Question

Mention practical use of Zener diode in a laboratory.

Answer 1

Hint: Zener diode is a special case which is constructed differently compared to a regular PN junction diode. The property of the Zener diode that makes it a special, is its a constant value of voltage across several ranges.

Complete step by step answer:
The Zener diode is a special purpose semiconductor diode which is named after its creator, C. Zener. It is specifically designed to operate under reverse bias conditions. The Zener diode is created by heavily doping the n and p regions.
Due to the heavy doping, the depletion region formed in the Zener diode is very small. Thus, it can breakdown at very small voltages under reverse-bias.
Here is the characteristics of the Zener diode:

Here, the Zener diode is operated in Reverse Bias only. When the voltage increases, there is less response of current up to the point where the voltage breakdown happens. This point is represented by $V_z$ in the graph. At this point, the voltage drop across the Zener diode remains the same even though higher amounts of current can pass through it.
This characteristic of the Zener diode is applicable in the voltage regulator circuit.

Voltage regulators are used to provide a constant voltage to the load irrespective of any fluctuations or spike in the input voltage.
The unregulated voltage is connected to a resistance in series with the Zener diode and the Zener diode is connected in parallel with the Load at which the regulated voltage is realized.
There are two cases of operation:
i) If the unregulated voltage is lesser than the breakdown voltage of the Zener diode:
In this case, the Zener diode allows the complete voltage to pass through the circuit to the load. However,
ii) If the regulated voltage is lesser than the breakdown voltage of the Zener diode:
In this case, the Zener diode allows only the breakdown voltage to flow through the load, and the remaining excess voltage is dropped on the series resistance connected, so as to ensure that the voltage across the load does not exceed the breakdown voltage of the Zener diode.

Note:
Voltage regulators are used in stabilizer devices that are connected to sensitive appliances viz. television, fridge. Due to unexpected voltage surges due to lighting etc, the input voltage spikes and to protect the appliances from this surge voltage, the voltage regulator circuit is used in the stabilizer.