UA741 opamp giving abnormally high output when used as a comparator!

[Vichitha Chinmaya]

So, when the opamp was biased with +12 V and -12V as Vcc and Vee, with a 1.2 V peak-peak sine wave (from a signal generator) given as input to the negative terminal and positive terminal grounded, the output was a square wave of 220V peak to peak (as measured in the oscilloscope). I couldn't think of where could that much of a high voltage come from. This is contradictory to what one expects from an opamp, where the max saturation voltage is +Vcc and -Vee.

The comparator circuit used is as follows -
http://www.electronics-micros.com/img/electronics/comparator1.jpg

Can anyone tell me what could have gone wrong?
Thank you!

 

[pjmelect]

I think that you are not reading your scope correctly, 22V peak to peak is more likely.

 

[kripacharya]

I think that you are not reading your scope correctly, 22V peak to peak is more likely.

Yes that must be it. Your 'scope is set for x10 but your probe is not. or some such combination.

 

[Venkadesh_M]

Your problem is in scope or prope, you can verify it by connecting your DVM at output in AC mode........

 

[Vichitha Chinmaya]

ok, but I can't think of what could've been wrong with the connections in scope and probe. The probe is connected as the second channel to the oscilloscope and is grounded with the biasing battery's (+12V) ground (same as the positive of the battery supplying -12V). And to read the value of the output, I used the direct measure function in the oscilloscope which reads the p-p value of the channel.

I tried using a Digital Voltmeter in the AC mode, which again din't work, as it was showing a 0 throughout. :/

 

[PA4TIM]

I think you have the probe attenuation wrong in the menu if it is a DSO or yiot groundwire is not connected.

A DMM is limmited in frequency and crest factor. .Cheap ones sometimes go wrong at frequencies as low as 1 kHz , good ones measure TRMS AC+DC together and sometimes upto 1 MHz with crestfactors as good as 9 or 10. The output of a comparator will not be a sinewave,

 

[Venkadesh_M]

ok, but I can't think of what could've been wrong with the connections in scope and probe. The probe is connected as the second channel to the oscilloscope and is grounded with the biasing battery's (+12V) ground (same as the positive of the battery supplying -12V). And to read the value of the output, I used the direct measure function in the oscilloscope which reads the p-p value of the channel.

I tried using a Digital Voltmeter in the AC mode, which again din't work, as it was showing a 0 throughout. :/

i think you lost the gnd line thats why it show you 0v..