Why do you need a power supply in a computer? Methodology for testing power supplies

1. Computer power supply
2. Power
3. Active or passive PFC?
4. Cooling the power supply
5. Connectors and cables
6. Brands and manufacturers
7. From the history
8. Development prospects

Computer power supply

Choosing the right power supply for your computer can sometimes not be as easy as it seems. The stability, as well as the service life of all used PC components, depends on this choice, and the issue of choosing a power supply must be taken seriously. In this review, we will try to consider the main points that will help you make the right choice.

Power

The output of the power supply contains the following constant voltages: +5 V, +12 V (also +3.3 V), and - auxiliary (minus 12 V and + 5 V when idle). The main load is now “customary” to load the +12 V line.

Output power (W - Watt) is calculated using a simple formula: it is equal to the product of U and J, where U is voltage (in Volts), J is current (in Amperes). Voltages are constant, therefore, the greater the power, the greater the current through the lines.

But it turns out that not everything is simple here either. If there is a heavy load on the combined line +3.3 / +5, the power on the +12 line may decrease. Example - marking of the power supply of the budget brand Cooler Master (model RS-500-PSAP-J3):

The maximum total power on the +3.3 and +5 lines is equal to 130W (as indicated on the packaging), and the maximum power on the “most important” +12V line is 360W.

But that’s not all. Let's pay attention to the inscription below:

3.3V and +5V and +12V, the total power should not exceed 427.9 W. As if, theoretically (looking at the “table”), we “see” 490W (360 plus 130), but here it is only 427.9.

What does this give us in practice: if the load on the +3.3V and 5V lines is in total, say 60W, then subtracting 427.9 from the power supplied by the manufacturer, i.e. 427.9 – 60, we get 367.9W. We will only get 360 Watts on the +12V line. From which the “main consumption” comes: current to the processor, video card.

Automatic power calculation

To calculate the power of power supplies, you can use a calculator in your browser: http://www.extreme.outervision.com/psucalculatorlite.jsp. Although it is in English, you can figure it out. There are quite a lot of such services on the Internet.

In general, here you can select almost everything you need, including the specific type of CPU, motherboard format (micro-ATX or ATX), the number of memory sticks, hard drives, fans... To calculate, you need to click on the rectangular “Calculate” button. The service will provide: both the recommended and the minimum possible power value (in Watts) for your system.

However, from experience, we can assume that an office computer (with a dual-core CPU) can be content with a 300W power supply. For a home (gaming, with a discrete video card) - a 450 - 500W power supply is suitable, but for powerful gaming PCs with a “top” (top) card (or two, in Crossfire or SLI mode) - Total Power (total power) starts from 600 - 700W.

The central processor, even at the maximum possible load, consumes 100 - 180W (with the exception of 6-core AMD), discrete video card - from 90 to 340W, the motherboard itself - 25-30W (memory strip - 5-7W), hard drive 15- 20W. Keep in mind that the main load (processor and video card) falls on the “12V” line. Well, it is advisable to add a power reserve (10-20%).

Efficiency - efficiency factor

An important criterion will be the efficiency of the power supply. Efficiency factor (efficiency) is the ratio of the useful power supplied by the power supply to that consumed by it from the network. If the PC power supply circuit contained only a transformer, its efficiency would be about 100%.

Let's consider an example when a power supply (with a known efficiency of 80%) provides an output power of 400W. If this number (400) is divided by 80%, we get 500W. A power supply with the same characteristics, but with lower efficiency (70%), will already consume 570W.

But – you don’t need to take these numbers “seriously”. Most of the time, the power supply is not fully loaded, for example, this value can be 200W (the computer will consume less from the network).

There is an organization whose functions include testing power supplies for compliance with the level of the declared efficiency standard. 80 Plus certification, however, is carried out only for 115 Volt networks (common in the USA), starting with the 80 Plus Bronze “class”, all units are tested for use in a 220V electrical network. For example, if certified in the 80 Plus Bronze class, the power supply efficiency is 85% at “half” power load, and 81% at the declared power.

The presence of a logo on the power supply indicates that the product meets the certification level.

The advantages of high efficiency: less energy is dissipated “in the form of heat”, and the cooling system, accordingly, will be less noisy. Secondly, the savings in electricity are obvious (although not very large). The quality of “certified” power supplies is usually high.

Active or passive PFC?

Power Factor Correction (PFC) – power factor correction. Power Factor - the ratio of active power to total (active plus reactive).

The load does not consume reactive power - it is 100% supplied back to the network in the next half-cycle. However, with increasing reactive power, the maximum (per period) current value increases.

Too much current in 220V wires - is this good? Probably not. Therefore, reactive power is combated whenever possible (this is especially true for really powerful devices that “cross” the limit of 300-400 Watts).

PFC – can be passive or active.

Advantages of the active method:

A power factor close to the ideal value is provided, up to a value close to 1. With PF=1, the current in the 220V wire will not exceed the value “power divided by 220” (in the case of lower PF values, the current is always somewhat more).

Disadvantages of active PFC:

As complexity increases, the overall reliability of the power supply decreases. The active PFC system itself requires cooling. In addition, it is not recommended to use active correction systems with autovoltage in conjunction with UPS sources.

Advantages of passive PFC:

There are no disadvantages of the active method.

Flaws:

The system is ineffective at high power values.

What exactly to choose? In any case, when purchasing a power supply unit of lower power (up to 400-450W), you will most often find PFC of a passive system in it, and more powerful units, from 600 W, are more often found with active correction.

Cooling the power supply

The presence of a cooling fan in any power supply is considered normal. The fan diameter can be 120 mm, there is a variant of 135 mm and, finally, 140 mm.

The system unit provides for installing a power supply at the top of the case - then choose any model with a horizontally located fan. Larger diameter - less noise (with the same cooling power).

The rotation speed should vary depending on the internal temperature. When the power supply does not overheat, why do you need to turn the “valve” at all speeds and annoy the user with noise? There are power supply models that completely stop their fan when the power consumption is less than 1/3 of the calculated one. Which is convenient.

The main thing in the PSU cooling system is its silence (or the complete absence of a fan, this also happens). On the other hand, cooling is necessary to prevent parts from overheating (high power, in any case, leads to heat generation). At high power, you can’t do without a fan.

Note: the photo shows the result of modding (removing the standard slot grille, installing a Noktua fan and a 120 mm grill).

Connectors and cables

When purchasing and choosing, pay attention to the number of available connectors and the length of the wires coming from the power supply. Depending on the geometry of the case, you need to choose a power supply with a cable harness of sufficient length. For standard ATX cases, a 40-45 cm harness will be sufficient.

The power supply used in home and office computers has the following connectors:

This is a 24-pin power connector on the PC motherboard. Usually there are 20 and 4 contacts separately, but sometimes it is monolithic, 24-pin.

Processor power connector. It is usually 4-pin, and only very powerful processors use 8-pin. You can choose the right power supply for your computer based on the corresponding connector on the motherboard itself.

The connector for powering the video card looks similar, and differs in that it is 6 or 8 pin.

Connectors (connectors) for powering SATA devices (hard drives, optical drives), four-pin Molex (for IDE), and for turning on an FDD (or card reader) are familiar to most users:

Note: the number of all additional connectors (SATA, MOLEX, FDD) must be sufficient to connect devices located inside the system unit.

