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Single supply and split / dual supply

Discussion in 'Electronic Basics' started by MRW, Jul 26, 2007.

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  1. MRW

    MRW Guest

    Hello. Is it true that all split or dual supply opamps can be operated
    in single supply mode, but the inverse is not true?

    Thanks!


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  2. All opamps can be operated by any combination of supplies
    that does not exceed their maximum voltage ratings, but add
    up to enough voltage to make their input and output stages
    function.

    Rail-to-rail opamps tend to have lower maximum voltage
    ratings, but also lower minimum voltage ratings. Their
    claim to fame is having both input and output stages that
    can deal with signal swings that fall anywhere between the
    supply rails.

    So called single supply opamps generally have lower minimum
    voltage requirements than dual supply opamps and also input
    and output stages that function very close to the negative
    supply rail.

    So called dual supply (anything not called rail-to-rail or
    single supply) generally have higher maximum voltage
    ratings, but need 1.5 to 4 volts between the input and
    output voltage swings and the supply rails for their inputs
    and outputs to function properly. A few JFET input opamps
    have input stages that function all the way to the positive
    supply rail.

    But any opamp has no way of 'knowing' whether it is being
    supplied by a single supply, with the inputs somehow biased
    between those two rails, or by two supplies in series, with
    the inputs somehow biased between the two supply rails.
     
  3. MRW

    MRW Guest

    Very informative! Thanks, John!


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  4. Eeyore

    Eeyore Guest

    The name 'single supply op-amp' is a little misleading. Any op-amp can be
    operated on a 'single supply' with appropriate biasing of the inputs.

    The difference is that 'single supply op-amps' function correctly when their
    inputs are at ground (negative supply) potential and typically their output can
    also swing (close) to ground as well. More average op-amps will only function
    correctly with their inputs several volts away from the supply (see input common
    mode and differential mode voltage range) and likewise the output will normally
    not swing close to the supply rails.

    Graham
     
  5. Jasen Betts

    Jasen Betts Guest

    I've not seen an op-amp that needed an earth connection to operate,
    but should such exist it would need a split supply.

    Some op-amps can't approach the rails, these may be unsuitable for
    some single-ended supply applications.


    Bye.
    Jasen
     
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