[mythtv-users] Proposed future power saving networked configuration (0.22 in mind)

[David Brodbeck]

> On Feb 18, 2009, at 7:42 PM, Michael T. Dean wrote:
>> Actually, taking it to a nice pretty sine wave would be a travesty.
>> Computers run on DC power, so if you attach your solar/wind/home-nuclear
>> generator to batteries, then attach an inverter to the batteries to make
>> AC, then feed that AC to the computer PSU, it will take the AC and turn
>> it back into DC...  So, you incur an efficiency loss going from DC->AC,
>> then compound the loss with a second efficiency loss going from AC->DC.

But even 12VDC-powered computer power supplies have to have an AC stage 
in them, to get the 5V, -5V, and -12V outputs.  Usually this is some 
kind of chopper circuit to make a high-frequency square wave.  This kind 
of circuit is often referred to as a "DC-DC converter" but internally 
it's still making AC.

In theory you could reduce 12V to 5V with a linear regulator, but it 
turns out you waste more power this way than with the other approach.