# Nice survey of higher end power supplies ...

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

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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?

rbw

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