With the current level of development of the element base of radio-electronic components, a simple and reliable power supply with your own hands can be made very quickly and easily. This does not require high-level knowledge of electronics and electrical engineering. You will soon see this.
Making your first power source is quite an interesting and memorable event. Therefore, an important criterion here is the simplicity of the circuit, so that after assembly it immediately works without any additional settings or adjustments.
It should be noted that almost every electronic, electrical device or appliance needs power. The difference lies only in the basic 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 novice electronics engineers, since it allows you to feel (not on yourself) the different magnitudes of currents flowing in devices.
The modern power supply market is divided into two categories: transformer-based and transformerless. The first ones are quite easy to manufacture for beginner radio amateurs. The second indisputable advantage is the relatively low level of electromagnetic radiation, and therefore 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 do not have the last drawback due to the absence of a transformer. Or rather, it is there, but not in the classical presentation, but works with high-frequency voltage, which makes it possible to reduce the number of turns and the size of the magnetic circuit. As a result, the overall dimensions of the transformer are reduced. The high frequency is generated by semiconductor switches, in the process of switching on and off according to a given algorithm. As a result, strong electromagnetic interference occurs, so such sources must be shielded.
We will be assembling a transformer power supply that will never lose its relevance, since it is still used in high-end audio equipment, thanks to the minimal level of noise generated, which is very important for obtaining high-quality sound.
Design and principle of operation of the power supply
The desire to obtain a finished device as compact as possible led to the emergence of various microcircuits, inside of 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 know well that the outlet 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 here 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 convert (rectify) it from AC to DC. In addition, its level must remain constant regardless of fluctuations in the input (in the socket). Otherwise, the device will be unstable. Therefore, another important function of the power supply is voltage level stabilization.
In general, the structure of the power supply consists of a transformer, rectifier, filter and stabilizer.
In addition to the main components, a number of auxiliary components are also used, for example, indicator LEDs that signal the presence of supplied voltage. And if the power supply 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. Galvanic isolation also increases the safety of 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 performs the function of a magnetic circuit, which is made of thin plates that conduct magnetic flux well, separated by a dielectric, which is a non-conductive varnish.
At least two windings are wound on the core rod. One is primary (also called network) - 220 V is supplied to it, and the second is secondary - reduced voltage is removed from it.
The operating principle of the transformer is as follows. If voltage is applied to the mains winding, then, since it is closed, alternating current will begin to flow through it. Around this current, an alternating magnetic field arises, which collects 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, under the influence of an alternating magnetic flux an electromotive force (EMF) is generated in it. When this winding is shorted to a load, 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 onto it, thereby obtaining the required secondary voltage, which is directly proportional to the number of turns.
The main parameters for us are two parameters of the transformer - voltage and current of the secondary winding. We will take the current value to be 1 A, since we will use zener diodes for the same value. About that a little further.
We continue to assemble the power supply with our own hands. And the next order element in the circuit is a diode bridge, also known as a semiconductor or diode rectifier. It is designed to convert the alternating voltage of the secondary winding of the transformer into direct voltage, or more precisely, into rectified pulsating voltage. This is where the name “rectifier” comes from.
There are various rectification circuits, but the bridge circuit is the most widely used. The principle of its operation is as follows. In the first half-cycle of the alternating voltage, current flows along the path through the diode VD1, resistor R1 and LED VD5. Next, the current returns to the winding through open VD2.
A reverse voltage is applied to the diodes VD3 and VD4 at this moment, so they are locked and no current flows 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 resistor R1 and LED VD5 will remain the same.
A diode bridge can be soldered from four diodes connected according to the diagram above. Or you can buy it ready-made. They come in horizontal and vertical versions in different housings. But in any case, they have four conclusions. The two terminals are supplied with alternating voltage, they are designated by the sign “~”, both are the same length and are the shortest.
The rectified voltage is removed from the other two terminals. They are designated “+” and “-”. The “+” pin has the longest length among the others. And on some buildings there is a bevel near it.
Capacitor filter
After the diode bridge, the voltage has a pulsating nature and is still unsuitable for powering microcircuits, and especially 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 capacitance, so an electrolytic capacitor should be used. Such capacitors often have polarity, so it must be observed when connecting to the circuit.
The negative terminal is shorter than the positive one and a “-” sign is applied to the body near the first one.
