ENGINEERING · FREE TOOL
DC LED series-resistor planner
Choose an E12 or E24 series resistor from nominal low-voltage DC inputs.
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R = (supply voltage − LED count × forward voltage) / current in amperes. The tool rounds resistance up to the next E12 or E24 nominal value, then recalculates current and resistor dissipation. At 5 V, one 2 V LED and 20 mA, the result is 150 Ω and 0.06 W. A nominal 2× power screen asks for at least 0.12 W; the first listed rating is 0.125 W.
The rating list is 0.125, 0.25, 0.5, 1, 2, 3, 5, 10 and 25 W. Available products may differ. The 2× screen does not replace thermal derating or worst-case design: check supply variation, forward-voltage spread, resistor tolerance, ambient temperature and LED maximum current in actual datasheets.
References: DigiKey LED resistor calculation and Vishay preferred values. The tool does not choose components for you or guarantee their suitability.