> Energy out per energy in, of which Wattage ratios are equivalent, is
> the only meaningful efficiency measure.

...
> ... Vo x Io / (Vin x Iin) is by far the best measure.

Pedant's hat on to respond to my own post.
I mean "energy out/Energy" or  "Wattage out/Wattage in" (not the
identical thing but equivalent results when interpreted sensibly.

ie by all means measure Vo^2/Rload or Iload^2 xRload if more convenient.
V^2/R is usually easier for a fixed resistive load, and V x I for an
eg LED load.

Note that, when optimising efficiencies or comparing converters you
have to decide whether to include or exclude any losses in sense
resistors and output rectifiers in your calculations. The merit in
including or excluding will depend on what you are trying to measure.
If end to end efficiency is what counts then higher losses in sense
components in one system (eg may use a 1,.2 V reference drop across a
resistor in series with a LED (a very unsensible circuit arrangement
but not unknown)) is fair game for exclusion from the delivered power
calculation. Similarly, when comparing synchronous vs Schottky
rectified systems for overall goodness you would account for the
Schottky losses in efficiency calculations. However, when eg
optimising inductor performance or switching frequency etc to
determine energy conversion efficiency of the converter proper you may
wish to consider the sense resistor as part of the load - it's not the
converter's fault that the designer has chosen to allow stupidly high
losses in the output circuitry, but may skew the results when trying
to optimise some other part of the system.

R
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