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119-476: Most modern desktop personal computer power supplies conform to the ATX specification , which includes form factor and voltage tolerances. While an ATX power supply is connected to the mains supply, it always provides a 5- volt standby (5VSB) power so that the standby functions on the computer and certain peripherals are powered. ATX power supplies are turned on and off by a signal from the motherboard . They also provide

238-521: A linear approximation will be useful in estimating the value R of a property at a temperature T , given its value R 0 at a reference temperature T 0 : where Δ T is the difference between T and T 0 . For strongly temperature-dependent α, this approximation is only useful for small temperature differences Δ T . Temperature coefficients are specified for various applications, including electric and magnetic properties of materials as well as reactivity. The temperature coefficient of most of

357-574: A 12 V rail, while it was done by a 5 V rail on older PCs (before the Pentium ;4). The power demands of PCI Express were incorporated in ATX12V 2.0 (introduced in February 2003), which defined quite different power distribution from ATX12V 1.x: This is a minor revision from June 2004. An errant reference for the −5 V rail was removed. Other minor changes were introduced. This

476-708: A 12 V supply from a custom-made PSU, which is typically rated at 250–300 W. DC-to-DC conversion , providing 5 V and 3.3 V, is done on the motherboard; the proposal is that 5 V and 12 V supply for other devices, such as HDDs, will be picked up at the motherboard rather than from the PSU itself, although this does not appear to be fully implemented as of January 2012. The reasons given for this approach to power supply are that it eliminates cross-load problems, simplifies and reduces internal wiring that can affect airflow and cooling, reduces costs, increases power supply efficiency, and reduces noise by bringing

595-411: A 24-pin motherboard power connector and an eight-pin +12 V connector. The standard also specifies two additional four-pin 12 V connectors for more power-hungry boards (one required on 700–800 W PSUs, both required on 850 W+ PSUs). EPS power supplies are in principle compatible with standard ATX or ATX12V motherboards found in homes and offices but there may be mechanical issues where

714-431: A 3.3 volt source, removing the need for motherboards to derive this voltage from the 5 V rail. Some motherboards, particularly those manufactured after the introduction of ATX but whilst LPX equipment was still in use, support both LPX and ATX PSUs. If using an ATX PSU for purposes other than powering an ATX motherboard, power can be fully turned on (it is always partly on to operate "wake-up" devices) by shorting

833-489: A computer is in ACPI S3 sleep mode, only +5 V SB rail is used. There are two basic differences between AT and ATX power supplies: the connectors that provide power to the motherboard, and the soft switch. In ATX-style systems, the front-panel power switch provides only a control signal to the power supply and does not switch the mains AC voltage. This low-voltage control allows other computer hardware or software to turn

952-421: A design consideration of early computer power supplies. These power supplies were generally not capable of power saving modes such as standby or "soft off", or scheduled turn-on power controls. Due to the always-on design, in the event of a short circuit , either a fuse would blow, or a switched-mode supply would repeatedly cut the power, wait a brief period of time, and attempt to restart. For some power supplies

1071-404: A desktop computer. Thus, for a 100 W load, losses for this supply would be 27 W; if the same power supply was put under a 450 W load, for which the supply's efficiency peaks at 89%, the loss would be only 56 W despite supplying 4.5 times the useful power. For a comparison, a 500-watt power supply carrying the 80 Plus Bronze efficiency rating (which means that such a power supply

1190-401: A feature under names like "rail fusion" or "current sharing".) The requirement was withdrawn as a result, however, the issue left its mark on PSU designs, which can be categorized into single rail and multiple rail designs. Both may (and often do) contain current limiting controllers. As of ATX 2.31, a single rail design's output current can be drawn through any combination of output cables, and

1309-506: A large number of memory slots. In 2004, Intel announced the BTX (Balanced Technology eXtended) standard, intended as a replacement for ATX. While some manufacturers adopted the new standard, Intel discontinued any future development of BTX in 2006. As of 2024 , the ATX design still remains the de facto standard for personal computers. On the back of the computer case, some major changes were made to

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1428-523: A limited amount of current through one or more cables, and each rail is independently controlled by its own current sensor which shuts down the supply upon excess current. Unlike a fuse or circuit breaker , these limits reset as soon as the overload is removed. Typically, a power supply will guarantee at least 17 A at 12 V by having a current limit of 18.5 A ± 8% . Thus, it is guaranteed to supply at least 17 A, and guaranteed to cut off before 20 A. The current limits for each group of cables

1547-421: A line-voltage power switch that extended through the side of the computer case. In a common variant found in tower cases, the line-voltage switch was connected to the power supply with a short cable, allowing it to be mounted apart from the power supply. An early microcomputer power supply was either fully on or off, controlled by the mechanical line-voltage switch, and energy saving low-power idle modes were not

1666-872: A linear regulator. The development of high-power and high-voltage transistors at economical prices made it practical to introduce switched-mode supplies that had been used in aerospace, mainframes, minicomputers and color television, into desktop personal computers. The Apple II design by Atari engineer Rod Holt was awarded a patent, and was in the vanguard of modern computer power supply design. Now all modern computers use switched-mode power supplies, which are lighter, less costly, and more efficient than equivalent linear power supplies. Computer power supplies may have short circuit protection, overpower (overload) protection, over-voltage protection, under-voltage protection, over-current protection, and over-temperature protection. Power supplies designed for worldwide use were once equipped with an input voltage selector switch that allowed

