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ELECTRONICS

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Consists of a specially treated semiconductor crystal

Has 3 terminal instead of 2 Emitter (E), base (B) and collector (C)

Can link 2 separate circuits current through one circuit controls currentthrough other.

2 types n-p-n transistors and p-n-p transistors

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Understanding Transistors

Consists of a specially treated semiconductor crystal

Has 3 terminal instead of 2 Emitter (E), base (B) and collector (C)

Can link 2 separate circuits current through one circuit controls currentthrough other.

2 types n-p-n transistors and p-n-p transistors

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The n-p-n Transistors

Consists a layer of p-type semiconductor sandwiches between 2 layers of n-typesemiconductors.

n-type layers emitter and collector

p-type layer base

Current flows from C to E

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The p-n-p Transistors

Consists of a layer of n-type semiconductor sandwiched between 2 layers of p-type semiconductors.

P-type layers emitter and collector

N-type layer base

Current flows from E to C

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Functions & Junctions in a Transistor

 A transistor has 2 p-n junctions

 Acts as a diode.

Terminal FunctionEmitter (E) Supply charge carriers to C

Collector (C) Receive charge carriers from E

Base (B) Control the flow of charge carriersfrom E to C

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The Flow of Current in a Transistor

Emitter-base junction forward biased

Base-collector junction reverse biased

2 parts to a transistor circuit base circuit & collector circuit Base current, IB  current flows in a base circuit

Collector current, IC  current flows in a collector circuit

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Consider an n-p-n transistor in a circuit… 

Switched on base-emitter junction is forward biased

Depletion layer narrows its resistance lowers

Cause majority charge carriers (e) in n-semiconductor to flow from E to B.

Number of holes in depletion layer also decreased

Few electrons combine with holes, some remaining electrons flow back into the basecircuit and the rest into the collector circuit.

Base-collector is reverse biased

Electrons cannot flow from collector terminal to the base terminal.

Instead, electrons are attracted across the base-collector junction due to ahigher potential difference at collector terminal.

Flow of current to collector collector current, IC

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•Bulb X and Y connected to a circuit with n-p-n transistor.

• Variable resistor, RB in the base circuit to control the amount of basecurrent, IB

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