# Amplifier Gain?

Discussion in 'General Electronics Chat' started by YazanJuve, Dec 28, 2009.

1. ### YazanJuve Thread Starter New Member

Dec 13, 2009
28
0
Hello

I need to know what is the gain of the amplifier shown in the circuit below in the 2 cases:

1- When R5 is short circuited.
2- When R5 is NOT short circuited.

Thanks

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2. ### YazanJuve Thread Starter New Member

Dec 13, 2009
28
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And if anyone wonders about the left input part, they are current transformers

Apr 20, 2004
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Dec 13, 2009
28
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oh thx alot

5. ### zhgart New Member

Dec 28, 2009
19
1
4
2o
approximately

6. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Actually, with R5 shorted the gain is approximately 4.571
With R5 shorted, it's approximately 22.43.

7. ### YazanJuve Thread Starter New Member

Dec 13, 2009
28
0
thx guys but i need to know which components are included in the gain calculation?

and does the CT turn ratio affect it?

8. ### YazanJuve Thread Starter New Member

Dec 13, 2009
28
0
thx guys but i need to know which components are included in the gain calculation?

and does the CT turn ratio affect it?

9. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
The gain is calculated as:

where:
R7 is R1, and
R2 is the sum of R6 and R5 when R5 is not shorted, or just R6 when R5 is shorted.

There is no transformer or coil shown on the schematic. However, it would not affect the gain of the opamp, but might affect the output of the circuit.

10. ### Ron H AAC Fanatic!

Apr 14, 2005
7,012
681
Errmm, that's not the equation for an inverting amplifier.

11. ### dsp_redux Active Member

Apr 11, 2009
182
5
Where is the "+1" coming? I tought you had
\begin{align}
\frac{V_{in}}{R_7} &= \frac{-V_{out}}{R_5+R_6}\\
A &= -\frac{R_5 + R_6}{R_7}
\end{align}

So "-1" for the two answers you gave SgtWookie. Or maybe I'm wrong?

12. ### YazanJuve Thread Starter New Member

Dec 13, 2009
28
0
I think the gain for the inverting amplifier is:

Gain= -R(feedback)/R(input)

Feedback resistance is : R5+R6 or R6 only
Input resistance is: R7

so Gain= -(R5+R6)/R7

but i am wondering if R8, R9 and the CT turn ratio is calculated here?

13. ### SgtWookie Expert

Jul 17, 2007
22,201
1,809
Oops, yeah - I goofed up.

I gotta quit posting when I'm tired.