All electronics repairers are aware of the importance of having a laboratory power supply that can produce various voltages and currents for use in charging devices, powering circuits, testing circuits, etc. There are many varieties of such devices on the market, but experienced radio amateurs are quite capable of making a laboratory power supply with their own hands. For this, you can use used parts and housings, supplementing them with new elements.

simple device

The simplest power supply consists of only a few elements. Beginning radio amateurs will find it easy to design and assemble these lightweight circuits. Main principle- create a rectifier circuit to obtain direct current. In this case, the output voltage level will not change, it depends on the transformation ratio.

The main components for a simple power supply circuit:

1. A step-down transformer;
2. rectifier diodes. You can turn them on in a bridge circuit and get full-wave rectification, or use a half-wave device with one diode;
3. Capacitor for smoothing ripples. The electrolytic type is selected with a capacity of 470-1000 microfarads;
4. Conductors for mounting the circuit. Their cross section is determined by the magnitude of the load current.

To design a 12-volt PSU, you need a transformer that would step down the voltage from 220 to 16 V, since the voltage decreases slightly after the rectifier. Such transformers can be found in used computer power supplies or purchased new. You can find recommendations on self-rewinding transformers, but at first it is better to do without it.

Diodes fit silicon. For devices of small power, ready-made bridges are on sale. It is important to connect them correctly.

This is the main part of the circuit, not yet quite ready for use. It is necessary to put an additional zener diode after the diode bridge to get a better output signal.

The resulting device is a conventional power supply without additional features and is capable of supporting small load currents, up to 1 A. In this case, an increase in current can damage circuit components.

To get a powerful power supply, it is enough to install one or more amplifying stages on TIP2955 transistor elements in the same design.

Important! To ensure the temperature regime of the circuit on powerful transistors, it is necessary to provide cooling: radiator or ventilation.

Adjustable power supply

Power supplies with voltage regulation will help to solve more complex tasks. Commercially available devices differ in terms of control parameters, power ratings, etc. and are selected according to the intended use.

A simple adjustable power supply is assembled according to the exemplary scheme shown in the figure.

The first part of the circuit with a transformer, a diode bridge and a smoothing capacitor is similar to the circuit of a conventional power supply without regulation. As a transformer, you can also use the device from the old power supply, the main thing is that it matches the selected voltage parameters. This indicator for the secondary winding limits the regulating limit.

How the circuit works:

1. The rectified voltage goes to the zener diode, which determines the maximum value of U (you can take 15 V). The limited current parameters of these parts require the installation of a transistor amplifying stage in the circuit;
2. Resistor R2 is variable. By changing its resistance, you can get different values ​​\u200b\u200bof the output voltage;
3. If the current is also regulated, then the second resistor is installed after the transistor stage. It does not exist in this diagram.

If a different control range is required, a transformer with the appropriate characteristics must be installed, which will also require the inclusion of another zener diode, etc. The transistor needs radiator cooling.

Measuring instruments for the simplest regulated power supply will suit any: analog and digital.

Having built an adjustable power supply with your own hands, you can use it for devices designed for different operating and charging voltages.

Bipolar power supply

The device of a bipolar power supply is more complex. Experienced electronics engineers can engage in its design. Unlike unipolar ones, such PSUs at the output provide voltage with a “plus” and “minus” sign, which is necessary when powering amplifiers.

Although the circuit shown in the figure is simple, its implementation will require certain skills and knowledge:

1. You will need a transformer with a secondary winding divided into two halves;
2. One of the main elements are integrated transistor stabilizers: KR142EN12A - for direct voltage; KR142EN18A - for the opposite;
3. A diode bridge is used to rectify the voltage, it can be assembled on separate elements or a ready-made assembly can be used;
4. Resistors with variable resistance are involved in voltage regulation;
5. For transistor elements, it is imperative to mount cooling radiators.

A bipolar laboratory power supply will also require the installation of monitoring devices. The assembly of the case is made depending on the dimensions of the device.

Power supply protection

The easiest way to protect the PSU is to install fuses with fusible links. There are self-recovery fuses that do not require replacement after a burnout (their resource is limited). But they do not provide a full guarantee. Often the transistor is damaged before the fuse blows. Radio amateurs have developed various circuits using thyristors and triacs. Options can be found online.

For the manufacture of the casing of the device, each master uses the methods available to him. With enough luck, you can find a ready-made container for the device, but you still have to change the design of the front wall in order to place control devices and control knobs there.

Some crafting ideas:

1. Measure the dimensions of all components and cut out the walls from aluminum sheets. Mark the front surface and make the necessary holes;
2. Fasten the structure with a corner;
3. The lower base of the PSU with powerful transformers must be reinforced;
4. For external processing, prime the surface, paint and fix with varnish;
5. Circuit components are reliably isolated from external walls in order to avoid stress on the case during breakdown. To do this, it is possible to glue the walls from the inside with an insulating material: thick cardboard, plastic, etc.

Many devices, especially high power ones, require the installation of a cooling fan. It can be done with continuous operation, or a circuit can be made to automatically turn on and off when the specified parameters are reached.

The scheme is implemented by installing a temperature sensor and a microcircuit that provides control. For cooling to be effective, free air circulation is required. This means that the back panel, near which the cooler and radiators are mounted, must have holes.

Important! During the assembly and repair of electrical devices, one must be aware of the danger of electric shock. Capacitors that are energized must be discharged.

It is possible to assemble a high-quality and reliable laboratory power supply with your own hands if you use serviceable components, clearly calculate their parameters, use proven circuits and the necessary devices.

Video

Hello everyone. Today is the final review, assembly of a laboratory linear power supply. Today there is a lot of locksmith work, hull manufacturing and final assembly. The review is posted on the DIY or DIY blog, I hope I don’t distract anyone here and don’t bother anyone to amuse my eyes with the charms of Lena and Igor))). Anyone who is interested in homemade products and radio engineering - Welcome !!!
ATTENTION: A lot of letters and photos! Traffic!

Welcome radio amateur and homemade lover! To begin with, let's remember the assembly steps for a laboratory linear power supply. It is not directly related to this review, therefore it is placed under the spoiler:

Assembly steps

Assembly of the power module. Board, heatsink, power transistor, 2 variable multi-turn resistors and a green transformer (from the Eighties®) As suggested by the wise kirich, I independently assembled a circuit that the Chinese sell in the form of a constructor for assembling a power supply. At first I was upset, but then I decided that, apparently, the circuit is good, since the Chinese are copying it ... At the same time, the children's sores of this circuit (which were completely copied by the Chinese) got out, without replacing the microcircuits with more “high-voltage ones”, you cannot apply to the input more than 22 volts of alternating voltage ... And a few smaller problems that our forum users suggested to me, for which many thanks to them. More recently, the future engineer " Anna Sun"offered getting rid of the transformer. Of course, everyone can upgrade their PSU as they please, you can put a pulser as a power source. But any pulser (maybe except resonant ones) has a lot of noise at the output, and this interference will partially go to the LabBP output ... And if there are impulsive interference, then (IMHO) this is not LabBP.Therefore, I will not get rid of the "green transformer".


Since this is a linear power supply, it has a characteristic and significant drawback, all excess energy is released on the power transistor. For example, we apply 24V AC voltage to the input, which after rectification and smoothing will turn into 32-33V. If you connect a powerful load to the output that consumes 3A at a voltage of 5V, all the remaining power (28V at a current of 3A), which is 84W, will be dissipated in the power transistor, turning into heat. One way to prevent this problem, and increase efficiency accordingly, is to install a manual or automatic winding switching module. This module has been reviewed in:

For the convenience of working with the power supply and the ability to instantly turn off the load, an additional relay module was introduced into the circuit, which allows you to turn the load on or off. It was dedicated to this.


