[SOLVED] LM741 op-amp

[lostintheether]

I'm currently working on the design of a differential amplifier and I'm observing a particular behavior in the output that I'm trying to understand better.

My circuit specifications are as follows:
Supply Voltage: +/- 12V
Input Signal Range (Differential): -2V to +2V
Using: LM741 op-amp in a standard differential amplifier configuration with Rf = 10kΩ and Ri = 1kΩ for both input pairs.
The issue I'm encountering is that the output seems to saturate at approximately +10V and -10V, even when the calculated gain (Rf/Ri = 10) multiplied by the input differential voltage should be within the supply rails for smaller input signals (e.g., +/- 0.5V should give +/- 5V output).

I've already tried checking the power supply connections, verifying the resistor values with a multimeter, and simulating the circuit in LTSpice (results attached). The simulation shows the expected gain without saturation for the same input range.

I've attached a schematic of the differential amplifier circuit and the LTSpice simulation results showing both the expected and the observed (saturated) output waveforms from my physical breadboard setup.

I would greatly appreciate any insights or suggestions on what might be causing this output saturation in my physical circuit, despite the simulation showing ideal behavior. Are there any specific limitations of the LM741 at these supply voltages or input levels that I should be aware of? Could there be a parasitic effect on my breadboard setup that's causing this?

Thanks in advance for your help!

 

[betwixt]

I think you are seeing a limitation of the 741. They are very old devices (designed about 50 years ago) and are not able to drive their outputs to the full range of the supply rails. For that you need a "rail-to-rail output" amplifier. Good data sheets will show how close to the supply the output can reach but within 2V as you observe is not unusual.

Brian.

 

[FvM]

I've attached a schematic of the differential amplifier circuit and the LTSpice simulation results

Not yet!

Although nobody uses 741 these days, it should be fine for +/- 5V output swing.

 

[KlausST]

I've attached a schematic of the differential amplifier circuit and the LTSpice simulation results

I don´t see any of this..

Regarding LM741:
I´m a professional electronics designer for more than 25 years now ... even at my early days the 741 was too outdated for me. I never used it.

Klaus

 

[crutschow]

simulating the circuit in LTSpice (results attached).

Your are missing that attachment.
But if you use a 741 model for the simulation, it will likely show the results similar to what you are seeing on the breadboard.
I would attach the model for you but this site, strangely enough, does not allow downloading of LTspice files.

 

[FvM]

I would attach the model for you but this site, strangely enough, does not allow downloading of LTspice files.

Yes, but no problem to zip the project.

 

[kd502]

What is your common mode voltage?

 

[crutschow]

Yes, but no problem to zip the project.

For you maybe, but it's more work for me, and I don't feel like doing that for an annoying restriction that other Forum sites I'm on, don't have.
I rather doubt that LTspice .asc, .asy, .lib or .sub files can be malicious.

Since I'm doing this for free, I think the Forum should cater to me, not vice versa.

 

[danadakk]

Basic sim shows combination of input CM limitation and output swing limitation -

15V supplies

And if we examine its structure we can see the reasons for this -