Voltage regulator L.M. 7805, L.M. 7809, L.M. 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 change in a proportional range at the output of the power supply. However, such vibrations are extremely undesirable and sometimes unacceptable for many electronic elements. Therefore, the voltage after the capacitor filter must be stabilized. 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 stabilizer is used. Let's consider the application of the latter.
In amateur radio practice, voltage stabilizers of the LM78xx and LM79xx series are widely used. Two letters indicate the manufacturer. Therefore, instead of LM there may be other letters, for example CM. The marking consists of four numbers. The first two - 78 or 79 - mean positive or negative voltage, respectively. The last two digits, in this case instead of two X's: xx, indicate the value of the output U. For example, if the position of two X's is 12, then this stabilizer produces 12 V; 08 – 8 V, etc.
For example, let's decipher the following markings:
LM7805 → 5V positive voltage
LM7912 → 12 V negative U
Integrated stabilizers have three outputs: input, common and output; designed for current 1A.
If the output U significantly exceeds the input and the maximum current consumption is 1 A, then the stabilizer gets very hot, 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 don’t have to install a radiator.
The classic design of the power supply circuit includes: a network 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 current-limiting element is the LM7805 stabilizer (allowable value 1 A), 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 reason, 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. A couple of volts more than its output value should be supplied to the input of the stabilizer. Otherwise it will not work correctly. For example, for LM7805 input U = 7 - 8 V; for LM7805 → 15 V. However, it should be taken into account that if the value of U is too high, the microcircuit will heat up very much, since the “extra” voltage is extinguished at its internal resistance.
The diode bridge can be made from 1N4007 type diodes, or take a ready-made one for a current of at least 1 A.
Smoothing capacitor C1 should have a large capacity of 100 - 1000 µF and U = 16 V.
Capacitors C2 and C3 are designed to smooth out high-frequency ripple that occurs when the LM7805 operates. They are installed for greater reliability and are recommendations from manufacturers of stabilizers of similar types. The circuit also works normally without such capacitors, but since they cost practically nothing, it is better to install them.
DIY power supply for 78 L 05, 78 L 12, 79 L 05, 79 L 08
Often it is 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, etc. series. They are designed for a maximum current of 100 mA = 0.1 A, but are very compact and no larger in size than a regular transistor, and also do not require installation on a radiator.
The markings and connection diagram are similar to the LM series discussed above, only the location of the pins differs.
For example, the connection diagram for the 78L05 stabilizer is shown. It is also suitable for LM7805.
The connection diagram for negative voltage stabilizers is shown below. The input is -8 V, and the output is -5 V.
As you can see, making a power supply with your own hands is very simple. Any voltage can be obtained by installing an appropriate stabilizer. You should also remember the transformer parameters. Next we will look at how to make a power supply with voltage regulation.
For radio amateurs, and modern people in general, an indispensable thing in the house is a power supply unit (PSU), because it has a very useful function - voltage and current regulation.
At the same time, few people know that it is quite possible to make such a device with due diligence and knowledge of radio electronics with your own hands. For any radio amateur who likes to tinker with electronics at home, homemade laboratory power supplies will allow him to practice his hobby without restrictions. Our article will tell you how to make an adjustable power supply with your own hands.
What you need to know
A power supply with current and voltage regulation is a must-have item in a modern home. This device, thanks to its special device, can convert the voltage and current available in the network to the level that a particular electronic device can consume. Here is an approximate scheme of work according to which you can make such a device with your own hands.
But ready-made power supplies are quite expensive to buy for specific needs. Therefore, today very often converters for voltage and current are made by hand.
Note! Homemade laboratory power supplies can have different dimensions, power ratings and other characteristics. It all depends on what kind of converter you need and for what purpose.
Professionals can easily make a powerful power supply, while beginners and amateurs can start with a simple type of device. In this case, depending on the complexity, a very different scheme can be used.
What to consider
The regulated power supply is a universal converter that can be used to connect any household or computing equipment. Without it, not a single home appliance will be able to function normally.
Such a power supply unit consists of the following components:
- transformer;
- converter;
- indicator (voltmeter and ammeter).
- transistors and other parts necessary to create a high-quality electrical network.
The diagram above shows all the components of the device.