Unfortunately, due to the lack of the necessary relays (normally closed), this module did not work correctly, therefore it will be replaced by another module, on a D-trigger, which allows you to turn the load on or off with a single button.

Briefly tell about the new module. The scheme is quite well-known (sent to me in PM):


I slightly modified it to fit my needs and collected the following board:


On the back side:


This time there were no problems. Everything works very clearly and is controlled by one button. When power is applied, the 13th output of the microcircuit is always a logical zero, the transistor (2n5551) is closed and the relay is de-energized - accordingly, the load is not connected. When the button is pressed, a logical unit appears at the output of the microcircuit, the transistor opens and the relay is activated by connecting the load. Pressing the button again returns the chip to its original state.

What is the power supply without a voltage and current indicator? Therefore, I tried to make an ampervoltmeter myself. In principle, it turned out to be a good device, but it has some non-linearity in the range from 0 to 3.2A. This error will not affect in any way when using this meter, say in charger for a car battery, but unacceptable for a Laboratory PSU, therefore, I will replace this module with Chinese precision panel boards and displays with 5 digits ... And the module I assembled will find application in some other homemade product.


Finally, higher-voltage microcircuits arrived from China, which I told you about in. And now you can apply 24V AC to the input without fear that it will break through the microcircuits ...

Now it's up to the "small", to make the case and assemble all the blocks together, which I will do in this final review on this topic.
Looking for a ready-made case, I did not find anything suitable. The Chinese have good boxes, but, unfortunately, their price, and especially ...

The “toad” didn’t allow me to give the Chinese 60 bucks, and it’s stupid to give that kind of money for the case, you can add a little more and buy it. At least the case will come out of this Bp good.

Therefore, I went to the construction market and bought 3 meters of aluminum corner. With it, the frame of the device will be assembled.
We prepare the parts of the desired size. We draw the blanks and cut the corners with a cutting disc. .



Then lay out the blanks of the top and bottom panels to figure out what happens.


Trying to place modules inside


The assembly goes on countersunk screws (under the head with a countersink, a hole is drilled so that the screw head does not protrude above the corner), and nuts on the reverse side. Slowly, the outlines of the frame of the power supply appear:


And now the frame is assembled ... Not very even, especially in the corners, but I think that the painting will hide all the bumps:


Dimensions of the frame under the spoiler:

Dimension measurement

Unfortunately, there is little free time, because locksmith work is progressing slowly. In the evenings, in a week, I made a front panel from a sheet of aluminum and a socket for the power input and fuse.






We draw future holes for the Voltmeter and Ammeter. The seat should be 45.5mm by 26.5mm
We glue the landing holes with masking tape:


And with a cutting disc, using a dremel, we make cuts (adhesive tape is needed so as not to go beyond the dimensions of the sockets and not to spoil the panel with scratches) Dremel quickly copes with aluminum, but it takes 3-4 per hole

Again there was a hitch, corny, the cutting discs for the dremel ran out, the search in all the shops in Almaty did not lead to anything, so I had to wait for the discs from China ... Fortunately, they came quickly in 15 days. Then the work went more fun and faster ...
I sawed holes for digital indicators with a dremel, and filed them.


We put a green transformer on the "corners"


We try on a radiator with a power transistor. It will be isolated from the case, since a transistor is installed on the radiator in the TO-3 case, and there it is difficult to isolate the transistor collector from the case. The radiator will be behind a decorative grille with a cooling fan.




I processed the front panel with sandpaper on a bar. I decided to try on everything that will be fixed on it. It turns out like this:


Two digital meters, a load enable button, two multi-turn potentiometers, output terminals, and a current limit LED holder. Didn't you forget something?


On the back of the front panel.
We disassemble everything and paint the frame of the power supply unit with black paint from a can.


We attach a decorative grille to the back wall (bought at the car market, anodized aluminum for tuning the radiator air intake 2000 tenge (6.13USD))


So it happened, the view from the back of the power supply housing.


We put a fan to blow the radiator with a power transistor. I attached it with plastic black clamps, it holds well, appearance does not suffer, they are almost invisible.


We return the plastic base of the frame to its place with the power transformer already installed.


We mark the places of fastening of the radiator. The radiator is isolated from the body of the device, because on it the voltage is equal to the voltage on the collector of the power transistor. I think that it will be well blown by a fan, which will significantly reduce the temperature of the radiator. The fan will be controlled by a circuit that reads information from a sensor (thermistor) mounted on a radiator. Thus, the fan will not “thresh” into an empty one, but will turn on when a certain temperature is reached on the power transistor heatsink.


We attach the front panel in place, see what happens.


There are a lot of decorative grilles left, so I decided to try to make a U-shaped cover for the power supply case (in the manner of computer cases), if I don’t like it, I’ll change it to something else.


Front view. While the grille is "baited" and is not yet firmly attached to the frame.


It seems to work well. The grille is strong enough, you can safely put something on top, but it’s not even worth talking about the quality of ventilation inside the case, the ventilation will be just excellent, compared to closed cases.

Well, let's continue with the build. We connect a digital ammeter. Important: do not step on my rake, do not use a regular connector, just solder directly to the connector pins. Otherwise, it will be in place of the current in Amperes, show the weather on Mars.


The wires for connecting the ammeter, and all other auxiliary devices, should be as short as possible.
Between the output terminals (plus or minus) I installed a socket made of foil textolite. It is very convenient to draw insulating grooves in copper foil to create platforms for connecting all auxiliary devices (ammeter, voltmeter, load disconnection board, etc.)

The main board is installed next to the heatsink of the output transistor.

The winding switching board is installed above the transformer, which made it possible to significantly reduce the length of the wire loop.

The time has come to assemble an additional power supply module for the winding switching module, ammeter, voltmeter, etc.
Since we have a linear - analog PSU, we will also use the option on a transformer, no switching power supplies. :-)
Etching the board:


Soldering the details:


We test, put brass “legs” and embed the module into the case:

Well, all the blocks are built in (except for the fan control module, which will be made later) and installed in their places. The wires are connected, the fuse is inserted. You can carry out the first inclusion. We overshadow ourselves with the cross, close our eyes and give nourishment ...
There is no boom and white smoke - it’s already good ... It seems that nothing is heating up at idle ... We press the load switch button - the green LED lights up and the relay clicks. Everything seems to be fine so far. You can start testing.

As the saying goes, "soon a fairy tale is told, but not soon the deed is done." Pitfalls surfaced again. The transformer winding switching module does not work correctly with the power module. At the switching voltage from the first winding to the next, a voltage jump occurs, i.e. when 6.4V is reached, a jump occurs up to 10.2V. Then, of course, you can reduce the voltage, but this is not the point. At first I thought that the problem was in the power supply of the microcircuits, since their power is also from the windings of the power transformer, and accordingly grows with each subsequent connected winding. Therefore, I tried to power the microcircuits from a separate power source. But it did not help.
Therefore, there are 2 options: 1. Completely redo the circuit. 2. Refuse the automatic winding switching module. I'll start with option 2. I can’t stay completely without switching the windings, because I don’t like the option of putting up with the stove, so I’ll put a toggle switch that allows you to choose the voltage supplied to the PSU input from 2 options 12V or 24V. This is of course a "half-measure", but better than nothing at all.
At the same time, I decided to change the ammeter to another similar one, but with a green glow of the numbers, since the red numbers of the ammeter glow rather weakly and are hard to see in sunlight. Here's what happened:


It seems so much better. It is also possible that I will replace the voltmeter with another one, because. 5 digits in the voltmeter is clearly redundant, 2 digits after the decimal point is enough. I have replacement options, so there will be no problems.

