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From: "Bill Sloman"
Subject: Re: opto isolators
Date: Wed, 6 Nov 2002 23:29:17 +0100
Organization: Planet Internet
NNTP-Posting-Date: 6 Nov 2002 23:29:02 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"Martin Griffith" wrote in message
> On Wed, 06 Nov 2002 16:13:31 GMT, "Dan"
> >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
> >find what I need in the data sheets I've found searching the web.
> HP ( they've probably changed their name again ) have an Opto
> isolators design guide
> Hewlett-Packard optocouplers
> can be used in an array of
> isolation applications ranging
> from power supply and motor
> control circuits to data communi-cation
> and digital logic interface
Not quite twenty years ago I spent quite some time screwing as much speed as
I could out of a fast HP (now Agilent) opto-isolator with a built-in
Schmitt-trigger buffer, and I ended up doing some very analog things to LED
drive to minimise the jitter - there was an inductor in there somewhere, to
reverse bias the LED at turn-off, and a catching diode to stop the inductor
from turning it back on (briefly) when it rang.
Like most "digital" components, opto-isolators' basically analog nature tend
to surface as soon as you starting pushing their limits.
Bill Sloman, Nijmegen
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