📖 IT Bible

Power Supplies

(OBJ 3.5)

Computers rely on DC power, or Direct Current

  • 3.3 VDC
  • 5 VDC
  • 12 VDC

Standard electrical outlets rely on AC power, or Alternating Current

  • In U.S., outlets usually provide around 120V AC

PSU (Power Supply Unit) - main purpose is to deliver DC power to all components inside PC when receiving an AC power supply such as a wall outlet

Modular PSU - allows user to unhook connectors and detach them from the unit; frees up space inside of computer

Power Supply Connectors

  • Main Board/Motherboard Adapter - provides power to motherboard
    • ATX Standard 20-pin connector
    • ATX 12V 24-pin connector (usually on newer, more modern PSUs)
    • 20+4 Pin Connector - two connectors are coupled together before plugging into a 24-pin connector
  • Processor Power/CPU Power - has 4, 6 or 8-pin connector (8-pin is more modern)
  • PCIe adapter card power ports
  • SATA Power Connector - used to power SATA drives (ex. CD, Blu-ray Disc, Hard Drive)
  • Molex Connector - used for older IDE and PATA hard disks, CDs and DVD drives
  • Y-Connector - one connector can support multiple devices

Input/Output Voltages

  • 120V AC (Low Line Power) is a U.S. based power supply
  • 230V AC (High Line Power) is a Europe and Asia based power supply

Most power supplies will support multi-voltage inputs

Voltage Sensing/Dual Voltage Power Supplies - automatically detects outlet voltage and converts it into the proper DC voltage levels needed by a computer

Rail - a wire that provides current at a particular voltage (ex. a 12 VDC rail)

  • 12 VDC rail is most commonly used voltage

Wattage Ratings

Wattage Rating - power supply unit’s output capacity or capability

  • Standard PC uses about 200-300 watts
  • Gaming PC between 500-900 watts

Amperage to Wattage: A x V or I x V (I = current)

Things to keep in mind when choosing a PSU:

  1. PSUs are sold in standard increments
  2. Future expansion needs (always get a PSU with a little more wattage than required to be able to accommodate for upgrades or expansions)
  3. Power supply efficiency; power supplies are NOT 100% efficient… most PSUs operate at 70-75% efficiency. The other 30% is converted to heat during transformation from high-voltage AC to low-voltage DC
  4. A higher-quality Energy-Star rated 80% compliant PSU can save nearly 100 watts of power