Most LED circuits require a current limiting resistor.
The loadline calculator makes resistor selection very simple.
Example 1: Chose a resistor to give 20 mA on a yellow LED and 5 V supply.
Solution: Choose 20 mA on the If axis. Slide across to the yellow LED curve. Find the nearest loadline: in this case it’s 120 Ω.
Example 2: Chose a resistor to give 10 mA on an infrared LED and 5 V supply.
Solution: Choose 10 mA on the If axis. Slide across to the IR LED curve. Find the nearest loadline: in this case it’s 390 Ω.
Example 3: Chose a resistor to give 30 mA on a white LED and 5 V supply.
Solution: Choose 30 mA on the If axis. Slide across to the white LED curve. Find the nearest loadline: in this case it’s between 50 and 68 Ω. 56 is the nearest standard value.