Zener diode-To plot the forward and reverse characteristics of zener diode b. To study the voltage regulation action of a zener diode. Skip to main content

Zener diode-To plot the forward and reverse characteristics of zener diode b. To study the voltage regulation action of a zener diode.

AIM:  a.   To plot the forward and reverse characteristics of zener diode
            b.   To study the voltage regulation action of a zener diode.

zener diode
zener diode
These diodes are special purpose diodes. They are heavily doped p-n diode due to which the width of the depletion region is very small. The breakdown voltage of these diodes is very precise and can be fixed to the desired value. Beyond the breakdown; the voltage across the diode remains constant. Hence these diodes are specially used as voltage regulators in d.c. power supplies. As it acts as a constant voltage source, it is often used as a voltage reference diode.

APPARATUS
                          a o to 15 V dc power supply, zener diode, voltmeters,  milliammeter
FORMULAE
               The dynamic resistance of the diode is given by           rz= ∆Vz /∆Iz

THEORY

ZENER DIODE :

These diodes are special purpose diodes. They are heavily doped p-n diode due to which the width of the depletion region is very small. The breakdown voltage of these diodes is very precise and can be fixed to the desired value. Beyond the breakdown; the voltage across the diode remains constant. Hence these diodes are specially used as voltage regulators in d.c. power supplies. As it acts as a constant voltage source, it is often used as a voltage reference diode.

The breakdown voltage depends on the width of the depletion region which in turn depends upon the doping level of the p-and n-regions. The large current at the breakdown is caused by two mechanisms, namely, zener effect and avalanche effect. Zener effect is predominant for breakdown voltages less than about 8V. The avalanche breakdown is predominant for the voltage greater than 8V. around 8 volts both the effects are predominant.
Zener breakdown does not result in the damage of the junction. Usually, a series resistor Rs, called a limiting resistor, is connected in series with the diode to avoid passing of very large current through the diode. As the zener diode is most often used in the reverse bias condition, the dynamic resistance of the diode in the breakdown region is an important parameter which is to be calculated by using the formula
 Rz = ∆Vz/ ∆ Iz.

PROCEDURE

1. TO PLOT FORWARD CHARACTERISTICS OF ZENER DIODE:

   1. Make the connections as shown in fig for respective diodes (Z1&Z2).
   2. Vary the voltage in steps of 0.25V/0.2V carefully till mA shows deflection.    
   3. Find voltage required for current of 1mA.
   4. Now vary the current in steps of 1mA till 10mA and note down the corresponding value of voltage.

   2. TO PLOT THE REVERSE CHARACTERISTICS:

   1.  Make the connections as shown in the fig.
   2. Vary the i/p voltage in steps of 0.5 V and note down the o/p  voltage(VZ) and  corresponding
       current in mA.
   3.  Observe breakdown voltage carefully at which suddenly current starts flowing.
        Now vary current by 1 mA till 10mA and note down i/p and o/p voltages.

RESULT

1. The forward and reverse characteristics of Zener diode has been studied and shown in Graph.
2. From the characteristics graph and voltage regulation curve, the breakdown voltage is found to be ------------------------------------
3. The voltage regulation using zener diode occurs beyond -------------
                                                       
Answer the followings:

1)      What is the aim of the experiment?
2)      What happens when the reverse bias of the diode is increased?
3)      What is meant by breakdown?
4)      How does the process of breakdown occur in diodes?
5)      What is meant by Zener breakdown?
6)      Under what conditions does zener breakdown occur?
7)      What are the applications of zener diodes?
8)      Which zener is used in the experiment? What is its breakdown voltage?
9)      What happens to the current through the diode if the reverse bias voltage is increased?
      What happens to the voltage?
10)  How does a zener diode behave under forward bias condition?
11)  How much forward voltage is needed to cause current through the diode?
12)  If a zener is rated at 6V, 1/2W, what is the maximum current that can be allowed through it?
13)  What is the need of voltage regulation?
14)  What happens when the input voltage to the regulation section increases?

15)  Interpret the voltage regulation curve with one of its practical application?
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