They are smaller and more efficient, but they are much more difficult to manufacture and often burn out due to incorrect transformer calculation or board layout (or something else wrong). You can make a low-power switching power supply with your own hands if you use one of the microcircuits:
TNY263 at 7.5W,
TNY264 at 9 W,
TNY265 for 11 W,
TNY266 for 15W,
TNY267 for 19 W,
TNY268 at 23 W (power for sources in an open design);
use a program, a freely distributed program, PI Expert, which can be downloaded (registration is required for downloading) from the official website www.powerint.com of Power Integrations and wire the board according to the recommendations in the documentation or the PI Expert program. The installer for this program takes up about 78MB of memory. At the time of this writing, for downloading, you need to go to Design Support-PI Expert TM Design Software-PI Expert Download - fill in the fields and click the "Submit" button (before all this, of course, you need to register and log into your account). The power supply circuit is generated by the program, but you can use this one:

Figure 1 - Switching power supply for 9V, 1A

This power supply is a switching buck flyback converter. A field-effect transistor is built into the TNY266 microcircuit, which opens at a frequency of 132 kHz, when this transistor is open, the current through the primary winding increases and energy accumulates in the transformer, when this transistor closes, an EMF occurs in the secondary winding, the VD3 diode opens and the current goes to the load. Diode VD3 should be a powerful Schottky diode or a regular one with a p-n junction, but fast. Elements C3, R2, VD2 are needed in order to protect the microcircuit from high voltage in the absence of sufficient load. the transformer will still bring the energy out. Despite the presence of protection, it is better not to turn on this power supply without a load, or you can put a resistor with a large resistance on the output just in case. A short circuit or too much output load is also better not to do. from a large current, the VD3 diode will burn out. Capacitor C2 is needed to power the microcircuit at those moments when the field effect transistor of this microcircuit is open, because. the frequency is high (132kHz), 0.1uF is enough. At the input there is a resistor with a resistance of 11 Ohm to attenuate current surges through the diode bridge. Optocoupler U2, zener diode VD4 and resistors R3-R5 create feedback for the correct operation of the U1 chip, the resistance of these resistors and the stabilization voltage of the zener diode are determined by the PI Expert program. If you need a source with a different output voltage and current, then it is enough to recalculate only the transformer and resistors R3-R5, if the output current is more than 3A, then select VD3 with a high current, the rest can be left as is. It’s better to start with a transformer, for it you need to find a core with a gap, for example, you can take a core from a transformer from a TV:

The core type is determined by its length, for example, if the length is 28mm, then this is an EE28 core.
There are also cores: EE16, EE19, EE20, EE22, etc. from EE5 to EE320 (or maybe there are some others). The transformer must have a gap and be suitable in terms of power. If the program displays an error message, then you need to make the necessary corrections. When you first start the program, select File-Create from the menu

Select in the field "Product line" TnySwitch click "Next"

Click "Add..." select voltage and current, click "OK"

Click "Select"

A diagram will appear in front of you, double-click on the transformer, select the core and click "OK"

Go to the "transformer design" tab and make the transformer as written in the instructions

It is necessary to wind the windings exactly turn to turn

It is very important not to make a mistake with phasing
Go to the "Scheme" tab

You can put such a zener diode and a resistor as in the diagram, you can choose another zener diode (similar to how it was done with a transformer), in this case the program will add a resistor in series to the zener diode, you can also assemble the power supply according to the scheme in the program. A recommended PCB layout example will appear if you click on the "Layout" tab

It is better to download the program in Russian.
The board can be made with a foil fiberglass file:

The main thing is to do it carefully and not break the needle file.

A more detailed example of assembly and testing of the block can be seen in the video:
The path from pin 5 of the TNY266 to the transformer should be as short as possible.
The DB107 diode bridge in the photo above is upside down. TNY266PN can be ordered inexpensively at http://ali.pub/txdeu, the transformer is removed (then rewound) from the TV board for free, the rest of the parts are not very expensive and most of them can also be removed from the TV or ordered inexpensively.
The power supply is ready! Finally, I remind you that such (flyback) sources cannot be overloaded and cannot be underloaded. Although there are protections in the scheme, it is better not to abuse them.