1785-543: A material lowers with increasing temperature, typically in a defined temperature range. For most materials, electrical resistivity will decrease with increasing temperature. Materials with a negative temperature coefficient have been used in floor heating since 1971. The negative temperature coefficient avoids excessive local heating beneath carpets, bean bag chairs, mattresses , etc., which can damage wooden floors , and may infrequently cause fires. Residual magnetic flux density or B r changes with temperature and it

1904-499: A personal computer may range from 250 W to more than 1000 W for a high-performance computer with multiple graphics cards. Personal computers without especially high performing CPUs or graphics cards usually require 300 to 500 W. Power supplies are designed around 40% greater than the calculated system power consumption . This protects against system performance degradation, and against power supply overloading. Power supplies label their total power output, and label how this

2023-415: A phenomenon known as doppler broadening , where resonance absorption of fast neutrons in fuel filler material prevents those neutrons from thermalizing (slowing down). In its more general form, the temperature coefficient differential law is: Where is defined: And α {\displaystyle \alpha } is independent of T {\displaystyle T} . Integrating

2142-576: A plate fitted, although there will be open gaps in the case which may compromise the EMI/RFI screening and allow ingress of dirt and random foreign bodies. Panels were made that allowed fitting an AT motherboard in an ATX case. Some ATX motherboards come with an integrated I/O plate. ATX also made the PS/2-style mini-DIN keyboard and mouse connectors ubiquitous. AT systems used a 5-pin DIN connector for

2261-453: A power button that is directly connected to the system computer power supply (PSU). The general configuration is a double-pole latching mains voltage switch with the four pins connected to wires from a four-core cable. The wires are either soldered to the power button (making it difficult to replace the power supply if it failed) or blade receptacles were used. An ATX power supply is typically controlled by an electronic switch connected to

2380-457: A power supply. Various initiatives exist to improve the efficiency of computer power supplies. Climate Savers Computing Initiative promotes energy saving and reduction of greenhouse gas emissions by encouraging development and use of more efficient power supplies. 80 Plus certifies a variety of efficiency levels for power supplies and encourages their use via financial incentives. Efficient power supplies also save money by wasting less power; as

2499-489: A rectangular area on the back of the system with an arrangement they could define themselves, though a number of general patterns depending on what ports the motherboard offers have been followed by most manufacturers. Cases are usually fitted with a snap-out panel, also known as an I/O plate or I/O shield, in one of the common arrangements. I/O plates are usually included with retail motherboards to allow installation in any suitable case. The computer will operate correctly without

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2618-401: A relatively rapid decrease with temperature, i.e. a lower coefficient. The lower the coefficient, the greater a decrease in electrical resistance for a given temperature increase. NTC materials are used to create inrush current limiters (because they present higher initial resistance until the current limiter reaches quiescent temperature), temperature sensors and thermistors . An increase in

2737-537: A result, energy-efficient PSUs waste less energy in heat and require less airflow to cool, resulting in quieter operation. As of 2012 some high-end consumer PSUs can exceed 90% efficiency at optimal load levels, though will fall to 87–89% efficiency during heavy or light loads. Google's server power supplies are more than 90% efficient. HP 's server power supplies have reached 94% efficiency. Standard PSUs sold for server workstations have around 90% efficiency, as of 2010. ATX ATX ( Advanced Technology Extended )

2856-408: A result, they use less electricity to power the same computer, and they emit less waste heat which results significant energy savings on central air conditioning in the summer. The gains of using an efficient power supply are more substantial in computers that use a lot of power. Although a power supply with a larger than needed power rating will have an extra margin of safety against overloading, such

2975-796: A section about Climate Savers, updated recommended power supply configuration charts, and updated the cross-regulation graphs. This is the unofficial name given to the later revisions of the v2.31 specifications, published in May 2020 The ATX12V 2.4 specifications were published in August 2021. It is specified in Revision 1.31 of the 'Design Guide for Desktop Platform Form Factors', which names this as ATX12V version 2.4. The specifications for ATXV12 2.51 were released in September 2021 and introduced support for Alternative Low Power Mode (ALPM) which supersedes

3094-587: A signal to the motherboard to indicate when the DC voltages are in spec, so that the computer is able to safely power up and boot. The most recent ATX PSU standard is version 3.0 as of mid 2024. The desktop computer power supply converts the alternating current (AC) from a wall socket of mains electricity to a low-voltage direct current (DC) to operate the motherboard, processor and peripheral devices. Several direct-current voltages are required, and they must be regulated with some accuracy to provide stable operation of

3213-400: A simple but inefficient linear regulator connected to the +5 V rail. The ATX connector provides multiple wires and power connections for the 3.3 V supply, because it is most sensitive to voltage drop in the supply connections. Another ATX addition was the +5 V SB (standby) rail for providing a small amount of standby power , even when the computer was nominally "off". When

3332-428: A special cutout in the back plane for the cable to come in from behind and bend around the board, making insertion and wire management very difficult. Many power supply cables barely or fail to reach, or are too stiff to make the bend, and extensions are sometimes required due to this placement. Modern power supplies often have longer cables to alleviate this issue. Several ATX-derived designs have been specified that use

3451-422: A standard system power supply, so the Pentium 4 established the practice of generating it with a DC-to-DC converter on the motherboard next to the processor, powered by the 4-pin 12 V connector. This is a minor revision from August 2000. The power on the 3.3 V rail was slightly increased and other smaller changes were made. A relatively minor revision from January 2002. The only significant change

3570-414: A sufficient +12 V rating will have adequate capacity at lower voltages. However, most hard drives or PCI cards will create a greater load on the +5 V rail. Older CPUs and logic devices on the motherboard were designed for 5 V operating voltage. Power supplies for those computers regulate the 5 V output precisely, and supply the 12 V rail in a specified voltage window depending on

