Hi,
I got myself a bunch of superbright LEDs from Hobby King, e.g. http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=28507
Trouble is, HK doesn't give any data on the current or voltage drop of those LEDs. I'd like to build a small board that connects to a 4S LiPo, the APM's ARM LED output and then drives 1 red, 1 green and 2 white of those superbright LEDs. Unfortunately, without knowing the LED data I have no clue, how to dimension the resistors - which anyway would need to be BIG (3W...). I wonder if there's maybe some integrated driver circuit somewhere which I could use?
Could someone help me out here? :)
-Stefan
Replies
"This is the main question - what do they mean with "input: 2.5 - 3 V"...?"
That's the typical voltage drop across the LED junction, probably at rated power (3W). This might help you as well.
http://www.superbrightleds.com/led_info.php
http://store.jdrones.com/jD_IOBoard_p/jdioboard10.htm
The HK link for your LED would lead me to believe that this LED will have a voltage drop of 2.5 - 3.0 volts while dissipating 3W. Using ohm's law (P=VI) (3watts / 3volts = 1amp). We will be running 1 amp through this circuit. Now if you want to drive this from a 4S at, say, 16 volts, we can again use ohm's law (V=IR) to determine a resister value... (16 volts from LiPo - 3 volts dropped across LED) / 1amp = 13 ohms. Finally we can determine the power which the 13 ohm resistor will dissipate (P=VI)... (16 volts from LiPo - 3 volts dropped across LED) * 1amp = 13 watts. This circuit is going to run HOT and suck up a LOT of power! A more practical resistor value might be 18 ohms or higher.
Now if you want to control it from the APM, you will require some sort of buffer or switch. I would suggest a power FET should do the job nicely.
Hope this helps.