Experiment - 2 Electronics Laboratory – PH 3204 (Spring 2025) Solution

Aim : Study of characteristics of an n-p-n bipolar junction transistor (BJT).
Electronic Parts Required :
(i) Power supply, 2 Nos : 0 ~ 15 V
(ii) RB , RC = 1.0 KΩ , 2 Nos
(iii) RB , = 220 Ω , 1 Nos (iv) 1.0 kΩ Potentio-meter, 1.0 W
(v) NPN Transistor = 1 No , CL 100 / SL 100 [CK 100 / SK 100 = PNP (equivalent) transistors] (vi) Breadboard = 1 No
(vii) Two DT-830D multi-meters for current measurements. One 8007 multimeter with probe for Voltage measurements.
(viii) single stand wires = 6 Nos

Theory :
A transistor is an electronic device which has huge applications – in amplifiers, oscillators, gates etc. In this lab we will study one kind of transistor – the Bipolar Junction Transistor (BJT). This device can be thought of schematically as a sandwitch – in which two n type semiconductors are separated by a p type semiconductor (this is the npn transistor – there is another kind – the pnp). Of the two n type regions, one is small and very heavily doped – called the emitter, while the other, called the collector, is large and comparatively lightly doped. The p type region, called the base, is very narrow and very lightly doped.
Thus, there are two pn junctions in a transistor – the base-emitter and the collector-base. When the transistor is used as an amplifier it is necessary to forward bias the base-emitter and reverse the collector-base junction. In this case, the base-emitter forward bias causes a large flow of electrons from the emitter to the base (there is also flow of holes from the base to the emitter – but that is much smaller, the base being lightly doped). Once these electrons enter the emitter, the base-collector reverse bias sweeps them almost entirely into the collector. Only a small fraction recombines in the base – giving rise to a small base current IB. Thus the collector current IC is almost equal to or slightly lower than IE.
Now we define a parameter  by
IC =  IE
Where  is a number very close to, but smaller than, 1. Since IE = IC + IB
We can easily see that IC =  IB , where 𝜷 = 𝛼 is usually quite large – in the order of 1−𝛼 100 -200.
Characteristics of Common Emitter Connection :
Since two terminals each are needed for a transistor’s input and output, while it has only three – one terminal must be common between the input and the output. This leads to the classification of transistor circuits as common emitter (CE), common base (CB) or common collector (CC). We will study the common emitter configuration where the input is applied between the base and the emitter and the output is taken between the collector and the emitter.
The important characteristics of CE arrangement are the input and output characteristics. In the CE configuration the input current and voltage are IB and VBE, while the output current and voltage are IC and VCE.


Figure: Circuit for transistor characteristics



i) CE input characteristics :

R_B = 1K Ohm, R_C = 1 Ohm , V_CE = 2 V
Sl.
No V_BB (V) V_BE (V) I_b (micro) V_CC (V) V_CE (V) I_c (micro)
1 0 0 0 2 2 2
2 0.1 0.999 0.1 2 2 2
3 0.2 0.1998 0.2 2 2 2
4 0.3 0.2997 0.3 2 2 2
5 0.4 0.3996 0.4 2 2 2.001
6 0.5 0.4995 0.5 2 2 2.024
7 0.6 0.5994 0.611 2 2 3.16
8 0.7 0.6988 1.24 2 2 56.09
9 0.8 0.7844 15.61 2.001 2 1.484 mA
10 0.9 0.8258 74.23 2.007 2 7.343 mA
11 1 0.845 155 2.015 2 15.42 mA
12 1.1 0.8567 243.3 2.024 2 24.25 mA
13 1.2 0.865 335 2.033 2 33.42 mA

It is the curve between base current IB and base-emitter voltage VBE at constant collector-emitter voltage VCE. In the above circuit diagram, set the voltage VCE at 2 Volts. Change the input voltage and measure the variation of IB with VBE. Note that you have to readjust the battery VCC to keep VCE fixed at 2 Volts. Repeat the same for VCE fixed at 3 and 4 Volts.
Table – I
Sl.
No VCE = 2 V VCE = 3 V VCE = 4 V
VBE (V) IB (A / mA) VBE (V) IB (A / mA) VBE (Volts) IB (A / mA)
1.
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10

ii) CE output characteristics :

R_B = 220 Ohm, R_C = 1K Ohm , I_b = 10 micro A
Sl.
No V_BB
(V) V_BE
(V) I_b (micro) V_CC
(V) V_CE (mV) I_c (micro)
1 0.6618 0.6596 10.01 0 6.561 6.561
2 0.7058 0.7036 10.04 0.1 52.13 47.87
3 0.7258 0.7236 10.06 0.2 74.51 125.5
4 0.7378 0.7356 10.06 0.3 89.42 210.6
5 0.7462 0.744 10.03 0.4 101.3 298.7
6 0.7526 0.7504 9.98 0.5 112 388
7 0.7578 0.7556 10.02 0.6 121.7 478.3
8 0.7658 0.7636 10.1 0.8 142.3 657.7
9 0.7715 0.7693 10.01 1 174.7 825.3
10 0.7743 0.7721 10.1 1.2 278.1 921.9
11 0.7744 0.7722 10.02 1.5 574.3 925.7
12 0.7744 0.7722 10.02 1.8 874 926
13 0.7744 0.7722 10.02 2.1 1.274 V 926.4
14 0.7744 0.7722 10.02 2.5 1.573 V 926.7
15 0.7744 0.7722 10.02 3 2.073 V 927.2
16 0.7744 0.7722 10.02 5 4.071 929.2
17 0.7744 0.7722 10.02 8 7.068 932.2
18 0.7744 0.7722 10.02 12 11.06 936.2

Sl. No IB = 10 A IB = 20 A IB = 30 A IB = 40 A
VCE (V) IC (mA) VCE (V) IC (mA) VCE (V) IC (mA) VCE (V) IC (mA)
1.
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10


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