Montage demontage

To dismantle the old power supply, disconnect its 220 Volt wire. Then, you need to wait 2-3 minutes, and only then start working. Attention! Failure to comply with this requirement may result in electrical injury.

The power supply in any PC is attached to the back wall with 4 screws (self-tapping screws). You can unscrew them only by disconnecting all internal connectors and plugs of the power supply (2 motherboard connectors, video cards, connectors for additional devices).

You can connect the power supply to the computer in the reverse order: first, mount it into the case, securing it with screws, then connect the connectors.

Note: when manipulating the power supply, the processor cooler may interfere. If it is possible to dismantle it, use this (put it in place later, before turning it on).

Turning on a computer with a new power supply

Having supplied 220 Volt power to the new power supply, you do not need to immediately turn on the computer. Wait 10-15 seconds at first: you will listen to see if anything “out of the ordinary” is happening. If we hear squeaking or ringing of chokes, we go and replace the power supply under warranty. If you hear a periodically repeating “metallic” click, do not turn on the computer with such a power supply.

If in standby mode, the power supply “clicks” - this is the protection system working. Turn off such a power supply, disconnect its connectors (connectors). You can try to assemble the same thing again - if the problem repeats, take the power supply to a service center (perhaps the unit itself is faulty).

A computer with a working power supply turns on almost immediately when you press the “Power” button of the ATX case. An image should appear on the monitor - now you can continue working, but with a new power supply.

Modular cables and connectors

Many more powerful power supply models now use what is called a “modular” connection. Adding internal cables with corresponding mating connectors is done as needed. This is convenient because you no longer need to keep extra (unused) wires in the computer case, and besides, there is less confusion. And the absence of unnecessary wires also improves the circulation of hot air. In modular power supplies, only cords with a connector for the motherboard/processor are made “non-removable”.

Brands and manufacturers

All companies (manufacturers of computer power supplies) belong to one of 3 main groups:

1. They produce entirely their own products - brands such as Hipro, FSP, Enermax, Delta, also HEC, Seasonic.
2. They produce products by shifting part of the manufacturing process to other companies - Corsair, Silverstone, Antec, Power&Cooling and Zalman.
3. They resell ready-made units under their own brand (some are “selected”, some are not): Chiftec, Gigabyte, Cooler Master, OCZ, Thermaltake.

Each brand listed above can be safely recommended. On the Internet, in addition, there are many reviews and tests for “branded” power supplies that the user can use to guide them.

Before buying a power supply, you should weigh it (it’s enough to hold it in your hand). This will allow you to more or less understand what is inside him. Of course, this method is inaccurate, but it allows you to immediately “sweep aside” an obviously “cheap” power supply.

The weight of the power supply depends on the quality of the steel, the dimensions of the fan, and (most importantly): the number of chokes and the weight of the radiators inside. If the power supply is missing some inductors (or, say, capacitors of reduced capacity), this indicates a “cheaper” electrical circuit: the power supply will weigh 700-900 grams. A good power supply unit (450-500W) usually weighs from 900 g. up to 1.4 kg.

From the history

In the market of personal computers, that is, not only IBM-compatible ones, but “computers” in a more general sense, IBM initially went to standardize components (power supply unit, motherboard). The rest then began to “copy” this. All known form factors for power supplies for IBM-compatible PCs are based on one of the power supply models: PC/XT, PC/AT, and Model 30 PS/2. All compatible PCs, in one way or another, could use one of the three original standards developed by IBM. These standards were popular until 1996, and even later - the modern ATX standard dates back to the physical layout of the PS/2 Model 30.

The new form factor, that is, the ATX we know, was defined in 1995 by Intel (then an IBM partner), introducing a standard for the board and power supply. The new standard gained popularity in 1996, and manufacturers gradually began to move away from the outdated AT standard. ATX and some of the “offshoots” of the standard that followed it use matte connectors different from the AT form factor. boards (not only with additional voltages, but also with signals that allow for greater power and additional capabilities).

All IBM standards physically provided the same connector that supplied power to the motherboard. To turn it on and off to supply power to the computer, a toggle switch (or button) was used, an interrupting wire with a voltage of 220 Volts. Which was not very convenient (especially when disassembling/repairing a PC). Therefore, a new standard has appeared that “does not allow” a voltage of more than 12 Volts inside the system unit (inside the case).

It must be said that the power supply circuit itself (the principle of its construction), starting from the first PC XT, has not received significant changes. The principle of energy conversion used in computer power supplies is called “pulse” (from an alternating voltage of 220 Volts a “constant” voltage is made, then it is converted and reduced to lower values ​​by the pulse method). The first power supplies for personal computers had a power of 60 W (XT), or, say, 100-120 W (AT 286). Simply, then the computer provided for the installation of: 1-2 disk drives, one hard drive (and the processor itself “consumed” very little).

Development prospects

800 Watt, 900 Watt, 1000 Watt... A power supply for a PC that supplies one Kilowatt of energy to the load will not surprise anyone. Of course, the price is significantly different (from “standard” 450-500 W boxes), however, such a power supply provides a sufficient level of reliability (and low noise level) even when fully loaded! Well, it's just a miracle.

If you calculate how much energy such a computer will consume from the outlet, it turns out that this is nothing more than the equivalent of an iron constantly turned on at full power. A good one, above average in power, heavy...

Recently, with the transition to new technological processes for the production of “main” chips for a computer (central processor, 3-D module), the movement has been just “reverse” - that is, a decrease in overall power while maintaining the same level of performance. Two years ago, the average 4-core “percent” consumed at least 90 W, now it’s already 65 (“new”, and faster). In any case (both 2 years ago and now), the choice is up to the user.

Linear and switching power supplies

Let's start with the basics. The power supply in a computer performs three functions. First, alternating current from the household power supply must be converted to direct current. The second task of the power supply is to reduce the voltage of 110-230 V, which is excessive for computer electronics, to the standard values ​​​​required by power converters of individual PC components - 12 V, 5 V and 3.3 V (as well as negative voltages, which we will talk about a little later) . Finally, the power supply plays the role of a voltage stabilizer.

There are two main types of power supplies that perform the above functions - linear and switching. The simplest linear power supply is based on a transformer, on which the alternating current voltage is reduced to the required value, and then the current is rectified by a diode bridge.

However, the power supply is also required to stabilize the output voltage, which is caused by both voltage instability in the household network and a voltage drop in response to an increase in current in the load.

To compensate for the voltage drop, in a linear power supply the transformer parameters are calculated to provide excess power. Then, at high current, the required voltage will be observed in the load. However, the increased voltage that will occur without any means of compensation at low current in the payload is also unacceptable. Excess voltage is eliminated by including a non-useful load in the circuit. In the simplest case, this is a resistor or transistor connected through a Zener diode. In a more advanced version, the transistor is controlled by a microcircuit with a comparator. Be that as it may, excess power is simply dissipated as heat, which negatively affects the efficiency of the device.

In the switching power supply circuit, one more variable appears, on which the output voltage depends, in addition to the two already existing: input voltage and load resistance. There is a switch in series with the load (which in the case we are interested in is a transistor), controlled by a microcontroller in pulse width modulation (PWM) mode. The higher the duration of the open states of the transistor in relation to their period (this parameter is called duty cycle, in Russian terminology the inverse value is used - duty cycle), the higher the output voltage. Due to the presence of a switch, a switching power supply is also called Switched-Mode Power Supply (SMPS).

