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Lee Roberts
16-03-2009, 12:50 PM
As it says on the "Tin":

http://www.ilewis.plus.com/images/leds/tn_calcnote1.jpg

:beer:

ZeroCount
17-03-2009, 12:51 AM
As it says on the "Tin":

http://www.ilewis.plus.com/images/leds/tn_calcnote1.jpg

:beer:

Just be careful, that equation assumes the LED requires 20 milli Amps of current, the proper equation is (Vsupply - Vled) = IR, or R = (Vsupply - Vled) / I in this case. V is in Volts, I is in Amps, and R in Ohms.

20 mA = 0.020 Amps.

Some minature LEDs go pop on less than 20mA :)

Technically speaking LEDs require a certain current, not a certain voltage, so it is possible to run a LED from a higher voltage supply without a current limiting resistor, as long as the supply is switched so that the average current is at or below the LEDs forward current.

karul
17-04-2012, 06:22 AM
I'm using this online calculator - you will also get the power requirements for the resistor - it calculates the Wattage of the resistor - depending of the voltage of the circuit

http://led.linear1.org/1led.wiz