EXPERIMENT NO.

OBJECT :- To study the different characteristics of CB mode of transistor.

APRRATUS REQUIRED :- Transistor trainer kit and connecting lead.

THEORY :- The bipolar junction transistor is fabricated with the semiconductor region. The three regions are called Emitter, Base and Collector. There are two P-N junctions in transistor the first junction is called base-emitter junction and second are called base-collector junction.

There are two types of transistor :-

1. NPN Transistor2. PNP Transistor

An NPN transistor is fabricated by P-type material between two N-type region and PNP transistor is fabricated by N-type material between two P-type type regions.

Thus in NPN Transistor :- Emitter-N-type Base-P-type Collector-N-type

And In PNP transistor :

Emitter-P-type Base-N-type Collector-P-type

The symbolic representation of PNP and NPN transistor is shown below :-

Collector Emitter

Base

Emitter Collector

Base

When we use transistor to amplify the signal we are required four terminals, two in input circuit and two in output circuit but in transistor only three terminals so found thus we have to require one terminal of transistor common in both input and output circuit due to this there are three mode of transistor :-

CB mode (common Base mode) CE mode (common Emitter mode)

P N P

N P N

CC mode (common Collector mode)

In the circuit diagram of cell modes always we keep the input circuit in forward bias and output circuit in reverse bias.

CB MODE :- In this mode the base terminal of transistor is used as a common terminal in input and output circuit .The circuit diagram for CB mode of PNP transistor is shown in figure:-

₊ ₋ Ie E C Ic ₊

mA1 mA2

B

₊ ₋ V1 V2

₋ ₊

CHARACTERISTICS OF CB MODE :- There are three characteristics in transistors :-

Input Characteristics Rin = ∆V1/∆I1 Output Characteristics Rout = ∆V2/I2 Transfer Characteristics Current gain = ∆I2/∆I1

INPUT CHARACTERISTICS :- This characteristics shows the change in input circuit. For this characteristic we get different-different change in input current when input voltages are applied at constant output voltage.

Observation table for input characteristics:

S.NO V1 (volt) IE(mA)V2=2V V2=4V V2=6V

1.2.3.4.5.6.7.

According to observation we plot the graph between input voltage and current at different values of constant output voltages as shown in following graph :

y

I (mA)

X V (Volt)

This characteristics is same as P-N junction diode by this characteristics we obtain input resistance by following formula :

Rin = ( ∆V1/∆I1) V2

OUTPUT CHARACTERISTICS : This characteristics gives the changes in output circuit when input current is constant .To plot this characteristics we get different changes in output circuit when output voltage is applied aat costant input current.

Observation table for Output characteristics:

S.NO V2 (volt) I2(mA)I1=2mA I1=4mA I1=6mA

1.2.3.4.5.6.7.

After taking observation we plot the graph between output voltage and output current at different constant input current as shown in following figure:

y

I 2 (mA)

X

V2 (volt)

Thus from graph we conclue that the current Iz saturated after some output voltage with the help of this characteristics we obtain output resistance by following formula

Rout=(∆V2/∆I2)II

TRANSFER CHARACTERISTICS:-This characteristics of transistor shows the change in output current with respect to input current at a constant voltage V2.

Observation table for Output characteristics:

S.NO I1(Ma) I2(mA)1.2.3.4.

Y

I2(mA) V2=4V

o X

I1(mA)

For this characteristics we plot the graph between input and output current at constant output voltage V2 as shown in above diagram from this graph we obtain the current gain of circuit by following:

Cgain = (∆I2/∆H)V2

RESULT:- After studying the different characteristics of CB mode transistor we get different graphs as shown in figure attached graph and with the help of graphs we will calculate the different parameters of transistors:

PRECAUTIONS:-

1. Always keep the input circuit of transistor in forward in forward bise and output circuit in reverse bias.

2. All the observation should be taken carefully with different different constant voltage and current.

OPTICAL BENCH SET UP

ZENER DIODE

TRANSISTOR

TELESCOPE

TRAVELLING MICROSCOPE

ZENER DIODE

VOLTMETER

POLARISATION OF

SUGAR SOLUTION

1. ELECTRIC VIBRATOR

LASER KIT

GEIGER MULLER