A Zener diode is a silicon semiconductor with a p-n junction designed to operate in a reverse biassed state. It functions like a regular signal diode when forward bias, but the voltage remains constant throughout various currents when reverse bias. It is used when reverse biased as a voltage regulator in a D.C. Circuit. As a voltage regulator, the Zener diode’s primary goal is to maintain a constant voltage. The Zener diode as voltage regulator has features to make a route for the current to travel and guard the load from currents. As a result, the Zener diode serves two purposes: The Zener diode serves as a voltage regulator and a current limiter for the load.

What is a Voltage Regulator, and how does it work?

Zener diode, as a voltage regulator, regulates voltage levels. It successfully reduces the input voltage to a safe level and maintains it throughout the supply. Even when a load is applied, the voltage does not drop. There are two basic reasons why a voltage regulator is used:

  • A Zener diode is used as a device to control or adjust the voltage
  • Regardless of supply voltage variations, maintain a steady output voltage at the appropriate value.

Voltage regulators control the plant’s output in power generators, computers, and alternators.

What is meant by Zener Diode as a Voltage Regulator?

Under varying load current conditions, Zener Diodes are used as a device to produce a steady voltage output with low ripple. The Zener diode will conduct enough current to maintain a voltage drop if a modest current is passed through it from a voltage source via an appropriate current limiting resistor (RS).

To limit the current into the diode, a series resistor is attached to the circuit and is connected to the terminal of the d.c. It’s designed so that it can work in breakdown situations as well. We don’t use a normal junction diode since reverse bias over its breakdown voltage can ruin the diode’s low power rating. The Zener current needs to be minimal when the maximum load current is provided and the minimum input voltage is used.

Because the input voltage and needed output voltage are known, selecting a Zener diode with a voltage close to the load voltage, i.e., VZ = VL, is more accessible.

The current through the diode grows as the voltage rises, resulting in a voltage drop across the resistor. Similarly, as the voltage across the diode lowers, the current through the diode decreases. The voltage drop across the resistor is tiny, and the output voltage is typical.

Application of Zener diode

1) Zener diode as a voltage regulator: A Shunt voltage controller manages voltage across small loads using a Zener diode. Zener diodes have a constant breakdown voltage throughout a large current range. The heap is connected to a Zener diode to alter its tendency, and when the Zener diode reaches knee voltage, the voltage across the heap becomes consistent.

2) Over-voltage protection with a Zener diode: When the information voltage exceeds the Zener breaking voltage, the voltage across the resistor lowers, causing a short. The Zener diode can be used to prevent this from happening.

3) Clipping circuits with a Zener diode: A clipping circuit with a Zener diode is used to regulate AC waveform cutting circuits by restricting the pieces of one or both half patterns of an AC waveform.

4) In multimeters, Zener diodes are used to safeguard the metre movement from damage caused by unintentional overloads. The Zener diode is linked in parallel with the metre from a safety standpoint.

Advantages

  • Zener is more expensive than regular diodes.
  • Smaller circuits use this.
  • Able to change the voltage
  • Control of current overflow
  • Simply cross-platform compatible and accessible
  • The voltage in the circuit can be altered and stabilised.
  • It delivers excellent results and is the most cost-effective option. 
  • It safeguards against over-voltage; hence, you need not worry about overvolting

Disadvantages

  • This diode is not appropriate for large load currents.
  • Because of Zener resistance, the DC o/p voltage can be somewhat altered.
  • It is impossible to change the output voltage, which is a big reason to worry. 
  • Zener current changes as load current changes.
  • Less control of voltage; hence this could be risky sometimes. 
  • The internal impedance of the circuit is very high.

Conclusion

A Zener diode is a type of diode that is specifically engineered to perform under reverse biassed situations. Because they are more strongly doped, they have a narrower depletion region than standard diodes. When the voltage across a conventional diode surpasses the reverse breakdown voltage, it breaks, whereas Zener diodes only work in this range. The depletion zone of a Zener diode recovers to its original state when the reverse voltage is removed. Because of this property, Zener diodes are useful as voltage regulators. The exciting part about this diode is that we can use it as a voltage regulator in our circuit by selecting a Zener diode with a sufficient breakdown voltage.