Russell McMahon wrote:

> > I think within these small ranges the price, size and
> > efficiency of each design could be optimised. I might
> > have a bash at it this weekend.
> > -Roman
>
> Try building a version of my circuit as well for comparison. Both are very
> simple and cheap.
> The regulation on my circuit is extremely good and I suspect the ripple may
> be lower.

Hi Russell, your circuit has much more sophisticated
looking feedback but the added complexity is probably
going to make it less attractive for the newbie.
2 transistors + a fet, 2 zeners, etc. Fets and zeners
scare newbies. :o)

We've seen a few newbie's making PIC projects with a
9v battery, and I think a super-simple SMPS regulator
just for that purpose would be very useful, even though
it won't perform nearly as well as your pickbukmin2
circuit. Efficiency is probably more important than
regulation for many of these circuits. I've reduced
Richard's circuit to 4R, 2C, 2Q, 2 diodes, and that's
including an RC filter on its output.

For simplicity I tried to build a single transistor
circuit, but the only thing that looked decent needed
3 separately wound coils on the inductor, and you can
imagine the newbie problems there with coil polarities
etc. No prizes for one transistor simplicity if the
thing is a real pain to build. :o)

> For very small power levels small potted inductors may suffice but these
> tend to have very low saturation currents. You can get quite small open form
> ferrite bobbins and small powdered iron toroids which likely to be better
> suited. Core volume is roughly related to power handling capability.

Yeah, I have a heap of toroids and formers here, but
again I think for total newbie proofing a cheap
pre-made inductor, and a variation of Richard's
2-transistor circuit might be best. Especially
appealing to me would be a 9v to 5v 10mA version
using one of those tiny RF style inductors that look
like resistors. I could have used a circuit like
that many times!!

Most "hobby" style shops sell small potted inductors.
Catalogue shows:
<0.8mH at 100mA max, 65 cents 6x8mm
>0.8mH at 50mA max, 65 cents 6x8mm
18mH to 120mH 100mA max, 65 cents, 10x14mm
and of course the tiny RF style ones, maybe 10mA??
The less exotic the inductor the better. :o)

Another option might be to use a very simple air-wound
coil of X turns, this is newbie proof and cheap. It
might push the switching speed through the roof, with
all the associated problems, but for low power stuff
the little transistors are very fast switchers and maybe
efficiencies could be maintained.

I'm looking forward to having a hardware fiddle, and
it will be nice to see what Dave D. finds with the
simulator too.
-Roman

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