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From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: net.analog
Subject: Re: strobe oscillator
Message-ID: <803@kitty.UUCP>
Date: Sun, 9-Feb-86 22:07:30 EST
Article-I.D.: kitty.803
Posted: Sun Feb  9 22:07:30 1986
Date-Received: Wed, 12-Feb-86 07:30:23 EST
References: <151@biomed.UUCP>
Organization: Recognition Research Corp., Clarence, NY
Lines: 50

>      Are there a few simple rules of thumb for designing an oscillator of
> the type used for camera strobe flash units.  The type I am talking about
> typically use a "simple" transistor oscillator feeding a subminiature
> transformer.
> ...
> HOW DO YOU  1) Easily determine the primary and secondary impedences of the
> transformer you want.  If you want to wind your own ,  say on a toroid
> ferrite, how do you select wire gage and # of turns.
> 2) How do you pick the frequency at which it will oscillate?
> 3) How do you select capacitor values to start experimenting with?
> 4) How do you insure that an oscillator like this will self-start and not
> just sit there and pour DC into the transformer, ultimately burning out the
> transistors?
>    What I am looking for are practical trade shortcuts and practices.
> Please don't tell me to go read a text on oscillators.  Reference to an old
> magazine article would be nice.  Thanks in advance.

	Some good references would be two books published by McGraw-Hill,
authored by John Markus, and entitled "Sourcebook of Electronic Circuits"
and "Electronic Circuits Manual" [the newer of the two books].  Both of
these books will provide a few dozen representative circuits of photoflash
units.  Please note: while the circuits in these books are complete with
component values, they should be used as examples, and NOT taken as gospel;
the point being, THINK before you build it.
	I don't know of any simple way to explain the design procedure for
such a circuit over the Net.  Please don't take offense, but the questions
which you ask indicate indicate a serious lack of circuit design knowledge,
and they cannot be answered in a few words.
	The most critical item in building a photoflash supply is the
transformer, which should be a toroid for small size.  Most commercial
photoflash units use a custom toroid which would not be readily available
to you as an individual component.  Based upon my comments in the above
paragraph, I would suggest that you forget about winding your own toroid.
	However, you can obtain off-the-shelf toroidal transformers which
will probably be okay (except for perhaps size, depending upon what you are
trying to do).  I would suggest Triad-Utrad, division of Litton, which many
industrial electronic distributors stock.  The Triad TY-series will give
you about 2 dozen transformers to chose from, designed for input voltages
ranging from 6 to 28 volts DC.  I believe that Triad has some application
design examples for use for their transformers.
	A proper photoflash power supply MUST be designed with the flash
tube characteristics in mind, regarding: watt-second rating, recommended
design voltage, self-ionization voltage, trigger voltage, etc.

==>  Larry Lippman @ Recognition Research Corp., Clarence, New York        <==
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