In ltspice I have 3.465v steady at the + input of an op amp. The negative input oscillates between 3.47168 and 3.47654. The output is oscillating between the + and - saturation voltages. I connected a .22 ohm between the + and -. This stopped the output from oscillating and I had a steady output voltage of 3v. The power supply is 8v. The op amp is lm324.
When I built the actual circuit I had approx. 0v at the output. I then tried a 1 ohm resistance with the same result although the ltspice simulation was ok.
It looks like I have a common mode input in the actual circuit. I can try larger resistance values but is this going to help?

 

Post the .asc file.

 

Post the .asc file.

the question is why doesn't the actual circuit work like the ltspice simulation? The LM324 was an imported model to ltspice as they did not have it in their models. I need the lm324 to work as it should without swinging to + and - saturation at the output.
Why am I getting 0v at the output with the actual circuit?

 

the question is why doesn't the actual circuit work like the ltspice simulation? The LM324 was an imported model to ltspice as they did not have it in their models. I need the lm324 to work as it should without swinging to + and - saturation at the output.
Why am I getting 0v at the output with the actual circuit?

Simulations are just that, simulations. They try to get the real life circuit as close as possible but they are just semi idealized versions of real life. It just so happens though that sometimes there are gross differences. I think that is what you are seeing.
For example, source voltages with zero output resistance will power tiny resistors like 0.001 ohms with no loss of voltage, but try that in the real world and the power supply voltage drops to very low values or shuts off completely.

 

the question is why doesn't the actual circuit work like the ltspice simulation? The LM324 was an imported model to ltspice as they did not have it in their models. I need the lm324 to work as it should without swinging to + and - saturation at the output.
Why am I getting 0v at the output with the actual circuit?

We cannot possibly answer that question without looking at the file. Why is that so hard to understand!!?

 

We cannot possibly answer that question without looking at the file. Why is that so hard to understand!!?

I agree that we should see the circuit first and then figure out what is going on.

 

try transistor model ← i however won't give any credits it would match the actual LM324 too well
zipped .asc subcircuit and it's symbol .asy need to be on the same folder and also at the same folder with the simulation .asc that uses them ...

 

the question is why doesn't the actual circuit work like the ltspice simulation?

A real op-amp has an input offset voltage. Have you taken that into account in your sim?
A real circuit layout has stray inductance and capacitance. Have you modelled that in your sim?

 

Re : #8 @ 2019.12.12 11:51 AM

as i got the "problem" is setting one (non-inverting) input to a certain voltage (in the Spice simulation) and leaving another one floating (inverting one) . . .

. . . so -- the REAL test won't generate oscillations ???

 

Of course the output of an opamp in an LM324 goes close to 0V when its - input is floating. The inputs are PNP transistors that pulls up the floating input (goes positive).
The opamp might oscillate if the other three opamps in the LM324 have floating inputs.

If you build the circuit on a Mickey Mouse solderless breadboard then the strips of contacts and wires all over the place are antennas that pickup all kinds of interference that the opamp with the floating input amplifies.

 

http://www.ti.com/lit/an/sboa204a/sboa204a.pdf