A transistor is a semiconductor device that can amplify signals or act as a switch in electronic circuits. It’s one of the most important components in electronics, powering everything from smartphones to computers.
—
Key Features of a Transistor
Terminals: 3 — Collector (C), Base (B), Emitter (E)
Polarity: Depends on type (NPN or PNP)
Symbol: Triangle with lines showing current direction
Unit: None specifically; it’s measured by gain (hFE or β)
Material: Usually silicon or germanium
—
How a Transistor Works
A transistor can operate in two main ways:
1. As a Switch
ON: Small current at the base allows a larger current to flow from collector to emitter.
OFF: No base current → collector-emitter path is blocked.
Used in digital circuits, microcontrollers, and logic gates.
2. As an Amplifier
Small input signal at the base controls a larger output signal from collector to emitter.
Used in audio amplifiers, radios, and signal processing.
—
Types of Transistors
1. Bipolar Junction Transistor (BJT)
Current-controlled device.
Two types:
NPN: Current flows from collector to emitter when base is positive.
PNP: Current flows from emitter to collector when base is negative.
Common in switching and amplification.
2. Field Effect Transistor (FET)
Voltage-controlled device.
Types:
JFET (Junction FET): Voltage at gate controls current flow.
MOSFET (Metal-Oxide-Semiconductor FET): High-speed switching, widely used in power electronics.
Common in digital circuits, microcontrollers, and power devices.
3. Darlington Transistor
Two BJTs in one package for high current gain.
Used in high-power amplifiers and motor drivers.
4. IGBT (Insulated Gate Bipolar Transistor)
Combines MOSFET ease of control with BJT high current capability.
Used in inverters, EVs, and industrial drives.
—
Applications of Transistors
Switching Circuits: Turning devices on/off electronically.
Amplifiers: Audio, radio, and signal amplification.
Oscillators: Generating repetitive signals for clocks and radios.
Voltage Regulation: Used in power supply circuits.
Digital Logic: Core component of microchips and processors.
—
Fun Facts
Modern CPUs contain billions of transistors in a single chip.
MOSFETs are the backbone of power electronics and renewable energy systems.
Darlington pairs allow a small base current to control very large loads.
—
Quick Reference
Type Control Type Key Feature Common Use Case
BJT Current Amplification, switching Audio, logic circuits
FET / MOSFET Voltage High-speed switching, low power Microcontrollers, power electronics
Darlington Current High current gain Motor drivers, amplifiers
IGBT Voltage High current + high voltage Inverters, EVs, industrial drives