3689-631: A two second delay for an improved user experience. The specifications for ATXV12 2.53 were released in December 2021 and constitute another minor update to the ATX standard. ATXV12 2.53 makes further recommendations on efficiency and references the Energy Star Computers Specification Version 8.0 which was finalized in April 2020. Temperature coefficient A temperature coefficient describes

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3808-399: A unit is often less efficient and wastes more electricity at lower loads than a more appropriately sized unit. For example, a 900-watt power supply with the 80 Plus Silver efficiency rating (which means that such a power supply is designed to be at least 85% efficient for loads above 180 W) may only be 73% efficient when the load is lower than 100 W, which is a typical idle power for

3927-490: Is 12 × 13 in (305 × 330 mm) most motherboard manufacturers also refer to motherboards with measurements 12 × 10.1 in (305 × 257 mm), 12 × 10.4 in (305 × 264 mm), 12 × 10.5 in (305 × 267 mm) and 12 × 10.7 in (305 × 272 mm) as E-ATX. While E-ATX and SSI EEB (Server System Infrastructure (SSI) Forum's Enterprise Electronics Bay (EEB)) share

4046-558: Is a minor revision from March 2005. The power was slightly increased on all rails. Efficiency requirements changed: minimum 65% at light load, 72% at typical load, and 70% at full load. Introduced recommended minimum values of 75% at light load, 80% at typical load, and 77% at full load. Also released in March 2005 it includes corrections and specifies High Current Series wire terminals for 24-pin ATX motherboard and 4-pin +12 V power connectors. Effective March 2007. Recommended efficiency

4165-462: Is a motherboard and power supply configuration specification, patented by David Dent in 1995 at Intel , to improve on previous de facto standards like the AT design . It was the first major change in desktop computer enclosure , motherboard and power supply design in many years, improving standardization and interchangeability of parts. The specification defines the dimensions; the mounting points;

4284-651: Is a potential source of confusion. A number of manufacturers have added one to three additional expansion slots (at the standard 0.8 inch spacing) to the standard 12-inch ATX motherboard width. Form factors considered obsolete in 1999 included Baby-AT, full size AT, and the semi-proprietary LPX for low-profile cases. Proprietary motherboard designs such as those by Compaq, Packard-Bell, Hewlett Packard and others existed, and were not interchangeable with multi-manufacturer boards and cases. Portable and notebook computers and some 19-inch rackmount servers have custom motherboards unique to their particular products. Although true E-ATX

4403-626: Is a power supply unit meant for high-power-consumption computers and entry-level servers. Developed by the Server System Infrastructure (SSI) forum, a group of companies including Intel, Dell, Hewlett-Packard and others, that works on server standards, the EPS form factor is a derivative of the ATX form factor. The latest specification is v2.93. The EPS standard provides a more powerful and stable environment for critical server-based systems and applications. EPS power supplies have

4522-408: Is broadly cited as important for reactor safety, but wide temperature variations across real reactors (as opposed to a theoretical homogeneous reactor) limit the usability of a single metric as a marker of reactor safety. In water moderated nuclear reactors, the bulk of reactivity changes with respect to temperature are brought about by changes in the temperature of the water. However each element of

4641-451: Is designed to be at least 82% efficient for loads above 100 W) may provide an 84% efficiency for a 100 W load, wasting only 19 W. Other ratings such as 80 plus gold, 80 plus platinum and 80 plus titanium also provide the same ratings respectively. 80 plus gold providing an 87% efficiency under 100% load, 80 plus platinum providing a 90% efficiency and 80 plus titanium providing the best efficiency at 94%. [1] A power supply that

4760-406: Is determined by the electric current limits for each of the voltages supplied. Some power supplies have no-overload protection. The system power consumption is a sum of the power ratings for all of the components of the computer system that draw on the power supply. Some graphics cards (especially multiple cards) and large groups of hard drives can place very heavy demands on the 12 V lines of

4879-462: Is impractical to deliver from off-board power supplies. Initially, this was supplied by the main +5 V supply, but as power demands increased, the high currents required to supply sufficient power became problematic. To reduce the power losses in the 5 V supply, with the introduction of the Pentium 4 microprocessor, Intel changed the processor power supply to operate on +12 V, and added

Power supply unit (computer) - Misplaced Pages Continue

4998-475: Is more complex and can achieve higher PF, up to 99%. The first active PFC circuits just delayed the inrush. Newer ones work as an input and output condition-controlled step-up converter, supplying a single 400 V filter capacitor from a wide-range input source, usually between 80 and 240 V. Newer PFC circuits also replace the NTC -based inrush current limiter, which is an expensive part previously located next to

5117-482: Is not a replacement for a current-limited bench laboratory DC power supply; instead it is better described as a bulk DC power supply . The original ATX specification called for a power supply to be located near to the CPU with the power supply fan drawing in cooling air from outside the chassis and directing it onto the processor. It was thought that in this configuration, cooling of the processor would be achievable without

5236-612: Is one of the important characteristics of magnet performance. Some applications, such as inertial gyroscopes and traveling-wave tubes (TWTs), need to have constant field over a wide temperature range. The reversible temperature coefficient (RTC) of B r is defined as: To address these requirements, temperature compensated magnets were developed in the late 1970s. For conventional SmCo magnets , B r decreases as temperature increases. Conversely, for GdCo magnets, B r increases as temperature increases within certain temperature ranges. By combining samarium and gadolinium in

5355-400: Is primarily used to provide the negative supply voltage for RS-232 ports and is also used by one pin on conventional PCI slots primarily to provide a reference voltage for some models of sound cards . The 5 V SB supply is used to produce trickle power to provide the soft-power feature of ATX when a PC is turned off, as well as powering the real-time clock to conserve the charge of

