This is a special diode operating in the steady-state mode of breakdown under conditions of reverse bias of the p – n junction.
The Zener Diode is used in its “reverse bias” or reverse breakdown mode, i.e. the diodes anode connects to the negative supply.
When a breakdown occurs, the current through the Zener diode rises sharply, and the voltage at the Zener diode is maintained with a given accuracy in a wide range of reverse currents
Zener diodes are widely used as independent stabilizing elements, as well as sources of reference voltages (reference voltages) in transistor stabilizers.
Sources:
https://www.electronics-tutorials.ws/diode/diode_7.html
https://en.wikipedia.org/wiki/Zener_diode
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