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From: email@example.com (Gregory L. Hansen)
Subject: Re: Camera Flashes
Date: Fri, 6 Dec 2002 16:41:52 +0000 (UTC)
Organization: Indiana University, Bloomington
References: <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: Fri, 6 Dec 2002 16:41:52 +0000 (UTC)
X-Newsreader: trn 4.0-test62 (21 February 1998)
In article <firstname.lastname@example.org>,
John Muchow wrote:
>>>>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.
>Yup, it's that simple. :-)
I hope you don't mind that I keep bugging you. You're a friendly voice of
>The circuit shows the MOC302X being used as a triac driver...you'll be
>using it directly. And they show the input being driven by that
>transistor. Any method that supplies at least 5mA (but way under the
>50mA limit) will drive that chip...even a 9V battery with a 1K
>resistor. The battery will be dead about the time the current drops
>BATT(+)-----\/\/\----| |--- FLASH
> 1K | MOC |
> ----| |--
> | | 302X |
> | --| |--- FLASH
> | ---------
That is simple. It seems too simple because a triac conducts one way or
the other depending on which direction the gate is biased, but this will
conduct both ways? I know the flash is nominally DC, but I didn't know
what kind of bouncing or other AC behavior would be involved, and I didn't
want to interfere with that.
But really 5mA will turn it on sufficiently? I was looking at the specs
around page 8, and got the impression that I wanted 20mA or so. And I was
thinking of driving ten units which would be 200mA from a nine volt
battery. So I started thinking in terms of enough capacitance to start at
50mA and end at 20mA in a time of 0.02 seconds, which is a little longer
than the 1/60 second shutter speed for flash sync.
But at 5mA each I'll bet I can drop the capacitor, if that really turns
them on fast enough.
>The 1-amp rating is a 1mS peak rating only so I'd limit the output to
>significantly less than that if it's going to be continuous. Your
>flash sync application *shouldn't* be a problem.
>There is still a chance that the MOV won't fire your flash units (or
>the unit will fire but the triac will stay conducting ("on") because
>the sync voltage never dropped to zero when the flash fired.
Hmm... Someone's borrowing my Horowitz and Hill, and I don't think they
say a lot about triacs, anyway. But do I remember something about them
turning on and staying on until the through-current drops?
Well, a thyristor flash knows how to turn itself off, and a pure manual
flash dumps everything it has, anyway. But if it's a problem, I can't
think of a way to fix it without using FETs, which were nixed for
isolation reasons. Or possibly the slower reed relays.
>I'd pick up a MOC3022 or MOC3023 at Radio Shack and give it a quick
>try with a 9V battery and a 1K resistor just to make sure it works
>before you spend any more money or time designing the circuit with
>these chips...just in case.
I was looking through the Radio Shack web page and didn't see that part
listed. That's one reason I'm asking so many questions, I wanted to think
I understand them pretty well before I pay for ten of them plus shipping.
"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.
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