Series LED Resistor Calculator

Series LED Resistor Formula:

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

Required Resistor (R):

Power Dissipation:

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1. What is the Series LED Resistor Calculator?

The Series LED Resistor Calculator helps determine the appropriate resistor value needed when connecting one or more LEDs in series with a power supply. It ensures the LEDs receive the correct current for optimal operation and longevity.

2. How Does the Calculator Work?

The calculator uses the following formula:

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

Where:

\( R \) — Required resistor value (Ω)
\( V_s \) — Supply voltage (V)
\( \sum V_{led} \) — Sum of voltage drops of all LEDs in series (V)
\( I \) — Desired current through LEDs (A)

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 Proper Resistor Calculation

Details: Using the correct resistor is crucial to prevent LED burnout (too little resistance) or insufficient brightness (too much resistance). The calculator also shows power dissipation to help select an appropriately rated resistor.

4. Using the Calculator

Tips:

Enter supply voltage in volts (e.g., 9V battery or 5V USB)
Sum the forward voltage of all LEDs in series (typically 1.8V-3.6V per LED depending on color/type)
Enter desired current in amps (common values: 0.01A-0.02A for indicator LEDs)
All values must be positive numbers

5. Frequently Asked Questions (FAQ)

Q1: What if my calculated resistor value isn't standard?
A: Use the next higher standard resistor value to ensure you don't exceed the LED's current rating.

Q2: How do I find my LED's forward voltage?
A: Check the LED's datasheet or use 2V for red, 2.1V for yellow/green, and 3-3.6V for blue/white LEDs as general estimates.

Q3: What happens if I don't use a resistor?
A: Without current limiting, most LEDs will draw excessive current and burn out almost instantly.

Q4: Can I connect multiple LEDs in parallel with one resistor?
A: It's not recommended as current may not divide evenly. Use separate resistors or connect in series.

Q5: How do I choose resistor power rating?
A: Select a resistor with power rating higher than the calculated dissipation (typically 0.25W or 0.5W for most LED circuits).