Understanding Diodes, Transistors, and Number Systems

Posted on May 10, 2025 in Technology

Basics of Diodes

• A diode is a two-terminal electronic component that allows current to flow in one direction only. It is formed by a p-n junction, where p-type and n-type semiconductors are joined together.
• When a forward bias is applied to the diode (positive terminal to p-type and negative terminal to n-type), the junction barrier is reduced, allowing current to flow.
• When a reverse bias is applied (positive terminal to n-type and negative terminal to p-type), the junction barrier is increased, preventing current flow.
• Diodes are commonly used in various applications, including rectification (converting AC to DC), switching, signal detection, and voltage regulation.

P-Type and N-Type Semiconductors

• P-type semiconductor: A semiconductor material that has an excess of holes (electron vacancies). These holes can act as positive charge carriers.
• N-type semiconductor: A semiconductor material that has an excess of electrons. These electrons can act as negative charge carriers.
• The doping process, which involves adding impurities to a pure semiconductor material, creates p-type and n-type semiconductors.

Diode Applications

• Rectification: Converting AC voltage to DC voltage using diodes in circuits like half-wave and full-wave rectifiers.
• Switching: Controlling the flow of current in circuits using diodes as switches.
• Signal detection: Detecting and recovering information from modulated signals using diodes in demodulators.
• Voltage regulation: Maintaining a constant voltage level using diodes like Zener diodes in voltage regulators.
• Light-Emitting Diodes (LEDs): Converting electrical energy into light energy.
• Photodiodes: Converting light energy into electrical energy.

Bipolar Junction Transistor (BJT)

A Bipolar Junction Transistor (BJT) is a three-terminal semiconductor device that amplifies or switches electrical signals. It consists of three regions: emitter, base, and collector. The emitter-base junction is forward biased, allowing current to flow from the emitter to the base. The base-collector junction is reverse biased, creating a small collector current. The transistor’s amplification property is due to the relationship between the base current and the collector current. Here’s a basic diagram of an NPN BJT:

Common Base NPN Transistor Characteristics

• Input characteristics: A plot of base current (I_B) versus emitter-base voltage (V_BE) for a fixed collector-emitter voltage (V_CE).
• Output characteristics: A plot of collector current (I_C) versus collector-emitter voltage (V_CE) for different values of base current (I_B).

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Input and output characteristics of a common base NPN transistor.

Number Systems: Binary and Decimal

Binary System

• Uses base 2 (two digits: 0 and 1).
• Each digit is called a bit.
• Represents numbers using a combination of 0s and 1s.

Decimal System

• Uses base 10 (ten digits: 0 to 9).
• Represents numbers using a combination of digits from 0 to 9.

Example: The decimal number 10 (base 10) is equivalent to the binary number 1010 (base 2).