[TowerTalk] Yaesu Rotor Light Bulb

[Charlie Gallo]

On 4/4/2010 Jim Brown wrote:

> Studying the schematic showed that the existing bulb is driven from 
> regulated 12VDC. On my workbench, I tried 5 LEDs in series on my 
> regulated and current limited HP supply. That wasn't enough to 
> overcome their barrier voltage, so I dropped down to 4 bulbs. That's 
> quite nice, draws less than 5 mA from 12V, and puts out a lot of 
> light. 

IF you are dealing with a variable voltage (unregulated) power source, and want to feed an LED (which are current devices), you can use an LM-117

http://cache.national.com/ds/LM/LM117.pdf

scroll down to page 18 or so, where there is an example of a 1A constant current regulator - if you change R1 to say 62 Ohms (nominal), you'll have a 20ma constant current source, which is right for most LEDS, and you won't fry them as voltage changes


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