Electronics > Beginners
Single supply vs Dual supply op-amp?
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hermitengineer:
I've seen datasheets for various op-amps.  Some advertise prominently that they are single-supply, while others seem to act as if they only work as dual supply.

But in the end, what, if any, is the difference?  Sure, I could have a +5 and a -5 supply voltage for my dual-supply op-amp.  But if I shift my reference point to where -5V is ground instead, then I have a +10V single-supply op-amp with a rail splitter to provide a bias voltage.  And the op-amp is none the wiser.

So is there any real reason to care if an op-amp says it's "single-supply"?
SeanB:
Those advertised as "single supply" tend to include one of the power rails in the input voltage range, and some even also include excursions slightly out of the power rail, typically having -0.5v to Vcc-1V as input voltage range. Dual supply ones tend to have large areas which the inputs must not go within, typically 2V or so from each power rail, making a dual supply more convenient to use. Yes mostly a semantics thing, but in single supply applications you tend to have inputs referenced to a supply rail in most cases, and it can be both hard and inconvenient having to scale and apply offsets to all the inputs to keep within the CMRR range, and many opamps can do odd things when you go out of the range, from the output inverting, to the opamp latching up either destructively or non destructively.
hermitengineer:
So, it sounds like the intent of advertising as "single supply" maybe implies that it is more useful than dual-supply in single-supply systems then, not that it cares either way.  In your example of one that requires a 2V buffer from each rail, it would be almost useless in a +5V and gnd situation since there's only 1V of useful range.  I've noticed that "single supply" and "rail to rail" are often used together.  Perhaps R2R is what typically qualifies it as single-supply?
thm_w:

--- Quote from: hermitengineer on November 15, 2019, 09:32:53 pm ---So, it sounds like the intent of advertising as "single supply" maybe implies that it is more useful than dual-supply in single-supply systems then, not that it cares either way.  In your example of one that requires a 2V buffer from each rail, it would be almost useless in a +5V and gnd situation since there's only 1V of useful range.  I've noticed that "single supply" and "rail to rail" are often used together. 

--- End quote ---

Correct. If you wanted a opamp for your 5V microcontroller system, best to look at "single supply" types, they will often be optimized for 3.3V to 5V supply for example.
https://www.ti.com/lit/an/sboa059/sboa059.pdf

Note that you won't find it in parametric search: https://www.ti.com/amplifier-circuit/op-amps/products.html so that tells you how useful it is as wording.


--- Quote ---Perhaps R2R is what typically qualifies it as single-supply?
--- End quote ---

Probably one of the important parameters yeah.
David Hess:
That brings up the question of why all operational amplifiers are not made to be single supply.

Single supply operation entails some design compromises.  Output stages must be common emitter/source instead of common collector/drain resulting in higher output impedance and greater stability problems.  With an input range which extends to either or both supplies, input bias current cancellation cannot be used.
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