1. Power Supply 8/16/20151

2. Objectives In this chapter, you will: – Understand power supply – The most common computer power supplies are built to conform with the ATX form factor. 8/16/20152

3. Power Supply: Switcher Technology Instead of the linear design, PCs use switching power supplies. The full name for this sort of design is actually "constant-voltage, half-bridge forward-converting switching power supply", but don't worry, that won't be on the final exam. :-) 8/16/20153

4. Power Supply Warning: Power supplies generate high voltages internally and can be dangerous. Unless you have been specifically trained to work inside power supplies, you should not open one. Even with the unit unplugged dangerous electricity can remain stored within its components for some time 8/16/20154

5. Power Supply Power supplies, often referred to as "switching power supplies", use switcher technology to convert the AC input to lower DC voltages. However, the PC power supply's job isn't as simple as that of a standard power converter, – such as the kind you might plug into your car's lighter socket to let you run a TV off your car battery. The power supply in your PC provides all of the different voltages your computer needs to operate properly. 8/16/20155

6. Watts The main specification of a power supply is in watts. A watt is the product of the voltage in volts and the current in amperes or amps. – The electrons that flow through the wire is referred to as Current, measured in AMPS. 8/16/20156 1W=1V×1A

7. Power Supply A Power Supply does not supply power; electrical power comes from your local utility company. The Power Supply converts the power from alternating current to direct current at levels that the system requires. 8/16/20157

8. AC vs. DC Alternating current works fine for certain appliances and has the added advantage of being easy to distribute over long distances, but many devices will not work on AC. – Just a few examples of this are telephone answering machines, many types of audio equipment, some kinds of battery chargers, and in the PC world, certain types of printers, external modems and other peripherals. Two indicators that a device actually uses DC inside are: the ability of the device to run on batteries, and the presence of a device outside the unit that powers it. – These small "bricks" with one plug for the wall and another for the device are often called AC adapters 8/16/20158

9. Power Supply: Switcher Technology The switching power supplies used today are much smaller and lighter. They convert the 60- Hertz (Hz, or cycles per second) current to a much higher frequency, meaning more cycles per second. – This conversion enables a small, lightweight transformer in the power supply to do the actual voltage step-down from 110 volts (or 220 in certain countries) to the voltage needed by the particular computer component. The main disadvantage of a switching supply is that it generates high-frequency signals within it as part of its conversion process, which can radiate out of the unit and cause interference to other electronic devices (inside or outside the PC). – For this reason, you will always see PC power supplies encased in metal boxes for shielding. 8/16/20159

10. Voltages Voltage is the pressure that pushes the electrons through the conductor (wire). Voltage is measured in Volts. PC usually uses120 volt power to the power supply. The typical voltages supplied are: – 3.3 volts – 5 volts – 12 volts The 3.3- and 5-volts are typically used by digital circuits, The 12-volt is used to run motors in disk drives and fans. 8/16/201510

11. Power Supply Standardization Over time, there have been at least six different standard power supplies for personal computers. Recently, the industry has settled on using ATX-based power supplies. ATX is an industry specification that means the power supply has the physical characteristics to fit a standard ATX case and the electrical characteristics to work with an ATX motherboard. PC power-supply cables use standardized, keyed connectors that make it difficult to connect the wrong ones. 8/16/201511

12. Power Supply Wattage Computer power supplies are rated based on their maximum output power. – Small Form Factor - 15A (250W) – Mini-Tower - 25A (300-350W) – Mid-Tower - 35A (400-500W) – Full Tower - 40A (600-650W) – Dual Video Card (SLI) - 60A (850W+) – Power supplies used by gamers and enthusiasts mostly range from 450 W to 1400 W. 8/16/201512

