From: glhansen@steel.ucs.indiana.edu (Gregory L. Hansen)
Newsgroups: sci.electronics.design
Subject: Re: Camera Flashes
Date: Wed, 4 Dec 2002 17:10:35 +0000 (UTC)
Organization: Indiana University, Bloomington
Message-ID:
References: <3decf79a.1137368@news.pipeline.com> <3ded954d.15633453@news.pipeline.com>
NNTP-Posting-Host: steel1.ucs.indiana.edu
NNTP-Posting-Date: Wed, 4 Dec 2002 17:10:35 +0000 (UTC)
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In article <3ded954d.15633453@news.pipeline.com>,
John Muchow wrote:
>>>>So what components could you recommend? The FETs I saw at Radio Shack top
>>>>out at 25V, which is clearly not sufficient.
>
>Digikey (http://www.digikey.com) has a few TO-92 and 4-DIP MOSFETS
>with over 200 Vds ratings. I don't have any specific ones to
>recommend but selecting the least expensive one with a high enough
>voltage rating, low enough Rds, and the highest current rating you can
>get, should be OK. Be sure that you have enough voltage to fully
>drive the gates...you may need logic-level versions.
>
>But, with voltage you're seeing on the sync input to the flash (and
>the dangerous voltages on the flash capacitors), I'd recommend
>optoisolating the flash units from the rest of your circuitry...just
>to be really safe. You can use optoisolators to drive the MOSFETS but
>a triac-output model like the MOC3023 has 400V rating and only needs
>5mA to fire the flash unit directly. In fact, most of the
>triac-output optoisolators have high voltage ratings as they are often
>used with standard AC line voltages. And the MOC3023 is inexpensive.
>
>There are transistor and SCR output version too.
>
>Just make sure the triac-output model works with your flash units...an
>inexpensive test.
>
>John Muchow
Found them, the specs look right, the price is right. I'm not married to
any particular design right now, but I have absolutely no experience with
these parts. My skill might be described as "electronics lite". I was
hoping for some sample circuits to study, but the on-line data sheet
wasn't very helpful. Is it as simple as a 5mA input across pins 1 and 2,
and that will turn on up to 400V, 1A AC across pins 4 and 6?
Looking at http://rocky.digikey.com/WebLib/Lite-on/Web%20Data/MOC302x.pdf
I suppose that's what the circuit at the bottom shows, but with a filter
between that and the load.
--
"A nice adaptation of conditions will make almost any hypothesis agree
with the phenomena. This will please the imagination but does not advance
our knowledge." -- J. Black, 1803.