Switched mode power supplies (SMPS) are usually quite complex devices, which is why novice radio amateurs tend to avoid them. However, thanks to the proliferation of specialized integrated PWM controllers, it is possible to design designs that are simple enough to understand and repeat, with high power and efficiency. The proposed power supply has a peak power of about 100 W and is built according to the flyback topology (flyback converter), and the control element is the CR6842S chip (pin-compatible analogues: SG6842J, LD7552 and OB2269).

Attention! In some cases, you may need an oscilloscope to debug the circuit!

Specifications

Block dimensions: 107x57x30 mm (dimensions of the finished block with Aliexpress, deviations are possible).
Output voltage: versions for 24 V (3-4 A) and 12 V (6-8 A).
Power: 100 W.
Pulsation level: no more than 200 mV.

On Ali, it is easy to find many options for ready-made blocks according to this scheme, for example, by requests like Artillery power supply 24V 3A, "Power supply XK-2412-24", "Eyewink 24V switching power supply" and the like. On amateur radio portals, this model has already been dubbed "folk", due to its simplicity and reliability. Circuitry options 12V and 24V differ slightly and have an identical topology.

An example of a finished power supply with Ali:

Note! In this PSU model, the Chinese have a very high percentage of defects, therefore, when buying a finished product, it is advisable to carefully check the integrity and polarity of all elements before turning it on. In my case, for example, the VD2 diode had the wrong polarity, because of which, after three inclusions, the unit burned out and I had to change the controller and the key transistor.

The detailed methodology for designing an SMPS in general, and specifically this topology in particular, will not be considered here, due to too much information - see separate articles.

100W switching power supply on the CR6842S controller.

Purpose of input circuit elements

We will consider the block diagram from left to right:

F1	Normal fuse.
5D-9	The thermistor limits the inrush current when the power supply is connected to the network. At room temperature, it has a small resistance that limits current surges; when current flows, it heats up, which causes a decrease in resistance, therefore, it does not affect the operation of the device in the future.
C1	Input capacitor, to suppress unbalanced noise. It is permissible to increase the capacitance slightly, it is desirable that it be an interference suppression capacitor of the type X2 or had a large (10-20 times) margin for operating voltage. For reliable interference suppression, it must have low ESR and ESL.
L1	Common mode filter, to suppress symmetrical interference. It consists of two inductors with the same number of turns, wound on a common core and connected in phase.
KBP307	Rectifier diode bridge.
R 5 , R 9	The circuit required to run the CR6842. Through it, the primary charge of the capacitor C 4 is carried out up to 16.5V. The circuit must provide a trigger current of at least 30 µA (maximum, according to the datasheet) over the entire input voltage range. Also, in the process of operation, this circuit controls the input voltage and compensates for the voltage at which the key closes - an increase in the current flowing into the third pin causes a decrease in the key closing threshold voltage.
R10	Timing resistor for PWM. Increasing the value of this resistor will decrease the switching frequency. The nominal value should lie in the range of 16-36 kOhm.
C2	smoothing capacitor.
R 3 , C 7 , VD 2	Snubber circuit that protects the key transistor from reverse surges from the primary winding of the transformer. R 3 is desirable to use a power of at least 1W.
C3	A capacitor that shunts the interwinding capacitance. Ideally, it should be Y-type, or it should have a large margin (15-20 times) in terms of operating voltage. Used to reduce interference. The rating depends on the parameters of the transformer; it is undesirable to make it too large.
R6, VD1, C4	This circuit, powered by the auxiliary winding of the transformer, forms the power supply circuit of the controller. Also, this circuit affects the key operation cycle. It works as follows: for correct operation, the voltage at the seventh output of the controller must be in the range of 12.5 - 16.5 V. The voltage of 16.5V at this output is the threshold at which the key transistor opens and energy begins to be stored in the transformer core (at this time, the microcircuit is powered from C 4). When it drops below 12.5V, the microcircuit is turned off, so capacitor C 4 must provide power to the controller until power is supplied from the auxiliary winding, so its value should be enough to keep the voltage above 12.5V while the key is open. The lower limit of the C 4 rating should be calculated based on the controller consumption of about 5 mA. From the charge time of this capacitor to 16.5V, the private key time depends and it is determined by the current that the auxiliary winding can give, while the current is limited by the resistor R 6. Among other things, through this circuit, the controller provides overvoltage protection in case of failure of the feedback circuits - if the voltage exceeds 25V, the controller will turn off and will not start working until power is removed from the seventh pin.
R13	Limits the gate charge current of the key transistor, and also ensures its smooth opening.
VD 3	Transistor gate protection.
R8	Pulling the shutter to the ground, performs several functions. For example, if the controller is turned off and the internal pull-up is damaged, this resistor will provide a fast discharge of the transistor gate. Also, with the correct layout of the board, it will provide a shorter gate discharge current path to ground, which should have a positive effect on noise immunity.
BT 1	key transistor. Installed on the radiator through an insulating gasket.
R 7 , C 6	The circuit serves to smooth out voltage fluctuations across the current-measuring resistor.
R1	current measuring resistor. When the voltage on it exceeds 0.8V, the controller closes the key transistor, thus adjusting the open key time. In addition, as mentioned above, the voltage at which the transistor will be closed also depends on the input voltage.
C 8	The filter capacitor of the feedback optocoupler. Let's increase the value a bit.
PC817	Optocoupler feedback circuit. If the optocoupler transistor closes, this will cause an increase in voltage at the second output of the controller. If the voltage on the second pin exceeds 5.2V for more than 56ms, this will cause the switching transistor to close. Thus, protection against overload and short circuit is implemented.

