Op-Amp Output Clipping

Thread Starter

lightbolt34

Joined Sep 23, 2019
5
Hi,
I was using an Op Amp in a differential configuration of the below circuit:

V2=5V
R1=1k
R2=1k
R3=10k
R4=835Ω
Op Amp: UA747CN

V1 was adjusted and I recorded these results with the following circuit:
upload_2019-9-23_20-25-42.png

Why doesn't vout exceed ~3V? Vcc- to the op amp was -15V and Vcc+ to the op amp was +15v.
 

Thread Starter

lightbolt34

Joined Sep 23, 2019
5
Thanks for your help Dana. Although i'm still not sure why it's clipping.

Yes it may be unequal, the input of this circuit was from a sensor.
 

Thread Starter

lightbolt34

Joined Sep 23, 2019
5
Thanks for your input E, I simulated this as well and I got the same result.
All wiring and values is correct. It is expected to clip from the teacher, although I'm having a hard time understanding as to why this occurs.
 

ericgibbs

Joined Jan 29, 2010
13,864
hi,
What results do measure when using Hall device as an input.?
The Hall Vout is ~ +1.5V thru +3V
Note the load impedance marked on the data sheet.
E
 

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Thread Starter

lightbolt34

Joined Sep 23, 2019
5
hi,
What results do measure when using Hall device as an input.?
The Hall Vout is ~ +1.5V thru +3V
Note the load impedance marked on the data sheet.
E
The results shown in the V1 column in the original post is from the output of the Hall sensor.
From out results, the hall sensor has an output voltage of 0.8V-4.36V.

The V1 measurements were measured from the sensor without the amplifier circuit attached, so could it be something to do with the output resistance of the sensor?

Unfortunately I don't have any actual measurements of V1/sensor output when it was used in the amplifier circuit.
 
Last edited:

danadak

Joined Mar 10, 2018
4,057
Thanks for your help Dana. Although i'm still not sure why it's clipping.

Yes it may be unequal, the input of this circuit was from a sensor.
Is because you are gaining up the CM voltage. If it was a real differential amp it would
reject CM voltage. The whole point of using diff amps.

You can use these amps unbalanced, purposely gain up CM voltage to provide
a bias, but my guess, not knowing sensor, is you have a CM voltage to contend
with.


Regards, Dana.
 
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