> Russell McMahon wrote:
>> 10 IC
>> =A0 2 Schottky
>> =A0 3 Inductor
>> =A0 2 2 x ecaps

> You can get a inductor for $.03!? =A0Unless this is a glorified ferrite b=
ead,
> which wouldn't have the inductance and current capability for a switching
> power supply beefy enough to run a PIC, I have never seen inductor prices
> anywhere near that. =A0What are the inductance and saturation current spe=
cs on
> this inductor? =A0What is the real inductance and saturation current (at =
this
> price from China I expect the spec and actuality not to have much
> correlation)? =A0Is there a web page that shows this in english with the
> price? =A0Right. =A0I didn't think so.

So quickly we jump to the end game :-).
And, you are correct. Web pages in English with such details on are
few and far between.
Hens teeth ads may be easier to come by.

But, the actual quote from a typical spreadsheet which I just looked
at to be sure was HKD0.30 / unit which, at an exchange rate of 7.5
HKD/$US is 4 cents US.
BUT that was for a rather more capable inductor than needed for the PIC psu.
100 uH, true mean DC operating current up to about 200 mA, saturation
current somewhere over 600 mA.
Resistance "low enough".
Adequacy of actual offered parts assessed by running a prototype with
a manifestly over-provisioned part and then comparing actual
efficiencies at various operating points. This is a useful approach
when parts are sourced with specs which are not fully able to be
controlled as eg wire thickness, turns, core material, bobbin shape,
actual inductance, core permance with temperature, core hysteresis and
more will affect the result.
So "how well does this work compared with an excessively specified
part under real conditions" is a reasonable test.

I provide samples and say "THIS part works", minimum spec is xxx (mA,
kHz, ohms, inducatnce at I etc as desired) and efficiency in operation
should be no worse than yyy.

Bobbin core, similar in performance and spec to the 22R104 here

              http://docs-asia.electrocomponents.com/webdocs/0539/0900766b8=
0539853.pdf

About 8mm tall, 7mm OD,
These parts were from RS and the company has since been bought by Murata AF=
AIR.

These cost me more than 4 cents each ! :-).

Spec of this part is 0.5 R max, 660 mA continuous. These parts worked
well and were used as comparison parts for Chinese sourced
equivalents.

I do not know ferrite used, wire diameter, turns (unless I count
them), ... BUT I know how well the end product works.

There are deficiencies in this approach, and I'd prefer the western
style certainty, but the Eastern style price with OK results is fairly
compelling.

Not having the real spec change with time is always an issue. Actual
performance is the final arbiter and the occasional detailed check of
randomly selected products is a good idea [tm].

If you want to test one you could buy a BOGO light :-).



                     Russell

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