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Tying both inputs of an opamp to the output

Discussion in 'Electronic Basics' started by Mimawl, Jul 4, 2013.

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  1. Mimawl

    Mimawl Guest

    Is there a possibility of something undesireable happening if
    *both* the inverting and non-inverting inputs of an opamp are
    tied to the output? A possible scenario is when one unit of a
    dual or quad type is unused and tying both inputs to the output
    is convenient in the PCB layout.
     
  2. Jasen Betts

    Jasen Betts Guest

    it'll probably rail, but could do anything, that may or may not be a problem.

    tie the non inverting input to something else instead.
     
  3. Mimawl

    Mimawl Guest

    Thanks. I asked the question while working on a layout using an
    LM358. Perhaps I should have mentioned that but I really wanted
    to know the answer in a wider context. I usually tie Vin- to
    Output and Vin+ to -Vcc, sometimes to +Vcc (The LM358 is rated
    for inputs up to 32V without damage regardless of supply
    voltage). But there are times when layout convenience makes it
    tempting to tie both inputs to Output, especially on a home-made
    single-layer PCB.
     
  4. YD

    YD Guest

    When I had a 1/4 TL84 left over I made it a follower (Vout to Vin-)
    and tied Vin+ to the nearest neighbouring output and just left it
    dangling there. This ensured that it would stay within bounds. Maybe
    some loading of the output could have been in order but it worked fine
    anyway.

    - YD.
     
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