No current flows through a closed transistor, and the resistance of an open transistor is ideally negligible. In reality, an open transistor has resistance and dissipates some of the power as heat. In addition, the transition between transistor states is not perfectly discrete. And yet, the efficiency of a pulsed current source can exceed 90%, while the efficiency of a linear power supply with a stabilizer reaches 50% at best.

Another advantage of switching power supplies is the radical reduction in the size and weight of the transformer compared to linear power supplies of the same power. It is known that the higher the frequency of alternating current in the primary winding of a transformer, the smaller the required core size and the number of winding turns. Therefore, the key transistor in the circuit is placed not after, but before the transformer and, in addition to voltage stabilization, is used to produce high-frequency alternating current (for computer power supplies this is from 30 to 100 kHz and higher, and as a rule - about 60 kHz). A transformer operating at a power supply frequency of 50-60 Hz would be tens of times more massive for the power required by a standard computer.

Linear power supplies today are used mainly in the case of low-power applications, where the relatively complex electronics required for a switching power supply constitute a more sensitive cost item compared to a transformer. These are, for example, 9 V power supplies, which are used for guitar effects pedals, and once for game consoles, etc. But chargers for smartphones are already entirely pulsed - here the costs are justified. Due to the significantly lower amplitude of voltage ripple at the output, linear power supplies are also used in those areas where this quality is in demand.

⇡ General diagram of an ATX power supply

A desktop computer's power supply is a switching power supply, the input of which is supplied with household voltage with parameters of 110/230 V, 50-60 Hz, and the output has a number of DC lines, the main ones of which are rated 12, 5 and 3.3 V In addition, the power supply provides a voltage of -12 V, and sometime also a voltage of -5 V, necessary for the ISA bus. But the latter was at some point excluded from the ATX standard due to the end of support for the ISA itself.

In the simplified diagram of a standard switching power supply presented above, four main stages can be distinguished. In the same order, we consider the components of power supplies in the reviews, namely:

1. EMI filter - electromagnetic interference (RFI filter);
2. primary circuit - input rectifier (rectifier), key transistors (switcher), creating high-frequency alternating current on the primary winding of the transformer;
3. main transformer;
4. secondary circuit - current rectifiers from the secondary winding of the transformer (rectifiers), smoothing filters at the output (filtering).

⇡ EMF filter

The filter at the power supply input is used to suppress two types of electromagnetic interference: differential (differential-mode) - when the interference current flows in different directions in the power lines, and common-mode - when the current flows in one direction.

Differential noise is suppressed by capacitor CX (the large yellow film capacitor in the photo above) connected in parallel with the load. Sometimes a choke is additionally attached to each wire, which performs the same function (not on the diagram).

The common mode filter is formed by CY capacitors (blue drop-shaped ceramic capacitors in the photo), connecting the power lines to ground at a common point, etc. a common-mode choke (LF1 in the diagram), the current in the two windings of which flows in the same direction, which creates resistance for common-mode interference.

In cheap models, a minimum set of filter parts is installed; in more expensive ones, the described circuits form repeating (in whole or in part) links. In the past, it was not uncommon to see power supplies without any EMI filter at all. Now this is rather a curious exception, although if you buy a very cheap power supply, you can still run into such a surprise. As a result, not only and not so much the computer itself will suffer, but other equipment connected to the household network - switching power supplies are a powerful source of interference.

In the filter area of ​​a good power supply, you can find several parts that protect the device itself or its owner from damage. There is almost always a simple fuse for short circuit protection (F1 in the diagram). Note that when the fuse trips, the protected object is no longer the power supply. If a short circuit occurs, it means that the key transistors have already broken through, and it is important to at least prevent the electrical wiring from catching fire. If a fuse in the power supply suddenly burns out, then replacing it with a new one is most likely pointless.

Separate protection is provided against short-term surges using a varistor (MOV - Metal Oxide Varistor). But there are no means of protection against prolonged voltage increases in computer power supplies. This function is performed by external stabilizers with their own transformer inside.

The capacitor in the PFC circuit after the rectifier can retain a significant charge after being disconnected from power. To prevent a careless person who sticks his finger into the power connector from receiving an electric shock, a high-value discharge resistor (bleeder resistor) is installed between the wires. In a more sophisticated version - together with a control circuit that prevents charge from leaking when the device is operating.

By the way, the presence of a filter in the PC power supply (and the power supply of a monitor and almost any computer equipment also has one) means that buying a separate “surge filter” instead of a regular extension cord is, in general, pointless. Everything is the same inside him. The only condition in any case is normal three-pin wiring with grounding. Otherwise, the CY capacitors connected to ground simply will not be able to perform their function.

⇡ Input rectifier

After the filter, the alternating current is converted into direct current using a diode bridge - usually in the form of an assembly in a common housing. A separate radiator for cooling the bridge is highly welcome. A bridge assembled from four discrete diodes is an attribute of cheap power supplies. You can also ask what current the bridge is designed for to determine whether it matches the power of the power supply itself. Although, as a rule, there is a good margin for this parameter.

⇡ Active PFC block

In an AC circuit with a linear load (such as an incandescent light bulb or an electric stove), the current flow follows the same sine wave as the voltage. But this is not the case with devices that have an input rectifier, such as switching power supplies. The power supply passes current in short pulses, approximately coinciding in time with the peaks of the voltage sine wave (that is, the maximum instantaneous voltage) when the smoothing capacitor of the rectifier is recharged.

The distorted current signal is decomposed into several harmonic oscillations in the sum of a sinusoid of a given amplitude (the ideal signal that would occur with a linear load).

The power used to perform useful work (which, in fact, is heating the PC components) is indicated in the characteristics of the power supply and is called active. The remaining power generated by harmonic oscillations of the current is called reactive. It does not produce useful work, but heats the wires and creates a load on transformers and other power equipment.

The vector sum of reactive and active power is called apparent power. And the ratio of active power to total power is called power factor - not to be confused with efficiency!

A switching power supply initially has a rather low power factor - about 0.7. For a private consumer, reactive power is not a problem (fortunately, it is not taken into account by electricity meters), unless he uses a UPS. The uninterruptible power supply is responsible for the full power of the load. At the scale of an office or city network, excess reactive power created by switching power supplies already significantly reduces the quality of power supply and causes costs, so it is being actively combated.

In particular, the vast majority of computer power supplies are equipped with active power factor correction (Active PFC) circuits. A unit with an active PFC is easily identified by a single large capacitor and inductor installed after the rectifier. In essence, Active PFC is another pulse converter that maintains a constant charge on the capacitor with a voltage of about 400 V. In this case, current from the supply network is consumed in short pulses, the width of which is selected so that the signal is approximated by a sine wave - which is required to simulate a linear load . To synchronize the current consumption signal with the voltage sinusoid, the PFC controller has special logic.

The active PFC circuit contains one or two key transistors and a powerful diode, which are placed on the same heatsink with the key transistors of the main power supply converter. As a rule, the PWM controller of the main converter key and the Active PFC key are one chip (PWM/PFC Combo).

