Power supply unit:

Introduction:

A computer's internal components receive low-voltage, regulated DC power from a power supply unit (PSU), which converts mains AC. Switched-mode power supply are utilized by all contemporary personal computers. While some power supplies automatically adjust to the mains voltage, others offer a manual switch for choosing the input voltage.

 

Power supply unit

The ATX specification, which specifies form factor and voltage tolerances, is followed by the majority of contemporary desktop personal computer power supplies. The 5-volt standby (5VSB) power that an ATX power supply always supplies when it is connected to the mains supply powers the computer's standby features and some peripherals. A signal from the motherboard turns on and off ATX power supplies. In order for the computer to safely power on and boot, they also send a signal to the motherboard when the DC voltages are within specs. Version 3.0 of the ATX PSU standard is the most recent as of mid-2022.

 

Functions:

For the motherboard, CPU, and peripheral devices to operate, the desktop computer power supply transforms the alternating current (AC) from a wall socket of mains energy into a low-voltage direct current (DC). For the computer to operate steadily, a number of direct-current voltages must be present, and they must be precisely regulated. A single voltage supplied by a PSU is referred to as a power supply rail or voltage rail.

 

Some power supply units (PSUs) can also provide a standby voltage, allowing the majority of the computer system to be switched down while getting ready for hibernation or shutdown and turned back on in response to an incident. If the motherboard supports it, standby power enables a computer to be started locally via Keyboard Power ON (KBPO) or remotely via wake-on-LAN and wake-on-ring. To save money and energy, the standby voltage may be produced by a tiny internal linear power supply or a switching power supply that shares some components with the main unit.

 

Power supply unit

History:

A massive step-down transformer and a linear power supply were employed in first-generation microcomputer and home computer power supply units, as seen, for instance, in the 1977-released Commodore PET. The switched-mode power supply of the Apple II, which debuted in 1977 as well, was notable for being thinner and lighter than an equivalent linear power supply and lacking a cooling fan. A high frequency transformer with a ferrite core and power transistors that switch thousands of times per second are used in the switched-mode supply. The output voltage can be tightly adjusted without generating heat in a linear regulator by modifying the transistor's switching time.It became feasible to integrate switch mode supplies, which were previously utilized in aerospace, mainframes, minicomputers, and color television, into desktop personal computers because to the development of high-power and high-voltage transistors at affordable prices. Rod Holt, an engineer with Atari, created the Apple II, which led the way in terms of contemporary computer power supply design and was given a patent. All contemporary computers now make use of switched-mode power sources, which are more portable, affordable, and effective than comparable linear power supplies.

 

Short-circuit, overpower (overload), over-voltage, under-voltage, over-current, and over-temperature protection are possible features of computer power supply.

 

Input voltage switch:

Previously, power supplies intended for global usage had an input voltage selector switch that the user may use to set the device up for use with a local power grid. When this switch is activated, the power grid voltage rectifier transforms into a voltage doubler in the lower voltage range, around 115 V. Because bleeder resistors and varistors were required in the upper input voltage range, around 230 V, the massive primary filter capacitor behind that rectifier was divided up into two capacitors linked in series and balanced.In most cases, connecting a device designed for a lower voltage range to a higher voltage grid caused instant and irreparable harm. These filter capacitors were changed out for higher-capacity ones when power-factor correction (PFC) was necessary, and a coil was added in series to slow the inrush current. This is how a passive PFC is constructed.

 

The complexity of active PFC allows for higher PF, up to 99%. The inrush was only postponed by the first active PFC circuits. The more recent ones feed a single 400 V filter capacitor from a wide-range input source, typically between 80 and 240 V, operating as an input and output condition-controlled step-up converter. The NTC-based inrush current limiter, a pricey component that was formerly installed next to the fuse, is also replaced with newer PFC circuits.