Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.
The load voltage equals breakdown voltage VZ of the diode. The series resistor limits the current through the diode and drops the excess voltage when the diode is conducting.
Zener diode in overvoltage protection
If the input voltage increases to a value higher than the Zener breakdown voltage, current flows through the diode and create a voltage drop across the resistor; this triggers the SCR and creates a short circuit to the ground. The short circuit opens up the fuse and disconnects the load from the supply
Zener Diode Clipping Circuits
Zener diodes are used to modify or shape AC waveform clipping circuits. The clipping circuit limits or clips off parts of one or both of the half cycles of an AC waveform to shape the waveform or provide protection.