Resistance Formula:
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Definition: This calculator determines the appropriate resistor value needed to safely limit current through an LED circuit.
Purpose: It helps electronics hobbyists and engineers prevent LED damage by calculating the correct series resistor.
The calculator uses Ohm's Law formula:
Where:
Explanation: The resistor value is calculated by subtracting the LED's voltage drop from the supply voltage, then dividing by the desired current.
Details: LEDs require precise current control. Without proper current limiting, LEDs can burn out instantly or degrade quickly.
Tips: Enter the supply voltage, LED voltage drop (default 2.1V for standard red LED), and desired current (default 20mA). All values must be > 0 and supply voltage must be greater than LED voltage.
Q1: What happens if I don't use a current limiting resistor?
A: The LED will draw excessive current, potentially burning out immediately or significantly reducing its lifespan.
Q2: What's a typical LED current?
A: Most standard LEDs operate at 20mA (0.02A), but high-power LEDs may require more (check datasheet).
Q3: How do I find my LED's voltage drop?
A: Check the datasheet or use these typical values: Red=1.8-2.1V, Blue/White=3.0-3.5V, Green/Yellow=2.1-2.4V.
Q4: What if my calculated resistor isn't a standard value?
A: Use the next higher standard resistor value to ensure safe current levels.
Q5: How do I calculate resistor power rating?
A: Power = I²R. For safety, choose a resistor rated for at least twice the calculated power.