This calculator finds the resistor value to be used with a LED (Light Emitting Diode) and a +24 Volt supply.
It also provides the power dissipation in the resistor – an important number for resistor selection.
Table of Contents
Table of Contents
LED Resistor Calculator
To find the resistor, enter the following for the LED
- Forward Voltage (Vf)
- Current (I)
LED Resistor Formula
R = (V-Vf)/I
In this case V = 24 Volt.
Example Calculation
The data sheet for a diode can be used to find its forward voltage and current.
For the diode with characteristics shown below, Vf = 2.1 V and we use I = 10 mA.
Use these values in the calculator above to find a resistor value of 2.19 kOhm. Approximately 220 mW of power is dissipated in the resistor.
Referring to the resistor data below only the 1206 size resistor rated at 250 mW can be used. The others are rated lower and hence would be damaged by the amount of current through the circuit.
Summary
For a supply voltage of 24V and a forward voltage of 2.1V, a 2.19 kOhm series resistor should be used to provide a forward current of 10 mA.