[Gllug] OT: Merging UPS outputs

[Chris Bell]

On Sun 04 Sep, Chris Hunter wrote:
> 
> Chris Bell wrote:
> 
> >    Ferrites only work properly at high frequencies, so I would have assumed
> > that when correctly specified should be ideal for the job.
> 
> Nice thought, but ferrites are (generally) very lossy - those losses 
> turn into heat....

   The efficiency is much higher at higher frequencies, which is why they
are used in switching power supplies.

> 
> >    I have been using variable output electronic flash, a discharge tube that
> > can be switched off. My portable units work over a range of several stops
> > without doing a power dump, but not sure about the 250 joule mains powered
> > units. The longest flash time is less than a millisecond, so the shortest is
> > probably a few microseconds. I do not have circuit diagrams.
> 
> The circuit will work by dumping the charge in a capacitor across the 
> tube.  Theoretically, if the tube was shorted, you could destroy the 
> thyristor, but this is unlikely.  The instantaneous discharge current 
> from the capacitor across the tube will be quite high, so you'll have 
> quite a high current-rated thyristor.
> 

   Yes, that is how you do a power dump, but at least the lower power
portable units do not power dump, so I assumed that there must be some extra
circuitry. There is a very short recharge time on the mains powered units,
so I am not sure whether they do a 250 joule power dump repeatedly (could
average every couple of seconds when using a modern digital still camera).
   My guess is that the voltage across the flash discharge tube is dropped
to zero by a very fast thyristor, but another componennt, perhaps a series
capacitor, limits the current spike for long enough to allow the thyristor
to switch off.


-- 
Chris Bell

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