Fundamental Physics/Electronics/Transistors

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Transistorer (cropped).jpg

A transistor is a three terminal electronic component which is made of semiconductor material. A transistor has three terminals namely, emitter, base and collector which forms two junctions BE and CE

Emitter is the region thru which majority carriers enter the transistor. Emitter is heavily doped. Base is the middle layer and it is very lightly doped. Collector is wide and moderately doped.

Transistors are fundamentally current amplifiers. The transistor is essentially a resistor which allows current to flow. The word transistor is a contraction of current-transferring resistor.

Transistors are commonly used in amplification , switching, and buffering signals or applied voltages.

Construction and Symbol[edit]

A Transistor is an electronic component created by joining two types of semiconductors. One type of semiconductor is "P-type" and the other is "N-type". The two types of bipolar-junction transistors (BJTs) that result are explained below.

NPN transistor[edit]

1) A P-type region lies between 2 N-Typed Semi Conductors . This kind of configuration is called NPN Transistor.

NPN BJT.svg     BJT symbol PNP.svg

PNP transistor[edit]

2) An N-type region lies between 2 P-Typed Semi Conductors . This kind of configuration is called PNP Transistor.

PNP BJT.svgBJT symbol NPN.svg

It is equivalent to two nose-to-nose diodes, but as before, just connecting two diodes will not work. Generally, a PNP diode is identical to an NPN diode, but with all currents reversed.


I V Curve[edit]

Manufacturer's IV Graph specification tell transistor operation

Current-Voltage relationship of BJT.png

Operation Modes[edit]

. Transistor is OFF
. Transistor is ON
. Transistor is saturated


With the right connection, by connecting transistor with resistor(s) Transistor can acts as

An electronics amplifier[edit]

Provided that, transistor should be turned ON with biased voltage at the base must be greater than diode's break over voltage


An electronics switch[edit]

Transistor is switch On when
Transistor is switch Off when

A buffer[edit]


See also[edit]