BP power supply. This type of design involves converting current in three stages. Types of power supplies and their differences

An important element in a computer is the power supply. It is thanks to it that energy is provided to all components that are included in system unit. You should purchase only a high-quality power supply for your PC. In this case, it will ensure a stable supply of energy to all computer components, and in addition, it will last a long time.

If the owner saved money and purchased an inexpensive power supply, this will lead to unstable operation of the PC when using it. The worst thing that can happen is motherboard and the processor will fail. Therefore, you should purchase only high-quality components for your computer.

What is the power supply for?

The power supply is a power source that supplies energy to all components that make up the system unit. It is the power supply that largely determines how durable and stable the system will be during use. In addition, thanks to him:

loss of information from the computer is eliminated;
energy surges are prevented.

Features of the system unit is that its components cannot receive energy directly from the outlet. That is why every PC uses a power supply. It is installed for several reasons:

V electrical network Alternating current predominates, while computer components require direct current. Current conversion is provided by the power supply. This device changes alternating current to direct current, while the components of the “machine” receive energy at the required voltage;
Each device that is part of the computer requires a certain voltage. Here again the power supply helps, which supplies the required current to the video card, processor and other computer components.

How to choose a power supply for a computer?

When a person purchases a computer for himself, the main attention is paid to the processor, video card and HDD. Preference is given to powerful, and therefore expensive, components. This leads to a situation where there is no money left for the BP, which is usually selected at the end. That's why buy the simplest model.

If you don't have enough money for good model and you purchased a component with low power, then expensive card, which you installed in your computer, a low-power power supply simply may not be able to handle it. Therefore, to ensure stable operation of your computer, you should focus on the power of the components installed in your PC. When selecting a device, you should pay attention to the many characteristics of this component. The most significant ones will be listed below.

Power

The main point when choosing a good power supply model for a computer is power. Here you should start from your personal needs, as well as focus on the power of the components installed in the computer. If you have a PC that is used to solve office tasks, then in this case a model with a power of 300-400 W will be quite sufficient. This component can be easily found in any store. Similar models are offered inexpensively in stores, so purchasing the right device will not cost you a lot of money.

If you are selecting a power supply for gaming computer, then you will have to seriously spend money. It would be a good idea to purchase a device in addition to the power supply. uninterruptible power supply. To calculate the power of a device that is suitable for your “machine”, you can use the PSU power calculator. After making calculations, you can find out which power supply unit will be the best choice for you.

Efficiency

This characteristic is very important, although many are new to it. special attention don't pay attention. You should know that the efficiency of the power supply will largely depend on device lifespan, as well as energy consumption. The thing is that during operation it takes in a certain amount of energy, but gives out much less. This happens because some of the energy is lost. But this problem was solved by manufacturers who divided all power supply models into classes.

Expensive devices are more efficient, and cheap components lose energy, so spending little money on the purchase of a model, the owner will have to come to terms with this disadvantage. The classification of these devices by efficiency level is carried out using Bronze, Silver, Gold, Platinum stickers.

Connectors

To choose the right component for a stable power supply to your PC, you should pay attention to connectors. In this case, there cannot be any specific recommendations, especially if you have already selected the main components of your system unit. When selecting a set of connectors, you should start from the rest of the hardware that will be present in your computer.

If, when assembling a computer, you decide to first choose a power supply, then you should consider latest models who have modern ports. However, when selecting a model, the buyer should focus on his financial opportunities. If speak about standard set connectors for the power supply, then it includes the following:

24-pin motherboard connector;
processor power supply, 4-pin connector;
15-pin SATA for power optical drives and hard drives;
6-pin connector for powering the video card.

Please note that if you have old system, then when purchasing a new power supply, the set of connectors may not be suitable. And besides, a rather serious problem is to find a component to power outdated components.

Protection

Failures that arose during the operation of the power supply forced manufacturers improve this component. As a result, these devices acquired Various types protection from adverse influences. Today, the list of features that protect components during operation includes various modes. Before purchasing, you should pay attention to the box and carefully read the instructions, in which you can find what the model is protected from: power surges, failure, etc. The more protective functions the selected model has, the more reliable and convenient it will be in operation.

Noise and cooling

These two characteristics are closely interrelated. If the device has low power, it does not heat up much, so its cooling system is represented only by a small fan.

