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Reply-To: "Geraldo Sazias"
From: "Geraldo Sazias"
References: <3DC9BE19.1980C7C0@webaccess.net> <firstname.lastname@example.org> <3DCA598F.58EDB5F4@webaccess.net>
Subject: Re: opto isolators
Date: Thu, 7 Nov 2002 14:19:52 +0100
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
NNTP-Posting-Date: 07 Nov 2002 13:20:43 GMT
"Chuck Simmons" wrote in message
> Geraldo Sazias wrote:
> > "Chuck Simmons" wrote in message
> > news:3DC9BE19.1980C7C0@webaccess.net...
> > > Dan wrote:
> > > >
> > > > Do opto isolators work as digital or analogue? IOW, are they used as
> > > > switches or can they measure incremental changes, like 0-5v? I can't
> > seem to
> > > > find what I need in the data sheets I've found searching the web.
> > > >
> > > > Dan
> > >
> > > Depending on type, they can be used analog. The best for analog use a
> > > photodiode instead of a phototransistor. The diode type are
> > > for analog applications. Most of these also have a transistor for use
> > > a buffer but it can be ignored for high linearity applications. I used
> > > such optoisolators to drive the high side tube circuit in a 0 to
> > > volt opamp having a totem pole output circuit. Remaining nonlinearity
> > > any was removed by closing the loop around the opamp.
> > >
> > > In the 70s, Burr-Brown Research made various isolated amplifier and
> > > power supply products. The amplifier products were split between
> > > feedback types (transformer coupled) and optocoupled types. These
> > > had very excellent linearity.
> > >
> > Some of the specs I've seen led me to believe that the linearity of a
> > optocoupler is far less than can be achieved with transformers. Is this
> > true?
> This seems to be true. Burr-Brown used two optocouplers in their
> optocoupler isolation amplifiers. The second was for local feedback. The
> flyback coupled devices did mot need this double structure. The flyback
> devices were more expensive anyway, however, in spite of a unique method
> of winding the transformer on the ceramic substrate using an automatic
> wire bonding machine.
Is the linearity inferiour, even with feedback?
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