Good day, forum users and site guests. Radio circuits! Wanting to put together a decent, but not too expensive and cool power supply, so that it has everything and it doesn’t cost anything. In the end, I chose the best, in my opinion, circuit with current and voltage regulation, which consists of only five transistors, not counting a couple of dozen resistors and capacitors. Nevertheless, it works reliably and is highly repeatable. This scheme has already been reviewed on the site, but with the help of colleagues we managed to improve it somewhat.

I assembled this circuit in its original form and encountered one unpleasant problem. When adjusting the current, I can’t set it to 0.1 A - at least 1.5 A at R6 0.22 Ohm. When I increased the resistance of R6 to 1.2 Ohms, the current during a short circuit turned out to be at least 0.5 A. But now R6 began to heat up quickly and strongly. Then I used a small modification and got a much wider current regulation. Approximately 16 mA to maximum. You can also make it from 120 mA if you transfer the end of the resistor R8 to the T4 base. The bottom line is that before the resistor voltage drops, a drop is added B-E transition and this additional voltage allows you to open T5 earlier, and as a result, limit the current earlier.

Based on this proposal, I conducted successful tests and eventually received a simple laboratory power supply. I am posting a photo of my laboratory power supply with three outputs, where:

• 1-output 0-22v
• 2-output 0-22v
• 3-output +/- 16V

Also, in addition to the output voltage regulation board, the device was supplemented with a power filter board with a fuse block. What happened in the end - see below.

Sergey Nikitin

Simple laboratory power supply.

With a description of this simple laboratory power supply, I am opening a series of articles in which I will introduce you to simple and reliable developments (mainly various sources power supply and chargers), which had to be assembled as needed from improvised means.
For all these structures, parts and pieces from old office equipment that were decommissioned were mainly used.

And so, I somehow urgently needed a power supply with adjustable output voltage within 30-40 volts and a load current of around 5 amperes.

There was a transformer available from a UPS-500 uninterruptible power supply, in which, when connecting the secondary windings in series, the result was about 30-33 Volts AC voltage. This suited me just fine, but I just had to decide which circuit to use to assemble the power supply.

If you make a power supply according to the classical scheme, then all the excess power at a low output voltage will be allocated to the regulating transistor. This didn’t suit me, and I didn’t want to make a power supply according to the proposed schemes, and I would also have to look for parts for it.
Therefore, I developed a diagram for those parts that are on this moment I had them in stock.

The circuit was based on a key stabilizer in order to heat the empty surrounding space with the power released on the regulating transistor.
There is no PWM regulation and the switching frequency of the key transistor depends only on the load current. Without load, the switching frequency is around one hertz or less, depending on the inductance of the inductor and the capacitance of capacitor C5. Switching on can be heard by a slight clatter of the throttle.

There were a huge number of MJ15004 transistors from previously disassembled uninterruptible power supplies, so I decided to install them over the weekend. For reliability, I put two in parallel, although one copes with its task quite well.
You can replace them with any powerful p-n-p transistors, for example KT-818, KT-825.

Inductor L1 can be wound on a conventional W-shaped (SH) magnetic circuit; its inductance is not particularly critical, but it is desirable that it be closer to several millihenries.
Take any suitable core, Ш, ШЛ, with a cross-section preferably at least 3 cm. Cores from output transformers of tube receivers, televisions, output transformers of frame scans of televisions, etc. are quite suitable. For example, the standard size is Ш, ШЛ-16х24.
Next, a copper wire with a diameter of 1.0 - 1.5 mm is taken and wound until the core window is completely filled.
I have a choke wound on iron from a TVK-90 transformer, with a 1.5 mm wire until the window is filled.
Of course, we assemble the magnetic circuit with a gap of 0.2-0.5 mm (2 - 5 layers of ordinary writing paper).

The only negative of this power supply is that under heavy load the inductor buzzes, and this sound changes depending on the load, which is audible and a little bothersome. Therefore, you probably need to saturate the throttle well, or maybe even better, completely fill it in some suitable housing with epoxy to reduce the “clicking” sound.

I installed the transistors on small aluminum plates, and just in case, I also put a fan inside to blow them.

Instead of VD1, you can install any fast diodes for the appropriate voltage and current, I just have a lot of KD213 diodes, so I basically install them everywhere in such places. They are quite powerful (10A) and the voltage is 100V, which is quite enough.

Don’t pay too much attention to my power supply design, the task was not the same. It had to be done quickly and efficiently. I made it temporarily in this case and in this design, and so far it has been working “temporarily” for quite some time.
You can also add an ammeter to the circuit for convenience. But this is a personal matter. I installed one head for measuring voltage and current, made a shunt for the ammeter from a thick mounting wire (you can see in the photographs, wound on a wire resistor) and set the “Voltage” - “Current” switch. The diagram just didn't show it.

When creating various electronic devices, sooner or later the question arises of what to use as a power source for homemade electronics. Let's say you've assembled some kind of LED flasher, now you need to carefully power it from something. Very often, various charging device for phones, computer power supplies, all kinds network adapters, which do not in any way limit the current supplied to the load.

