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Light-Emitting Diode (LED)
f-alpha.net » Electronics » Optoelectronics » Light-Emitting Diode (LED) » Let's go... » Experiment 3 - Current-Limiting Resistor

Experiment 3 - Calculation of the Current-Limiting Resistor

Look to the Circuit diagram shown. You want to calculate the resistance of the current-limiting resistor Rv. According to Ohm's law...

Rv = Uv ÷ I

With Kirchhoff's Voltage Law (KVL) you can calculate Uv...

Uv = ( U0 - ULED )

and calculate the current-limiting resistor Rv of the LED...

Rv = ( U0 - ULED ) ÷ I

Circuit diagram calculation current-limiting resistor.

Assuming the maximum forward current is 20 mA, you might want to limit the current to 15 mA. Hence you calculate ...

Rv = ( U0 - ULED ) ÷ I

     = ( 9 V - 2.0 V ) ÷ 0.015 A

     = 466 Ω

Maximum forward current

You can find the maximum forward current of your LED in data sheets.

Since you can not find a standard resistance of 466 Ω, you use the next higher resistance of 470 Ω.

Next, you look at several LEDs in a circuit.

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