The standby power source was a small linear power supply with conventional transformer, which was later changed to a switching power supply, sharing some components of the main unit due to cost- and energy-saving requirements.Power supplies designed for worldwide use were equipped with an input voltage selector switch that allowed the user to configure the unit for use on local power grid. This standby voltage is generated by a smaller power supply inside the unit. When the computer is powered down but the power supply is still on, it can be started remotely via Wake-on-LAN and Wake-on-ring or locally via Keyboard Power ON (KBPO) if the motherboard supports it. 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.The ATX standard followed some manufacturers design to have power supplies also supply a standby voltage, so that most of the computer system could be powered off after preparing for hibernation or shutdown, and powered back on by an event. The Apple II design by Atari engineer Rod Holt was awarded a patent, and was in the vanguard of modern computer power supply design. The development of high-power and high-voltage transistors at economical prices made it practical to introduce switch mode supplies, that had been used in aerospace, mainframes, minicomputers and color television, into desktop personal computers. By adjusting the switching time of the transistor, the output voltage can be closely controlled without dissipating energy as heat in a linear regulator. The switched-mode supply uses a ferrite-cored high frequency transformer and power transistors that switch thousands of times per second. The Apple II, also introduced in 1977, 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. A power supply rail or voltage rail refers to a single voltage provided by a power supply unit (PSU).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. Several direct-current voltages are required, and they must be regulated with some accuracy to provide stable operation of the computer. multiple 12 V rail2.3 12 V–only supplies3 Power rating4 Efficiency5 Appearance5.1 Connectors5.2 Modular power supplies6 Other form factors7 Life span8 Wiring diagrams9 Testing10 Monitoring11 See also12 Notes13 References14 External links14.1 Computer power supply calculators14.2 ATX power supply specificationsFunctionsSimplified circuit diagram of a typical PSUDiagram of a typical XT and AT voltage regulator circuitInternals of a PSU with passive PFC (left) and active PFC (right)The desktop computer power supply changes alternating current from a wall socket of mains electricity to low-voltage direct current to operate the processor and peripheral devices. The most recent ATX PSU standard is version 2.31 as of mid-2008.Contents1 Functions2 Development2.1 Original IBM PC, XT and AT standard2.2 ATX standard2.2.1 ATX12V standard2.2.2 3.3 V and 5 V rails2.2.3 Entry-Level Power Supply Specification2.2.4 Single vs. They also provide 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.
ATX power supplies are turned on and off by a signal from the motherboard.
While an ATX power supply is connected to the mains supply, it always provides a 5 Volt standby (5VSB) voltage so that the standby functions on the computer and certain peripherals are powered.
Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage.Most modern desktop personal computer power supplies conform to the ATX specification, which includes form factor and voltage tolerances. Modern personal computers universally use switched-mode power supplies.
From Wikipedia, the free encyclopedia Jump to navigation Jump to search An ATX power supply unit with top cover removedA power supply unit (or PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer.