1. Power Supply

2. Power Supply Function & Operation
Converts 120-volt AC power source into
3.3v, 5v, 12v, -5v, -12v DC power source.
To run the system
Negative voltages typically not used in modern systems
used in older floppy drives and serial ports and LAN circuits.
Sends Power Good signal during POST
the power supply also ensures that the system does not run unless the power supplied is sufficient to operate the system properly.

3. Devices Powered by different Voltages
Voltage Devices Powered
+3.3V Chipsets, DIMMs, PCI/AGP cards, miscellaneous chips
+5V Disk drive logic, SIMMs, PCI/AGP cards, ISA cards, voltage regulators, miscellaneous chips
+12V Motors, voltage regulators (high output)
-5V Older Floppy Disk drives
-12V Serial Ports and LAN circuits

4. The Power_Good Signal
In the absence of Power_Good, the timer chip holds the reset line on the processor, which prevents the system from running under bad or unstable power conditions.
When the timer chip receives the Power_Good signal, it releases the reset, and the processor begins executing whatever code is at address FFFF:0000 (usually the ROM BIOS).

5. PS_ON Power Supply
PS_ON, can be used to turn the power supply (and thus the system) on or off via software.
It is sometimes known as the soft-power feature.
PS_ON is most evident when you use it with an operating system, such as Windows 9x, that supports the Advanced Power Management (APM) or Advanced Configuration and Power Interface (ACPI) specification.
When you select the Shut Down the Computer option from the Start menu, Windows automatically turns off the computer after it completes the OS shutdown sequence.
A system without this feature only displays a message that it’s safe to shut down the computer.

6. Technically the Power Supply is:
Technically, the power supply in your PC is described as a constant voltage half-bridge forward converting switching power supply:
Constant voltage means that the power supply puts out the same voltage to the computer’s internal components, no matter what the voltage of AC current running it or the capacity (wattage) of the power supply.
Half-bridge forward converting switching refers to the design and power regulation technique used by most suppliers. This design is commonly referred to as a switching supply. Compared to other types of power supplies, this design provides an efficient and inexpensive power source and generates a minimum amount of heat. It also maintains a small size and a low price.

7. Power Supply Form Factors
The shape and general physical layout (size) of a component is called the form factor.
PC/XT
AT/Desk
AT/Tower
Baby-AT
LPX
Allows us to upgrade and repair our systems by easily replacing physically (and electrically) interchangeable components.
Having interchangeable parts means that we have a better range of choices for replacement items, and the competition makes for better pricing, too.
SFX
ATX

8. Power Supply Form Factors
1995

9. Motherboard Form Factors

10. Power Supply Form FactorsXT
8 3/4 " x 5 1/2" x 4 3/4"

11. AT Baby-AT
8.35" x 5.9" x 5.9 " 6.5" x 5.9" x 5.9"

12. LPX
5.9 " x 5.5 " x 3.4 "

13. ATX NLX
5.9 " x 5.5 " x 3.4 " 5 1/2" x 5 7/8" x 3 3/8"

14. AT Power Supply Connectors

16. LPX/AT Power Supply Lacks 3.3 Volt Output
Uses two 6-pin connectors P8 and P9
Incorrect installation can damage system
Some power switch wires are live

17. LPX /AT Power Supply Switch
Brown and blue wires are the live and neutral feed. Always hot when power supply is plugged in.
Black and white wires carry AC from the switch to the power supply. Hot only when power supply is ON.
Green wire or green with yellow stripe is ground lead. Should be connected to case.

18. ATX Power Supply Provides 3.3 Volt Output. Single 20-pin connector.
Case switch goes to motherboard
- uses 5v instead of 120v circuit.
A few models have a true on-off switch on the rear of the unit.

19. ATX Power Supply for NLX style
NLX systems were designed to use ATX power supplies,
even though the case and motherboard dimensions are different.
NLX - defines a low-profile case and motherboard design.

20. SFX Power Supply
SFX (Small form factor) power supply designed to go with smaller Micro-ATX motherboard form factor in December of 1997.
Used in many compact systems.
90w continuous/135wpeak - is enough for a system with 4 expansion slots and 3 devices.
Lacks -5v.
Lacks both Auxiliary (3.3V and 5V) and ATX12V power connectors.

21. Power Supply Connectors
Power connector to motherboard
Power connector to CD and hard drives
Power connector to floppy drive
Y-adapter

22. AT/LPX Power Connectors P8/P9 or P1/P2

23. ATX 20-pin Connector Bottom view
Terminal side view: facing the terminal side.

24. ATX 20-pin Connector Top view1 11

25. ATX 20-pin Connector Top view (wire side)

26. ATX 6-pin Auxiliary Connector

27. ATX12V Power Connector

28. ATX 6-pin (2x3) Optional Connector

29. Dell ATX 20-pin Connector Top view (wire side)

30. ATX 20-pin Connector Top view (wire side)

31. Dell ATX 6-pin Connector

32. ATX 6-pin Auxiliary Connector

33. Peripheral Power Connectors

34. Power Supply Ratings
P = V x I
Watts = Volts × Amps

35. ATX Power Supply Output Ratings

36. Compute ATX Power Output Ratings
If you compute the total output using the formula described earlier, these power supplies seem to pro-duce an output that is much higher than their ratings.
The 300W model, for example, comes out at watts.
However, notice that the supply also has a maximum combined output for the +3.3V and +5V of 150 watts.
This means you cannot draw the maximum rating on both the 5V and 3.3V lines simultaneously, but must keep the total combined draw between them at 150W.
This brings the total output to a more logical watts (150W + 12Vx12A + 12w + 2w).

