you need
  • Handbook of light emitting semiconductor devices, knowledge of standard denominations resistors (series E6, E12, E24, E48), or access to the Internet to obtain the necessary data.A piece of paper with a pen and calculator.
Learn electrical parameters of LEDs used.To calculate the resistor, it is necessary to know the forward voltage and rated current of the device.Knowing the model in the directory or on the Internet to find the required parameters.Remember or write down th
eir value.
Determine power supply voltage, which will be powered LED.If the power supply is supposed to use electrochemical cells or batteries, their rated voltage.If the LED is to be powered by a circuit with a large spread-voltage (for example, the grid of the car), to determine the maximum possible voltage circuit.
Calculate resistance to LED .Make the calculation according to the formula R = (Vs - Vd) / I, where Vs - the supply voltage, Vd - LED forward voltage, and I - the rated current.Pick the next higher resistance value in a nominal series resistances.It makes sense to use a range of E12.The tolerance in the nominal resistance of the series is 10%.Thus, if the calculated resistance value R = 1011 ohms, as a real impedance must be set to 1200 ohms.
Calculate the minimum power required damping resistor.Calculate the value of the formula P = (Vs - Vd) ² / R. The values ​​of variables Vs and Vd values ​​are similar to the previous step.The value of R - resistance is , calculated earlier.