What is the difference between a single and a dual supply opamp? - Page 1
Forum section: electronics / beginners

author: ali80
author_rank: Contributor
timestamp: January 29, 2015, 06:11:41 pm
content: Why are the some opamps labled as single supply while others are labled as dual supply and what is difference?for example cant I just connect -2.5v and 2.5v to the rails of opa2376? what is really the difference of supply specification of this opamp with something like opa2350would there be any performance penalties if someone replaces a dual supply opamp with a single supply one?

author: c4757p
author_rank: Super Contributor
timestamp: January 29, 2015, 06:27:11 pm
content: The only difference is the allowable input and output voltage ranges. "Single-supply" opamps are opamps where the ranges are convenient for use in a single-supply configuration (typically, voltages very near ground are allowable). And yes, of course, you can use a dual supply with a single-supply op amp. You can use a single supply with a dual-supply op amp too, you just have to mind the voltage ranges.

author: w2aew
author_rank: Super Contributor
timestamp: January 29, 2015, 07:10:47 pm
content: Quote from: c4757p on January 29, 2015, 06:27:11 pm^^^^^Yes, what c4757c said.For a more "visual" explanation, check out my video on the topic:

author: ali80
author_rank: Contributor
timestamp: January 29, 2015, 07:12:31 pm
content: well that's odd, why even bother with saying single supply or dual supply, also the two opamps mentioned (opa2376 single supply, opa2350 dual supply) have the same voltage range and both have rail to rail inputs and outputs but one is called single supply and another not!

author: c4757p
author_rank: Super Contributor
timestamp: January 29, 2015, 07:22:33 pm
content: Hmm? They're both single-supply:

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 07:24:38 pm
content: QuoteOne is better at extracting a price premium from fools?Seriously, they both work in single rail / dual rail applications. Generally (not always true), single rail opamps can do a better job to the negative rail (=ground often).

author: c4757p
author_rank: Super Contributor
timestamp: January 29, 2015, 07:26:59 pm
content: Quote from: dannyf on January 29, 2015, 07:24:38 pmThis comment comes up all the time and it's disingenuous. There is a significant difference in required signal headroom between devices classed as dual-supply, single-supply, and rail-to-rail. It's hardly marketing lies.

author: ali80
author_rank: Contributor
timestamp: January 29, 2015, 07:35:38 pm
content: Quote from: w2aew on January 29, 2015, 07:10:47 pmyeah I always follow your videos(except the radio stuff which I dont underestand) and I love the way you teach, but as I said that's just odd why even mention such a thing if that is not important at all?for example for ADCs when it is specified as single supply you cant use it in dual supply configuration ( I think you can if you convert digital signals to be relative to the ADC's negative supply)

author: ali80
author_rank: Contributor
timestamp: January 29, 2015, 07:38:43 pm
content: Quote from: c4757p on January 29, 2015, 07:22:33 pmyeah you are right, I picked a wrong example but there are plenty out there, trust meI think when it is specified as dual supply the supply range is usually much more and also as danny said"Generally (not always true), single rail opamps can do a better job to the negative rail (=ground often)"

author: w2aew
author_rank: Super Contributor
timestamp: January 29, 2015, 07:53:46 pm
content: Quote from: ali80 on January 29, 2015, 07:38:43 pmA lot of it will also come down to where/how the specs are guaranteed. Take a look at the header of the various specification tables - the specs are written around specific supply configurations, which are often dictated by the intended applications for the device. That's not to say it won't work with a different supply configuration, it's just that certain performance parameters might not be specifically guaranteed or tested under that configuration.

