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Voltage Divider

Discussion in 'Electronic Design' started by dbvanhorn, Jan 26, 2009.

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  1. dbvanhorn

    dbvanhorn Guest

    I just got handed a requirement for a circuit that I've not seen yet,
    an op-amp based voltage divider.
    Didn't see it in Horowitz and Hill either.

    This is not a resistive divider, for example the output of 3V and 1.5V
    would be 2V.
    Can anyone suggest a source? Seems like something that ought to be in
    a NatSemi analog book somewhere.
     
  2. linnix

    linnix Guest

    Google on summing junction.
     
  3. Guest

    Probably is. While you're looking for it, and assuming discrete
    parts, how about a log amp driven by each signal, those feeding a
    subtraction circuit, and that followed by an anti-log amp. Four op
    amps and a handful of discrete parts depending on input ranges,
    accuracy, etc.

    A nice bit on log/antilog amps:

    http://www.electronics.dit.ie/staff/ypanarin/Lecture Notes/DT021-4/6LogAntiLogAmplifiers.pdf
     
  4. Tim Shoppa

    Tim Shoppa Guest

    NatSemi was never very big in analog multipliers or dividers.

    TI (formerly Burr-Brown) has the MPY634.

    Analog devices has the AD633.

    Those are nominally multipliers but with a feedback loop they become
    dividers, see the data sheets for examples. The AD633 needs an
    external op-amp to help out with division, but the MPY634 with its
    extra pins doesn't need an external op-amp. Accuracy of X/Y becomes
    worse and worse as Y gets smaller and smaller due to offset voltages,
    some manual trimming can help out.

    Tim.
     
  5. Guest

  6. Eeyore

    Eeyore Guest

    No, you need to learn basic Norton and Thevenin. What year are you in ?

    Graham
     
  7. Eeyore

    Eeyore Guest

    Since when is that a 'voltage divider' ?

    I think the OP chappie wants a circuit that outputs 2V when it has 2 inputs of
    1.5V and 3V. I fear for his future. Cross-posted to basics.

    More and more courses are getting kids who don't understand even basic
    electricity.

    Graham
     
  8. Eeyore

    Eeyore Guest

    Where are you lot getting all these log amp ideas from ?

    I think he just wants to actively sum some signals. It'll be in TI's "op-amps for everyone'
    available from ti.com as a pdf file. They also do a similar (ex Burr Brown ?) basics throught to
    not so basics book.

    Graham
     
  9. Eeyore

    Eeyore Guest

    I think he means you sum 3V and 1.5V - get 4.5V and multiply it by +0.44444
    to get 2V.

    In any case, he's not going to be an electronics designer if he can't even
    ask the question intelligently.

    Graham
     
  10. Sylvia Else

    Sylvia Else Guest

    Or maybe he wants to sum the squares, and divide by 5.625.

    But the most natural interpretation of his admittedly unclear question
    is that he wants a circuit that divides one voltage by the other (and
    multiples the result by 1V).

    Sylvia.
     
  11. Eeyore

    Eeyore Guest

    It didn't seem terribly natural to me. For one thing, that's not called a
    'voltage divider'.

    Graham
     
  12. Sylvia Else

    Sylvia Else Guest

    It may not be what is normally thought of when the expression "voltage
    divider" is encountered, but by normal language usage, something that
    divides one voltage by a nother is reasonably called a voltage divider.

    Sylvia.
     
  13. Eeyore

    Eeyore Guest

    That's actually a voltage multiplier with scaled factors.

    Graham
     
  14. Nobody

    Nobody Guest

    Well, he knows enough to have said:
    IOW, he knows what the term "voltage divider" normally means, but not the
    correct term for the part in question.

    FWIW, what *is* the correct term? I don't buy "multiplier, with scale
    factors", because it's not multiplying, with or without scale factors.
    "Inverse multiplier"? "Reciprocal multiplier"?
     
  15. Guest

    Dear Mr/Ms Van Horn (guessing from your username, sorry if it's
    inaccurate),

    Before this thread degenerates any further into the usual
    sci.electronics.design slag-fest, do you suppose you could enlighten
    us further about what you're after? And whether or not any of the
    replies you've seen have been of any use to you?
     
  16. Daniel

    Daniel Guest

    i used an analog devices 'divider' once. it was used in an x-ray kV
    measuring unit that i designed and it depended on the ration between 2
    signals. the first signal was the output of a set of diodes, whilst
    the second was the output of another set of diodes placed under a rare
    earth and copper attenuating screen. the output apparently of this
    ratio was proportional to the beam energy. i did that 30 years ago so
    please don't press me on the details...
     
  17. dbvanhorn

    dbvanhorn Guest


    Wow.. So much argument over terminology.
    FWIW I'm no "beginner". I know what I'm after is NOT a resistive
    divider, and I didn't want to fend off 1000 replies telling me to use
    two resistors.
    That's why I included the part illustrating that what I wanted was the
    division of voltage A by voltage B, and not the division of voltage A
    by some constant.

    The end result is a circuit to do monopulse resolution enhancement of
    two sensors with overlapping detection fields.

    The circuit needs to take two inputs, A and B, and give the result of
    (A+B)/abs(A-B)
    I had everything worked out at that point except for the analog
    divider.

    I've found several approaches using log-antilog now, and I'm satisfied
    with that at this point.
    I didn't know what to call it when I asked, as I'd not seen such a
    circuit in quite some time, and looking thru H+H I also came up blank.
    It's hard to ask for something precisely when you don't yet know what
    the name of it is..

    So thanks for the helpful replies, but I think I'll pass on the
    "attitude" replies.
     
  18. dbvanhorn

    dbvanhorn Guest

    Right, I don't have that one handy, but I have found some examples in
    NS app notes.
    Monopulse resolution enhancement.

    Think of two sensors, could be phototransistors, CdS cells, etc
    looking out with their detection fields overlapping.
    If you plot the response of either, you get a broad hump.
    If you sum them, you get a broader hump with a dip in the middle, but
    still indistinct.
    Difference is similarly unhelpful.
    But if you sum them, and divide that by the absolute value of the
    difference, you get a very sharp peak.
     
  19. dbvanhorn

    dbvanhorn Guest

  20. dbvanhorn

    dbvanhorn Guest

    Only in the strictest sense..
    I can satisfy those requirements. Thanks for the pointer.
     
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