Roman Black wrote...

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

I tried playing around with the idea of relocating D1, but didn't get
very far.

One way of keeping Q1 from being fried by inductive kickback would be
to place D1 right across the main inductor L1, in the same manner in
which one would place a snubber diode across a relay coil.  This would
certainly protect Q1; the energy stored in the inductor would be
dissipated harmlessly in the diode.  But alas, "harmlessly" in this
instance must necessarily also mean "wastefully".  Efficiency would be
wretched, negating the benefit of having a switching regulator.

Another way of protecting Q1, while doing something useful with L1's
stored energy (like driving the output) would be to connect D1 across
the output terminals in series with a third inductor winding phased
appropriately so that when Q1 turns off, the inductor's stored energy
is dumped harmlessly- and usefully- into the output circuit in the
manner of a flyback converter.

This would probably work fine.  But we're now up to three windings on
this inductor, and it would very likely have to be a custom part; and
custom inductors are sufficiently costly that we've probably wiped out
the initial advantage sought with this one-transistor blocking
oscillator design.

I may be wrong, but this is beginning to look like one of those
"you-can't-get-there-from-here" situations.

Dave

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