Electronics & Circuits
Basic

LED Series Resistor

Resistor to safely drive an LED.

Formula

R=Vs−VfIR = \frac{V_s - V_f}{I}

Variables

V_sSupply
V_fLED forward voltage
ILED current

Example

(5−2)/0.02 = 150Ω

Did You Know?

LEDs need a series resistor because, unlike bulbs, they draw runaway current and burn out without one.

ledresistorcurrent limit