And if, for example, on this same board LED flasher did two closed paths accidentally go unnoticed? By connecting it to a powerful computer power supply, the assembled device can easily burn out if there is any installation error on the board. It is precisely to prevent such unpleasant situations from happening that there are laboratory power supplies with current protection. Knowing in advance approximately how much current the connected device will consume, we can prevent short circuits and, as a result, burnout of transistors and delicate microcircuits.
In this article we will look at the process of creating just such a power supply to which you can connect a load without fear that something will burn out.

Power supply diagram

PCB fabrication and assembly

(downloads: 941)

Setting up the power supply

Indication

Today we will assemble a laboratory power supply with our own hands. We will understand the structure of the block, select the right components, learn how to solder correctly, and assemble elements onto printed circuit boards.

This is a high-quality laboratory (and not only) AC power supply adjustable voltage from 0 to 30 volts. The circuit also includes an electronic output current limiter that effectively regulates the output current to 2 mA from the circuit's maximum current of 3 A. This characteristic makes this power supply indispensable in the laboratory, as it makes it possible to regulate power, limit the maximum current that the connected device can consume, without fear of damage if something goes wrong.
There is also a visual indication that this limiter is in effect (LED) so you can see if your circuit is exceeding its limits.

The schematic diagram of the laboratory power supply is presented below:

Technical characteristics of laboratory power supply

Input voltage: ……………. 24 V-AC;
Input current: ……………. 3 A (max);
Output voltage: …………. 0-30 V - adjustable;
Output current: …………. 2 mA -3 A - adjustable;
Output voltage ripple: .... 0.01% maximum.

Peculiarities

- Small size, easy to make, simple design.
— Output voltage is easily adjustable.
— Output current limitation with visual indication.
— Protection against overload and incorrect connection.

Principle of operation

Let's start with the fact that the laboratory power supply uses a transformer with a secondary winding of 24V/3A, which is connected through input terminals 1 and 2 (the quality of the output signal is proportional to the quality of the transformer). The AC voltage from the secondary winding of the transformer is rectified by a diode bridge formed by diodes D1-D4. The ripples of the rectified DC voltage at the output of the diode bridge are smoothed by a filter formed by resistor R1 and capacitor C1. The circuit has some features that make this power supply different from other units in its class.

Instead of using feedback to control the output voltage, our circuit uses operational amplifier to provide the necessary voltage for stable operation. This voltage drops at the output of U1. The circuit operates thanks to the D8 - 5.6 V Zener diode, which here operates at zero temperature coefficient of current. The voltage at the output of U1 drops across the diode D8 turning it on. When this happens, the circuit stabilizes and the voltage of the diode (5.6) drops across resistor R5.

The current that flows through the opera. the amplifier changes slightly, which means the same current will flow through resistors R5, R6, and since both resistors have the same voltage value, the total voltage will be summed up as if serial connection. Thus, the voltage obtained at the output of the opera. amplifier will be equal to 11.2 volts. Chain from oper. amplifier U2 has a constant gain of approximately 3, according to the formula A = (R11 + R12) / R11 increases the voltage of 11.2 volts to approximately 33 volts. Trimmer RV1 and resistor R10 are used to set the voltage output so that it does not drop to 0 volts, regardless of the value of other components in the circuit.

Another very important characteristic of the circuit is the ability to obtain the maximum output current that can be obtained from the p.s.u. To make this possible, the voltage drops across a resistor (R7), which is connected in series with the load. The IC responsible for this circuit function is U3. An inverted signal to input U3 equal to 0 volts is supplied through R21. At the same time, without changing the signal of the same IC, you can set any voltage value through P2. Let's say that for a given output the voltage is several volts, P2 is set so that there is a signal of 1 volt at the input of IC. If the load is amplified, the output voltage will be constant and the presence of R7 in series with the output will have little effect due to its low magnitude and due to its position outside the feedback loop of the control circuit. As long as the load and output voltage are constant, the circuit operates stably. If the load is increased so that the voltage on R7 is greater than 1 volt, U3 is turned on and stabilizes to its original parameters. U3 operates without changing the signal to U2 through D9. Thus, the voltage through R7 is constant and does not increase above a predetermined value (1 volt in our example), reducing the output voltage of the circuit. This device is capable of maintaining the output signal constant and accurate, which makes it possible to obtain 2 mA at the output.

Capacitor C8 makes the circuit more stable. Q3 is needed to control the LED whenever you use the limiter indicator. To make this possible for U2 (changing the output voltage down to 0 volts) it is necessary to provide a negative connection, which is done through the circuit C2 and C3. Is the same negative connection used for U3. Negative voltage is supplied and stabilized by R3 and D7.

U1 is a reference voltage source, U2 is a voltage regulator, U3 is a current stabilizer.

Power supply design.

