n> Where did you find these for $0.50?  I was looking at these 
National
> parts
> recently, and Digikey has the LM3578AM for US$0.80/1k.  Would really
> appreciate a lower-cost source.

I may have got that wrong - was from (recent) memory.

> I believe the MC33063/MC34063 can do what you want, and is much
> lower-cost at
> ~US$0.28/1000.

I tried it. Alas, it has a poor quiescent current drain - about 3 mA 
at
no load in a typical configuration.  Usually this would not be a major
issue but as my load current is in that range it badly hurts the
total current draw. Also, its switch is an internal Darlington and
unless you can get very creative the voltage drop is an appreciable
part of the 4v minimum supply and further hurts efficiency. One way to
get creative is to use it to drive an external FET switch (which is
what I did in the inverter I did for Jinx a few months ago) BUT that
adds to parts count and cost which are at a premium here.

I'm about to try an LM393 design to see if I can get it all entirely
internal - no transistors at all - use an inverter section or two as
the switch. It will be close to its capabilities probably and I have
to watch typical versus worst case/min parameters.

I tried a capacitor pump but the CD40106 boost converter was better
overall.

> BTW, aren't you on the other side of the planet?  Curious why you
> check
> pricing at Digikey -- do you buy from here and have them ship to
> you, or does
> Digikey have a branch over yonder?

Digikey are a good universal reference - many people know them, they
have a good range of prices and you can say that in real volume the
prices won't be worse than they charge :-). I do in fact buy SOME
parts from them when there's no better easy source and even the
Taiwanese company who build some stuff I design, buy from Digikey on
occasion! But they have no branch here. When I want it soonish and
Farnell & RS haven't got it and /or charge far too much (as they do)
in volume then Digikey are a good source.

The other side of the planet is only a few days away once they get it
shipped. Or a week or two at much better rates.


        RM


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