Nice survey of higher end power supplies ...

Richard Walsh rbw at
Wed Jun 11 11:22:15 EDT 2003

Wanting to make sure I have these power related terms straight, I wrote up 
definitions for myself based on recent discussions and would be grateful if 
folks would validate and/or correct them.

1. Idealized or VA Rated Power:  An idealized measure of power delivered
   (or drawn) that assumes the voltage and amperage are in phase, 
   sinusoidal, and of the magnitudes (RMS) used in the calculation.
   Most often used to rate/describe line power.

2. Active or Watt Rated Power:  The power truly delivered (or drawn) and
   averaged over some period of time (integral divided by time). Typically
   less than 1 above (but measured in the same units of course) because 
   most loads are not perfectly resistive and supplied power has non-
   sinusoidal waveforms, out of phase voltage and amperage, less than 
   ideal magnitudes (RMS) for V and A. (The complicating effects of Bob's
   line harmonics, etc. would register here as well I suppose.) Often used 
   to describe power drawn/used by a device (a PC power supply) and distinct
   from line power. The ratio of 2 to 1 is the Power Factor.

3. Power Efficiency:  Not to be confused with the Power Factor, the ratio 
   of the power delivered from a device to a given load to the power consumed 
   on input by the device. In the case of a typical PC power supply, this would 
   be the ratio of the power drawn (by lines [3.3, 5, 12V] in use for a particular 
   load over a specific time) over the power consumed by the PC power supply 
   which includes its own draw and heat related losses (my guess is that active 
   power [2 above] should be used in the denominator here).

Too wordy, but are these definitions accurate, sufficiently complete?  


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