Designing Simple Circuits with Voltage Followers

Discussion in 'General Electronics Chat' started by moot, Sep 20, 2009.

  1. moot

    Thread Starter Member

    Sep 20, 2009
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    I'm a newcomer to circuit design. My question is simple: When is it necessary to include an op-amp voltage follower in a circuit? Most places give the function of a follower something along the lines of:

    "Voltage followers act as a buffer between high and low impedance circuits"

    Alright. I have a stack of old, hand-drawn circuit schematics here, and flipping through them, I see followers almost everywhere. This is totally confusing to me - if you have a simple, one input/one output circuit with a bunch of op-amps, wouldn't you only "need" a follower at the very beginning of the circuit?

    An example I found is attached.

    As I've written in - which followers actually do anything? Could I remove Followers 2-4 without changing the circuit's function?

    Any help is greatly appreciated!
     
    Last edited: Sep 20, 2009
  2. hgmjr

    Moderator

    Jan 28, 2005
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    I don't seem to be able to see your attachment.

    Can you see it?

    hgmjr
     
  3. moot

    Thread Starter Member

    Sep 20, 2009
    46
    1
    Hmmm...yes, I can. But I'm using Google's Picasa to host it, which I've never tried before. I've changed some of the sharing options, so it might work now... Tell me if it's still not visible. (Thanks!)
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    Nope. Still can't see it.

    I will wait and see if others are able to see it.

    Can you try attaching it using the forum's attachment feature?

    hgmjr
     
  5. moot

    Thread Starter Member

    Sep 20, 2009
    46
    1
    Nope, it's too large - and resizing it (to within the allowed limit for attachements) with any of the programs on this computer makes the text unreadable. I'm linking to it.

    I'll try once more, and if it still doesn't work, attach a fuzzy one using this forum's attachment utility. And then, for a long term solution, I'll finally suck it up and get a Flickr account... :p
     
  6. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    I see the picture
    Hmm, maybe 1 follower will be useful, the rest followers you can easily
    remove.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    I can see the attachment now.

    hgmjr
     
  8. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    The first follower (Follower #1) is the only one that I believe is contributing to the performance of the circuit.

    hgmjr
     
  9. moot

    Thread Starter Member

    Sep 20, 2009
    46
    1
    Great! Thanks to both of you. And thanks for your patience with the photo, hgmjr.
     
  10. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    None of the followers are doing anything.
    The first inverting opamp has an input impedance of 10k ohms but is fed from a 50 ohm source so it does not need a buffer.
    The second inverting opamp, the adder, has a 3.92k ohm input impedance that is easily driven from the extremely low output impedance of the first inverting opamp.
    The integrator can easily be driven by the output of the adder.
    The output inverting amp can easily be driven by the output of the integrator.
     
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