In this circuit, the 5th output of the controller is not used. However, according to the datasheet on the controller, you can hang an NTC thermistor on it, which will ensure that the controller turns off in case of overheating. The stabilized output current of this output is 70 μA. Temperature protection actuation voltage 1.05V (protection will turn on when the resistance reaches 15 kOhm). The recommended thermistor rating is 26 kΩ (at 27°C).

Pulse transformer parameters

Since a pulse transformer is one of the most complex elements of a pulse block in designing, the calculation of a transformer for each specific block topology requires a separate article, so there will be no detailed description of the methodology here, however, to repeat the described design, you should specify the main parameters of the transformer used.

It should be remembered that one of the most important design rules is the correspondence between the overall power of the transformer and the output power of the power supply, so first of all, in any case, choose the cores that suit your task.

Most often, this design is supplied with transformers made on cores of the EE25 or EE16 type, or similar. It was not possible to collect enough information on the number of turns in this SMPS model, since different modifications, despite similar circuits, use different cores.

An increase in the difference in the number of turns leads to a decrease in switching losses of the key transistor, but increases the requirements for its load capacity in terms of the maximum drain-source voltage (VDS).

For example, we will focus on standard cores of the EE25 type and the value of the maximum induction Bmax = 300 mT. In this case, the ratio of turns of the first-second-third winding will be 90:15:12.

It should be remembered that the indicated ratio of turns is not optimal and adjustment of the ratios according to the test results may be required.

The primary winding should be wound with a conductor no thinner than 0.3 mm in diameter. It is desirable to carry out the secondary winding with a double wire with a diameter of 1 mm. A small current flows through the auxiliary third winding, so a wire with a diameter of 0.2 mm will be enough.

Description of the elements of the output circuit

Next, briefly consider the output circuit of the power supply. It is, in general, completely standard, it differs minimally from hundreds of others. Only the feedback circuit on the TL431 may be interesting, but we will not consider it in detail here, because there is a separate article about feedback circuits.

VD 4	Dual rectifier diode. Ideally, select with a margin of voltage / current and with a minimum drop. Installed on the radiator through an insulating gasket.
R2, C12	Snubber circuit to facilitate the operation of the diode. R 2 is desirable to use a power of at least 1W.
C 13 , L 2 , C 14	output filter.
C 20	Ceramic capacitor shunting output capacitor C 14 to RF.
R17	Load resistor providing load for idle. Also, output capacitors are discharged through it in the event of start-up and subsequent shutdown without load.
R16	Current limiting resistor for LED.
C 9 , R 20 , R 18 , R 19 , TLE431, PC817	Feedback circuit on a precision power supply. Resistors set the TLE431 mode of operation, while PC817 provides galvanic isolation.

What can be improved

The above circuit is usually supplied ready-made, but if you assemble the circuit yourself, nothing prevents you from slightly improving the design. Both input and output circuits can be modified.