author: katzohki
author_rank: Frequent Contributor
timestamp: January 29, 2015, 08:12:44 pm
content: Dual supply opamps will operate on + and - for their supply voltages (e.g. +15V and -15V). Single supply opamps will operate on single supply rail and ground (e.g.+5V and GND).A dual supply opamp will be able to work with signals that swing above and below ground (e.g. 5V pk-pk sine wave with no DC offset) and will be able to put out positive and negative voltages. A single supply rail will only work with signals above DC ground (e.g. 0-5V square wave) and put out only positive voltage. If the signal goes below ground the lowest a single rail opamp can output is 0V (or however close it can get to ground).I think you might be able to do a negative and gnd single supply opamp, but you really have to look at the individual opamp to see how it is specified.Some will handle both depending on how you have it set up, check to see how they are specified. W2AEW's comment about how specs are guaranteed is very important. I recently fell into that trap using an "on hand" opamp as a single supply where it was not able to source enough current.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: January 29, 2015, 08:21:49 pm
content: Quote from: katzohki on January 29, 2015, 08:12:44 pmWhat is "ground" except some random net that you decide to label as such? Single supply and dual supply op-amps are basically the same thing, some are just more "directed" at one situation or another based on their ability to drop down to the negative rail (or ground rail, whatever you want to call it...the lower one!). In fact most rail-to-rail op-amps are labeled as both single and dual-supply, and the spec sheet lists both options.If you draw up the schematic for an op-amp buffering a 1v signal with 0 and 5v supplies, versus an op-amp buffering a -1.5v signal with -2.5v and +2.5v supplies, you'll see that they're identical, apart from the names you stick on the rails. Since the dual-rail op-amp has no ground reference, as far as it's concerned it IS operating on a single rail, how does it know that you're arbitrarily calling its lower rail "-2.5v"?As with choosing any part, make sure your operational conditions fall within the part's accepted range. Whether the manufacturer chose to call that particular op-amp a "single" or "dual" supply part makes no difference.

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 08:39:26 pm
content: QuoteSo do single supply opamps.A circuit has no concept of "ground" - they are not ground-aware. They just know potential differences - you will notice that very rarely you see an opamp with a "ground" pin.With some exceptions (as noted above), single supply opamps are a marketing thing.

author: c4757p
author_rank: Super Contributor
timestamp: January 29, 2015, 08:42:45 pm
content: Quote from: dannyf on January 29, 2015, 08:39:26 pmSo, you're saying that (with some exceptions), single-supply opampsdon'tgenerally have a lower negative end to VICMand VO?

author: ali80
author_rank: Contributor
timestamp: January 29, 2015, 08:51:53 pm
content: Quote from: suicidaleggroll on January 29, 2015, 08:21:49 pmI get what you wanna say, it was part of my original question too, you just put it in much better words.but if it is just a marketing thing, the best marketing format would be to specify the opamp as both single and dual supply and not just one, I'm just saying from marketing perspective that's much better.but maybe there is a catch, if your opamp works fine in both modes why not just say so?

author: dannyf
author_rank: Super Contributor
timestamp: January 29, 2015, 08:59:53 pm
content: QuoteVery rarely an opamp is called a "dual rail opamp". Sometimes people call an opamp "single rail", for marketing purposes there it helps justify charging a premium for a feature that's already there.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: January 29, 2015, 09:06:15 pm
content: Quote from: dannyf on January 29, 2015, 08:59:53 pmIt also makes it a PITA to search for a suitable op-amp based on acceptable supply voltage range on most suppliers' websites, since 0-5v and -2.5-2.5v are the same damn thing.

author: ali80
author_rank: Contributor
timestamp: January 30, 2015, 05:25:18 am
content: thank you all guys my conclusion so far from your comments is:1. it(single supply) is a marketing term, but it mostly correlates to the opamps which both their inputs and outputs can work near negative rail.2. as Alan said if the manufacturers didn't specify some kind of operation in datasheet, that also mean they won't guaranty operation in datasheet specs in that kind of operation but that doesn't mean it wont work of course.

author: vikasbly44
author_rank: Contributor
timestamp: January 30, 2015, 12:02:15 pm
content: The single supply opamp is designed to work well with inputs.single-supply often have rail-to-rail output.A dual output power supply is a power source that provides two separate direct current or alternating current voltage outputs

author: katzohki
author_rank: Frequent Contributor
timestamp: January 30, 2015, 05:09:18 pm
content: The most important point from my message is that you need to pay attention to how the part is guaranteed to work. Just wanted to make that clear since a lot of people seemed to be focusing on Voltage being a "relative" measurement. That is true, but I was describing what it generally means you are doing when you say "single supply."