# Fundamental Physics/Electronics/Transistors

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

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

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

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

## Chracteristics

### I V Curve

Manufacturer's IV Graph specification tell transistor operation ### Operation Modes

$V>V_{d}.I=0$ . Transistor is OFF
$V=V_{d}.I=1mA$ . Transistor is ON
$V $V=V_{S}.I=I_{s}$ . Transistor is saturated

## Usage

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

### An electronics amplifier

$i_{b}>0$ $i_{e}>\alpha i_{b}$ $i_{c}>\beta i_{b}$ Provided that, transistor should be turned ON with biased voltage at the base must be greater than diode's break over voltage

$v_{b}>v_{be}$ . $v_{be}=v_{d}$ ### An electronics switch

Transistor is switch On when $V_{b}>V_{be}$ Transistor is switch Off when $V_{b} ### A buffer

$v_{c}=v_{b}$ 