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Transistor as a switch and amplifier
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Small base current controls a large collector current.
A small base current in a bipolar transistor controls a larger collector current (I_C = βI_B). Used as a switch (saturated/off) or as a linear amplifier.
β = 100: 0.1 mA controls 10 mA.
Needs a proper bias.
In more detail
A transistor controls a large current with a small signal. As a switch it turns current on and off, and as an amplifier it increases the size of a signal.
Real-world uses
- Microprocessors contain billions of transistors used as switches.
- Audio amplifiers use transistors to boost signals.
- Engineers use transistors to switch loads on and off in digital circuits and to amplify weak signals in radios.
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Frequently asked questions
How does a transistor work?
A small current or voltage at the base controls a larger current between collector and emitter.
Are transistors still made from silicon?
Mostly, though other materials are used for specialised applications.
How does a small current control a large one?
The base current controls the flow of charge through the transistor, so a small input regulates a much larger output current.
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