If your outlets have a ground wire connected to a good ground (and not just not connected to anything, as is often the case), you can add two additional Y-capacitors, each connected to its own mains wire and ground, between L 1 and the input capacitor C1. This will ensure the balancing of the potentials of the network wires relative to the housing and the best suppression of the common mode component of the interference. Together with the input capacitor, two additional capacitors form the so-called. "protective triangle".

After L 1, it is also worth adding another X-type capacitor, with the same capacitance as C 1 .

To protect against high-amplitude surge voltage, it is advisable to connect a varistor in parallel with the input (for example, 14D471K). Also, if you have a ground, for protection in the event of an accident on the power supply line, in which instead of phase and zero, the phase falls on both wires, it is advisable to make a protective triangle from the same varistors.

When the voltage rises above the operating voltage, the varistor reduces its resistance and current flows through it. However, due to the relatively low speed of varistors, they are not able to shunt voltage surges with a fast rising edge, therefore, for additional filtering of fast voltage surges, it is advisable to also connect a bidirectional TVS suppressor (for example, 1.5KE400CA) in parallel with the input.

Again, if there is a ground wire, it is advisable to add two more Y-capacitors of small capacity to the output of the block, connected according to the "protective triangle" scheme in parallel with C 14.

To quickly discharge the capacitors when the device is turned off, it is advisable to add a megaohm resistor in parallel with the input circuits.

It is desirable to shunt each electrolytic capacitor along the RF with low-capacity ceramics located as close as possible to the capacitor terminals.

It would not be superfluous to put a TVS limiting diode on the output as well - to protect the load from possible overvoltages in case of problems with the unit. For the 24V version, for example, 1.5KE24A is suitable.

Conclusion

The circuit is simple enough to repeat and stable. If you add all the components described in the "What can be improved" section, you get a very reliable and low-noise power supply.

The scope of switching power supplies in everyday life is constantly expanding. Such sources are used to power all modern household and computer equipment, to implement uninterruptible power supplies, chargers for batteries for various purposes, to implement low-voltage lighting systems, and for other needs.

In some cases, buying a ready-made power supply is not very acceptable from an economic or technical point of view, and assembling a switching power supply with your own hands is the best way out of this situation. Simplifies this option and the wide availability of modern element base at low prices.

The most popular in everyday life are switching sources powered by a standard AC network and a powerful low-voltage output. The block diagram of such a source is shown in the figure.

The mains rectifier CB converts the alternating voltage of the supply network into a constant one and smoothes out the ripples of the rectified voltage at the output. The high-frequency VChP converter converts the rectified voltage into an alternating or unipolar one, having the form of rectangular pulses of the required amplitude.

In the future, such a voltage either directly or after rectification (HV) is supplied to a smoothing filter, to the output of which a load is connected. The VChP is controlled by a control system that receives a feedback signal from the load rectifier.

Such a structure of the device can be criticized due to the presence of several conversion links, which reduces the efficiency of the source. However, with the right choice of semiconductor elements and high-quality calculation and manufacture of winding units, the level of power losses in the circuit is small, which makes it possible to obtain real values ​​of efficiency above 90%.

Schematic diagrams of switching power supplies

Structural block solutions include not only the rationale for choosing circuit implementation options, but also practical recommendations for choosing the main elements.

To rectify the mains single-phase voltage, one of the three classic schemes shown in the figure is used:

• half-wave;
• zero (two-half-wave with a midpoint);
• two-half-wave bridge.

Each of them has advantages and disadvantages that determine the scope.

Half wave circuit characterized by ease of implementation and a minimum number of semiconductor components. The main disadvantages of such a rectifier are a significant amount of output voltage ripple (in the rectified one there is only one half-wave of the mains voltage) and a low rectification factor.

Rectification ratio Kv determined by the ratio of the average value of the voltage at the output of the rectifier Udk effective value of the phase mains voltage Uph.

For a half-wave circuit, Kv \u003d 0.45.

To smooth out the ripple at the output of such a rectifier, powerful filters are required.

Zero, or full-wave circuit with a midpoint, although it requires a double number of rectifier diodes, however, this disadvantage is largely offset by a lower level of rectified voltage ripple and an increase in the rectification factor to 0.9.

