Calculate the current-limiting resistor for one or more LEDs. Picks the next higher standard E-series value so the LED is never overdriven, and recommends a resistor power rating with a 2ร safety margin.
LED Type
Standard Resistor (E12)
150 ฮฉ
Exact: 150 ฮฉ ยท Rating: 1/8 W or higher
Actual LED Current
20 mA
With the standard resistor value
Voltage across resistor 3 V
Power in each resistor 60 mW
Power in LEDs (total) 40 mW
Total current from supply 20 mA
Total power from supply 100 mW
Efficiency 40.0 %
R = (Vs โ Vf) / I = (5 V โ 2 V) / 20 mA = 150 ฮฉ