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Resistor Size???

442 Views 6 Replies 4 Participants Last post by  RideRed0331

I need to know what voltage the resistor from my diagram needs to be in order for all 10 of my LED's to get an even 5 volts of power. How do I figure this out? (been awhile since Physics...)

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Do you have the specs for the LED's? Nominal voltage and current? Typically, a 5mm LED will take around 60ma and 3 volts. Yours are 5 volt? Also, if your serious about an "even 5 volts", then you need a voltage regulator (not hard to do at all. RS has them in fixed output voltage ranges). You also need to calculate the wattage. Power (watts) is Voltage time current. So if ALL of your LED use 50ma each, and you have 10 of them. Then .050 x 10 = .5 amps, x 5 volts = 2.5 watts. Typical resistors are .25 watts.
(Note: Blue LED generally take more power than yellow or green LED. Just FYI)
(Nuther Note: Just FYI: depending in what your doing. be aware that you also want to consider the "diffusion" angle of the LED. As above. Blue LED have poor diffusion).
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