In addition, this type of power supply must have protection for high and low current. Otherwise, any emergency situation may lead to the fact that the converter and the electrical device connected to it simply burn out. This result can also be caused by improper soldering of board components, incorrect connection or installation.
If you are a beginner, then in order to make an adjustable type of power supply with your own hands, it is better to choose a simple assembly option. One of the simple types of converter is a 0-15V power supply. It has protection against excess current in the connected load. The diagram for its assembly is located below.
Simple assembly diagram
This is, so to speak, a universal type of assembly. The diagram here is easy to understand for anyone who has held a soldering iron at least once in their hands. The advantages of this scheme include the following points:
- it consists of simple and affordable parts that can be found either on the radio market or in specialized radio electronics stores;
- simple type of assembly and further configuration;
- here the lower limit for voltage is 0.05 volts;
- dual-range protection for current indicator (at 0.05 and 1A);
- wide range for output voltages;
- high stability in the functioning of the converter.
Diode bridge
In this situation, the transformer will provide a voltage that is 3V higher than the maximum required output voltage. It follows from this that a power supply capable of regulating voltage up to 20V requires a transformer of at least 23 V.
Note! The diode bridge should be selected based on the maximum current, which will be limited by the available protection.
A 4700 µF filter capacitor will allow equipment sensitive to power supply noise to avoid background noise. To do this, you will need a compensation stabilizer with a suppression coefficient for ripples of more than 1000.
Now that we have understood the basic aspects of assembly, we need to pay attention to the requirements.
Device requirements
To create a simple, but at the same time high-quality and powerful power supply with the ability to regulate voltage and current with your own hands, you need to know what requirements exist for this type of converter.
These technical requirements look like this:
- adjustable stabilized output for 3–24 V. In this case, the current load must be at least 2 A;
- unregulated 12/24 V output. This assumes a large current load.
To fulfill the first requirement, you should use an integral stabilizer. In the second case, the output must be made after the diode bridge, so to speak, bypassing the stabilizer.
Let's start assembling
Transformer TS-150–1
Once you have determined the requirements that your permanent regulated power supply must meet, and the appropriate circuit has been selected, you can begin the assembly itself. But first of all, let's stock up on the parts we need.
For assembly you will need:
- powerful transformer. For example, TS-150–1. It is capable of delivering voltages of 12 and 24 V;
- capacitor. You can use a 10000 µF 50 V model;
- chip for stabilizer;
- strapping;
- details of the circuit (in our case, the circuit shown above).
After this, according to the diagram, we assemble an adjustable power supply with our own hands in strict accordance with all the recommendations. The sequence of actions must be followed.
Ready power supply
The following parts are used to assemble the power supply:
- germanium transistors (mostly). If you want to replace them with more modern silicon elements, then the lower MP37 should definitely remain germanium. MP36, MP37, MP38 transistors are used here;
- A current-limiting unit is assembled on the transistor. It provides monitoring of the voltage drop across the resistor.
- Zener diode D814. It determines the regulation of the maximum output voltage. It absorbs half of the output voltage;
Note! Since the D814 zener diode takes exactly half the output voltage, it should be selected to create a 0-25V output voltage of approximately 13V.
- the lower limit in the assembled power supply has a voltage indicator of only 0.05 V. This indicator is rare for more complex converter assembly circuits;
- dial indicators display current and voltage indicators.
Parts for assembly
To accommodate all the parts, you must choose a steel case. It will be able to shield the transformer and power supply board. As a result, you will avoid situations of various types of interference for sensitive equipment.
The resulting converter can be safely used to power any household equipment, as well as experiments and tests carried out in a home laboratory. Also, such a device can be used to assess the performance of a car generator.
Conclusion
Using simple circuits for assembling an regulated type of power supply, you will be able to get your hands on and in the future make more complex models with your own hands. You should not take on backbreaking work, as in the end you may not get the desired result, and a homemade converter will work ineffectively, which can negatively affect both the device itself and the functionality of the electrical equipment connected to it.
If everything is done correctly, then at the end you will get an excellent power supply with voltage regulation for your home laboratory or other everyday situations.
Selecting a street motion sensor to turn on the lights
Step-by-step instructions for creating a laboratory power supply - diagram, necessary parts, installation tips, video.
