Evening Mike,
>>At 09:42 AM 10/17/2006, you wrote:
I want to build a couple of LED navigation lights for my sailboat
Depending on the voltage drop of the LED's used, 3 or 4 per string for
two strings will draw 40ma and give constant brightness
Are going to series the strings? Else why worry about voltage drop?
Seems applied voltage and the adequate voltage source would be all
that you need to be concerned with.
What am I missing?
from about 8 or 9 volts up to the 16v or so that is a reasonable
design max in a 12v system.
You could use a carefully calculated ( or measured ) resistor and
use the 12 VDC. You should have 12 VDC, and ample current capacity
Using something like a 7805 makes perfect sense. Cheap and readily
available. I don't need anything esoteric.
Calculate the total load, and it may exceed the capability of the 7805.
I can see 50 or 75 LEDS, maybe more, maybe less.
I think the 7805 has only a one amp output. A heavier duty model does exist.
I like for power supplies to have a capacity of 3 to 5 times the rated load.
Continuous duty does interesting things when warm or hot environments
exist. You can use heat sinks and fans.
I'm cloning the design and engineering from these folks:
http://www.bebi-electronics.com
Heck, it may all be figured out and you already knew what little
I told you anyway.
I built a neat supply for one of my medical products. It had
5 V, 12 V, and 16 Volts out. I believe this was in a small inverter
and the 16 volts was to charge the battery.
Still, I would consider using the 12 VDC. It is already there.
You might be able to series two strings and get the voltage you want
to each string. No muss, no fuss, and no regulators to worry about.
Wayne
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