“The zener diode is a special type of diode designed to operate in the reverse bias direction and is used to stabilize or regulate a voltage”
As stated previously, a semiconductor junction diode blocks the flow of current in the reverse direction. However, if we increase the reverse voltage across the diode sufficiently high enough, the diode’s PN-junction will breakdown and the diode will become damaged allowing current to flow. The reverse voltage level at which this breakdown occurs is called the breakdown voltage, or peak reverse voltage.
A zener diode is a special type of diode that conducts normally in the forward-biased mode but is designed to operate in the reverse-biased mode so that at a certain breakdown voltage point, the reverse voltage causes the diode to conduct in a controlled way allowing a reverse current to flow through a series limiting resistor, (Rz). This breakdown voltage is called the zener voltage, (Vz).
The breakdown voltage point of a zener diode, Vz is determined by the resistivity of the diodes junction which is controlled by the doping technique used during its manufacture with zener breakdown voltages ranging from 2.7V to about 200V. The voltage across the zener diode, Vz, remains reasonably constant over a wide range of reverse currents passing through the zener diode.
Zener Diode I-V Characteristics
The zener diode has a region in its reverse bias characteristics of almost a constant negative voltage regardless of the value of the current flowing through the diode and remains nearly constant even with large changes in load current. This ability to control itself can be used to great effect to regulate or stabilize a voltage source against supply or load variations.