DIYbanter - View Single Post - What characterizes a powerFET for audio use?

Maynard A. Philbrook Jr.

In article ,
says...

On 01/02/2014 04:05 AM, William Sommerwerck wrote:
"Jeff Liebermann" wrote in message
...

http://www.eznec.com/Amateur/RMS_Power.pdf
On Pg 6 it says:
"The RMS value of power is not the equivalent heating power and,
in fact, it doesn't represent any useful physical quantity."
and:
"The RMS power is different than the average power, and therefore
isn?t the equivalent heating power. In fact, the RMS value of the
power doesn?t represent anything useful."

I remember a Popular Electronics quiz with questions about how a
voltmeter (at that time, a moving-coil device) would read, depending on
the waveform supplied. A key point was that the deflection was
proportional to the average current flowing through the coil, but the
meter was usually calibrated for the RMS value of a sinewave.

Why do you keep quoting notes from Llewelen? He wrote a modeling program
for wire antennas. We are talking about FETs.

I think AVG = RMS only if waveform is pure sinewave. Otherwise you must
use calorimeter or thermocouple to find true RMS.

AVG and RMS is not the same with sine waves..

Avg = 2/pi * peak Voltage.

And RMS is simply sqr( VP^2 / 2).
you'll notice the root his to look for the square not the
average of total voltage for example.

One can shorten that to say RMS = Vp * .707

Just think of a half round circle an draw and find the
area where you can evenly fit a square box in that half circle,
the value will be .707 times the Peak value of that circle.

Averaging ends up to be 2/pi = 0.637 * the peak voltage which
obviously gives you a different number..

And of course, no matter how you slice it, square waves at 50%
duty give you the same all around. AVG and RMS = peak.. cause there
is no slope in time for the avg and the nice square box I stated
fits perfectly in the already square wave for RMS. etc..

Jamie