Non-inverting amplifier output shorted

Discussion in 'General Electronics Chat' started by ElectricMagician, Apr 13, 2013.

  1. ElectricMagician

    Thread Starter Member

    Jul 26, 2012
    57
    0
    Hello everybody,

    The output of an inverting amplifier based on a UA741 seems to be "die" once it is connected to a signal processing circuit (which has a separate power source.)

    This does not happen if I connect a source to the 2nd circuit directly, and the amplifier works fine on its own.

    I'm suspecting that this could be due to the second circuit pulling more current from the amplifier than the ua741 can handle. Am I right in this suspicion, or could there be other reasons?

    And if so, is replacing this amplifier with a mosfet amplifier or so the only solution?

    Also, the quality (not the gain) of the amplifier output seems to drastically improve if I add a resistor in parallel to the input voltage. What could be the explanation for this?

    Thanks for your generous help!
     
    Last edited: Apr 13, 2013
  2. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    A schematic would make all the difference in our understanding.
    Can you post a schematic?

    (Inside joke) Insert rant from AG here.
     
    Last edited: Apr 13, 2013
  3. patricktoday

    Member

    Feb 12, 2013
    157
    42
    Do you have a schematic?
     
  4. ElectricMagician

    Thread Starter Member

    Jul 26, 2012
    57
    0
    Here it is

    Correction: its an inverting amplifier. I have no idea why I wrote non-inverting.
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    See my questions on the attachment.

    Also, what is the input impedance of the signal processing circuit?
     
  6. ElectricMagician

    Thread Starter Member

    Jul 26, 2012
    57
    0
    1. Yes it's a connection

    As for the other question I'll try to answer them as soon as I get to the circuit again

    Thanks.
     
  7. #12

    Expert

    Nov 30, 2010
    16,337
    6,821
    One part of this is that the 741 chip is not rated to work with an input within 3 volts of ground or 3 volts of the positive voltage. The fact that it works at all with one input grounded is a matter of luck.

    Next, you are inputting a positive signal to the inverting input and the expected output of the chip is a negative voltage. If the input signal does not have a DC level in the positive, the chip can not output the more negative voltage that is required to null it's inputs.

    A lot of, "if's" here because you have not defined your input and you have not defined the "separate power source".
     
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