Explain junction transistors (npn and pnp), Electrical Engineering

Assignment Help:

Explain junction transistors (npn and pnp).

Junction Transistor:

This transistor consists of two p-n junctions combined in one crystal as demonstrated in figure below.

710_npn and pnp.png

There are two major forms of junction transistors depending on whether the middle section is on a p material or an n material. The middle sector is termed as the base and the outer regions are termed as the emitter and the collector correspondingly.

The transistor is a 3-terminal device and its properties may be given in terms of characteristic curves involving the three currents and the three voltages demonstrated in figure below.

521_3 terminal device of transistor.png

Within a transistor there is zero resultant current of electrons and holes across all junctions. If the collector is connected directly to the base and a small positive voltage is applied among emitter and base after that a current flows just as in a p-n junction diode in the forward direction. Likewise if the emitter is joined to the base and a negative voltage is applied in between collector and base, current flows in the reverse direction, demonstrating a saturation of collector current.

These voltages with similar polarity are applied simultaneously as demonstrated in figure below.

2109_voltages with similar polarity in transistor.png

The potential barrier in between base and emitter is decreased and the flow of holes across the barrier greatly rises. There is an increased flow of electrons from base to emitter but because the hole density in the p- region is much higher than the electron density in the n- area, the current may be seem to be mainly because of the holes. The holes enter the n- region and diffuse by this, and combine with the electrons in that area as the base region is made sufficiently thin, many of holes reach the collector and base junction and very little arrive at the base terminal. Holes fall easily into the collector region on account of field at the collector base junction. Therefore the collector current is very nearly equivalent to the emitter current and the base current is almost zero. VCB has little effect on the current as long as its magnitude is above various minimum values and the base is adequately thin. A small change in VEB causes a change in IC resulting in an approximately equal change in IC.


Related Discussions:- Explain junction transistors (npn and pnp)

Explain working of single-phase induction motors, Q. Explain working of Sin...

Q. Explain working of Single-Phase Induction Motors? For reasons of simplicity and cost, a single-phase power supply is universally preferred for fractional-horsepower motors.

Simple zener voltage regulator, Consider a simple zener voltage regulator w...

Consider a simple zener voltage regulator with the circuit diagram shown in Figure (a). (a) For a small reverse resistance R Z S and V S - R S i out > V Z , show that v ou

Sub threshold, Sub Threshold The sub threshold I-V curve depends expon...

Sub Threshold The sub threshold I-V curve depends exponentially on the threshold voltage, introducing a strong reliance on any manufacturing variation that influences threshol

Draw a one-line diagram of three-phase distribution system, Q. A three-phas...

Q. A three-phase transformer bank consisting of three 10-kVA, 2300:230-V, 60-Hz, single-phase transformers connected in Y- is used to step down the voltage. The loads are connecte

Amplifier, Amplifier Usually, an amplifier or simply amp, is any devic...

Amplifier Usually, an amplifier or simply amp, is any device which changes, generally increases, the amplitude of a signal. The connection of the input to the output of an amp

Depletion zone in p-n junction, Depletion Zone in P-N Junction The pow...

Depletion Zone in P-N Junction The power of the depletion zone electric field gets increases as the reverse-bias voltage increases. One time the electric field intensity incre

Illustrate process characterics of ultrasonic machining, Discribe the ultra...

Discribe the ultrasonic machining with main emphasis on the following (a) Basic working Principle and machining set up (b) Accuracy and surface complete on work materials

What is meant by doping, What is meant by doping? How does it affect a semi...

What is meant by doping? How does it affect a semiconductor? Doping: The process through which an impurity is added to semiconductor is termed as doping. A semiconductor to th

Physics, what is the significant of damping coficient

what is the significant of damping coficient

Pneumatics, 3. Design and draw a circuit using the cascade system to operat...

3. Design and draw a circuit using the cascade system to operate two cylinders (A and B) which, on the operation of a start valve, produces the sequence A – B + B – A+. The cylinde

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd