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LED Resistor Calculator

To use LED Resistor Calculator, enter the values, and hit calculate button

R = (Vs - VLED)lLED

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LED Resistor Calculator

LED Resistor Calculator finds the value of the resistor for the LED circuit to limit the current. This calculator provides accurate results and ensures the LED will operate safely without burning out due to overcurrent.

What is an LED Resistor?

Light Emitting Diodes (LEDs) are semiconductor devices. When a current passes through LEDs, it emits light in various colors, like red, green, and yellow. Excessive current can potentially damage the LED. It is common practice to use a series resistor to control the current flow and prevent damage.

Accurately calculating the series resistor is essential to choosing LED resistors that can handle the amount of current flowing through them to avoid damaging the circuit.

The manual calculation of LED series resistors carries the risk of errors that may result in circuit failures or even fires. Use our calculator to obtain precise calculations of LED resistance and power.

LED resister

LED Voltage Ranges for Different Colors

The following table shows some forward voltages of LEDs of different colors.

LED Color

VLED  Range

Red

1.8v - 2.1v

Orange

1.9v  -  2.2v

Yellow

1.9v  -  2.2v

Green

2v  -  3.1v

Blue

3v  -  3.7v

White

3v  -  3.4v

Calculation of LED Resistor

To calculate the value of the resistor needed to limit the current flowing through an LED, you can use the following equation:

R = (Vs - VLED)/lLED

Where:

  • R is the resistance of the resistor in ohms (Ω)
  • Vs is the source voltage in volts (V)
  • VLED is the forward voltage drop across the LED in volts (V)
  • ILED is the desired LED current in ampere (A)

Power Dissipation for LED Resistor

The power dissipation of an LED resistor is the power lost in the resistor while current is flowing through it. It is often measured in watts.

The formula for calculating power dissipation is

P = (Vs - VLED) x lLED

Choosing a resistor with a power rating that is at least 2 times the calculated power dissipation is recommended to ensure it can handle the heat generated.

Example of Resistor and Power Dissipation

To calculate the resistor and power manually, follow the below example. 

Example:

Calculate the resistor required for an LED with a forward voltage of 6 volts and a current of 15 mA when using a supply voltage of 9 V. Also, find the power of Dissipation.

Solution:

Give:

Source voltage (Vs) = 9V

Forward voltage drop across the LED (VLED) = 6V

LED current (ILED) = 15mA = 15 / 1000 = 0.015 A

We have to find the resistance and Power for the LED circuit.

∴ Resistance (R) = (Source voltage – Drop Voltage from LED) / LED current

R = (9 V - 6 V) / 0.015A

R = 3 / 0.015

R = 200 Ω

Therefore, a 200-Ohm resistor is required to limit the current to 15 milliamps.

To calculate the power of dissipation, we can use the formula:

Power = (Source voltage – Drop Voltage from LED) x LED Current  

P = (9 V - 6V) x 0.015 A

P = 0.045 Watts

Therefore, the power dissipated by the resistor is 0.045 Watts.

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