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From: jmuchow@SPAMMENOTcamlight.com (John Muchow)
Subject: Re: Camera Flashes
Date: Wed, 04 Dec 2002 05:55:07 GMT
Organization: MindSpring Enterprises
References: <firstname.lastname@example.org> <email@example.com>
X-Server-Date: 4 Dec 2002 05:54:18 GMT
X-Newsreader: Forte Free Agent 1.21/32.243
>>>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
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