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From: Fred Bloggs
X-Mailer: Mozilla 4.7 [en]C-CCK-MCD EBM-Compaq1 (Win95; U)
Subject: Re: OP Amp Output Resistance
References: <3D8D30C9.firstname.lastname@example.org> <3D8D4F02.991FC7CA@webaccess.net>
Date: Tue, 24 Sep 2002 03:16:26 GMT
NNTP-Posting-Date: Mon, 23 Sep 2002 20:16:26 PDT
Organization: EarthLink Inc. -- http://www.EarthLink.net
> You are absolutely right. The output is non linear. I have answered this
> question many times with non-engineers who don't seem to understand how
> the output impedance can go down with something simple like feedback. I
> always say with confidence that the feedback causes the output voltage to
> try to stay at the same level no matter what the load, which would not
> happen without the feedback and all I get are blank stares.
Why don't you try explaining that the feedback amplifier is amplifying
the scaled error between input and output in such a way as to drive it
to zero, and then since the feedback tap is at the output, the voltage
drop due to output resistance becomes part of the error and is therefore
nulled too. You don't need calculus to understand this basic concept.
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