Introduction:- Transistor is a device which works on the phenomena of transfer of resistance. Transistor is a device which are made by sandwich the to p-n diode.
Types of Transistor:-
There are two types of transistors:
1) N-P-N Transistor.
2) P-N-P Transistor.
1) N-P-N Symbolic Diagram
Fig. (1)
2) P-N-P Symbolic Diagram:-
Fig. (2)
Working of Transistor:-
Fig. (3)
The systematic diagram of transistor is shown is in fig. (3) .
1) For working of transistor the emitter is forward bias w.r.t base and collector is reverse bias w.r.t base.
2) The forward bias are at the emitter base Junction reduce the barrier potential and narrow the depletion region. However the relative Lite drop bass light doped base and collector regions produce a width depletion region under the reverse bias. The worth nothing point is that the effective base width w b between the depletion region is very narrow.
Electron are injected into the emitter region by the emitter bias supply voltage emitter base. conduction band electrons have enough energy to overcome the emitter base barrier potential. The injected electrons enter the very thin, lightly doped this region. because the base is very lightly doped related to the emitter region, only a few of the electrons are We combine with the holes dropped into the base.
injection of electrons make the electrons consideration on the amateur junction very large and on the collector junction the constitution of the electrons is extremely small and as such the gradients of the electrons concentration is very large in the base. Injected electrons diffuse into the collective region to to extremely small thickness of base which is much less than the diffusion length. Most of the electrons process into the collector region for stop collector is Reverse Biased and creates a strong electrostatic field between the base and collector. The field and immediately immediately Ee collects the diffuse electrons which enter the collector Junction. Flow of electrons into the base region when confronted with the holds a few electrons se 12 5% combined and utilise and rest of the electron se 95 to 95% of the injected electron diffuse into the collector region and collected by the collector electrodes. To maintain the base neutrality the base electrodes provide equal number of electrons which have combined with holes and result in a base current. Does the emitter current I is equal to the sum of collector current IC and base current IB. The ratio of collector current ic2 emitter current I is called alpha and it is measured of possible current amplification. In a transistor Alpha cannot be higher than Unity, but practical value of 0.95 to 0.9 and are attend in commercial transistor.
The operation of both PNP and NPN transistor are same on the basis of above as explained.
How to find Emitter, Base & Collector Terminal:-
To find the emitter, base and collector terminal the following step to be taken:
1) First we have to find out the type of transistors. As we know that transistor is made up of by sandwiching to P-N junction diode. So first find out the terminal "Base".
2) Base is a common terminal between emitter and collector. It's resistance is intermediate with emitter and collector. Put the negative terminal of the multi meter on one terminal at positive terminal on the other two terminal one by one. If the multi meter shows continuity with both the rest of terminal than this terminal is base. You have to check like this with all three terminal and find out the base.
3) Emitter is a terminal with the resistance grater than base and lower than collector. Similarly Collector is a terminal with the resistance more grater than base and emitter . Put the terminal of the multi meter with the other's two terminal and find out the resistance value. The lower resistance value with respect to base shows the " Emitter Terminal" and the grater resistance value with respect to base shows the " Collector Terminal".
Application:-
Transistor is used in many application such as switches, amplifiers etc.
Operating condition for a transistor
1. Forward reverse biasing- For normal operation of a transistor emitter base Junction is always forward biased and collector base junction is always reverse biased full stop this type of icing is known as forward reverse biasing for the purpose of this battery e v e p is connected between ammeter and base while battery vcb is connected between collector and base. In forward reverse biasing the transistor is in region and the collector current Ic depend upon the emitter current Ie. Generally transistor is operated in this region for amplification.
2. Forward-Forward Biasing- In this by saying both the collector and emitter a foreword by. The transistor operated in saturation region. In this region the collector current comes independent of the base current. Thus the transition act like a closed switch.
3. Reverse reverse biasing:- In this biasing both junctions are reverse biased first off this by saying the transistor are practically zero current because the amateur does not emit charge carrier into the base and no charge carrier are collected by the collector, accept a few thermally generated minority carriers. Thus the transistor acts like and open switches.
4. Reverse forward Biasing:- In this emitter - base junction is reverse biased while base-collector junction is forward biased. So the emitter dose not emit any charge carrier hence no any carrier injected to base as the depletion layer between the emitter - base is broader wide. On the other side the depletion region between the base-collector is very thin but no majority charge carriers injected to base therefore little bit carriers enter in the collector and negligible current flow through the collector.
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