PAGE 038 OF 150 · POWERING LEDS
Powering an LED from 5 V USB
USB's 5 V suits most single LEDs with a resistor.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Why 5 V is popular
USB supplies a steady 5 V that suits red, yellow, green, blue and white LEDs with a resistor.
Resistor examples at about 10 to 14 mA
- Red, Vf 2 V: 3 V across the resistor, 220 ohms gives about 13.6 mA.
- White, Vf 3.2 V: 1.8 V across the resistor, 150 ohms gives 12 mA.
Safety
A USB port can supply hundreds of milliamps, so it will not limit LED current for you. Always include the resistor, and avoid shorting the supply lines.
REMEMBER
The resistor sets the current, so the resistor sets the safety.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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