Differential amp

Discussion in 'General Electronics Chat' started by TAKYMOUNIR, Sep 26, 2012.

  1. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
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    What is the input on pin2 and pin3 and what is the vo
    thanks AND IF I NEED THE VO TO BE 10 V WHEN THE INPUT VOLTAGE 1000V WHAT IS THE VALUE OF RESISTORS IN THIS CASE
     
    Last edited: Sep 26, 2012
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Your drawing is wrong , where is the ground in relation to the battery input?
     
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  3. ramancini8

    Member

    Jul 18, 2012
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    Your circuit doesn't make sense. What are you trying to do?
     
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  4. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    sorry i forget the ground ,i attach new drawing
     
  5. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    i change the drawing can you look to new schematic
    thanks
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Pin 2 will have 0.6v as the diode d2 is forward biased and the wrong way round, what are the voltages of d1&d2
     
  7. crutschow

    Expert

    Mar 14, 2008
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    The circuit is a differential input design so the differential gain is R5 / (R3+R4) for ideal resistors (much less than 1 in this case). Vo thus is equal to the total value of the input voltage (V1-V2) times this gain value. I'll leave the calculations as an exercise for the reader.

    Note that for real resistors you will need to take the resistor tolerance into account.
     
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  8. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
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    v1-v2=0v or 600v and what is the voltage across d1 and d2
    thanks
     
  9. TAKYMOUNIR

    Thread Starter Active Member

    Jun 23, 2008
    351
    1
    and how can i make vo =10
     
  10. Dodgydave

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    Jun 22, 2012
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    Last edited: Sep 26, 2012
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  11. ramancini8

    Member

    Jul 18, 2012
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    The sad news is that unless the external components are matched you get an error because the mismatch creates a differential signal. If you use 3% resistors, and the mismatch between input resistors is 3%, you get an 18V error. Differential amps are very hard to make.
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I'll believe 18mV error.:confused:
     
  13. crutschow

    Expert

    Mar 14, 2008
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  14. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I think Dodgydave forgot about the feedback.
     
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