Transistors Explained - How transistors work

This paragraph introduces transistors as one of the most significant inventions in electronics, highlighting their versatility in shape and type, with a focus on bipolar transistors. Transistors serve dual roles: as switches to control circuits and as amplifiers to boost signals. The physical construction varies from low power transistors in resin cases to high power ones with metal casings attached to heat sinks for cooling. The paragraph also delves into the identification of transistors through part numbers and datasheets, explaining the significance of voltage and current ratings. The anatomy of a transistor is discussed, with pins labeled E, B, and C for emitter, base, and collector, respectively. The explanation includes how these components work in a circuit, with the base pin controlling the flow of current through the main circuit, exemplified by a light bulb analogy. The paragraph concludes with the concept of using transistors for automation and remote control, emphasizing the need for a minimum voltage for the transistor to function effectively.

This section delves into the two primary types of bipolar transistors, NPN and PNP, explaining their physical similarities and the necessity of checking part numbers for differentiation. It describes how current flows through these transistors when connected to a battery and a switch, using a simplified model to illustrate the flow of current in both types. The paragraph further explains the combination of current in the NPN transistor and the division in the PNP transistor, providing specific values for each type. It also introduces the electrical symbols for transistors and the conventional current direction used in circuit design. A metaphor of water flowing through pipes with a gate is used to analogize the functioning of an NPN transistor. The paragraph touches on the historical discovery of electron flow by Joseph Thompson and the difference between conventional current theory and actual electron flow. It also briefly discusses the role of conductors and insulators in electronic circuits.

This paragraph explores the atomic structure of metals and insulators, focusing on the behavior of electrons in different materials. It explains the concept of valence and conduction bands and how they relate to the conduction of electricity in materials like copper (a conductor) and rubber (an insulator). The paragraph then introduces semiconductors, such as silicon, which can act both as an insulator and a conductor when doped with specific materials to form P type and N type materials. The process of creating a PN junction by combining these doped materials is described, along with the formation of a depletion region and the resulting electric field. The dynamics of voltage application and the resulting forward and reverse biases are explained, detailing the movement of electrons and the creation of an electric field that prevents further electron movement. The paragraph also discusses the doping process in more detail, illustrating how the addition of phosphorus and aluminum changes the electrical properties of silicon, leading to the formation of NPN and PNP transistors.

The final paragraph focuses on the operation of NPN transistors, detailing the structure with two N type layers and one P type layer. It explains the concept of barriers and how they prevent current flow under normal conditions. The paragraph describes the process of creating a forward bias by connecting a battery across the base and emitter, leading to the collapse of the barrier and the movement of electrons. The role of doping in the transistor's function is emphasized, with the heavily doped emitter releasing excess electrons and the lightly doped base allowing few electrons to occupy holes. The paragraph also explains the reverse bias scenario and how it affects electron and hole movement. The impact of varying voltage on the base pin and its effect on transistor operation is discussed, with a higher voltage leading to increased current and electron movement. The summary includes an overview of the electron flow in the emitter and collector sides of the transistor and concludes with a call to action for further learning in electronic engineering.