LED Series Resistor Calculator

LED Resistor Formula:

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

Supply Voltage:

volts

LED Voltage Drop:

volts

Number of LEDs:

Desired Current:

amps

Resistor Value (Ω):

Power Dissipation (W):

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1. What is an LED Series Resistor Calculator?

Definition: This calculator determines the appropriate series resistor value for LEDs based on power supply voltage, LED voltage drop, and desired current.

Purpose: It helps electronics enthusiasts and engineers properly limit current through LEDs to prevent damage and ensure proper operation.

2. How Does the Calculator Work?

The calculator uses Ohm's Law formula:

\[ R = \frac{V_{supply} - (V_{led} \times N)}{I} \]

Where:

\( R \) — Resistor value (ohms)
\( V_{supply} \) — Power supply voltage (volts)
\( V_{led} \) — Voltage drop across one LED (volts)
\( N \) — Number of LEDs in series
\( I \) — Desired current through LEDs (amps)

Explanation: The resistor value is calculated by subtracting the total LED voltage drop from the supply voltage, then dividing by the desired current.

3. Importance of LED Current Limiting

Details: LEDs require precise current control. Too much current can destroy the LED, while too little makes it dim. The series resistor provides this current limiting.

4. Using the Calculator

Tips: Enter the power supply voltage, LED forward voltage (typically 1.8-3.3V depending on color), number of LEDs in series, and desired current (usually 10-30mA for standard LEDs).

5. Frequently Asked Questions (FAQ)

Q1: Why do we need a series resistor for LEDs?
A: LEDs have very low internal resistance and would draw excessive current without a current-limiting resistor.

Q2: What's a typical LED forward voltage?
A: Red LEDs ~1.8-2.2V, Blue/White ~3.0-3.6V. Check your LED's datasheet for exact values.

Q3: What current should I use for standard LEDs?
A: 20mA is common for indicator LEDs, but high-power LEDs may require more (check specifications).

Q4: What if my calculated resistor value isn't available?
A: Use the next higher standard resistor value to ensure safe current.

Q5: How do I choose resistor power rating?
A: The calculator shows power dissipation - choose a resistor with at least double this wattage for safety.