Short Answer:

A Zener diode is a special type of diode designed to allow current to flow in the reverse direction when a specific voltage, called the Zener breakdown voltage, is reached. Unlike regular diodes, which block reverse current, Zener diodes are used in circuits where a stable voltage is required.

Zener diodes function as voltage regulators by maintaining a constant output voltage despite changes in input voltage or load conditions. When the input voltage exceeds the breakdown voltage, the Zener diode conducts in reverse, stabilizing the voltage and preventing fluctuations, making it ideal for power supply and protection circuits.

Detailed Explanation:

Zener Diode

A Zener diode is a semiconductor device that operates in both forward and reverse bias, but its primary function is to regulate voltage in reverse bias. It is designed to conduct in the Zener breakdown region, where it maintains a constant voltage across its terminals even if the input voltage varies.

Unlike a standard diode that allows current to flow in one direction and blocks reverse current, a Zener diode is constructed to handle reverse breakdown safely. It is made from doped silicon to control its breakdown characteristics. The breakdown voltage, also called the Zener voltage, is determined during manufacturing and can range from a few volts to several hundred volts.

Zener diodes are widely used in voltage regulation, overvoltage protection, and reference voltage applications in electronic circuits. Their ability to provide a stable voltage makes them essential in power supplies, digital circuits, and communication systems.

How a Zener Diode Functions as a Voltage Regulator

1. Reverse Bias Operation and Voltage Regulation
   A Zener diode functions as a voltage regulator by operating in the reverse bias condition. When the input voltage applied across the diode is below the Zener voltage, the diode remains in its non-conducting state, acting like an open circuit. However, when the voltage exceeds the breakdown point, the diode starts conducting, allowing excess current to pass through while maintaining a stable voltage across its terminals.

This voltage regulation property is used in power supply circuits, where a stable voltage is necessary to prevent fluctuations that could damage electronic components. A series resistor is typically used with a Zener diode to limit the current and ensure proper operation.

2. Clipping and Overvoltage Protection
   Zener diodes are also used to clip voltage spikes and protect sensitive circuits from overvoltage conditions. In protection circuits, they absorb excessive voltage surges and prevent damage to transistors, microcontrollers, and other electronic devices.
3. Voltage Reference in Circuits
   Zener diodes provide a stable reference voltage in electronic circuits. This property is used in analog and digital electronics, where a precise voltage level is required for calibration, measurement, and signal processing.

Conclusion

A Zener diode is an essential electronic component that regulates voltage by allowing controlled reverse current flow beyond its breakdown voltage. It ensures a stable and consistent voltage supply, protecting circuits from fluctuations and overvoltage damage. Because of its reliability, the Zener diode is widely used in power supplies, reference voltage circuits, and electronic protection systems.