Single supply and split / dual supply

[MRW]

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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[John Popelish]

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

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.

 

[MRW]

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.

Very informative! Thanks, John!


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[Eeyore]

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

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

 

[Jasen Betts]

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

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