🚀 go-pugleaf

In article <17660122@hpfcdj.HP.COM>, myers@hpfcdj.HP.COM (Bob Myers) writes... 
>One other *disadvantage of switchers that I believe Henry forgot to mention
>is a typically atrocious power factor, as the switching action plays merry
>hell with the input current waveform.  This has become quite a concern at
>sites which have a large number of independent switchers (such as a bunch
>of PCs or workstations) on their AC lines.

     They also have a negative resistance characteristic.  If the AC mains sag
(brown out) the switching supply will simply adjust its duty cycle and draw
more current.  Imagine a whole city of switchers during a brown out...as the
voltage drops each power supply draws more current which makes the voltage drop
some more...

     A couple of years ago I went to Britain on business with a microprocessor
emulator with a Panasonic 5V switching power supply.  The company provided me
with one of the rinky dink shaver adapters to plug it into the 220V over there.
Just before the fuse popped, that switcher was providing 5V out with less than
20VAC in!  (An intermittent 5V, which is why I happened to be measuring the
input.)

Philip Munts N7AHL
NRA Extremist, etc.
University of Alaska, Fairbanks