All main characteristics and requirements are described to one degree or another in documents known as ATX12V Power Supply Design Guide Version 2.2, SSI EPS12V Power Supply Design Guide Version 2.91 and similar. This documentation is intended for power supply manufacturers to ensure compatibility of their equipment with the generally accepted ATX standard. This includes the geometric, mechanical and, of course, electrical characteristics of the devices. All documentation is available in open form on the Internet (ATX12V PSDG/SSI EPS PSDG). Here are the main topics covered in this documentation. It’s worth starting with the most important value, which is indicated on every power supply available in retail sale.

· Permissible load power

Each power supply has several output channels with different voltages and is designed for a certain long-term power for each of them. The modern standard requires the presence of channels with voltages +5V, +12V, +3.3V, -12V and standby voltage+5V. The total power is usually indicated in watts on a sticker (in English it sounds like Total Power). This value is the sum of all powers for each channel and is easily calculated by summing the product of currents and the corresponding voltages. For example, we have a power supply with a power of 500 watts, with the indicated permissible currents: +3.3V 30A, +5V 30A, +12V 40A, -12V 0.8A, +5Vd 2.5A. Multiplying and summing, we get the final figure (250+480+9.6+12.5) = 752.1 W. Why does the sticker say 500W? The fact is that there is a mutual dependence of the channels of their joint maximum power. The sticker states that the maximum power on the +3.3V and +5V channels cannot exceed 152 W in any case, and the total total power of the +12V and +3.3 & 5V channels should not exceed 480 W. That is, we can load the block at full power at +12V, leaving the low-voltage channels unloaded, or with full power at +3.3 and +5V channels (152 W in our case), we can use only 328 W at +12V. Therefore, when making calculations, you need to be careful and always pay attention to the permissible load combination for each line. This is usually indicated on a sticker, in the form of a common cell with a single power value for several channels.

Or maybe at some intermediate value? Let's consider this point in more detail later.

Also, do not confuse the parameters of maximum long-term power and peak power (Total Peak Power), permissible for a short period of time (17 seconds according to ATX 2.2 and 12 seconds according to EPS 2.91). For example, a power supply with a rated power of 500 W can output up to 530 W at peak, but it is undesirable for a power supply to constantly operate above the rated power, because the safety margin of the components may not be very large, and unpleasant fireworks will occur in the hot summer.

· Permissible level of voltage deviation

This characteristic is one of the main ones and determines the permissible deviation of each voltage. It will be more convenient and clearer to present these values ​​as two tables taken from the EPS 2.91 standard:

Table 20 reflects the maximum permissible level of deviations, and table 21 is optional, with more stringent limits relevant for graphics stations and servers. If the voltage deviation is below 5-10% of the threshold, computer malfunctions or spontaneous reboots during heavy load on the processor or video card are likely to occur. Too high a voltage negatively affects the thermal operation of converters on the motherboard and expansion cards, and can also damage sensitive hard drive circuits or cause increased wear. The more loyal ATX Power Supply Design Guide additionally regulates for channels with a voltage of +12V a permissible 10% deviation at peak load on these channels.

In this case, the voltage of the +12V2 channel (usually used to power the processor) should not drop below +11 V.

Ripple level

No less important is the minimum possible voltage spikes (ripples) on each line. The acceptable framework is described in the standard as mandatory and looks like this:

Hard drives and the magnetic head unit they contain can also create bursts of interference during frequent movement, but their power is much less.

Input voltage, efficiency and PFC

There is a myth that a more powerful power supply will consume more power from the outlet compared to its low-power, cheap counterpart. In fact, the opposite situation often occurs in reality. Each block has energy losses during conversion mains voltage into low-voltage DC going to the computer components. The efficiency (efficiency) of a modern cheap unit usually hovers around 65-70%, while more expensive models can provide operating efficiency of up to 85%. For example, connecting both units to a load of 200 W (about what most computers consume), we will get a loss of 70 W in the first case and only 30 W in the second. 40 watt savings at daily work computers for 5 hours a day and a 30-day month will help save 6 kW on your electricity bill. Of course, this is a tiny figure for one PC, but if you take an office with 100 computers, then the figure can be noticeable. It is also worth considering that the conversion efficiency varies depending on different power loads. And since the peak efficiency occurs in the 50-70% load range, there is no practical sense in purchasing a power supply with a double or more power reserve.

