On Mon, 19 Dec 2005 23:51:48 -0800, philkryder wrote:

Steve - How many equal "steps" are necessary for the MSW inverter to be
a sufficiently close approximation to a "rotary" sine wave?

It depends how you count "steps". I once worked with an inverter that
used two, count'em, two, output transformers, each driven by a plain
vanilla square wave, but they were in series, and the regulation
took place by controlling the phase of the two square waves - 120
times a second, the two secondaries flipped from "buck" to "boost".
The output waveform was essentially a positive pulse, then zero, then
a negative pulse, then zero, then another positive pulse, and so on.

It ran everything we plugged into it, even an induction motor bench
grinder. Lamps are trivial, and series motors, like a hand drill,
don't care.

We didn't plug a computer into it, however, or anything with an SMPS,
so I guess my recommendation would be to check the spec on what it
is you're plugging into it.

Good Luck!
Rich