4.1 Power Supplies

• Meaning and function of a power supply in an electronic system
• Direct current sources: cells, batteries and solar cells
• Alternating current mains supply and the need for conversion
• Types of power supplies: battery, linear and switched mode
• The block diagram of a d.c. power supply: transformer, rectifier, filter and regulator
• The step down transformer and the turns ratio
• Half-wave rectification using a single diode
• Full-wave rectification using a centre tap transformer
• The bridge rectifier using four diodes
• Smoothing with a reservoir capacitor and ripple voltage
• The zener diode voltage regulator
• Voltage regulator integrated circuits such as the 7805
• Technical specifications: output voltage, current rating, power rating and efficiency
• Efficiency of a power supply and power lost as heat
• Construction of a power supply on a breadboard or copper strip board
• Soldering techniques for a sound electrical joint
• Testing a power supply with a multimeter and oscilloscope
• Common faults in power supply circuits and systematic fault finding
• Switched mode power supplies and modern advancements
• Applications of power supplies in electronic devices
• Safety precautions when constructing and testing power supplies

• describe the operation of a power supply unit in an electronic system
• construct a power supply circuit from a given schematic circuit diagram
• troubleshoot common faults in power supply circuits
• interpret technical specifications of different power supply units
• embrace advancements in power supply technology in electronic devices

“How do power supplies work?”

“How is a power supply constructed and tested?”

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1. The function of a power supply
   40 min · 1 practice tasks · quiz
   Explain the job of a power supply in an electronic system.
2. Types of power supplies
   40 min · 1 practice tasks · quiz
   Describe battery, linear, switched mode and DC to DC supplies.
3. The block diagram of a DC power supply
   40 min · 1 practice tasks · quiz
   Follow the four stages that change mains AC into steady DC.
4. The step down transformer
   40 min · 1 practice tasks · quiz
   Describe how a transformer steps the mains voltage down.
5. The half-wave rectifier
   40 min · 1 practice tasks · quiz
   Explain how a single diode gives half-wave rectification.
6. The full-wave rectifier
   40 min · 1 practice tasks · quiz
   Explain how a centre tap transformer and two diodes rectify both halves.
7. The bridge rectifier
   40 min · 1 practice tasks · quiz
   Explain how four diodes rectify both halves without a centre tap.
8. Smoothing the rectified output
   40 min · 1 practice tasks · quiz
   Explain how a reservoir capacitor reduces ripple.
9. The zener diode voltage regulator
   40 min · 1 practice tasks · quiz
   Explain how a zener diode holds the output voltage steady.
10. Voltage regulator integrated circuits
    40 min · 1 practice tasks · quiz
    Describe the fixed three terminal voltage regulator IC such as the 7805.
11. Reading power supply specifications
    40 min · 1 practice tasks · quiz
    Interpret output voltage, current rating, power rating and efficiency.
12. Efficiency and heat loss in a power supply
    40 min · 1 practice tasks · quiz
    Calculate the efficiency of a supply and explain its heat loss.
13. Building a power supply on a breadboard
    40 min · 1 practice tasks · quiz
    Assemble and test a power supply from a schematic diagram.
14. Soldering a sound joint
    40 min · 1 practice tasks · quiz
    Make safe, reliable solder joints on a power supply board.
15. Testing a power supply
    40 min · 1 practice tasks · quiz
    Test each stage of a supply with a multimeter and oscilloscope.
16. Troubleshooting power supply faults
    40 min · 1 practice tasks · quiz
    Find and correct common faults in a power supply.
17. Switched mode power supplies and advancements
    40 min · 1 practice tasks · quiz
    Describe the switched mode supply and advances in power supply technology.
18. Applications of power supplies
    40 min · 1 practice tasks · quiz
    Describe where power supplies are used in day to day life.
19. Safety and maintenance of power supplies
    40 min · 1 practice tasks · quiz
    Observe safety rules and maintain power supplies in good order.