We put the switch and connect the wires to it. We check.
With the switch in the "down" position - the maximum voltage without load was about 16V

When the switch is up, the maximum voltage available for this transformer is 34V (no load)

Now the handles, for a long time I did not come up with options and found plastic dowels of a suitable diameter, both internal and external.


We cut off the tube of the required length and put it on the rods of variable resistors:


Then we put on the handles and fix them with screws. Since the dowel tube is quite soft, the handle is fixed very well, it takes considerable effort to rip it off.

The review is very large. Therefore, I will not take your time and briefly test the Laboratory Power Supply.
We already looked at interference with an oscilloscope in the first review, and since then nothing has changed in circuitry.
Therefore, we check the minimum voltage, the adjustment knob is in the leftmost position:

Now the maximum current

1A current limit

Maximum current limit, current adjustment knob in the far right position:

That's all my dear radio killers and sympathizers ... Thanks to everyone who read to the end. The device turned out to be brutal, heavy and, I hope, reliable. See you on the air!

UPD: Oscillograms at the output of the power supply when the voltage is turned on:


And turn off the voltage:

UPD2: Friends from the Soldering Iron forum gave an idea on how to start the winding switching module with minimal alterations to the circuit. Thank you all for your interest, I will finish the device. Therefore, to be continued. Add to favorites Liked +72 +134

This article is intended for people who can quickly distinguish a transistor from a diode, know what a soldering iron is for and which side to hold it on, and finally came to the understanding that without a laboratory power supply their life no longer makes sense ...

This scheme was sent to us by a person under the nickname: Loogin.

All images are reduced in size, to view in full size, click the left mouse button on the image

Here I will try as much as possible in detail - step by step to tell how to do it with minimal cost. Surely everyone has at least one power supply unit lying under their feet after home hardware upgrades. Of course, you will have to buy something, but these sacrifices will be small and most likely justified by the end result - this is usually about 22V and 14A ceiling. Personally, I invested in $10. Of course, if you collect everything from the "zero" position, then you need to be ready to shell out about another $ 10-15 to buy the PSU itself, wires, potentiometers, knobs and other loose stuff. But, usually - everyone has such rubbish in bulk. There is another nuance - you have to work a little with your hands, so they should be “without displacement” J and you can get something similar:

First you need to get by any means an unnecessary but serviceable ATX PSU with a power of> 250W. One of the most popular schemes is Power Master FA-5-2:

I will describe the detailed sequence of actions specifically for this scheme, but they are all valid for other options.
So, at the first stage, you need to prepare a BP donor:

1. Remove diode D29 (you can just lift one leg)
2. We remove the jumper J13, we find it in the circuit and on the board (you can use wire cutters)
3. The PS ON jumper to ground must be in place.
4. We turn on the PB only for a short time, since the voltage at the inputs will be maximum (approximately 20-24V) Actually, this is what we want to see ...

Do not forget about the output electrolytes, designed for 16V. Maybe they get a little warm. Considering that they are most likely "swollen", they still have to be sent to the swamp, it's not a pity. Remove the wires, they interfere, and only GND and + 12V will be used, then solder them back.

5. Remove the 3.3 volt part: R32, Q5, R35, R34, IC2, C22, C21:

6. Remove 5V: Schottky assembly HS2, C17, C18, R28, you can also "type choke" L5
7. Remove -12V -5V: D13-D16, D17, C20, R30, C19, R29

8. We change the bad ones: replace C11, C12 (preferably with a large capacity C11 - 1000uF, C12 - 470uF)
9. We change the inappropriate components: C16 (preferably at 3300uF x 35V like mine, well, at least 2200uF x 35V is a must!) and I advise you to replace the R27 resistor with a more powerful one, for example 2W and take the resistance 360-560 Ohm.

We look at my board and repeat:

10. We remove everything from the legs TL494 1,2,3 for this we remove the resistors: R49-51 (we release the 1st leg), R52-54 (... 2nd leg), C26, J11 (... 3rd leg)
11. I don’t know why, but my R38 was cut by someone J I recommend that you cut it too. He participates in feedback voltage and is parallel to the R37th. Actually R37 can also be cut.

12. we separate the 15th and 16th legs of the microcircuit from "everyone else": for this we make 3 cuts in the existing tracks, and to the 14th leg we restore the connection with a black jumper, as shown in my photo.

13. Now we solder the cable for the regulator board to the points according to the diagram, I used the holes from the soldered resistors, but by the 14th and 15th I had to tear off the varnish and drill holes, in the photo above.
14. The core of loop No. 7 (controller power supply) can be taken from the + 17V TL supply, in the area of ​​\u200b\u200bthe jumper, more precisely from it J10. Drill a hole in the track, clear the varnish and there! It is better to drill from the printing side.

It was all, as they say: "minimal refinement" to save time. If time is not critical, then you can simply bring the circuit to the following state:

I would also advise you to change the high-voltage conduits at the input (C1, C2) They are of small capacity and are probably already pretty dry. There normally will be 680uF x 200V. Plus, it’s nice to remake the L3 group stabilization choke a little, either use 5-volt windings by connecting them in series, or remove everything altogether and wind about 30 turns with a new enamel wire with a total cross section of 3-4mm 2.

To power the fan, you need to “prepare” it with 12V. I got out in this way: Where there used to be a field effect transistor to form 3.3V, you can “settle” a 12-volt KREN-ku (KREN8B or 7812 imported analogue). Of course, there is no way to do without cutting tracks and adding wires. In the end, it turned out, in general, even “nothing”:

The photo shows how everything harmoniously coexisted in the new quality, even the fan connector fit pretty well and the rewound throttle turned out to be quite good.

Now the regulator. To simplify the task with different shunts there, we do this: we buy ready-made ammeter and voltmeter in China, or on the local market (you can probably find them there from resellers). You can buy combined. But, we must not forget that they have a current ceiling of 10A! Therefore, in the regulator circuit, it will be necessary to limit the current limit at this mark. Here I will describe the option for individual devices without current regulation with a maximum limit of 10A. Regulator circuit:

To make the current limit adjustment, instead of R7 and R8, you need to put a 10kΩ variable resistor, just like R9. Then it will be possible to use the all-measurement. Also worth paying attention to R5. In this case, its resistance is 5.6kΩ, because our ammeter has a 50mΩ shunt. For other options R5=280/R shunt. Since we took one of the cheapest voltmeters, so it needs to be slightly modified so that it can measure voltages from 0V, and not from 4.5V, as the manufacturer did. The whole alteration consists in separating the supply and measurement circuits by removing the diode D1. We solder the wire there - this is the + V power supply. The measured part remained unchanged.

The regulator board with the location of the elements is shown below. The image for the laser-ironing manufacturing method comes in a separate Regulator.bmp file with a resolution of 300dpi. Also in the archive there are files for editing in EAGLE. Last off. version can be downloaded here: www.cadsoftusa.com. There is a lot of information about this editor on the Internet.

Then we fasten the finished board at the ceiling of the case through insulating spacers, for example, cut from a used lollipop stick 5-6 mm high. Well, do not forget to pre-do all the necessary cutouts for measuring and other devices.

We pre-assemble and test under load:

We are just looking at the correspondence of the readings of various Chinese devices. And below already with a "normal" load. This is a car headlight bulb. As you can see, there is almost 75W. At the same time, do not forget to put an oscilloscope in there and see ripples of about 50mV. If there is more, then we remember about the “large” electrolytes on the high side with a capacity of 220uF and immediately forget after replacing them with normal ones with a capacity of 680uF, for example.

In principle, we can stop at this, but in order to give a more pleasant look to the device, well, so that it does not look 100% homemade, we do the following: we leave our lair, go up to the floor above and remove a useless sign from the first door that comes across.

