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Light-Emitting Diode (LED)
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# 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. Experiment 4 - Parallel Circuit

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