The power factor of switching power supplies with active PFC reaches 0.95 and higher. In addition, they have one additional advantage - they do not require a 110/230 V mains switch and a corresponding voltage doubler inside the power supply. Most PFC circuits handle voltages from 85 to 265 V. In addition, the sensitivity of the power supply to short-term voltage dips is reduced.

By the way, in addition to active PFC correction, there is also a passive one, which involves installing a high-inductance inductor in series with the load. Its efficiency is low, and you are unlikely to find this in a modern power supply.

⇡ Main converter

The general principle of operation for all pulse power supplies of an isolated topology (with a transformer) is the same: a key transistor (or transistors) creates alternating current on the primary winding of the transformer, and the PWM controller controls the duty cycle of their switching. Specific circuits, however, differ both in the number of key transistors and other elements, and in qualitative characteristics: efficiency, signal shape, noise, etc. But here too much depends on the specific implementation for this to be worth focusing on. For those interested, we provide a set of diagrams and a table that will allow you to identify them in specific devices based on the composition of the parts.

	Transistors	Diodes	Capacitors	Transformer primary legs
Single-Transistor Forward	1	1	1	4
	2	2	0	2
	2	0	2	2
	4	0	0	2
	2	0	0	3

In addition to the listed topologies, in expensive power supplies there are resonant versions of Half Bridge, which are easily identified by an additional large inductor (or two) and a capacitor forming an oscillatory circuit.

Single-Transistor Forward

⇡ Secondary circuit

The secondary circuit is everything that comes after the secondary winding of the transformer. In most modern power supplies, the transformer has two windings: 12 V is removed from one of them, and 5 V from the other. The current is first rectified using an assembly of two Schottky diodes - one or more per bus (on the highest loaded bus - 12 V - in powerful power supplies there are four assemblies). More efficient in terms of efficiency are synchronous rectifiers, which use field-effect transistors instead of diodes. But this is the prerogative of truly advanced and expensive power supplies that claim the 80 PLUS Platinum certificate.

The 3.3V rail is typically driven from the same winding as the 5V rail, only the voltage is stepped down using a saturable inductor (Mag Amp). A special winding on a transformer for a voltage of 3.3 V is an exotic option. Of the negative voltages in the current ATX standard, only -12 V remains, which is removed from the secondary winding under the 12 V bus through separate low-current diodes.

PWM control of the converter key changes the voltage on the primary winding of the transformer, and therefore on all secondary windings at once. At the same time, the computer's current consumption is by no means evenly distributed between the power supply buses. In modern hardware, the most loaded bus is 12-V.

To separately stabilize voltages on different buses, additional measures are required. The classic method involves using a group stabilization choke. Three main buses are passed through its windings, and as a result, if the current increases on one bus, the voltage drops on the others. Let's say the current on the 12 V bus has increased, and in order to prevent a voltage drop, the PWM controller has reduced the duty cycle of the key transistors. As a result, the voltage on the 5 V bus could go beyond the permissible limits, but was suppressed by the group stabilization choke.

The voltage on the 3.3 V bus is additionally regulated by another saturable inductor.

A more advanced version provides separate stabilization of the 5 and 12 V buses due to saturable chokes, but now this design has given way to DC-DC converters in expensive high-quality power supplies. In the latter case, the transformer has a single secondary winding with a voltage of 12 V, and the voltages of 5 V and 3.3 V are obtained thanks to DC-DC converters. This method is most favorable for voltage stability.

Output filter

The final stage on each bus is a filter that smoothes out voltage ripple caused by the key transistors. In addition, the pulsations of the input rectifier, whose frequency is equal to twice the frequency of the supply network, penetrate to one degree or another into the secondary circuit of the power supply.

The ripple filter includes a choke and large capacitors. High-quality power supplies are characterized by a capacitance of at least 2,000 uF, but manufacturers of cheap models have reserves for savings when they install capacitors, for example, of half the nominal value, which inevitably affects the ripple amplitude.

⇡ Standby power +5VSB

A description of the components of the power supply would be incomplete without mentioning the 5 V standby voltage source, which makes the PC sleep mode possible and ensures the operation of all devices that must be turned on at all times. The “duty room” is powered by a separate pulse converter with a low-power transformer. In some power supplies, there is also a third transformer, which is used in the feedback circuit to isolate the PWM controller from the primary circuit of the main converter. In other cases, this function is performed by optocouplers (an LED and a phototransistor in one package).

⇡ Methodology for testing power supplies

One of the main parameters of the power supply is voltage stability, which is reflected in the so-called. cross-load characteristic. KNH is a diagram in which the current or power on the 12 V bus is plotted on one axis, and the total current or power on the 3.3 and 5 V buses is plotted on the other. At the intersection points for different values ​​of both variables, the voltage deviation from the nominal value is determined one tire or another. Accordingly, we publish two different KNHs - for the 12 V bus and for the 5/3.3 V bus.

The color of the dot indicates the percentage of deviation:

• green: ≤ 1%;
• light green: ≤ 2%;
• yellow: ≤ 3%;
• orange: ≤ 4%;
• red: ≤ 5%.
• white: > 5% (not allowed by ATX standard).

To obtain KNH, a custom-made power supply test bench is used, which creates a load by dissipating heat on powerful field-effect transistors.

Another equally important test is determining the ripple amplitude at the power supply output. The ATX standard allows ripple within 120 mV for a 12 V bus and 50 mV for a 5 V bus. A distinction is made between high-frequency ripple (at double the frequency of the main converter switch) and low-frequency (at double the frequency of the supply network).

We measure this parameter using a Hantek DSO-6022BE USB oscilloscope at the maximum load on the power supply specified by the specifications. In the oscillogram below, the green graph corresponds to the 12 V bus, the yellow graph corresponds to 5 V. It can be seen that the ripples are within normal limits, and even with a margin.

For comparison, we present a picture of ripples at the output of the power supply of an old computer. This block wasn't great to begin with, but it certainly hasn't improved over time. Judging by the magnitude of the low-frequency ripple (note that the voltage sweep division is increased to 50 mV to fit the oscillations on the screen), the smoothing capacitor at the input has already become unusable. High-frequency ripple on the 5 V bus is on the verge of permissible 50 mV.

The following test determines the efficiency of the unit at a load from 10 to 100% of rated power (by comparing the output power with the input power measured using a household wattmeter). For comparison, the graph shows the criteria for the various 80 PLUS categories. However, this does not cause much interest these days. The graph shows the results of the top-end Corsair PSU in comparison with the very cheap Antec, and the difference is not that great.

A more pressing issue for the user is the noise from the built-in fan. It is impossible to directly measure it close to the roaring power supply testing stand, so we measure the rotation speed of the impeller with a laser tachometer - also at power from 10 to 100%. The graph below shows that when the load on this power supply is low, the 135mm fan remains at low speed and is hardly audible at all. At maximum load the noise can already be discerned, but the level is still quite acceptable.

It is no secret that the operation of the device on which it is loaded depends on the correct choice of power supply (hereinafter referred to as PSU), its design and build quality. Here I will try to talk about the main points of selection, calculation, design and use of power supplies.