13. Power Supply Wattage Power Requirements for typical systems. Item Power requirement Voltage used OLDER CPUs 20-40 Watts 3.3 Volts Athlon XP – Pentium IV 60-90 Watts 12 Volts motherboard 20-60 Watts 3.3, 5.0, 12 Volts RAM 20 Watts /256 MB 3.3 Volts PCI Card 5–10 Watts 3.3 Volts AGP Video 20–50 Watts and more 5, 12 Volts CPU Case Fan 2 – 4 Watts 12 Volts 5400 RPM Hard Drive 5 – 10 Watts 5, 12 Volts 7200 RPM Hard Drive 5 – 15 Watts 5, 12 Volts 10000 RPM Hard Drive 5 – 20 Watts 5, 12 Volts Floppy Drive 5 Watts 5, 12 Volts CD / DVD 10 – 20 Watts 5, 12 Volts 8/16/201513

14. Power Supply Wattage A 400-watt switching power supply will not necessarily use more power than a 250-watt supply. A larger supply may be needed if you use every available slot on the motherboard or every available drive bay in the personal computer case. It is not a good idea to have a 250- watt supply if you have 250 watts total in devices, since the supply should not be loaded to 100 percent of its capacity. 8/16/201514 Mother Board with a Pentium 4 processor, 256 MB RAM, a 7200 Rpm Hard Drive, a floppy drive, a CD and an AGP Card. o Mother Board ----------------------------- 50 Watts o Pentium 4 ---------------------------------- 90 Watts o 256 MB RAM ------------------------------ 20 Watts o Hard Drive --------------------------------- 15 Watts o Floppy Drive ------------------------------- 5 Watts o CD -------------------------------------------- 20 Watts o AGP Video Card -------------------------- 50 Watts Total System Power: 250 Watts

15. Power Supply Problems The PC power supply is probably the most failure-prone item in a personal computer. Typically, a stalled cooling fan is a predictor of a power supply failure due to subsequent overheated components. A typical failure of a PC power supply is often noticed as a burning smell just before the computer shuts down. Failure symptoms include random rebooting or failure in Windows for no apparent reason. 8/16/201515

16. Power Supply Problems Despite its critical role, the power supply is one of the most ignored and under-studied components in the PC. In fact, some people don't even bother to check out what power supply is included when they purchase a case! 8/16/201516

17. Case and Cover Every PC power supply comes surrounded by a metal case with a metal cover. The case isolates the components inside the power supply from the rest of the PC. Power supplies are usually intended to be considered as "black boxes" and not serviced by individual PC owners. Ventilation slots or holes are placed into the case in key locations to allow the power supply fan to provide air flow over critical components. 8/16/201517

18. PC Power Switch Older form factor desktop XT cases had the power switch at the back of the machine, usually on the right side of the case. – This switch was actually inside the power supply itself, with a hole cut out in the case so that it could be reached from the outside. 8/16/201518 Baby AT power supply

19. Turn on PC Today you turn on the power with a little push button, and you turn off the machine with a menu option. These capabilities were added to standard power supplies several years ago. The operating system can send a signal to the power supply to tell it to turn off. The push button sends a 5-volt signal to the power supply to tell it when to turn on. The power supply also has a circuit that supplies 5 volts, called VSB for "standby voltage" even when it is officially "off", so that the button will work. 8/16/201519 remote PC power supply switch

20. PC Power Switch One consequence of the "soft power" method of operating the power supply comes into play if there is a power failure. – Imagine that you have a PC running unattended. There's a power outage, and the system shuts down. – Several hours later, the power comes back on. – With an old-fashioned mechanical power switch, the system would immediately restart, because as soon as the power was restored the power supply would turn on. – With an ATX/NLX, SFX or WTX form factor supply however, the power supply would sit there waiting for a "turn on" signal from the motherboard! 8/16/201520

21. External Voltage Selector Switch PC power supplies support 110V input, 220V input or both. – Dual-voltage supplies normally have a selector in the back that controls which voltage you are using; obviously, you want to make sure it is set correctly. There are also some supplies that will automatically support either 110V or 220V without a selector switch, but these are often found only on more expensive units. – 100-127V in North America, parts of South America, Japan, and Taiwan; – 220-240V in most of the rest of the world 8/16/201521

