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

 

And if anyone wonders about the left input part, they are current transformers

 

You are in luck - our Ebook has a chapter devoted to the subject - http://www.allaboutcircuits.com/vol_3/chpt_8/5.html

 

oh thx alot

 

4
2o
approximately

 

Actually, with R5 shorted the gain is approximately 4.571
With R5 shorted, it's approximately 22.43.

 

thx guys but i need to know which components are included in the gain calculation?

and does the CT turn ratio affect it?

 

thx guys but i need to know which components are included in the gain calculation?

and does the CT turn ratio affect it?

 

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.

 

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.

Errmm, that's not the equation for an inverting amplifier.

 

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?

 

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?

 

Oops, yeah - I goofed up.

I gotta quit posting when I'm tired.