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

Presented by Zalavadiya Dhaval Wuppuluri Rahul (140120111021) (140120111022)

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)

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

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

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 .

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)

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.

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)

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

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

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 .

Transistor Applications: Transistor can act as a Switch