Hi Russell, I'm too busy this week to do it, but would
really love to.

I seee a one transistor self excited device which
uses one of the choke coils for neg feedback to
continue oscillation. Basically it allows a decent max
current in normal oscillation, say 150mA, then as the
output voltage reaches a setpoint this biases the
oscillator off, giving both a fixed max current and
crude voltage regulation. But with very low parts cost
and small size.

The dual-coil could be made from a tiny "balun" 8 former,
like used in TV antenna fittings and available for a few
cents, or a cheap small toroid.

I think this would be a nice solution, as a ringing-choke
style design is max current limited to start with, and
it's easy to add another feedback wire to give max
voltage regulation. A final zener can be added if the
expected 5% voltage regulation is not good enough.
:o)
-Roman

Russell McMahon wrote:
>
> > I'd say it can be done with one transistor and
> > a very small coil with two windings...
> > :o)
> > -Roman
>
> I tend to agree - with reservations.
> Part of the reason for my doing it this way was to bring out the good ideas.
> A self oscillating "ringing choke" / flyback converter is indeed one
> possible solution.
>
> Tell us how.
> How many of the design requirements are met by this.
>
>             Russell McMahon
>
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