Power supply units Flashcards
PSU
The power supply unit (PSU) delivers direct current (DC) at a low voltage to the PC components by converting AC power from the wall outlet to DC power.
The PSU usually contains a fan, which dissipates the heat generated.
Input voltage
Refers to the voltage supplied to the PSU. A PSU designed only for use in North America, where the input voltage for most homes and offices is 120 VAC (low-line), will not work in the UK, where the voltage is 230 VAC (high-line). Also, facilities such as data centers typically use high-line voltage because it is more efficient.
The low-line range is 100-127 VAC, while the high-line range is 220-240 VAC.
Wattage Rating
Power is the rate at which things generate or use energy. Power is measured in watts (W), calculated for electrical components as voltage multiplied by current (V*I).
The PSU’s output capability is measured as its wattage rating . A PSU designed for use in a standard desktop PC is typically rated at around 200–300 W.
Enterprise workstation PCs and servers often have units rated over 300 W to meet the demands of multiple CPUs, additional memory modules, disk drives, and tape units.
Rail
A rail is a wire providing current at a particular voltage. The output voltages (3.3 VDC, 5 VDC, and 12 VDC) are used by the components in the computer system.
For a modern computer, the output rating of the +12 VDC rail (or rails) is the most important factor, as +12 VDC is the most heavily used.
Power Supply Connectors
The power connectors supply DC voltage to the motherboard and devices at 3.3 VDC, 5 VDC, and 12 VDC.
The motherboard’s power port is referred to as the P1 connector. A PSU will also have a number of Molex and/or SATA device power connectors and 4/6/8-pin connectors for use with CPU and PCIe adapter card power ports.
20-pin to 24-pin Motherboard Adapter
The original ATX specification, the P1 connector is 20-pin.
The ATX12V version 2 specification defines a 24-pin. Some PSUs have a 20+4-pin P1 adapter cable for compatibility with older motherboards with a 20-pin port.
The P1 connector is the main power supply for the motherboard.
Modular Power Supplies
A modular PSU has power connector cables that are detachable from the unit. Reducing the number of cables to the minimum required minimizes clutter within the chassis, improving airflow and cooling.
Redundant Power Supplies
A redundant PSU configuration requires a compatible motherboard. This configuration is more commonly found on server systems than on desktop PCs.
Typically each PSU plugs into a backplane and is hot-swappable. This allows a faulty unit to be removed and replaced without having to open the case and without the server ever losing power.
Heat Sinks
A heat sink is a block of copper or aluminum with fins. The fins expose a larger surface area to the air around the component to achieve a cooling effect by convection. The heat sink is affixed to the surface of the chip
A heat sink is a passive cooling device. Passive cooling means that it does not require extra energy (electricity) to work.
Thermal Paste
thermal paste is used to ensure the best transfer of heat between thee CPU and the heat sink by eliminating small air gaps.
Fans
A fan is a active cooling device it improves airflow, which helps to dissipate heat. Fans are used for the power supply and chassis exhaust points
The fan system will be designed to draw cool air from the low vents in the front of the case over the motherboard and expel warmed air from the fan positioned at the top of the back of the case.
Thermometer sensors are used at each fan location to set an appropriate speed and to detect whether a fan has failed.
Liquid Cooling Systems
A liquid-based cooling system refers to a system of pumping water around the chassis. Water is a more effective coolant than air convection, and a good pump can run more quietly than numerous fans.
There are two main types closed loop and open loop systems. An open-loop system will usually need draining, cleaning, and refilling periodically.
What is the significance of a PSU’s wattage rating when you are designing a custom-build PC?
It determines the CPU model and number and type of memory modules, expansion cards, and storage devices that can be installed. The PSU’s wattage rating must be higher than the sum of the power requirements of all the PC’s components.
Your company has recently closed a foreign branch office, and you are repurposing some PCs that were shipped from the old location. What feature of the PSUs must you check before powering the systems on?
You must check that the voltage selector is set to the correct voltage or, if there is no selector, that the PSU is suitable for the voltage used by the building power circuit.
One of the PCs has a faulty CPU, and one has a faulty power supply. You can use the CPU from one machine in the other. You have opened the case and taken antistatic precautions. What steps must you perform to access the CPU?
You will have to remove the fan and heat-sink assembly,disconnect the fan’s power connector,release the pins or screws that attach the assembly to the motherboard, and remove the assembly (a gentle twisting motion may be required if the thermal paste has stuck the heat sink firmly to the CPU).
