A power supply unit (PSU) converts AC power to regulated, low-voltage DC power for a computer’s internal components. Modern personal computers generally use switched-mode power supplies what is a (PSU) Power supply unit.
Some power supplies have a manual switch to select the input voltage, while others use line voltage. Most modern desktop PC power supplies conform to the ATX specification, which includes form factor and voltage tolerances.
Power is supplied to standby functions on the computer and certain peripheral devices. ATX power supplies are turned on and off by a signal from the motherboard.
They also provide a signal to the motherboard to indicate when DC voltages are within specifications so the computer can safely turn on and boot up. The latest ATX power supply standard is version 3.0 from mid-2022.
Power supply unit Functions
The desktop computer power supply converts alternating current (AC) from an electrical outlet to a low-voltage direct current (DC) to power the motherboard, processor, and peripherals.
Various DC voltages are required and must be regulated with some accuracy to ensure stable computer operation. A power supply rail or voltage rail refers to a single voltage provided by a power supply.
Prepare for hibernation or power cycle by the event. Standby power allows a computer to boot remotely via WakeonLAN and Wakeonring, or locally via Keyboard Power ON (KBPO) if the motherboard supports it.
This standby voltage can be generated by a small linear power supply inside the unit or by powering some components with the main unit to save cost and energy.
In the lowest voltage range, around 115 V, this switch turns on by changing the mains voltage. Rectifier into a voltage doubler in Delon circuit design. As a result, the large primary filter capacitor behind this rectifier split into two series-connected capacitors symmetrical with bleeder resistors and
varistors needed in the upper input voltage range, around 230 V.
Devices normally set for the lower range up to higher voltage mains resulted in immediate permanent damage. When power factor correction (PFC) was required, these filter capacitors were replaced with higher capacitance capacitors, along with an inductor installed in series to delay the inrush current.
This is the simple construction of a passive PFC. Active PFC is more complex and can achieve higher PF up to 99%. The first active PFC circuits only delayed the breakthrough.
Newer ones act as input and output state-controlled boost converters, driving a single 400V filter capacitor from a wide range input supply, typically between 80 and 240VThe newer PFC circuits also replace the NTC-based inrush current limiter, which is an expensive part that used to sit next to the fuse.
Power supply unit History
First-generation power supplies for microcomputers and home computers used a heavy step-down transformer and linear power supply, such as that used in the Commodore PET, introduced in 1977. Also introduced in 1977,
The Apple II was notable for its switching power supply, which was lighter and smaller than an equivalent linear power supply and which had no fan. The switching power supply uses a ferrite core 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 precisely controlled without dissipating power as heat in a linear regulator. The development of low-cost, high-power, high-voltage transistors made it practical to introduce switching power supplies used in aerospace,
Mainframe, minicomputers, and color televisions to desktop personal computers. Atari engineer Rod Holt’s Apple II design received a patent. , and was a leader in the design of modern computer power supplies.
Now all modern computers use switching power supplies, which are lighter, less expensive, and more efficient than the equivalent
linear power supplies.
Power supplies for computers can provide short circuit protection, overload (overload) protection, overvoltage protection, under-voltage protection, overcurrent protection, and overtemperature protection.