>> The method simply consists of PWMing an input (usually mains) 50/60 
>> Hz AC
>> waveform so that its amplitude is effectively reduced.
>
> Like a lamp dimmer, right?

No - not in the usual case. Lamp dimmers tend to switch once per half 
cycle. This switches many times per cycle. I do have a speed 
controller which does do just this though. Electronics Australia 
circuit - I'll dig up the reference.

> In this case, where we want (IIRC), a low-voltage, high current 
> supply,
> I'm not sure I see how it's possible to get there.  If you're simply
> going to take the ~3V P-P part of the ~300V P-P waveform,

It's not, fortunately. Power is taken across the whole aveform ina 
series of "slices".

> ... and the instantaneous
> current that you draw during that part of the phase would have to be
> very high

As it's taken across the whole cycle current draw peak is load 
current. As I notes previously, using a transformer to bring peak 
voltage down to slightly above max load voltage helps reduce current.



        RM 

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