The operating efficiency should exceed 70% for full load, and 65% for 20% load. In this case, the recommended efficiency is at least 75% or better. There is a voluntary certification system for manufacturers known as Plus 80. All power supplies participating in this program have a conversion efficiency of over 80%.

Also, the efficiency of the power supply should not be confused with such a characteristic as the power factor (Power Factor). There is reactive power and active power, and power factor reflects the ratio of reactive power to the total total power consumption. Most power supplies without any correction circuits have a power factor of 0.6-0.65. Therefore, switching power supplies produce a significant amount of reactive power, and their consumption appears as powerful pulses during peaks of the mains sine wave. This creates interference on the power supply, which may affect other devices powered by the same power supply. To eliminate this feature, schemes with passive power factor correction (Passive PFC) and active (Active PFC) are used. An active PFC effectively copes with this task, essentially being a converter between the power supply itself and the mains. The power factor in blocks using APFC easily reaches 0.97-0.99, which means there is almost a complete absence of a reactive component in the power supply consumption. The passive Power Factor correction circuit is a massive inductor connected in series with the power supply wires. However, it is significantly less effective and in practice increases the factor to 0.7-0.75. From the point of view of the computer and the consumer, there is practically no difference between a unit with APFC and a unit without any correction at all; the use of the former is beneficial to power supply companies.

Signal lines PSON and PWOK

PSON (Power Supply ON) is a special signal line for turning on/off the power supply by the logic of the motherboard. When this signal is not connected to ground, the power supply should remain off, except for the +5V channel (standby). At logical zero (voltage below 1 V), the logic turns on the power supply. PWOK (Power OK) is a signal line through which the power supply informs the motherboard that all output lines are in normal condition and stabilization is carried out within the limits specified by the standard. The delay time for the signal to appear during normal operation of the power supply from the moment a logical zero is applied via PSON is 900 ms.

· Protection circuits

The power supply must have protection circuits that will turn off the main outputs in emergency situations. The protection should block restart until the power-on signal appears again on the PSON wire. Overcurrent protection (OCP) is required for lines +3.3, +5, +12, -12, +5 (standby), minimum response threshold - 110%, maximum 150%. In case of overload, the unit should turn off and not turn on until the turn-on signal appears, or until the mains voltage is completely de-energized. Over Voltage Protection (OVP) is also required and must be monitored within the power supply itself. The voltage should never exceed those specified in Table 29 at any time.

Some manufacturers calculate and indicate the power of the power supply at a low temperature of +25, or even +15°C, and an attempt to load such a product with the indicated power in hot weather can lead to an unpleasant ending. This is exactly the case when the note sixth point from the bottom matters. If we can find an acceptable temperature range for a specific block model during tests, we indicate this explicitly in the table with characteristics.

Defence from short circuit(Short Curcuit Protection, SCP) – is mandatory for all power supplies, checked by briefly connecting the power bus between the channels and the ground of the power supply.

· A little about dividing the +12V channel into several “virtual” ones

The annoying channel separation is caused by the requirement of the EN60950 safety standard, which requires the current limit on user-accessible contacts to be limited to 240 VA. Since the total total power of the +12V channel in powerful power supplies can exceed this value, it was decided to introduce division into several separate channels with individual current protection of less than 20A. These separate channels are not required to have individual stabilization inside the power supply unit. Therefore, in fact, almost all power supplies have one high-current +12V channel, regardless of the number of virtual channels. Although there are several models on the market with truly separate stabilizers and several independent +12V lines, this is only an exception. general rule. For computer components, virtual as well as real channel separation does not affect in any way, and those components that may require a current of more than 18-20A have the ability to connect two separated channels. So the 8-pin processor power connector on motherboards has two contacts for each of the two channels, and top-end NVIDIA video cards and AMD have two 6-pin (or a combination of 6-pin and 8-pin, like the Radeon 2900 XT, Radeon HD 3870 X2, GeForce 9800 GX2) connectors.

In addition to electrical characteristics, there are also physical ones. Each block that claims to comply with the ATX form factor must have a width of 150mm and a height of 86mm. The depth of the block can vary from 140mm to 230mm or more.

