DPRG
DPRG List  



DPRG: op amp question

Subject: DPRG: op amp question
From: john.r.strohm at bix.com john.r.strohm at bix.com
Date: Tue Aug 3 13:49:05 CDT 1999

>Maybe this is a dumb question, I don't know. (Are there any op-amp
>tutorials
>on the Internet? Something like the Encoder basics articles would be nice.
>:) Is there any reason for V+ and V- supplies on an op amp? Can I connect
>ground to V-? I have a RadShack TL082 "dual bifet op amp" which doesn't
>need
>a ground connection, only V+ and V-...  For other op amps that have gnd,
>why
>can't I use a voltage divider to create a level between V+ and the real
>ground?

There was a wonderful paperback book in the 1970s.  I can't remember the
title, but the authors were Hoenig and Payne.  It spent almost the entire
book on simple circuits involving op amps.

You have V+ and V- supplies because any signal you are going to feed into
or out of the op amp must lie between those rails.  For some applications,
it is more convenient to have bipolar signals referenced to ground rather
than unipolar signals referenced to 1/2 of V+.

Op amps grew out of analog computers: it is EXTREMELY convenient to use
bipolar signals to represent things like force, velocity, or acceleration.

You can use the voltage divider to develop a reference ground.  Best way to
do it is make a voltage divider and then feed a unity gain follower from
the reference node: this gives you a zero impedance reference source.  (For
a unity gain follower, you feed the signal into the noninverting input of
the op amp, and tie the inverting input directly to the output.)

It is an EXTREMELY worthwhile exercise to work through the equations of the
basic op amp inverting gain amplifier circuit, using the standard
simplifying assumptions: zero output impedance, infinite input impedance,
infinite gain.  It is not a pleasant thing for the
algebraically-challenged.

------------------------------

More information about the DPRG mailing list