Hi John



 RM> The only ways I can see of faking a 240V sinewave are (a) synth it

 RM> with fast pwm, as above, (b) do a squarewave and filter it at hi

 RM> power with caps and big fat heavy expensive inductors, (c) synth it

 RM> as in (a) and filter the output as in (b), and (d) drive the

 RM> transformer with a linear amp, and waste a bit of the 240 output to

 RM> drive its cooling fans.



 JT> The way they usually do it, is convert the incoming DC to 340v, and

 JT> use a push-pull arrangement with PWM to simulate a sine wave. Then

 JT> filter it anyway, using more or less standard mains filters. You

 JT> will get a small amount of switching noise in the mains, but it

 JT> mostly depends on how quick the PWM was.



I see, a two stage arrangement. Stage 1 is a regulated dc-dc

converter running at some random freq, optimized for efficiency,

and stage 2 is a transformerless switching array with no regulation

but tight control of switching times.



I'll add it to the list, but it's a bit too complex for the job I

have in mind. A vaguely filtered squarewave should do the job.



The choo choo inverters, btw, use method 1, but their main

purpose in life is to drive motors.



Cheers, and thanks



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