# Thread: Resistor Calculator

1. As it says on the "Tin":

2. Originally Posted by Lee Roberts
As it says on the "Tin":

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.
Last edited by ZeroCount; 17-03-2009 at 12:58 AM. Reason: Additional information

3. 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

4. ## The Following User Says Thank You to karul For This Useful Post:

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