As you can see, someone has already been here before us.

In general, we quietly do this dirty business and start working with files of different styles and at the same time master AutoCad.

Then we sharpen a piece of a three-quarter pipe on sandpaper and cut it out of a fairly soft rubber of the desired thickness and sculpt the legs with superglue.

As a result, we get a fairly decent device:

A few points should be noted. The most important thing is not to forget that the GND of the power supply and the output circuit should not be connected., so you need to exclude the connection between the case and the GND of the PSU. For convenience, it is desirable to take out the fuse, as in my photo. Well, try to restore the missing elements of the input filter as much as possible, they most likely do not exist at all in the source.

Here are a couple more options for such devices:

On the left is a 2-story ATX case with an all-measurement box, and on the right is a heavily altered old AT case from a computer.

A simple and reliable do-it-yourself power supply at the current level of development of the element base of radio-electronic components can be made very quickly and easily. It does not require knowledge of electronics and electrical engineering to high level. You will soon see this.

Making your first power supply is quite an interesting and memorable event. Therefore, an important criterion here is the simplicity of the circuit, so that after assembly it will immediately work without any additional settings and adjustments.

It should be noted that almost every electronic, electrical device or device needs power. The difference is only in the main parameters - the magnitude of voltage and current, the product of which gives power.

Making a power supply with your own hands is a very good first experience for beginner electronics engineers, because it allows you to feel (not on yourself) the various values ​​\u200b\u200bof the currents flowing in devices.

The modern market for power supplies is divided into two categories: transformer and transformerless. The first are quite simple to manufacture for beginner radio amateurs. The second indisputable advantage is the relatively low level of electromagnetic radiation, and, accordingly, interference. A significant drawback by modern standards is the significant weight and dimensions caused by the presence of a transformer - the heaviest and most bulky element in the circuit.

Transformerless power supplies are deprived of the last drawback due to the lack of a transformer. Rather, it is there, but not in the classical representation, but works with a high frequency voltage, which makes it possible to reduce the number of turns and the dimensions of the magnetic circuit. As a result, the overall dimensions of the transformer are reduced. The high frequency is formed by semiconductor switches, in the process of switching on and off according to a given algorithm. As a result, strong electromagnetic interference occurs, therefore, such sources are subject to mandatory shielding.

We will assemble a transformer power supply that will never lose its relevance, since it is still used in high-end audio equipment, due to the minimum level of noise generated, which is very important for obtaining high-quality sound.

The device and principle of operation of the power supply

The desire to get the finished device as compact as possible led to the emergence of various microcircuits, inside which there are hundreds, thousands and millions of individual electronic elements. Therefore, almost any electronic device contains a microcircuit, the standard power supply of which is 3.3 V or 5 V. Auxiliary elements can be powered from 9 V to 12 V DC. However, we are well aware that the socket has an alternating voltage of 220 V with a frequency of 50 Hz. If it is applied directly to a microcircuit or any other low-voltage element, they will instantly fail.

From this it becomes clear that the main task of the mains power supply (PSU) is to reduce the voltage to an acceptable level, as well as converting (rectifying) it from AC to DC. In addition, its level must remain constant regardless of fluctuations in the input (in the outlet). Otherwise, the device will be unstable. Therefore, another important function of the PSU is the stabilization of the voltage level.

In general, the structure of the power supply consists of a transformer, a rectifier, a filter and a stabilizer.

In addition to the main nodes, a number of auxiliary ones are also used, for example, indicator LEDs that signal the presence of the applied voltage. And if the PSU provides for its adjustment, then naturally there will be a voltmeter, and possibly also an ammeter.

Transformer

In this circuit, a transformer is used to reduce the voltage in a 220 V outlet to the required level, most often 5 V, 9 V, 12 V or 15 V. At the same time, galvanic isolation of high-voltage and low-voltage circuits is also carried out. Therefore, in any emergency situations, the voltage on the electronic device will not exceed the value of the secondary winding. Also, galvanic isolation increases the safety of the operating personnel. In case of touching the device, a person will not fall under the high potential of 220 V.

The design of the transformer is quite simple. It consists of a core that acts as a magnetic circuit, which is made of thin, well-conductive magnetic flux plates, separated by a dielectric, which is a non-conductive varnish.

At least two windings are wound on the core rod. One primary (also called network) - 220 V is supplied to it, and the second - secondary - reduced voltage is removed from it.

The principle of operation of the transformer is as follows. If a voltage is applied to the mains winding, then, since it is closed, an alternating current will begin to flow in it. Around this current, an alternating magnetic field arises, which is collected in the core and flows through it in the form of a magnetic flux. Since there is another winding on the core - the secondary one, then under the action of a variable magnetic flux, an electromotive force (EMF) is seen in it. When this winding is shorted to a load, an alternating current will flow through it.

Radio amateurs in their practice most often use two types of transformers, which mainly differ in the type of core - armored and toroidal. The latter is more convenient to use in that it is quite easy to wind the required number of turns on it, thereby obtaining the necessary secondary voltage, which is directly proportional to the number of turns.

The main two parameters of the transformer for us are the voltage and current of the secondary winding. We will take the current value equal to 1 A, since we will take the zener diodes for the same value. About what a little further.

We continue to assemble the power supply with our own hands. And the next ordinal element in the circuit is a diode bridge, also known as a semiconductor or diode rectifier. It is intended to convert the alternating voltage of the secondary winding of the transformer into a constant, or rather, into a rectified pulsating one. This is where the name "rectifier" comes from.

There are various rectification schemes, but the bridge circuit has received the most use. Its principle of operation is as follows. In the first half-cycle of the alternating voltage, the current flows along the path through the VD1 diode, the R1 resistor and the VD5 LED. Next, the current returns to the winding through the open VD2.

A reverse voltage is applied to the diodes VD3 and VD4 at this moment, so they are locked and the current does not flow through them (in fact, it only flows at the moment of switching, but this can be neglected).

In the next half-cycle, when the current in the secondary winding changes its direction, the opposite will happen: VD1 and VD2 will close, and VD3 and VD4 will open. In this case, the direction of current flow through the resistor R1 and the LED VD5 will remain the same.

The diode bridge can be soldered from four diodes connected according to the diagram above. And you can buy ready-made. They come in horizontal and vertical versions in different cases. But in any case, they have four conclusions. The two leads are supplied with AC voltage, they are indicated by the sign "~", both of the same length and the shortest.

The rectified voltage is removed from the other two conclusions. They are designated "+" and "-". The “+” terminal has the longest length among the others. And on some cases, a bevel is made near it.

Condenser filter

After the diode bridge, the voltage has a pulsating character and is still unsuitable for powering microcircuits, and even more so microcontrollers, which are very sensitive to various kinds of voltage drops. Therefore, it needs to be smoothed out. To do this, you can use a choke or a capacitor. In the circuit under consideration, it is enough to use a capacitor. However, it must have a large capacity, so an electrolytic capacitor should be used. Such capacitors often have polarity, so it must be observed when connected to the circuit.

The negative terminal is shorter than the positive one and a “-” sign is applied on the case near the first one.

Voltage regulator LM 7805, LM 7809, LM 7812

You probably noticed that the voltage in the outlet is not equal to 220 V, but varies within certain limits. This is especially noticeable when connecting a powerful load. If you do not apply special measures, then it will also change at the output of the power supply in a proportional range. However, such fluctuations are highly undesirable, and sometimes unacceptable for many electronic elements. Therefore, the voltage after the capacitor filter is subject to mandatory stabilization. Depending on the parameters of the powered device, two stabilization options are used. In the first case, a zener diode is used, and in the second, an integrated voltage regulator. Let's consider the use of the latter.

