Why Use a Resistor with LEDs?
LEDs are current-sensitive devices that can burn out if not protected. A resistor limits the current passing through the LED to a safe level, preventing damage and ensuring a long lifespan.
LED Resistor Calculation Formula
To calculate the appropriate resistor value for your LED circuit, use the formula:
R = (Vsupply - VLED) / ILED
- Vsupply: Supply voltage (e.g., 5V, 12V)
- VLED: Forward voltage of LED (usually 2V–3.2V depending on color)
- ILED: Desired current in amperes (typically 20mA = 0.02A)
Online LED Resistor Calculator
Use this online calculator to quickly determine the correct resistor value:
Example Calculations
Here are some common examples:
| Supply Voltage (V) | LED Voltage (V) | LED Current (A) | Required Resistor (Ω) |
|---|---|---|---|
| 5V | 2V | 0.02 | 150Ω |
| 12V | 3.2V | 0.02 | 440Ω |
| 9V | 2.2V | 0.015 | 453Ω |
LED Resistor Value Chart (Quick Reference)
For quick designs, refer to the chart below:
Video Tutorial
Watch this video for a visual explanation on calculating and connecting LED resistors:
Frequently Asked Questions
Q: What happens if I use no resistor with an LED?
A: The LED may draw excessive current, heat up, and burn out quickly.
Q: Can I use a higher value resistor?
A: Yes, but it will reduce the brightness of the LED.
Q: Can I connect multiple LEDs to one resistor?
A: Only if they are in series. For parallel connections, each LED should have its own resistor.
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Recommended Reading: Ultimate Guide to Resistors