The main disadvantage of such a scheme for use in domestic conditions is the need to organize the midpoint of the mains voltage, which implies the presence of a mains transformer. Its dimensions and weight turn out to be incompatible with the idea of ​​a small-sized self-made pulsed source.

full wave bridge rectification has the same indicators in terms of ripple level and rectification factor as the zero circuit, but does not require a network. This compensates for the main drawback - twice the number of rectifier diodes, both in terms of efficiency and cost.

To smooth out the ripple of the rectified voltage, the best solution is to use a capacitive filter. Its use allows you to raise the value of the rectified voltage to the amplitude value of the mains (at Uph=220V Ufm=314V). The disadvantages of such a filter are considered to be large values ​​of the pulsed currents of the rectifier elements, but this disadvantage is not critical.

The choice of rectifier diodes is carried out according to the average forward current Ia and the maximum reverse voltage U BM.

Taking the value of the output voltage ripple coefficient Kp=10%, we obtain the average value of the rectified voltage Ud=300V. Taking into account the load power and the efficiency of the RF converter (80% is taken for calculation, but in practice it will turn out higher, this will allow you to get some margin).

Ia is the average current of the rectifier diode, Рн is the load power, η is the efficiency of the RF converter.

The maximum reverse voltage of the rectifier element does not exceed the amplitude value of the mains voltage (314V), which allows the use of components with a value of U BM =400V with a significant margin. You can use both discrete diodes and ready-made rectifier bridges from various manufacturers.

To ensure a given (10%) ripple at the rectifier output, the capacitance of the filter capacitors is taken at the rate of 1 μF per 1 W of output power. Electrolytic capacitors with a maximum voltage of at least 350V are used. Filter capacities for various capacities are shown in the table.

High frequency converter: its functions and circuits

The high-frequency converter is a single-cycle or two-cycle key converter (inverter) with a pulse transformer. Variants of circuits of RF converters are shown in the figure.

Single cycle circuit. With a minimum number of power elements and ease of implementation, it has several disadvantages.

1. The transformer in the circuit operates on a private hysteresis loop, which requires an increase in its size and overall power;
2. To provide output power, it is necessary to obtain a significant amplitude of the pulsed current flowing through the semiconductor switch.

The scheme has found the greatest application in low-power devices, where the influence of these disadvantages is not so significant.

To change or install a new meter yourself, no special skills are required. Choosing the right one will ensure that the current consumed is correctly accounted for and will increase the safety of the home electrical network.

In modern lighting conditions, both indoors and outdoors, motion sensors are increasingly being used. This gives not only comfort and convenience to our homes, but also allows you to save a lot. You can find out practical tips on choosing an installation site, connection diagrams.

Push-Pull Circuit with Transformer Midpoint (Push-Pull). It got its second name from the English version (push-pull) of the job description. The circuit is free from the shortcomings of the single-cycle version, but has its own - a complicated design of the transformer (it is required to manufacture identical sections of the primary winding) and increased requirements for the maximum voltage of the switches. Otherwise, the solution deserves attention and is widely used in do-it-yourself switching power supplies and not only.

Push-Pull Half-Bridge. In terms of parameters, the circuit is similar to the circuit with a midpoint, but does not require a complex configuration of the transformer windings. The inherent disadvantage of the circuit is the need to organize the middle point of the rectifier filter, which entails a fourfold increase in the number of capacitors.

Due to the ease of implementation, the circuit is most widely used in switching power supplies up to 3 kW. At high powers, the cost of the filter capacitors becomes unacceptably high compared to the semiconductor switches of the inverter, and the bridge circuit turns out to be the most profitable.

Push-Pull Bridge. Similar in parameters to other push-pull circuits, but without the need to create artificial "midpoints". The price for this is a doubled number of power switches, which is beneficial from an economic and technical point of view for building powerful pulsed sources.

The choice of inverter keys is carried out according to the amplitude of the collector (drain) current I KMAX and the maximum collector-emitter voltage U KEMAC. For the calculation, the load power and the transformation ratio of the pulse transformer are used.

However, first you need to calculate the transformer itself. The pulse transformer is made on a core made of ferrite, permalloy or transformer iron twisted into a ring. For powers up to units of kW, ferrite cores of an annular or W-shaped type are quite suitable. The calculation of the transformer is based on the required power and conversion frequency. To exclude the appearance of acoustic noise, it is desirable to move the conversion frequency outside the audio range (make it higher than 20 kHz).

