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 $U_S=7.0 ... 13.0V$ (e.g. via sinusoidal input voltage with $f = 50 Hz$),
• series resistor $R_V=1.0k\Omega $
• load resistor $R_L=10k\Omega $
• Z-diode $D_Z$ as $BZX84C6V2$ ($U_Z = 6.2 V$)

An ideal (Z) diode would be assumed to hold the breakdown voltage $U_Z$ at all reverse currents $I_S$.
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 $U_L$ to $U_S$. In particular, measure the maximum and minimum values of $U_L$.
3. Change the load resistance to $R_L=1.0k\Omega $ and perform the same comparison of $U_L$ to $U_S$ again.
4. How can the difference be explained?