A laboratory power supply is a device that generates the necessary voltage and current for further use when connected to the network. In most cases, it converts alternating current from the network into direct current. Every radio amateur has such a device, and today we will look at how to create it with your own hands, what you will need for this, and what nuances are important to consider during installation.
Advantages of a laboratory power supply
First, let's note the features of the power supply unit that we are going to manufacture:
- The output voltage is adjustable within 0–30 V.
- Protection against overload and incorrect connection.
- Low ripple level (the direct current at the output of the laboratory power supply is not much different from the direct current of batteries and accumulators).
- The ability to set a current limit of up to 3 Amps, after which the power supply will go into protection (a very convenient function).
- On the power supply, by short circuiting the crocodiles, the maximum permissible current is set (current limit, which you set with a variable resistor using an ammeter). Therefore, overloads are not dangerous, since in this case the LED indicator will work, indicating that the set current level has been exceeded.
Laboratory power supply - diagram
Laboratory power supply diagram
Now let's look at the diagram in order. It has been on the Internet for a long time. Let's talk separately about some of the nuances.
So, the numbers in circles are contacts. You need to solder wires to them that will go to radio elements.
- See also how to do
- 1 and 2 - to the transformer.
- 3 (+) and 4 (-) - DC output.
- 5, 10 and 12 - on P1.
- 6, 11 and 13 - on P2.
- 7 (K), 8 (B), 9 (E) - to transistor Q4.
Diodes D1...D4 are connected into a diode bridge. You can take 1N5401...1N5408, some other diodes, and even ready-made diode bridges that can withstand forward current up to 3 A and higher. We used KD213 tablet diodes.
Microcircuits U1, U2, U3 are operational amplifiers. Their pin locations, viewed from above:
The eighth pin says “NC” - this means that it does not need to be connected to either the minus or the plus of the power supply. In the circuit, pins 1 and 5 also do not connect anywhere.
- See also step-by-step instructions for creating
Transistor Q1 pinout diagram
It is better to take transistor Q2 from the Soviet KT961A. But don't forget to put it on the radiator
Transistor Q3 brand BC557 or BC327:
Transistor Q4 is exclusively KT827!
Here is its pinout:
Transistor Q4 pinout diagram
The variable resistors in this circuit are confusing - this is. They are designated here as follows:
Variable resistor input circuit
Here they are designated as follows:
Here is also a list of components:
- R1 = 2.2 kOhm 1W
- R2 = 82 Ohm 1/4W
- R3 = 220 Ohm 1/4W
- R4 = 4.7 kOhm 1/4W
- R5, R6, R13, R20, R21 = 10 kOhm 1/4W
- R7 = 0.47 Ohm 5W
- R8, R11 = 27 kOhm 1/4W
- R9, R19 = 2.2 kOhm 1/4W
- R10 = 270 kOhm 1/4W
- R12, R18 = 56kOhm 1/4W
- R14 = 1.5 kOhm 1/4W
- R15, R16 = 1 kOhm 1/4W
- R17 = 33 Ohm 1/4W
- R22 = 3.9 kOhm 1/4W
- RV1 = 100K multi-turn trimmer resistor
- P1, P2 = 10KOhm linear potentiometer
- C1 = 3300 uF/50V electrolytic
- C2, C3 = 47uF/50V electrolytic
- C4 = 100nF
- C5 = 200nF
- C6 = 100pF ceramic
- C7 = 10uF/50V electrolytic
- C8 = 330pF ceramic
- C9 = 100pF ceramic
- D1, D2, D3, D4 = 1N5401…1N5408
- D5, D6 = 1N4148
- D7, D8 = zener diodes at 5.6V
- D9, D10 = 1N4148
- D11 = 1N4001 diode 1A
- Q1 = BC548 or BC547
- Q2 = KT961A
- Q3 = BC557 or BC327
- Q4 = KT 827A
- U1, U2, U3 = TL081, operational amplifier
- D12 = LED
How to make a laboratory power supply with your own hands - printed circuit board and step-by-step assembly
Now let's look at the step-by-step assembly of a laboratory power supply with our own hands. We have a transformer ready from the amplifier. The voltage at its outputs was about 22 V. We prepare the case for the power supply.
