On Tue, 11 Nov 2008 19:47:03 +0000, Larry wrote:

"Roger Long" wrote in
:

And one of those surges they protect from is the spikes caused by the
power grid response to strikes far from you cmputer. Turning off
electronics is a good idea, not because the little switch will protect
from strike current, as Larry points out, but because power
instability from a strike across town might overwhelm the surge
protector of a dip as power is restored might let the head of your
hard disk briefly contact the platter surface (although disk designs
have greatly improved in this regard).


Naw. The power supplies in your computer equipment are all switching
power supplies. Here's a block diagram:

LINE IN---rectifierbig capacitorsswitching transistors===*

*===high freq transformer===rectifiers===filter caps===voltage
measuring=*

*===regulated DC output to computer circuits from several
rectifier/filters on several windings of the HF transformer.

The output voltage measuring stage controls the pulse width of the IC
that drives the switching transistors. More load, simply widens the
pulse width fed to the switching transistors. That's how it regulates.

What's important is the first two stages. The AC line, WHATEVER YOU
FEED IT, is simply CONSUMED by the rectifiers...any frequency, any
voltage between about 80 and 250VAC, DC, 50, 60, 400, 1000 Hz, it
doesn't care. Whatever you feed it, sinewaves, squarewaves, triangle
waves, pure DC, is all converted to high voltage DC between about 150VDC
and 400VDC and any pulses, noises, crazy waveforms are simply consumed
charging the very large input filter capacitors which smooth them all
out into whatever unregulated DC just happens. The power supply cares
less unless the voltage is SO high it blows the switcher transistors or
big filter caps...destroying it. The range of nonsense you can feed it
and get pure, exact, DC out of it is simply amazing. IT'S NOT AN OLD
ANALOG POWER SUPPLY that operated over some narrow range of input and
waveform.

No matter even if there's some noise left on the feed DC input to the
switchers....THEY convert it all to really UGLY-looking, high frequency
pulses that vary in pulse width caused by the pulsing custom IC, in a 1
then 2 then 1 then 2 alternating pulsing of 2 sets of 1 or more pulse
transistors designed specifically for this high voltage switching at
several hundred kilohertz. Using high frequency, this allows them to
use a cheap, really light ferrite core transformer, instead of the 60 hz
soft iron monster you can hardly lift. The ferrite core makes the
pulses even uglier when they feed them out SEVERAL different windings to
different rectifiers and tiny capacitors. Tiny filter caps are fine
because we are filtering very high frequency ugly DC pulses...not those
60 Hz pulses of the old power supplies with LONG rest times between when
the filter caps had to run whatever the power supply was driving.

As you can see, there is a LOT of electronics between those power line
pulses you've been trying to protect it against, and that disk drive.
The switcher doesn't really care, unless lightning strikes OR POWER
STOPS! Filtering all the noise out of the input is just crazy. These
power supplies will even run on a hundred volts of Rock Music fed to the
input. I've seen it demonstrated! As long as the music doesn't STOP,
like the AC line must not STOP, you get perfect DC power to the
computer, or whatever it's driving.

If you're going to protect your computer, buy it an UNINTERRUPTABLE
power source...the kind with the battery powered inverter in it that
will keep AC coming no matter what, even power failures. A momentary
SAG in output voltage during a disk drive or memory WRITE is what kills
most computers...not power line surges that are very profitable to
outlet strip makers....and useless.

Have you noticed those REALLY LIGHT little wall wart power supplies for
your sellphone and mp3 players? Those, too, are switching power
supplies, not heavy 60 hz transformer/rectifier/filters. Their output
is perfect. Look closely at the INPUT voltage/freq specs and you'll see
something like 100-240VAC 50/60 hz. ANY power plug in the world will
work just fine by simply plugging them into a straight plug
adapter...115V/60Hz to 240V/50Hz...no problem...no voltage selecting.

As they are already rated for 240VAC, a peak voltage of around 350
volts...do you think ANY voltage spike that's not a lightning hit on
your 115VAC line will kill it? Nope...it won't. That silly little
power supply will keep on putting out pure DC while all the light bulbs
in the house explode....(c;]



All that is swell, Larry, but most computers and Televisons don't get
fried through the AC cord. They get fried via network and POTS
connections.