Single supply opamps are designed so input and output can be near ground. 'normal' opamps often can't get near the power rails, so using them near ground doesn't work out so well.
However, if you are using a rail-to-rail opamp, it should be ok.
-- Regards, Bob Monsen
I was wondering, what are the downsides to using a dual-supply op amp in a single-supply configuration?
Stephen
To put it more technically, the input common mode range of a single supply op amp pretty much has to include the negative rail, and the output stage has to be able to sink a milliamp or so when the load is only of the order of a hundred millivolts more positive than the negative rail.
If input and output don't have to get within a few volts of the positive or negative rails, there isn't any technical necessity to use a single supply op amp. Since the LM324 is probably the cheapest op amp around, you will find it used in situations that don't really call for a single supply amp, but that's economics ....
---------------- Bill Sloman, Nijmegen
To put it more technically, the input common mode range of a single supply op amp pretty much has to include the negative rail, and the output stage has to be able to sink a milliamp or so when the load is only of the order of a hundred millivolts more positive than the negative rail.
If input and output don't have to get within a few volts of the positive or negative rails, there isn't any technical necessity to use a single supply op amp. Since the LM324 is probably the cheapest op amp around, you will find it used in situations that don't really call for a single supply amp, but that's economics ....
---------------- Bill Sloman, Nijmegen
Really there's no such thing as a single supply op-amp. If they run off a single supply, they are biased to the half way point, so in effect they do see a dual supply. Run it off a 12v supply, and bias it to 6volts, and the opamp sees 6volts on the positive supply line and -6volts on the negative supply line, relative to that bias point. This isn't any different from running the opamp off a -6/+6 power supply, since the opamp will have 12 volts across it.
One disadvantage of running an op-amp off a single supply is that the input and output will not be at ground, but at half of the supply voltage (as a result of the biasing). So there won't be zero DC volts on those lines (unless you measure in reference to the bias point), and so DC coupling may be out of the question depending on applications.
The real thing is that "single supply op-amps" are designed so the output can go closer to the supply voltage. This is useful since if you're running it off a single supply, usually that is a lower voltage than the sum when you've got a bipolar power supply,
12volts versus 24volts. The greater headroom of the "single supply op-amps" means they work better at those lower voltages.Michael
On 24 May 2005 06:32:14 GMT, snipped-for-privacy@FreeNet.Carleton.CA (Michael Black) wroth:
That last statement is wrong. Single-supply opamps do not need to be biased if they have input and output voltages that are not outside the rail voltages. They can be biased, but it is not because that's the only way to make them work.
Jim
Depends what you're doing with it. There may be no downside at all.
Graham
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