· Cable equipment of the unit

Existing power supplies are equipped with a mass of cables with different types connectors. Information about their lengths and quantity will allow you to determine before purchasing whether a particular model will fit the desired case, or whether you will have to purchase additional adapters and extensions. All these parameters are displayed in table form for each of the tested blocks. The upper part contains non-removable cables, and below, in the case of detachable wires, the number and lengths of all cables with connectors are indicated indented. If there are several connectors on one wire, the lengths to each are written down in a row. For example, the total cable length in the example above for the last SATA connector is 45+15+15 = 75cm. Non-standard connectors, for example, a 3-pin fan speed monitoring cable, or adapters are indicated in the lower lines of the table. In addition to listing the cables and their types, the thickness of the wires used in the cables is determined, the presence of additional wires for monitoring and compensating the resistance of the wires to the connector (the so-called Vsense wires).

Noisy cooling system

Almost all power supplies are equipped with a fan to actively cool the components inside the case. In addition, the fan also throws the heated air inside the computer case outside into environment. Most modern power supplies have a 120 mm fan located on the bottom wall. Increasingly, there are models with a 135 or even 140 mm fan, thanks to which noise levels can be reduced while maintaining cooling efficiency. However, older powerful models still use an 80 mm fan in the rear end wall, which exhausts air from the power supply unit to the outside. Variations are also possible using different fan locations, or using several fans. Almost all units are equipped with a circuit for dynamically controlling fan speed, depending on the temperature inside the power supply unit (most often the temperature of the radiator with stabilizer diodes).

Currently practically not used.

• The −5 V voltage was used only by the ISA interface, and due to the virtual absence of this interface on modern motherboards, the −5 V wire is missing in new power supplies.
• Voltage −12 V is required only for full implementation of the standard serial interface RS-232 is therefore also often missing.

In most cases, a switching power supply is used, made according to a half-bridge (push-pull) circuit. Power supplies with energy-storing transformers (flyback circuit) are naturally limited in power by the dimensions of the transformer and therefore are used much less frequently.

Device (circuitry)

Switching computer power supply (ATX) with the cover removed: A - input diode rectifier, visible below input filter; B - input smoothing capacitors, the radiator is visible to the right high voltage transistors; C- pulse transformer, to the right the low-voltage radiator is visible diode rectifiers; D- group stabilization choke; E- output filter capacitors

A widely used switching power supply circuit consists of the following parts:

Input circuits

• A separate low-power power supply that produces +5 V standby mode mat. boards and +12 V to power the converter chip of the UPS itself. It is usually made in the form of a flyback converter using discrete elements (either with group stabilization of output voltages through an optocoupler plus an adjustable zener diode TL431 in the OS circuit, or linear stabilizers 7805/7812 at the output) or (in top models) on a TOPSwitch type microcircuit.

• Half-bridge converter based on two bipolar transistors
• A circuit for controlling the converter and protecting the computer from over/under supply voltages, usually on a specialized microcircuit (TL494, UC3844, KA5800, SG6105, etc.).
• Pulse high-frequency transformer, which serves to generate the required voltage ratings, as well as for galvanic isolation of circuits (input from output, and also, if necessary, output from each other). The peak voltages at the output of the high-frequency transformer are proportional to the input supply voltage and significantly exceed the required output.
• Feedback circuit, which maintains a stable voltage at the output of the power supply.
• Voltage driver PG (Power Good, “voltage is normal”), usually on a separate op-amp.

• Output rectifiers. Positive and negative voltages (5 and 12 V) use the same transformer output windings, with different switching directions for the rectifier diodes. To reduce losses, at high current consumption, Schottky diodes, which have a low forward voltage drop, are used as rectifiers.
• Output group stabilization choke. The inductor smoothes the pulses by storing energy between pulses from the output rectifiers. Its second function is the redistribution of energy between output voltage circuits. So, if the current consumption in any channel increases, which reduces the voltage in this circuit, the group stabilization choke, like a transformer, will reduce the voltage in other circuits. The feedback circuit will detect a decrease in the output circuits, increase the overall power supply, and restore the required voltage values.
• Output filter capacitors. The output capacitors, together with the group stabilization choke, integrate the pulses, thereby obtaining the required voltage values, which are significantly lower than the voltages from the transformer output
• One (per line) or several (several lines, usually +5 and +3.3) 10-25 Ohm load resistors to ensure safe idle operation.

Advantages such a power supply:

• Simple and time-tested circuit design with satisfactory quality of output voltage stabilization.
• High efficiency (65-70%). The main losses occur in transient processes, which last significantly less time than the steady state.
• Small dimensions and weight, due to both less heat generation on the control element and smaller dimensions of the transformer, due to the fact that the latter operates at a higher frequency.
• Less metal consumption, making powerful pulsed sources power supplies are cheaper than transformer ones, despite their greater complexity
• Possibility of connecting a wide range of voltages and frequencies, or even direct current, to the network. Thanks to this, it is possible to unify the equipment produced for various countries world, and hence its reduction in price during mass production.

