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Opamp test circuit.

HellasTechn

Apr 14, 2013
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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 !opamp2.jpg
 

bertus

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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

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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

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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.
 

Harald Kapp

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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

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HellasTechn

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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.


IMG_20231207_0002.jpg
 
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