Atx Power Supplies The Main Features 1

ATX Power Supplies: The Main Features


The power supply is the device responsible for providing electrical power to the components of a computer. Therefore, it is a type of equipment that should be chosen and manipulated with care, after all, any mistake can result in providing inadequate electricity or damage to the machine. Is for this reason that the AbbreviationFinder this article presents. In it, you know the main characteristics of the sources, such as voltage, power, PFC, efficiency, types of connectors, etc. The focus of the article will be the sources of the type ATX, this is the most popular type. We’re going there?

Types of power sources

As already said, the power supplies are equipment responsible for providing energy electrical devices of the computers. To do this, convert alternating current (AC – Alternating Current) – roughly speaking, the energy received by means of the generators, such as hydro – – in direct current (DC – Direct Current), a voltage suitable for use in electronic devices. Thus, the energy that arrives in taken from their home in 110 V (Volts) or 220 V is transformed at voltages like 5 V and 12 V.

Computers use power supplies of the type switched. This is a pattern that makes use of capacitors and inductors in the the process of energy conversion, and receives this name because it has,roughly speaking, a control switching device that “connects and disconnects” the passage of energy in order to generate and set the output voltage. There is also a category called source linear but this type is not suitable to computers for several reasons, among them the physical size and high weight, in addition to lower efficiency (a concept that will be explained later in this text), once that line sources use an “excess” of energy to maintain its output voltage, generating also more heat. In supplies this does not occur because this type simply disables the flow of energy instead of dissipating “left over”. In addition addition, supplies also require less power, since they use virtually all the energy that “enters” on the device.

It is a equipment that generates electromagnetic field (since it is able to work with high frequencies),the sources should be shielded to avoid interference to other devices and the computer itself.

Before you turn on your computer in the electrical network, it is of utmost importance to check if the voltage selector of the power supply corresponds to the voltage of the outlet (in Brazil, 110 V or 220V). If the selector is in the wrong position, the source may be damaged, as well as other components of the machine. Less common, there are models of sources that are able to do the selection automatically.

Patterns of power sources

As with any technology produced by more than one the manufacturer, the power supply should be provided within the standards set by the fashion industry to ensure its compatibility with other devices and its operation regular. In the case of fonts, the most widely used standard in the days of today is the ATX (Advanced Technology Extendend), which emerged in mid-1996 and which also specifies the formats of the enclosures of computers and motherboards.

With this standardization, a person will know that, when to assemble a computer, the motherboard will fit properly in the cabinet of the machine, as well as the power supply. There will also be assurance of the provision of certain resources, for example: the sources for ATX are able to provide voltage 3.3 V, characteristic that did not exist in the standard earlier, the AT (Advanced Technology). The standard ATX is, in truth, it is an evolution of the latter, therefore, adds improvements in points deficient AT. This is evident, for example, in the power connector for the motherboard: in the default AT, this plug was divided in two, and you can easily do with that the user invertesse and ocasionasse damage. In the standard ATX, this connector is a single piece, and can only be be seated in a way, avoiding problems due to incorrect connection.

The sources ATX also brought in a feature that allows you to shutdown the computer by software. For this, the sources of this type have a signal is TTL (Transistor-Transistor Logic), called PS_ON(Power Supply Online). When it is turned on and in use, the motherboard keeps the PS_ON low level, as if I was leaving in a state considered to be “off”. If the motherboard you are in disuse, or to be, not receiving the voltages, it does not generate the low level and the PS_ON is at a high level. This signal can change its level when you receive orders activation or disabling of certain features, for example:

– Soft Power Control: used to turn on or turn off the source by software. It is thanks to this feature that the operating system can you turn off the computer without the user having to tighten a button for this;

– Wake-on-LAN: turn on or off the font on the card network.

The signal PS_ON depends on the existence of the other: the signal +5 VSB or Standby. As the name indicates, this signal enables certain circuits to be fed when the voltages at continuous current are suspended, keeping active only the voltage of 5 V. In other words, this feature is what allows the computer to enter in “sleep mode”. That is why the board video or HD, for example, can be turned off and the computer remains switched on.

There is also another important signal called Power Good which has the function of communicating to the machine that the font is showing correct operation. If the signal Power Good does not exist or is interrupted, usually the computer shuts down automatically. This occurs because the interrupt signal indicates that the device is operating with voltages changed and this can permanently damage a component. The Power Good is able to prevent the operation of the chip while there are no tensions acceptable. This signal, in truth, there is provided the default AT AT AT AT AT. In the case of the standard ATX, its name is PWR_OK (Power Good OK), and its existence referred to in at voltages of +3.3 V and +5 V.

