A Zener regulator in code

You will write four functions that describe a Zener regulator and its limits.

The idea. The series resistor carries $I_s = \dfrac{V_{in} - V_z}{R_s}$. The load takes $\dfrac{V_z}{R_L}$ and the Zener diode takes the rest. The limits on $R_s$ come from the worst cases of the input and of the load.

Your tasks.

1. In zener_current, return the Zener current in A for an input vin, a series resistor rs, a Zener voltage vz and a load rl.
2. In max_series_resistor, return the largest $R_s$ in ohm from vin_min, vz, iz_min and il_max.
3. In min_series_resistor, return the smallest $R_s$ in ohm from vin_max, vz, iz_max and il_min.
4. In regulates, return True if the Zener current is at least iz_min, and False if it is not.