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Wednesday, October 5, 2011

TRANSISTOR COMMON -BASE CONFIGURATION


TRANSISTOR COMMON -BASE CONFIGURATION
AIM: 1.To observe and draw the input and output characteristics of a transistor connected in common base configuration.
          2. To find α of the given transistor.

APPARATUS:      Transistor, BC 107
                            Regulated power supply (0-30V, 1A)
                            Voltmeter (0-20V)
                            Ammeters (0-100mA)
                             Resistor, 1000Ω
                             Bread board
                             Connecting wires
THEORY:

A transistor is a three terminal active device. T he terminals are emitter, base, collector. In CB configuration, the base is common to both input (emitter) and output (collector). For normal operation, the E-B junction is forward biased and C-B junction is reverse biased.
                                In CB configuration, IE is +ve, IC is –ve and IB is –ve. So,
                                 VEB=f1 (VCB,IE) and
                                  IC=f2 (VCB,IB)
With an increasing the reverse collector voltage, the space-charge width at the output junction increases and the effective base width ‘W’ decreases. This phenomenon is known as “Early effect”. Then, there will be less chance for recombination within the base region. With increase of charge gradient with in the base region, the current of minority carriers injected across the emitter junction increases.The current amplification factor of CB configuration is given by,
                                                           α= ∆IC/ ∆IE

CIRCUIT DIAGRAM



PROCEDURE:
INPUT CHARACTERISTICS:

1. Connections are made as per the circuit diagram.
2. For plotting the input characteristics, the output voltage VCE is kept constant at 0V and for different values of VEB note down the values of IE.
3. Repeat the above step keeping VCB at 2V, 4V, and 6V.All the readings are tabulated.
4. A graph is drawn between V­EB and IE for constant VCB.

OUTPUT CHARACTERISTICS:

1.    Connections are made as per the circuit diagram.
2.    For plotting the output characteristics, the input IE iskept constant at 10m A and for different values of VCB, note down the values of IC.
3.    Repeat the above step for the values of  IE  at 20 mA, 40 mA, and 60   mA, all the readings are tabulated.
4.    A graph is drawn between VCB and I­c for constant IE

OBSERVATIONS:
INPUT CHARACTERISTICS:

S.No
VCB=0V
VCB=1V
VCB=2V
VEB(V)
IE(mA)
VEB(V)
IE(mA)
VEB(V)
IE(mA)








OUTPUT CHARACTERISTICS:


S.No
IE=10mA
IE=20mA
IE=30mA
VCB(V)
IC(mA)
VCB(V)
IC(mA)
VCB(V)
IC(mA)









 

 MODEL GRAPHS:
INPUT CHARACTERISTICS


OUTPUT CHARACTERISTICS

               
PRECAUTIONS:

1.    The supply voltages should not exceed the rating of the transistor.
2.    Meters should be connected properly according to their polarities.

RESULT:
1.    The input and output characteristics of the transistor are drawn.
2.    The α of the given transistor is calculated.

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