Zener Diode

 Zener Diode

What is a Zener Diode: -

A Zener diode is a special type of semiconductor diode designed to allow current to flow not only from its anode to its cathode (like a regular diode) but also in the reverse direction, when the voltage across it exceeds a specific value known as the Zener breakdown voltage.

This characteristic makes it ideal for voltage regulation, surge protection, and voltage reference applications. The Zener diode maintains a constant output voltage even when the input voltage or load current changes.

" A Zener Diode is designed to have a specific breakdown voltage so that it will conduct current in reverse when the cathode reaches its threshold voltage. "

Structure and Symbol of Zener Diode: -

Symbol:

The symbol of a Zener diode looks like a regular diode symbol with bent edges on the cathode line, indicating the Zener property.

ZENER DIODE

Construction: 

Zener diodes are made of heavily doped p-n junctions to achieve a narrow depletion region. This allows breakdown to occur at a low reverse voltage, and the breakdown process is controlled and repeatable.

Working Principle of Zener Diode: -

The Zener diode works based on the Zener effect and avalanche breakdown:

1. Forward Bias Operation:

In forward bias (positive voltage to anode), the Zener diode behaves like a regular diode, allowing current to pass when the forward voltage exceeds about 0.7 V for silicon diodes.

2. Reverse Bias Operation:

In reverse bias (positive voltage to cathode), a regular diode blocks current until breakdown. However, the Zener diode is specifically designed to conduct in reverse when the voltage reaches the Zener breakdown voltage (Vz), typically ranging from 2V to 200V depending on the diode.

Once this voltage is reached, the diode maintains a constant voltage across it even if the current through the diode increases. This makes it perfect for voltage regulation.

Zener Diodes Functionality: -

Current going throughout the terminals in opposite bias (backward) is known as the Zener effect. When the voltage capacity is met, this causes the Zener voltage (Vz)/breakdown voltage. Zener diodes uniquely include a heavily doped P-N junction that lets in cutting-edge electrons drift in reverse when accomplishing Vz. A well-defined Vz can behave cutting-edge constantly in reverse bias without getting damaged. Current then increases to a most-decidable level through a chain resistor and stabilises, lasting consistently over more than a few applied voltages. Therefore, Zener diodes are relevant for use as voltage regulators.

A Zener diode operates in the ordinary range of forward bias, with a turn-on voltage between 0.3V and 0.7V. When connected in reverse bias, the modern-day flows backward, consequently inflicting a small leakage of modern-day to go with the flow. As the opposite voltage will increase to the organised Vz, current flows through the diode. Current increases to a maximum decided through the collection resistor and then stabilises to remain constant over a range of applied voltages.

Zener diodes have two breakdown voltages. Knowing those two consequences helps with knowing their capability. First is the Zener effect, familiar in voltages under 5.5V and related to a tunnelling effect to cause the breakdown. The 2nd is the avalanche breakdown or impact ionisation, which takes place in voltages above 5.5V. These breakdowns each result in the identical behaviour, and they do not require distinctive circuitry, but each does have a different temperature coefficient. The Zener effect has an anode (terrible) terminal temperature coefficient, even as the avalanche has a cathode (fantastic) terminal temperature coefficient. Both temperature outcomes are nearly identical to 5.5V. They cancel each other out, making Zener diodes.

Zener Breakdown vs Avalanche Breakdown: -

• Zener Breakdown (below 5V): Occurs due to quantum tunnelling in highly doped diodes with narrow depletion layers.
• Avalanche Breakdown (above 5V): Caused by impact ionisation in lightly doped diodes with wider depletion regions.

In Zener diodes, both effects can occur, but the device is designed to operate safely in breakdown without damage.

V-I Characteristics of Zener Diode: -

The Voltage-Current (V-I) characteristics of a Zener diode clearly show its unique reverse breakdown behaviour.

1. Forward Region: Similar to a normal diode, a small current flows until forward voltage (~0.7V) is reached.

2. Reverse Region: Tiny leakage current flows until the Zener breakdown voltage is reached.

3. Breakdown Region: After reaching Vz, the current rises sharply, but the voltage remains nearly constant.

This constant voltage across the diode in breakdown is the key to its use in voltage regulation.

Zener Diode as Voltage Regulator: -

Circuit Description:

A typical Zener voltage regulator circuit consists of:

• A Zener diode connected in reverse bias
• A series resistor connected to the input voltage

How It Works:

1. The resistor limits the current flowing into the diode.

2. When the input voltage exceeds the Zener voltage, the diode conducts and clamps the voltage to its Zener value.

3. Any excess voltage is dropped across the resistor, protecting the load.

Applications of Zener Diode: -

Zener diodes are utilised in a wide range of digital programmes. Some essential programmes encompass:

1. Voltage Regulation

Used to maintain a steady output voltage in power delivery circuits, regardless of variations in input voltage or load.

2. Overvoltage Protection

Zener diodes can protect circuits by way of clamping high voltages. If the voltage spikes above the Zener voltage, the diode conducts and protects sensitive electronics.

3. Voltage Reference

In analogue and digital circuits, Zener diodes offer a solid reference voltage for comparators, ADCs, and DACs.

4. Waveform Clipping

Zener diodes are used in clipping circuits to restrict voltage swings and protect against transients in signal processing.

5. Meter Protection

In analogue meters, Zener diodes protect against unintentional excessive voltages that would harm sensitive components.

6. Switching Operations

Zener diodes are used to define specific switching factors in good judgment and timer circuits.

Advantages of Zener Diode: -

• Simple and easy to use
• Inexpensive and widely available
• Provides excellent voltage stability
• Requires minimal external components
• Can protect against voltage surges

Limitations of Zener Diode: -

• Not suitable for high power law
• Low efficiency in excessive modern-day applications
• Generates heat below continuous excessive-current waft
• Regulation is confined to low- to slight-voltage packages
• Cannot reply to very speedy voltage fluctuations successfully

Zener Diode vs Regular Diode: -

Feature	Zener Diode	Regular Diode
Reverse Bias Operation	Conducts in reverse after Vz	Blocks current
Primary Use	Voltage regulation	Rectification
Breakdown	Controlled and safe	Destructive
Doping Level	Heavily doped	Moderately doped
Voltage Regulation	Yes	No

How to Select a Zener Diode: -

When choosing a Zener diode for a circuit, consider:

1. Zener Voltage (Vz): Choose a value slightly above the desired output voltage.

2. Power Rating (Pz): Pz = Vz × Iz; ensure it can handle the power dissipation.

3. Tolerance: ±5% or ±10% is typical; tighter tolerances offer better voltage accuracy.

4. Package Type: Through-hole or SMD, depending on the circuit design.

5. Temperature Stability: Important for precision applications.

Conclusion: -

The Zener diode is a cornerstone of modern-day electronics. Its potential to adjust voltage, protect circuits, and provide strong references has made it critical in both analogue and digital electronics. From powering microcontrollers to guarding against voltage spikes, Zener diodes quietly make certain the safety and stability of our gadgets.