+AD4-
I understand that its needed if the psu droops but does this happen that
often in reality?



YES YES YES YES.  Brownouts are caused by many events on power lines -
switching, reclosers, temporary short circuits, fried squrrels that pick the
wrong two conductors to jump between, Birds with birdbrains, other people
turning on their Dr. Frankenstien 2000 amp arc generators, and so on.  We
nearly had a recall of a product which was not brownout proof, and caused
headaches whenever  one of these events occurred.

Every time the wind blows hard, sticks, squirrels, birds, and other detritus
touches power lines.  If these sticks and squirrels are wet (usually) they
make a short circuit.  Big circuit breakers, called reclosers, are located
in substations around the power network.  These babies will interrupt the
power for a few milliseconds, hoping the fault will clear itself, whenever
Rocky tries to surf on both power lines.  Generally, Rocky is roast after a
few milliseconds, and falls to his doom.  If the recloser turns back on, and
still finds a short circuit, it interrupts power for a longer period, maybe
1 second.  Most reclosers are programmed to try a third time, and interrupt
for up to 7 seconds.  Every power company programs their reclosers
differently, for different numbers of seconds and different number of tries.
Your product has to survive this abuse.  No AC powered product should be
without brownout protection in some form.


Check my web page for more diatribes on brownouts:
http://members.socket.net/+AH4-llile/acad1.htm

-- Lawrence Lile



+ACo- For non-US readers: Rocky the Squirrel is a famous US cartoon character.

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