1. Selecting a power supply

The first step is to clearly understand what exactly will be connected to the power supply. We are mainly interested in the load current. This will be the main point of the technical specifications. Based on this parameter, the circuit and element base will be selected. I will give examples of loads and their average current consumption

1. LED lighting effects (20-1000mA)

2. Light effects on miniature incandescent lamps (200mA-2A)

3. Light effects on powerful lamps (up to 1000A)

4. Miniature semiconductor radio receivers (100-500mA)

5. Portable audio equipment (100mA-1A)

6. Car radios (up to 20A)

7. Automotive UMZCH (via 12V line up to 200A)

8. Stationary semiconductor UMZCH (with an output power not higher than 1 kW up to 40 A)

9. Tube UMZCH (10mA-1A – anode, 200mA-8A – filament)

10. Tube HF transceivers [the output stage in class C is characterized by the highest efficiency] (with transmitter power up to 1 kW, up to 5A - anode, up to 10A - filament)

11. Semiconductor HF transceivers, CB (with transmitter power up to 100W, 1 - 5A)

12. Tube VHF radio stations (with transmitter power up to 50W, up to 1A - anode, up to 3A - filament)

13. Semiconductor VHF radios (up to 5A)

14. Semiconductor TVs (up to 5A)

15. Computer equipment, office equipment, network devices [LAN hubs, access points, modems, routers] (500mA - 30A)

16. Chargers for batteries (up to 10A)

17. Control units for household appliances (up to 1A)

2. Safety rules

Let's not forget that the power supply is the highest voltage component in any device (except perhaps the TV). Moreover, it is not only the industrial electrical network (220V) that poses a danger. The voltage in the anode circuits of lamp equipment can reach tens and even hundreds (in X-ray installations) of kilovolts (thousands of volts). Therefore, all high-voltage areas (including the common wire) must be isolated from the housing. Anyone who has placed their foot on the system unit and touched the battery knows this well. Electric current can be dangerous not only to humans and animals, but also to the device itself. This means breakdowns and short circuits. These phenomena not only damage radio components, but are also very fire hazardous. I came across some insulating structural elements that, as a result of the high voltage supply, were pierced and burned out to charcoal, and they did not burn out completely, but in a channel. Coal conducts current and thus creates a short circuit (hereinafter short circuit) to the housing. Moreover, it is not visible from the outside. Therefore, between the two wires soldered to the board there should be a distance of approximately 2mm per volt. If we are talking about deadly voltages, then the housing must be equipped with microswitches that automatically de-energize the device when the wall is removed from a dangerous area of ​​the structure. Structural elements that become very hot during operation (radiators, powerful semiconductor and vacuum devices, resistors with a power of over 2W) must be removed from the board (the best option) or at least raised above it. It is also not allowed to touch the housings of heating radio elements, except in cases where the second element is a temperature sensor of the first. Such elements are not allowed to be filled with epoxy resin or other compounds. Moreover, air flow must be ensured to areas with high power dissipation, and, if necessary, forced cooling (up to evaporative cooling). So. I've caught up with fear, now about work.

3. Ohm's and Kirchhoff's laws have been and will be the basis for the development of any electronic device.

3.1. Ohm's law for a circuit section

The current strength in a section of a circuit is directly proportional to the voltage applied to the section and inversely proportional to the resistance of the section. The operation of all limiting, quenching and ballast resistors is based on this principle.

This formula is good because “U” can mean both the voltage at the load and the voltage at the section of the circuit connected in series with the load. For example, we have a 12V/20W light bulb and a 17V source to which we need to connect this light bulb. We need a resistor that will lower 17V to 12.

Fig.1

So, we know that when elements are connected in series, the voltages across them may differ, but the current is always the same in any part of the circuit. Let's calculate the current consumed by the light bulb:

This means that the same current flows through the resistor. As voltage we take the voltage drop across the quenching resistor, because this is really the same voltage that acts on this resistor ( )

From the above example it is quite obvious that. Moreover, this applies not only to resistors, but also, for example, to speakers, if we calculate what voltage needs to be applied to a speaker with a given power and resistance so that it develops this power.

Before we move on to it, we need to clearly understand the physical meaning of internal and output resistance. Let's assume we have some source of EMF. So, the internal (output) resistance is an imaginary resistor connected in series with it.

Fig.2

Naturally, in fact, there are no such resistors in current sources, but generators have winding resistance, sockets have wiring resistance, batteries have electrolyte and electrode resistance, etc. When connecting a load, this resistance behaves exactly like a series-connected resistor.

Where: ε – EMF
I – current strength
R – load resistance
r – internal source resistance

It is clear from the formula that as the internal resistance increases, the power decreases due to a drawdown in the internal resistance. This can also be seen from Ohm’s law for a section of a chain.

3.3 Kirchhoff's rule we will be interested in only one thing: the sum of currents entering the circuit is equal to the current (sum of currents) leaving it. Those. whatever the load and no matter how many branches it consists of, the current strength in one of the supply wires will be equal to the current strength in the second wire. Actually, this conclusion is quite obvious if we are talking about a closed circuit.

Everything seems to be clear with the laws of current flow. Let's see how it looks in real hardware.

4. Filling

All PSUs are largely similar in design and element base. This is due to the fact that, by and large, they perform the same functions: voltage change (always), rectification (most often), stabilization (often), protection (often). Now let's look at ways to implement these functions.

4.1. Voltage change most often implemented using various transformers. This option is the most reliable and safe. There are also transformerless power supplies. They use the capacitance of a capacitor connected in series between the current source and the load to reduce the voltage. The output voltage of such power supplies depends entirely on the load current and its presence. Even with a short-term load shutdown, such power supplies fail. In addition, they can only lower the voltage. Therefore, I do not recommend such power supplies for powering REA. So, let's focus on transformers. Linear power supplies use transformers at 50Hz (industrial network frequency). A transformer consists of a core, a primary winding and several secondary windings. Alternating current entering the primary winding creates a magnetic flux in the core. This flow, like a magnet, induces an emf in the secondary windings. The voltage on the secondary windings is determined by the number of turns. The ratio of the number of turns (voltage) of the secondary winding to the number of turns (voltage) of the primary winding is called the transformation ratio (η). If η>1 the transformer is called a step-up transformer, otherwise – a step-down transformer. There are transformers with η=1. Such transformers do not change the voltage and serve only for galvanic isolation chains ( circuits are considered galvanically isolated if they do not have a direct common electrical contact. Although the currents flowing through them can act on each other. For example "Blue Tooth"or a light bulb and a solar battery brought to it or the rotor and stator of an electric motor or a neon lamp brought to the transmitter antenna). Therefore, there is no point in using them in power supply. Pulse transformers work on the same principle with the only difference being that they are not supplied with voltage directly from the outlet. First, it is converted into pulses of a higher frequency (usually 15-20 kHz) and these pulses are supplied to the primary winding of the transformer. The repetition rate of these pulses is called the pulse power supply conversion frequency. As the frequency increases, the inductive reactance of the coil increases, so the windings of pulse transformers contain fewer turns compared to linear ones. This makes them more compact and lighter. However, pulsed power supplies are characterized by a higher level of interference, worse thermal conditions and are more complex in circuit design, therefore less reliable.

4.2. Straightening involves the conversion of alternating (pulse) current into direct current. This process consists of decomposing positive and negative half-waves into their respective poles. There are quite a lot of schemes that allow you to do this. Let's look at those that are most often used.