Flaws half-bridge power supply with bipolar transistors:

Standards

AT (obsolete)

In power supplies for form factor computers, the power switch breaks the power circuit and is usually located on the front panel of the case with separate wires; There is no standby power supply with the corresponding circuits at all. However, almost all AT+ATX motherboards had a power supply control output, and the power supplies, at the same time, had an input that allowed the AT motherboard to control it (turn it on and off).

The AT standard power supply is connected to the motherboard with two six-pin connectors that plug into one 12-pin connector on the motherboard. Multi-colored wires go to the connectors from the power supply, and the correct connection is when the contacts of the connectors with black wires converge in the center of the motherboard connector. The pinout of the AT connector on the motherboard is as follows:

ATX (modern)

For a 24-pin ATX connector, the last 4 pins can be removable to ensure compatibility with the 20-pin socket on the motherboard

The requirements for +5VDC have been increased - now the power supply must supply a current of at least 12 A (+3.3 VDC - 16.7 A, respectively, but the total power should not exceed 61 W) for a typical 160 W power consumption system. A skew in the output power was revealed: previously the main channel was +5 V, now requirements for a minimum current of +12 V were dictated. The requirements were due to a further increase in the power of components (mainly video cards), whose requirements could not be satisfied by +5 V lines due to for very high currents in this line.

PSU / power supply connectors

Pinout of SATA connectors

ATX PS 12V connector (P4 power connector)

One of two six-pin AT power connectors

• 20-pin main power connector +12V1DCV used with the first ATX form factor motherboards, before the advent of PCI-Express motherboards.

Also on the power supply unit are located:

Efficiency - “80 PLUS”

Manufacturers of computer power supplies

• Cooler Master
• Corsair

see also

Notes

1. to comply with the requirements of the legislation of countries on electromagnetic radiation, in Russia - the requirements of SanPiN 2.2.4.1191-03 2.2.4.1191-03.htm “Electromagnetic fields in industrial conditions, in the workplace. Sanitary and epidemiological rules and regulations"
2. B.Yu. Semenov Power electronics: from simple to complex. - M.: SOLOMON-Press, 2005. - 415 p. - (Engineer's Library).
3. At peak load +12 VDC, the output voltage range +12 VDC can fluctuate within ± 10.
4. The minimum voltage level is 11.0 VDC during peak load at +12 V2DC.
5. The shutter speed in the range is required by the main power connector of the motherboard and the S-ATA power connector.
6. The total power along the +3.3 VDC and +5 VDC lines should not exceed 61 W
7. The total power along the +3.3 VDC and +5 VDC lines should not exceed 63 W
8. The total power along the +3.3 VDC and +5 VDC lines should not exceed 80 W

The power supply provides electricity to all PC components. We will tell you how this device works.

Even though your computer plugs into a standard electrical outlet, its components cannot draw power directly from the electrical outlet for two reasons.

First, the network uses alternating current, while computer components require direct current. Therefore, one of the tasks of the power supply is to “rectify” the current.

Secondly, different computer components require different supply voltages to operate, and some require several lines with different voltage. The power supply provides each device with current with the necessary parameters. For this purpose, it has several power lines. For example, the power connectors for hard drives and optical drives supply 5 V for electronics and 12 V for the motor.

Power supply characteristics

The power supply is the only source of electricity for all PC components, so the stability of the entire system directly depends on the characteristics of the current it produces. The main characteristic of a power supply is power. It should be at least equal to the total power that the PC components consume at maximum computing load, and even better if it exceeds this figure by 100 W or more. Otherwise, the computer will turn off at times of peak load or, what is much worse, the power supply will burn out, taking other system components with it to the next world.

For most office computers, 300 W is sufficient. The power supply of a gaming machine must have a power of at least 400 W - high-performance processors and fast video cards, as well as the additional cooling systems they require, consume a lot of energy. If the computer has several video cards, then 500- and 650-watt power supplies will be required to power it. There are already models on sale with a power of more than 1000 W, but buying them is almost pointless.

