BJT or Bipolar Transistor is a very famous transistor in Electronics. In this Presentation we tried our best to describes about Bipolar Transistor in details

1. Welcome to Our Presentation
PRESENTATION TOPIC: BIPOLAR JUNCTION TRANSISTOR

2. Group Members:
• Sumaiyya
• Yeasin
• Rifat
• Bappy
• Anik
• Salim

3. Transistor
• A transistor consists of two pn junctions formed by
sandwiching either p-type or n-type semiconductor
between a pair of opposite types.
• There are two types of transistors,
• n-p-n Transistor
• n-p-n Transistor

4. Bipolar Junction Transistor
In each transistor following points to be noted
i) There are two junction, so transistor can be
considered as two diode connected back to back.
ii) There are three terminals.
iii)The middle section is thin than other.

5. Naming of Transistor Terminals
• Transistor has three section of doped
semiconductor.
• The section one side is called
“emitter” and
the opposite side is called “collector”.
• The middle section is called “base”.

6. Emitter
• The section of one side that supplies carriers is
called emitter.
• Emitter is always forward biased wr to base so it can
supply carrier.
• For “npn transistor” emitter supply holes to its
junction.

7. Base
• The middle section which forms two pn junction between
emitter and collector is called Base.

8. Collector
• The section on the other side that collects carrier is
called collector.
• The collector is always reversed biased wr to base.
• For “npn transistor” collector receives holes to its
junction.

9. Working of npn transistor
Forward bias Is applied to emitterbase junction
and reverse bias is applied to collectorbase
junction.
The forward bias in the emitter-base junction
causes electrons to move toward base. This
constitute emitter current, IE

10. Working of npn transistor
As this electrons flow toward p-type base,
they try to recombine with holes. As base is
lightly doped only few electrons recombine
with holes within the base.
These recombined electrons constitute
small
base current.
The remainder electrons crosses base and
constitute collector current.
IE = IB + IC

11. Transistor Operating Modes
• Active Mode
• Base- Emitter junction is forward and Base Collector junction is reverse
biased.
• Saturation Mode
• Base- Emitter junction is forward and Base Collector junction is forward
biased.
• Cut-off Mode
• Both junctions are reverse biased

12. Transistor Connection
• Transistor can be connected in a circuit in following
three ways-
• Common Base
• Common Emitter
• Common Collector

13. Common Base Connection
• In this circuit arrangement, input is applied between emitter and
base and output is taken from collector and base. Here, base of the
transistor is common to both input and output circuits and hence
the

14. Common Base Connection
•
Total emitter current does not reach the collector
terminal, because a small portion of it constitute
base current. So , IE = IC + IB
• As collector is reversed bias so there will be a small
amount of leakage current, ICBO
• So, collector current constitute of portion of
emitter current and leakage current ICBO
• IC = αIE + ICBO

15. Expression for Collector Current
• Current amplification factor (α): The ratio of change in collector
current to the change in emitter current at constant collector-base
voltage VCB is known as current amplification factor
α =
∆𝐼𝑐
∆𝐼𝐸
IC = αIE + ICBO
IC = α (IC + IB) + ICBO [since IE = IC + IB]
IC (1 - α) = α IB + ICBO
IC =
𝛼
1−𝛼
IB +
𝐼𝐶𝐵𝑂
1−𝛼

16. Common Emitter Connection
• In this circuit arrangement, input is applied between base and
emitter and output is taken from the collector and emitter. Here,
emitter of the transistor is common to both input and output
circuits and

17. Expression for Collector Current
• Base current amplification factor ( β): The ratio of change in
collector current (ΔIC) to the change in base current (ΔIB) is known
as base current amplification factor. β =
ΔIC
ΔIB
• IC =
𝛼
1−𝛼
IB +
𝐼𝐶𝐵𝑂
1−𝛼
• Ic =
𝛼
1−𝛼
IB + ICEO [since ICEO =
𝐼𝐶𝐵𝑂
1−𝛼
]
• Ic = βIB + ICEO

18. Relation Between α and β
• We know, α =
𝐼𝑐
𝐼𝐸
-----(i) and β =
I𝐶
I𝐵
---------(ii)
• IE = IB + IC. Now from (i), α =
I𝐶
I𝐵+𝐼𝐶
=
(
𝐼𝐶
𝐼𝐵
)
𝐼𝐸
𝐼𝐵
+ (
𝐼𝐶
𝐼𝐵
)
=
β
1+β
• IB = IE – IC. Now from (ii), β =
I𝐶
I𝐸−𝐼𝐶
=
(
𝐼𝐶
𝐼𝐸
)
𝐼𝐸
𝐼𝐸
− (
𝐼𝐶
𝐼𝐸
)
=
α
1−α

19. Common Collector connection
• In this circuit arrangement, input is applied between base and
collector while output is taken between the emitter and collector.
Here, collector of the transistor is common to both input and
output circuits

20. Common Collector connection
• Current amplification factor γ : The ratio of change in emitter
current (ΔIE) to the change in base current (ΔIB) is known as current
amplification factor. γ =
ΔI𝐸
ΔIB
• IC =
𝛼
1−𝛼
IB +
𝐼𝐶𝐵𝑂
1−𝛼
• Ic or IE = (β+1)IB + (β+1)ICBO [since
𝛼
1−𝛼
= (β+1)]

21. Thank You