22. Connectors Typically, power supplies have the following connectors: PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire (it is usually green). This connector is the largest of all the connectors. ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor. 4-pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the red wire is +5 V, and the yellow wire is +12 V. 4-pin Berg power connectors (usually called Mini-connector or "mini-Molex"): This is one of the smallest connectors that supplies the floppy drive with power. In some cases. Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional power if it is needed. Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and +12 volts. 6-pin Most modern computer power supplies include 6-pin connectors which are generally used for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power supplies. 6+2 pin For the purpose of backwards compatibility, some connectors designed for use with PCI Express graphics cards feature this kind of pin configuration. 8/16/201522

23. Connectors Typically, power supplies have the following connectors: PC Main power connector (usually called P1): Is the connector that goes to the motherboard to provide it with power. The connector has 20 or 24 pins. One of the pins belongs to the PS-ON wire (it is usually green). This connector is the largest of all the connectors. ATX12V 4-pin power connector (also called the P4 power connector). A second connector that goes to the motherboard (in addition to the main 24-pin connector) to supply dedicated power for the processor. 8/16/201523

24. Connectors 4-pin Peripheral power connectors (usually called Molex for its manufacturer): These are the other, smaller connectors that go to the various disk drives of the computer. Most of them have four wires: two black, one red, and one yellow. Unlike the standard mains electrical wire color-coding, each black wire is a ground, the red wire is +5 V, and the yellow wire is +12 V. 4-pin Berg power connectors (usually called Mini-connector or "mini-Molex"): This is one of the smallest connectors that supplies the floppy drive with power. In some cases. 8/16/201524

25. Connectors Auxiliary power connectors: There are several types of auxiliary connectors designed to provide additional power if it is needed. Serial ATA power connectors: a 15-pin connector for components which use SATA power plugs. This connector supplies power at three different voltages: +3.3, +5, and +12 volts. 8/16/201525

26. Connectors 6-pin Most modern computer power supplies include 6-pin connectors which are generally used for PCI Express graphics cards, but a newly introduced 8-pin connector should be seen on the latest model power supplies. 6+2 pin For the purpose of backwards compatibility, some connectors designed for use with PCI Express graphics cards feature this kind of pin configuration. 8/16/201526

27. Power outage Power outages are categorized into three different phenomena, relating to the duration and effect of the outage: – A dropout is a momentary (milliseconds to seconds) loss of power typically caused by a temporary fault on a power line. Power is quickly (and sometimes automatically) restored once the fault is cleared. – A brownout is a drop in voltage in an electrical power supply, so named because it typically causes lights to dim. Such malfunctions are particularly damaging to electric motors. The voltage from power companies is generally between 115 and 120 Volts AC, during a brownout the power could drop to less than 110 volts. – A blackout refers to the total loss of power to an area and is the most severe form of power outage that can occur. 8/16/201527

28. Protecting computer systems from power outages Computer systems and other electronic storage devices are susceptible to data loss or hardware damage that can be caused by the sudden loss of power. To protect against this, the use of an Uninterruptible power supply or UPS can provide a constant flow of electricity in the event that a primary power supply becomes unavailable for a short period of time. 8/16/201528

29. Power Surge An unexpected increase in the amount of electrical voltage in an electrical line. A power surge can provide too much power to a computer or electrical device generally causing damage to that device making the device not operate at all or improperly. – In electrical engineering, spikes are fast, short duration electrical transients in voltage (voltage spikes), current (current spike), or transferred energy (energy spikes) in an electrical circuit. Users can help prevent power surges with surge protectors. 8/16/201529

30. Review Alternation Current – The type of power delivered by the electric company where current flows in one direction then stops and reverses direction AMP - The measure of current in an electrical circuit Blackout – Total loss of power Brownout - When the voltage delivered by the power company drops to a less than expected level Direct Current – The type of power delivered by batteries, the voltage is constant EMI – Electromagnetic Interference is electrical interference caused by nearby devices that have electromagnets, like motors, or transformers RFI – Radio Frequency Interference is electrical interference caused by other electronic devices operating nearby Spike – When the power increases for a very short period of time Surge - When the voltage increases to higher than normal for a duration of time Surge Suppressor – Device used to absorb voltage spikes Volt - The Measure for Voltage Watt - The measure of Power 8/16/201530