Often, power supply manufacturers shamelessly inflate the rated power value; this is most often encountered by buyers of cheap models. We advise you to choose a power supply based on testing data. In addition, the power of a power supply is most easily determined by its weight: the larger it is, the higher the likelihood that the actual power of the power supply matches the declared one.

In addition to the total power of the power supply, its other characteristics are also important:

Maximum current on individual lines. The total power of the power supply consists of the powers that it can provide on individual power lines. If the load on one of them exceeds the permissible limit, the system will lose stability even if the total power consumption is far from the power supply rating. The load on lines in modern systems is usually uneven. The 12-volt channel has the hardest time, especially in configurations with powerful video cards.

Dimensions. When specifying the dimensions of a power supply, manufacturers, as a rule, limit themselves to the designation of the form factor (modern ATX, outdated AT or exotic BTX). But manufacturers of computer cases and power supplies do not always strictly adhere to the norm. Therefore, when purchasing a new power supply, we recommend comparing its dimensions with the dimensions of the “seat” in your PC case.

Connectors and cable lengths. The power supply must have at least six Molex connectors. A computer with two hard drives and a pair of optical drives (for example, a DVD-RW writer and a DVD reader) already uses four such connectors, and other devices can also be connected to Molex - for example, case fans and video cards with an AGP interface.

The power cables must be long enough to reach all required connectors. Some manufacturers offer power supplies whose cables are not soldered into the board, but are connected to connectors on the case. This reduces the number of wires dangling in the case, and therefore reduces the clutter in the system unit and promotes better ventilation of its interior, since it does not interfere with the air flow circulating inside the computer.

Noise. During operation, the components of the power supply become very hot and require increased cooling. For this purpose, fans built into the PSU case and radiators are used. Most power supplies use one 80 or 120 mm fan, and the fans are quite noisy. Moreover, the higher the power of the power supply, the more intense the air flow is required in order to cool it. To reduce noise levels, high-quality power supplies use circuits to control fan speed in accordance with the temperature inside the power supply.

Some power supplies allow the user to determine the fan speed using a regulator on the back of the power supply.

There are power supply models that continue to ventilate the system unit for some time after the computer is turned off. This allows PC components to cool down faster after use.

Presence of a toggle switch. The switch on the back of the power supply allows you to completely de-energize the system if you need to open the computer case, so its presence is welcome.

Additional power supply characteristics

High power supply power alone does not guarantee high-quality performance. In addition to it, other electrical parameters are also important.

Efficiency factor (efficiency). This indicator indicates what proportion of the energy consumed by the power supply from electrical network goes to the computer components. The lower the efficiency, the more energy is wasted on wasteful heat. For example, if the efficiency is 60%, then 40% of the energy from the outlet is lost. This increases power consumption and leads to strong heating of the power supply components, and therefore to the need for increased cooling using a noisy fan.

Good power supplies have an efficiency of 80% or higher. They can be recognized by the “80 Plus” sign. Recently, three new, more stringent standards have been in effect: 80 Plus Bronze (efficiency of at least 82%), 80 Plus Silver (from 85%) and 80 Plus Gold (from 88%).

The PFC (Power Factor Correction) module allows you to significantly increase the efficiency of the power supply. It comes in two types: passive and active. The latter is much more efficient and allows you to achieve an efficiency level of up to 98%; a power supply with passive PFC is characterized by an efficiency of 75%.

Voltage stability. The voltage on the lines of the power supply fluctuates depending on the load, but it should not go beyond certain limits. Otherwise, system malfunctions or even failure of individual components may occur. The first thing you can rely on for voltage stability is the power of the power supply.

Safety. High-quality power supplies are equipped various systems for protection against power surges, overloads, overheating and short circuits. These features protect not only the power supply, but also other components of the computer. Note that the presence of such systems in the power supply does not eliminate the need to use sources uninterruptible power supply and network filters.

Main characteristics of the power supply

Each power supply has a sticker indicating its technical characteristics. The main parameter is the so-called Combined Power or Combined Wattage. This is the maximum total power for all existing power lines. In addition, the maximum power for individual lines also matters. If there is not enough power on a certain line to “feed” the devices connected to it, then these components may operate unstably, even if the total power of the power supply is sufficient. As a rule, not all power supplies indicate the maximum power for individual lines, but all of them indicate the current strength. Using this parameter, it is easy to calculate the power: to do this, you need to multiply the current by the voltage in the corresponding line.