5474-552: Is raised. Materials which have useful engineering applications usually show a relatively rapid increase with temperature, i.e. a higher coefficient. The higher the coefficient, the greater an increase in electrical resistance for a given temperature increase. A PTC material can be designed to reach a maximum temperature for a given input voltage, since at some point any further increase in temperature would be met with greater electrical resistance. Unlike linear resistance heating or NTC materials, PTC materials are inherently self-limiting. On

5593-422: Is resistance at temperature T 0 {\displaystyle T_{0}} . Therefore, many materials that produce acceptable values of R 0 {\displaystyle R_{0}} include materials that have been alloyed or possess variable negative temperature coefficient (NTC), which occurs when a physical property (such as thermal conductivity or electrical resistivity ) of

5712-545: Is self-certified by its manufacturer may claim output ratings double or more than what is actually provided. To further complicate this possibility, when there are two rails that share power through down-regulating, it also happens that either the 12 V rail or the 5 V rail overloads at well below the total rating of the power supply. Many power supplies create their 3.3 V output by down-regulating their 5 V rail, or create 5 V output by down-regulating their 12 V rails. The two rails involved are labeled on

5831-416: Is the value of the partial differential of reactivity with respect to temperature and is referred to as the "temperature coefficient of reactivity". As a result, the temperature feedback provided by α T {\displaystyle \alpha _{T}} has an intuitive application to passive nuclear safety . A negative α T {\displaystyle \alpha _{T}}

5950-521: Is then documented so the user can avoid placing too many high-current loads in the same group. Originally at the time of ATX 2.0, a power supply featuring "multiple +12 V rails" implied one able to deliver more than 20 A of +12 V power, and was seen as a good thing. However, people found the need to balance loads across many +12 V rails inconvenient, especially as higher-end PSUs began to deliver far greater currents up to around 2000 W, or more than 150 A at 12 V (compared to

6069-515: Is used to prevent digital circuitry operation during the initial milliseconds of power supply turn-on, where output voltages and currents are rising but not yet sufficient or stable for proper device operation. Once the output power is ready to use, the Power Good signal tells the digital circuitry that it can begin to operate. Original IBM power supplies for the PC (model 5150), XT and AT included

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6188-493: Is version 2.2. The most recent ATX12V power supply unit specification is ATX 3.0 released in February 2022. EATX (Extended ATX) is a bigger version of the ATX motherboard with 12 × 13 in (305 × 330 mm) dimensions. While some dual CPU socket motherboards have been implemented in ATX, the extra size of EATX makes it the typical form factor for dual socket systems, and with sockets that support four or eight memory channels, for single socket systems with

6307-470: The +12 V Power Connector , this is commonly referred to as the P4 connector because this was first needed to support the Pentium 4 processor. Before the Pentium 4, processors were generally powered from the 5 V rail. Later processors operate at much lower voltages, typically around 1 V and some draw over 100 A. It is infeasible to provide power at such low voltages and high currents from

6426-613: The CMOS battery . A −5 V output was originally required because it was supplied on the ISA bus; it was removed in later versions of the ATX standard, as it became obsolete with the removal of the ISA bus expansion slots (the ISA bus itself is still found in any computer which is compatible with the old IBM PC specification; e.g., not found in the PlayStation 4 ). Originally, the motherboard

6545-541: The Intel Skulltrail motherboard that could accommodate two Intel Core 2 Quad processors and has a total of seven PCI-E slots and 12 DDR3 RAM slots. The new design is dubbed "HPTX" and is 13.6 × 15 in (345 × 381 mm). The ATX specification requires the power supply to produce three main outputs, +3.3 V, +5 V and +12 V. Low-power −12 V and +5 V SB (standby) supplies are also required. The −12 V supply

6664-436: The "power-on" pin on the ATX connector (pin 16, green wire) to a black wire (ground), which is what the power button on an ATX system does. A minimum load on one or more voltages may be required (varies by model and vendor); the standard does not specify operation without a minimum load and a conforming PSU may shut down, output incorrect voltages, or otherwise malfunction, but will not be hazardous or damaged. An ATX power supply

6783-649: The 12 V connector and in the case of older boards connector overhang the sockets. Many PSU vendors use connectors where the extra sections can be unclipped to avoid this issue. As with later versions of the ATX PSU standard, there is also no −5 V rail. As power supply capacity increased, the ATX power supply standard was amended (beginning with version 2.0) to include: 3.2.4. Power Limit / Hazardous Energy Levels Under normal or overload conditions, no output shall continuously provide more than 240 VA under any conditions of load including output short circuit, per

6902-525: The 140 mm depth, is frequently varied, with depths of 160, 180, 200 and 230 mm used to accommodate higher power, larger fan and/or modular connectors. Original AT cases (flat case style) have an integrated power switch that protruded from the power supply and sits flush with a hole in the AT chassis. It utilizes a paddle-style DPST switch and is similar to the PC and PC-XT style power supplies. Later AT (so-called "Baby AT") and LPX style computer cases have

7021-439: The 240 or 500 W of earlier times). When the assignment of connectors to rails is done at manufacturing time it is not always possible to move a given load to a different rail or manage the allocation of current across devices. Rather than add more current limit circuits, many manufacturers chose to ignore the requirement and increase the current limits above 20 A per rail, or provided "single-rail" power supplies that omit

7140-406: The 3.3 V rail to maximum (33 W), would leave the 5 V rail only able to output 77 W. A test in 2005 revealed computer power supplies are generally about 70–80% efficient. For a 75% efficient power supply to produce 75 W of DC output it would require 100 W of AC input and dissipate the remaining 25 W in heat. Higher-quality power supplies can be over 80% efficient; as

7259-540: The 4-pin connector as described below. Numbering of the ATX revisions may be a little confusing: ATX refers to the design, and goes up to version 2.2 in 2004 (with the 24 pins of ATX12V 2.0), while ATX12V describes only the PSU. For instance, ATX 2.03 is quite commonly seen on PSUs from 2000 and 2001 and often includes the P4 12V connector, even if the norm itself did not define it yet. The main changes and additions in ATX12V 1.0 (released in February 2000) were: Formally called

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7378-412: The 5 V and converting the product of voltage drop and current to heat. Later regulators managed all the 3.3, 5 and 12 V rails. As CPUs increased in current consumption (due to higher static current due to higher transistor count and much higher dynamic current due to both higher count and switching frequency) in CPU generations after the i386 , it became necessary to place voltage regulators close to

7497-410: The 5 V rail. Jumpers or dip switches set the output voltages to the installed CPU's specification. When newer CPUs required higher currents, switching mode voltage regulators like buck converters replaced linear regulators for efficiency. Since the first revision of the ATX standard, PSUs were required to have a 3.3 V output voltage rail. Rarely, a linear regulator generated these, supplied from

7616-423: The AT standard. Originally AT style cases had only a keyboard connector and expansion slots for add-on card backplates. Any other onboard interfaces (such as serial and parallel ports ) had to be connected via flying leads to connectors which were mounted either on spaces provided by the case or brackets placed in unused expansion slot positions. ATX allowed each motherboard manufacturer to put these ports in

7735-501: The ATX specification was that it was last revised when power supplies were normally placed at the top of many old computer cases rather than at the bottom, as with many modern computer cases. This has led to some problematic standard locations for ports, in particular the 4/8 pin CPU power, which is normally located along the top edge of the board, convenient for top-mounted power supplies. This makes it very difficult for cables from bottom-mounted power supplies to reach, and commonly requires

7854-465: The CPU. In order to reduce power consumption of regulation (and thus to remain thermally feasible), these regulators are of switch-mode power supply design . To keep conduction losses at bay, it is desirable to transport the same power on the higher-voltage +12 V rail at lower current, instead of on +5V at higher current. Thus, Pentium-era power supplies tend have their highest current capacity on these rails. Entry-Level Power Supply Specification (EPS)

7973-715: The I/O panel; and the power and connector interfaces among a computer case , a motherboard , and a power supply . ATX is the most common motherboard design. Other standards for smaller boards (including microATX , FlexATX , nano-ITX , and mini-ITX ) usually keep the basic rear layout but reduce the size of the board and the number of expansion slots. Dimensions of a full-size ATX board are 12 × 9.6 in (305 × 244 mm), which allows many ATX chassis to accept microATX boards. The ATX specifications were released by Intel in 1995 and have been revised numerous times since. The most recent ATX motherboard specification

8092-526: The IS8XM motherboard. In 2019 Intel released a new standard based on an all-12V design: ATX12VO. The power supply only provides 12 V voltage output; 5 V, 3.3 V powers, as needed by USB , hard disk drive and other devices, are transformed on the motherboard ; and the ATX motherboard connector is reduced from 24-pin to 10-pin. Called ATX12VO, it is not expected to replace current standards but to exist alongside it. At CES 2020, FSP Group showed

8211-586: The January 2008 CES was the Lian Li Armorsuit PC-P80 case with 10 slots designed for the motherboard. The name "XL-ATX" has been used by at least three companies in different ways: In 2010, EVGA Corporation released a new motherboard, the "Super Record 2", or SR-2, whose size surpasses that of the "EVGA X58 Classified 4-Way SLI". The new board is designed to accommodate two Dual QPI LGA1366 socket CPUs (e.g. Intel Xeon ), similar to that of

8330-453: The PSU, and for these loads, the PSU's 12 V rating is crucial. The total 12 V rating on the power supply must be higher than the current required by such devices so that the PSU can fully serve the system when its other 12 V system components are taken into account. The manufacturers of these computer system components, especially graphics cards, tend to over-rate their power requirements, to minimize support issues due to too low of

8449-474: The alloy, the temperature coefficient can be reduced to nearly zero. The temperature dependence of electrical resistance and thus of electronic devices ( wires , resistors) has to be taken into account when constructing devices and circuits . The temperature dependence of conductors is to a great degree linear and can be described by the approximation below. where ρ 0 {\displaystyle \rho _{0}} just corresponds to

8568-669: The cable. The connector pin pitch is 4.20 mm (about one sixth of an inch). Four wires have special functions: Generally, supply voltages must be within ±5% of their nominal values at all times. The little-used negative supply voltages, however, have a ±10% tolerance. There is a specification for ripple in a 10 Hz–20 MHz bandwidth: The 20–24-pin Molex Mini-Fit Jr. has a power rating of, 9 amperes maximum per pin). As large server motherboards and 3D graphics cards have required progressively more and more power to operate, it has been necessary to revise and extend

8687-416: The computer. A power supply rail or voltage rail refers to a single voltage provided by a PSU. Some PSUs can also supply a standby voltage , so that most of the computer system can be powered off after preparing for hibernation or shutdown, and powered back on by an event. Standby power allows a computer to be started remotely via wake-on-LAN and Wake-on-ring or locally via Keyboard Power ON (KBPO) if

8806-419: The core has a specific temperature coefficient of reactivity (e.g. the fuel or cladding). The mechanisms which drive fuel temperature coefficients of reactivity are different from water temperature coefficients. While water expands as temperature increases , causing longer neutron travel times during moderation , fuel material will not expand appreciably. Changes in reactivity in fuel due to temperature stem from

8925-408: The current limit circuitry. (In some cases, in violation of their own advertising claims to include it.) Because of the above standards, almost all high-power supplies claimed to implement separate rails, however this claim was often false; many omitted the necessary current-limit circuitry, both for cost reasons and because it is an irritation to customers. (The lack was, and is, sometimes advertised as

9044-426: The event of a short circuit , or can melt the wire or its insulation in the case of a fault, or potentially start a fire or damage other components. The rule limits each output to below 20  amps , with typical supplies guaranteeing 18 A availability. Power supplies capable of delivering more than 18 A at 12 V would provide their output in groups of cables (called "rails"). Each rail delivers up to

9163-602: The first prototype based on the new ATX12VO standard. According to the Single Rail Power Supply ATX12VO design guide officially published by Intel in May 2020, the guide listed the details of 12V-only design and the major benefit which included higher efficiency and lower electrical interruption. The overall power draw on a PSU is limited by the fact that all of the supply rails come through one transformer and any of its primary side circuitry, like switching components. Total power requirements for

9282-409: The form of 12 V power. Thus, GPU manufacturers, to ensure 200–250 W of 12 V power (peak load, CPU+GPU), recommended power supplies of 500–600 W or higher. More modern ATX power supplies can deliver almost all (typically 80–90%) of their total rated capacity in the form of +12 V power. Because of this change, it is important to consider the +12 V supply capacity, rather than

9401-405: The function and the value of resistivity at a given temperature. For both, α {\displaystyle \alpha } is referred to as the temperature coefficient of resistance (TCR). This property is used in devices such as thermistors. A positive temperature coefficient (PTC) refers to materials that experience an increase in electrical resistance when their temperature

9520-492: The fuse. The first IBM PC power supply unit (PSU) supplied two main voltages: +5  V and +12 V. It supplied two other voltages, −5 V and −12 V, but with limited amounts of power. Most microchips of the time operated on 5 V power. Of the 63.5  W these PSUs could deliver, most of it was on this +5 V rail. The +12 V supply was used primarily to operate motors such as in disk drives and cooling fans. As more peripherals were added, more power

9639-756: The keyboard and were generally used with serial port mice (although PS/2 mouse ports were also found on some systems). Many modern motherboards are phasing out the PS/2-style keyboard and mouse connectors in favor of the more modern Universal Serial Bus . Other legacy connectors that are slowly being phased out of modern ATX motherboards include 25-pin parallel ports and 9-pin RS-232 serial ports . In their place are onboard peripheral ports such as Ethernet , FireWire , eSATA , audio ports (both analog and S/PDIF ), video (analog D-sub , DVI , HDMI , or DisplayPort ), extra USB ports, and Wi-Fi. A notable issue with

9758-516: The load ratio of both rails. The +12 V supply was used for computer fan motors, disk drive motors and serial interfaces (which also used the −12 V supply). A further use of the 12 V came with the sound cards, using linear chip audio power amplifiers , sometimes filtered by a 9 V linear regulator on the card to cut the noise of the motors. Since certain i386 variant CPUs use lower operating voltages such as 3.3 or 3.45 V, motherboards had linear voltage regulators supplied by

9877-422: The management and safe allocation of that load is left for the user. A multiple rail design does the same, but limits the current supplied to each individual connector (or group of connectors), and the limits it imposes are the manufacturer's choice rather than set by the ATX standard. Since 2011, Fujitsu and other tier-1 manufacturers have been manufacturing systems containing motherboard variants that require only

9996-516: The motherboard supports it. This standby voltage may be generated by a small linear power supply inside the unit or a switching power supply, sharing some components with the main unit to save cost and energy. First-generation microcomputer and home computer power supply units used a heavy step-down transformer and a linear power supply, as used, in for example, the Commodore PET introduced in 1977. The Apple II , also introduced in 1977,

10115-505: The need of an active heatsink. This recommendation was removed from later specifications; modern ATX power supplies usually exhaust air from the case. ATX, introduced in late 1995, defined three types of power connectors: The power distribution specification defined that most of the PSU's power should be provided on 5 V and 3.3 V rails, because most of the electronic components (CPU, RAM, chipset, PCI, AGP and ISA cards) used 5 V or 3.3 V for power supply. The 12 V rail

10234-445: The other hand, NTC material may also be inherently self-limiting if constant current power source is used. Some materials even have exponentially increasing temperature coefficient. Example of such a material is PTC rubber . A negative temperature coefficient (NTC) refers to materials that experience a decrease in electrical resistance when their temperature is raised. Materials which have useful engineering applications usually show

10353-419: The overall power capacity, when using an older ATX power supply with a more recent computer. Low-quality power supply manufacturers sometimes take advantage of this overspecification by assigning unrealistically high power supply ratings, knowing that very few customers fully understand power supply ratings. +3.3 V and +5 V rail voltage supplies are rarely a limiting factor; generally, any supply with

10472-399: The power button on the computer case and allows the computer to be turned off by the operating system . In addition, many ATX power supplies have a manual switch on the back that also ensures no power is being sent to the components. When the switch on the power supply is turned off, the computer cannot be turned on with the front power button. The power supply's connection to the motherboard

10591-469: The power supply fan speed under the control of the motherboard. At least two of Dell's business PCs introduced in 2013, the OptiPlex 9020 and Precision T1700, ship with 12 V–only power supplies and implement 5 V and 3.3 V conversion exclusively on the motherboard. Afterwards, Lenovo ThinkCentre M93P adopted 12 V–only PSU and performs 5 V and 3.3 V conversion exclusively on

10710-430: The power supply with a combined current limit. For example, the 5  V and 3.3  V rails are rated with a combined total current limit. For a description of the potential problem, a 3.3 V rail may have a 10 A rating by itself ( 33  W ), and the 5 V rail may have a 20  A rating ( 100  W ) by itself, but the two together may only be able to output 110 W. In this case, loading

10829-455: The reactions lies between 2 and 3. Most ceramics exhibit negative temperature dependence of resistance behaviour. This effect is governed by an Arrhenius equation over a wide range of temperatures: where R is resistance, A and B are constants, and T is absolute temperature (K). The constant B is related to the energies required to form and move the charge carriers responsible for electrical conduction – hence, as

10948-526: The relative change of a physical property that is associated with a given change in temperature . For a property R that changes when the temperature changes by dT , the temperature coefficient α is defined by the following equation: Here α has the dimension of an inverse temperature and can be expressed e.g. in 1/K or K . If the temperature coefficient itself does not vary too much with temperature and α Δ T ≪ 1 {\displaystyle \alpha \Delta T\ll 1} ,

11067-517: The repeated restarting is audible as a quiet rapid chirping or ticking emitted from the device. When Intel developed the ATX standard power supply connector (published in 1995), microchips operating on 3.3 V were becoming more popular, beginning with the Intel 80486DX4 microprocessor in 1994, and the ATX standard supplies three positive rails: +3.3 V, +5 V, and +12 V. Earlier computers requiring 3.3 V typically derived that from

11186-438: The requirement of UL 1950 / CSA 950 / EN 60950 / IEC 950. The requirement was later deleted from version 2.3 (March 2007) of the ATX12V power supply specifications, but led to a distinction in modern ATX power supplies between single and multiple rails. The rule was intended to set a safe limit on the current able to pass through any single output wire. A sufficiently large current can cause serious damage in

11305-451: The same dimensions, the screw holes of the two standards do not all align; rendering them incompatible. In 2008, Foxconn unveiled a Foxconn F1 motherboard prototype, which has the same width as a standard ATX motherboard, but an extended 14.4" length to accommodate 10 slots. The firm called the new 14.4 × 9.6 in (366 × 244 mm) design of this motherboard "Ultra ATX" in its CES 2008 showing. Also unveiled during

11424-508: The same power supply, mountings and basic back panel arrangement, but set different standards for the size of the board and number of expansion slots. Standard ATX provides seven slots at 0.8 in (20 mm) spacing; the popular microATX size removes 2.4 inches (61 mm) and three slots, leaving four. Here width refers to the distance along the external connector edge, while depth is from front to rear. Note each larger size inherits all previous (smaller) colors area. AOpen has conflated

11543-405: The separate four-pin P4 connector to the new ATX12V 1.0 standard to supply that power. Modern high-powered graphics processing units do the same thing, resulting in most of the power requirement of a modern personal computer being on the +12 V rail. When high-powered GPUs were first introduced, typical ATX power supplies were "5 V-heavy", and could only supply 50–60% of their output in

11662-527: The specific PSU is not too long for the specific case. As transistors become smaller on chips, it becomes preferable to operate them on lower supply voltages, and the lowest supply voltage is often desired by the densest chip, the central processing unit . In order to supply large amounts of low-voltage power to the Pentium and subsequent microprocessors, a special power supply, the voltage regulator module began to be included on motherboards . Newer processors require up to 100 A at 2 V or less, which

11781-407: The specific resistance temperature coefficient at a specified reference value (normally T = 0 °C) That of a semiconductor is however exponential: where S {\displaystyle S} is defined as the cross sectional area and α {\displaystyle \alpha } and B {\displaystyle B} are coefficients determining the shape of

11900-444: The standard beyond the original 20-pin connector, to allow more current using multiple additional pins in parallel. The low circuit voltage is the restriction on power flow through each connector pin; at the maximum rated voltage, a single Mini-Fit Jr pin would be capable of 4800 watts. ATX power supplies generally have the dimensions of 150 × 86 × 140 mm (5.9 × 3.4 × 5.5 in), with

12019-420: The system on and off. Since ATX power supplies share both the same dimensions (150 × 86 mm (5.9 × 3.4 in)) and the same mounting layout (four screws arranged on the back side of the unit), with the prior format, there is no major physical difference preventing an AT case from accepting an ATX PSU (or vice versa, if the case can host the power switch needed by an AT PSU), provided that

12138-488: The temperature coefficient differential law: Applying the Taylor series approximation at the first order, in the proximity of T 0 {\displaystyle T_{0}} , leads to: The thermal coefficient of electrical circuit parts is sometimes specified as ppm /° C , or ppm / K . This specifies the fraction (expressed in parts per million) that its electrical characteristics will deviate when taken to

12257-435: The temperature coefficient of reactivity is a measure of the change in reactivity (resulting in a change in power), brought about by a change in temperature of the reactor components or the reactor coolant. This may be defined as Where ρ {\displaystyle \rho } is reactivity and T is temperature. The relationship shows that α T {\displaystyle \alpha _{T}}

12376-560: The temperature of a semiconducting material results in an increase in charge-carrier concentration. This results in a higher number of charge carriers available for recombination, increasing the conductivity of the semiconductor. The increasing conductivity causes the resistivity of the semiconductor material to decrease with the rise in temperature, resulting in a negative temperature coefficient of resistance. The elastic modulus of elastic materials varies with temperature, typically decreasing with higher temperature. In nuclear engineering ,

