LED Current Limiting Resistor Calculator

The Formulas

The formulas for calculating the LED current limiting resistor value and its power dissipation are:

\[Resistor Value (R) = \frac{Supply Voltage - LED Forward Voltage}{LED Forward Current}\] \[Power Dissipation (P) = (Supply Voltage - LED Forward Voltage) \times LED Forward Current\]

Where:

• Resistor Value (R): The resistance needed to limit the current (in ohms, Ω)
• Supply Voltage: The voltage of the power source (in volts, V)
• LED Forward Voltage: The voltage drop across the LED (in volts, V)
• LED Forward Current: The current flowing through the LED (in amperes, A)
• Power Dissipation (P): The power dissipated by the resistor (in watts, W)

Calculation Steps

1. Identify the supply voltage, LED forward voltage, and LED forward current
2. Calculate the resistor value using the first formula
3. Calculate the power dissipation using the second formula
4. Choose a resistor with the nearest standard value above the calculated resistance and with an appropriate power rating

Example Calculation

Let's calculate the resistor value and power dissipation for an LED circuit with:

• Supply Voltage: 5V
• LED Forward Voltage: 2V
• LED Forward Current: 20mA (0.02A)

\[R = \frac{5V - 2V}{0.02A} = 150Ω\] \[P = (5V - 2V) \times 0.02A = 0.06W\]

Visual Representation

This visual shows an LED circuit with the calculated resistor value and power dissipation based on our example calculation.