[Beowulf] DC Power Dist. Yields 20%

Geoff Jacobs gdjacobs at gmail.com
Tue Aug 15 19:07:17 EDT 2006

Jim Lux wrote:
> At 08:41 AM 8/11/2006, Geoff Jacobs wrote:
> Sure you would.. Actually, these days, you might use an IGBT, depending
> on the switch rate..

Well, it was just a guess based on the bare pcb of PicoPSU supplies.

> Switching PSUs all rely on rectifying the AC supply to generate a DC bus
> voltage, that is then converted to the DC voltage you want.  There's a
> half dozen or so circuit topologies, but they all basically rely on
> turning the DC on and off quickly and then doing something useful with
> it.  The two basic strategies are: You turn it into high frequency AC,
> then run that through a transformer, and rectify and filter it to low
> voltage DC.  THis saves the iron and copper cost of a high power
> transfomer (since the core mass is inversely proportional to
> frequency... 20kHz or 100kHz saves a bunch over 60Hz)

Okay, just like modern inverter-based TIG supplies. :) But aren't they
already doing this at the prime rectifier to step up to 300-ish V DC?

> The other strategy is to take the HV DC, and pulsewidth modulate it,
> then filter it, to make a lower voltage (the classic "buck" converter). 
> That is, take 100VDC, turn it on and off with a 5% duty cycle, low pass
> filter, and get 5V.

I see, and switching speed is dictated by factors like desired ripple in
the output voltage for a given load while still avoiding the use of
those coke-bottle caps in the LC filter (preserving such supplies for
USAF rail-gun experiments).

Anyway, where do you see these people trying to derive their power
savings and/or reliability improvement by pushing DC to the racks?

p.s. Forgive any dupes -- I don't know if I got to them in time.

Geoffrey D. Jacobs

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