I certainly agree with you that a Zener diode could be used in the typical Zener regulator circuit, but it would be slightly more helpful to point to his mistake. In his example Vin=5V, Vout=3.3V ...

The circuit does not require an AC power transformer. Instead, the voltage is reduced by series capacitor (C1) connected directly to the 230V AC mains voltage. The AC mains voltage is rectified by ...

Transistor VT2 provides the regulator short-circuit protection. ... The circuit is similar to using a Zener diode for voltage regulation.

If you tie the reference pin to the cathode, the TL431 does behave like a zener diode that has a breakdown voltage of 2.5 V, ... “The basic circuit is a voltage regulator, ...

R 1 ‘s voltage drop limits the zener diode’s voltage value that the circuit measures. If R 1 ‘s value is 1Ω, then the voltage drop across it is insignificant and, in millivolts, is equal to the zener ...

For each diode, the analysis is then linked to the corresponding SPICE model. Finally, the power diode losses - both on-state losses and switching losses - are examined in a converter circuit, ...