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UET102 Module 3 - Diodes, Transistors, and RL-RC Circuits

Module 3 Overview of UET102

  • Focus on diodes and transistors.

    • Diodes: Allow current to flow in one direction; critical for rectification from AC to DC.

    • Transistors: Used for amplification and switching.

    • Compare RL (Resistive-Inductive) and RC (Resistive-Capacitive) circuits.

Lesson 1: Diodes

Introduction to Diodes

  • Definition: Diodes are semiconductor devices that permit current to pass in one direction while blocking it in the opposite direction.

  • Functions of Diodes:

    • Convert alternating current (AC) to direct current (DC).

    • Protect circuitry from voltage spikes.

    • Facilitate charging processes (critical for UAS).

Types of Diodes

  • Regular Diodes: Standard applications in rectification.

  • Zener Diodes: Provide stable reference voltages; operate in reverse breakdown for voltage regulation.

  • Schottky Diodes: Characterized by their fast switching and low voltage drop.

  • LEDs (Light Emitting Diodes): Produce light when current flows.

  • Photodiodes: Respond to light; used in solar cells and optical applications.

Diode Construction

  • Composed of p-type and n-type materials, forming a pn junction.

    • n-region: Abundant electrons.

    • p-region: Abundant holes.

  • Depletion Region: Area at the junction devoid of charge carriers, creating a potential barrier.

Biasing of Diodes

  • Forward Bias:

    • Connected such that the positive side of the power source is attached to the p-region.

    • Allows current to flow through.

    • Barrier Potential for Silicon Diodes: Approximately 0.7V (barrier against forward current).

  • Reverse Bias:

    • Positive side connected to n-region, negative to p-region.

    • Prevents current flow until breakdown point.

    • Resulting depletion region widens, effectively disabling current flow.

Lesson 2: Transistors

Introduction to Transistors

  • Transistor Types: Bipolar Junction Transistors (BJTs) and Field-Effect Transistors (FETs).

  • Functionality:

    • Act as amplifiers, switching devices in electronic circuits.

Bipolar Junction Transistors (BJTs)

  • Structure: Composed of three layers (Emitter, Base, Collector) and two junctions (Base-Emitter and Base-Collector).

    • n-p-n or p-n-p configurations.

  • Operation Principle: Current at the base controls larger currents between the collector and emitter.

Field-Effect Transistors (FETs)

  • Control Mechanism: Operated through voltage applied to the gate rather than current.

  • Types include Junction FETs (JFETs) and Metal-Oxide-Semiconductor FETs (MOSFETs).

Lesson 3: RC Circuits

Analysis of Series and Parallel RC Circuits

  • Series RC Circuit:

    • Current is constant; voltage across resistor and capacitor fluctuates based on AC input.

    • Phase Differences: Voltage across resistor aligns with current. Voltage across capacitor lags by 90 degrees.

  • Parallel RC Circuit:

    • When voltage is applied, both currents flow through the resistor and capacitor simultaneously.

    • The capacitor current leads voltage by 90 degrees.

Power in RC Circuits

  • Energy Transfer: In certain setups, the energy stored in the capacitor can be returned to the circuit without loss.

  • Applications: Timing devices, signal conditioning in UAVs.

Lesson 4: RL Circuits

Analysis of RL Circuits

  • RL Series Circuit:

    • Impedance varies with frequency; inductive reactance increases with frequency.

  • Power Dynamics: Power is dissipated as heat by resistors, while inductors can store energy.

Applications in UAVs

  • Cleaning up electrical signals, power management, and stabilizing energy outputs.

Lesson 5: Diode Rectifiers

Full-Wave vs Half-Wave Rectification

  • Full-Wave Rectification: Converts AC to DC using both halves of the input signal.

  • Half-Wave Rectification: Uses only one half of the AC cycle, resulting in a pulsating DC output.

Rectifying Diodes

  • Rectifier Diodes: Handle high current and thermal output.

Conclusion

  • Understanding diodes and transistors, including their operations, properties, and applications, is foundational for electronics.

  • Anticipate various applications in real-world devices, including UAV systems, power supplies, and signal management.