Zener Diode

This is a special kind of diode which permits current flow not only in forward direction, but also in reverse direction. A normal diode, when operated in reverse bias, gets damaged if the reverse current above a certain value is passed through it. This “certain value” is called as the Breakdown voltage.

The breakdown voltage of a Zener diode is very low. But this diode allows the reverse current to pass through it, once this breakdown voltage is exceeded. That breakdown voltage is called as Zener Voltage. Hence there is a controlled breakdown which does not damage the diode when a reverse current above the Zener voltage passes through a Zener diode.

A Zener diode in its reverse bias, exhibits a controlled breakdown voltage and it allows the current flow to keep the value of voltage across that Zener diode close to the Zener breakdown voltage value. This value of Zener breakdown voltage makes any Zener diode to be chosen for certain applications.

Avalanche diode is another diode which has the similar characteristics of Zener diode. The avalanche breakdown takes place across the entire PN junction, when the voltage drop is constant and is independent of current. This avalanche diode is used for photodetection.

Characteristics of a Zener diode

The V-I Characteristics of a Zener diode are common for any diode when operated in forward bias. But the reverse bias operation of a Zener diode makes it very important to consider. Let us have a look at the graph.

The point where the bent is shown in the reverse bias operation, is the Zener breakdown voltage, after which the diode allows high reverse currents through it. This Zener voltage is indicated by V_Z. This incredible quality of Zener diode made it the most reliable one and have got many applications too.

Applications of Zener diode

This diode has many applications such as −

• It is mostly used as a Voltage Regulator.
• Provides fixed reference voltage in transistor biasing circuits.
• For peak clipping or limiting in wave shaping circuits.
• As a Surge protector in many circuits.
• For meter protection against damage from accidental applications.