LED Resistor Rechner — Formel

## How to Size a Resistor for an LED

An LED needs a series resistor to limit current.

### Formula

**R = (V_supply - V_led) / I_led**

Where:
- **V_supply** = Source voltage
- **V_led** = LED forward voltage drop
- **I_led** = Desired LED current (commonly 20 mA)

Power dissipated in the resistor is **P = (V_supply - V_led) x I_led**.

Lösungsbeispiel

Drive a red LED (2.0 V forward) at 20 mA from a 5 V supply.

  1. Voltage across resistor = 5 - 2.0 = 3.0 V
  2. Current in amps = 20 / 1000 = 0.02 A
  3. R = 3.0 / 0.02 = 150 ohms
  4. Power = 3.0 x 0.02 = 0.06 W = 60 mW