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Op Amp

Discussion in 'Electronics Homework Help' started by kingofjong, Aug 14, 2014.

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  1. kingofjong

    kingofjong

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    Aug 14, 2014
    I set up an amplifier circuit using tlc272cp op amp
    I check the current using an multimeter but I don't see any gain

    I was wondering if some one could tell me where I am going wrong?

    I attached a picture of the circuit
     

    Attached Files:

  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi there
    welcome to EP :)


    from the poor photo, there appears to be some problems with your layout

    you have a resistor coming off the lower left pin of the chip to that rail that goes along the bottom of the board
    BUT you also have a red wire doing the same and shorting out the resistor

    that bottom rail is it the + or - rail ------ I think its supposed to be - ( negative)
    meaning the top one is the positive one
    You also have a blue? wire going from the pot to the top rail but that top rail isn't connected to anything else

    because of the poor pic, I cannot tell what way around the chip is connected

    Also provide a schematic of the circuit you were trying to construct

    cheers
    Dave
     
  3. kingofjong

    kingofjong

    30
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    Aug 14, 2014
    I have attached the schematic
     

    Attached Files:

  4. davenn

    davenn Moderator

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    Sep 5, 2009
    OK thanks for that

    now you need to start rewiring you board to match the circuit :)

    Dave
     
  5. LvW

    LvW

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    Apr 12, 2014
    1.) It is not clear which current you are speaking of.
    For checking the gain it is much more meaningful to measure input and output voltages.

    2.) For linear amplification it is necessary to bias the opamp in its linear range. Normally, this is done using dual supply voltages with negative feedback.
    You have negative feedback but single supply only. Thus the input voltage at the non-inv. opamp terminal must have a certain positive value for proper biasing. Are you familiar with biasing schemes for single supply?
     
  6. davenn

    davenn Moderator

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    Sep 5, 2009

    all true :)
    But he has to get the circuit wired properly first before worrying about actually doing measurements ;)

    Dave
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That circuit is just an experiment to demonstrate how a single-supply non-inverting amplifier with a gain of 10 (Edit: ... gain of 11...) and a reference voltage of 0V will behave as the non-inverting input voltage is adjusted from 0V to VCC. There is no need to worry about biasing. It is not supposed to amplify any signal. It is just an experiment, designed to facilitate understanding of that op-amp circuit.

    Edit: We need to see a good clear picture of the used section of the breadboard, as well as the overview picture.
     
  8. LvW

    LvW

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    Apr 12, 2014
    Sorry - I didn´t know too much about the intentions of the questioner. I was of the opinion, he wants to find a proper bias point for some further experiments.
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    It's one of those "100-in-1 experiments"-type kits for learning electronics by tinkering.
     
  10. kingofjong

    kingofjong

    30
    1
    Aug 14, 2014
    Okay I think I figured it out, I had the wrong wiring. I see a gain in the output when I move the resistor from the first pin to the third pin.
     
  11. davenn

    davenn Moderator

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    Sep 5, 2009
    please show us another pic of your layout
     
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