At the same time, it must be remembered that at frequencies close to 100 kHz, losses in ferrite magnetic circuits increase significantly. The calculation of the transformer itself is not difficult and can be easily found in the literature. Some results for various power sources and magnetic cores are shown in the table below.

The calculation was made for a conversion frequency of 50 kHz. It is worth noting that when operating at a high frequency, the effect of current displacement to the surface of the conductor takes place, which leads to a decrease in the effective winding area. To prevent this kind of trouble and reduce losses in conductors, it is necessary to wind from several cores of a smaller cross section. At a frequency of 50 kHz, the permissible diameter of the winding wire does not exceed 0.85 mm.

Knowing the load power and the transformation ratio, it is possible to calculate the current in the primary winding of the transformer and the maximum collector current of the power switch. The voltage on the transistor in the closed state is selected higher than the rectified voltage supplied to the input of the RF converter with a certain margin (U KEMAH>=400V). Based on this data, keys are selected. Currently, the best option is to use IGBT or MOSFET power transistors.

For rectifier diodes on the secondary side, one rule must be observed - their maximum operating frequency must exceed the conversion frequency. Otherwise, the efficiency of the output rectifier and the converter as a whole will be significantly reduced.

Video on the manufacture of the simplest switching power supply

!
In this article, together with Roman (the author of the YouTube channel "Open Frime TV"), we will assemble a universal power supply on the IR2153 chip. This is a kind of "Frankenstein", which contains the best qualities from different schemes.

The Internet is full of power supply circuits on the IR2153 chip. Each of them has some positive features, but the author has not yet met a universal scheme. Therefore, it was decided to create such a scheme and show it to you. I think you can go straight to it. So, let's figure it out.

The first thing that catches your eye is the use of two high voltage capacitors instead of one for 400V. Thus we kill two birds with one stone. These capacitors can be obtained from old computer power supplies without spending money on them. The author specially made several holes in the board for different sizes of capacitors.

If the block is not available, then the prices for a pair of such capacitors are lower than for one high-voltage one. The capacitance of the capacitors is the same and should be at the rate of 1 uF per 1 W of output power. This means that for 300 watts of power output you will need a pair of 330uF capacitors.

Also, if we use this topology, there is no need for a second decoupling capacitor, which saves us space. And that is not all. The voltage of the decoupling capacitor should no longer be 600 V, but only 250 V. Now you can see the sizes of 250V and 600V capacitors.

The next feature of the circuit is the power supply for the IR2153. Everyone who built blocks on it faced unrealistic heating of the supply resistors.

Even if they are set from a break, a lot of heat is released. An ingenious solution was immediately applied, using a capacitor instead of a resistor, and this gives us the fact that there is no heating of the element by supply.

The author of this homemade product saw such a decision from Yuri, the author of the YouTube channel "Red Shade". Also, the board is equipped with protection, but in the original version of the circuit it was not.

But after tests on the layout, it turned out that there was too little space to install the transformer and therefore the circuit had to be increased by 1 cm, this gave extra space on which the author installed the protection. If it is not needed, then you can simply put jumpers instead of a shunt and do not install the components marked in red.

The protection current is regulated using this trimming resistor:

The shunt resistor values ​​vary depending on the maximum output power. The more power, the less resistance needed. For example, for power below 150 W, 0.3 ohm resistors are needed. If the power is 300 W, then we need 0.2 Ohm resistors, well, at 500 W and above, we put resistors with a resistance of 0.1 Ohm.

This block should not be assembled with a power higher than 600 W, and you also need to say a few words about the operation of the protection. She hiccups here. The trigger frequency is 50 Hz, this is because the power is taken from the AC, therefore the latch is reset at the mains frequency.

If you need a latched option, then in this case the power supply of the IR2153 chip must be taken constant, or rather from high-voltage capacitors. The output voltage of this circuit will be taken from a full-wave rectifier.

The main diode will be a Schottky diode in the TO-247 package, choose the current for your transformer.

If there is no desire to take a large case, then in the Layout program it is easy to change it to TO-220. There is a 1000 uF capacitor at the output, it is enough for any currents, since at high frequencies the capacitance can be set less than for a 50 hertz rectifier.

