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)

What are the modes used in keyboard modes, What are the modes used in keybo...

What are the modes used in keyboard modes? 1. Scanned Keyboard mode with 2 Key Lockout. 2. Scanned Keyboard particular Error Mode. 3. Scanned Keyboard with N-key Rollover

Features and usage of peripheral component interconnect bus, Discuss featur...

Discuss features and usage of Peripheral Component Interconnect bus. Peripheral Component Interconnect bus has plug as well as play characteristics and the capability to func

What do you mean by fm stereo, Q. What do you mean by FM Stereo? IT  sh...

Q. What do you mean by FM Stereo? IT  shows the block diagram of an FM stereo transmitter and an FM stereo receiver. The following notation is used: • f L (t), fR(t): Left a

Define the baud rate with respect to serial communication, With respect to ...

With respect to serial communication define the baud rate. The rate of data transfer into serial data communication is denoted in bps. Bits per second (bps) are the rate of in

Torque required to turn a self excited generator, Work must be done against...

Work must be done against the electromagnetic torque in order to generate the voltage (and current) supplied to the electrical load connected to the generator. Therefore energy con

Rectifiers - Rectifiers and inverters , Rectifiers As discussed  above...

Rectifiers As discussed  above the  purpose  of the  rectifier is to  convert the incoming  ac from a transformer or other ac  source  to some  form of  pulsating dc. That it i

Logical operations , Logical Operations Various  operations like and  ...

Logical Operations Various  operations like and  or exclusive  or complement compare and rotate are called  logical  operations. Generally flags ( not all always) are modified

What are the various tones used in stronger telephony, Q. What are the vari...

Q. What are the various tones used in stronger telephony? When called party line is obtained, exchange control equipment transmits out the ringing current to telephone set of t

Silicon Photonics, How does a Mach-Zehnder Modulator work in Silicon?

How does a Mach-Zehnder Modulator work in Silicon?

Explain the properties of low resistivity materials, Explain the properties...

Explain the properties of low resistivity materials. Low resistivity materials: The conducting materials containing resistivity from 10 -8 to 10 -6 ohm-m come under this cl

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