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Better op-amp buffer configuration?

Hi All,

I realize that using a single-supply op-amp as a buffer may be one of the easiest circuit configurations in the world; just tie the chip's output back to the inverting input, and insert the signal into its non-inverting input. That's how the books show it anyway, but are their any real-life op-amp issues that I have to look out for with this basic circuit? Anything I can do to make this circuit operate better under temperature, along with the unavoidable op-amp variations? Perhaps to help with any stability or voltage offset issues? Or is this circuit simply the way op-amp buffers are done, even in real life?

Thank You,

Bill

Cross posted to sci.electronics.design and sci.electronics.basics

Reply to
billcalley
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For many (but not all) opamps that configuration will work fine. Quirk I had with LM324 as a follower, fast rise or fall times exceeded speed of the amp and cross coupled (through the bias system?) to other amps in the package. TL084s fixed that. Current feedback opamps can be used this way but would require a feedback resistor to prevent oscillations. Best bet, check manufacturers data sheets to verify usage. GG

Reply to
Glenn Gundlach

Check whether the chosen op-amp needs external compensation to be unity-gain stable (the NE5534 does).

Check whether a resistor may be needed in series with the output to prevent problems if you are driving a capacitive load such as a long screened cable.

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~ Adrian Tuddenham ~
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Reply to
Adrian Tuddenham

Thanks for all of your help guys!

Cheers,

Bill

Reply to
billcalley

Put the isolating R in series with the output of the opamp, and take the feedback to the -i/p After the resistor. Generally works, and compensates for attenuation that you would get when you drive a lowish Z load

martin

Reply to
martin griffith

Actually, if you take the feedback from after the resistor, the stability will normally be even worse than without the resistor at all. If you need to take feedback from after the resistor for accuracy reasons, then put a capacitor directly from the op-amp o/p pin to the inverting input, and a resistor between the load and the inverting input, and of course the original low value between the op-amp output pin and the load.

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Chris

Reply to
Chris Jones

snip

excellent article, thanks

martin

Reply to
martin griffith

Instead of just connecting output to inverting input, use a resistor to approximate impedance of input to minimize offset drift due to input bias current.

Reply to
Ol' Duffer

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