4.3 Understanding Transistors
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Transcript of 4.3 Understanding Transistors
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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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