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)

Write a short note dispersion shifted dispersion flat fiber, Write a short ...

Write a short note on dispersion shifted and dispersion flatted fibers? The dispersion features of a fiber is display below: The overall dispersion is the sum of materi

Role of gis in distribution reforms, Role of GIS in Distribution Reforms: ...

Role of GIS in Distribution Reforms: You will agree which distribution is the weakest link in the chain of power supply and has been identified as the key focus area in power

Reduce the circuit to a thevenin and a norton equivalent, Q. Reduce the cir...

Q. Reduce the circuit of Figure to a Thévenin and a Norton equivalent circuit with respect to terminals a-b.

Explain the operation as a buffer, Q. An interesting application of the SRF...

Q. An interesting application of the SRFF is as a buffer in overcoming contact bounce in mechanical switches. These switches, of the toggle type, may be used to change the logic st

Seal management - meter field testing, Seal Management - Meter Field Testin...

Seal Management - Meter Field Testing For an effective seal management system it is necessary that: i) The  seals  used  are  tamper  proof,  that is they  cannot  be  remo

Mobile communication, #qConsider a point-to-point radio link between two hi...

#qConsider a point-to-point radio link between two highly directional antennas in a stationary environment. The antennas have antenna gains of 30 dB, distance attenuation is 150 dB

L filters, L filters: An L filter contains two reactive elements that ...

L filters: An L filter contains two reactive elements that are one in series and one in parallel. T and π filters: Main article: Capacitor-input filter

Calculate the resistance of the coil of a transistor, A 6 V / 2.5 mA relay ...

A 6 V / 2.5 mA relay is connected in the output stage of a transistor.  The coil is made of aluminium having α = 0.004. The resistance of the coil is 600 ? at 32 o C. Calculate th

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