs are nearer 0V, bad things are likely to happen.

To correct it, get rid of the negative sign.

Are you commenting on post #1, or the new diagram?

In the new
The V- pin shows "-2.5v"
The V+ pin shows "+2.5v"

That should be 5v rail-to-rail, +2.5 to -2.5

I'm talking about the new diagram. Both sides of the op-amp supply are now positive.

As others have mentioned, the battery symbol is not the right one to use in this situation.

The original schematic was correct, other than the battery symbols, although I consider it to be a minor issue.

Here's what happens if I enter the new schematic into a simulator and ask it to calculate the steady state voltages.


Verses the orginal one.

[magic]

The original schematic was correct, other than the battery symbols, although I consider it to be a minor issue.

It's a major issue and the whole reason why this increasingly silly thread exists.

There are no negative voltage batteries whose positive terminal is marked negative and whose negative terminal is marked positive. Using such notation on paper is of course possible, but it only creates confusion, as observed here.

If you want to create negative voltage with batteries, flip the battery so that + goes to ground and either mark the battery simply "2.5V" (without minus) or mark the generated voltage rail (not the battery) "-2.5V".

The purpose of circuit simulators is simulating circuits, not being standards on what notation is good or bad. A circuit simulator may use the dumbest notation imaginable and still simulate correctly if you understand the notation and input the schematic in a manner which will be interpreted the way you want.

[Randy222]

The original schematic was correct, other than the battery symbols, although I consider it to be a minor issue.

It's a major issue and the whole reason why this increasingly silly thread exists.

There are no negative voltage batteries whose positive terminal is marked negative and whose negative terminal is marked positive. Using such notation on paper is of course possible, but it only creates confusion, as observed here.

If you want to create negative voltage with batteries, flip the battery so that + goes to ground and either mark the battery simply "2.5V" (without minus) or mark the generated voltage rail (not the battery) "-2.5V".

The purpose of circuit simulators is simulating circuits, not being standards on what notation is good or bad. A circuit simulator may use the dumbest notation imaginable and still simulate correctly if you understand the notation and input the schematic in a manner which will be interpreted the way you want.

I think you are saying what I was trying to say.

V- really needs to be below gnd, so showing a "+" sign on the V- pin makes no sense if the intention was to have a neg voltage (-2.5) on V-

There's another way the original ckt illustration could have been goofed, they could have literally flipped the batt symbol over on V- and kept "+" sign on V-, which would still be wonky.

[zapta]

You are right, the bottom battery symbol is reversed. A schematic typo.

[Zero999]

The battery symbol didn't confuse me, because I've seen it used for a voltage source in the past. A simulator program I used when I was a child just used the battery symbol to represent a voltage source by default. The fact it's 2.5V, made it obvious it's a voltage source, rather than a real battery.

This is how I would prefer to draw it.

[Gyro]

Is it really so important to you that you don't loose face by simply acknowledging that you put the battery symbol the wrong way round and correcting it?!

The schematic symbol polarity is perfectly clear and assigning a negative value to it in an unpublished sim just isn't ok. Magic is right, it is a big issue, schematics should read correctly.

The alternative is that you attach asc files with any schematic you post in case you've played games with the component parameters! It's such a trivial representation anyway that there was no reason to to guess that you had bothered to simulate it, and that it only worked in sim.