> I looked at the datasheet and the page 2 schematic looks like it has a
mistake. I think the LEDs would burn up ( depending on the ability of the
power
source to supply current ) .
/>

That would be true if V_LEDs was less than Vin.
But it's specifically intended as aboost converter with  series string of
LEDS that will not run from the Vin voltage.

The topology i a typical boost converter one.
An excellent IC which does similar with a single NimH call as input is the
Zetex ZXSC100.
This too has 3 sense inputs - voltage feedback, load current and driver
current. It can provide over 80% efficiency at 1 Volt input.

data sheet http://www.diodes.com/datasheets/ZXSC100.pdf

Note the general topology similarity to the Micrel circuit.

I'm just in the process of pricing this IC from Asian sources to see if I
can afford to use it.
Digikey volume pricing says I can't - but DK often speaks with forked
pricebook on such matters.  DK say $US0.85 ish at 25000 but I suspect far
far lower is available.

Alternative is something like NCP1450 fron OnSemi (cloned (probably) in Asia
as eg CE6360). Like the Zetex and Micrel parts these use an external switch
(FET or bipolar) meaning that the typical limitations of poor on-chip
MOSFETS does not apply. However, the Zetex and Micrel parts have both switch
and load current sense and proper voltage feedback so they are far superior
if affordable. Indications are that I can source the CE6360 for under 0.5
RMB (well under $US0.10) in not too high volume. I'm hoping the ZXSc100 will
not be too too much more than that.

I have a CE6360 boost converter working 'on the bench' and its main problem
is too much enthusiasm. At 0.9V charging in and a Lithium Ion cell (via some
basic device electronics) it happilt takes 2 Amps from an Alkaline AA cell.
OK for a 1 use battery but not nice for a lower capacity NimH if long life
and prosperity is desired. The ZXSC100 can be tailored to limit top current
draw. I'm hoping it will prove cheaper than adding an opamp to what is meant
to be a simple and cheap circuit. (I can limit current using a transistor
circuit but the Vbe drop adds excessively to losses.) With a single NimH
cell every bit of efficiency is useful.


 Russell McMahon
.






Lithium Ion driven version

 http://www.diodes.com/datasheets/ZXSC410_420.pdf

Many Zetex application notes here

           http://www.diodes.com/destools/


Russell

2009/8/8 AGSCalabrese <agscal@gmail.com>

> I looked at the datasheet and the page 2 schematic looks like it has a
> mistake.
> I think the LEDs would burn up ( depending on the ability of the power
> source
> to supply current ) .
> Gus
>
>
> > On Aug 7, 2009, at 4:06 AM, cdb wrote:
> >
> > Thought this might interest the resident Leeding person (hmm sounds
> > better when you say it). No idea of price, because I haven't looked.
> >
> > http://www.micrel.com/_PDF/mic3230.pdf
> >
> > Colin
> > --
> > cdb,   3/07/2009
> >
> > --
> >
> >
> >
> >
> > colin@btech-online.co.uk
> >
> > --
> > http://www.piclist.com PIC/SX FAQ & list archive
> > View/change your membership options at
> > http://mailman.mit.edu/mailman/listinfo/piclist
> >
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist