Tag: loadline

Loadline resistance graphic tool

Most LED circuits require a current limiting resistor.

R + LED on 5 V supply.
R + LED on 5 V supply.

The loadline calculator makes resistor selection very simple.

Loadlines for various resistors on 5 V supply.
Loadlines for various resistors on 5 V supply.

Example 1: Chose a resistor to give 20 mA on a yellow LED and 5 V supply.

Loadline 20 mA yellow.
Loadline for 20 mA yellow on 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.

Loadline 10 mA IR on 5 V supply.
Loadline 10 mA IR on 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.

Loadline 30 mA on a white LED.
Loadline 30 mA on a white LED.

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.