Transistors: Types and Basics

Transistors Overview

• Semiconductor devices that amplify or switch electronic signals and electrical power.
• Fundamental building blocks of modern electronics.
• Key features include being made from semiconductors (like silicon or germanium), having three terminals, and being capable of amplification and switching.

Types of Transistors

Bipolar Junction Transistors (BJTs)

• Current-controlled devices.
• A small current at the base controls a larger current between the collector and emitter.

NPN Transistor

• It has two layers of N-type semiconductor material separated by a layer of P-type material.
• Current flows from collector to emitter when a small current is applied to the base.

PNP Transistor

• Has two layers of P-type semiconductor material separated by a layer of N-type material.
• Current flows from emitter to collector when a small current is drawn from the base.

Field-Effect Transistors (FETs)

• Voltage-controlled devices.
• The voltage at the gate controls the current between the source and drain.

Junction Field-Effect Transistor (JFET)

• The voltage applied to the gate modulates the conductivity of the channel between the source and drain.
• Types include N-channel and P-channel JFETs.

Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET)

• A voltage applied to the gate modulates the conductivity of the channel between the source and drain.
• Types include N-channel MOSFET (NMOS) and P-channel MOSFET (PMOS).
• Operates in Enhancement Mode and Depletion Mode.

Transistor Parameters

Key Parameters

• Current Gain (β or hFE): The ratio of collector current to base current in a BJT, formula: β = IC/IB.
• Transconductance (gm): The change in drain current with respect to the change in gate-source voltage in a FET, formula: gm = ΔID/ΔVGS.
• Threshold Voltage (Vth): The gate voltage to create a conducting channel in a MOSFET.

Applications of Transistors

• Amplifiers: Used to amplify weak signals in audio, radio frequency, and instrumentation amplifiers.
• Switches: Used as electronic switches in digital circuits, power supplies, and control systems.
• Oscillators: Used in oscillator circuits to generate signals of specific frequencies.
• Logic Gates: Used to implement logic gates (AND, OR, NOT, etc.) in digital circuits.
• Voltage Regulators: Used to maintain a stable output voltage despite input voltage or load current variations.

Advantages of Transistors

• Small Size: Much smaller.
• Low Power Consumption: Consume less power.
• High Reliability: More reliable with a longer lifespan.
• Versatility: Usable in a wide range of applications.

Disadvantages of Transistors

• Temperature Sensitivity: Performance affected by temperature changes.
• Voltage Limitations: They have voltage limitations.
• Susceptibility to Radiation: Can be damaged by radiation.