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From: R_Tim_Coslet@cup.portal.com
Newsgroups: sci.electronics
Subject: Re: Good Clamping Circuit
Message-ID: <40085@cup.portal.com>
Date: 13 Mar 91 04:25:01 GMT
References: <1991Mar06.181426.10500@cdsmn.mn.org> <1041@eplunix.UUCP>
  <1991Mar10.093752.18289@neon.Stanford.EDU>
Organization: The Portal System (TM)
Lines: 38

In Article: <1991Mar10.093752.18289@neon.Stanford.EDU>
	zimmer@calvin.stanford.edu (Andrew Zimmerman) writes:
>How about the following circuit instead?
>
>     --------R1----------R1--------
>     |            |  |\           |       a
>    ---           ---|  \         |     --|>|-- +5
>     -               |    \       |     |
>                     |      \_____|_____|_____  Vout
>V1------R1----|      |      /           |
>              |------|    /             |  /  z
>V2------R1----|      |  /               |--|<|---
>                     |/                    /    |
>                                               ---
>                                                -
>
>
>This actually is two different methods.  (a) The first just uses a diode.
>(The +5 reference should be closer to 4.3 to take into account the voltage
>drop on the diode.)
>
>The second method (z) uses a 5 volt zener diode to clamp the circuit.
>
>(I haven't done op-amps in a while, but I believe the above is correct.)
You obviously havn't. NEVER directly clamp the output of an opamp... the
opamp and the clamp will fight each other, and generally damage the opamp
output transistors. The clamping circuit should always be in the "feedback"
network.

It would take longer for me to design and draw the appropriate circuit than
I have while reading news, but the place to put the clamps are either across
the feedback resistor (in an inverting amplifier) or from the noninverting
opamp input to ground (in a noninverting amplifier like the one above).

                                        R. Tim Coslet

Usenet: R_Tim_Coslet@cup.portal.com             BIX:    r.tim_coslet
California could REALLY use 40 days and 40 nights of rain right now!