Using an after market nominal 12V in X volt out laptop 
supply with minor modifications may work. Any number of 
modern ICs will implement a converter to do this. An also a 
few oldies. If OK but not utterly superb efficiency is Ok 
then the time honoured MC34063 or one of its new upgrades 
would do this with ease with a small handful of parts. 
Efficiencies of over 80% should be achievable.

Many modern SMPS ICs targeted at LED driving don't like more 
than about 20 V out and two parallel strings may be  needed 
with them. With an external FET driver the voltage is not 
constrained by the IC. A FET is highly desirable here as the 
current gain of most bjts at the currents involved has a 
noticeable effect on efficiency unless you are willing to 
provide a seperate low voltage winding for the base drive - 
not really sensible at these lower  power levels.



        Russell

>I have been looking for an LED driver solution that can 
>drive seven or eight
> Luxeon K2 LEDs from a DC input.  I need a boost design 
> with an input that
> can vary from 8 to 30 volts, and an output drive 
> capability of up to 1.5A at
> up to 30 volts.  My preference is for something that I can 
> change a resistor
> on to vary the output current while I am in the prototype 
> stage and a
> minimum of external parts with the FET internal.  Can 
> anyone recommend a
> part?
>
> The ones I have been finding either can not go up to that 
> voltage or current
> or can not easily operate in constant current mode.  Some 
> are also made to
> drive lots of LEDs, but in a series/parallel arrangement 
> and I can not do
> that if I have seven LEDs.

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