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unclejed613 8th August 2007 12:41 AM

having a hard time finding....
an externally compensated FET input op amp. i have an amp design i've been modelling, and most of the time it's unstable, and compensating the VAS has no effect. i finally figured out that it's most likely that the op amps i'm using in the model are internally compensated, so compensating "after the fact" won't have an effect.
i've done searches on,, and with no results.

gootee 8th August 2007 12:50 AM

You could also look at; one of the best.

Maybe I don't understand what you mean when you say that compensating an internally-compensated opamp won't have an effect. They're usually just internally compensated to be stable with a gain as low as 1. But you can still also compensate them externally.

A few details of your circuit might help to expose some other problem, in case there is one.

- Tom Gootee

djk 8th August 2007 04:30 AM

Use a slower opamp.

When using an opamp for the front end of a power amplifier, a slower opamp will give better stability when you close the loop around the power stage.

(can't remember if that came from Linear or Analog app notes).

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