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Op amp non inverting amplifier not working

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I14R10

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Hello

I'm trying to build an amplifier with Op amp (TL072). I built a simple circuit like this

opamp-opamp15.gif


But I don't get anything on output. Weird thing is, I get huge amplification if I don't connect R_f and R_2. As soon as I put any resistor there, my output drops to 0.

I've also simulated a random 2 op amps in LTSpice and this exact circuit doesn't work there either.


Screenshot_20220705_155749.png


What am I doing wrong?
 

You have to provide a bias return path for the NI input. Say a 1M to ground,
since you are AC coupling. Or DC couple and offset V2 waveform.

When no fdbk is used the OpAmp is open loop with a typical G of

1657030479301.png


Regards, Dana.
 
Yes, missing N.I. bias. To achieve useful operation point with given feedback network, it should be biased to e.g. 0.5 V.
 
Yes, missing N.I. bias. To achieve useful operation point with given feedback network, it should be biased to e.g. 0.5 V.

I want only positive half of the signal to be amplified. Do I still need to do N.I.bias?

Also, I'm starting to doubt if my opamps are good. I've also made voltage follower (wire from output to - input) and my opamps are still getting a huge amplification on the output.
 

Thanks everybody. Somehow I thought op amps were some magical devices that doesn't need biasing.
 

I want only positive half of the signal to be amplified. Do I still need to do N.I.bias?
Thanks everybody. Somehow I thought op amps were some magical devices that doesn't need biasing.
They are very useful devices, but certainly not magical.
Both inputs need a path for their input bias current no matter how small it is.

Also if you want to operate them from a single-supply they need to be single-supply or rail-rail types, or the inputs need to be biased at 1/2 the supply voltage (virtual ground).
 

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