Calculators for LED Series Resistor

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Whenever using a LED (Light Emitting Diode) a series resistor is required to limit the current flowing through the diode and thereby limiting the applied voltage to the diode.
These calculators allow you to find a suitable resistor for a given supply voltage and LED (or multiple LEDs in series).

"Forward" calculation: find series resistor Rs

The supply voltage × amount of LEDs in series needs to be > the forward voltage per LED.

Inputs
Supply voltage [V] (> 0)
LEDs in series (> 0)
Forward voltage per LED [V] (> 0)
Total forward current of LED(s) [mA] (> 0)
Result
Required series resistor [Ω]
Power dissipation of resistor [mW]

"Backward" calculation: find forward current If

The supply voltage × amount of LEDs in series needs to be > the forward voltage per LED.

Inputs
Supply voltage [V] (> 0)
LED(s) in series (> 0)
Forward voltage per LED [V] (> 0)
Series resistor [Ω] (> 0)
Result
Total forward current of LED(s) [mA]
Power dissipation of resistor [mW]

Illustration:

Illustration LED Series Resistor

"Forward" calculation: find series resistor Rs

Formula LEDs forward calculation

"Backward" calculation: find forward current If

Formula LEDs backward calculation

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