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I am trying to use the TL071 for a project. I run my simulations on Proteus.

After I ran the simulations and verified the circuit behaves as I want, I ordered the parts and put the circuit together.

Later on I realized that the TL071 doesn't work as it worked in the simulation. I checked the simulation and I realized I didn't check the "attach hierarchy module" box which makes the component behave like the specific component, rather than a generic op-amp.

After checking the box I saw that the TL071 behaves exactly like it behaves in the real circuit.

The problem is I can't understand why. I wanted to use a TL071 to make a comparator, which didn't work.

I tried using an LM311, but it didn't work in the simulation either (0 volts as output in every sceneraio.)

As a last resort I wanted to use the TL071 as a simple amplifier.

Even then it did not work as intended.

Below I post the simple amplifier setup. I should get about 12-10 volts output, but instead I get 0 volts.

I tried it in the real circuit and I saw that when I put together the same amplifier with the TL071 I get 0 volts again so the simulation is not the problem.

After unchecking the "attach hierarchy module" option I saw that the op-amp behaves as expected and produces 10.5 volts output. I use the exact supplies in the real circuit. I tried amplifying a sine wave signal it doesn't work either.

circuit

Below is when simulation running:

Sim running

Edit2: The whole circuit. This simulation works but in a real circuit I get the result below.

circuit

edit: I tried the actual circuit with using +12/-12 volt supplies, 0 volt ground and a sinewave as input. VCC is 12V, VEE is -12V, inverting input is connected to the ground and non inverting input is connected to the sinewave. I get this weird wavefrom instead of a square wave as result.

Edit3: In real circuit I realized the op-amp gets very, very hot. I almost burnt my hand.

waveform

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  • \$\begingroup\$ Can you post with the simulation values? \$\endgroup\$
    – Damien
    Jun 17, 2021 at 8:11
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    \$\begingroup\$ Feedback goes to - input not + \$\endgroup\$
    – bobflux
    Jun 17, 2021 at 8:54
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    \$\begingroup\$ The problem with swapping of the op-amp input pins was pointed out to you in the second comment to your previous question. \$\endgroup\$
    – Transistor
    Jun 17, 2021 at 9:29
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    \$\begingroup\$ OK, but deliberately wiring them incorrectly definitely won't work so why are you still doing it? \$\endgroup\$
    – Transistor
    Jun 17, 2021 at 10:19
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    \$\begingroup\$ "Below I post the simple amplifier setup" Maybe that sentence explains the confusion, since your circuit clearly is not an amplifier. \$\endgroup\$
    – devnull
    Jun 17, 2021 at 13:14

4 Answers 4

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Firstly, you don't need to attach hierarchy module. This is used to edit the child sheet to turn the component into a module and attach subcircuits etc. Which can be useful when designing your own component. With nothing on the child sheet, it won't really do much.

Secondly, you have the amplifier incorrectly configured. It looks like you are going for the non-inverting amplifier configuration, but you have the feedback going into the non-inverting terminal, so the behavior will not be as expected. You need to have the input voltage going in to the non inverting input, and the feedback goes to the inverting input.

The reason you are getting 10.5V is because the gain is 1+(R6/R5) = 1+(10k/1k) = 11. With 6V in, your output should be 66V, but because the supply rail only goes up to 12V, it is limited. Looking at the DATASHEET for this device, you can see the output voltage swing isn't rail-to-rail. The positive output for a ± 15V supply is typically about 13.5V, so around 10.5V is to be expected.

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  • \$\begingroup\$ I know, but I get 0 Volts both on real life and simulation. \$\endgroup\$
    – Tombeki
    Jun 17, 2021 at 9:59
  • \$\begingroup\$ That's because the simulation is correct; this schematic isn't an amplifier. \$\endgroup\$ Jun 17, 2021 at 11:48
  • \$\begingroup\$ @Tombeki your simulation isn't correct. With the heirarchy module ticked, it won;t work correctly as it is waiting for something on the child sheet, so you will get 0V. As it is wired now, you will get -10.5V as it is not configured correctly. Make sure your real life circuit actually has ±12V supply. If pin 4 is connected to GND and it is wired up as shown, then you will be getting close to 0V \$\endgroup\$
    – MCG
    Jun 17, 2021 at 13:54
  • \$\begingroup\$ @MCG My circuit has +- 12V supply. I get 24 volts, divide it with a step-down module and obtain 12 volts. I use 24v as +12v, 12v as ground and 0 as -12v. Both my real life and simulation circuit are not working. Not even in comparator config. In given setup pin 4 is connected to -12, 7 is connected to +12. \$\endgroup\$
    – Tombeki
    Jun 17, 2021 at 18:41
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First things first. As you've shown it, you should be getting something like -10 to -12 volts. Not +10 to +12.

