On 04/12/2007, Apptech <apptech@paradise.net.nz> wrote:
>
> I'm in the process of implementing the lowest possible cost
> white LED driver able to drive 6 LEDs at up to 20 mA from 3
> x NiCd/NimH cells.
> This isn't rocket science and there are many circuits 'out
> there' but few if any meet my needs. I don't THINK I can do
> better than what I'm doing, but please prove me wrong :-) .
>
> Output will be close to constant brightness across battery
> life with some intentional taper at the end.
>
> There are any number of LED driver ICs available. Most are
> priced at too much, to too too too much.
> I'm looking at a non conventional solution (or course ;-) ).
>
> Pricing need only be approximate - the brilliance and
> manifest low cost of the circuit is the key thing.
>
> **** MUST **** be.
>
> > 80% efficiency across 3V-4V battery range. More better.
>
> All parts in spec at all battery voltages above 3V.
>
> All LEDs in series.
>
> Constant and fully designable LED current within 10% across
> 3V - 4V battery range.
>
> Low low low parts cost.
> Assembly cost not stupid but not as important as low parts
> cost.
>
> Always starts when power applied.
>
> ___
>
> Other:
>
> Brightness taper in say last 10% of battery charge to
> prevent sudden extinguishing from full brightness when flat.
>
> Multiple or variable brightness a bonus.
>
> Always on-power with enable line OK if standby current vvv
> low. (< 10 uA?)
>
> Low voltage shutdown to prevent battery being flattened
> dangerously a bonus. Costed separately if extra cost.
>
> ________
>
> High volume production.
> Assembly costs not counted unless liable to be extreme.
> Surface mount or through hole OK for this exercise.
> Digikey lowest listed pricing for parts used as costing
> guide unless better prices can be shown elsewhere.
>
> Glue parts can be assigned sensible price estimates. (eg
> small resistors < 1 cent, small zeners ~1c, small bipolars a
> few cents or less.
> More special parts (eg decent FET switch) at Digikey prices
> (at as high a volume as you can find listed).
>
> I will share the essential portions of my final circuit
> ****IF**** I get enough competitive suggestions to make me
> feel it worth the exchange.
>
>
>
>        Russell
>
> Russell


How about sharing some of the proceeds instead?   :-)

RP
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