741 Op Amp not working as expected

Discussion in 'The Projects Forum' started by darrough, Apr 8, 2015.

  1. darrough

    Thread Starter Member

    Jan 18, 2015
    86
    19
    I found the following circuit in "Make: Analog Synthesizers" by Ray Wilson. The book says that this configuration should amplify the input by a factor of 11. In fact the output is about 1/3 of the input. It seems like the chip is not giving any output at all. I tried a couple different chips and they all seem to have the same results.

    For this particular IC, 2 is inverting in, 3 is non inverting in and 6 is output.

    Do I need to provide a current limiting resistor for the supply?
     
  2. darrough

    Thread Starter Member

    Jan 18, 2015
    86
    19
    This is what the oscope shows.
     
  3. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    No, you need to provide +5V and 0V/Gnd and -5V
    Or use a virtual ground
     
  4. RamaD

    Active Member

    Dec 4, 2009
    254
    33
    The connections are interchanged. Make the connections as below.

    Also, the output will be limited to a max. of +5V and -5V even on a rail to rail opamp. This will be specified in the datasheet. For 741, it would be much less. Assuming +/-2.5V output swing, max input should be 2.5/11, about +/-225mV.
     
  5. Søren

    Senior Member

    Sep 2, 2006
    472
    28
    Yes, that would help too :)
     
  6. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,546
    1,252
    In the original schematic you need to reverse pins 2 and 3. Also, 2 x 11 = 22, which is much greater than your 10V power supplies, so the circuit will clip and distort. Also, note that a 741 output stage cannot swing rail-t0-rail, so the max output swing with +/-5 supplies is only about +/-3V.

    ak
     
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