In amateur radio practice, voltage stabilizers of the LM78xx and LM79xx series have been widely used. Two letters indicate the manufacturer. Therefore, instead of LM, there may be other letters, such as CM. The marking consists of four digits. The first two - 78 or 79 mean respectively positive or negative voltage. The last two digits, in this case, instead of them, two x's: xx, indicate the value of the output U. For example, if there are 12 in the position of two x's, then this stabilizer outputs 12 V; 08 - 8 V, etc.

For example, let's decipher the following markings:

LM7805 → 5V positive voltage

LM7912 → 12V negative U

Integral stabilizers have three outputs: input, common and output; rated for 1A.

If the output U significantly exceeds the input and at the same time a limiting current of 1 A is consumed, then the stabilizer heats up very much, so it should be installed on a radiator. The design of the case provides for this possibility.

If the load current is much lower than the limit, then you can not install a radiator.

The classic power supply circuit includes: a mains transformer, a diode bridge, a capacitor filter, a stabilizer and an LED. The latter acts as an indicator and is connected through a current-limiting resistor.

Since in this circuit the LM7805 stabilizer is the limiting element flow ( permissible value 1 A), then all other components must be rated for a current of at least 1 A. Therefore, the secondary winding of the transformer is selected for a current of one ampere. Its voltage should not be lower than the stabilized value. And for good, it should be chosen from such considerations that after rectification and smoothing, U should be 2–3 V higher than the stabilized one, i.e. the input of the stabilizer should be fed a couple of volts more than its output value. Otherwise, it will not work correctly. For example, for LM7805 input U = 7 - 8 V; for LM7805 → 15 V. However, it should be borne in mind that if the U value is too high, the microcircuit will heat up very much, since the “extra” voltage is quenched on its internal resistance.

The diode bridge can be made from diodes of the 1N4007 type, or you can take it ready for a current of at least 1 A.

The smoothing capacitor C1 should have a large capacitance of 100 - 1000 uF and U = 16 V.

Capacitors C2 and C3 are designed to smooth out the high frequency ripple that occurs when operating the LM7805. They are installed for greater reliability and are advisory in nature from manufacturers of stabilizers of this type. Without such capacitors, the circuit also works fine, but since they cost practically nothing, it is better to put them on.

Do-it-yourself power supply for 78 L 05, 78 L 12, 79 L 05, 79 L 08

It is often necessary to power only one or a pair of microcircuits or low-power transistors. In this case, it is not rational to use a powerful power supply. Therefore, the best option would be to use stabilizers of the 78L05, 78L12, 79L05, 79L08 series, etc. They are designed for a maximum current of 100 mA = 0.1 A, but at the same time they are very compact and no larger than a conventional transistor in size, and also do not require installation on a radiator.

The marking and connection diagram are similar to those of the LM series discussed above, only the pin arrangement differs.

For example, the connection diagram of the stabilizer 78L05 is shown. It is also suitable for LM7805.

The scheme for switching on negative voltage stabilizers is shown below. The input is -8V and the output is -5V.

As you can see, making a power supply with your own hands is very simple. Any voltage can be obtained by installing the appropriate stabilizer. You should also remember about the parameters of the transformer. Next, we will look at how to make a voltage regulated power supply.

Many already know that I have a weakness for all kinds of power supplies, here is a two-in-one review. This time there will be an overview of the radio designer, which allows you to assemble the basis for a laboratory power supply and a variant of its real implementation.
I warn you, there will be a lot of photos and text, so stock up on coffee :)

To begin with, I will explain a little what it is and why.
Almost all radio amateurs use such a thing as a laboratory power supply in their work. Whether it's complex with software control or very simple on the LM317, it still does almost the same thing, powering different loads in the process of working with them.
Laboratory power supplies are divided into three main types.
With impulse stabilization.
with linear stabilization
Hybrid.

The former incorporate a pulsed controlled power supply, or simply a pulsed power supply with a PWM buck converter. I have already reviewed several options for these power supplies. , .
Advantages - high power with small dimensions, excellent efficiency.
Disadvantages - RF ripple, the presence of capacitive capacitors at the output

The latter do not have any PWM converters on board, all adjustment is carried out in a linear way, where the excess energy is dissipated simply on the control element.
Pros - Virtually no ripple, no need for output capacitors (almost).
Cons - efficiency, weight, size.

Still others are a combination of either the first type with the second, then the linear stabilizer is powered by a slave PWM buck converter (the voltage at the output of the PWM converter is always maintained at a level slightly higher than the output, the rest is regulated by a transistor operating in linear mode.
Either this is a linear power supply, but the transformer has several windings that switch as needed, thereby reducing losses on the regulating element.
This scheme has only one minus, the complexity, it is higher than the first two options.

Today we will talk about the second type of power supply, with a regulating element operating in linear mode. But consider this power supply using the example of a designer, it seems to me that this should be even more interesting. Indeed, in my opinion, this is a good start for a novice radio amateur, to assemble one of the main instruments for himself.
Well, or as they say, the right power supply should be heavy :)

This review is more aimed at beginners, experienced comrades are unlikely to find anything useful in it.

I ordered a constructor for review, which allows you to assemble the main part of the laboratory power supply.
The main characteristics are as follows (from the ones declared by the store):
Input voltage - 24 Volts AC
The output voltage is adjustable - 0-30 Volts DC.
Output current adjustable - 2mA - 3A
Output voltage ripple - 0.01%
The dimensions of the printed board are 80x80mm.

A little about the packaging.
The designer came in a regular plastic bag, wrapped in a soft material.
Inside, in an anti-static bag with a latch, were all the necessary components, including the circuit board.

Inside, everything was a mound, but nothing was damaged, the printed circuit board partially protected the radio components.

I will not list everything that is included in the kit, it's easier to do it later in the course of the review, I can only say that I had enough of everything, even something left.

A little about the printed circuit board.
The quality is excellent, the circuit is not included, but all the ratings on the board are indicated.
The board is double-sided, covered with a protective mask.

Board coating, tinning, and the very quality of the textolite is excellent.
I only managed to tear off a patch from the seal in one place, and then, after I tried to solder a non-native part (for some reason, it will be further).
In my opinion, the most for a novice radio amateur, it will be hard to spoil.

Before installation, I drew a diagram of this power supply.

The scheme is quite thoughtful, although not without flaws, but I will talk about them in the process.
Several main nodes are visible in the diagram, I separated them with a color.
Green - voltage regulation and stabilization unit
Red - current adjustment and stabilization unit
Violet - node indicating the transition to the current stabilization mode
Blue - reference voltage source.
Separately, there are:
1. Input diode bridge and filter capacitor
2. Power control unit on transistors VT1 and VT2.
3. Protection on the transistor VT3, turning off the output until the power of the operational amplifiers is normal
4. Fan power stabilizer, built on the 7824 chip.
5. R16, R19, C6, C7, VD3, VD4, VD5, unit for forming the negative pole of the power supply of operational amplifiers. Due to the presence of this node, the PSU will not work simply from direct current, it is the AC input from the transformer that is needed.
6. C9 output capacitor, VD9, output protection diode.

First, I will describe the advantages and disadvantages of the circuit design.
Pros -
I am glad that there is a stabilizer to power the fan, but the fan is needed for 24 volts.
I am very pleased with the presence of a negative polarity power supply, this greatly improves the operation of the PSU at currents and voltages close to zero.
In view of the presence of a source of negative polarity, protection was introduced into the circuit, until this voltage is present, the PSU output will be turned off.
The PSU contains a reference voltage source of 5.1 Volts, which not only made it possible to correctly regulate the output voltage and current (with such a scheme, the voltage and current are regulated from zero to the maximum linearly, without “humps” and “dips” at extreme values), but also makes it possible to control external power supply, just change the control voltage.
The output capacitor is very small, which allows you to safely test the LEDs, there will be no inrush current until the output capacitor is discharged and the PSU enters current stabilization mode.
The output diode is necessary to protect the PSU from applying reverse polarity voltage to its output. True, the diode is too weak, it is better to replace it with another one.

