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)

Define sampling below the nyquist rate, Define Sampling below the Nyquist R...

Define Sampling below the Nyquist Rate? A further reduction of the sampling frequency will reason one sample to be taken each period. The Case 3 plot depicts the effect of this

Characteristics of an n-channel enhancement mosfet, Q. Find idealized expre...

Q. Find idealized expressions for the active and ohmic states and sketch the universal characteristics of an n-channel enhancement MOSFET operated below breakdown.

Net force on the wire due to the interaction of the b-field, Q. (a) Show by...

Q. (a) Show by applying Ampere's circuital law that themagnetic field associated with a long straight, current-carrying wire is given by B φ = µ 0 I/(2πr), where the subscript φ d

#bode plots.., #how to draw bode plots for a transfer function

#how to draw bode plots for a transfer function

Determine the equivalent inductance, Determine the equivalent inductance: ...

Determine the equivalent inductance: Two coils of inductances 4H and 6H are connected in parallel. If their mutual inductance is 3 H, determine the equivalent inductance of th

Explain the signals hold and sid, Explain the signals HOLD, READY and SID ...

Explain the signals HOLD, READY and SID HOLD indicates that a peripheral such as DMA controller is requesting the use of address bus, data bus and control bus. READY is used to

Find the cutoff frequency, Q. A rigid 50- coaxial transmission line has ai...

Q. A rigid 50- coaxial transmission line has air as dielectric. If the radius of the outer conductor is 1 cm, find the cutoff frequency

Find the current through the diode in the circuit, Q. A diode is connected ...

Q. A diode is connected in series with a voltage source of 5 V and a resistance of 1 k. The diode's saturation current is given to be 10 -12 A and the I-V curve is shown in Find

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