Electrical Lab Experiments

To find the forward and reverse bias characteristics of a given Zener diode.

Sep 24 2023

Aim

Apparatus Required:

S.No.	Name	Range	Quantity
1	R.P.S	(0-30)V	1s
2	Ammeter	(0-30)mA	2
3	Voltmeter	(0-10)V (0-1)V	1 1

Components Required:

S.No.	Name	Range	Quantity
1	Zener Diode	FZ5.1	1
2	Resistor	1KΩ	1
3	Bread Board	-	1
4	Wires		Required

Theory:

A properly doped crystal diode, which has a sharp breakdown voltage, is known as Zener diode.

Forward Bias

On forward biasing, initially no current flows due to barrier potential. As the applied potential increases, it exceeds the barrier potential at one value and the charge carriers gain sufficient energy to cross the potential barrier and enter the other region. The holes, which are majority carriers in p-region, become minority carriers on entering the N- regions and electrons, which are the majority carriers in the N-regions become minority carriers on entering the P-region. This injection of minority carriers results current, opposite to the direction of electron movement.

Reverse Bias

When the reverse bias is applied, due to majority carriers small amount of current (i.e.,) reverse saturation current flows across the junction. As the reverse bias is increased to breakdown voltage, sudden rise in current takes place due to Zener effect.

Zener Effect

Normally, PN junction of Zener Diode is heavily doped. Due to heavy doping the depletion layer will be narrow. When the reverse bias is increased the potential across the depletion layer is more. This exerts a force on the electrons in the outermost shell. Because of this force the electrons are pulled away from the parent nuclei and become free electrons. This ionization, which occurs due to electrostatic force of attraction, is known as Zener effect. It results in large number of free carriers, which in turn increases the reverse saturation current.

Procedure Forward Bias

Connect the circuit as per the diagram
Vary the power supply in such a way that the readings are taken in steps of 0.1V in the voltmeter till the needle of power supply shows 30 V.
Note down the corresponding Ammeter readings I.
Plot a graph between V & I
Find the dynamic resistance r = δV / δI

Reverse Bias

Connect the circuit as per the diagram.
Vary the power supply in such a way that the readings are taken in steps of 0.1V in the voltmeter till the needle of power supply shows 30 V.
Note down the corresponding Ammeter readings I.
Plot a graph between V & I
Find the dynamic resistance r= δV/δI
Find the reverse voltage V _rat I _z=20 mA.