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

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

   
   
   

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