4.2.1. Quarterbridge

Fig.3

The simplest circuit of a half-wave rectifier. It works as follows. The positive half-wave passes through the diode and charges C1. The negative half-wave is blocked by the diode and the circuit appears to be broken. In this case, the load is powered by discharging the capacitor. Obviously, to operate at 50Hz, capacitance C1 must be relatively large to ensure low ripple levels. Therefore, the circuit is used mainly in switching power supplies due to the higher operating frequency.

4.2.2 Half-bridge (Latour-Delon-Grenachere doubler)

Fig.4

The principle of operation is similar to a quarter bridge, only here they are connected in series. The positive half-wave passes through VD1 and charges C1. On the negative half-wave, VD1 closes and C1 begins to discharge, and the negative half-wave passes through VD2. Thus, a voltage appears between the cathode VD1 and the anode VD2, which is 2 times higher than the voltage of the secondary winding of the transformer (Fig. 4a). This principle can be used to build split BP. This is the name for power supply units that produce 2 voltages that are identical in magnitude but opposite in sign (Fig. 4b). However, we should not forget that these are 2 quarter-bridges connected in series and the capacitor capacities must be large enough (based on at least 1000 μF per 1A of current consumption).

4.2.3. Full bridge

The most common rectifier circuit has the best load characteristics with a minimum level of ripple and can be used in both unipolar (Fig. 5a) and split power supplies (Fig. 5b).

Fig.5

Figure 5c,d shows the operation of a bridge rectifier.

As already mentioned, different rectifier circuits are characterized by different values ​​of the ripple factor. The exact calculation of the rectifier contains cumbersome calculations and is rarely necessary in practice, so we will limit ourselves to an approximate calculation that can be performed using the table

where: U 2 – voltage of the secondary winding
I 2 – maximum permissible current of the secondary winding
U rev – Maximum permissible reverse voltage of diodes (kenotrons, thyristors, gastrons, ignitrons)
I pr.max – Maximum permissible forward current of diodes (kenotrons, thyristors, gastrons, ignitrons)
q 0 – output ripple factor
U 0 – Rectifier output voltage
I 0 – maximum load current

The capacity of the smoothing capacitor can be calculated using the formula

where: q – pulsation coefficient
m – phasing
f – pulsation frequency
R n – load resistance ()
R f – resistance of the filter resistor ( This is a formula for RC filters, but as a resistor you can take the output resistance of the rectifier [internal resistance of the transformer + impedance of the valves])

4.3. Filtration

Ripple interferes with the operation of the device, which is powered by the power supply. In addition, they make it impossible for stabilizers to operate due to the fact that in the intervals between half-waves (absolute sine wave) the voltage drops to almost zero. Let's look at some types of anti-aliasing filters.

4.3.1. Passive filters can be resistive-capacitive, inductive-capacitive and combined.

Fig.6

Resistive-capacitive filters (Fig. 6) are characterized by a relatively large voltage drop. This is due to the use of a resistor in them. Therefore, such filters are not suitable for working with currents greater than 500 mA due to high losses and power dissipation. The resistor is calculated as follows

where: U out – rectifier output voltage
U p – load supply voltage
I n – load current

Fig.7

Inductive-capacitive filters are characterized by a relatively high smoothing ability, but are inferior to others in terms of weight and size parameters. The basic idea of ​​an inductive-capacitive filter in the ratio of the reactances of its components , i.e. The filter must have a good quality factor. The filter itself is calculated using the following formula

Where: q – smoothing coefficient
m – phasing
f – frequency
- inductance of the choke
– capacitance of the capacitor.

In amateur conditions, instead of a choke, you can use the primary winding of a transformer (not the one from which everything is powered), and short-circuit the secondary.

4.3.2. Active filters are used in cases where passive filters are not suitable in terms of weight, size or temperature parameters. The fact is that, as already mentioned, the greater the load current, the greater the capacity of the smoothing capacitors. In practice, this results in the need to use bulky electrolytic capacitors. An active filter uses a transistor in an emitter follower circuit (a cascade with a common collector), so the signal at the emitter practically repeats the signal at the base (Fig. 8)

Fig.8

Circuit R1C1 is calculated as a resistive-capacitive filter, only the current in the base circuit is taken as the consumed current

However, as can be seen from the formula, the filter mode (including the smoothing coefficient) will depend on the current consumed, so it is better to fix it (Fig. 9)

Fig.9

The circuit operates under the condition that , in which the output voltage will be approximately 0.98U b due to a voltage drop in the repeater. We take R2 as the load resistance.

4.3.3 Noise filters

It must be said that radio interference can penetrate not only from the network into the device, but also from the device into the network. Therefore, both directions must be protected from interference. This is especially true for switching power supplies. As a rule, this comes down to connecting small capacitors (0.01 - 1.0 μF) in parallel with the circuit, as shown in Fig. 10.

Fig.10

As in the case of smoothing filters, noise filters operate under the condition that the capacitance of the capacitors at the frequency of interference is much less than the load resistance.

It is possible that the interference does not arise from a spontaneous change in current in the network or device, but from constant “vibration”. This applies, for example, to pulse power supplies or transmitters in telegraph mode. In this case, inductive isolation may also be required (Fig. 11).

Fig.11

However, capacitors must be selected so that resonance does not occur in the windings of chokes and transformers.

4.4. Stabilization

There are a number of devices, blocks and assemblies that can only operate from stabilized current sources. For example, generators in which the charging/discharging speed of capacitors in OS circuits and, consequently, the frequency and shape of the generated signal depend on the voltage. Therefore, in power supplies it is the output voltage that is most often stabilized, while the current is most often stabilized in chargers and UPSs, and even then not always. There are many ways to stabilize voltage, but in practice the most common are parametric stabilizers in one form or another. Let's take a look at their work.

4.4.1. The simplest stabilizer consists of a zener diode and a limiting resistor (Fig. 12).

Fig.12

The operating principle of such a stabilizer is based on changing the voltage drop in the limiting resistor depending on the current. Moreover, the whole scheme works provided that
Indeed, if the current flowing through the load exceeds the stabilization current, then the zener diode will not be able to provide the required drop according to the parallel connection rule

As can be seen from the formula, the smallest resistance has the greatest influence on the overall resistance of the circuit. The fact is that as the reverse voltage increases, its reverse current increases, which is why it keeps the voltage within certain limits (Ohm’s law for a section of a circuit).

4.4.2. Emitter follower

Then what to do if the consumed current must exceed the stabilization current of the zener diode?

Fig.13

Our good old emitter follower, a natural current amplifier, comes to the rescue. After all, what is a 2% voltage drop compared to a 1000% current increase!? Let's implement (Fig. 13)! The current increased approximately h 21 times compared to a zener diode stabilizer. At the emitter there will be approximately 0.98U B

4.4.3. Increasing stabilization voltage

The problem is solved, but what if you need to stabilize the voltage, say, 60V? In this case, you can connect the zener diodes in series. Thus, 60V is 6 zener diodes of 10V or 5 of 12V (Fig. 14).

Fig.14

As with any sequential circuit, the rule applies here

where: - total chain stabilization voltage
n – number of zener diodes in the circuit
- stabilization voltage of each zener diode.

Moreover, the stabilization voltage of zener diodes may differ, but the stabilization current should be the same.

