LED Resistor Calculator

How to Calculate LED Resistor Values

Calculating the correct resistor value for an LED circuit is crucial for proper operation and longevity of the LED. This process involves using Ohm's Law and considering the characteristics of both the power supply and the LED.

LED Resistor Formula

The basic formula for calculating the resistor value in an LED circuit is:

$$R=\frac{V_s-V_f}{I_f}$$

Where:

• R is the resistor value in ohms (Ω)
• V_s is the supply voltage in volts (V)
• V_f is the forward voltage of the LED in volts (V)
• I_f is the forward current of the LED in amperes (A)

Calculation Steps

1. Determine the supply voltage (V_s)
2. Find the forward voltage (V_f) of the LED from its datasheet
3. Identify the required forward current (I_f) for the LED
4. Calculate the voltage drop across the resistor (V_s - V_f)
5. Apply the formula to calculate the resistor value
6. Choose the nearest standard resistor value

Example Calculation

Let's calculate the resistor value for a circuit with:

• Supply voltage (V_s) = 5V
• LED forward voltage (V_f) = 2V
• LED forward current (I_f) = 20mA (0.02A)

Applying the formula:

$$R=\frac{5V-2V}{0.02A}=\frac{3V}{0.02A}=150\Omega$$

Therefore, a 150Ω resistor would be suitable for this LED circuit. However, since 150Ω is not a standard resistor value, you would typically choose the next higher standard value, which is 160Ω or 180Ω, to ensure the LED receives slightly less than its rated current, which is safer for the LED.

LED Circuit Diagram

This diagram illustrates a simple LED circuit. The voltage source (V_s) provides the power, the resistor (R) limits the current, and the LED emits light. The current flows from the positive terminal of the voltage source, through the resistor and LED, and back to the negative terminal. The resistor ensures that the LED receives the correct amount of current, protecting it from damage due to excessive current flow.