As this is a standard relatively old, the ATX has passed – and passes – through some changes to suit the needs that were – and will – appearing on account of evolution technology of other devices. With this, there have been many versions:

– ATX12V 1.x: this new specification came in the mid-2000s and consists, basically, in a connector, additional 12 “V” formed by 4 pins, and the other, optional, 6-pin and voltage 3.3 V or 5 V. This version was suffering minor revisions from time to time. The last, the 1.3, had as a main novelty the implementation of a power connector for devices SATA;

– ATX12V 2.x: series of revisions that launched a connector to the motherboard 24-pin (until then,the standard was 20 pins) and added, in version 2.2, a plug for video cards that use the slot PCI Express, a feature necessary because of the high consumption of energy of these devices. In this pattern, the connector optional 6-pin has been removed;

– EPS12V: specification very similar to that series ATX12V 2.x, defined by the SSI (Server System Infrastructure) initially to be applied in servers. Its main differential is the provision of a connector additional 8-pin connector (which can be a combination of the two connectors 4-pin) and an optional 4. To meet the expressive the market, many manufacturers offer sources that are, at the same time, ATX12V v2.x and EPS12V.

Worth mentioning that there are also several other formats are less common to meet certain needs, such as variations of the ATX (eatx power, microATX, etc.), EBX, ITX (and their versions), etc.

With so many standards, you may be wondering what to choose, is it? This decision can be more easier than it seems. A rule of thumb, if you’re riding a new computer, with components fully recent, just choose the last standard available, that is very likely it will be the easiest to find in the market. In the case of doubt, just refer to the description of your motherboard to see what standard it uses and check if the source by which are you interested to support this specification.

Voltages of the power sources

The devices that make up a computer are so varied that require different levels of voltage for its functioning. Therefore, the sources of power provide, essentially, the following voltages: +3.3 V, +5 V, +12 V, -5 V and -12 V (the ancient sources ACTS do not provide the voltage +3.3 V). The outputs of +3.3 V and +5 V are more targeted the smaller devices, such as memory chips. The voltage +12 V is used for devices that consume more energy, such as those who rely on “engines”, such as HDs (whose engine is responsible for spinning the disks) and DVD-drives or Blu-ray (which have motors to open the drawer, and to rotate the disk). Tensions -5 V and -12 V are rarely used – they were to the old bus ISA, for example.

It is clear that there are devices that require voltages lower. Memories of RAM type DDR3, for example, can work with up to +1.5 V. For these cases, the motherboard account with regulators that convert an output voltage of the source power to the voltage required to the component in question.

Power of the power sources

This is the aspect most considered by any person at the time of purchase a source. And it should be the same. If you purchase a source with the lowest power that your computer needs, multiple problems may happen, such as sudden shutdown of the machine or reboots constant. The ideal is to opt for a source that provides a certain “slack” in this aspect. But choosing a requires some care.

The main problem lies in the fact that some sources, mainly the low-cost, does not always provide all the power that is described on its label. For example, a power supply you can have in your description to 500 W (Watts) of power, but under normal conditions of use can offer, a maximum of 400 W. it turns out that the manufacturer may have reached the capacity of 500 W in the laboratory tests with temperatures below those that are found within the computer, or to have informed this number based on calculations dubious, for example. Therefore, at the time of purchase, it is important to learn about the power the actual source.

For this, it is necessary to make a calculation that considers some aspects, being the most important of them is the concept of power combined. Before we understand what this means, let’s understand the following: as you have already seen, in relation to sources ATX, we have the following outputs: +3.3 V, +5 V, +12 V, -5 V, and -12 V. There is more of a call of +5 VSB (standby). The manufacturer must report, for each of these outputs, the value of the current, which is measured in amperes (A). The definition the power of each output is then calculated by multiplying the value in volts by the number of amps. By example, if the output of +5 V is 30 A, just do 5×30, which is equal to 150. From there, left to do this calculation for all of the outputs and to sum up all the results to know the powerful source, right? Wrong! This, incidentally, is one of the calculations doubtful that some manufacturers use to “make up” the power of its sources.

That is where that comes into play the combined power. The outputs +3.3 V and +5 V are combined, as well as all outputs +12 V. The maximum power of each one is can be achieved when the output “nearby” it is not in use. That is, in the previous example, the power the output of +5 V would be possible only if the voltage +3.3 V was not used. There is still another detail: a another measure of the combined strength considers the three types output mentioned: +3.3 V, +5 V, +12 V. This value is so combined with the powers of the outputs of -12 V (note that the sign of the negative should be ignored in the calculation) and +5 VSB. Hence in order to obtain the total power of the source.