4.4.4. Load current increase

This solves the issue with high voltage. If it is necessary to increase the load capacity (maximum permissible load current), cascades of emitter followers are used, forming composite transistor(Fig. 15) .

Fig.15

The parametric stabilizer and emitter follower are calculated in the same way as in the previous circuits. R2 is included in the circuit to drain potentials from the base of VT2 when VT1 is closed, however, the condition must be met, where Z VT 1 is the impedance of VT1 in the open state.

4.4.5. Output voltage adjustment

In some cases, it may be necessary to adjust or regulate the output voltage of the stabilizer (Fig. 16).

Fig.16

In this circuit, R2 is considered the load, and the current through the zener diode must exceed the current through R2. It should be remembered that if the voltage is reduced to “0”, then the full input voltage acts at the collector-base junction. If the declared mode of the transistor does not reach this voltage, then the transistor will inevitably fail. It should also be noted that large capacitors at the output of stabilizers with emitter followers are very dangerous. The fact is that in this case the transistor is sandwiched between two large capacitors. If you discharge the output capacitor, the smoothing capacitor will discharge through the transistor and the transistor will fail due to overcurrent. If you discharge the smoothing capacitor, the voltage at the emitter will become higher than at the collector, which will also inevitably lead to breakdown of the transistor.

4.4.6 Current stabilization used quite rarely. For example, battery chargers. The simplest and most reliable way to stabilize the current is to use a cascade with a common base and an LED as a stabilizing element.

Fig.17

The principle of operation of such a circuit is very simple: as the current through the load decreases, the voltage drop in the cascade decreases. Thus, the voltage across the load increases, and therefore (according to Ohm’s law) the current. And the current mode fixed by the LED does not allow the current to grow above the required limit, i.e. the gain does not allow such a current to be output at the output, because the transistor operates in saturation mode.

where: R1 – resistance of resistor R1
U pr.sv – forward voltage on the LED
U BE.us – voltage between emitter and base in saturation mode
I H – required load current.

where: R2 – resistance of resistor R2
E – stabilizer input voltage
U pr.sv – maximum forward voltage of the LED
I pr. max – maximum forward current of the LED.

Pulse power supplies will be discussed in the second part of the article.

The power supply is the most important component of any personal computer, on which the reliability and stability of your build depends. There is quite a large selection of products on the market from various manufacturers. Each of them has two or three lines or more, which also include a dozen models, which seriously confuses buyers. Many people do not pay due attention to this issue, which is why they often overpay for excess power and unnecessary bells and whistles. In this article we will figure out which power supply is best for your PC?

A power supply (hereinafter referred to as PSU) is a device that converts high voltage 220 V from an outlet into computer-friendly values ​​and is equipped with the necessary set of connectors for connecting components. It seems to be nothing complicated, but upon opening the catalog, the buyer is faced with a huge number of different models with a bunch of often incomprehensible characteristics. Before we talk about choosing specific models, let’s look at what characteristics are key and what you should pay attention to first.

Main parameters.

1. Form factor. In order for the power supply to fit into your case, you must decide on the form factors, based on from the parameters of the system unit case itself. The dimensions of the power supply in terms of width, height and depth depend on the form factor. Most come in the ATX form factor, for standard cases. In small system units of the microATX, FlexATX, desktops and others, smaller units are installed, such as SFX, Flex-ATX and TFX.

The required form factor is specified in the characteristics of the case, and it is by this that you need to navigate when choosing a power supply.

2. Power. The power determines what components you can install in your computer, and in what quantity.
It is important to know! The number on the power supply is the total power across all of its voltage lines. Since the main consumers of electricity in a computer are the central processor and video card, the main power line is 12 V, when there are also 3.3 V and 5 V to power some components of the motherboard, components in expansion slots, power drives and USB ports. The power consumption of any computer along the 3.3 and 5 V lines is insignificant, so when choosing a power supply for power, you should always look at the "characteristic" power on line 12 V", which ideally should be as close as possible to the total power.

3. Connectors for connecting components, the number and set of which determine whether you can, for example, power a multiprocessor configuration, connect a couple or more video cards, install a dozen hard drives, and so on.
The main connectors, except ATX 24 pin, are:

To power the processor, these are 4 pin or 8 pin connectors (the latter can be detachable and have a 4+4 pin entry).

To power the video card - 6 pin or 8 pin connectors (8 pin is most often collapsible and is designated 6+2 pin).

For connecting 15-pin SATA drives

Additional:

4pin MOLEX type for connecting older HDDs with an IDE interface, similar disk drives and various optional components such as rheobass, fans, etc.

4-pin Floppy - for connecting floppy drives. They are very rare these days, so such connectors most often come in the form of adapters with MOLEX.

Extra options

Additional characteristics are not as critical as the main ones in the question: “Will this power supply work with my PC?”, but they are also key when choosing, because affect the efficiency of the unit, its noise level and ease of connection.

1. Certificate 80 PLUS determines the efficiency of the power supply unit, its efficiency (efficiency factor). List of 80 PLUS certificates:

They can be divided into the basic 80 PLUS, on the far left (white), and the colored 80 PLUS, ranging from Bronze to the top Titanium.
What is efficiency? Let's say we are dealing with a unit whose efficiency is 80% at maximum load. This means that at maximum power the power supply will draw 20% more energy from the outlet, and all this energy will be converted into heat.
Remember one simple rule: the higher the 80 PLUS certificate in the hierarchy, the higher the efficiency, which means it will consume less unnecessary electricity, heat less, and, often, make less noise.
In order to achieve the best efficiency indicators and obtain the 80 PLUS “color” certificate, especially at the highest level, manufacturers use their entire arsenal of technologies, the most efficient circuitry and semiconductor components with the lowest possible losses. Therefore, the 80 PLUS icon on the case also speaks of the high reliability and durability of the power supply, as well as a serious approach to creating the product as a whole.

2. Type of cooling system. The low level of heat generation of power supplies with high efficiency allows the use of silent cooling systems. These are passive (where there is no fan at all), or semi-passive systems, in which the fan does not rotate at low powers, and starts working when the power supply becomes “hot” under load.

When selecting a power supply, you should pay attention to for the length of the cables, the main ATX24 pin and the CPU power cable when installed in a case with a bottom-mounted power supply.

For optimal installation of power wires behind the rear wall, they must be at least 60-65 cm long, depending on the size of the case. Be sure to take this point into account so you don’t have to bother with extension cords later.
You need to pay attention to the number of MOLEX only if you are looking for a replacement for your old and antediluvian system unit with IDE drives and drives, and even in significant quantities, because even the simplest power supplies have at least a couple of old MOLEX, and in more expensive models There are dozens of them in general.

I hope this small guide to the DNS company catalog will help you with such a complex issue at the initial stage of your acquaintance with power supplies. Enjoy the shopping!

The power supply is designed to supply electrical current to all computer components. It must be powerful enough and have a small margin for the computer to work stably. In addition, the power supply must be of high quality, since the service life of all computer components greatly depends on it. By saving $10-20 on the purchase of a high-quality power supply, you risk losing a system unit worth $200-1000.

The power of the power supply is selected based on the power of the computer, which mainly depends on the power consumption of the processor and video card. It is also necessary that the power supply has at least 80 Plus Standard certification. The optimal price/quality ratio are Chieftec, Zalman and Thermaltake power supplies.

