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Calculates resistor value needed to limit current through an LED to safe operating levels. Prevents LED burnout and extends lifespan.
公式
Formula: R = (V - Vf) ÷ I
- R
- (V - Vf) ÷ I — (V - Vf) ÷ I
- V
- V value — Variable used in the calculation
- Vf
- Vf value — Variable used in the calculation
- I
- I value — Variable used in the calculation
ステップバイステップガイド
- 1Supply voltage (V)
- 2LED forward voltage (typically 1.5-3.5V)
- 3Desired LED current (typically 2-20mA)
- 4Formula: R = (V - Vf) ÷ I
- 5Select nearest standard resistor value
解いた例
入力
LED 2V, supply 5V, 20mA
結果
150ohm resistor
避けるべきよくある間違い
- ✕Using incorrect LED forward voltage for color
- ✕Not accounting for voltage supply variation
よくある質問
What happens without current limiting resistor?
LED draws maximum current, burns out immediately, and can damage power supply.
How do I select resistor wattage?
Power = V × I; select resistor rated 2× calculated power for safety margin.
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