Series LED Resistor Calculator

What Is a Series LED Resistor Calculator?

A series LED resistor calculator is used to determine the resistor value needed for multiple LEDs connected in series. In this configuration:

• Current remains constant across all LEDs.
• Voltage adds up for all LEDs.
• A single resistor is placed in series with the LEDs to limit current.

This calculator simplifies the process by using Ohm’s Law and the LED voltage values to find the ideal resistor.

How to Calculate Resistors for LEDs in Series

To calculate the correct resistor, input the following values:

• Source Voltage (): The voltage from your power supply.
• LED Voltage (): The forward voltage of a single LED.
• LED Current (): The recommended operating current for the LED (in mA).
• LED Count (): The number of LEDs in the series circuit.

Formula for Calculating Resistor Value

• Voltage Drop across the resistor:

• Resistor Value (Ω):

• Power Dissipation (W):

In a series LED circuit, the current flowing through the resistor and all LEDs is identical. For example, if your LED current () is 20mA, the same 20mA will pass through the resistor. This simplifies calculations since you only need to determine the resistor value once for the entire chain.

Example: Series LED Resistor Calculation

Example 1: Single Resistor for 3 LEDs in Series

• Source Voltage (): 12V
• LED Voltage (): 2V
• LED Current (): 20mA (0.02A)
• LED Count (): 3

Step-by-Step Calculation:

1. Total LED Voltage:
2. Voltage Drop Across Resistor:
3. Resistor Value:
4. Power Dissipation:

(A ¼-watt resistor is sufficient.)

Example 2: Series Resistor Calculation for 4 High-Power LEDs

• Source Voltage: 24V
• LED Voltage: 3.2V
• LED Current: 350mA (0.35A)
• LED Count: 4

Calculation:

1. Total LED Voltage:
2. Voltage Drop Across Resistor:
3. Resistor Value:
4. Power Dissipation:

(A 5W resistor is recommended for safety.)

If your project involves LEDs wired in parallel instead, try our Parallel LED Resistor Calculator for accurate resistor values

FAQs