I have a circuit that works correctly with either an LM358 or a TL072 of which I am sure neither is original. Although on both the pin assignments are the same as the original LM358 and TL072, electrically they exhibit the same behavior as an LM324.

But LM324 is a quadruple op-amp and I need a compatible dual op-amp replacement (LM358 pin assignment) with the same behavior as the LM324. No need to say the original circuit cannot be modified or replaced by another one.

Any help would be appreciated.

Snapshots of simulations performed with LM324, LM358 and TL072.

 

The LM324 is the same as two LM358s.

 

You post is more than a bit ambiguous.

1. What do you mean when you say "... I am sure neither is original."
2. Why can't you use an LM358?
3. Simulations are not necessarily a reliable guide to device performance.

It looks to me like the LM324 and LM358 are the same internally and the following app note may be helpful to you
Application Design Guidelines for LM324 and LM358 Devices (Rev. B)

 

You post is more than a bit ambiguous.

Sorry about that.

What do you mean when you say "... I am sure neither is original."

The op-amps in the circuit are Chinese fakes labeled as LM358P, TL072CP and sometimes even as RC4558 but actually they are all the same fake op-amp.

Why can't you use an LM358?

Replacing the fake LM358P with an LM358P from Arrow, Digikey, Farnell or Mouser causes the circuit stops working as it should.

Simulations are not necessarily a reliable guide to device performance.

Same tests on a breadboard confirm the same results as shown in the screenshots.

 

Replacing the fake LM358P with an LM358P from Arrow, Digikey, Farnell or Mouser causes the circuit stops working as it should.

And how does it stop working?

 

Replacing the fake LM358P with an LM358P from Arrow, Digikey, Farnell or Mouser causes the circuit stops working as it should.

In that case your statement "as it should" is questionable.

 

In that case your statement "as it should" is questionable.

I know it is tricky. “As it should work” with the op-amp that is built in the device but not ‘as it should work’ if swapped for a genuine LM358P.

And how does it stop working?

It should work as shown in this snapshot,



but instead it works as this other one.

 

The problem is that you have the inverting input tied to the negative rail.
Many op amps will not work under that condition.

 

It's confusing when you draw the circuit upside-down (ground connections on top).
It's like trying to read upside-down writing.

Where did you get the model for the bottom simulation?

 

The problem is that you have the inverting input tied to the negative rail.
Many op amps will not work under that condition.

The LM324/358 should.

 

It's confusing when you draw the circuit upside-down (ground connections on top).
It's like trying to read upside-down writing.

I agree. It comes from the default orientation for displaying the op-amp in this simulator.

Where did you get the model for the bottom simulation?

The simulator models are built into Micro-cap 12, I assume that most of them come from SPICE.

At last, possibly I have not expressed myself clearly enough, English is not my first language, but I cannot stress enough that the circuit comes from a real working device and the specific question is which dual op-amp (with the same pin arrangement as the LM358P) could be used as a replacement for the fake LM358P knowing that it behaves like the LM324 in the snapshot.

 

What is the power supply voltage?

 

VC=+5V VE=0V

V1=+5V square wave (low=0V high=+5V)

Measured in the device or breadboard Vo is ~+3V (<+3.55V) when Vi is high, ~0V (<+300mV) when Vi is low.

 

A more objective test might include a comparison of the op amp's characteristic such as slew rate, which can vary.
An LM358 could have a slew rate of 0.3 V/us
A TL072 could have a slew rate 13 V/us

There are other parameters that give more meaning to performing a test on an op amp.
A specified detail of interest usually related to an application, it may not include every detail but at least a few meaningful details,
for example ringing and overshoot might be important as it may cause unwanted distortion for an application under certain conditions.

We learn about an op amp's limitations by studying a set of parametric characteristics that are appropriate for an application.
The testing of an op amp can be complex, not over simplified. Usually we learn transistors first so we have enough background and skill to approach
op amps, those who already have the pre-requisite ask, why are we spending valuable time playing guessing games?

 

VC=+5V VE=0V


Measured in the device or breadboard Vo is ~+3V (<+3.55V) when Vi is high, ~0V (<+300mV) when Vi is low.

OF COURSE! That is completely normal behavior.
A LM358’s output can only swing high to Vcc-1.5 volt, and swing low to above 0.2 volt.
Read the data sheet. Look for the Voh, Vol specs.

 

OF COURSE! That is completely normal behavior.

Measured in the device Vo is ~+3V (<+3.55V) when Vi is high, ~0V (<+300mV) when Vi is low

... with the unknown dual op-amp labeled as LM358P built into the device as shown in this snapshot:

but replacing that op-amp for a genuine LM358P the behavior changes to this:

 

VC=+5V VE=0V

V1=+5V square wave (low=0V high=+5V)

Measured in the device or breadboard Vo is ~+3V (<+3.55V) when Vi is high, ~0V (<+300mV) when Vi is low.

The input common mode range is from 0 to about 1.5V less than the positive supply. An LM358 is not going to work properly when the input is at the same voltage as the positive supply.

 

Thanks.
So which do you think the unknown op-amp may be?

 

Thanks.
So which do you think the unknown op-amp may be?

No idea. I don't buy dodgy components. I just use proper distributors.

 

Of course, I am just trying to figure out a genuine replacement.