When choosing a power supply for gaming computer, then there is no doubt that in terms of heating it can be compared with a conventional stove. The only exception is expensive models power supplies from well-known companies. Using powerful device serious noise arises, which comes not only from it, but also from other powerful components present in the system unit.

Modern manufacturers offer currently models of power supplies that are equipped with fans that vary in size. The most common cooler option is 120mm. The power supplies are also equipped with 80 and 140 mm fans. The first option is different loud noise. During operation, it provides poor cooling. The second's main drawback is the difficulty of replacing the fan when the cooler fails.

How much does a good power supply cost?

It’s impossible to buy a quality power supply today big problem. IN retail networks, offering computers and components, you can choose suitable model. Depending on the manufacturer, the price of this component will vary. Along with the manufacturer, Power matters too.

The most inexpensive component for an office PC costs 1,500-3,000 rubles. If you need an element for a gaming PC, then the desired model should be selected from devices in price category from 7,000 rubles.

Power supply power calculation

In order for the power supply to work reliably and provide comfortable work at the computer, it is necessary to calculate in advance when selecting this component optimal power. In order to determine it correctly, on the Internet at specialized resources You can find a calculator to calculate the power of the power supply. However, this option is not optimal for everyone. Many people use simple mathematics to determine required characteristics. The method itself is to calculate the total energy consumption of the components that are present in the system unit.

By adding up all the values, you can get the power of the power supply, which will provide stable work"cars". When choosing a power supply, you should know that the maximum power of the selected device must be greater than the total power consumption of all components included in the system.

Usually power consumption of components, present in the PC, is as follows:

CPU. It consumes 50-120 W. It should be understood that the more powerful the chip is in your computer, the greater the energy consumption will be;
. It consumes 15-30 W. Its energy consumption increases with increasing functions;
video card. It requires 60-300 W;
RAM. The energy consumption of this component is 15-60 W.
HDD. It consumes the same amount of energy as RAM. However, here everything depends on its characteristics, as well as the load placed on it.
CD-DVD drive. This component of the system unit consumes 10-25 W. It all depends on maximum speed disk rotation, as well as operating mode;
sound card. This element of the system unit requires energy in the amount of 5-50 W;
fans. One cooler requires 1-2 W to operate. Here everything depends on the rotation speed, as well as the number of fans and their dimensions.

Conclusion

Life modern man impossible without a PC. It is used for work and entertainment. Stable computer operation depends on the power supply. This component provides power supply to all elements of the system unit. In order for the “machine” to serve for a long time, you need a high-quality power supply from famous company. Using it as part of a computer, surprises will be excluded when using the machine in the form of unexpected malfunctions. In order not to make a mistake with your choice, it is worth learning about the best power supplies for computers.

What is the price good block food? It all depends on what kind of PC you have. For office computer good choice there will be a component priced at 1,500 - 3,000 rubles, and for a gaming one you should look for a model in the price category from 7,000 rubles. Having picked up reliable device, your computer will work stably, and its components will delight you long term services.

Many users who are trying to understand the structure of their PC do not understand what a power supply is in a computer. Meanwhile, this is one of the most important elements in the system, without which not a single component will work. Let's figure out what power supplies are, define their structure, types, pros and cons.

Definition

What is a power supply in a computer? In short, this is a device for converting network AC voltage to constant power to power all components in the system unit. In particular, the power supply supplies voltage to the components: video card, RAM, hard drive, network card, processor, connected peripherals. If all these components are connected directly to a 220 V network, they will simply burn out. Components for operation require a voltage of 12 or 24 V (mostly), and the task of the power supply is to provide the required voltage.

There is also another task of this element - to protect computer components from possible voltage surges. Essentially, this is a voltage changer that looks like a small black box with a fan. It is installed in the system unit, and it is where the network cable goes.

Required voltage

The computer's power supply is supplied from a 220 V network. different countries The current voltage and its frequency in the network may vary. For example, in Russia and in most European countries The mains voltage is 220/230 V at a frequency of 50 Hz. However, in the USA the mains voltage is 120 V at 60 Hz. Australia is also different in this regard - there the voltage is 240 V/50 Hz. Consequently, when creating a power supply, the network parameters of the country to which deliveries are planned are taken into account. That is, if you bring a power supply purchased in the USA to Russia, it most likely will not work.

