The main function of current limiting resistor is to reduces the current flow in the circuit. Here we are talking about current limiting resistor with leds.
Required informations to calculate the value of resistor is
- Current rating of the led(I led)
- Forward voltage of led(Vf)
- Supply voltage (Vs)
That is R=(Vs-Vf)/I led
The necessary information will be included in the component datasheet like Vf,I led etc.
Example
Find the value of current limiting resistor for 5MM led with source voltage 5V.
Electrical characteristics of 5mm LED is given below.
If you wants to see the full datasheet clik here
Here we take Red led.
Vf=2.5V(We assumes a value between minmum and maximum)
I led=20mA
Our source volatage = +5V
Example
Find the value of current limiting resistor for 5MM led with source voltage 5V.
Electrical characteristics of 5mm LED is given below.
Here we take Red led.
Vf=2.5V(We assumes a value between minmum and maximum)
I led=20mA
Our source volatage = +5V
Vs-Vf = 5- 2.5 = 2.5V
R=2.5/20mA=125Ω
Here I provide a link that helps you to calculate the resistor value.LED Resistor Calculator
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