Definition of Zener Diode

A Zener diode is a specific type that permits current flow in one direction only and features a low breakdown voltage. This makes them ideal for use as voltage regulators in electronic circuits. They will maintain a stable voltage output regardless of the level of input current or stress placed on them. Zener diodes are also employed as sensing devices in temperature transducers. The property of this diode was invented by a man named Clearance Zener and named after him as a sign of respect. This is simply a single reverse-biased diode, and the circuit shown can positively reverse-bias the Zener diode. 

Zener Diode: Which symbol is Used? 

Mainly used for high power consumption, this diode can be encapsulated in various ways, including surface mount formats. A glass capsule encloses the most commonly used type of Zener diode. At one end of this glass, there is a band around the cathode side of the diode, which is marked. The bands around the package correspond to the rows of symbols, making it easier to remember the diode connections. The Zener diode circuit symbol includes two tags at the end of the bar, one in the upward direction and the other in the downward direction. As a result, it aids in distinguishing these diodes from other types of diodes in the circuit. Now let us understand what Zener diode is made of?

Zener Diode: Construction 

The Zener diode structure is diffused because substrates, such as P and N are diffused together. A SiO2 (silicon dioxide) layer can be applied to the junction area. The entire structure can be metalized simultaneously to create an anode-cathode connection during construction. As a result, the SiO2 layer primarily contributes to the prevention of link overflow. Therefore, it is used to build Zener diodes. 

The operation of this diode is mainly determined by the doping range of the PN junction. The depleted area is very thin, the electric field is very high, and a small reverse bias occurs. It allows electrons to move from the valence to the conduction bands. 

The breakdown voltage of a Zener diode can be precisely controlled at the time of doping level. The breakdown voltage of Zener diodes can range from 1.2 V to 200 V. If the breakdown voltage is less than 5.6 V, the breakdown is caused by the avalanche effect rather than the Zener effect. 

What is Zener Diode? Types 

The Zener diode can be classified based on several parameters, including the ones listed below: 

 Nominal Voltage 

•  Maximum Reverse Current 
•  Power Dissipation 
•  Packaging type 
•  Forward drive current 
•  Forward voltage 

How does a Zener Diode Work?

The bias mode mainly determines the operation of the Zener diode, such as forward or reverse. If this diode is forward biased, it behaves like a normal diode. However, if connected in reverse, a small leakage current will flow through the diode. 

Current flows through the diode when the reverse voltage exceeds the fixed breakdown voltage (Vz). As a result, when stable, the current flow increases to the maximum level seen by the series resistance and remains stable over a wide range of applied voltages. There are two types of Zener diode breakdowns: avalanche and Zener breakdown. 

Avalanche Breakdown 

This type of breakdown occurs on both regular and Zener diodes at maximum blocking voltage. When the maximum blocking voltage is applied to the P-N junction, the electrons have enough energy to accelerate at high speed. 

These electrons start moving at high speed and collide with other atoms to blow off more electrons. As a result of this continuous impact, many free electrons are generated, and the current in the diode increases rapidly. 

Therefore, this unexpected increase in current can permanently destroy a normal diode, but this diode can be designed to function under avalanche breakdown and maintain an unexpected current spike. This type of breakdown is most common with Zener diodes with Zener voltages (Vz) above 6V. This is one of the major applications of the Zener diode, which makes it a voltage regulator. 

Zener Breakdown 

As the applied voltage approaches the Zener voltage, the electric field in the depleted region becomes strong enough to pull the electrons out of the valence band. As a result, valence electrons get enough energy from the electric field in the depleted region and escape from the main atom. As the voltage in the Zener breakdown region rises, so does the current. 

The diode can be packaged in a variety of ways. Some are used for high power consumption, and others are housed in surface mount format. The most common Zener diodes are housed in a small glass case. A band at one end indicates the cathode side of the diode. 

Application of Zener Diode

Zener diodes are commonly used as shunt regulators or voltage regulators. The main uses for this type of diode are voltage regulators, surge protectors, and voltage references.

Conclusion

A Zener diode is a semiconductor diode that, starting from a reverse-biased condition, allows current to flow in the forward direction only after the voltage has exceeded a certain threshold. This property makes them ideal for use as voltage regulators or protectors in electronic circuits. Zener diodes are named after Clarence Zener, who discovered their unique electrical properties in 1933.

The invention of Zener diodes in 1934 has revolutionalized the industrial world and has been extensively used in our daily lives. At least one Zener diodes support every appliance around us. From TV to FM, from AC to complex personal computers, Zener diodes have become an integral part of our life.