Nice post, and great information.

I have a couple points on the zener regulator circuit. You stated that, "The reverse biased zener diode is connected in parallel across the load to ensure that relatively constant output Voltage Vs is supplied across the load." I consider the output voltage Vz rather than Vs. I always consider Vs the source or supply, and Vz is the zener voltage, but that is just a label.

At any rate, while input voltage is a factor as you mentioned, regulation depends on the load current versus source current as shown in the equation. Is = Iz + I(load) The load resistor removes current from the zener diode, and the zener is considered regulated if zener current is above Izk (zener knee current). In other words if there is too much load current, the zener falls out of regulation.

The worst case as far as power dissipation for the diode is when the load is removed, or no load, as all of the current flows through the zener. Care must be taken if the load is removed that the zener can withstand Iz(max).

Again great topic, and I enjoyed the post! --3D