zener diode

Zener diode

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Definition

A Zener diode is a heavily doped PN junction diode that is designed to operate in the reverse breakdown region

A Zener diode is a special purpose p-n junction diode that is designed to operate in the reverse direction. When reverse voltage applied across the Zener diode (anode terminal is negative w.r.t cathode terminal) and the potential reaches the Zener Voltage (knee voltage), the junction breaks down and the current flows in the reverse direction. This effect is known as the Zener Effect.

The breakdown voltage of a Zener diode is carefully set by controlling the doping level during manufacture.

The name Zener diode was named after the American physicist Clarence Melvin Zener who discovered the Zener effect.

Read More What is Diode and its Working?

Read More V-I characteristics of p-n junction diode.


Symbol of Zener diode

Symbol of Zener diode

Circuit Diagram or layer structure of Zener Diode

Zener diode is always connected in reverse direction because it is specifically designed to work in reverse direction. The reverse biasing means the anode of the diode is connected to the positive terminal of the supply and the cathode is connected to the negative terminal of the supply. The depletion region of the diode is very thin because it is made of the heavily doped p and n type semiconductor material.

Circuit diagram or layer structure of Zener diode

Zener diode video explained in Hindi.


Working of Zener Diode

Zener diode is heavily doped than the normal p-n junction diode. Hence, it has very thin depletion region.

When Zener diodes work in forward biased condition it work like a normal p-n junction diode. However, In reverse biased condition a small leakage current flows through the diode. This current is called reverse leakage current or also called reverse saturation current.

If this reverse biased voltage across the diode is increased continually, high electric field develop across the junction. This strong electric field break all the covalent near the junction and the junction breakdown and a large reverse current starts flowing through the diode. This large reverse current may damage the diode. To protect the diode from damage a resistance is connected in series with Zener diode that resistance is called current limiting resistance (Rs). This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage (Vz). If the applied reverse voltage across the diode is more than Zener voltage, the diode provides a conductive path to the current through it. Hence there is no chance of further avalanche breakdown in it.


V-I characteristics of Zener diode

The VI characteristic of the Zener diode is shown in the figure below. When the diode is connected in forward bias, this diode work like a normal diode. But When a reverse voltage is applied across the diode. initially a small reverse saturation current Io flows across the diode. As the reverse voltage is increased, at a certain value of reverse voltage, the junction will be breakdown and drastically a large reverse current flow through the device. This breakdown is called Zener breakdown. The voltage at which this breakdown occurs is called Zener voltage.

VI characteristics of Zener Diode

Application of Zener Diode

The Zener diode is mostly used as a voltage regulator or voltage stabilizers, voltage reference, clipping circuits, overvoltage protection etc.

  • Zener diode is used as a voltage regulator or voltage stabilizers: The Zener diode is used for regulating the output voltage. It provides the constant output voltage from the fluctuating input voltage. The Zener diode is connected in parallel across the load and maintain the constant voltage VZ and hence stabilizes the voltage.

Read More: Zener Diode as a Voltage Regulator

  • Zener diodes are used in clipping circuits: Zener diodes are used to modify or shape AC waveform clipping circuits. The clipping circuit limits or clips off parts of one or both of the half cycles of an AC waveform to shape the waveform or provide protection.
  • Zener diode in overvoltage protection: If the input voltage increases to a value higher than the Zener breakdown voltage, current flows through the diode and create a voltage drop across the resistor; this triggers the SCR and creates a short circuit to the ground. The short circuit opens up the fuse and disconnects the load from the supply.

English video on what is Zener Diode?

https://youtu.be/Gv1Oj7XYeM0

Frequently Ask Questions FAQ’s –

What is Zener Diode?

A Zener diode is a heavily doped PN junction diode that is designed to operate in the reverse direction.

What is Zener Breakdown?

The Zener breakdown mainly occurs because of a high electric field. When the high electric-field is applied across the PN junction diode, then the electrons start flowing across the PN-junction. Consequently, expands the little current in the reverse bias.

What is differenece between Zener Diode and normal P-N junction diode?

The main difference between a normal P-N junction diode and Zener diode is normal P-N Junction allows current to flow only in one direction while Zener diode allows current to flow in both directions.

Applications of Zener Diode

Zener diodes are used for voltage regulation, as reference elements, surge suppressors, and in switching applications and clipper circuits.

Advantages of Zener Diode

Power dissipation capacity is very high
• High accuracy
• Small size
• Low cost

What is current limiting resistance?

To protect the diode from damage a resistance is connected in series with Zener diode that resistance is called current limiting resistance (Rs).

What is Zener Voltage?

The breakdown voltage in the Zener diode when connected in the reverse biased is called Zener voltage.
The Zener diode holds its Zener voltage so steady and constant, it has huge application in circuits, most importantly, voltage regulation.


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