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4.3 Transistor
Electrical Technology · Grade 10 · 16 lessons in the design
What this covers
- The transistor: structure (NPN and PNP) and its three terminals
- The operation of a transistor (a small base current controls a large collector current)
- The transistor as a switch and as an amplifier
- Selecting, testing and constructing transistor circuits
What you will be able to do
- describe the operation of a semiconductor transistor
- verify the voltage-current characteristic of a transistor
- select an appropriate transistor for a given application
- construct transistor circuits in a workplace
- appreciate the importance of transistors in electronics
Key questions
“How does a transistor work, and why is it so important in electronics?”
Lessons
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The transistor
40 min · 1 practice tasks · quizHow a transistor uses a small base current to control a much larger current, its structure (NPN/PNP) and three terminals, its use as a switch and as an amplifier, how to select and test one, and why the transistor is the most important component in electronics.
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The bipolar junction transistor
40 min · 1 practice tasks · quizHow a BJT differs from a diode: two PN junctions and three terminals so a small current can control a large one.
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NPN and PNP structure
40 min · 1 practice tasks · quizHow NPN and PNP sandwiches are layered, why the base is thin, and which majority carriers flow in each type.
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Base, collector and emitter
40 min · 1 practice tasks · quizThe job of each BJT terminal, the current law Ie = Ic + Ib, and why the collector is the heat terminal.
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Transistor circuit symbols
40 min · 1 practice tasks · quizHow to draw NPN and PNP symbols, why the arrow sits on the emitter, and why package pinouts must be read from the datasheet.
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Biasing the two junctions
40 min · 1 practice tasks · quizHow forward and reverse bias on the base-emitter and collector-base junctions set cut-off, active and saturation.
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Current gain (beta)
40 min · 1 practice tasks · quizHow beta (hFE) is Ic divided by Ib, a typical range of 50 to 300, and why you must not treat beta as an exact constant.
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Cut-off, active and saturation
40 min · 1 practice tasks · quizThe three BJT regions: cut-off for switch off, saturation for switch on, and the active region for amplifying.
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The transistor as a switch
40 min · 1 practice tasks · quizHow an NPN in cut-off and saturation turns an LED, lamp or relay on and off with no moving contacts.
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The transistor as an amplifier
40 min · 1 practice tasks · quizHow a small changing base current in the active region produces a larger copy in the collector, used in radios and sound systems.
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Voltage-current characteristics
40 min · 1 practice tasks · quizHow to read and verify the Ic against Vce family of curves for steps of Ib, the curriculum practical for the transistor characteristic.
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Selecting a transistor
40 min · 1 practice tasks · quizHow to choose NPN or PNP, voltage, current, power, gain and package from a datasheet for a given job.
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Testing a transistor
40 min · 1 practice tasks · quizHow to test a BJT on a meter in diode mode as two junctions, identify NPN versus PNP, and spot short, open or leaky faults.
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Building a transistor switch
40 min · 1 practice tasks · quizWorkplace steps to construct, power and test an NPN LED (or relay) switch with the correct resistors and pinout.
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Building a simple amplifier
40 min · 1 practice tasks · quizHow a common-emitter stage with bias resistors and coupling capacitors amplifies a small sound into an earpiece.
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Why transistors matter
40 min · 1 practice tasks · quizHow switching and amplifying made computing, radio and Kenya electronics jobs possible, answering the sub-strand inquiry.