12 V. 12 volts are supplied primarily to powerful consumers of electricity - the video card and the central processor. The power supply must provide as much power as possible on this line. For example, a 12-volt power supply line is designed for a current of 20 A. At a voltage of 12 V, this corresponds to a power of 240 W. High-end graphics cards can deliver up to 200W or more. They are powered via two 12-volt lines.

5 V. The 5V lines supply power to the motherboard, hard drives, and optical drives of the PC.

3.3 V. The 3.3V lines go only to the motherboard and provide power to the RAM.

Updated 03/11/2013 23:29

Hi all! Today we will talk about the ATX form factor power supply.

The choice of power supply for a personal computer should be approached with special responsibility, since the stability and reliability of the entire computer as a whole largely depends on it. This article describes design features PSU, characteristics... Read more...

The power supply is an integral part of every computer. The functioning of the entire personal computer (PC) depends on its normal operation. But at the same time, power supplies are rarely purchased, since once purchased, a good power supply can provide several generations of continuously evolving systems. Considering all this, the choice of power supply must be approached very seriously.

The power supply generates voltage to power all functional blocks of the PC. It generates the main supply voltages for computer components: +12 V, +5 V and 3.3 V. The power supply also generates additional voltages: -12 V and -5 V and in addition it provides galvanic isolation from the 220 V network.

Internal design of ATX PSU

The figure (Fig. 1) shows the internal design and arrangement of elements of a typical power supply with an active power factor correction (PFC) "GlacialPower GP-AL650AA". The following elements are indicated by numbers on the power supply board:

1. Current protection control module;
   
2. Output voltage filter choke +12 V and +5 V, which also performs the function of group stabilization;
3. Filter choke +3.3 V;
4. Radiator with rectifier diodes for output voltages;
5. Main converter transformer;
6. Main converter key control transformer;
7. Transformer that forms the standby voltage of the auxiliary converter;
8. Power factor correction controller (separate board);
9. Radiator with diodes and keys of the main converter;
10. Mains voltage filter;
11. KKM throttle;
12. Mains voltage filter capacitor.

This design of ATX power supplies is the most common and is used in power supplies of various powers.

Types of PSU connectors ATX

On the back wall of the power supply there is a connector for connecting a network cable and a network switch. Some power supply models do not have a power switch installed. Sometimes, in older models, you can find a connector next to the network connector for connecting the monitor’s network cable. In modern power supplies, on the rear wall, manufacturers can install the following connectors (Fig. 2):

• Mains voltage indicator;
• Fan control button;
• Button for manual switching of input voltage (110 V / 220 V);
• USB ports built into the power supply.
  

In modern models, an exhaust fan is rarely installed on the rear wall. Now it is located at the top of the power supply unit. This allows the installation of a large and quiet cooling element. On high-power power supplies, such as the Chieftec CFT-1000G-DF power supply, two fans are installed on the top and on the back cover (Fig. 3).

A wiring harness with connectors for connecting the motherboard, hard drives, video card and other components comes out of the front wall of the power supply. system unit.

In a modular power supply unit, instead of a wiring harness, there are connectors on the front wall for connecting wires with different output connectors. This allows you to organize the power wires in the system unit and connect only those that are necessary for this configuration (Fig. 9 and 10).

The pinout of the power supply output connectors connected to the motherboard and other devices is shown in the figure (Fig. 4).

It should be noted that the colors of the wires are unified, and each color corresponds to its own voltage:

• Black - common bus (Ground);
• Yellow - +12 V;
• Red - +5 V;
• Orange - +3.3 V.
  

The figure (Fig. 5) shows the output connectors of ATX power supplies.

Not shown in the figures (Fig. 4 and 5) are the additional power connectors for video cards, their pinouts and appearance similar to the pinout for additional processor power connectors.

Electrical parameters and characteristics of the power supply

Modern power supplies for PCs have a large number of electrical parameters, some of which are not noted in the data sheets. technical specifications", since they are considered unimportant to the user. The main parameters are indicated by the manufacturer on a sticker located on the side wall.

Power supply power

Power - this is one of the main parameters of the power supply. It characterizes how much electrical energy can supply the power supply to devices connected to it (hard drive, motherboard with processor, video card, etc.). To select a power supply, it would seem that it is enough to sum up the consumption of all components and select a power supply with a small power reserve.