It is also necessary to note such auxiliary elements as snubbers (Snubber) in the transformer piping;

smoothing capacitors;

as well as a Y-capacitor between the grounds of the high and low sides, which dampens noise on the output winding of the power supply.

There is an excellent video about these capacitors on YouTube (the author attached the link in the description under his video (link SOURCE at the end of the article)).

You can not skip the frequency-setting part of the circuit.

This is a 1 nF capacitor, the author does not recommend changing its value, but he put a tuning resistor in the driving part, there were reasons for this. The first of them is the exact selection of the desired resistor, and the second is a small adjustment of the output voltage using the frequency. And now a small example, let's say you are making a transformer and you see that at a frequency of 50 kHz the output voltage is 26V, and you need 24V. By changing the frequency, you can find a value at which the output will be the required 24V. When installing this resistor, we use a multimeter. We clamp the contacts into crocodiles and rotate the resistor knob, we achieve the desired resistance.

Now you can see the 2nd breadboards on which the tests were carried out. They are very similar, but the protection board is slightly larger.

The author made mock-ups in order to order the manufacture of this board in China with peace of mind. In the description under the author's original video, you will find an archive with this board, schematic and seal. There will be two scarves and the first and second options, so you can download and repeat this project.

After ordering, the author was looking forward to the board, and now they have arrived. We open the package, the boards are packed well enough - you won’t find fault. We visually inspect them, everything seems to be fine, and immediately proceed to soldering the board.

And now she is ready. Everything looks like this. Now let's quickly go through the main elements not previously mentioned. First of all, these are fuses. There are 2 of them, on the high and low side. The author used such round ones, because their sizes are very modest.

Next we see the filter capacitors.

You can get them from an old computer power supply. The author wound the choke on the t-9052 ring, 10 turns with a 0.8 mm 2 wire, but you can use a choke from the same computer power supply.
Diode bridge - any, with a current of at least 10 A.

There are also 2 resistors on the board to discharge the capacitance, one on the high side, the other on the low side.

Switching power supplies are often used by radio amateurs in homemade designs. With relatively small dimensions, they can provide high output power. With the use of a pulse circuit, it became realistic to obtain an output power from several hundred to several thousand watts. At the same time, the dimensions of the pulse transformer itself are no larger than a matchbox.

Switching power supplies - principle of operation and features

The main feature of switching power supplies is an increased operating frequency, which is hundreds of times greater than the mains frequency of 50 Hz. At high frequencies with a minimum number of turns in the windings, a high voltage can be obtained. For example, to obtain a 12 Volt output voltage at a current of 1 Ampere (in the case of a network transformer), you need to wind 5 turns of wire with a cross section of approximately 0.6–0.7 mm.

If we talk about a pulse transformer, the driving circuit of which operates at a frequency of 65 kHz, then to get 12 Volts with a current of 1A, it is enough to wind only 3 turns with a wire of 0.25–0.3 mm. That is why many electronics manufacturers use a switching power supply.

However, despite the fact that such blocks are much cheaper, more compact, have high power and low weight, they have electronic filling, therefore, they are less reliable when compared with a network transformer. Proving their unreliability is very simple - take any switching power supply without protection and close the output terminals. At best, the block will fail, at worst, it will explode and no fuse will save the block.

Practice shows that the fuse in the switching power supply burns out last, the power switches and the master generator fly out first, then all parts of the circuit in turn.

Pulse power supplies have a number of protections both at the input and at the output, but they do not always save. In order to limit the inrush current at the start of the circuit, almost all SMPS with a power of more than 50 watts use a thermistor that is at the input of the circuits.

Let's now look at the TOP 3 best switching power supply circuits that you can assemble with your own hands.

A simple do-it-yourself switching power supply

Consider how to make the simplest miniature switching power supply. Any novice radio amateur can create a device according to the presented scheme. It is not only compact, but also operates in a wide range of supply voltages.

A home-made switching power supply has a relatively small power, within 2 watts, but it is literally indestructible, not afraid of even long-term short circuits.

Scheme of a simple switching power supply

The power supply is a low-power switching autogenerator type power supply, assembled on just one transistor. The oscillator is powered from the network through a current-limiting resistor R1 and a half-wave rectifier in the form of a diode VD1.