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

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

Computer PSU power

Today there are many different units that are capable of delivering power over a huge range. IN modern laptops power can vary in the range of 25-100 W. Concerning personal computers, then here, depending on the energy consumption of the components, you can use a 2000 W power supply.

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

However, today on store shelves there are mainly 400-500 W devices available. The power of such components is quite sufficient to provide power standard computer with good hardware. But they are not capable of ensuring stable operation of a powerful gaming computer.

Types and differences of BP

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

Transformer

This is the most common type and the one sold most often. In the majority modern systems A similar computer power supply device, which is represented by the following elements, is practically not used:

Transformer.
Rectifier.
Network filter.

One of these blocks is shown in the photo below.

Principle of operation

The operating principle of such a device is relatively simple: through the primary winding, the transformer receives the mains voltage. Then, with the help of a rectifier, the alternating multidirectional current is converted into direct and unidirectional current. In this case, different rectifiers can be used: single- or full-wave. In any case, diode bridges are used, which consist of:

Two diodes - in the first type.
Four diodes - in the second type.

The use of two elements in a rectifier is typical for BCs with double voltage or in three-phase devices.

A network filter in a computer's power supply device is ordinary capacitor With large capacity. It smoothes out current ripples, which is why a relatively clean and uniform current is supplied to the components.

Also, instead of conventional transformers, automatic devices can be used inside such units.

Operation of transformer power supplies

To understand in more detail what a power supply is in a computer and how they work, you need to have at least basic knowledge laws of electrical engineering. The dimensions of transformer-type power supplies directly depend on the dimensions of the transformers used inside. The dimensions of the devices are calculated using the formula:

In this formula:

N is the number of turns per 1 V voltage;
f - frequency of current (alternating);
B - induction generated in the magnetic circuit magnetic field;
S is the cross-sectional area of the magnetic circuit.

Therefore, the more turns and cross-section of the wire, the larger the transformer will be. This entails an increase in the dimensions of the block itself. However, if the cross-section of the wire is reduced, then the number of turns (N) will have to be increased, which will not be possible in compact transformers. If the transformer is low-power, then many turns with a small cross-section will not affect the operation of the power supply itself, since the current strength in such devices will be low. However, as power increases, the current will increase, resulting in thermal power dissipation.

Consequently, 50 Hz transformer power supplies can only be large and heavy. Similar devices impractical to use in modern computers due to their weight and dimensions, as well as low efficiency.

However, there is also positive sides: reliability and simplicity, ease of repair (all elements are easy to replace in case of breakdown), absence of radio interference.

Switching power supplies

These devices use other design solutions to increase the frequency of the current. Below is a classic power supply of this type.

A similar power supply works as follows:

Alternating current from the network enters the device, is rectified and becomes constant.
Direct current is converted into frequency pulses.
These pulses are sent to the transformer. If galvanic isolation is provided, then rectangular pulses are supplied to the output low-pass filter.

Note that there are fundamental differences between these two types of power supply. In particular, pulsed ones have the following features:

As the current frequency increases, the efficiency of the transformer increases.
The requirements for the core cross-section are minimal.
The ability to create compact and lightweight power supplies by installing efficient and small transformers.
Application of negative feedback makes it possible to stabilize output voltage, which will positively affect the stability of all components and the system as a whole.

Advantages of switching power supplies

High efficiency, which reaches 92-98%.
Light weight and dimensions.
Reliability.
Ability to work in a wide range frequency range. The same pulse unit can operate in different countries of the world.
Short circuit protection.
Low cost.

Poor maintainability. If normal transformer block easy to repair by replacing almost any element on the board, then with pulse device everything is more complicated. Therefore, remaking a pulse-type computer power supply is considered challenging task. Workshop repairs can be expensive.
Emission of high frequency interference.

Now we have found out what a power supply is in a computer and how they work. On this moment Mostly pulsed devices are sold on the market, while transformer devices are practically absent.

How to check the computer's power supply?

If the computer does not turn on, then the problem may lie in the power supply. To check the device we need a multimeter. So, before you check the computer’s power supply for functionality, you need to disconnect all components and the power supply itself. Then we take a regular paper clip, straighten it into a U shape. Take a 20/24 pin connector (the largest) and use our paper clip to close the black and green contacts. Considering that your fingers will touch metal, you need to make sure that the power supply is unplugged from the outlet.

Now lower the paperclip and plug the power supply into the outlet. If the fan starts to rotate when the device is turned on, it means that it is working.

