Lecture 13
Transistor
• A semiconductor device that acts as
– An electrically controlled switch
– A current amplifier
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BJT, JFET, and MOSFET
• Bipolar Junction Transistor
– NPN and PNP
• Junction Field Effect Transistor
• Metal Oxide Semiconductor FET
BJT transistor
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JFET
MOSFET
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BJT
• NPN: a small input current and a positive voltage applied
at base allows to flow from collector to emitter
• PNP: a small output current and a negative voltage at base
allows a much larger current to flow from emitter to
collector
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BJT Water Analogy
NPN (VB > VE)
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PNP (VB < VE)
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NPN Transistor in a Circuit 1
NPN (VB > VE)
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NPN Transistor in a Circuit 2
NPN (VB = VE)
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Transistor Experiment 1
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Transistor Experiment 2
C1
1uF
L1
LED
Q1
NPN transistor
Q2
PNP transistor
R1
4.7kΩ
R2
10MΩ
R3
100Ω
Oscillator
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JFET
•
•
•
•
Junction field effect transistor
Electrically controlled switches
Current amplifiers
Voltage-controlled resistors
– Do not require a bias current
• Normally on when VG - VS = 0
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JFET: How It Works
N-channel JFET: a negative voltage is applied at gate to
reduce current flow from drain to source
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JFET Water Analogy 1
N-channel JFET
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JFET Water Analogy 2
P-channel JFET
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JFET Current
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Full Current Passes
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Reduced Current Passes
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No Current Passes
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MOSFET
• Metal oxide semiconductor FET
• Similar to JFET
• High impedence (1014 Ω)
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MOSFET Type
• Depletion type
– Normally on (VG = VS)
• Enhancement type
– Normally off
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MOSFET: How It Works
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MOSFET Experiment 1
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MOSFET Experiment 2
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MOSFET Experiment 3
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Transistor Experiments
Experiments
What’s micro controller
Chapters
Basic A and D
Earth measurements
Robotics
StampWorks
Others
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