We make a printed circuit board using LUT:
Printed circuit board diagram for laboratory power supply
Let's etch it:
Wash off the toner:
When you assemble any electronic homemade product, you need a power supply to test it. There is a wide variety of ready-made solutions on the market. Beautifully designed, have many functions. There are also many kits for DIY production. I'm not even talking about the Chinese with their trading platforms. I bought step-down converter module boards on Aliexpress, so I decided to make them on it. The voltage is regulated, there is enough current. The unit is based on a module from China, as well as radio components that were in my workshop (they had been lying around for a long time and were waiting in the wings). The unit regulates from 1.5 volts to the maximum (it all depends on the rectifier used to the adjustment board.
Description of components
I have a 17.9 Volt transformer with a current of 1.7 Ampere. It is installed in the housing, which means there is no need to select the latter. The winding is quite thick, I think it will handle 2 Amps. Instead of a transformer, you can use a switching power supply for a laptop, but then you also need a housing for the remaining components.
The AC rectifier will be a diode bridge; it can also be assembled from four diodes. An electrolytic capacitor will smooth out the ripples; I have 2200 microfarads and an operating voltage of 35 volts. I used it used, it was in stock.
I will regulate the output voltage. There are a wide variety of them on the market. It provides good stabilization and is quite reliable.
To conveniently adjust the output voltage, I will use a 4.7 kOhm adjustment resistor. The board has 10 kOhm installed, but I’ll install whatever I had. The resistor is from the early 90s. With this rating, adjustment is ensured smoothly. I also picked up a handle for it, also from a shaggy age.
The output voltage indicator is . It has three wires. Two wires power the voltmeter (red and black), and the third (blue) is measuring. You can combine red and blue together. Then the voltmeter will be powered from the output voltage of the unit, that is, the indication will light up from 4 volts. Agree, it’s not convenient, so I’ll feed it separately, more on that later.
To power the voltmeter, I will use a domestic 12-volt voltage stabilizer chip. This will ensure that the voltmeter indicator operates at a minimum. The voltmeter is powered through the red plus and black minus. The measurement is carried out through the black minus and blue plus output of the block.
My terminals are domestic. They have holes for banana plugs and holes for clamping wires. Similar . I also selected wires with lugs.
Power supply assembly
Everything is assembled according to a simple sketched diagram.
The diode bridge must be soldered to the transformer. I bent it for comfortable installation. A capacitor was soldered to the output of the bridge. It turned out not to go beyond the height dimensions.
I screwed the power supply arm of the voltmeter to the transformer. In principle, it does not heat up, and so it stands in its place and does not bother anyone.
I removed a resistor on the regulator board and soldered two wires under the remote resistor. I also soldered wires under the output terminals.
Mark holes on the case for everything that will be on the front panel. I cut holes for a voltmeter and one terminal. I install the resistor and the second terminal at the junction of the box. When assembling the box, everything will be fixed by compressing both halves.
The terminal and voltmeter are installed.
This is how it turned out to install the second terminal and the adjusting resistor. I made a cutout for the resistor key.
Cut out a window for the switch. We assemble the housing and close it. All that remains is to wire the switch and the regulated power supply is ready for use.
This is how the regulated power supply turned out. This design is simple and can be repeated by anyone. The parts are not rare.
Good luck with making everyone!
Hi all. Today is the final review, assembly of a laboratory linear power supply. Today there is a lot of metalwork, body fabrication and final assembly. The review is posted on the blog “DIY or Do It Yourself”, I hope I’m not distracting anyone here and preventing anyone from pleasing their eyes with the charms of Lena and Igor))). Anyone who is interested in homemade products and radio equipment - Welcome!!!
ATTENTION: Lots of letters and photos! Traffic!