But things are much more complicated. The power supply generates various voltages distributed over different power buses (12 V, 5 V, 3.3 V and others), each voltage bus (line) is designed for a certain power. One would think that these powers are fixed, and their sum is equal to the output power of the power supply itself. But ATX power supplies have one transformer installed to generate all these voltages, so the power on the lines floats. When the load on one of the lines increases, the power on the remaining lines decreases and vice versa.

The manufacturer indicates in the passport the maximum power of each line; summing them up, the resulting power is greater than the power supply can actually provide. Thus, often, the manufacturer declares a rated power that the power supply is not able to provide, thereby misleading users. An insufficiently powerful power supply installed in the system unit causes freezes, random reboots, clicking and cracking of heads hard drive, and other incorrect operation of devices.

Permissible maximum line current

This is one of the most important parameters of a power supply, but users often do not pay due attention to this parameter when purchasing a power supply. But when the line current exceeds the power supply, the power supply turns off (protection is triggered). You will need to disconnect it from the 220 V network and wait about a minute. It is necessary to take into account that the most powerful consumers - the processor and video card - are powered by a 12 V line, so when purchasing a power supply, you need to pay attention to the current values ​​​​specified for it. To reduce the current load on the power connectors, the 12 V line is divided into two parallel (sometimes more) and designated as +12V1 and +12V2. When calculating, the currents on parallel lines are summed up.

For high-quality power supplies, information about the maximum current loads along the lines is indicated on the side sticker in the form of a plate (Fig. 6).

If such information is not indicated, then one can doubt the quality of this power supply and the correspondence of the real and declared power.

Operating voltage range

This characteristic means the range of mains voltage at which the power supply will remain operational. Modern power supplies are produced with AKKM (active power factor correction), which allows the use of an input voltage range from 110 V to 230 V. But inexpensive power supplies with a small operating voltage range from 220 V to 240 V are also available (for example, FPS FPS400-60THN- P). As a result, such a power supply will turn off when the mains voltage drops, which is not uncommon for our power networks, or it may not start at all.

Internal resistance

Differential internal resistance (electrical impedance) characterizes the losses of the power supply unit when alternating current flows. To combat this, low-pass filters are included in the power supply circuit. But the impedance can be significantly reduced only by installing high-capacity capacitors with low series resistance (ESR) and chokes wound with thick wire. It is quite difficult to implement this constructively and physically.

Output voltage ripple

The power supply of a personal computer is a converter that converts AC voltage to DC voltage. As a result of such transformations, ripples (pulse changes in voltage) are present at the output of the power lines. The problem with ripple is that, if not properly filtered, it can distort the performance of the entire system, leading to false switching of comparators and incorrect perception of input information. This, in turn, leads to operational errors and disconnection of PC devices.

To combat ripple, LC filters are included in the circuit of the output voltage lines, which smooth out the ripples of the output voltages as much as possible (Fig. 8).

Voltage stability

During operation of the power supply unit, its output voltages change. An increase in voltage causes an increase in quiescent currents, this in turn causes an increase in power dissipation and overheating of circuit elements connected to the power supply. A decrease in the output voltage leads to deterioration in the operation of the circuits, and when it decreases to a certain level, the PC elements stop working. Computer hard drives are especially sensitive to a drop in supply voltage.

Permissible voltage deviations of output lines for the ATX standard should not exceed ±5% of the rated line voltage.

Efficiency

The efficiency of the power supply determines how much useful energy the system unit will receive from the energy consumed by the power supply. Most modern power supplies have an efficiency of at least 80%. And power supplies equipped with PKKM (PPFC) and AKKM (APFC) significantly exceed this figure.

Power factor

This is a parameter that you should pay attention to when choosing a power supply; it directly affects the efficiency of the power supply. With a low power factor, the efficiency will also be low. Therefore, automatic power factor correctors (APCC) are built into the circuits of modern power supply units, which significantly improve the characteristics of the power supply unit.

The first step when choosing a power supply is to determine its power. To determine the required power, it is enough to sum up the power of all components of the system unit. But sometimes individual video cards have special requirements for the amount of current on the +12 line. B, this must be taken into account when choosing. Typically, for an average system unit equipped with one video card, a power supply of 500-600 watts is sufficient.

When choosing a model and manufacturer, you should read reviews and reviews of this power supply model. It is advisable to choose a power supply with an AAFC circuit. In other words, you need to choose a power supply that is powerful, quiet, of high quality and meets the stated characteristics. It's not worth saving a dozen or two dollars. It must be remembered that the stability, durability and reliability of the entire computer as a whole largely depends on the operation of the power supply..

