This diagram is from https://www.homemade-circuits.com/simple-voltage-regulator-circuits-using-transistor-and-zener-diode/
The article says that when the input voltage exceeds the zener diode's rating, current will pass through the zener diode and that this will somehow cause the input voltage to drop and therefore cause the output voltage to do the same.
Why does the voltage drop? There is a current limiting resistor stopping the input source from being overburdened, and if there wasn't, that would be a short circuit.
Also, how does this circuit relate to a chopper circuit?
Best Answer
Easy one first:
Unrelated. The chopper chops, i.e., there's some kind of control that turns a switch (e.g. a transistor) on and off. There's nothing like that in here, it's not a switch-mode power supply.
The current through a diode grows very quickly if you increase the voltage after you've crossed the breakdown voltage. A little more voltage, way, way, way more current.
Way, way, way more current has to come from somewhere: it must flow through your orange resistor. That means way, way, way more voltage drop across that resistor, so that the voltage across the zener doesn't increase very much. That's the "regulated voltage".
(It's not a great regulator. If I see a design where anyone uses this, unless it's a very special case, it's probably a very bad design. Don't do this in the wild, there's always a better way. All the circuits on the page you've linked to have been obsolete since ca the early 1970's. Also, they are colorized scanned photocopies of photocopies of copies from copies ... maybe find a better source for schematics, honestly.)
Well, that resistor is half of the regulating mechanic, the other half being the Zener diode.