Welcome radio amateur and DIY enthusiast! First, let's remember the stages of assembling a laboratory linear power supply. It is not directly related to this review, so I posted it under a spoiler:
Assembly steps
Assembling the power module. Board, radiator, power transistor, 2 variable multi-turn resistors and a green transformer (from the Eighties®) As the wise one suggested kirich, I independently assembled a circuit that the Chinese sell in the form of a construction kit 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 childhood problems of this circuit (which were completely copied by the Chinese) came out; without replacing the microcircuits with more “high-voltage” ones, it is impossible to apply to the input more than 22 volts of alternating voltage... And several smaller problems that our forum members suggested to me, for which I thank them very much. Most recently, the future engineer" AnnaSun"suggested getting rid of the transformer. Of course, anyone can upgrade their power supply as they wish, you can also use a pulse generator as a power source. But any pulse generator (maybe except resonant ones) has a lot of interference at the output, and this interference will partially transfer to the LabBP output... What if there is pulse interference, then (IMHO) this is not a 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 the excess energy is released on the power transistor. For example, we supply 24V alternating voltage to the input, which after rectification and smoothing will turn into 32-33V. If a powerful load is connected to the output, consuming 3A at a voltage of 5V, all the remaining power (28V at a current of 3A), which is 84W, will be dissipated by the power transistor, turning into heat. One way to prevent this problem, and accordingly increase efficiency, is to install a module for manual or automatic switching of windings. This module was reviewed in: 
For 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, allowing you to turn the load on or off. This was dedicated to this. 
Unfortunately, due to the lack of the necessary relays (normally closed), this module did not work correctly, so it will be replaced by another module, on a D-trigger, which allows you to turn the load on or off using one button.
I'll tell you briefly about the new module. The scheme is quite well known (sent to me in a private message): 
I slightly modified it to suit my needs and assembled the following board: 
On the back side: 
This time there were no problems. Everything works very clearly and is controlled with one button. When power is applied, the 13th output of the microcircuit is always logical zero, the transistor (2n5551) is closed and the relay is de-energized - accordingly, the load is not connected. When you press the button, a logical one appears at the output of the microcircuit, the transistor opens and the relay is activated, connecting the load. Pressing the button again returns the chip to its original state.
What is a power supply without a voltage and current indicator? That's why I tried to make an ampere-voltmeter myself. In principle, it turned out to be a good device, but it has some nonlinearity in the range from 0 to 3.2A. This error will not affect in any way when using this meter, say, in a charger for a car battery, but is unacceptable for a Laboratory power supply, therefore, I will replace this module with Chinese precision panel boards and with displays having 5 digits... And the module I assembled will find application in some other homemade product. 
Finally, higher-voltage microcircuits arrived from China, as I told you about in. And now you can supply 24V AC to the input without fear that it will break through the microcircuits... 
Now the only thing left to do is to make the case and assemble all the blocks together, which is what I will do in this final review on this topic.
Having searched 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 a body; you can add a little more and buy it. At least this PSU will make a good case.
So I went to the construction market and bought 3 meters of aluminum angle. With its help, the frame of the device will be assembled.
We prepare the parts of the required size. We draw out the blanks and cut off the corners using a cutting disc. . 
Then we lay out the blanks for the top and bottom panels to see what will happen. 
Trying to place the modules inside 
Assembly is carried out using countersunk screws (under the head with a countersink, a hole is countersunk so that the screw head does not protrude above the corner), and nuts on the reverse side. The outlines of the power supply frame are slowly appearing: 
And now the frame is assembled... It’s not very smooth, especially in the corners, but I think that painting will hide all the unevenness: 
Dimensions of the frame under the spoiler:
Dimensions
Unfortunately, there is little free time, so the plumbing work is progressing slowly. In the evenings, over the course of a week, I made a front panel from a sheet of aluminum and a socket for the power input and fuse. 
We draw out future holes for the Voltmeter and Ammeter. The seat size should be 45.5mm by 26.5mm
Cover the mounting 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 size of the sockets, and not spoil the panel with scratches) The Dremel quickly copes with aluminum, but it takes 3-4 for 1 hole 
Again there was a hitch, it’s trivial, we ran out of cutting discs for the Dremel, a search in all the stores in Almaty did not lead to anything, so we had to wait for the discs from China... Fortunately, they arrived quickly in 15 days. Then the work went more fun and quickly...
I sawed holes for the digital indicators with a Dremel and filed them. 
We put a green transformer on the “corners” 
Let's try on a radiator with a power transistor. It will be isolated from the housing, since a transistor in a TO-3 housing is installed on the radiator, and there it is difficult to isolate the transistor collector from the housing. The radiator will be behind a decorative grille with a cooling fan. 
I sanded the front panel on a block. I decided to try on everything that would be attached to it. It turns out like this: 
Two digital meters, a load switch, two multi-turn potentiometers, output terminals and a “Current Limit” LED holder. It seems like you forgot nothing? 
On the back of the front panel.
