What is a power supply in a computer

what is power supply

Many users who are trying to figure out the device of their PC do not understand what the power supply is in the computer. Meanwhile, this is one of the most important elements in the system, without which no component will work at all. Let’s figure out what are the power supplies, determine their device, types, pros and cons.


Power Supply Definition

A computer power supply unit (PSU) is an electronic device that generates the voltage required for a specific PC component from the voltage of the electrical network.

The main parameter of the power supply is power, which is calculated in watts (W). The more powerful the computer, the more powerful the power supply is required. Usually this is 300-500 watts in budget and office computers and 600 watts or more in powerful stations and gaming PCs. More demanding on the power of the PSU top-class graphics cards that need more than a kilowatt of power.

The power supply is a kind of energy center of any computer. It is he who supplies electricity to all components of the computer, and allows the PC to work. From the mains, the cable goes to the power supply, and already it will distribute the required voltage throughout the rest of the computer.

From the PSU, cables go to the motherboard, video card, hard drive, drive, coolers and fans, to other devices. High-quality and expensive blocks are resistant to voltage drops in the electrical network. This helps prevent failure, both of the power supply itself and of all computer components.

What is necessary for stable smooth operation of the computer?

Powerful processor, modern graphics card, good motherboard. But almost everyone forgets to add a reliable power supply to this list, which, as the center of power supply for all other computer components. He must cope with the tasks 100%. Otherwise, the stable and trouble-free operation of the computer, there can be no question.

What is the danger of lack of power in a PC?
If the power supply of the installed power supply is not enough for all elements of the computer, then this will result in both minor problems and complete inability to turn on the PC.
Here are the main dangers of a weak PSU:

  • There is a chance of failure or partial damage to the hard drive. This is due to the fact that in the hard disk due to lack of power the read heads will not be able to function normally and slide on the surface of the disk and will begin to scratch it. In this case, characteristic sounds may be heard.
  • There may be problems with the video card (until the image disappears on the monitor). This is especially evident in modern computer games.
  • Removable hard drives and flash drives that connect to USB ports, as well as other devices without additional power, may not be detected by the operating system or may be disabled during operation.
  • At times of greatest power consumption, the computer may turn off or restart.

How to get rid of this? It is very simple to install a more powerful and reliable power supply.

How is a high quality and reliable power supply different from a cheap one?

  1. Good, high-quality and expensive provides protection against unforeseen power surges. In the event that it fails itself, it must “at the cost of its own life” protect other computer devices.
  2. The power supply should provide the PC user with a modern and convenient cable system in every respect. It is convenient when it is possible to disconnect each power cable from the unit, thereby freeing up a large amount of space inside the case for ventilation and cooling of the system unit.
  3. The PSU must have a good cooling system, it must be protected from overheating and not emit strong noise from its fan.

Power supply Modular cables and connectors

One of the trends in the development of modern PSUs is an increase in the usability of cables. The main goal is to remove from the computer case that node of wires and cables, which can now be seen in almost any personal computer.

In the cheapest power supplies, all cables are inextricably connected. This leads to the fact that all cables not used for powering devices are in any case located inside the system unit. This, in turn, impairs air circulation and makes the process of repairing and upgrading PCs extremely uncomfortable .

It is much more convenient when all unnecessary and idle cables can be disconnected. When required, can be quickly connected via connectors. This not only significantly improves cooling inside the case, but also makes the appearance of the contents of the system unit look nice if the case has a window.

It is recommended that you select and buy a power supply after the power consumption of the entire PC is accurately calculated . This can be done by adding up the power consumption of all components. After that, add about 30% as a margin of safety. If in the future it is planned to install any more components, then we must still increase the stock.

Required voltage

The computer PSU is powered from a network with a voltage of 220 V. But in different countries, the voltage and its frequency in the network can vary. For example, in Russia and in most European countries, the voltage in the network is 220/230 V at a frequency of 50 Hz. However, in the United States, the mains voltage is 120 V at a frequency of 60 Hz. Australia is also different in this respect – there the voltage is 240 V / 50 Hz. Therefore, when creating a power supply, the network parameters of the country to which deliveries are planned are taken into account. That is, if you bring a power supply purchased in the USA to Russia, then it most likely will not work.

power supply unit

There are also universal power supplies with a special voltage regulator. That is, on the block, you can set the voltage value in the network, and the device will be adapted to it independently.

If the computer does not turn on when you press the power button, then first of all you need to look for the reason in the block and replace it if necessary. Unfortunately, the inexpensive models that the Russian market is flooded with today break down too often.

Power PSU computer

Today there are many different units that are capable of delivering power in a huge range. In modern laptops, power can vary in the range of 25-100 watts. As for personal computers, here, depending on the power consumption of components, you can use a 2000 W PSU.

