How to Power a LED
- 1). In order to calculate the resistance needed, Ohm's Law is used. Ohm's Law can be stated as V = I x R, where V is voltage, I is current and R is resistance. Since we are calculating resistance, we can rearrange the formula to read R = V ÷ I.
- 2). Plug the values you have into the formula. Performing the calculation will give you the value of the necessary resistor.
- 3). For example, suppose you have a 12 V supply, a white LED with a forward voltage of 3.4 V, and a current of 20 milliamps (0.020 amps.) First calculate the voltage by subtracting 3.4 from 12, giving 8.6.
- 4). Now calculate the following: R = 8.6 ÷ 0.020, or 430 Ω (ohms.)
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