We disassemble everything and paint the power supply frame with black spray paint. 
We attach a decorative grille to the rear wall with bolts (purchased at the car market, anodized aluminum for tuning the radiator air intake, 2000 tenge (6.13USD)) 
This is how it turned out, view from the back of the power supply housing. 
We install a fan to blow the radiator with a power transistor. I attached it to plastic black clamps, it holds well, the appearance does not suffer, they are almost invisible. 
We return the plastic base of the frame with the power transformer already installed. 
We mark the mounting locations for the radiator. The radiator is isolated from the device body, because the voltage across it is equal to the voltage at 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 takes information from a sensor (thermistor) attached to the radiator. Thus, the fan will not “thresh” on empty, but will turn on when a certain temperature is reached on the radiator of the power transistor. 
We attach the front panel in place and see what happens. 
There was a lot of decorative grille left, so I decided to try to make a U-shaped cover for the power supply housing (in the manner of computer cases); if I don’t like it, I’ll remake it with something else. 
Front view. While the lattice is “baited” and does not yet fit tightly to the frame. 
It seems to be working out well. The grille is strong enough, you can safely put anything on top, but you don’t even need to talk about the quality of ventilation inside the case, the ventilation will be simply excellent compared to closed cases. 
Well, let's continue the assembly. We connect a digital ammeter. Important: do not step on my rake, do not use a standard connector, only solder directly to the connector contacts. Otherwise, it will be in place of the current in Amperes, showing 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 PCB. It is very convenient to draw insulating grooves in copper foil to create platforms for connecting all auxiliary devices (ammeter, voltmeter, load disconnect 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 has significantly reduced the length of the wire loop. 
Now it’s time to assemble an additional power module for a winding switching module, ammeter, voltmeter, etc.
Since we have a linear analog power supply, we will also use the option on a transformer, no switching power supplies. :-)
We etch the board: 
Soldering in the details: 
We test, install brass “legs” and build the module into the body: 
Well, all the blocks are built in (except for the fan control module, which will be manufactured later) and installed in their places. The wires are connected, the fuses are inserted. You can start the first time. We sign ourselves with the cross, close our eyes and give food...
There is no boom and no white smoke - that’s good... It seems like 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 they say, “soon the tale is told, but not soon the deed is done.” Pitfalls emerged again. The transformer winding switching module does not work correctly with the power module. When the switching voltage from the first winding to the next occurs, a voltage jump occurs, i.e., when it reaches 6.4V, a jump occurs to 10.2V. Then, of course, you can reduce the tension, but this is not the point. At first I thought that the problem was in the power supply of the microcircuits, since their power supply is also from the windings of the power transformer, and accordingly grows with each subsequent connected winding. Therefore, I tried to supply power to 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 putting up with the stove as an option, so I’ll install a toggle switch that allows you to select the supplied voltage to the power supply 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 green numbers, since the red numbers of the ammeter glow rather faintly and are hard to see in sunlight. Here's what happened: 
It seems better this way. It is also possible that I will replace the voltmeter with another one, because... 5 digits in a voltmeter are clearly excessive, 2 decimal places are quite enough. I have replacement options, so there won't be any problems.
We install the switch and connect the wires to it. Let's check.
When the switch was positioned “down”, the maximum voltage without load was about 16V 
When the switch is positioned up, the maximum voltage available for this transformer is 34V (no load) 
Now for the handles, I didn’t spend a long time coming up with options and found plastic dowels of a suitable diameter, both internal and external. 
We cut the tube to the required length and put it on the rods of the variable resistors: 
Then we put on the handles and secure them with screws. Since the dowel tube is quite soft, the handle is fixed very well; considerable effort is required to tear it off. 
The review turned out to be very large. Therefore, I will not take up your time and will 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 the circuitry.
Therefore, let’s check the minimum voltage, the adjustment knob is in the extreme left position: 
Now the maximum current 
Current limit 1A 
Maximum current limitation, current adjustment knob in the extreme right position: 
That's all for my dear radio destroyers and sympathizers... Thanks to everyone who read to the end. The device turned out to be brutal, heavy and, I hope, reliable. See you again on 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 me an idea on how to launch a winding switching module with minimal circuit modifications. Thank you all for your interest, I will finish the device. Therefore - to be continued. Add to favorites Liked +72 +134
