![]() ![]() The −12 V rail was used primarily to provide the negative supply voltage to the RS-232 serial ports. However, since most of the power is consumed by chips, the 5 V rail still delivered most of the power. As more peripherals were added, more power was delivered on the 12 V rail. The +12 V supply was used primarily to operate motors such as in disk drives and cooling fans. Of the 63.5 W these PSUs could deliver, most of it was on this +5 V rail. Most microchips of the time operated on 5 V power. It supplied two other voltages, −5 V and −12 V, but with limited amounts of power. Psu shroud Pc#The first IBM PC power supply unit (PSU) supplied two main voltages: +5 V and +12 V. Newer PFC circuits also replace the NTC-based inrush current limiter, which is an expensive part previously located next to the fuse.Ī typical XT PSU power switch, which is an integral part of the PSU. Newer ones are working 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. ![]() The first active PFC circuits just delayed the inrush. This is the simple design of a passive PFC.Īctive PFC is more complex and can achieve higher PF, up to 99%. Psu shroud series#When the 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. Connecting the unit configured for the lower range to a higher-voltage grid usually resulted in an immediate permanent damage. ![]() 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 the upper input voltage range, around 230 V. ![]() 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. Power supplies designed for worldwide use were once equipped with an input voltage selector switch that allowed the user to configure the unit for use on local power grid. Now all modern computers use switched-mode power supplies, which are lighter, less costly, and more efficient than equivalent linear power supplies.Ĭomputer power supplies may have short circuit protection, overpower (overload) protection, over-voltage protection, under-voltage protection, over-current protection, and over-temperature protection. 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. 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.įirst-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. 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 the motherboard supports it. 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. A power supply rail or voltage rail refers to a single voltage provided by a PSU. Several direct-current voltages are required, and they must be regulated with some accuracy to provide stable operation of the computer. 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. Internals of a PSU with passive PFC (left) and active PFC (right) ![]()
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