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