There are rumors among users that the more powerful the unit, the better, although in reality this is not entirely true. Not every user needs such a powerful and expensive device. If you judge, the purchase of an expensive and powerful PSU for a weak computer is a waste of money not only when buying the unit itself, but also during operation, since it will consume a lot of excess power.


However, today on the shelves of stores mainly presented devices for 400-500 watts. The power of such components is quite enough to provide power to a standard computer with good hardware. But they are not able to provide stable operation of a powerful gaming computer.

Types and differences of power supply

Now that we understand what power supply (PSU) is in a computer, we can talk about their types and distinctive features. Today there are pulse and transformer units. Each species has its advantages and disadvantages, which must be considered in more detail.

What the power supply consists of

Each power supply, regardless of its price and quality, consists of the following :

  • functional units:
  • network rectifier,
  • generator,
  • transformer,
  • low voltage rectifier,
  • stabilizer.

The latter is connected with the generator and controls it. Why is it so difficult, because you can just put the transformer and get the necessary voltage on it? But a 500-watt transformer for a conventional power grid will weigh a dozen kilograms. And it’s far from 5 kopecks. In computer power supplies there is a transformer of much smaller dimensions, operating at a frequency of tens of kilohertz. At the same power!

The principle of operation of the power supply

  1. The mains voltage is rectified first.
  2. Next charges the filter capacitors.
  3. It is cleared of interference by the PFC unit and converted into a sinusoid with a frequency of 50-150 kilohertz.
  4. Further, the voltage drops to 5 and 12 volts.

The block takes +3.3 volts from the same winding as +5, so for any block the total power of the channels +3.3 and +5 is indicated.

Comfortable voltage
According to the ATX standard, the voltage deviation of the power supply must not exceed 5%. Theoretically, it is safe for all components of the computer. But in practice, everything is always as friend.
For example, subsidence of the +12 volt channel below 11.75 practically guarantees a quick and painful death for the Maxtor hard drive. And other hard drives will also live much less. With sagging voltages, you can forget about a good overclocking of the processor and the video card (although slightly overstated voltages will benefit). So it’s better to forget about the recommended 5%, especially on a test bench that consumes energy evenly.
A comfortable voltage range for a computer power supply looks something like this:

  • Line + 3V – from 3.20 to 3.45 volts,
  • Line + 5V – from 4.85 to 5.30 volts
  • Line + 12V – from 11.80 to 12.5 volts.

With such values ​​shown by the unit on the stand, it is possible to guarantee the stable operation of the computer and its good overclockability. But do not forget about the thermal package – the power supply capacity should be 30-40% higher than the power of all components released in the form of heat. For processors and video cards, this can be found in the descriptions, for hard drives to count through currents of consumption.

Power supply Factor Correction (PFC)

Modern Power supply are becoming more powerful, and the wires in the sockets do not change. This leads to the occurrence of impulse noise – the power supply is also not a light bulb and consumes energy, like the processor, by pulses. The stronger and more uneven the load on the unit, the more interference it will release into the power grid.
To combat this phenomenon, PFC was developed.
This is a powerful inductor installed after the rectifier to filter capacitors.
The first thing he does is to limit the charge current of the above filters.
When a PSU without PFC is connected to the network, a characteristic click is often heard – the consumed current in the first milliseconds can be several times higher than the nameplate and this leads to sparking in the switch. During the operation of the computer, the PFC module absorbs the same impulses from the charge of various capacitors inside the computer and the promotion of the hard drive motors.
There are two options for the execution of modules – passive and active.
The second is characterized by the presence of a control circuit associated with the secondary (low voltage) cascade of the power supply. This allows you to quickly respond to interference and better smooth them.

What and on what lines the power supply is powered.

Power supplies produce three basic voltages: +3.3, +5 and +12 V.

  • +3.3 is designed to power the output stages of the system logic
  • +5 – it feeds the logic of almost all PCI and IDE devices
  • +12 – it is the base voltage for powering the processor and core video cards

VRM voltage regulation unit

Used to adjust the voltage applied to all devices on the motherboard. For example, modern processors operate at lower voltage than other components of the system. It is not a secret that new computing devices, such as various chips and processors, which have a small transistor size, consume less power.
The central processor works better at high voltage, but worse at high temperature. The heat generated by the processor is quadratic in relation to the voltage level supplied to the processor.

