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Transistors, Sarah Faisal -(cs) - Coggle Diagram
Transistors
A device with three terminals.
Collector
Moderately doped
Has the largest area amongst the other two regions
Emitter
Heavily Doped
Has an area larger than base but smaller than collector
Base
lightly doped
Has the smallest area amongst the other 2 regions.
Two types of bipolar junction transmitter(BJT) transistors.
N-P-N transistor :
collector and emitter are negative while the base in positive
WORKING
As emitter is N-type, then it has majority electrons.
Base has lesser holes due to thin area and light doping.
Collector has electrons, moderately doped.
since there are few holes in base, some electrons move to IB and the rest are attracted by the positive terminal of Vcc. Since Vcc has greater potential electrons move from base to collector to Ic.
If the base is at a higher voltage than emitter, current flows from collector to emitter.
P-N-P transistor
collector and emitter are positive while the base in negative
N-type material is sandwiched between two P-type materials.
It has holes in majority.
If the base is at a lower voltage than emitter, current flows from emitter to collector.
Current gain:
B
=
I
c/
I
b
Beta does not have unit.
there is fixed beta value for each transistor.
APPLICATIONS
Transistor as a switch
Transistor as an Amplifier
Working
The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition.
This forward bias is maintained regardless of the polarity of the signal.
The low resistance in input circuit, lets any small change in input signal to result in an appreciable change in the output.
The emitter current caused by the input signal contributes the collector current, which when flows through the load resistor RL, results in a large voltage drop across it.
Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier.
Amplifies the voltage.
It mainly works as an amplifier.
Has 3 semi-conductors and 2 PN junctions.
Normally, for normal operation of transistor the base-emitter junction is forward biased.
Sarah Faisal -(cs)
