op-amp design advice

Discussion in 'General Electronics Chat' started by raffter, Jun 30, 2008.

  1. raffter

    Thread Starter Active Member

    Feb 28, 2008
    113
    0
    Hello all,

    how do I design about this:

    input will (example) accept +/-5v and output will be 0V->5V only.... for a -5 input, output will be 0V....0V input would be 2.5V..and +5V input would be 5V out...

    :rolleyes:

    -Ralph
     
  2. DC_Kid

    Distinguished Member

    Feb 25, 2008
    638
    9
    to me sounds like some form of a comparator, perhaps with the 2nd input being tied to a ref voltage...?
     
  3. raffter

    Thread Starter Active Member

    Feb 28, 2008
    113
    0
    nvm, I have done one.. :)
     
  4. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    I might do this by first using an inverting summing amplifier with +5V on the second input and unity gain. Output of the first amp I would send to a second inverting amp with gain of 0.5.
    fivefive.jpg
    Obviously, this will need a negative rail of -10V or more.


    Another option might be to use a voltage divider to get the i/p down to +/- 2.5V and sum with 2.5V.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    See the attached schematic for one approach.

    An LF353 is a dual opamp with similar characteristics to a TL072.
    I used the first opamp as a unity gain buffer to avoid loading the input signal. If loading is not a factor to the input, it could be omitted.

    The remaining resistors act as a voltage divider network.

    The 2nd opamp is also a unity gain buffer. If loading on the output is not a factor, it could also be omitted.

    Note that for this scheme to work, a dual polarity supply is necessary. It might be done with a single positive supply and an opamp that had rail-to-rail inputs and outputs, but the input signal would have some loading on it.
     
  6. raffter

    Thread Starter Active Member

    Feb 28, 2008
    113
    0
    thanks for the addtl inputs guys.. :)

    I did mine non-inv, and with single supply only(but had to do some voltage boosting for the op-amp..too bad I cant find rail2rail o/p op-amps here(but its all OK now with raising up the supply for op-amp)...

    now im thinking a way for an easy switching between level shifted into a plain unity gain(voltage follower)... oh well :) back to simulations...
     
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