Using the circuit in Figure 1. compute the resistance RL for which VL value is at 20% of the Zener voltage VZ.
First, we obtain the necessary values from 1N4735 datasheet:
We can compute now the desired value for VL:
At 1.24V voltage drop, the Zener diode is off (high impedance state, no current flowing though it), therefore the circuit becomes a simple resistive divider.
Knowing the differential input voltage VIN=10V, Rs=1KΩ we can compute RL as follows: