P3D Re: Flash Circuitry

[Bob Wier <wier@xxxxxxxxxxxxxxxxx>]

At 10:12 PM -0600 on 5/22/98, Michael Kersenbrock wrote:


|However, the Vivitar 292 isn't a quench tube flash.  At 
|least not according to my Vivitar manual for it
|that talks about its Thyristor circuit "...saves the
|excess energy not needed for a proper exposure thereby
|providing incredibly fast recycling and a 
|greater number of flashes per charge".  It also 
|has an IC based "sleep mode" so when it's left
|turned on, it doesn't kill the battery.  I've found
|

Hmmm -  it sounds (to me at least) like there is a quench tube, but
it's controlled by a thyristor which can cut the high voltage, but it
apparently does dissipate some energy in a quench tube... Here's the
relevant (edited) sequence...


Vivitar Auto/Thyristor 292 exposure control operation:
-----------------------------------------------------

The power inputs, X and Y, may come from the a circuit similar to the Vivitar
Auto 253 power supply circuit (but of higher power probably), other battery/AC
adapter powered inverter, or other AC line operated power supply.

1. Quench trigger capacitor, C7, charges from energy storage capacitor, C1,
   through voltage divider formed by R7 and R8.  SCR shutoff capacitor, C11
   charges from C1 through R11 and R12.

2. When shutter contacts close, a pulse is applied to the trigger of the
   main SCR (SCR2, or it is already triggered on continuously while the main
   filter capacitor is charged).  Flashlamp is triggered by 4-5 KV pulse
   from main trigger transformer, T2 (not shown).  Note: SCR2 must be turned
   on before flashlamp is triggered.

steps 3 - 5 deleted...

6. When enough light has been detected indicating proper exposure, SCR1
   is triggered dumping C7 through quench trigger transformer.  Resulting
   4-5 KV pulse ionizes (xenon) gas in quenchtube.

7. The quenchtube has a discharges C11 applying a voltage pulse in reverse
   across SCR2.  This biases the SCR in cutoff long enough for the flashlamp
   to extinguish.  Very little energy is lost.

THANKS

              Bob Wier
     mailto:wier@xxxxxxxxxxxxxxxxx
   11:06 PM Friday, May 22, 1998
   Rocky Mountain College, Billings MT.
 keeper of the Photo-3d and Overland-Trails
mailing lists and the USA GPS Waypoint server



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