Re: Nav Lights using Luxeon LEDs

I have done the efficiency analysis, and had concluded that a switching
regulator did not perform much better than a straight DC current
regulator. Firstly, the LM2576 is a voltage converter. You would still
need to follow this with a constant current source to drive the LED. A
more efficient approach is to use a current-mode converter, such as the
ADP1864, which has a seperate current-sense pin. In either case, the
benefits are not that overwhelming.

The green LEDs need 700mA at 10V. There is an additional 0.5V drop
across the wiring (cockpit to wingtip) that is unrecoverable. The
conversion efficiency of ADP1864 chip is around 85% for 700mA at 10V.
The overall efficiency of the system will be 82%, which is almost
exactly the same as the simple DC current source. So there is no
advantage in this case.

The red LEDs need 1.4A at 6V. Doing the same analysis, the overall
efficiency with the switching circuit will be 81%. The straight DC
source has an efficiency of only 50%, so there is some advantage here.
However, in real numbers, this difference amounts to only 250mA. I
didn't think that was enough to justifying installing a switching
system. The potential of a noise problem made the decision even easier.




deanwil@xxxxxxx wrote:
Andrew,

Your powersupply is way too inefficient... use a National Semiconductor
simple switcher LM2576 and you'll be much better off. Don't worry, it
won't emit a bunch of RF with the toroidal inductor it uses...

Dean Wilkinson

.

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