I have just got three different versions of the TL082CP, two from vendors in China and one from an authorized Texas Instruments distributor. All the chips are newly purchased and have never been used.

I have done a basic test with them. Connect their inverting input (pin 2) to the output (pin 1), the non-inverting input (pin 3) to ground, power the circuit with V+=+5VDC (pin 8) and V-=ground (pin 4) and measure with a multimeter the voltage between output and ground.

In theory in this configuration the output should measure approximately 0V.

The two Chinese TL082CPs show the same behavior, the output is ~0V as expected but with the original Texas Instruments the output is ~+4.492VDC.

If the basic test circuit is modified by connecting the non-inverting input (pin 3) to V+, on the two Chinese TL082CPs the output is ~+3.7VDC while on the original Texas Instruments the output remains at ~+4.492VDC.

What is the cause of this difference in behavior?

Thanks

 

Try connecting pin 4 to a negative supply, say -5V, and doing the tests again. The chances are that the ones from China aren't TL082's but some version of LM358, whose inputs and outputs CAN operate with a single supply near to GND, whereas the TL082 cannot. The TL082 also exhibits phase reversal when the input gets too close to the negative rail, which you are seeing .

 

I guessed the ones from China are LM358 and in fact an original Texas Instruments LM358 exhibits the same behavior.
Thank you.

 

Exactly, it is a LM358 sold to you as TL082.
The LM358 its input common mode range includes the V(-) pin.. The TL082 CMR should be a couple of volts above.
Also, because of its old JFET input structure, it can also have polarity reversal as mentioned above. The output of the LM358 swings very close to ground, whereas the TL082 there will be perhaps a couple of volts above ground.

So what are the advantages of the TL082, you may wonder? Well, for starters, orders of magnitude higher input impedance. And a faster Slew Rate which equals a higher usable bandwidth.

Purchasing ICs from Chinese vendors follows the old dictum: Caveat Emptor.
You wouldn't be the first one nor the last one to be scammed like that.

 

I guessed the ones from China are LM358 and in fact an original Texas Instruments LM358 exhibits the same behavior.

Consider yourself lucky that you even got an opamp. The counterfeiters only care about package style.

Some obvious signs of counterfeit parts are pitting on the shoulders of the leads from sand blasting, black topping (the texture/color of the top of the package doesn't match the bottom), poor facsimile of company logo, and eroded pin 1 dimple. Sometimes they even try to repair broken leads.

 

My name is Julian I am just began my first year as student of engineering.

I am very interested in this discussion and would like to have some tips from you guys to choose, just by reviewing the datasheets, operational amplifiers with inputs and outputs that can operate near to GND and, if possible, also to know whether or not it would produce that phase reversal.

 

Don't test them with Vcc=5V, GND=0V, because they need 6V to operate.
https://www.st.com/resource/en/datasheet/tl082.pdf

 

Welcome to AAC!

Instead of hijacking another member's thread, you should have started your own.

I am very interested in this discussion and would like to have some tips from you guys to choose, just by reviewing the datasheets, operational amplifiers with inputs and outputs that can operate near to GND and, if possible, also to know whether or not it would produce that phase reversal.

Datasheets will specify the allowed input voltage range and the output swing. If you follow the guidelines in the datasheet, you don't need to worry about phase reversal.

Datasheets for older parts don't specify whether the opamp will experience phase reversal, so you need to analyze the circuit (the older datasheets also provided a schematic with sufficient detail to do this). The schematics will also show you whether (and why) input and outputs will include GND.

 

Consider yourself lucky that you even got an opamp. The counterfeiters only care about package style.

They were checked as good with an op-amp tester. Otherwise, they would have been returned.

 

Don't test them with Vcc=5V, GND=0V, because they need 6V to operate.

Thank you. I believe it is slightly different with the Texas Instruments' TL082CP.
https://www.ti.com/lit/ds/symlink/tl082.pdf

 

Instead of hijacking another member's thread, you should have started your own.

Thank you Dennis but that's fine. I don't care, I guess I'm done here.

 

Thank you. I believe it is slightly different with the Texas Instruments' TL082CP.
https://www.ti.com/lit/ds/symlink/tl082.pdf

Their datasheet omits the essential piece of information that is the minimum supply voltage, but the latest version TL082H does work at 5V, which makes me think that earlier version didn't and were equivalent to the ST part.

 

They were checked as good with an op-amp tester. Otherwise, they would have been returned.

You didn't get what you paid for and are settling for something else. That's what the seller's business model depends on.

I think LM358 is a fine general purpose opamp. But, if you needed the benefits of a JFET input, LM358 isn't a viable substitution. There was another member who bought what he expected to be LM318. He got some opamps that passed his DORA (Dead OR Alive) testing, but they didn't have the high slew rate that is a major benefit of LM318.