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The most common version of the power supply involves converting 220 Volts of alternating voltage (U) into a reduced direct voltage. In addition, power supplies can provide galvanic isolation between input and output circuits. In this case, the transformation ratio (the ratio of input and output voltages) can be equal to unity.

An example of such use would be to supply power to areas where there is a high degree of electrical hazard, such as bathrooms.

In addition, quite often household power supplies can be equipped with built-in additional devices: stabilizers, regulators. indicators, etc.

TYPES AND TYPES OF POWER UNITS

First of all, the classification of power supplies is carried out according to the principle of operation. There are two main options here:

• transformer (linear);
• pulse (inverter).

Transformer block consists of a step-down transformer and a rectifier that converts alternating current into direct current. Next, a filter (capacitor) is installed that smooths out ripples and other elements (output parameter stabilizer, short-circuit protection, high-frequency (RF) interference filter).

Advantages of a transformer power supply:

• high reliability;
• maintainability;
• simplicity of design;
• minimal or no interference;
• low price.

Disadvantages - heavy weight, large dimensions and low efficiency.

Impulse power block- an inverter system in which alternating voltage is converted into direct voltage, after which high-frequency pulses are generated, which undergo a series of further transformations (). In a device with galvanic isolation, pulses are transmitted to a transformer, and in the absence of one, directly to the low-pass filter at the output of the device.

Thanks to the formation of RF signals, small-sized transformers are used in switching power supplies, which allows reducing the size and weight of the device. A negative voltage is used to stabilize the voltage. Feedback, thanks to which a constant voltage level is maintained at the output, independent of the load.

Advantages pulse block power supply:

• compactness;
• light weight;
• affordable price and high efficiency(up to 98%).

In addition, it should be noted that there are additional protections that ensure the safety of using the device. Such power supplies often provide protection against short circuits (short circuits) and failure when there is no load.

Disadvantages - the operation of a larger component of the circuit without galvanic isolation, which complicates repairs. In addition, the device is a source of high frequency interference and has a lower load limit. If the power of the latter is less than the permissible parameter, the unit will not start.

PARAMETERS AND CHARACTERISTICS OF THE POWER SUPPLY

When choosing a power supply, you should take into account a number of characteristics, including:

• power;
• output voltage and current;
• as well as the availability of additional options and capabilities.

Power.

A parameter that is measured in W or V*A. When choosing a device, you should take into account the presence of inrush currents in many electrical receivers (pumps, irrigation systems, refrigerators, and others). At the moment of start-up, power consumption increases by 5-7 times.

As for other cases, the power supply is selected taking into account the total power of the powered devices with a recommended margin of 20-30%.

Input voltage.

In Russia this parameter is 220 Volts. If you use a power supply in Japan or the USA, you will need a device with an input voltage of 110 Volts. In addition, for inverter power supplies this value can be 12/24 Volts.

Output voltage.

When choosing a device, you should focus on the rated voltage of the consumer used (indicated on the device body). It could be 12 Volts, 15.6 Volts and so on. When choosing, you should buy a product that is as close as possible to the required parameter. For example, to power a 12.1 V device, a 12 V unit is suitable.

Output voltage type.

Most devices are powered by stabilized DC voltage, but there are also those for whom constant, unstabilized or variable is suitable. Taking this criterion into account, the design is also selected. If an unstabilized constant U at the input is enough for the consumer, a power supply with a stabilized voltage at the output is also suitable.

Output current.

This parameter may not be indicated, but if you know the power, it can be calculated. Power (P) is equal to voltage (U) times current (I). Therefore, to calculate the current, it is necessary to divide the power by the voltage. This parameter is useful for selecting a suitable power supply for a specific load.

As a rule, the operating current should exceed the maximum current consumption of the device by 10-20%.

Efficiency.

High power supply power is not a guarantee of good performance. An equally important parameter is efficiency, which reflects the efficiency of energy conversion and its transmission to the device. The higher the efficiency, the more efficiently the unit is used, and the less energy is spent on heating.

Overload protection.

Many sources are equipped with overload protection, which ensures that the power supply is turned off if the level of current consumed from the network is exceeded.

Deep discharge protection.

Its task is to break the power circuit when the battery is completely discharged (typical for uninterruptible power supplies). After power is restored, the device's functionality is restored.

In addition to the options listed above, the power supply may provide protection against short circuits, overheating, overcurrent, overvoltage and undervoltage.

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