If you had +12 on the output, the + input would be at about 1 volt, the - input at + 6 is greater than the +, so the output will go negative.

If both your simulation and circuit show 0 volts, I suggest that you are confused about your schematic. The most likely problem is that pin 4 is not connected to -12, it is connected to ground. In your physical circuit, measure both supplies. I doubt very much that you'll get +12 and -12.

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I wanted to use TL071 to make a comparator, which didnt work.

To use an op-amp as a comparator,

  • If you have a bipolar power supply (you do), and
  • If you want to compare a signal to ground (OV) (I think you do)

You may use this circuit:

schematic

simulate this circuit – Schematic created using CircuitLab

The output, if you use a rail-to-rail op-amp, looks like this:

enter image description here

If you do not use a rail-to-rail op-amp, the voltage swing will be less. You can simulate this circuit yourself using the link provided.

Note that there is no feedback loop at all. A vanilla comparator should not have a feedback loop.

  • If you have a bipolar supply, and
  • If you want to compare a signal to some other fixed voltage

You may use a circuit like this:

schematic

simulate this circuit

In this circuit, the resistor values provide a reference voltage of 4V. The sine wave input is +/- 8V, and the output looks like this:

enter image description here

Once again, feedback is not used.

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  • \$\begingroup\$ I have been working on this for 5 days, and it doesnt work. I always get this weird waveform I added to the actual question. \$\endgroup\$
    – Tombeki
    Jun 22, 2021 at 12:16
  • \$\begingroup\$ The schematic does not match the description you give of your physical test. Please add a schematic that corresponds to the waveform in your physical test. Are you still using any resistors? What is the frequency in your test? You may have reached maximum slew rate. \$\endgroup\$ Jun 22, 2021 at 13:41
  • \$\begingroup\$ Also, what is the op-amp driving? And, how are you probing the result? Unless your input is really tiny, or your frequency too high, the output, if correctly wired, should be near +/- 10V. \$\endgroup\$ Jun 22, 2021 at 13:47
  • \$\begingroup\$ Op-amp is driving a sine wave I created with an oscillator and amplified with another op-amp. Mainly a sine wave with 2V peak. Frequency is around 16kHz. I will post the whole schematic when I get home, sorry. \$\endgroup\$
    – Tombeki
    Jun 22, 2021 at 14:01
  • \$\begingroup\$ Op-amp is driven by a sine wave from an amplifier. What is it driving? What is the output of the op-amp connected to? Also, how are you connecting the op-amp output to the oscilloscope? \$\endgroup\$ Jun 22, 2021 at 14:07
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The TL071 and TL081 have Jfet inputs which cause the problem called Phase Inversion where the output suddenly goes as high as it can if an input voltage becomes within 4V to the negative power supply voltage.

Your sinewave is probably 0.7V peak and the first TL071 opamp with a gain of 16 times produces a clipping waveform with plus and minus 11.2V peaks which is too much negative input voltage for the second TL071 and third TL071 opamps.

Which opamp gets hot?? The loads are not shown on your schematic. The load on an opamp must be 2k ohms or higher.

phase inversion

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  • \$\begingroup\$ Oh I didnt know that there should be a 2k load on an op-amp thank you. When I run tests, I attach no loads to the first TL071 which is why I think it gets hot. About this phase inversion, what should I do? Should I just replace TL071? I chose it because it has high slew rate. Any other substitudes in mind? \$\endgroup\$
    – Tombeki
    Jun 22, 2021 at 15:15
  • \$\begingroup\$ first two op-amps are not TL071 they are UA741. It creates a sinewave just fine, not clipped. Around 7V peak. \$\endgroup\$
    – Tombeki
    Jun 22, 2021 at 15:16
  • \$\begingroup\$ On second thought, impedance of the probe is way more than 2k, shouldnt it be enough? \$\endgroup\$
    – Tombeki
    Jun 22, 2021 at 19:48
  • \$\begingroup\$ I added 100k ohm load to the output of the first TL071 and it still gets pretty hot that it burns my hand. \$\endgroup\$
    – Tombeki
    Jun 23, 2021 at 11:29
  • \$\begingroup\$ Your schematic shows TL071 opamps but now you said they are 741 opamps. \$\endgroup\$
    – Audioguru
    Jun 23, 2021 at 16:20

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