RE: [SI-LIST] : coming up with average power estimates for buffer

Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Mon, 2 Aug 1999 15:53:29 -0500

I do not think I have heard of calculating "RMS average power", as a useful
thing to do.

However, in a resistive circuit under steady-state AC conditions, the power
consumed by an element equals the RMS voltage times the RMS current; or the
RMS voltage squared divided by the resistance. The heat dissipated by a
resistor is a function of the RMS voltage across it. Hence people often use
RMS voltage (and current) when thinking in terms of what their effects will
be on power. But this is *not* the same thing as an RMS power calculation.

Years ago, I recall the audio electronics world got stuck on a notion of
"RMS power" which really meant "average power", or (Vrms^2/Rload). Many
recognized the fact that the terminology was wrong, but it stuck. I think
it was meant to emphasize the fact that it came from an RMS voltage
measurement using an undistorted sinewave, as opposed to things like "peak
power" which could mean the instantaneous peak (>2*average) if one's
marketing department was not very scrupulous.

Andy Ingraham

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