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					                                                              EXPERIMENT NO. 2
                 ZENER DIODE CHARACTERISTICS

AIM:
             To study the V-I Characteristics of given Zener diode and also to find
the Zener breakdown Voltage, Static Resistance and Dynamic Resistance in
forward and reverse bias connections.

APPARATUS REQUIRED:
                    1. Zener Diode ------------------------------------- 1No.
                    2. Resistor – 1KΏ --------------------------------- 1No.
                    1. Bread Board ------------------------------------ 1No.
                    2. Voltmeter (0-1V, 0-10V) --------------------- 1No.
                    3. Ammeter (0-50mA, 0-250µA)---------------- 1No.
                    4. Regulated Power Supply (0-30V) ----------- 1N0.
                    5. Connecting wires (required as per circuit) – 1N0.
FORMULAE:
                    1. Static Resistance (Rs) = V/I
                    2. Dynamic Resistance (RD) = ΔV/ΔI
THEORY:
            A Zener diode is also called a voltage-reference, ;voltage regulator or
breakdown diode. The zener diode is a silicon PN junction device, which differs
from a rectifier diode, in the sense, that it is operated in the reverse break kown
region. The breakdown voltage of a zener diode is set by carefully controlling the
doping level during manufacture. When a reverse voltage across a diode is
increased, a critical voltage called breakdown voltage is reached at which the
reverse current increases sharply as shown in the model graph by the KM.
            The reverse breakdown of a PN junction may occur either due to
avalanche or zener effect. The avalanche breakdown occurs, when the accelerated
free electrons acquire sufficient energy to ionize a lattice atom by bombardment.
The additional free electrons, created in this way, are accelerated by the reverse
field causing more and more ionization. The multiplication of the number of free
carriers causes the reverse current to increase rapidly.

           The zener diodes, with breakdown voltages of less than 6V, operate
predominantly in zener breakdown. Those with breakdown, voltages greater than
6V, operate predominantly in avalanche breakdown.
PROCEDURE:
         1. Connections are given as per the circuit diagram.
         2. By using RPS increase the applied voltage in small levels and note
            down the readings.
         3. The voltage across the diode is noted by the voltmeter of range (0-1V)
            in forward bias and (0-10V) in reverse bias.
         4. The current across the diode is noted by the ammeter of range (0-
            50mA) in forward bias and (0-250µA) in reverse bias.
         5. From the readings obtained draw the graphs.
         6. From the graph find out the parameters such as Breakdown voltage,
            Static resistance and Dynamic resistance.
CALCULATIONS:
   FORWARD BIAS:
      1. Static Resistance = V/I
      2. Dynamic Resistance = ΔV/ΔI
      3. Cut in Voltage =

   REVERSE BIAS:

         1. Static Resistance = V/I
         2. Dynamic Resistance = ΔV/ΔI
         3. Cut in Voltage =

RESULT:
         Thus the V–I characteristics of given PN junction diode is studied and the
following parameters are calculated from forward bias condition.

         1. Breakdown voltage of the given diode =
         2. Static resistance (Rs) : V/I =
         3. Dynamic Resistance (RD) : ΔV/ΔI =
TABULAR COLUMN:

  FORWARD BIAS:

     S.No.   Voltage across the diode   Current through the diode
                     in Volts                    in mA




REVERSE BIAS:

     S.No.   Voltage across the diode   Current through the diode
                     in Volts                     in µA
CIRCUIT DIAGRAM :-
FORWARD BIAS :-

             R1
                          A
           1kΩ
                         (0-50mA)                  V   (0-1V)
   V                                      D2
   (0-30V)                                1N3008

                                  0


REVERSE BIAS :-

             R1
                          A
           1kΩ
                         (0-250µA)                 V (0-20V)
   V1                                     D2
   (0-30) V                               1N3008




V-I CHARACTERISTICS :-
MODEL GRAPH :-
                                      If (mA)




   VR(V)          VBR                                           VF(V)

                  V
                              I



                                        IR(µ A)

				
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posted:11/8/2011
language:English
pages:4