For an office computer (documents, Internet), a 400 W power supply is sufficient; take the most inexpensive Chieftec or Zalman, you won’t go wrong.
Power supply Zalman LE II-ZM400

For a multimedia computer (movies, simple games) and an entry-level gaming computer (Core i3 or Ryzen 3 + GTX 1050 Ti), the most inexpensive 500-550 W power supply from the same Chieftec or Zalman will be suitable; it will have a reserve in case of installing more powerful video card.
Chieftec GPE-500S power supply

For a mid-class gaming PC (Core i5 or Ryzen 5 + GTX 1060/1070 or RTX 2060), a 600-650 W power supply from Chieftec is suitable, if there is an 80 Plus Bronze certificate, then good.
Chieftec GPE-600S power supply

For a powerful gaming or professional computer (Core i7 or Ryzen 7 + GTX 1080 or RTX 2070/2080), it is better to take a 650-700 W power supply from Chieftec or Thermaltake with an 80 Plus Bronze or Gold certificate.
Chieftec CPS-650S power supply

2. Power supply or case with power supply?

If you are assembling a professional or powerful gaming computer, then it is recommended to select a power supply separately. If we are talking about an office or regular home computer, then you can save money and purchase a good case complete with a power supply, which will be discussed.

3. What is the difference between a good power supply and a bad one?

The cheapest power supplies ($20-30) by definition cannot be good, since in this case manufacturers save on everything possible. Such power supplies have bad heatsinks and a lot of unsoldered elements and jumpers on the board.

At these places there should be capacitors and chokes designed to smooth out voltage ripples. It is because of these ripples that the motherboard, video card, hard drive and other computer components fail prematurely. In addition, such power supplies often have small radiators, which cause overheating and failure of the power supply itself.

A high-quality power supply has a minimum of unsoldered elements and larger radiators, which can be seen from the installation density.

4. Power supply manufacturers

Some of the best power supplies are made by SeaSonic, but they are also the most expensive.

Well-known enthusiast brands Corsair and Zalman recently expanded their range of power supplies. But their most budget models have rather weak filling.

AeroCool power supplies are among the best in terms of price/quality ratio. The well-established cooler manufacturer DeepCool is closely joining them. If you don't want to overpay for an expensive brand, but still get a high-quality power supply, pay attention to these brands.

FSP produces power supplies under different brands. But I would not recommend cheap power supplies under their own brand; they often have short wires and few connectors. Top-end FSP power supplies are not bad, but they are no longer cheaper than famous brands.

Of those brands that are known in narrower circles, we can note the very high-quality and expensive be quiet!, the powerful and reliable Enermax, Fractal Design, the slightly cheaper but high-quality Cougar and the good but inexpensive HIPER as a budget option.

5. Power supply

Power is the main characteristic of a power supply. The power of the power supply is calculated as the sum of the power of all computer components + 30% (for peak loads).

For an office computer, a minimum power supply of 400 watts is sufficient. For a multimedia computer (movies, simple games), it is better to take a 500-550 Watt power supply, in case you later want to install a video card. For a gaming computer with one video card, it is advisable to install a power supply with a power of 600-650 Watts. A powerful gaming PC with multiple graphics cards may require a power supply of 750 watts or more.

5.1. Power supply power calculation

• Processor 25-220 Watt (check on the seller’s or manufacturer’s website)
• Video card 50-300 Watt (check on the seller’s or manufacturer’s website)
• Entry class motherboard 50 Watt, mid class 75 Watt, high class 100 Watt
• Hard drive 12 Watt
• SSD 5 Watt
• DVD drive 35 Watt
• Memory module 3 Watt
• Fan 6 Watt

Don’t forget to add 30% to the sum of the powers of all components, this will protect you from unpleasant situations.

5.2. Program for calculating power supply power

To more conveniently calculate the power of a power supply, there is an excellent program “Power Supply Calculator”. It also allows you to calculate the required power of an uninterruptible power supply (UPS or UPS).

The program works on all versions of Windows with Microsoft .NET Framework version 3.5 or higher installed, which is usually already installed for most users. You can download the “Power Supply Calculator” program and if you need the “Microsoft .NET Framework” at the end of the article in the “” section.

6.ATX standard

Modern power supplies have the ATX12V standard. This standard can have several versions. Modern power supplies are manufactured according to ATX12V 2.3, 2.31, 2.4 standards, which are recommended for purchase.

7. Power correction

Modern power supplies have a power correction function (PFC), which allows them to consume less energy and heat less. There are passive (PPFC) and active (APFC) power correction circuits. The efficiency of power supplies with passive power correction reaches 70-75%, with active power correction - 80-95%. I recommend purchasing power supplies with active power correction (APFC).

8. Certificate 80 PLUS

A high-quality power supply must have an 80 PLUS certificate. These certificates come in different levels.

• Certified, Standard – entry-level power supplies
• Bronze, Silver – mid-class power supplies
• Gold – high-end power supplies
• Platinum, Titanium – top power supplies

The higher the certificate level, the higher the quality of voltage stabilization and other parameters of the power supply. For a mid-range office, multimedia or gaming computer, a regular certificate is sufficient. For a powerful gaming or professional computer, it is advisable to take a power supply with a bronze or silver certificate. For a computer with several powerful video cards - gold or platinum.

9. Fan size

Some power supplies still come with an 80mm fan.

A modern power supply should have a 120 or 140 mm fan.

10. Power supply connectors

	ATX (24-pin) - motherboard power connector. All power supplies have 1 such connector.
	CPU (4-pin) - processor power connector. All power supplies have 1 or 2 of these connectors. Some motherboards have 2 processor power connectors, but can also operate from one.
	SATA (15-pin) - power connector for hard drives and optical drives. It is advisable that the power supply have several separate cables with such connectors, since connecting a hard drive and an optical drive with one cable will be problematic. Since one cable can have 2-3 connectors, the power supply must have 4-6 such connectors.
	PCI-E (6+2-pin) - video card power connector. Powerful video cards require 2 of these connectors. To install two video cards, you need 4 of these connectors.
	Molex (4-pin) - power connector for older hard drives, optical drives and some other devices. In principle, it is not required if you do not have such devices, but it is still present in many power supplies. Sometimes this connector can supply voltage to the case backlight, fans, and expansion cards.
	Floppy (4-pin) - drive power connector. Very outdated, but can still be found in power supplies. Sometimes some controllers (adapters) are powered by it.

Check the configuration of power supply connectors on the seller's or manufacturer's website.

11. Modular power supplies

In modular power supplies, excess cables can be unfastened and they will not get in the way in the case. This is convenient, but such power supplies are somewhat more expensive.

12. Setting up filters in the online store

1. Go to the “Power Supplies” section on the seller’s website.
2. Select recommended manufacturers.
3. Select the required power.
4. Set other parameters that are important to you: standards, certificates, connectors.
5. Look through the items sequentially, starting with the cheapest ones.
6. If necessary, check the connector configuration and other missing parameters on the manufacturer’s website or another online store.
7. Buy the first model that meets all parameters.

Thus, you will receive the best price/quality ratio power supply that meets your requirements at the lowest possible cost.

13. Links

Corsair CX650M 650W power supply
Thermaltake Smart Pro RGB Bronze 650W power supply
Power supply Zalman ZM600-GVM 600W