Bipolar Junction transistor...

2.  GROUP MEMBERS Roll no
1. Muhammad Fahim 42
2. Abdur Rehman 41
3. Athar Gul 54
4. Adeel Abbasi 56
5. Nasir Rafique 13

3. The BJT (Bipolar junction transistor) is
connected with three doped semiconductor
region separated with two p-n junction. The
three region are called emitter, base, and
collector. The physically representation of
two types of BJT’s are
N
P
N
collector
base
emitter
Base
collector
junction
Base
emitter
junction
B
E
C

4. One type consist of two n-region
separated by p-region called N-P-N
transistor. Similarly the other type
consist of two p-region which is
separated by n-region are called P-N-P
region. The p-n junction joining the
base and emitter region is called base-
emitter junction. A wire lead is
connected to each region and is
indicated by B, E, C. the base region is
lightly doped and very thin while the
emitter is heavily doped and the
collector is moderately doped.

5. Symbolic representation of n-p-n and p-n-p BJT’s are
shown as
B
C
E
n-p-n
transistor
C
B
E
P-n-p transistor

6. In order to make transistor as an amplifier the
two p-n junction must be correctly biased with
external D.C voltage. The proper bias
arrangement for both n-p-n and p-n-p transistor
for operation as an amplifier in both cases base-
emitter(BE) is forward bias and the base-
collector(BC) junction is reversed biase

7. Diagram of Operation of
Transistor:

8. The forward bias from base to emitter (BE)
depletion is narrow and the reverse bias
from base to collector (BC) depletion is
wider. Since the emitter region is heavily
doped there are large number of electron in
conduction band. These electrons easily
diffused through the forward biased base
emitter junction. In the p-type (in case of n-
p-n) transistor. Since base region is thin and
lightly doped thus maximum electrons goes
to base collector (BC) region.

9. Which are pulled by heavily battery connected
in reverse bias this forms the collector current
(Ic) while small number of free electron flow
out the base lead wire and that current is
called base current (IB)

10. N
P
N
base
emitter
Base
collector
junction
Base
emitter
junction
B
E
N
P
N
base
emitter
Base
collector
junction
Base
emitter
junction
B
E
Transistor Diagram

11. In above slide notice that the arrow on the emitter
of the transistor symbol point in the direction of
conventional current the both diagram shows that
the emitter current (IE) is the sum of collector
current IC and base current IB mathematically
IE=IC+IB
Base current is very small compare to emitter and
collector current

12. Dc Beta(βDc)and Dc alpha (αDc)
The ratio of the dc collector current Ic to the base
current IB is called Dc beta.
β= Ic ÷ Ib
From 20 to 200 typical value of b dc.
The ratio of Dc collector current Ic to the dc emitter
current IE.
αDc= Ic / IE
Transistor current and voltage
analysis

13.  The ratio of alpha dc is 0.095 to 0.99 a Dc
is always less then 1.
 The reason is that Ic is always slightly less
than IE

14.  VBc=DC voltage at Base w.r.t collector.
 VCB=DC voltage at collector w.r.t base.
 VCE= DC voltage at collector w.r.t emitter.
 VBB forward biase the base emitter junction
and Vcc reverse biase the base collector
junction.
 When base emitter junction is forward biase
it act like a forward biased voltage.

15.  VBE=0.7 V
 Since the emitter is ground (0v).
 Apply (kvl) across RB
 VRB=VBB-VBE
 BY ohm law
 V=IR
 VRB=IB .RB
 Put in
 IB.RB=VBB-VBE
 IB=(VBB-VBE)/RB
1
2
3 2
3
4

16.  Similarly the voltage at the collector w.r.t
emitter.
 VCE=VCC-VRC
 By ohm law
 V=IR
 VRC=IC.RC
 6 in 5
 VCE=VCC-IRC
5
6
7

17.  βDC=IC/Ib
 IB=IC/βDC
 The voltage across reverse biased base
collector junction.
 VCB=VEB-VEB
9
8