37. Power Supply Certifications
In Canada, electric and electronic products are listed by the Canadian Standards Agency (CSA).
In the United States is Underwriters Laboratories, Inc. (UL). UL standard #1950—the Standard for Safety of Information Technology Equipment, Including Electrical Business Equipment, Third Edition—covers power supplies and other PC components.

38. Power-Use Calculations

39. Maximum Current draw in Amps per Bus Slot

40. Power Management Turning the system off and on (soft control)
Cost of operation
Damage to parts due to expansion (heating) and contraction (cooling)
Changing the state of operation of a component
Surge current

41. Power Protection Systems
Surge Protectors
Absorb high voltage produced by lightning strikes.
SPS (Standby Power Supplies)
Switches to a battery when power is cut off
UPS (Uninterruptible Power Supplies)
System always runs from battery power

42. Power Supply Troubleshooting
The following problems might be caused by a faulty power supply or house current to the PC.
Computer hangs for no reason. Might reboot itself.
Memory errors occur occasionally.
Data is written incorrectly to hard drive.
Keyboard stops working at odd times.
Systemboard fails or is damaged.
Power supply overheats and becomes hot to touch.

43. Energy Star Computers (The Green Star)
Energy Star computers and peripherals have the Green Star, which indicates that they satisfy the requirements of the U.S. Environmental Protection Agency (EPA).
The green standards are a set of specifications designed by the EPA to reduce overall power consumption in the U.S.
The green PCs or devices has a standby program that causes the device to go into sleep mode when it is not being used.
Sleep mode could be more properly labeled reduced power consumption mode.
This is a state that an EPA compliant PC will go into when it is not in use.
The EPA requirement for sleep mode is the device can use no more that 30 watts of power while asleep.

44. Energy Star PCs:
There are four types of power management methods available for PCs:
Advanced Power Management (APM). APM is used in almost every new system today and is championed by Microsoft and Intel.
AT Attachment (ATA) for IDE drives.
Display Power Management Signalling (DPMS) standards for monitors and video cards.
Advanced Configuration and Power Interface (ACPI) - only with newer system BIOS and Windows 98
The energy star features can normally be adjusted in the CMOS setup.

45. Green timer on the systemboard:
Four system states, dependant on system’s current activity
Doze time The doze time is the amount of time specified before the system will reduce its power consumption by 80%.
Standby time The standby time is the amount of time specified before the system will reduce its power consumption by 92%.

46. Suspend time The suspend time is the amount of time specified before the system will reduce its power consumption by 99%. Note that when a system has gone into suspend mode it will require a short warm-up period when activated again.
Hard drive standby time The hard drive standby time is the amount of time specified before the system will temporarily shut down the hard drive.

47. Advanced Power Management
Five states:
Full On - no power management
APM Enabled - operational, cpu slowed and unused devices powered down.
APM Standby - not operational, in memory
APM Suspend - not operational, in disk
Off - power supply is off.

48. Power Protection Systems
Protect system from surges, spikes, power failures.
High-quality power supplies are capable off shutting down systems during power disturbances.

49. Power-Protection Systems
Four common protection systems:
Surge Suppressors
Line Conditioners
Standby power supplies (SPS)
Uninterruptible power supplies (UPS)

50. Case Form Factors Full Tower Mini-Tower Desktop
Low Profile (also called Slimline)
ATX motherboards require ATX cases

51. Form Factors Systemboards have different physical dimensions.
known as form factor
Have to match systemboard to case.
Obsolete Form Factors
Baby-AT
Full-size AT
LPX (semi-proprietary, Western Digital)

52. Form Factors Modern Form Factors Proprietary Designs
ATX (used in most full-sized desktop/tower systems.
Micro-ATX (smaller ATX)
Flex-ATX (smaller than Micro-ATX, used in low-cost home PCs)
NLX (corporate desktop models)
WTX (workstations and servers)
Proprietary Designs
Compaq, Packard Bell, Hewlett-Packard...

53. Components - Case Styles: Tower case Desktop case.
The tower is like a desktop flipped on its side and can sit on the floor or on the desk.
Desktop case.
Rectangular case that is wider than it is tall and sits on the desk.

54. Tower Cases

55. Desktop Cases

56. Desktop Cases

57. Power Supplies Important component of PC
Supplies clean, reliable DC power to computer.
Converts 120V, 60 Hz, AC signal to +3.3V, +5V, +12V, -5V and -12V DC.
Rated in WATTS
Before power is provided to computer power supply runs through self-check.
Sends “Power Good” signal to computer when it has passed the check.

58. Power Supplies Newer power supplies have PS_ON signal.
This allows the computer to be powered off with software.