lagasse@biomed.UUCP (Robert C. Lagasse) (02/04/86)
Dear gentlemen:
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. It operates usually from 3-9V DC and charges a large (about
300 uF) capacitor to about 300 V in a few seconds between flashes. The
oscillator operates in the audio range as the transformer can be heard
sweeping a range of frequencies as the capacitor charges. The transformer
used is of conventional (laminated frame) or toroidal (even more fun)
design. The circuit typically derives a feedback from the transformer,
sometimes by a separate winding. Here come the how-do's:
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.
Bob Lagasse @ Mass. General Hospital
******"Most problems can be remedied by the addition of a few blowholes and
a toilet-tank float" *********larry@kitty.UUCP (Larry Lippman) (02/10/86)
> 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 <== ==> UUCP {decvax|dual|rocksanne|rocksvax|watmath}!sunybcs!kitty!larry <== ==> VOICE 716/741-9185 {rice|shell}!baylor!/ <== ==> FAX 716/741-9635 {G1, G2, G3 modes} duke!ethos!/ <== ==> seismo!/ <== ==> "Have you hugged your cat today?" ihnp4!/ <==