Transformer of a simple switching power supply

The pulse transformer has three windings, collector or primary, base winding and secondary.

An important point is the winding of the transformer - both the printed circuit board and the diagram indicate the beginning of the windings, so there should be no problems. We borrowed the number of turns of the windings from a transformer for charging cell phones, since the circuitry is almost the same, the number of windings is the same.

First we wind the primary winding, which consists of 200 turns, the wire cross section is from 0.08 to 0.1 mm. Then we put the insulation and wind the base winding with the same wire, which contains from 5 to 10 turns.

We wind the output winding on top, the number of its turns depends on what voltage is needed. On average, about 1 volt per turn is obtained.

Video about testing this power supply:

Do-it-yourself stabilized switching power supply on the SG3525

Consider step by step how to make a stabilized power supply on the SG3525 chip. Let's talk about the advantages of this scheme. The first and most important is the stabilization of the output voltage. There is also a soft start, short circuit protection and self-recording.

First, let's look at the device diagram.

Beginners will immediately pay attention to 2 transformers. In the circuit, one of them is power, and the second is for galvanic isolation.

Do not think that because of this the scheme will become more complicated. On the contrary, everything becomes easier, safer and cheaper. For example, if you put a driver at the output of the microcircuit, then you need a strapping for it.

Let's look further. In this scheme, a microstart and self-starter are implemented.

This is a very productive solution, it allows you to get rid of the need for a standby power supply. Indeed, making a power supply for a power supply is not a good idea, but such a solution is just perfect.

Everything works as follows: a capacitor is charged from a constant, and when its voltage exceeds a predetermined level, this block opens and discharges the capacitor into the circuit.

Its energy is quite enough to start the microcircuit, and as soon as it starts, the voltage from the secondary winding begins to feed the microcircuit itself. It is also necessary to add this output resistor to the microstart, it serves as a load.

Without this resistor, the unit will not start. This resistor is different for each voltage and must be calculated from such considerations that at the rated output voltage 1 W of power was dissipated on it.

We consider the resistance of the resistor:

R = U squared/P
R = 24 squared/1
R = 576/1 = 560 ohms.

Also on the diagram there is a soft start. It is implemented using this capacitor.

And current protection, which in the event of a short circuit will begin to reduce the width of the PWM.

The frequency of this power supply is changed with the help of this resistor and a condender.

Now let's talk about the most important thing - stabilizing the output voltage. These elements are responsible for it:

As you can see, 2 zener diodes are installed here. With their help, you can get any voltage at the output.

Calculation of voltage stabilization:

U out \u003d 2 + U stub1 + U stub2
U out \u003d 2 + 11 + 11 \u003d 24V
An error of + - 0.5 V is possible.

In order for the stabilization to work correctly, a voltage margin in the transformer is needed, otherwise, if the input voltage decreases, the microcircuit simply will not be able to produce the desired voltage. Therefore, when calculating the transformer, you should click on this button and the program will automatically add voltage to the secondary winding for a reserve.

Now we can move on to the consideration of the printed circuit board. As you can see, everything is pretty compact here. We also see a place for a transformer, it is toroidal. Without any problems, it can be replaced with a W-shaped one.

The optocoupler and zener diodes are located near the microcircuit, and not at the output.

Well, there was nowhere to put them on the way out. If you don't like it, make your own PCB layout.

You may ask, why not increase the fee and do everything right? The answer is the following: this was done with the expectation that it would be cheaper to order a board in production, since boards larger than 100 square meters. mm are much more expensive.

Well, now it's time to assemble the scheme. Everything is standard here. We solder without any problems. We wind the transformer and install it.

Check the output voltage. If it is present, then it can already be included in the network.

First, let's check the output voltage. As you can see, the block is designed for a voltage of 24V, but it turned out a little less due to the spread of the zener diodes.

This error is not critical.

Now let's check the most important thing - stabilization. To do this, take a 24V lamp with a power of 100W and connect it to the load.

As you can see, the voltage did not subside and the block withstood without problems. You can load even more.

Video about this switching power supply:

We reviewed the TOP 3 best switching power supply circuits. Based on them, you can assemble a simple PSU, devices on the TL494 and SG3525. Step-by-step photos and videos will help you understand all the installation issues.