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 :)
     
  2. YazanJuve

    Thread Starter New Member

    Dec 13, 2009
    28
    0
    And if anyone wonders about the left input part, they are current transformers
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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  4. YazanJuve

    Thread Starter New Member

    Dec 13, 2009
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    oh thx alot :D
     
  5. zhgart

    New Member

    Dec 28, 2009
    19
    1
    4
    2o
    approximately
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    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
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    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
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    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
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    The gain is calculated as:
    [​IMG]
    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
    7,050
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    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}<br />
\frac{V_{in}}{R_7} &= \frac{-V_{out}}{R_5+R_6}\\<br />
A &= -\frac{R_5 + R_6}{R_7}<br />
\end{align}<br />
    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
    22,182
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    Oops, yeah - I goofed up. :rolleyes:

    I gotta quit posting when I'm tired.
     
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