[rescue] WTB/Advice: UPSs

[Scott Newell]

At 05:24 PM 4/6/2002 -0500, Larry Snyder wrote:
>Sharkfin regulators depend on the slope of that sine to work.  Give 'em

What's a sharkfin regulator?


>a step function and they'll puke all over themselves and whatever
>they're powering.  If it conducts for the first 45 deg after zero-
>crossing and cuts off, the peak it hits is 70% of the sine peak.  With
>a square wave it's 100%.  That's nearly 50% above the design center
>value, and definitely bad juju.

This description sounds (to me) like a 60Hz phase controlled triac circuit,
such as a light dimmer.


I still don't understand why a square wave input would be bad for most
SMPS.  Don't they usually rectify and filter the incoming AC to generate an
internal high voltage rail, then do all the switch mode goodness to step
down, regulate, and isolate?  (In which case a square wave or DC input
would actually be better than a sine wave!)  Is it the PFC circuit that
causes a problem with non-sine inputs?  (Most of the circuits I've studied
are older, fairly simple, and omitted the PFC circuitry.)


newell