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TL07x, TL08x eBay fakery

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magic:
Also try 5k load and see if crossover artifacts move 50% closer to ground :)
Outputs pre-biased with 80~150µA to VEE is within possibility, 358 does it too although it's supposed to be 50µA.

John B:

--- Quote from: magic on August 20, 2019, 06:10:07 am ---Also try 5k load and see if crossover artifacts move 50% closer to ground :)
Outputs pre-biased with 80~150µA to VEE is within possibility, 358 does it too although it's supposed to be 50µA.

--- End quote ---

Yes it does move the crossover distortion closer to ground. I also put a 910R load on, which moved the distortion just under ground.

Also, the TLOL72 clocks in a whopping 0.55v/us slew rate.



--- Quote from: David Hess on August 20, 2019, 03:17:46 am ---
--- Quote from: John B on August 19, 2019, 01:19:04 am ---Below is a comparison of an eBay sourced "TL072CP" and "TL082CP", vs an LCSC sourced TL072CP. Each op amp is powered at +/- 5V, +/- 15V, with a 10k load to ground. All configured as a non inverting buffer.
--- End quote ---

It is interesting that the crossover distortion occurs so far below ground;  I would have expected it to be much closer to ground.  The symmetry between the positive and negative edges indicates no capacitive loading which is consistent with the description of your test.

Is the distortion different in inverting mode where there is no common mode voltage?  Maybe it is not coming from the output stage.


--- End quote ---

To clarify, you want a unity gain inverting configuration, with the input connected to ground, or left floating?

Link to falstad diagram

magic:
0.5V/µs is typical of 358. Also a bit under 1mA supply current. I guess it is indeed some kind of 358-like design, maybe with slightly improved specs (less input bias, more output bias).

I wonder if somebody specifically designs those things for faking other parts or if they are just off-the-shelf Chinese jellybeans with changed markings. Probably the latter, but who knows. Fakes of digital chips like DS18B20 or PL2303 certainly need some die customizations even if derived from off-the-shelf MCU designs. Somebody actually invests in it :)

David Hess:

--- Quote from: Nominal Animal on August 20, 2019, 12:17:22 am ---I wonder if it would make sense to create a microcontroller/DSP circuit with a 24-bit ADC+DAC, just to characterize opamps at unity gain with different wave forms down to DC behaviour?
--- End quote ---

It would not take that much resolution to quantify DC behavior.  In the past it was often done using a triangle wave generator and oscilloscope in XY mode and this was sufficient even for precision parts down to picoamps and microvolts.


--- Quote from: magic on August 20, 2019, 06:10:07 am ---Outputs pre-biased with 80~150µA to VEE is within possibility, 358 does it too although it's supposed to be 50µA.
--- End quote ---

The 324/358 are among the few or only with that feature.  Contemporary single supply parts with class-AB emitter follower output stages did not bother and required an external pull down unless their schematics are wrong which makes me wonder if that 50 microamp internal pull-down was patented.


--- Quote from: John B on August 20, 2019, 08:13:10 am ---
--- Quote from: David Hess on August 20, 2019, 03:17:46 am ---It is interesting that the crossover distortion occurs so far below ground;  I would have expected it to be much closer to ground.  The symmetry between the positive and negative edges indicates no capacitive loading which is consistent with the description of your test.

Is the distortion different in inverting mode where there is no common mode voltage?  Maybe it is not coming from the output stage.
--- End quote ---

To clarify, you want a unity gain inverting configuration, with the input connected to ground, or left floating?
--- End quote ---

I mean ground the non-inverting input and drive the input resistor as shown in your example.  Instead of exercising the operational amplifier in a gain of +1 configuration (voltage follower), exercise it in a gain of -1 configuration where the common mode voltage is constant.


--- Quote from: magic on August 20, 2019, 09:30:22 am ---0.5V/µs is typical of 358. Also a bit under 1mA supply current. I guess it is indeed some kind of 358-like design, maybe with slightly improved specs (less input bias, more output bias).

I wonder if somebody specifically designs those things for faking other parts or if they are just off-the-shelf Chinese jellybeans with changed markings. Probably the latter, but who knows. Fakes of digital chips like DS18B20 or PL2303 certainly need some die customizations even if derived from off-the-shelf MCU designs. Somebody actually invests in it :)
--- End quote ---

More likely they are parts which failed testing or are completely different parts which were remarked.  The TL07x series is the low cost jelly bean part for audio and low input bias current.

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