Opamp test circuit.

[HellasTechn]

Hello everyone. today i was thinking of a test circuit for opamps like the 741. i made a diagram. What do you think of it ?
Thanks !

 

[bertus]

Hello,

I would place a voltage divider at the - input of the opamp.
It can be that driving opamps to close to the powersupply may distroy the opamp.

Bertus

 

[Harald Kapp]

Hi Constantine,

haven't seen you here for quite some time. To use an operational amplifier as a comparator you should include positive feedback for stability, see e.g. here. It is, by the way, possible but not good practice to use an opamp as a comparator. These chips are designed for linear operation. When used as a comparator they can saturate (and yes, they do) and will come out of saturation rather slowly. Very much contrary to a true comparator which you want to switch very fast.

As a test circuit your design is imho not suitable. It will check only wheter the opamp can switch between "+" and "-" output in a rather coarse fashion. To test the function of an opamp one would put it into an anlog amplifier circuit and measure gain, distortion, bandwidth etc.


Cheers,

Harald

 

[HellasTechn]

Hello,

I would place a voltage divider at the - input of the opamp.
It can be that driving opamps to close to the powersupply may distroy the opamp.

Bertus

Or passing Vi through a diode to use it's forward bias voltage drop.

 

[HellasTechn]

Hi Constantine,

haven't seen you here for quite some time.

To test the function of an opamp one would put it into an anlog amplifier circuit and measure gain, distortion, bandwidth etc.


Cheers,

Harald

Yes it's been a while since my last visit. Im into alot...
Do you have something in mind ?

 

[Harald Kapp]

Do you have something in mind ?

Not specifically.
Any amplifier circuit should work, assuming you have the necessary signal generator and e.g. an oscilloscope for analyzing the output.
Typically the datasheet of the opamp in question shows a test circuit that can be used.
Alternativel I found this simple opamp tester for 741 chips.

 

[bertus]

Hello,

Perhaps this page might give you ideas:

Opamp parameter tester | PA4TIM's opvangtehuis voor buizenbakken

PA4TIM's opvangtehuis voor buizenbakken - En nog een WordPress site

www.pa4tim.nl

And a kind of go-nogo circuit:

Operational Amplifier Tester Circuit – Electronics Projects Circuits

This wiring is a module that makes it easy and easy to distinguish good operational amplifiers from defective ones. The op amp tester is designed to test simple

320volt.com

Bertus

 

[HellasTechn]

Hello everyone. today i was thinking of a test circuit for opamps like the 741. i made a diagram. What do you think of it ?
Thanks !View attachment 61804

I noticed one more mistake in my above circuit. The smoothing capacitors must be placed at the other end of each rectifier diode...

 

[HellasTechn]

Here is the corrected diagram and a comment.

At the cathode of D3, which is actually the inverting input of the opamp, the waveform should be exactly same as at it's anode since there should be no current flowing through it due to the very high impedance of the opamp's inputs. A potentially bad opamp with a low inputimpedance will cause the waveform to appear semi rectified on the oscilloscope at the cathode of D3.

 

[danadak]

Various circuit configurations to test opamp parameters :

https://www.analog.com/en/analog-dialogue/articles/simple-op-amp-measurements.html

Regards, Dana.