Olin Lathrop wrote:

> For example, with a 1mH inductor (those are quite available), a 10uS
> pulse at 50V builds up the current to 500mA.  That's an average
> current of 250mA for 10uS from the reservoir cap.  This would only
> cause a 25mV drop on a 100uF cap.
>
> A more serious problem is how to power the control electronics without
> eating into a substantial portion of the power budget.

I was going to ask about this.  I've been looking over some information
about SMPS theory, and I haven't seen any detail on how the feedback is
supposed to work.  I mean it's fine to talk about comparing the output
of the supply against a reference and setting the pulse width
accordingly, but I still haven't come to the part where they explain how
to obtain the reference efficiently?  This process seems very much like
the crude sigma-delta ADC using a comparator to switch between charging
and discharging a cap.  It seems quite simple (theory wise) as long as
you have a reference voltage.

> Again, this is an interesting intellectual exercise, but in the end
> trying to draw any real power from the phone line is a bad idea.

Of course it is, but where's the fun in that?  ;-)

michael brown (bucking the system as usual ;-)

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