Minuses.
The current sense shunt has too high a resistance, because of this, when operating with a load current of 3 Amperes, about 4.5 watts of heat is generated on it. The resistor is rated at 5 watts, but the heating is very large.
The input diode bridge is made up of 3 Amp diodes. For good, diodes should be at least 5 Amperes, since the current through the diodes in such a circuit is 1.4 of the output, respectively, in operation, the current through them can be 4.2 Amperes, and the diodes themselves are designed for 3 Amperes. The situation is only facilitated by the fact that the pairs of diodes in the bridge work alternately, but still this is not entirely correct.
The big minus is that Chinese engineers, when selecting operational amplifiers, chose an op-amp with a maximum voltage of 36 Volts, but did not think that there was a negative voltage source in the circuit and the input voltage in this embodiment was limited to 31 Volts (36-5 = 31 ). With an input of 24 volts AC, the constant will be about 32-33 volts.
Those. The OU will operate in an extreme mode (36 is the maximum, standard 30).

I will talk about the pros and cons, as well as about the upgrade later, but now I will move on to the actual assembly.

First, let's lay out everything that is included in the kit. This will facilitate the assembly, and it will simply be more clearly visible what has already been installed and what is left.

I recommend starting the assembly with the lowest elements, because if you set high ones first, then it will be inconvenient to set low ones later.
It is also better to start by installing those components that are more of the same.
I'll start with resistors, and these will be 10 kΩ resistors.
The resistors are of high quality and have an accuracy of 1%.
A few words about resistors. Resistors are color coded. To many, this may seem inconvenient. In fact, this is better than alphanumeric marking, since the marking is visible in any position of the resistor.
Do not be afraid of color marking, at the initial stage you can use it, and over time it will be possible to determine it already without it.
To understand and conveniently work with such components, you just need to remember two things that will be useful to a novice radio amateur in life.
1. Ten basic marking colors
2. Ratings of the series, they are not very useful when working with precise resistors of the E48 and E96 series, but such resistors are much less common.
Any radio amateur with experience will list them simply from memory.
1, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2, 2.2, 2.4, 2.7, 3, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1.
All other denominations are the multiplication of these by 10, 100, etc. For example 22k, 360k, 39ohm.
What does this information give?
And she gives that if the resistor of the E24 series, then for example a combination of colors -
Blue + green + yellow in it is impossible.
Blue - 6
Green - 5
Yellow - x10000
those. according to calculations, it turns out 650k, but there is no such value in the E24 series, there is either 620 or 680, which means that either the color is recognized incorrectly, or the color is changed, or the resistor is not the E24 series, but the latter is rare.

Okay, enough theory, let's move on.
Before mounting, I shape the resistor leads, usually with tweezers, but some people use a small homemade device for this.
We are not in a hurry to throw away the cuttings of the conclusions, it happens that they can be useful for jumpers.

Having set the main amount, I reached single resistors.
It can be harder here, you will have to deal with the denominations more often.

I don’t solder the components right away, but I just bite and bend the conclusions, and I bite it first, and then bend it.
This is done very easily, the board is held in the left hand (if you are right-handed), at the same time the installed component is pressed.
There are side cutters in the right hand, we bite the conclusions (sometimes even several components at once), and immediately bend the conclusions with the side edge of the side cutters.
This is all done very quickly, after a while already on automatism.

So we got to the last small resistor, the value of the required and the one that remains is the same, already not bad :)

Having installed the resistors, we move on to diodes and zener diodes.
There are four small diodes here, these are the popular 4148, there are two 5.1 Volt zener diodes each, so it is very difficult to get confused.
They also form conclusions.

On the board, the cathode is indicated by a strip, as well as on diodes and zener diodes.

Although the board has a protective mask, I still recommend bending the leads so that they do not fall on adjacent tracks, in the photo the diode lead is bent away from the track.

The zener diodes on the board are also marked as markings on them - 5V1.

There are not very many ceramic capacitors in the circuit, but their marking can confuse a novice radio amateur. By the way, it also obeys the E24 series.
The first two digits are the value in picofarads.
The third digit is the number of zeros to be added to the face value
Those. for example 331 = 330pF
101 - 100pF
104 - 100000pF or 100nF or 0.1uF
224 - 220000pF or 220nF or 0.22uF

The main number of passive elements has been established.

After that, we proceed to the installation of operational amplifiers.
I would probably recommend buying sockets for them, but I soldered them as is.
On the board, as well as on the microcircuit itself, the first output is marked.
The rest of the pins are counted counterclockwise.
The photo shows a place for an operational amplifier and how it should be placed.

For microcircuits, I do not bend all the conclusions, but only a couple, usually these are the extreme conclusions diagonally.
Well, it's better to bite them so that they stick out about 1mm above the board.

Everything, now you can go to soldering.
I use the most common soldering iron with temperature control, but a regular soldering iron with a power of about 25-30 watts is quite sufficient.
Solder diameter 1mm with flux. I specifically do not indicate the brand of solder, since there is non-native solder on the coil (native coils weighing 1Kg), and few people will know its name.

As I wrote above, the board is of high quality, it is soldered very easily, I did not use any fluxes, only what is in the solder is enough, you just need to remember to shake off the excess flux from the tip sometimes.

Here I took a photo with an example of good soldering and not very good.
A good solder should look like a small droplet enveloping the lead.
But in the photo there are a couple of places where the solder is clearly not enough. This will happen on a double-sided board with metallization (where the solder also flows inside the hole), but this cannot be done on a single-sided board, over time such soldering can “fall off”.

The conclusions of the transistors must also be pre-molded, this must be done in such a way that the conclusion is not deformed near the base of the case (the elders will remember the legendary KT315, in which the conclusions liked to break off).
I shape powerful components a little differently. Molding is done so that the component is above the board, in which case less heat will transfer to the board and will not destroy it.

This is what the molded powerful resistors on the board look like.
All components were soldered only from the bottom, the solder that you see on the top of the board penetrated through the hole due to the capillary effect. It is advisable to solder in such a way that the solder penetrates a little to the top, this will increase the reliability of the soldering, and in the case of heavy components, their better stability.

If before that I molded the conclusions of the components with tweezers, then for the diodes I will already need small pliers with narrow jaws.
The conclusions are formed in much the same way as for resistors.

But there are differences when installing.
If for components with thin leads, installation first occurs, then biting, then for diodes the opposite is true. You simply won’t bend such a conclusion after biting, so first we bend the conclusion, then we bite off the excess.

The power unit is assembled using two transistors connected according to the Darlington circuit.
One of the transistors is mounted on a small heatsink, preferably through thermal paste.
There were four M3 screws in the kit, one goes here.

A couple of photos of an almost soldered board. I will not describe the installation of terminal blocks and other components, it is intuitive, and you can see it from the photo.
By the way, about the terminal blocks, there are terminal blocks on the board for connecting the input, output, fan power.

I have not washed the board yet, although I often do this at this stage.
This is due to the fact that there will be a small part of the refinement.

After the main assembly step, we are left with the following components.
Power transistor
Two variable resistors
Two board connectors
Two connectors with wires, by the way, the wires are very soft, but of a small cross section.
Three screws.

Initially, the manufacturer intended to place variable resistors on the board itself, but this way they are placed so inconveniently that I didn’t even solder them and showed them just for example.
They stand very close and it will be extremely inconvenient to regulate, although it is real.