Now you need to measure the voltage at the connectors. Depending on the power supply model, the voltage at the connectors may vary slightly. Therefore, you need to find information in the instructions (or on the Internet) about what voltage parameters should be on different connectors and measure them with a multimeter. If the parameters differ from normal, it means that there is something wrong with the power supply.

power unit is a device that is used to create the voltage needed to operate a computer from the voltage at home. In Russia, the power supply (hereinafter simply PSU) converts the variable electricity home electrical network with a voltage of 220 V and a frequency of 50 Hz at a given D.C.. Home electrical standards vary from country to country. In the USA, for example, alternating current with a voltage of 120 V and a frequency of 60 Hz is supplied to the homes of ordinary residents.

To calculate the conductor resistance, you can use the conductor resistance calculator.

Types of power supplies and their differences.

There are two main type of power supply: transformer and pulse. Their devices and differences, as well as advantages and disadvantages, will be discussed below.

Transformer power supply and its device.

This type of power supply is classic and, at the same time, simplest. Below is its diagram with a two-pole rectifier:

The most important element of this type of power supply is a step-down transformer (instead of which an autotransformer can be used). The primary outline of this element is precisely designed for incoming mains voltage. Another important detail of such a power supply is the rectifier. It performs the function of converting alternating voltage into unidirectional and pulsating direct voltage. In the vast majority of cases, a half-wave or full-wave rectifier is used. The first consists of one diode, and the last of four diodes that form diode bridge. In some cases, other circuits of this element can be used, for example, in three-phase rectifiers or rectifiers with double voltage. The last important part of the transformer power supply is the filter, which smoothes out the ripples created by the rectifier. Typically this part is represented by a capacitor with a large capacity.

Transformer dimensions. The following formula is derived from the basic laws of electrical engineering:

(1/n)~fSB

In this formula, n is the number of turns per 1 volt, f is the frequency alternating current, S is the cross-sectional area of the magnetic core, B is the magnetic field induction in the magnetic core.

The formula does not describe the instantaneous value, but the amplitude B!

In practice, the magnitude of the magnetic field induction (B) is limited by hysteresis in the core. This leads to overheating of the transformer and losses due to magnetization reversal.

If the alternating current frequency (f) is 50 Hz, then only S and n remain variable parameters when designing a transformer. In practice, the following heuristic is used: n (in a value from 55 to 70) / S in cm^2

An increase in the cross-sectional area of the magnetic core (S) leads to an increase in the dimensions and weight of the transformer. If you lower the value of S, this increases the value of n, which in small transformers leads to a decrease in the cross-section of the wire (otherwise the winding will not fit on the core)

As the value of n increases and the cross-sectional area decreases, significant increase active resistance windings In low power transformers this can be ignored because the current passing through the winding is small. However, as the power increases, the current passing through the winding increases, and this, together with the high winding resistance, leads to the dissipation of significant thermal power.

All of the above leads to the fact that the standard frequency of 50 Hz transformer high power(needed to power the computer) can only be designed as a device with large weight and dimensions.

In modern power supplies they follow a different path - increasing the value of f, which is achieved using switching power supplies. Such power supplies are much lighter and to a large extent smaller in size than transformer ones. Also, switching power supplies are not so demanding on input voltage and frequency.

Advantages of transformer power supplies

Simplicity of the product;
Reliability of the design;
Availability of elements;
Absence generated radio interference.

Disadvantages of transformer power supplies

Large weight and dimensions, which increase with power;
Metal consumption;
The need for a compromise between efficiency reduction and output voltage stability.

Switching power supply and its device.

Below is a diagram of a single-pin pulse power supply (this diagram is the simplest):

Actually Power supplies pulse type are inverter system. In this power supply unit, the electrical energy entering it is first rectified (i.e., a direct electric current is formed), and then converted into rectangular pulses certain frequency and duty cycle. After this, these rectangular pulses are sent to the transformer (if the power supply design includes galvanic isolation) or directly to the output low-pass filter (if there is no galvanic isolation). Due to the fact that in pulsed power supplies the efficiency of the transformer increases with increasing frequency and the requirement for the core cross-section is significantly reduced, they can use much more small-sized transformers than in classical solutions.

In most cases, the core of a pulse type transformer can be made of ferrimagnetic materials, in contrast to low-frequency transformers that use electrical steel.

