1. Gandhinagar Institute of Technology
Subject : Electronics device and circuit
Presentation Topic : Transistor Fundamentals
Branch : Electronics and Communication engg.
Guided by : Proff. Gunjan jani

2. Presented by Zalavadiya Dhaval Wuppuluri Rahul (140120111021)
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3. Transistor Fundamentals
transistor fundamentals Invented in 1948 by Bardeen, Brattain and Shockley .
Contains three adjoining, alternately doped semiconductor regions:
Emitter (E)
Base (B)
Collector (C)

4. The middle region, base, is very thin compared to the diffusion length of minority carriers .
1 . npn
2 . pnp

5. Bipolar Junction Transistors: Basics+ - IE IB IC
IE = IB + IC ………(KCL)
VEC = VEB + VBC ……… (KVL)

6. DC Load Line The straight line is know as the DC load line.
Its significance is that regardless of the behavior of the transistor, the collector current IC and the collector-emitter voltage VCE must always lie on the load line, depends ONLY on the VCC, RC and RE .

7. The dc load line is a graph that represents all the possible combinations of IC and VCE for a given amplifier. For every possible value of IC, and amplifier will have a corresponding value of VCE.)
It must be true at the same time as the transistor characteristic. Solve two condition using simultaneous equation : 1. graphically
2. Q-point
(FIG > 1)

8. Q-Point (Static Operation Point)
When a transistor does not have an ac input, it will have specific dc values of IC and VCE.
These values correspond to a specific point on the dc load line. This point is called the Q-point.
The letter Q corresponds to the word (Latent) quiescent, meaning at rest.
A quiescent amplifier is one that has no ac signal applied and therefore has constant dc values of IC and VCE.

9. The intersection of the dc bias value of IB with the dc load line determines the Q-point.
It is desirable to have the Q-point centered on the load line. Why?
When a circuit is designed to have a centered Q-point, the amplifier is said to be midpoint biased.
Midpoint biasing allows optimum ac operation of the amplifier.
The co-ordinates
of the Q-point are:
Q = (Vceq , Icq)

10. Selection of Q point
Depending on the application , we can select the position of the Q point on the load line . The shape of amplifire output signal depends on the position of Q point . This is shown in table ,
Application
Position of Q point
Open switch
In the cut off region
Close switch
In the Saturation region
Amplifire
In the Active region

11. Operation Region IB or VCE Char. BC and BE Junctions Mode Cutoff
IB = Very small
Reverse & Reverse
Open Switch
Saturation
VCE = Small
Forward & Forward
Closed Switch
Active Linear
VCE = Moderate
Reverse &
Forward
Linear Amplifier
Break-down
VCE = Large
Beyond Limits
Overload

12. Saturation Point Cut off Point
Point A in fig 1 is called as the saturation point . It corresponds to the maximum possible value of Ic I.e Ic(max) and located on the Y axis as shown . Saturation point is the point of intersection of Y axis and the dc load line .
Cut off Point
Point B in fig 1 . It corresponds to Ic = 0 mA and Vce = Vcc i.e maximum possible value of Vce. It is located on the X axis as shown . Cut off point is the point of intersection of Y axis and the dc load line .

13. Transistor Applications: Transistor can act as a Switch