Electrical

LED Current-Limiting Resistor Circuit

Electrical Diagrams · made in Skemio

Ladder circuit schematic showing a 9V battery powering a switch, 330 ohm resistor, red LED, and ammeter measuring 21 mA in series.
Ladder circuit schematic showing a 9V battery powering a switch, 330 ohm resistor, red LED, and ammeter measuring 21 mA in series.
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What it shows

  • LED forward current surges exponentially beyond its forward voltage knee.
  • Ohm's law formula: R = (V_supply - V_forward) / I_target.
  • Round up to the nearest standard E24 resistor value to stay safe.

The takeaway

Always drop excess supply voltage across a series resistor to prevent thermal runaway.

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