Topic 2 Circuit Theorems

Electrical Technology Overview

• Subject: Circuit Theorems

• Presented By: Abdul Hakim Hj Abu Bakar

Active and Passive Electronic Components

Definitions

• Active Devices:

  • Capable of controlling voltages or currents.

  • Can create switching actions in the circuit.

  • Referred to as "devices with smarts!"

• Passive Devices:

  • Contribute no power gain (amplification) to a circuit.

  • No control action needed; require only a signal to function.

  • Referred to as "components with no brains!"

Active Devices Examples

• Diodes:

  • Act as a one-way valve for electrical current; flow from positive to negative.

  • Indicated by a painted line on one end (white side is negative).

• LEDs (Light Emitting Diodes):

  • Emit light and are used as indicators (e.g., LED lit = machine on).

  • Available in various sizes and colors, some emit infrared light.

• Transistors:

  • Function as switches and amplifiers; output is a magnified version of the input signal.

  • Available in various sizes for different applications.

• Integrated Circuits (ICs):

  • Complex circuits in a compact package, made from silicon and metals.

  • Used in a vast range of applications from simple timers to microcontrollers with erasable memory.

• Microprocessors (MPUs):

  • Large scale ICs at the core of most electronic devices providing logic.

  • Packaging is continuously becoming smaller due to advancements in transistor technology.

Passive Devices Examples

• Inductors:

  • Store energy in a magnetic field; current is produced in the opposite direction when the field collapses.

  • Utilized in AC circuits to oppose changes in current. Typically have a coil appearance and are mostly green.

• Capacitors:

  • Store electrical energy as electrostatic charge; size determines charge capacity.

  • Available in various types like ceramic disc and electrolytic capacitors.

• Resistors:

  • Control current and voltage; identified by color-coded bands (measured in Ohms).

  • Potentiometer is a variable resistor type.

Circuit Theorems Overview

• Kirchhoff’s Laws:

  • KCL (Kirchhoff's Current Law): Algebraic sum of currents at a junction is zero.

  • KVL (Kirchhoff's Voltage Law): Algebraic sum of e.m.f.s in a closed loop equals the sum of the potential differences.

• Thevenin's Theorem:

  • Any network supplying a load can be replaced by a voltage source in series with an internal resistance.

• Norton’s Theorem:

  • Any network supplying a load can be replaced by a current source in parallel with an internal resistance.

• Superposition Theorem:

  • Analyze one source at a time to simplify circuit analysis.

• Delta-Star Transformation:

  • Replaces any three loads connected in delta with equivalent loads in star, and vice versa.

Summary

• Active components require power to operate and can amplify signals.

  • Passive components do not amplify signals and require only an external signal to function.

References

• Alexander, C. K., & Sadiku, M. N. O. (2000). "Fundamentals of Electric Circuit.” McGraw-Hill

• Hughes, E. (8th Edition). “Electrical Technology.” Prentice Hall

• Rashid, M. H. (2nd Edition). “Power Electronics.” Prentice Hall