There is a dilemma: with increasing voltage, the processor should work faster, but its temperature increases, which entails a deterioration in its performance. Excessive heat from the processor is removed by heat sinks and fans. If the voltage and temperature of the processor are too high, it may overheat and burn out.
That is why the processor socket on the motherboard is located as close as possible to the power supply, in which the exhaust fan runs. Hot air from the processor (and now from other hot devices, such as video cards and some hard drives) is immediately pulled out of the case.
For the best ratio of power, speed and voltage, Intel has developed a special type of voltage regulator for its new processors, which has a voltage from the power supply at the input and supplies a stable voltage of the required value to the processor itself. In addition, the new voltage regulator is programmable, which uses 5 VID (voltage identification) signals, with the help of which the voltage supplied to it is regulated. VID contacts usually come directly from the processor. For example, to perform a particularly complex task, the processor requires more computing power. Then it sends a request to the voltage regulator, which increases the voltage by the value that the processor “sent”. Overclockers will love these features,

What is power supply efficiency

Efficiency ( K oeffitsient n Usable D Procedure) – is the ratio of useful work to the energy expended. Efficiency is measured as a percentage. The higher this coefficient, the higher the efficiency of the power supply and the less energy loss. Reduced losses, in turn, have a positive effect on the temperature inside the computer case and on the frequency of rotation (noise) of the cooling fans.
Types of certificates:

The load on the power supply is 20%, 50%, 100%, respectively.

  • 80 Plus (80%, 80%, 80%)
  • 80 Plus Bronze (81%, 85%, 81%)
  • 80 Plus Silver (85%, 89%, 85%)
  • 80 Plus Gold (88%, 92%, 88% )
  • 80 Plus Platinum(90%, 94%, 91%)

It happens that people ask the question, “if I have a 550 W unit, then it will give out 83% of its power?”
It is not right. The power supply will produce 550 watts, and from the outlet take 550 / 0.83 = 662.65 watts.
The higher the efficiency, the less energy is converted into heat and the less electricity the PSU will take from the outlet.
A quality PSU will deliver the declared power, regardless of the level of efficiency.

how to choose a power supply

When choosing a new PSU, you should first pay attention to its following characteristics:

  • Mains voltage for which it is designed. When buying a unit in a Russian store, of course, it is difficult to find a unit designed to work exclusively with some American network, where 115 V instead of 220, and in connection with this, this criterion may be considered unimportant, but, nevertheless, if it is known in advance that in the place where the unit will be used, a chronically reduced mains voltage (for example, in an area with an overloaded power grid or in a village), it makes sense to check the range of the mains voltage for which the unit is designed to avoid then failures and sudden inexplicable for prison.
  • The declared power of the PSU. It is long-term and peak. Peak can be issued within a short time (several seconds, after which either protection will work or the unit will fail), long-term may be issued for a long time. The required power is determined by the filling of the system unit. A certain margin of power should be provided so that the unit does not work in extreme conditions. If in the future it is planned to upgrade the system with this unit, it makes sense to provide for a power reserve even more. The concept of “honest watts” and “Chinese watts” is widespread. The reason for this is the dishonesty of manufacturers (mainly the so-called “Chinese noname”), which, in order to give solidity to their products, indicate one large value of power, which in fact turns out to be peak power, which, moreover,
  • The version of the standard according to which the block is made. When acquiring a new unit for a new system, problems of incompatibility of standards arise very rarely, but when repairing old computers or trying to use the old unit to power the new system, such problems may arise.
  • Manufacturer (for more details, see Power supplies which manufacturers are better .).
  • Cross section and length of cable wires for powering devices. The marking of the wires in the device’s power cables, determining the cross-section, should be 18AWG (or 16AWG, which is better), the use of 20AWG wires is a cost reduction by unscrupulous manufacturers and a departure from the standard, which is becoming less common. The cable length should be sufficient to power all devices inside the system unit without the use of additional extension cords.
  • Required connector configuration for powering the system board. It can contain 20 or 24 contacts and be monolithic or collapsible. Power supplies with a 24-pin connector with a detachable 4-pin part are well suited for installation in older systems where it is planned to replace the motherboard that requires an old 20-pin connector with a more modern one that needs a 24-pin one.
  • The number and range of power connectors for the system board and peripherals. The unit must have a sufficient number of connectors of the required types to power all devices. If the system has (or plans to install) SATA hard drives with special power connectors, it is desirable for the PSU to have connectors for powering such drives. If there is a PCI-Express graphics card that requires additional power (6-pin or 8-pin dual-row connector), the PSU must have such a connector. If there are two such cards, it makes sense to look for such a unit that has two such connectors.
  • Form factor. Generally speaking, most power supplies fit into a standard size of 150x146x86 mm, but there are exceptions. First of all, it concerns microATX-cases, in which units of reduced size can be installed. Barebone-kits are also equipped with unique blocks, which are very difficult to replace. But, if you do not consider this class of systems and restrict yourself to classic cases, the relevance of size matching may remain if the new power supply has fans or radiators that extend beyond the standard dimensions or has an elongated case, like some new blocks of very high power.

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