Re:

01c01bf2689$280d5280$5708b2d0@aarons>
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Aaron Howald wrote:

> 0a@
> daytrader2>
> Subject: Re: New Vector Monitor Project: DEFLECTION SCHEMATIC FOR REVIEW
> Date: Wed, 3 Nov 1999 21:55:10 -0800
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> ----- Original Message -----
> From: James Nelson <nelsonjjjj@didactics.com>
> To: <vectorlist@lists.cc.utexas.edu>
> Sent: Wednesday, November 03, 1999 6:36 AM
> Subject: Re: New Vector Monitor Project: DEFLECTION SCHEMATIC FOR REVIEW
>
> > Excellent comments! (be as hard on me as you can) This is a technical
> > discussion.
> > Some of the issues I was planning to address with more protection
> circuitry.
> > I will address each issue mentioned and drop another schematic.
> > By the way, Op Amps don't blow up and aren't even taxed when they go full
> > rail
> >
> > Thanks,
> > James
> >
> > ----- Original Message -----
> > From: Rodger Boots <rlboots@cedar-rapids.net>
> > To: <vectorlist@lists.cc.utexas.edu>
> > Sent: Wednesday, November 03, 1999 4:58 AM
> > Subject: Re: New Vector Monitor Project: DEFLECTION SCHEMATIC FOR REVIEW
> >
> >
> > > Well, it IS a try, but it needs more work. Here's where you went wrong.
> > >
> > > First thing is the opamp running from + and - 15 volts, but the output
> of
> > > the opamp has to be able to swing to the negative rail of the output
> stage
> > > if the output stage is ever to swing positive. As it is the output
> stage
> > is
> > > going to go full negative until the opamp output blows up. Then it will
> > > either stay full negative or swing full positive. At this point you
> will
> > > have wished you had a (next paragraph).
>
> I found out too that fet op-amps act funny near the supply rails...
> set-up as a simple buffer, if the input gets too close to the supply rails,
> the output flips over!!! In tests, on +-12volt supplies, with an in of -10
> volts or more, the output jumped to +11!! something to think about if
> op-amps are used...
>
> Aaron Howald
> ahowald@w-link.net

Not just FET opamps, most ALL older opamps will phase reverse the output if the
input pins are taken too close to the negative rail. Newer ones don't do this,
the key there is to look for them to say that the inputs work rail-to-rail.
HOWEVER, in a vector amplifier it would be doubtful the input would go outside
the +/- 5 volts range, a good 10 volts from either rail.
Received on Thu Nov 4 03:40:25 1999