Fundamental Of Transistors

1. TRANSISTORS
“The building blocks of
electronics world”

2. Intrinsic Vs Extrinsic Semiconductor
Intrinsic Extrinsic
It is pure semi-conducting material and no
impurity atoms are added to it.
It is prepared by doping a small quantity
of impurity atoms to the pure semi-
conducting material.
Examples: crystalline forms of pure silicon
and germanium.
Examples: crystalline forms of pure silicon
and germanium.
The number of free electrons in the
conduction band and the no. of holes in
valence band is exactly equal and very
small indeed.
The number of free electrons and holes is
never equal. There is excess of electrons
in n-type semi-conductors and excess of
holes in p-type semi-conductors.
Its electrical conductivity is low. Its electrical conductivity is high.
Its electrical conductivity is a function of
temperature alone.
Its electrical conductivity depends upon
the temperature as well as on the
quantity of impurity atoms doped the
structure.

3. Knee Point Voltage
• Knee Point voltage is the minimum voltage
after which the PN junction diode starts
conducting overcoming the barrier potential
• Si– 0.7 volts
• Ge- 0.4 volts
• Si- Silicon
• Ge- Germanium

4. V/I Characteristics of a diode

5. How does Transistor Look Like ??

7. The first transistor
In 1947, John
Bardeen and
Walter Brattain
deviced - the first
"point contact"
transistor.

8. Moore’s Law
It’s an observation made by Gordon E. Moore, in
which he predicted that the number of transistors,
inside an Integrated Circuit, could be
doubled every 24 months.
At the density that also
minimized the cost of a transistor.

9. Transistor Definition
• Transistor is an electronic device made of
three layers of semiconductor material
that can act as an insulator and a
conductor.
• The three layered transistor is also
known as the bipolar junction transistor.

10. Bipolar Junction Transistors (BJT’s)
• The term bipolar refers to the use of both
holes and electrons as charge carriers in the
transistor structure
• There are two types of BJTs, the NPN and PNP

11. Basic construction

12. Regions of a transistor
• A transistor has three regions namely,
• Emitter- heavily doped
• Base- lightly doped
• Collector- moderately doped

13. Transistor symbols

14. Transistor operation
force – voltage/current
water flow – current
- amplification

15. Transistor biasing
• The base-emitter (BE) junction is forward
biased
• The base-collector (BC) junction is reverse
biased.
IE=IB+IC

16. Operating regions of BJT
Cut off region
Linear region
Saturation region

17. Types of transistor
• BJT - Bipolar Junction Transistor
• UJT- Unipolar Junction Transistor
• FET - Field Effect Transistor
• MOS - Metal Oxide Semiconductor

18. Transistor applications
Transistor as a switch
When used as an electronic switch, the
transistor is normally operated alternately in
cut-off and saturation regions.

19. Transistor as amplifier
• Due to the small changes in
base current the collector
current will mimic the input
with greater amplitude