Voltage stabilization in switching power supplies provided through negative feedback. It allows you to maintain the output voltage at a relatively constant level. Such a connection can be constructed different ways. If there is galvanic isolation in the power supply design, the most often used method is to use communication through one of the output windings of the transformer or the optocoupler method. The duty cycle at the output of the PWM controller depends on the feedback signal, which, in turn, depends on the output voltage. In the event that decoupling is not provided in the power supply, a conventional resistive voltage divider is used. Thereby impulse blocks power supplies can maintain stable output voltage.

Advantages of switching power supplies.

Much less weight and dimensions (this is achieved due to the fact that when the frequency increases, transformers with smaller dimensions can be used with the same power. Most linear stabilizers are made mostly from powerful low-frequency power transformers and radiators that operate in linear mode;
Much more high efficiency(up to 98%). Such a high ratio useful action is achieved due to the fact that most of the time the key elements are in a stable state (and losses occur during switching on/off of the key elements);
Lower cost (this advantage was achieved thanks to the widespread release of a unified element base and development of high-power transistors);
Reliability on par with linear stabilizers;
Large range of input frequency and voltage electrical energy. Thanks to this, the same power supply can be used in various countries peace with various standards home electrical network;
Availability of protection against unforeseen situations (short circuit).

Disadvantages of switching power supplies

Difficulty in repairing the power supply due to the fact that most of the circuit operates in the absence of galvanic isolation from the electrical network
It is a source of high-frequency interference. This drawback comes from the very principle of operation of switching power supplies. Because of him power supply manufacturers it is necessary to take noise reduction measures, which, in most cases, cannot completely eliminate this problem
The harmonic effect is a multiple of three (with power factor correctors and filters this disadvantage irrelevant)

Secondary power supply- a device that converts the electricity parameters of the main power supply source (for example, an industrial network) into electricity with the parameters necessary for the operation of auxiliary devices.

The power supply can be integrated into general scheme(usually in simple devices; or when even a slight voltage drop on the supply wires is unacceptable - for example, the computer motherboard has built-in voltage converters to power the processor), made in the form of a module (power supply, power rack, etc.), or even located in a separate room (power shop).

Secondary power supply tasks

Ensuring power transmission- the power source must ensure the transmission of the given power with minimal losses and compliance given characteristics at the exit without harm to yourself. Usually the power of the power source is taken with some reserve.
Voltage waveform conversion- conversion of alternating voltage into direct voltage, and vice versa, as well as frequency conversion, formation of voltage pulses, etc. Most often, it is necessary to convert alternating voltage of industrial frequency into direct voltage.
Voltage value conversion- both increase and decrease. Often a set of several voltages of different values is needed to power different circuits.
Stabilization- voltage, current and other parameters at the output of the power source must lie within certain limits, depending on its purpose when influenced large quantity destabilizing factors: changes in input voltage, load current, and so on. Most often, it is necessary to stabilize the voltage at the load, but sometimes (for example, to charge batteries) current stabilization is necessary.
Protection- the voltage or load current in the event of a malfunction (for example, a short circuit) of any circuits may exceed permissible limits and damage the electrical appliance or the power source itself. Also, in many cases, protection against the passage of current along the wrong path is required: for example, the passage of current through the ground when touched by a person or foreign object to live parts.
Galvanic isolation of circuits- one of the measures to protect against current flow along the wrong path.
Adjustment- during operation it may be necessary to change any parameters to ensure proper operation electrical appliance.
Control- may include adjustment, turning on/off any circuits, or the power source as a whole. It can be either direct (using controls on the device body), or remote, as well as software (ensuring on/off, adjustment in specified time or with the occurrence of any events).
Control- display of parameters at the input and output of the power source, switching circuits on/off, protection activation. It can also be direct or remote.

Most often, secondary power supplies are faced with the task of converting electricity from an alternating current network of industrial frequency (for example, in Russia - 240 V 50 Hz, in the USA - 120 V 60 Hz).

The two most typical designs are transformer and switching mode power supplies.

Transformer

Linear power supply

The classic power supply is a transformer power supply. IN general case it consists of a step-down transformer or autotransformer, whose primary winding is designed for mains voltage. Then a rectifier is installed that converts the alternating voltage into direct voltage (pulsating unidirectional). In most cases, the rectifier consists of one diode (half-wave rectifier) or four diodes forming a diode bridge (full-wave rectifier). Other circuits are sometimes used, such as in voltage-doubling rectifiers. After the rectifier, a filter is installed to smooth out oscillations (pulsations). Usually it is simply a high-capacity capacitor.

