Overview of Power Supply Fundamentals

Aug 22, 2024

Lecture Notes: Understanding Power Supplies

Introduction to Power Supplies

  • Power supplies convert mains voltage (240V/110V, 50/60Hz AC) into isolated DC.
  • Used extensively to power modern technology.

Evolution of Power Supplies

  • Comparison of an 1980s Aztec power supply (12V, 2A, 24W) vs. a modern 30W phone charger from Anker.
  • Modern power supply is over 50 times smaller.
  • Improvements in power density have been gradual and linear.

Key Components of Power Supplies

Inductors

  • Inductors store energy like springs.
  • Example: Live and neutral pins connected to an inductor.
  • When voltage applied, current rises and stabilizes due to resistance.
  • Inductor stores energy in a magnetic field.

Energy Release

  • Energy can be released suddenly, leading to high voltage arcs (thousands of volts).
  • Ratio of charging and discharging time affects output voltage.

Isolation in Power Supplies

  • Essential for safety, prevents dangerous currents from flowing back to ground.
  • Isolation means no direct current path between output terminals.

How Inductors Provide Isolation

  • Inductor is essentially a coil of wire wound around a ferrite core.
  • By adding a second coil (coupled inductor), we can separate input and output while storing energy.

Inductor Size and Energy Storage

  • Energy storage is proportional to the inductor's size.
  • Smaller inductors require faster switching frequencies, leading to higher losses.

Basic Power Supply Components

  1. Mains AC Input: 3 pins (Earth, Neutral, Live).
  2. Full Bridge Rectifier: Converts AC to DC.
  3. Capacitor: Smooths rectified DC, holds high voltage (around 350V).
  4. Mosfet: Acts as an electronic switch to control energy flow into the inductor.
  5. Diode: Prevents energy from flowing back into the inductor.
  6. Output Capacitors: Smoothes the output DC.

Additional Components for Functionality

  • LED and Resistor: Indicate when the power supply is on.
  • Small Inductor and Capacitor: Further filter and smooth the DC output.
  • Resistors: Discharge output capacitors when power supply is off.
  • Current Shunt Resistors: Measure current passing through the inductor.
  • Input Filter Components: Prevent high-frequency noise from affecting the mains.
  • Input Protection: Includes fuses, thermistors (NTC), varistors (MOV), and resistors for discharging capacitors.
  • Y Capacitors: Connect input/output to ground, filter out EMI (Electromagnetic Interference).
  • Snubber Circuits: Protect against voltage spikes and help with EMC (Electromagnetic Compatibility).

Conclusion

  • Understanding the components and their functions helps in grasping how power supplies work.
  • Components serve various purposes, including safety, filtering, and regulation.
  • Consideration of EMC regulations is crucial in design.

Future Topics

  • Potential for deeper exploration into specific types of power supplies (e.g., gallium nitride technology).
  • Audience invited to subscribe for more content.