A study of input and output characteristics of a transistor in common emitter configuration

EXPERIMENT NO. 9

AIM:- A study of input and output characteristics of a transistor in common emitter configuration

APPARATUS :- Two d.c power supplies (0 to 10 V), two voltmeters (0 to 1 & 0 to 10), one milliammeter (0 to 50), one microammeter (0 to 250), two rheostats, a pnp transistor, connecting wires.

FORMULAE:-
i) Input resistance, r_i = [delta(V_BE) / delta(I_B)] at V_CE = constant
ii) Output resistance, r_o = [delta(V_CE) / delta(I_C)] at I_B = constant
iii) DC current gain, beta_DC = (I_C) / (I_B) at V_CE = constant
iv) AC current gain, beta_AC = [delta(I_C) / delta(I_B)] at V_CE = constant.

CIRCUIT DIAGRAM:-

PROCEDURE:-

a) Input Characteristics
Make the connections as shown in the circuit diagram. The collector - emitter voltage V_CE is kept constant at 0 V. The emitter - base voltage V_EB is varied in steps of 0.05 or 0.1 V and for each setting of the voltage, the current I_B is noted. The value of V_CE is then set at 5 V and the above procedure is repeated. The value of V_CE is then set at 10 V and the above procedure is repeated again. The reading are recorded in table 1.

b) Output characteristics
The input current, i.e. base current, I_B is kept constant at 50 microA. Voltage V_CE is varied in steps of 1 V from 0 to 10 V and for each setting of the voltage, the output current, i.e. collector current I_C is noted. For each new value of collector voltage, the base current is checked and adjusted to the value at which it is to be kept constant. The value of I_E is then set at 150 microA and the above procedure is repeated. The value of I_B is then set at 250 microA and the above procedure is again repeated.The readings are recorded in table 2.

c) Transfer characteristics
The collector voltage V_CE is kept constant at some value. Base current is varied in steps and corresponding collector current I_C is noted and recorded in table 3.

OBSERVATIONS:-

For input characteristics

V_CE = 0 V		V_CE = 5 V		V_CE = 10 V
V_BE V	I_B microA	V_BE V	I_B microA	V_BE V	I_B microA
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4		0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4		0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

For output characteristics

I_B = 50 microA		I_B = 150 microA		I_B = 250 microA
V_CE V	I_C mA	V_CE V	I_C mA	V_CE V	I_C mA
0 1 2 3 4 5 6 7 8 9 10		0 1 2 3 4 5 6 7 8 9 10		0 1 2 3 4 5 6 7 8 9 10

For transfer characteristics

V_CE = constant at 5 V.

I_B microA	I_C mA
0 5 10 15 20 25 30 35 40

GRAPH:-

i) To draw input characteristics, V_BE values are taken along x - axis and I_B values are taken along y - axis and the graphs are plotted for all three constant V_CE values.
ii) To draw outut characteristics, V_CE values are taken along x - axis and I_C values are taken along y - axis and the graphs are plotted for all three constant I_B values.
iii) To draw transfer characteristics, I_B values are taken along x - axis and I_C values are taken along y - axis and the graph is plotted.

CALCULATIONS:-

i) r_i = [delta(V_BE) / delta(I_B)] at V_CE = constant =
ii) r_o = [delta(V_CE) / delta(I_C)] at I_B = constant =
iii) beta_DC = (I_C) / (I_B) at V_CE = constant
iv) beta_AC = [delta(I_C) / delta(I_B)] at V_CE = constant =

RESULT:-

i) Input dynamic resistance, r_i =
ii) Output dynamic resistance, r_o =
iii) DC current gain, beta_DC =
iv) AC current gain, beta_AC =

PRECAUTIONS:-

Make sure that the connections are tight.
Take care to apply i)suitable forward voltage across base - emitter junction and ii) suitable reverse voltage across the collector - emitter junction. Otherwise the transistor may be damaged.