LED Resistor Calculator:
Enter the values of forward voltage of the LED, Vl(V), supply voltage, Vs(V) and desired current, IL(A) to determine the value of Resistance, R(Ω).
LED Resistor Formula:
An LED (Light Emitting Diode) resistor is a crucial component used to limit the current flowing through an LED to ensure its longevity and prevent damage.
LEDs are current-sensitive devices and require a resistor to control the current since excessive current can overheat and destroy the LED.
The resistor is typically connected in series with the LED in a circuit. The role of the resistor is to drop the excess voltage that the LED does not require. The value of the resistor depends on the supply voltage, the forward voltage of the LED, and the desired current in the LED.
The forward voltage is the voltage required for the LED to emit light, which varies by LED type (e.g., red, blue, or white). The desired current is the safe operating current for the LED, typically measured in milliamperes (mA).
To calculate the required resistor value (R), subtract the forward voltage of the LED from the supply voltage and divide the result by the desired current. This calculation ensures that the resistor limits the current to a safe level while maintaining proper brightness for the LED.
Resistance, R(Ω) in Ohms is calculated by subtracting the forward voltage of the LED, Vl(V) in volts from the supply voltage, Vs(V) in volts and then divide the result by the desired current, IL(A) in amperes flowing through the LED.
Resistance, R(Ω) = Vs(V) – Vl(V) / IL(A)
R(Ω) = resistance in Ohms, Ω.
Vs(V) = supply voltage in volts, V.
Vl(V) = forward voltage in volts, V.
IL(A) = desired current in amperes, A.
LED Resistor Calculation:
1.Given: Vs(V) = 9V, Vl(V) = 2V, IL(A) = 0.02A.
Resistance, R(Ω) = Vs(V) – Vl(V) / IL(A)
R(Ω) = 9 – 2 / 0.02
R(Ω) = 7 / 0.02
R(Ω) = 350 Ω.
2.Given: R(Ω) = 220 Ω, Vl(V) = 3.3V, IL(A) = 0.015A.
Resistance, R(Ω) = Vs(V) – Vl(V) / IL(A)
Vs(V) = R(Ω) * IL(A) + Vl(V)
Vs(V) = 220 * 0.015 + 3.3
Vs(V) = 3.3 + 3.3
Vs(V) = 6.6V.