Led Leds Resistors
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Leds, resistors, and such things?
assume i wanted to light mod a Netgear router and wanted to use 5mm blue led's which use 12v of current but 20 mA max current and the router uses 12v at 1 amp current. what would i need between the power poles of the router and the led not to fry them and would there be any other conflictions?
thanks in advance for any help. I will choose a best answer.
i do have experienced with smd parts and soldering.
i wanted to run 30 gage solid core wire from the dc jack inside the router to the led.
not wanting to drag this out but im looking into leds with resistors with them and the stock resistors are rated for a 12v batt.
the led's are rated for 3.2v-3.4v
First of all, I sincerely doubt any LED uses 12V. 20mA I believe, but not 12V. The forward voltage of most LEDs ranges from about 1V to 3V. When they say "20mA max" that means that is the maximum current you can pass through the LED without damage. Now, the Netgear power supply says 12V 1A. The 1A is really the maximum current that it can deliver - so it will work UP TO 1A. We can assume that the Netgear router uses something less than 700mA or so (they always build some padding in). I am also assuming that the power supply for the netgear is 12V DC and not AC. If it is AC that isn't the end of the world - it just requires a slightly different solution.
Now, to your question...FDor argument's sake lets say we are using a 2V LED (it will say in the data sheet what the forward voltage is). 20Ma is the maximum, so lets use 15mA as our target. Ohm's law states that V=I*R. We know that the voltage across the LED is 2V, so therefore the voltage across our resistor must be 10 (12-2). We also know the current (I) is going to be 15mA. Therefore, we calculate our resistor by 10/.015 = 666 ohms.
If you hook a 666(ish) ohm resistor in series with the LED across the + and - of the netgear supply it should work well. Make sure you don't put the LED in backwards - it only conducts current in 1 direction. You won't damage it if it is backwards, it just won't work.
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