Enter any three known values and press "Calculate" to solve for the other


Source Voltage (Vs): volts
Forward Voltage (Vf): volts
Forward Current (If): mAmps


Resistor (R): ohms
Power: watts

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Every LED (light emitting diode) has a current that they can safely handle. This calculator will help you determine the value of the resistor to add in series with the LED to limit the current.


Going beyond that maximum current, will damage the LED. Thus, limiting the current through the LED with the use of a series resistor is a common and simple practice. Note that this method is not recommended for high current LEDs, which need a more reliable switching current regulator.


To find the Resistor value:

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where, R = Resistor Value, Vs = Source Voltage, Vf = Forward Voltage, If = Forward Current.

To find the Power value:

Power = V f * I f

where, Vf = Forward Voltage, If = Forward Current.


1. Most of the processor/FPGA based Evaluation board will have user LED’s having current limiting resistors.

2. In FPGA once if you program the FPGA the done pin will goes high. This can be indicated with LED.

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