Short Answer:

A Zener diode is a special type of diode designed to allow current to flow not only in the forward direction but also in the reverse direction when the voltage exceeds a certain value called the Zener breakdown voltage. It is mainly used to regulate voltage in electronic circuits and protect components from voltage spikes.

The working of a Zener diode depends on its ability to maintain a constant voltage across itself, even when the input voltage or load current changes. When reverse-biased and the voltage reaches the Zener breakdown point, the diode conducts in reverse, keeping the voltage stable. This makes it ideal for voltage regulation and protection circuits.

Detailed Explanation:

Zener diode

A Zener diode is a specially doped semiconductor diode that allows current to flow in the reverse direction when the applied voltage reaches a particular value, known as the Zener breakdown voltage. Unlike a normal diode, which blocks reverse current and may get damaged if the reverse voltage is too high, a Zener diode is built to operate safely in this breakdown region. This unique feature makes Zener diodes very useful in circuits where maintaining a steady voltage is important.

In normal operation, the Zener diode behaves like a regular diode when forward-biased—it conducts current freely in the forward direction. However, when it is reverse-biased, it does not conduct until the voltage across it reaches the breakdown point. Once the reverse voltage hits the breakdown level, the Zener diode starts to conduct in reverse, and the voltage across it remains nearly constant, regardless of changes in current. This property is used to create a stable reference voltage in circuits.

Construction and Behavior

Zener diodes are made using heavily doped p-n junctions so that they have a sharp breakdown voltage, typically ranging from 2V to 200V depending on design. The breakdown mechanism in Zener diodes is either Zener effect (for voltages below 5V) or avalanche effect (for higher voltages). In both cases, the result is the same—sharp voltage regulation.

When connected in reverse bias across a load, the Zener diode maintains a fixed voltage. If the input voltage increases beyond the breakdown voltage, the diode allows extra current to flow through it, effectively absorbing the excess and protecting the load. If the input voltage is below the breakdown voltage, the diode does not conduct, and the full input appears across the load.

Working Principle – Step by Step:

1. Below Breakdown Voltage:
   When a Zener diode is reverse-biased but the voltage is below the breakdown level, it acts like a normal diode—blocking current flow.
2. At Breakdown Voltage:
   When the reverse voltage reaches the Zener breakdown voltage, the diode starts conducting in the reverse direction, allowing current to pass through while keeping the voltage across it constant.
3. Voltage Regulation:
   As current increases beyond this point, the voltage across the diode stays the same, making it perfect for regulating voltage in circuits.

Applications of Zener Diode:

1. Voltage Regulation:
   The most common use of Zener diodes is to maintain a constant voltage across a load, even when supply voltage or load resistance changes.
2. Overvoltage Protection:
   Zener diodes can protect sensitive electronic components from voltage spikes by clamping the voltage to a safe level.
3. Reference Voltage:
   In analog and digital circuits, Zener diodes are used to provide a stable reference voltage for comparison or control purposes.
4. Switching Operations:
   They can also be used in waveform clippers, shifters, and switch-mode power supplies.

Practical Example:
Suppose a Zener diode has a breakdown voltage of 5V. If you apply 12V to a circuit and connect the Zener diode in reverse across a load, it will allow only 5V across the load and divert the extra 7V through itself. This keeps your connected device safe and running on steady voltage.

Important Notes:

• Zener diodes must be used with a series resistor to limit the current and prevent the diode from burning out.
• The power rating of a Zener diode determines how much current it can handle while regulating voltage.

Conclusion

A Zener diode is a vital component in electronics that helps keep voltages stable and safe. It is specially designed to conduct in reverse once a certain voltage is reached, making it perfect for voltage regulation, overvoltage protection, and creating reference voltages. Its ability to provide constant voltage in varying conditions makes it a key part of many power supply and protection circuits in modern electronics.