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LED TROUBLE

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windozeuser

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I Know How To Calculate the Resistor Values of led's connected in series but how do u do it for parallel

I Got 4 led's with a operating voltage of 1.8 volt's each at 20 milliamps
I Need To Run This From A 12 volt Source


4 led's * 1.8 volts = 7.2 volts Led's Require 7.2 Volts in series

12 vdc - 7.2 volts = 4.8 volts Isnt Needed

R = 4.8 volts / 0.02 amp = 240 ohm :)

So I Would Need a 240 Ohm Resistor To Power These Led's Safely. But How Would I Do This In A Paralel Config.
 

Exo

Active Member
windozeuser said:
I Know How To Calculate the Resistor Values of led's connected in series but how do u do it for parallel

I Got 4 led's with a operating voltage of 1.8 volt's each at 20 milliamps
I Need To Run This From A 12 volt Source


4 led's * 1.8 volts = 7.2 volts Led's Require 7.2 Volts in series

12 vdc - 7.2 volts = 4.8 volts Isnt Needed

R = 4.8 volts / 0.02 amp = 240 ohm :)

So I Would Need a 240 ohm Resistor To Power These Led's Safely. But How Would I Do This In A Paralel Config.
Leds require 1.8V in parallel
12 vdc - 1.8 volts = 10.2 volts isn't needed

Need the TOTAL current for 4 leds in parallel
4 * 0.020 Amps = 0.080 Amps

R = 10.2volts / 0.080 Amps = 127.5 ohm -> E12 = 120ohm connected to power supply and 4 leds in parallel behind this resistor

OR

1 led * 1.8 volts = 1.8 volts Leds require 1.8Volts in parallel

12 vdc - 1.8 volts = 10.2 volts isn't needed

R = 10.2 volts / 0.02 amp = 510ohm -> E12: 470 or 560ohm between each led - 4 resistors
 
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