But thank you for not forgetting to give wires with connectors in the kit, it's much more convenient.
In this form, the resistors can be placed on the front panel of the device, and the board can be installed in a convenient place.
Along the way, soldered a powerful transistor. This is an ordinary bipolar transistor, but with a maximum power dissipation of up to 100 watts (of course, when installed on a radiator).
There are three screws left, I didn’t understand where to even apply them, if at the corners of the board, then four are needed, if you attach a powerful transistor, then they are short, in general, a mystery.

You can power the board from any transformer with an output voltage of up to 22 Volts (24 is stated in the specifications, but I explained above why such a voltage cannot be used).
I decided to use a transformer for the Romantik amplifier that I had for a long time. Why for, and not from, but because he has not yet stood anywhere :)
This transformer has two output power windings of 21 Volts, two auxiliary windings of 16 Volts and a shielding winding.
The voltage is indicated for the input 220, but since we now have a standard of 230, the output voltages will also be slightly higher.
The calculated power of the transformer is about 100 watts.
I paralleled the output power windings to get more current. Of course, it was possible to use a rectification circuit with two diodes, but it won’t be better with it, so I left it as it is.

For those who do not know how to determine the power of a transformer, I made a short video.

First trial run. I installed a small radiator on the transistor, but even in this form there was quite a lot of heating, since the PSU is linear.
Adjustment of current and voltage occurs without problems, everything worked right away, so I can already fully recommend this designer.
The first photo is voltage stabilization, the second is current.

To begin with, I checked what the transformer outputs after rectification, as this determines the maximum output voltage.
I got about 25 volts, not a lot. The capacity of the filter capacitor is 3300uF, I would advise you to increase it, but even in this form the device is quite efficient.

Since for further verification it was already necessary to use a normal radiator, I proceeded to assemble the entire future structure, since the installation of the radiator depended on the intended design.
I decided to use the Igloo7200 radiator that I have. According to the manufacturer, such a radiator is capable of dissipating up to 90 watts of heat.

The device will use a Z2A case based on the idea of ​​Polish production, the price is about 3 dollars.

Initially, I wanted to move away from the case that bored my readers, in which I collect all sorts of electronic things.
To do this, I chose a slightly smaller case and bought a fan with a mesh for it, but I couldn’t put all the stuffing into it and a second case was purchased and, accordingly, a second fan.
In both cases, I bought Sunon fans, I really like the products of this company, and in both cases, 24 Volt fans were bought.

This is how I planned to install a radiator, a board and a transformer. There is even a little space left for expanding the filling.
There was no way to put the fan inside, so it was decided to place it outside.

We mark the mounting holes, cut the threads, screw them for fitting.

Since the selected case has an internal height of 80mm, and the board is also of this size, I fixed the heatsink so that the board is symmetrical with respect to the heatsink.

The conclusions of a powerful transistor also need to be molded a little so that they do not deform when the transistor is pressed against the radiator.

A small digression.
For some reason, the manufacturer decided on a place to install a rather small radiator, because of this, when installing a normal one, it turns out that the fan power regulator and the connector for connecting it interfere.
I had to solder them out, and seal the place where they were with tape so that there was no connection with the radiator, since there was voltage on it.

I cut off the extra tape on the reverse side, otherwise it turned out somehow completely sloppy, we will do it according to Feng Shui :)

This is how the printed circuit board looks like with the heatsink finally installed, the transistor is installed through thermal paste, and it is better to use good thermal paste, since the transistor dissipates power comparable to a powerful processor, i.e. about 90 watts.
At the same time, I immediately made a hole for installing the fan speed controller board, which in the end still had to be re-drilled :)

To set zero, I unscrewed both regulators to the extreme left position, disconnected the load and set the output to zero. Now the output voltage will be adjusted from zero.

A few tests follow.
I checked the accuracy of maintaining the output voltage.
Idling, voltage 10.00 Volts
1. Load current 1 Amp, voltage 10.00 Volts
2. Load current 2 Amperes, voltage 9.99 Volts
3. Load current 3 Amperes, voltage 9.98 Volts.
4. Load current 3.97 Amps, voltage 9.97 Volts.
The characteristics are very good, if desired, they can be improved a little more by changing the connection point of the voltage feedback resistors, but as for me, it’s enough.

I also checked the ripple level, the test took place at a current of 3 Amperes and an output voltage of 10 Volts

The ripple level was about 15mV, which is very good, though I thought that in fact the ripples shown in the screenshot were more likely to climb from the electronic load than from the PSU itself.

After that, I proceeded to assemble the device itself as a whole.
I started by installing a radiator with a power supply board.
To do this, I marked out the installation location of the fan and the power connector.
The hole was marked not quite round, with small "cuts" at the top and bottom, they are needed to increase the strength of the back panel after cutting the hole.
Holes are usually the hardest part. complex shape, for example under the power connector.

A large hole is cut from a large pile of small ones :)
Drill + drill with a diameter of 1mm sometimes work wonders.
Drill holes, lots of holes. It may seem that it is long and tedious. No, on the contrary, it is very fast, the complete drilling of the panel takes about 3 minutes.

After that, I usually put the drill a little more, for example 1.2-1.3mm and go through it like a cutter, it turns out such a cut:

After that, we take a small knife in our hands and clean the resulting holes, at the same time we cut the plastic a little if the hole turned out to be a little smaller. The plastic is quite soft, so it's comfortable to work with.

The last stage of preparation is drilling mounting holes, we can say that the main work on the back panel is over.

We install a heatsink with a board and a fan, try on the result, if necessary, “finish it with a file”.

Almost at the very beginning, I mentioned refinement.
I will work on it a little.
To begin with, I decided to replace the native diodes in the input diode bridge with Schottky diodes, I bought four pieces of 31DQ06 for this. and then I repeated the mistake of the board developers, buying by inertia diodes for the same current, but I had to have a larger one. But all the same, the heating of the diodes will be less, since the drop on Schottky diodes is less than on conventional ones.
Secondly, I decided to replace the shunt. I was not satisfied not only with the fact that it heats up like an iron, but also with the fact that about 1.5 Volts falls on it, which can be put into action (in the sense of a load). For this, I took two domestic 0.27 Ohm 1% resistors (this will also improve stability). Why the developers didn’t do this is not clear, the price of the solution is absolutely the same as in the version with a native 0.47 Ohm resistor.
Well, rather as an addition, I decided to replace the native filter capacitor 3300uF with a better and more capacious Capxon 10000uF ...

This is what the resulting design looks like with the replaced components and the fan thermal control board installed.
It turned out a little collective farm, and besides, I accidentally ripped off one patch on the board when installing powerful resistors. In general, it was possible to safely use less powerful resistors, for example, one 2-watt resistor, I just didn’t have this available.

A few components have also been added to the bottom.
3.9k resistor, parallel to the extreme contacts of the connector for connecting the current regulation resistor. It is needed to reduce the adjustment voltage, since the voltage on the shunt is now different.
A pair of 0.22uF capacitors, one in parallel with the output from the current control resistor, to reduce interference, the second is just at the output of the power supply, it is not really needed, I just accidentally took out a pair at once and decided to use both.

The entire power part is connected, a board with a diode bridge and a capacitor is installed on the transformer to power the voltage indicator.
By and large, this board is optional in the current version, but I didn’t raise my hand to power the indicator from its limiting 30 Volts and I decided to use an additional 16 Volt winding.

The following components were used to organize the front panel:
Load terminals
Pair of metal handles
Power switch
Red light filter, declared as a light filter for KM35 housings
To indicate current and voltage, I decided to use the board that I had left after writing one of the reviews. But I was not satisfied with small indicators and therefore larger numbers with a height of 14mm were bought, and a printed circuit board was made for them.

In general, this solution is temporary, but I even wanted to temporarily do it carefully.

