# problem with op amp positive and negative feed back at a time?

Discussion in 'General Electronics Discussion' started by chaitanya2k6er, Dec 9, 2010.

1. ### chaitanya2k6er

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Dec 9, 2010
hi!!
I got stuck up with the op amp circuit which has both the positive and negative feed backs? What is the use of using op amp with both feed backs at a time? How to analyze the circuit? Please suggest me the solution with the required formulas.
Thank u..

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,271
2,718
Jan 21, 2010
Do you want to post a link to the schematic?

And why do you want the circuit explained (it may help us in formulating a suitable reply)?

3. ### chaitanya2k6er

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Dec 9, 2010
i have attached the circuits related to this.
no specific reason, i want to implement the circuit for some application.

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4. ### Laplace

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184
Apr 4, 2010
The basic technique for analyzing an op-amp circuit is to calculate the voltage at the (-) input to the op-amp as a function of the output and/or input voltage. Then do the same for the (+) input. Set these two expressions equal to each other, V(-)=V(+), then crank the algebra to get the output voltage as a function of the input voltage. So if I did the algebra right, the answer is Vo = V1(R1R4+R2R4)/(R2R4-R1R3).

5. ### chaitanya2k6er

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Dec 9, 2010
thank u..
but i have not understood what you have suggested. Could you please elaborate it.

6. ### Laplace

1,252
184
Apr 4, 2010
Just write the node equations at the op-amp inputs, then solve for the output voltage as a function of the input voltage. See attachment.

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