This calculator finds the resistor value to be used with an LED and a +5 Volt supply. It also provides the power dissipation in the resistor – an important number for resistor selection.
[ez-toc]
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 = 5 Volt.
Example Calculation
The data sheet for a diode can be used to find its forward voltage and current.
For this diode, Vf = 2.1 V and we use I = 10 mA.
Use these values in the calculator above to find a resistor value of 290 Ohm. Approximately 29 mW of power is dissipated in the resistor.
Referring to this datasheet, any of the resistors below can be used. The 0402 resistor for instance, is able to dissipate 63 mW of power which provides adequate margin.
Summary
For a supply voltage of 5V and a forward voltage of 2.1V, a 290 ohm series resistor should be used to provide a forward current of 10 mA.