The breakdown region of a p n diode can be made very sharp and almost vertical Diodes with almost vertical breakdown region are known as Zever Diodes.

A zever diodes operating in the breakdown region is equivalent to a battery. Because of this current through zever diode can change but the voltage remains constant. It is this constant voltage that has made the zever diode an important device in voltage regulation.

VOLTAGE REGULATOR :

The output remains constant despite changes in input voltage due to Zever effect.   _{Your Comment}