Also, filters for high-frequency interference, surges (varistors), short-circuit protection (short circuit), voltage and current stabilizers can be installed in the circuit.

Transformer dimensions

E e f f 1 = S 33...70 , (\displaystyle E_(eff1)=(\frac (S)(33...70)),)

Here S (\displaystyle S) expressed in cm 2, E e f f 1 (\displaystyle E_(eff1))- in volts. Smaller denominator values are chosen for low-power transformers, larger ones for high-power ones.

Another way to increase the power of a transformer is to increase the operating frequency. Approximately, we can assume that for a given transformer size, its power is directly proportional to the operating frequency. Therefore, an increase in frequency in k (\displaystyle k) times with constant power allows you to reduce the size of the transformer by ∼ k (\displaystyle \sim (\sqrt (k))) times (the cross-sectional area of the magnetic circuit decreases by ∼ k (\displaystyle \sim k) times), or, accordingly, its mass in ∼ k 3 / 2 (\displaystyle \sim (\sqrt[(3/2)](k))) once.

In particular, including these considerations, a frequency of 400 Hz with a voltage of 115 V is usually used in on-board power networks of aircraft and ships.

But increasing the frequency worsens magnetic properties magnetic cores, mainly due to an increase in hysteresis losses, therefore, at operating frequencies above a few kHz, ferrodielectric magnetic cores of transformers are used, for example, ferrite or made of carbonyl iron.

Modern sources of secondary power supply of various household appliances, computers, printers, etc. are now almost entirely carried out according to circuits and have almost completely replaced classical transformers. In such sources, the galvanic separation of the powered circuit and the supply network, obtaining a set of the necessary secondary voltages, is carried out using high-frequency transformers with ferrite cores. The source of high-frequency voltage is pulsed switching circuits with semiconductor switches, usually transistor ones. The use of such devices, often called inverters, makes it possible to significantly reduce the weight and dimensions of the device, and also, additionally, to improve the quality and reliability of the power supply, since pulsed sources are less critical to the quality of the power supply in the primary network - they are less sensitive to surges and dips in the mains voltage, changes in its frequency.

Advantages and disadvantages

Advantages of transformer power supplies. Disadvantages of transformer power supplies.

Large weight and dimensions, proportional to power.
Metal consumption.
Trade-off between efficiency reduction and output voltage stability: to ensure stable voltage a stabilizer is required, which introduces additional losses.

Switching power supply

Transformer power supplies

The classic power supply is a transformer power supply. In general, it consists of a step-down transformer or autotransformer, whose primary winding is designed for mains voltage. Then a rectifier is installed that converts the alternating voltage into direct voltage (pulsating unidirectional). In most cases, the rectifier consists of one diode (half-wave rectifier) or four diodes forming a diode bridge (full-wave rectifier). Other circuits are sometimes used, such as in voltage-doubling rectifiers. After the rectifier, a filter is installed to smooth out oscillations (pulsations). Usually it is simply a large capacitor.

Also, filters for high-frequency interference, surges, short-circuit protection, voltage and current stabilizers can be installed in the circuit.

Transformer dimensions

There is a formula that can be easily derived from the basic laws of electrical engineering (and even Maxwell’s equations):

(1/n)~f*S*B

where n is the number of turns per 1 volt (on the left side of the formula is the EMF of one turn, which is the derivative of the magnetic flux according to Maxwell’s equation, the flux is something in the form sin (f * t), f is taken out of the bracket in the derivative), f - frequency of alternating voltage, S - cross-sectional area of the magnetic circuit, B - magnetic field induction in it. The formula describes the amplitude of B, not the instantaneous value.

The value of B in practice is limited from above by the occurrence of hysteresis in the core, which leads to losses due to magnetization reversal and overheating of the transformer.

If we assume that f is the mains frequency (50 Hz), then the only two parameters available for selection when designing a transformer are S and n. In practice, the heuristic n = (from 55 to 70) / S in cm^2 is accepted.

An increase in S means an increase in the dimensions and weight of the transformer. If you follow the path of reducing S, then this means increasing n, which in a small transformer means reducing the cross-section of the wire (otherwise the winding will not fit on the core).

