For what purposes are Zener diodes used?

For what purposes are Zener diodes used?
  1. Using Zener diodes as constant-voltage diodes
    The Zener voltage across a diode remains constant over a wide range of Zener current. Because of this property, Zener diodes are widely used as constant-voltage devices.
  2. Using Zener diodes as voltage detection devices
    A Zener diode permits Zener current, Iz, to flow when the voltage is above the specified Zener voltage.
    Thus, a Zener diode can be used for voltage detection by sensing Zener current with some other device.
  3. A Zener diode provides voltage clipping if it is used over the entire region highlighted as 1 and 2 in the following figure.
    It helps to clip all noise above a certain magnitude such as an electrostatic discharge.
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