Non linear operation of an OP-AMP used as a non-inverting amplifier

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nareshgtr

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hi guys,
I am operating OP-AMP as a non-inverting amplifier. My problem is op-amp is not operating linearly. Always
output = gain * input + offset.
The problem is offset is not constant. It is varying with different values of input. I am attaching my schematic and data sheet TLE2142 of my design. Please let me know any error in the circuit. Please give suggestions to over come this problem.
Regards
V. Naresh Kumar
 

Op AMP Non linearity

Without knowing quantitative results, no one can determine if they are just normal operation or indicating a specific problem. Generally, you have to take care of keeping the OPs common mode range, your circuit doesn't answer this question.
 

Re: Op AMP Non linearity

Dear FVM,
Thanks for your reply, I updated my schematic. According to updated schematic when 4-6 current flows through the resistor R19 the output value is 1.16(200V offset) to 1.64. When increases beyond the 6A the output is always 1.75V.
you have to take care of keeping the OPs common mode range, your circuit doesn't answer this question
Click to expand...
I could not understand please explain some more
 

Re: Op AMP Non linearity


At first, your opamp is not operated as a non-inverter. Instead, it is a differential amplifier because both input terminals are connected with the input circuitry.
Secondly, how could we detect any "error" without knowing the purpose and specifications of your design ?
More than that, what do you call "input" ? Voltage or current at which input pin ?
If you expect a valued answer you should describe your problem in more detail !
Regards
 

Re: Op AMP Non linearity


Your schematic has a resistor missing in the noninverting input
**broken link removed**

And is a good practice with low level voltages, the offset nulling.
See the TLE2142 datasheet, page 56.
 

Re: Op AMP Non linearity

Dear Lvw
I updated the my schematic. Now it should work as a non-inverting amplifier. Input to non-inverting pin (IN+) is voltage across R19. IN- pin is ground through resistor network. My application is current sensing circuit.
Regards
V. Naresh Kumar
 

Re: Op AMP Non linearity

Why you post file as doc? Using a simple image format is much better as everybody can read the file directly from the browser. Using any program (t.ex Faststone Image Viewer, Irfanview, XnView etc...) that can save file as png will make it more easy for everybody.

Thanks for attention

 

Re: Op AMP Non linearity

According to updated schematic when 4-6 current flows through the resistor R19 the output value is 1.16(200V offset) to 1.64. When increases beyond the 6A the output is always 1.75V.
Click to expand...
Don't understand "200V offset".
The 4-6 A values are fine according to my calculation. Please consider, that TLE2041 hasn't rail-to-rail output and that you are operating it below the specified supply voltage range (4V min). So the output saturation may occur slightly below the specified limits.
 

Re: Op AMP Non linearity

thanks FVM,
If VCC is connected to 5V, my problem may solve.
Regards
V. Naresh Kumar
 

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