An increase in n and a decrease in cross-section means a strong increase in the active resistance of the winding. In low-power transformers, where the current through the winding is small, this can be neglected, but with increasing power, the current through the winding increases and, with high winding resistance, dissipates significant thermal power on it, which is unacceptable.

The considerations listed above lead to the fact that at a frequency of 50 Hz, a high-power transformer (from tens of watts) can only be successfully implemented as a device of large size and weight (by increasing S and the wire cross-section with decreasing n).

Therefore, in modern power supplies they follow a different path, namely the path of increasing f, i.e. transition to switching power supplies. Such power supplies are several times lighter (and the bulk of the weight falls on the shielding cage) and are significantly smaller in size than classic ones. In addition, they are not demanding on input voltage and frequency.

Advantages of transformer power supplies

Simplicity of design
Element base availability
Absence of generated radio interference (as opposed to pulsed interference, which creates interference due to harmonic components)

Disadvantages of transformer power supplies

Large weight and dimensions, especially with high power
Metal intensity
The trade-off between reduced efficiency and output voltage stability: to ensure stable voltage, a stabilizer is required, which introduces additional losses.

Switching power supplies

Switching power supplies are an inverter system. In switching power supplies, the AC input voltage is first rectified. The resulting DC voltage is converted into rectangular pulses increased frequency and a certain duty cycle, either supplied to a transformer (in the case of pulse power supplies with galvanic isolation from the supply network) or directly to the output low-pass filter (in pulse power supplies without galvanic isolation). In pulse power supplies, small-sized transformers can be used - this is explained by the fact that with increasing frequency, the efficiency of the transformer increases and the requirements for the dimensions (section) of the core required to transmit equivalent power decrease. In most cases, such a core can be made of ferromagnetic materials, in contrast to the cores of low-frequency transformers, for which electrical steel is used.

In switching power supplies, voltage stabilization is provided through negative feedback. Feedback allows you to maintain the output voltage at a relatively constant level, regardless of fluctuations in the input voltage and load size. Feedback can be arranged different ways. When pulse sources with galvanic isolation from the supply network, the most common methods are to use communication through one of the output windings of the transformer or using an optocoupler. Depending on the magnitude of the feedback signal (depending on the output voltage), the duty cycle of the pulses at the output of the PWM controller changes. If decoupling is not required, then, as a rule, a simple resistive voltage divider is used. Thus, the power supply maintains a stable output voltage.

Advantages of switching power supplies

Comparable in output power with linear stabilizers, their corresponding switching stabilizers have the following main advantages:

lighter weight due to the fact that as the frequency increases, transformers can be used smaller sizes at the same transmitted power. The mass of linear stabilizers consists mainly of powerful, heavy low-frequency power transformers and powerful radiators of power elements operating in linear mode;
significantly higher efficiency (up to 90-98%) due to the fact that the main losses in pulse stabilizers associated with transient processes at the moments of switching the key element. Since most of the time the key elements are in one of the stable states (i.e. either on or off), energy losses are minimal;
lower cost, thanks to the mass production of a unified element base and the development of key transistors high power. In addition, it should be noted that the cost is significantly lower pulse transformers with comparable transmitted power, and the possibility of using less powerful power elements, since their operating mode is key;
reliability comparable to linear stabilizers. (Power supplies computer technology, office equipment, household appliances are almost exclusively pulsed).
wide range of supply voltage and frequency, unattainable for a comparable price linear one. In practice, this means the possibility of using the same switching power supply for a wearable digital electronics in different countries of the world - Russia/USA/England, very different in voltage and frequency in standard sockets.
the presence in most modern power supplies of built-in protection circuits from various unforeseen situations, for example from short circuit and from the absence of load at the output.

Disadvantages of switching power supplies

Operation of the main part of the circuit without galvanic isolation from the network, which, in particular, somewhat complicates the repair of such power supplies;
Without exception, all switching power supplies are a source of high-frequency interference, since this is due to the very principle of their operation. Therefore, it is necessary to take additional noise suppression measures, which often do not eliminate the interference completely. In this regard, the use of pulsed power supplies for some types of equipment is often unacceptable.
In distributed power systems: the effect of harmonics that are multiples of three. If there are effective power factor correctors and filters in the input circuits, this drawback is usually not relevant.