TL071 doesn't work like a generic op-amp

Question

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.

Below is when simulation running:

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

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.

Answer 1

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.

Answer 2

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.

Answer 3

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:

^{simulate this circuit – Schematic created using CircuitLab}

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

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:

^{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:

Once again, feedback is not used.

Answer 4

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.