Zener Diode as a Voltage Regulator

What is a voltage regulator?

There are several types of voltage regulators. They effectively reduce the input voltage to the desired level and maintain that level throughout the supply. This ensures that the voltage does not drop even when a load is applied. There are two primary purposes for which the voltage regulator is employed:

• To alter or control the voltage output
• To maintain a steady output voltage regardless of input voltage fluctuations.

Zener Diode as a voltage regulator-

The diode is protected from overheating by a series resistor in the circuit. DC’s positive terminal is connected to it. As a result, the reverse-biased can work even in the event of an outage. Diodes with lower power ratings aren’t used since they can be destroyed when a reverse bias is applied over their breakdown voltage. The zener diode current should always be the lowest when the minimum input voltage and the highest load current are applied.

Choosing a zener diode with a voltage roughly equal to the load voltage (VZ = VL) is easy since the input and output voltages are known.

Avalanche and zener effects

Anode to cathode current flow is possible when the zener diode is forward biassed, which makes it act like any other silicon diode with a PN junction. In contrast to a typical diode, which inhibits current flow when reverse-biased, the zener diode begins to conduct with a current flowing in the opposite direction upon reaching a specified reverse voltage threshold.

Reverse voltage given to zener diodes causes avalanche breakdown in the semiconductor depletion area, after which the diode generates current in order to limit the increase in voltage to a predetermined level. Free electrons collide with nearby atoms, creating electric charges, which leads to the generation of heat and the potential for permanent damage to the device. When a diode has a depletion area that is very thin and heavily doped, a reverse current can be generated as a result of the development of a high-intensity electric field at the junction of the diode. 

Zener breakdown is reversible and does not harm the diode throughout this process. When the voltage on the zener diode stabilises at a certain point on the horizontal axis, this point is known as the zener voltage (VZ) and its value can range from a few volts to a few hundred volts. 

Standard Zener Voltages-

Zener diodes are available in voltages ranging from a little over 1 volt to a few hundred volts on the market today. From slightly under 1 W to over 5 W are typically available for each voltage setting that is offered. The BZX55 small-signal series of zener diodes has VZ voltages ranging from 2.4 V to 75 V and a maximum power of 500 mW, making it one of the most prevalent zener diode families. Another popular zener power diode is the BZX85, with voltages between 2.7V and 100V (VZ) and 1,300mW (maximum current).

Zener diode and avalanche diode

A zener diode is used as a PN junction diode that mainly works in a reverse-biassed state. The zener diode is heavily doped. 

 Working on the zener diode

The zener diode is used as  an ordinary diode when it is connected in forwarding bias conditions. When it is connected in reverse bias, the depletion layer becomes wider. Its width gradually increases as the reverse-biassed voltage increases. The minority carriers get kinetic energy and collide with ions present in the depletion layer. More free electrons are produced, and the zener diode becomes more conductive.

Zener breakdown

When the reverse bias voltage is applied across the pn terminals, the depletion region begins to increase. As a result, more electrons and holes are generated.

These electrons and holes produce a very powerful electric field across the junction of the diode. The magnitude of the electric field will depend on the magnitude of the applied reverse voltage.

The electric field exerts an electron force which is present in the valence band. This will enter the conduction band and the conduction process begins.

This phenomenon is called zener breakdown.

Advantages of zener diode-

• Dissipation power is really high.
• High precision
• Small in size 
• Low cost

Applications-

• As a voltage reference, it is frequently employed.
• Shunt regulators and voltage stabilisers employ zener diodes.
• In switching processes, zener diodes are employed.
• Clipping and clamping circuits use zener diodes, which are sometimes referred to as zeners.
• Protection circuits rely on zener diodes.

Conclusion 

Zener diodes are available in a wide range of voltages, some of which are adjustable. This is known as the zener effect, after Clarence zener, because electron quantum tunnelling happens in the narrow gap between the p and n regions of a zener diode, resulting in reverse conduction. Zener diodes have both breakdown types. Electronic devices of various kinds rely on zener diodes, which are the building blocks of electronic circuits.They are, for example, used to generate low-power stabilised supply rails from a higher voltage and to provide reference voltages for circuits, notably stabilised power supplies. Overcurrent and electrostatic discharge can also be prevented by using these devices (ESD).