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[OM] Re: OM3 flash with no batteries????

Subject: [OM] Re: OM3 flash with no batteries????
From: Moose <olymoose@xxxxxxxxxxxxxxx>
Date: Thu, 06 Jan 2005 14:20:55 -0800
Simon Worby wrote:

>Piers Hemy wrote:
>
>>>>Silicon Controlled Rectifier, nowadays 'colloquially' termed Thyristor
>>>>
Thyristors include SCRs, as well as other junction devices used to 
switch current.
Silicon - made of silicon, ather than germanium or other semiconductors
Controlled - The flow of current may be controlled, turned on and off
Rectifier - current may only flow in one direction when "on".

So an SCR may be used to switch direct current. Any voltage in the 
opposite direction is blocked, just as in an oridnary rectifier. A very 
useful device that has largely replaced mechanical relays for most uses. 
Functionally equivalent to a relay with series rectifier, although with 
greater capabilities. One of its most important uses is in automatic 
electronic flashes.

Another form of thyristor, a triac, is much like two SCRs wired up in 
parallel with their polarities reversed and their gates connected 
together. Thus it can control current in both directions. Although used 
in all kinds of circuits, the one most familiar to the average 
non-technician is the incandescent light dimmer. One of its most 
important uses is in automatic electronic flashes.

>>>Like the bit in the "O"lympus on the T20/32?
>>>      
>>>
>>No, that sensor is not a thyristor.  
>>
>What is it, then?
>
It is a light sensitive transistor, designed to vary its transmittance 
of current rather linearly in response to the amount of light falling on it.

>And (to come back to the other point) what would an OM-3 do with a
>tyristor if it can't control the flash unit anwyay?
>
The SCR would be to replace the mechanical switch that fires the flash, 
not to control any flash function beyond triggering it. I say "would be" 
because of an earlier post by Mark, which nobody else posting on this 
topic seems to have read.

"The OM-3 and OM-3Ti both use a mechanical switch to trigger the flash, no
batteries are required.  I just double checked it in the manuals...."

I have no personal interest in or experience with OM-3(Ti) bodies other 
than briefly holding one to admire the finish. But I don't like muddled 
info.

Moose



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