cavelamb himself wrote in
:

Wouldn't adding something like a starting capacitor fix that?



No, the circuit is just too simple...4 diodes in a bridge, caps
across the DC output of the rectifiers about 160VDC to power the
power MOSFET switching transistors running at 100 Khz or so. The
custom IC made to run all this measures the output DC volts and
varies the pulse width fed to the power transistors to regulate
the voltage. There's nothing analog about it. The MOSFETS are
either OFF, no heat generated or SATURATED, very little heat
generated because they are nearly a short at saturation...full
on. The DC output comes from another set of higher frequency
rectifiers hooked to a high frequency toroid transformer,
sometimes with more than one secondary winding like the DC power
supply in your desktop computer to get different voltages and
polarities....

When the load increases and output voltage TRIES to drop, the IC
senses this very fast and widens the pulse with to the switching
transistors, pulling the voltage back up with more power to the
toroid transformer. If the line voltage changes, the output also
tries to change, causing the sensing of the IC to vary the pulse
width in the appropriate direction to compensate. Some switching
power supplies, like those very light wall bricks that run and
charge your cellphones, pocket PCs, and laptop computers will
tolerate a voltage change so huge you don't even have to worry
about what line voltage you're plugging it into from 80VAC to
280VAC! If you plug it into 115 in USA, the pulse width is wider
than if you plug it into 240 in Europe. It doesn't care what
frequency because we're just going to directly rectify AC into DC
and feed it to the big input caps to store for the switchers.

What's hilarious in all this is someone with a very wide input
Switching powersupply plugging it into some kind of "SURGE
PROTECTOR" to keep any power line surges from "damaging" it. The
switcher could care less! If a big pulse of voltage comes into
it, the huge input caps just absorb it, turning the pulse into
more power for the switchers to use. Hell, if you surge it at
300V that's well within "normal" peak voltage on the 240VAC
system it was also designed for! The surge protector IS the
power supply itself! It's output is steady as a rock until the
big input filter caps drop below about 70VDC...on power down.

Switchers are neat.

Larry
--
Merry Christmas!
http://youtube.com/watch?v=Qi_NhFS4xEE