From: firstname.lastname@example.org (Gregory L. Hansen)
Subject: Re: Camera Flashes
Date: Wed, 4 Dec 2002 17:10:35 +0000 (UTC)
Organization: Indiana University, Bloomington
References: <email@example.com> <firstname.lastname@example.org>
NNTP-Posting-Date: Wed, 4 Dec 2002 17:10:35 +0000 (UTC)
X-Newsreader: trn 4.0-test62 (21 February 1998)
In article <email@example.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
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.