Hi Brooke,

LM2675 has worked pretty well for me in that application. And if you use 
the adjustable voltage version you can use it as a constant current 
regulator for your LEDs and your losses will be small and you'll have 
fairly consistent light output through temperature.

Cheers,

Bob


Brooke Clarke wrote:
> Hi:
> 
> I'm looking at powering some 1 Watt LEDs using a ZXLD1350 that has a 
> maximum input voltage of 30 Volts from a battery that might be as high 
> as 32.8 Volts when fully charged.  I'm trying to come up with a way to 
> keep the voltage at or below 30 volts without wasting any more battery 
> power than necessary.  One way would be to use 5 diodes in series with 
> the battery input then when the voltage gets down to 30 short them out.
> 
> Or is there another IC with equal or better efficiency (>90% from 20 to 
> 30 Vin) when driving 5 each 1 Watt LEDs (340 ma @ 3.3V) that has a 
> higher input voltage rating?
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