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Problem with Op-Amp differential amplifier

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imanjohn

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Hello,

I have implemented a simple differential amplifier with an OP07 IC. R4 = R3 = 47K, R1 = R2 = 2K.

When I connect inputs (V1 and V2) so that the voltage difference be 0 at the inputs, I always see 1.5V on output. When I apply small differences at the input, the output does not vary and it is 1.5V. I did not do anything for offset nulling and I checked on several ICs. Would you please let me know the problem?


opamp18.gif
 

imanjohn

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Just connect or connect both to ground?
Just connect! But I will check with GND and voltage applied.

If I connect both inputs to the GND, the output will be 7V (the V+ is 10V and V- is GND).

If I connect inputs to 2V, then the output remains 1.5V.
 
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LvW

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If I connect both inputs to the GND, the output will be 7V (the V+ is 10V and V- is GND).
So you work with single supply ?
Do you know about the restrictions for single supply (proper biasing)?
 

imanjohn

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So you work with single supply ?
Do you know about the restrictions for single supply (proper biasing)?
Yes, I do. I want to have a simple subtractor to make a current limiter.

Unfortunately I don't know anything about proper biasing for single-supply op-amp circuits. Could you please introduce some text to refer? Do you have any idea to solve the problem?

Thank you very much.
 
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