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.

Dave

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