You want to drive a red light-emitting diode on a voltage source of $U_{\rm s} = 5.0 ~\rm V$ with a current of $I_{\rm D} = 20 ~\rm mA$. On the web, you have found a voltage drop of $U_{\rm D} = 2.3 ~\rm V$ for red LEDs. Now you want to know which resistor from the E12 series (available to you) is the correct one.

1. Draw the circuit of the LED with a series resistor and plot the voltages.
2. What must be the value of the series resistor $R_\rm V$ to give the voltage drop $U_\rm S$ above?
3. In the red LED datasheet TLUR6400, find the relationship between forward voltage and forward current. What voltage drop $U_\rm D$ can be determined from this for $I_{\rm D} = 20 ~\rm mA$ and what is the correct series resistance?

   
   
   

4. Briefly compare the different results considering the E12 series.