Op Amp Compensation

The out of loop resistive compensation is a bit confusing to me. We add a resistor to essentially slow down the op amp which prevents it from ringing.

But when one says "... driving a capacitive load" what one really means is driving a capacitive reactive load? Because if we are driving a low pass filter the resistor also compensates. So really the issue with op amps is purely capacitive loads and is what is meant by the terminology?

So as long as the impedance of the load is not close to being purely capacitive, even if it uses large capacitors, it is not considered a capacitive load?

e.g., 10k resistor in series with 1u is fine but driving a 1n capacitor directly is much different?

Reply to
Kodfk Dleepd
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Yeah that's right. The simplist way of compensating for cap loading is just to put a bit of resistance between the opamp output and the cap.

I couldn't seem to find my favorite app note from AD about cap loading... Maybe someone else will have it?

George H.

Reply to
George Herold

Think about where the feedback is taken from, and imagine the output impedance of the op-amp as an internal resistor (that is

Reply to
Spehro Pefhany

This one?

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Reply to
Spehro Pefhany

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Yes! Much thanks. There's also a trick where you increase the noise gain of the circuit. (I've never tried it though.)

George H.

Reply to
George Herold

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IOW you can turn a good op amp into a crappy one and make it stable that way. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
Reply to
Phil Hobbs

Have fun with this!

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Reply to
mook johnson

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