Understanding Power Supply Components and Functions

Aug 22, 2024

Power Supply Lecture Notes

Introduction to Power Supplies

  • Power supplies convert mains voltage (240V/110V, 50/60Hz AC) to isolated DC.
  • Importance in powering modern technology.

Evolution of Power Supplies

  • Comparison between a 1980s Aztec power supply and a modern Anker phone charger.
  • Power output: 12V at 2A (24W) vs 30W in a compact design.
  • Progress over 40 years has led to power supplies being over 50 times smaller.
  • Improvements have been gradual and linear in power density.

Key Components of Power Supplies

Inductors

  • Essential for energy storage in power circuits.
  • Comparison to springs for energy storage.
  • Behavior shown through example of connecting voltage across an inductor.

Functionality of Inductors

  • Energy can be released from an inductor in a controlled manner.
  • Discussed ratios of energy input to output voltage.

Isolation in Power Supplies

  • Importance of Isolation: Essential for safety to prevent electrical shock.
  • Isolation prevents direct current paths between input and output.

Transformer Concept

  • Inductor can act similarly to a transformer, with primary and secondary windings.
  • Allows for voltage transformation while maintaining isolation.

Inductor Size and Energy Storage

  • Size of an inductor affects its energy storage capacity.
  • Explanation using buckets analogy for energy storage and discharge.

Components in Power Supply Circuits

Basic Components

  1. AC Input: Comes from three pins - Earth, Neutral, Live.
  2. Full Bridge Rectifier: Converts AC to DC using four diodes.
  3. Large Capacitor: Smooths the rectified DC.
  4. Inductor and MOSFET: Controls energy flow to the output.
  5. Diode: Ensures energy flows in one direction to the output.
  6. Output Capacitors: Further smooth the DC output.

Additional Components

  • LED: Indicates when the power supply is powered.
  • Small Inductor: Filters the DC output further.
  • Resistors: Discharge capacitors safely when the power supply is turned off.
  • Current Shunt Resistors: Enables current measurement for control.
  • Common Mode Choke: Filters out high-frequency noise from the input.
  • Fuse: Protects against excess current.
  • NTC Thermistor: Limits inrush current during startup.
  • MOV (Metal Oxide Varistor): Clamps voltage spikes.
  • Class Y Capacitors: Prevent EMI by connecting outputs to ground.

Snubber Circuits

  • Protect components from voltage spikes during switching events.
  • Important for both device protection and EMI mitigation.

Control of the Power Supply

  • Main control chip regulates output voltage.
  • Potentiometer allows for adjustment of output voltage.

Conclusion

  • Summary of all components and their purposes in power supplies.
  • Importance of understanding both the functionality and necessity of each component.
  • Encouragement to subscribe for more content related to switch mode power supplies.