On Sep 10, 2006, at 5:04 AM, Gerhard Fiedler wrote:

>> between large numbers of LEDs without any Vf matching.
>
> Why would he do that?

If you connect large numbers of LEDs in parallel, the devices
with slightly lower Vf will steal current from the ones with
higher Vf (leading to lower efficiency and faster degradation.)

> If you use a switcher supply anyway, wouldn't it be
> better to have them in series and supply the chain with a controlled
> current? Only slightly more complicated, and easier layout...
>
I dunno.  The headlamps in question has 40 or more LEDs.  I don't
think I'd want a 150+V 20mA power supply sitting on my head :-)
(but if I designed the thing, it would certainly combine several
smaller series chains of LEDs, say with each chain having 5 LEDs
and nominally ~24V supply.)

BillW

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