Dave Dilatush wrote:
>
> Roman Black wrote...
>
> >* L1 and D1 are slightly unconventional, load
> >current is supplied only when Q1 is on, and when
> >Q1 turns off the flyback dumps excess energy back
> >to the supply.
>
> Take a careful, close look, while ignoring what you intended to have
> happen, at what actually transpires at the instant Q1 turns off.
>
> Just before that instant, current is flowing through L1 from top to
> bottom, dutifully recharging C1.  When Q1 turns off, where is all that
> current going to go?  It can't go through Q1, which has just turned
> off; and it can't go through D1 either, because D1 is pointing in the
> wrong direction for current flow.
>
> But inductors being inductors, that current is darned well going to go
> somewhere.
>
> What ends up happening at that moment in time is a brief, violent, and
> probably fatal contest between Q1 and D1 to see who can best withstand
> the voltages generated by the inductor's stubborn insistence on
> continuing the flow of current and ridding itself of its stored
> energy.
>
> My bet is that Q1 loses, but I don't think it matters much.


Whoops! Obviously D1 needs to have its position
in the curcuit adjusted. I said it was a quickie! :o)
-Roman

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