Non-inverting amplifier

Discussion in 'The Projects Forum' started by ching fong kee, Jul 30, 2010.

  1. ching fong kee

    Thread Starter Member

    Jun 23, 2010
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    [​IMG]
    hi, guys
    For the UA741CN, i connect it as a non-inverting amplfier,
    and when there is no input voltage supply just only the Vcc and -Vcc
    and the output it show high voltage...
    should be in Zero or very small value right??
    And, now im supplying 0.45V to the input pin of amplifier and no matter how much i changing the value of resistor with R1 and R2
    the Output voltage is also same as the value that when there is no input voltage...
    is it got any reasons will cause it??
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Did you have a look at this page of the eBook:

    Divided feedback


    Can you post a schematic so we can give our comments?

    Bertus
     
  3. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
  4. hgmjr

    Moderator

    Jan 28, 2005
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    Assuming that you are using a dual power supply for your opamp, you will need to have a high valued resistor to ground on the positive input. Leaving the input open permits the input to float to an indeterminant voltage that is governed by the leakage current present at the input.

    hgmjr
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,649
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    Hello,

    Are you using a double powersupply?
    What are the +Vcc and -Vcc values?

    Bertus
     
  6. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    yes, im using two power supply
    with +5V and -5V to op amp

    and i use +5V and -5V still cannot get the Vout i want
    i increase it to +15V and -15V but it show the output voltage is 0V
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    What is the nature of the input signal that you are applying?

    hgmjr
     
  8. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    i am using DC supply
     
  9. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    So when you apply, for example, a 1 volt DC signal to the positive input of the non-inverting opamp, your output remains at zero volts?

    hgmjr
     
  10. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    ya, it is happended at zero volts when i'm varying the positive input from 0V to 5V when i'm using +15V and -15V to op amp

    but when i'm using +5V and -5V it shown 4.xxV
     
  11. hgmjr

    Moderator

    Jan 28, 2005
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    What are the values of R1 and R2 in your circuit?

    hgmjr
     
  12. rajbex

    New Member

    Nov 2, 2009
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  13. ching fong kee

    Thread Starter Member

    Jun 23, 2010
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    R1 i'm using 70K ohm
    R2 i'm using 10K ohm

    then the output voltage measured is 4.31V
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    Have you rechecked your wiring to make sure that you have the proper connections?

    hgmjr
     
  15. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    ya, i'm rechecked again and again..
     
  16. hgmjr

    Moderator

    Jan 28, 2005
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    You may have a damaged opamp. Do you have another opamp you can try?

    hgmjr
     
  17. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    yes, i'm change with 3 op amps already
    shown same result..
     
  18. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Either your opamp:

    1. is damaged.
    2. has one or more of its pins short to another pin.
    3. has an open connection.

    hgmjr
     
  19. ching fong kee

    Thread Starter Member

    Jun 23, 2010
    42
    0
    then from datasheet, it Vcc supply is give as +22V and -22V
    then i need to follow it?will it spoil?
     
  20. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    There is no need to power the opamp with anything more that +5 and -5 volts until you have determined what is keeping it from working. Raising the supply voltage could damage the part if something is wired wrong.

    hgmjr
     
    Last edited: Jul 30, 2010
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