Note that the powers combined of the voltages +3.3 V, + 5 V and +12 V is 477,8 W, which is summed with the power outputs – 12 V and +5 VSB, which is 22,2 W (7,2 + 15). Thus, the source has 500 W of total power. But here’s a tip: at the time of purchase, please note if the outputs of +12 V (yes, usually there are more than one), provide a combined power reasonable. This is the most important because it consists in the tension that is used by devices that most require energy, such as the processor and the video card. In our example, this value is 384 W.

But you must be wondering: how do you know the power suitable for my computer? You already know that you will have problems if you purchase a source with a power insufficient. On the other hand, if you buy a font very powerful for a PC that does not need to all of this, will be how to buy a bus for the family of 5 people. The following table can help you out with this. It provides a estimate how the major components of a computer can consume:

As already said, processors and video cards are the devices that most require energy. To make matters worse, this measure can vary a lot from model to model. Therefore, it is important to consult the specifications of these items to knowing your average consumption. Suppose, for example, that you have chosen the following configuration:

See that the total is 260 W, without considering other items, such as motherboards, memory sticks, etc. In this case, a source with at least 400 W real it would be the ideal (remember the tip always having a “slack”).

Efficiency of power supplies

This is another aspect of extreme importance in choosing a source. In a few words, the efficiency it is a measure of a percentage that indicates how much the power of the network electrical, that is, of the alternating current, is effectively transformed into continuous current. To better understand, let’s a quick example: suppose you have a computer that requires 300 W, but the source is drawing 400 W. The efficiency here is then 75%. The 100 W to more that are not used are disposed of in the form of heat.

Based on this, note the following: the higher the efficiency of the source, the lower is the heat generator and the lower the waste energy, doing good for your pocket and preventing your computer you have an issue caused by excessive heating. So that efficiency it is a very important factor to be considered. Sources of greater quality has efficiency of at least 80%, therefore, these are the most indicated. Sources with efficiency between 70% and 80% are until acceptable, but below this are not recommended.


Power Factor Correction (PFC)

The PFC (Power Factor Correction or, in good Portuguese, Correction factor of Power) is, in a few words, a means to allow the maximum optimization possible in the distribution of energy. Let’s understand better: devices consisting of motors, transformers, reactors, etc., deal with two types of power: active and reactive. The basic difference between both is that the reactive power is the one that is used only to magnetize certain components of motors, transformers, etc.

The issue is that the excess of reactive power can cause various problems, such as heating, overload, etc. This happens because the reactive energy is not energy “work”, while the active energy in this role, but you can use the features that could be dedicated to the latter. Therefore, the less reactive power is used, the better.

One way to measure the usage of reactive energy is by comparing it with the active energy. This is called the Power Factor. The measurement is made by analyzing the values between 0 and 1. The closer 1, the lower is the use of reactive power. By less in industrial applications, the ideal is that the power factor is, at least, 0,92.

In power supplies, the Correction Factor Power is used to maintain this relationship at levels acceptable. There are two types of mechanisms for this: active PFC and PFC passive. The first makes use of the components that cannot stop the power factor to 0.95 or more – by least theoretically – and that can also reduce interference. The second type, in turn, is less efficient, since it uses components that are not able to offer a “balance” so optimized as the active PFC. The power factor for sources with PFC liability is around 0.80, but models of lower quality can reach 0.60.

It is clear that sources with active PFC are more recommended, the same because they can offer a feature quite interesting: check automatic voltage. Note, however, that in terms of benefits for the end user, the PFC is advantageous in aspects protection. There is no relevance in terms saving energy, for example. Manufacturers started to adopt this resource, for determination of regulatory authorities in a few countries.

The advantage of using a source of this latter type is that the fan is larger, therefore, requires a smaller number of spins to direct the flow of air. In this way the source also manages to be more silent.

More sophisticated models also have a temperature sensor that is able to speed up the rotation of the fan in the case of an increase of heat. This feature is interesting not only by providing protection against excessive increase temperature, as well as serve as a warning that any thing is hindering the air circulation needed for the proper functioning of the machine.


As you may have noticed in the course of the article, the source of power has more importance to a computer than you think. Therefore, it is necessary to direct greater attention this item in the time you make an upgrade or assemble a machine. As a final tip, an orientation that is common in buy of any product: search. Give preference for models brands, that provide all the details of your products and warranty. And, even so, search on the Internet for the models that you interessatrm, because even among the recognized manufacturers there products that disappoint. It is clear that most of the times it is not necessary to acquire a source top of the line, on the other hand, sources of very low cost, termed “generic”, should be avoided whenever possible, since almost always are low quality and may even pose some risk to your computer.

Atx Power Supplies The Main Features 1