12495-508: The term Mini ATX with a more recent 15 × 15 cm (5.9 × 5.9 in) design. Since references to Mini ATX have been removed from ATX specifications since the adoption of microATX, the AOpen definition is the more contemporary term and the one listed above is apparently only of historical significance. This sounds contradictory to the now common Mini-ITX standard (17 × 17 cm (6.7 × 6.7 in)), which

12614-546: The traditional S3 power state . Windows 10 implements this functionality as Modern Standby . The specifications for ATXV12 2.52 were released in October 2021 introduces minor changes to the standard, most notably it requires power supply manufacturers to ensure power supplies with Alternative Low Power Mode (ALPM) support are able to withstand power cycles every 180 seconds (480 times per day or 175,200 per year). Power supply fans are also recommended to turn on with at least

12733-418: The upper input voltage range, around 230 V. Connecting the unit configured for the lower range to a higher-voltage grid usually resulted in immediate permanent damage. When a power-factor correction (PFC) was required, those filter capacitors were replaced with higher-capacity ones, together with a coil installed in series to delay the inrush current. This is the simple design of a passive PFC. Active PFC

12852-469: The user to configure the unit for use on local power grid. In the lower voltage range, around 115 V, this switch is turned on changing the power grid voltage rectifier into a voltage doubler in Delon circuit design. As a result, the large primary filter capacitor behind that rectifier was split up into two capacitors wired in series, balanced with bleeder resistors and varistors that were necessary in

12971-400: The value of B increases, the material becomes insulating. Practical and commercial NTC resistors aim to combine modest resistance with a value of B that provides good sensitivity to temperature. Such is the importance of the B constant value, that it is possible to characterize NTC thermistors using the B parameter equation: where R 0 {\displaystyle R_{0}}

13090-417: The width and height being the same as the preceding LPX (Low Profile eXtension) form factor (which are often incorrectly referred to as "AT" power supplies due to their ubiquitous use in later AT and Baby AT systems, even though the actual AT and Baby AT power supply form factors were physically larger) and share a common mounting layout of four screws arranged on the back side of the unit. That last dimension,

13209-475: Was changed from the older AT and LPX standards; AT and LPX had two similar connectors that could be accidentally interchanged by forcing the different keyed connectors into place, usually causing short-circuits and irreversible damage to the motherboard (the rule of thumb for safe operation was to connect the side-by-side connectors with the black wires together). ATX uses one large, keyed connector which can not be connected incorrectly. The new connector also provides

13328-464: Was delivered on the 12 V rail. However, since most of the power is consumed by chips, the 5 V rail still delivered most of the power. The −12 V rail was used primarily to provide the negative supply voltage to the RS-232 serial ports. A −5 V rail was provided for peripherals on the ISA bus (such as soundcards), but was not used by any motherboard other than the original IBM PC motherboard. An additional wire referred to as 'Power Good'

13447-411: Was determined that it would be much cheaper and more practical to power most PC components from 12 V rails, instead of from 3.3 V and 5 V rails. In particular, PCI Express expansion cards take much of their power from the 12 V rail (up to 5.5 A), while the older AGP graphics cards took only up to 1 A on 12 V and up to 6 A on 3.3 V. The CPU is also driven by

13566-447: Was increased to 80% (with at least 70% required) and the 12 V minimum load requirement was lowered. Higher efficiency generally results in less power consumption (and less waste heat ) and the 80% recommendation brings supplies in line with new Energy Star 4.0 mandates. The reduced load requirement allows compatibility with processors that draw very little power during startup. The absolute over-current limit of 240 VA per rail

13685-440: Was noted for its switched-mode power supply , which was lighter and smaller than an equivalent linear power supply would have been, and which had no cooling fan. The switched-mode supply uses a ferrite-cored high frequency transformer and power transistors that switch thousands of times per second. By adjusting the switching time of the transistor, the output voltage can be closely controlled without dissipating energy as heat in

13804-576: Was only used by computer fans and motors of peripheral devices (HDD, FDD, CD-ROM, etc.) While designing the Pentium 4 platform in 1999/2000, the standard 20-pin ATX power connector was found insufficient to meet increasing power-line requirements; the standard was significantly revised into ATX12V 1.0 (ATX12V 1.x is sometimes inaccurately called ATX-P4). ATX12V 1.x was also adopted by AMD Athlon XP and Athlon 64 systems. However, some early model Athlon XP and MP boards (including some server boards) and later model lower-end motherboards do not have

13923-455: Was powered by one 20-pin connector. An ATX power supply provides a number of peripheral power connectors and (in modern systems) two connectors for the motherboard: an 8-pin (or 4+4-pin) auxiliary connector providing additional power to the CPU and a main 24-pin power supply connector, an extension of the original 20-pin version. 20-pin Molex 39-29-9202 at the motherboard. 20-pin Molex 39-01-2200 at

14042-550: Was removed, allowing 12 V lines to provide more than 20 A per rail. This revision became effective in February 2008. It added a maximum allowed ripple/noise specification of 400 millivolts to the PWR_ON and PWR_OK signals, requires that the DC power must hold for more than 1 millisecond after the PWR_OK signal drops, clarified country-specific input line harmonic content and electromagnetic compatibility requirements, added

14161-426: Was that the −5 V rail was no longer required (it became optional). This voltage was required by the ISA bus, which is no longer present on almost all modern computers. Introduced in April 2003 (a month after 2.0). This standard introduced some changes, mostly minor. Some of them are: ATX12V 2.x brought a significant design change regarding power distribution. By analyzing the power demands of then-current PCs, it

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