Calculating Resistor Value For LED

LED Resistor Formula:

\[ R = \frac{V_{supply} - V_{led}}{I_{led}} \]

Resistor Value (R):

Unit Converter ▲

Unit Converter ▼

From:	To:

1. What is the LED Resistor Calculation?

The LED resistor calculation determines the appropriate resistor value needed to limit current through an LED when connected to a power supply. This prevents the LED from burning out due to excessive current.

2. How Does the Calculator Work?

The calculator uses the LED resistor formula:

\[ R = \frac{V_{supply} - V_{led}}{I_{led}} \]

Where:

\( R \) — Resistor value in ohms (Ω)
\( V_{supply} \) — Supply voltage in volts (V)
\( V_{led} \) — LED forward voltage drop in volts (V)
\( I_{led} \) — Desired LED current in amperes (A)

Explanation: The formula calculates the resistor needed to drop the excess voltage (supply voltage minus LED voltage) at the desired current.

3. Importance of Proper LED Resistor Selection

Details: Selecting the correct resistor is crucial for LED longevity and proper brightness. Too little resistance allows excessive current that can damage the LED, while too much resistance results in dim operation.

4. Using the Calculator

Tips: Enter the supply voltage, LED forward voltage (typically 1.8-3.3V depending on LED color), and desired current (typically 0.01-0.03A for standard LEDs). All values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What if my calculated resistor value isn't a standard value?
A: Use the next higher standard resistor value to ensure the LED current doesn't exceed the desired level.

Q2: How do I determine the LED forward voltage?
A: Check the LED datasheet. Typical values are: red (1.8-2.2V), yellow (2.0-2.4V), green (2.2-3.3V), blue (2.5-3.7V), white (3.0-3.6V).

Q3: What's a typical current for standard LEDs?
A: Standard 5mm LEDs typically operate at 20mA (0.02A), but always check the specific LED's datasheet for maximum ratings.

Q4: Can I use this calculator for multiple LEDs?
A: For series connections, sum the LED voltages. For parallel connections, calculate resistors for each LED separately.

Q5: What about resistor power rating?
A: Calculate power using P = I²R and select a resistor with at least twice the calculated power rating for safety.