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The output of Op-Amp[LM324] has error as non-inverting Amp

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  1. Apr 25, 2015 #1
    Hi everybody
    I'm a newbie and working on LM324 to learn Op-Amp. this is my circuit:

    http://img4.uplood.fr/free/qx3o_20150425_172843.jpg [Broken]
    One of the resistors is 217ohm and another 978ohm. then the gain should be 4.50691 as you can see. so far so good. I know this is for ideal Op-Amp. I applied 0.15v to the input and got 0.94v in the output. then the gain is 6.26667. again I applied 0.35v to the input and got 2.03v then gain should be 5.8!?o_O
    again I applied 1.86v and got 10.31 then the gain is 5.54301! holy crap! :wideeyed: why isn't the gain stable? because of input offset voltage? How can I stabilize it?
     
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Apr 25, 2015 #2

    Averagesupernova

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    You need a split supply to make this work.
     
  4. Apr 25, 2015 #3

    jim hardy

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    LM324 should be okay with single supply so long as everything stays positive,.
    But if you're inputting AC then yes, you need dual supply.

    Did you bypass your supply with a small cap near the IC?

    What is voltage at junction of 217 - 978 resistors?
    Is it the same as your input?
    If opamp is making its inputs equal , the problem is not offset.

    Possibly it's your layout. When power supply current shares a wire with signal, the drop along the wire adds to signal.
    Is there any AC in your output?
    How are your input source and 217 tied to common ?
     
  5. Apr 25, 2015 #4

    Averagesupernova

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    The gain for a non-inverting op-amp is not how you are computing it. The gain in this case is 5.50691. (978/217) + 1. Keep your input voltages farther away from the supply rail with a 324.
     
  6. Apr 25, 2015 #5

    jim hardy

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    Thanks - i missed that !
    Big ten-duh on me, good buddy !
     
  7. Apr 25, 2015 #6
    Thanks guys
    I used 145.6kohm as Rf and 2.14kohm as Rin and got an acceptable output. for example 70.1mv in the input, I got 4.93v in the output.
     
  8. Apr 26, 2015 #7
    MultiSim is my best friend when troubleshooting circuits like this. Just a suggestion.
     
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