Several stages of preparation of the front panel.
1. Draw the layout of the front panel in full size (I use the usual Sprint Layout). The advantage of using identical enclosures is that it is very easy to prepare a new panel, since the required dimensions are already known.
We apply the printout to the front panel and drill marking holes with a diameter of 1mm in the corners of the square / rectangular holes. With the same drill we drill the centers of the remaining holes.
2. According to the resulting holes, we mark the places of the cut. Change the tool to a thin disc cutter.
3. We cut straight lines, clearly in size in front, a little more in the back, so that the cut is as full as possible.
4. We break out the cut pieces of plastic. I usually don't throw them away as they might still come in handy.

Similarly to the preparation of the back panel, we process the resulting holes with a knife.
I recommend drilling large diameter holes, it does not "bite" the plastic.

We try on what we got, if necessary, modify it with a needle file.
I had to slightly widen the hole for the switch.

As I wrote above, for indication, I decided to use the board left over from one of the previous reviews. In general, this is a very bad solution, but more than suitable for a temporary option, I will explain why later.
We solder the indicators and connectors from the board, call the old indicators and the new ones.
I painted for myself the pinout of both indicators so as not to get confused.
In the native version, four-digit indicators were used, I used three-digit ones. because I no longer fit into the window. But since the fourth digit is needed only to display the letter A or U, their loss is not critical.
I placed the LED for indicating the current limiting mode between the indicators.

I prepare everything necessary, from the old board I solder a 50mΩ resistor, which will be used as before, as a current-measuring shunt.
This shunt is the problem. The fact is that in this version I will have a voltage drop at the output of 50mV for every 1 ampere of load current.
There are two ways to get rid of this problem, use two separate meters, for current and voltage, while powering the voltmeter from a separate power source.
The second way is to install a shunt in the positive pole of the PSU. Both options did not suit me as a temporary solution, so I decided to step on the throat of my perfectionism and make a simplified version, but far from the best.

For the construction, I used the mounting posts left over from the DC-DC converter board.
With them, I got a very convenient design, the indicator board is attached to the ampervoltmeter board, which in turn is attached to the power terminal board.
It turned out even better than I expected :)
I also placed a current-measuring shunt on the power terminal board.

The resulting front panel design.

And then I remembered that I forgot to install a more powerful protective diode. I had to solder it later. I used a diode left after replacing the diodes in the input bridge of the board.
Of course, for good it would be necessary to add a fuse, but this is no longer in this version.

But I decided to put the current and voltage adjustment resistors better than those suggested by the manufacturer.
The native ones are quite high-quality, and have a smooth run, but these are ordinary resistors, and as for me, the laboratory power supply should be able to more accurately adjust the output voltage and current.
Even when I was thinking of ordering a power supply board, I saw them in the store and ordered them for a review, especially since they had the same denomination.

In general, I usually use other resistors for such purposes, they combine two resistors inside themselves at once, for coarse and smooth adjustment, but recently I can’t find them on sale.
Maybe someone knows their imported counterparts?

The resistors are quite high quality, the angle of rotation is 3600 degrees, or in simple terms - 10 full turns, which provides a tuning of 3 Volts or 0.3 Amperes per 1 turn.
With such resistors, the adjustment accuracy is about 11 times more accurate than with conventional ones.

New resistors in comparison with relatives, the size is certainly impressive.
Along the way, I shortened the wires to the resistors a little, this should improve noise immunity.

I packed everything in the case, in principle, there was even a little space left, there is room to grow :)

I connected the shielding winding to the grounding conductor of the connector, the additional power board is located directly on the transformer terminals, this is of course not very neat, but I have not yet come up with another option.

Check after assembly. Everything started up almost the first time, I accidentally mixed up two digits on the indicator and for a long time could not understand what was wrong with the adjustment, after switching everything became as it should.

The last stage is gluing the light filter, installing handles and assembling the body.
The light filter has a thinning around the perimeter, the main part is recessed into the housing window, and the thinner part is glued with double-sided tape.
The handles were originally designed for a shaft diameter of 6.3mm (if I don’t confuse), the new resistors have a thinner shaft, I had to put a couple of layers of heat shrink on the shaft.
I decided not to design the front panel in any way yet, and there are two reasons for this:
1. Management is so intuitive that there is no special meaning in the inscriptions yet.
2. I plan to modify this power supply, so changes in the design of the front panel are possible.

A couple of photos of the resulting design.
Front view:

Back view.
Attentive readers must have noticed that the fan is positioned in such a way that it blows hot air out of the case, and does not force cold air between the radiator fins.
I decided to do this because the heatsink is slightly smaller than the case, and so that hot air does not get inside, I put the fan in reverse. This, of course, significantly reduces the efficiency of heat dissipation, but it allows you to slightly ventilate the space inside the PSU.
Additionally, I would recommend making a few holes from the bottom of the bottom half of the case, but this is more of an addition.

After all the alterations, I got a current slightly less than in the original version, and amounted to about 3.35 Amperes.

And so, I will try to paint the pros and cons of this board.
pros
Excellent workmanship.
Almost correct circuitry of the device.
A complete set of parts for assembling the power supply stabilizer board
Good for beginner radio amateurs.
In a minimal form, only a transformer and a radiator are additionally required, in a more advanced form, an ampervoltmeter is also required.
Fully functional after assembly, although with some nuances.
The absence of capacitive capacitors at the PSU output, it is safe when checking LEDs, etc.

Minuses
The type of operational amplifiers is incorrectly selected, because of this, the input voltage range should be limited to 22 Volts.
Not a very suitable current measurement resistor value. It works in its normal thermal mode, but it is better to replace it, since the heating is very large and can harm the surrounding components.
The input diode bridge is working at maximum, it is better to replace the diodes with more powerful ones

My opinion. During the assembly process, I got the impression that the circuit was developed by two different person, one applied the correct adjustment principle, reference voltage supply, negative polarity voltage supply, protection. The second one incorrectly selected a shunt, operational amplifiers and a diode bridge for this case.
I really liked the circuitry of the device, and in the refinement section, I first wanted to replace the operational amplifiers, I even bought microcircuits with a maximum operating voltage of 40 volts, but then I changed my mind about modifying it. but otherwise the solution is quite correct, the adjustment is smooth and linear. Of course there is heating, without it nowhere. In general, as for me, for a beginner radio amateur this is a very good and useful constructor.
Surely there will be people who will write that it is easier to buy ready-made, but I think that it is more interesting to assemble it yourself (probably this is the most important thing) and more useful. In addition, many quite calmly at home have both a transformer and a heatsink from an old processor, and some kind of box.

Already in the process of writing a review, I had an even stronger feeling that this review would be the beginning of a series of reviews dedicated to a linear power supply, there are thoughts for improvement -
1. Translation of the indication and control circuit into a digital version, possibly with a connection to a computer
2. Replacing operational amplifiers with high-voltage ones (I don’t know which ones yet)
3. After replacing the op amp, I want to make two automatically switching stages and expand the output voltage range.
4. Change the principle of current measurement in the display device so that there is no voltage drop under load.
5. Add the ability to turn off the output voltage with a button.

That's probably all. Maybe I'll remember something and add, but more I'm waiting for comments with questions.
I also plan to devote a few more reviews to designers for beginner radio amateurs, maybe someone will have suggestions about certain designers.

Not for the faint of heart

At first I didn’t want to show it, but then I decided to take a photo anyway.
On the left is the power supply that I used for many years before.
This is a simple linear PSU with an output of 1-1.2 Amperes at a voltage of up to 25 Volts.
So I wanted to replace it with something more powerful and correct.

The product was provided for writing a review by the store. The review is published in accordance with clause 18 of the Site Rules.