In a voltage reference circuit, a Z-diode enables - despite a fluctuating input voltage - an output voltage to be kept relatively constant.
In the simplest case, a circuit as shown on the right can be used for this purpose. The following quantities are to be used for the task:

• Source voltage $U_{\rm S}=7.0 ... 13.0~\rm V$ (e.g. via sinusoidal input voltage with $f = 50 ~\rm Hz$),
• series resistor $R_{\rm V}=1.0~\rm k\Omega $
• load resistor $R_{\rm L}= 10~\rm k\Omega $
• Z-diode $D_\rm Z$ as $\rm BZX84C6V2$ ($U_\rm Z = 6.2 ~\rm V$)

An ideal (Z) diode would be assumed to hold the breakdown voltage $U_\rm Z$ at all reverse currents $I_\rm S$.
This is to be checked for the real diode.

1. Model the circuit in Tina TI and insert a picture of the circuit.
2. Compare the progression of $U_\rm L$ to $U_\rm S$. In particular, measure the maximum and minimum values of $U_\rm L$.
3. Change the load resistance to $R_\rm L=1.0~\rm k\Omega $ and perform the same comparison of $U_\rm L$ to $U_\rm S$ again.
4. How can the difference be explained?