DC on ouput equal to power supply on uA741 power amplifier

Discussion in 'General Electronics Chat' started by DJ Fahed 1, Sep 1, 2016.

  1. DJ Fahed 1

    Thread Starter New Member

    Sep 1, 2016
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    Hi all,

    I have 10 units of the uA741 opamps, and I made a simple amplifier circuit with a power supply of 0 and +5V, and a gain equal to 2. No matter what the input signal is, the output is always equal to 5V.

    I don't know what am I doing wrong, or could it be that all the opamps are bad?

    The circuit works as it should be when using LM358P.

    Any help is appreciated.:)
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Welcome to AAC
    Post Ur schematic
     
  3. OBW0549

    Well-Known Member

    Mar 2, 2015
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    Two points:

    First, a 741 op amp cannot operate on a total supply voltage of only 5 volts. It simply will not function, at least not in any usable fashion. Use an op amp designed to operate on low voltages, and consult the op amp data sheet for the details. Pay particular attention to input common mode range and output voltage range and make sure your circuit complies with those limits. In many cases, operating on only a 5 volt supply will require use of a rail-to-rail I/O op amp which can function with its inputs and outputs at any voltage between the voltages on the (+) and (-) supply terminals.

    And second, no one here can give you ANY meaningful help until you post a complete, accurate schematic diagram of your circuit showing all components and their values and connections. Until you do that, we would be just guessing based on zero information.
     
  4. DJ Fahed 1

    Thread Starter New Member

    Sep 1, 2016
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    Here it is.
     
  5. BobTPH

    Active Member

    Jun 5, 2013
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    Put a load on the output. It will no longer be 5V.

    Bob
     
  6. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The lm741 needs a negative supply to make it zero output.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    I suggest you (gasp) read the 741 data sheet.
     
  8. DickCappels

    Moderator

    Aug 21, 2008
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    Re-read OBW0549's post #3. That is the key to getting your circuit to work.
     
  9. hp1729

    Well-Known Member

    Nov 23, 2015
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    Look at the limitations for V in for the LM741. Running at 5 V doesn't give you much room to operate. It may not see an input voltage within 3 V of the low power rail or the high power rail. So at 5 V it probably won't recognize an input at all.
    lm358, or other newer op amp, is much better.
     
    Last edited: Sep 1, 2016
  10. hp1729

    Well-Known Member

    Nov 23, 2015
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    Design 823.PNG
     
  11. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Look again, running at 5V doesn´t give it ANY room to operate, as the minimum recommended supply voltage is a dual supply of +/-10V, or a single supply of 20V.
     
  12. DJ Fahed 1

    Thread Starter New Member

    Sep 1, 2016
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    Got it, I think I just didn't read the datasheet carefully.

    Thank you all.
     
  13. hp1729

    Well-Known Member

    Nov 23, 2015
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    You are most correct, of course.
     
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