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Reply-To: "Geraldo Sazias"
From: "Geraldo Sazias"
Subject: Re: opto isolators
Date: Thu, 7 Nov 2002 08:57:49 +0100
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NNTP-Posting-Date: 07 Nov 2002 07:58:40 GMT
"Chuck Simmons" wrote in message
> 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
> > 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 specifically
> for analog applications. Most of these also have a transistor for use as
> 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 10,000
> volt opamp having a totem pole output circuit. Remaining nonlinearity if
> 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 flyback
> feedback types (transformer coupled) and optocoupled types. These parts
> 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
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