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Get an LM317 and check the date sheet for a schematic to work with. Should be able to put an LED directly on the 2V output, with current limiting resistor of course.
+1 use a 317 and this tabe to figure out what resistor you need
If you ONLY need a few microamps, or possibly a few milliamps, (not more than 50mA) then you can probably get away with using a simple LM317T adjustable voltage regulator, or something similar. If you still have a radioshack open in your area, they will probably have that in stock.
However, note that the the linear voltage regulators are NOT efficient, and you can effectively figure out their efficiency by dividing the output voltage by the input voltage. In this case, 2V / (11.1V nominal) = 18% ish.
Another way to see how much power is being wasted is to multiply the voltage drop (nominal 11.1V input -- 2V output) to the current that comes from a battery, and goes into the load, say, 500mA. that is 9.1Vdrop * 0.5A = 4.55W of power being just radiated away as waste heat. You will need a BIG heatsink!!!!!!
So if we cannot have efficiency, of course the next best thing is to use as little power as possible, and since the voltage drop is not possible to lower, the only thing we can do is lower the current to something small enough it will not make much difference in the grand scheme of things. Say, 50mA. then, we only dissipate 0.455W of heat. You will probably be able to get away without a heatsink, as the wasted power is less than one watt.
*Well* there is one exception when linear regs are super duper efficient, and that is when the difference in the input voltage and output voltage is really small. Say you have dirty 14.4V Xformer will lots of ripple, and you need a 12V steady regulated output. I would use a LDO regulator, and since the Vdrop is only 2.4V, and you do that calculation by dividing output voltage by the input voltage, 12V/14.4V, the regulator *Can* be more efficient than even the best switch mode regulators! In this case, 83%!!!
Obviously that is not your case, though. SO don't worry about it. :)
Use a switching mode converter. If you needed 5V, you can easily get a buck converter from a car cigarette USB charger (which is a simple type of switch mode converter, just for stepping down voltages.) But this may not fit your application, so you will probably need to get a adjustable one, and probably one that is really easy to wire up and get working.
This will probably be the best and simplest solution for you:
On some of the models, you can adjust a current and voltage maximums, and have a display showing the output voltage/current, too!
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Posted:Mar 11, 2015
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