First of all, let's look at the basics of building electronic circuits on printed circuit boards - the basics of any laboratory power supply. The board is made of a thin insulating material covered with a thin conductive layer of copper, which is formed so that the circuit elements can be connected by conductors as shown in schematic diagram. It is necessary to design the PCB properly to avoid the device from malfunctioning. To protect the board from oxidation in the future and keep it in excellent condition, it must be coated with a special varnish that protects against oxidation and makes soldering easier.
Soldering elements into a board is the only way to assemble a laboratory power supply efficiently, and the success of your work will depend on how you do this. This is not very difficult if you follow a few rules and then you will not have any problems. The power of the soldering iron you use should not exceed 25 watts. The tip should be thin and clean throughout the entire operation. To do this, there is a damp sponge of sorts and from time to time you can clean the hot tip to remove all the residues that accumulate on it.

• DO NOT attempt to clean a dirty or worn tip with a file or sandpaper. If it cannot be cleaned, replace it. There are many different soldering irons on the market and you can also buy a good flux to get good connection elements during soldering.
• DO NOT use flux if you are using solder that already contains it. A large number of flux is one of the main causes of circuit failure. If, however, you must use additional flux as when tinning copper wires, you must clean the work surface after finishing the job.

In order to solder the element correctly, you must do the following:
— Clean the terminals of the elements with sandpaper (preferably with a small grain).
— Bend component leads at the correct distance from the exit from the case for convenient placement on the board.
— You may encounter elements whose leads are thicker than the holes in the board. In this case, you need to widen the holes a little, but do not make them too large - this will make soldering difficult.
— The element must be inserted so that its leads protrude slightly from the surface of the board.
- When the solder melts, it will spread evenly throughout the entire area around the hole (this can be achieved by using the correct soldering iron temperature).
— Soldering one element should take no more than 5 seconds. Remove excess solder and wait until the solder on the board cools naturally (without blowing on it). If everything was done correctly, the surface should have a bright metallic tint, the edges should be smooth. If the solder appears dull, cracked, or bead-shaped, it is called dry soldering. You must delete it and do everything again. But be careful not to overheat the traces, otherwise they will lag behind the board and break easily.
— When you solder a sensitive element, you need to hold it with metal tweezers or tongs, which will absorb excess heat so as not to burn the element.
- When you complete your job, trim off the excess from the element leads and you can clean the board with alcohol to remove any remaining flux.

Before you start assembling the power supply, you need to find all the elements and divide them into groups. First, install the ICs sockets and external connections pins and solder them in place. Then resistors. Remember to place R7 at a certain distance from printed circuit board because it gets very hot, especially when high current flows, and this can damage it. This is also recommended for R1. then place the capacitors not forgetting the polarity of the electrolytic and finally solder the diodes and transistors, but be careful not to overheat them and solder them as shown in the diagram.
Install the power transistor in the heatsink. To do this you need to follow the diagram and remember to use an insulator (mica) between the transistor body and the heatsink and a special cleaning fiber to insulate the screws from the heatsink.

Connect an insulated wire to each terminal, being careful to make a good quality connection as there is a lot of current flowing here, especially between the emitter and collector of the transistor.
Also, when assembling the power supply, it would be nice to estimate where each element will be located, in order to calculate the length of the wires that will be between the PCB and the potentiometers, the power transistor and for the input and output connections.
Connect the potentiometers, LED and power transistor and connect two pairs of ends for input and output connections. Make sure from the diagram that you are doing everything correctly, try not to confuse anything, since there are 15 external connections in the circuit and if you make a mistake, it will be difficult to find it later. It would also be a good idea to use wires of different colors.

Printed circuit board of a laboratory power supply, below there will be a link to download the signet in .lay format:

Layout of elements on the power supply board:

Connection diagram of variable resistors (potentiometers) to regulate the output current and voltage, as well as connection of the contacts of the power transistor of the power supply:

Designation of transistor and operational amplifier pins:

Terminal designations on the diagram:
— 1 and 2 to the transformer.
— 3 (+) and 4 (-) DC OUTPUT.
- 5, 10 and 12 on P1.
- 6, 11 and 13 on P2.
- 7 (E), 8 (B), 9 (E) to transistor Q4.
— LED must be installed on the outside of the board.

When all external connections are made, it is necessary to check the board and clean it to remove any remaining solder. Make sure there is no connection between adjacent tracks that could cause short circuit and if all is well, connect the transformer. And connect the voltmeter.
DO NOT TOUCH ANY PORTION OF THE CIRCUIT WHILE IT IS LIVE.
The voltmeter should show a voltage between 0 and 30 volts depending on the position of P1. Turning P2 counterclockwise should turn on the LED, indicating that our limiter is working.

List of elements.

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 trimmer
P1, P2 = 10KOhm linear potentiometer
C1 = 3300 uF/50V electrolytic
C2, C3 = 47uF/50V electrolytic
C4 = 100nF polyester
C5 = 200nF polyester
C6 = 100pF ceramic
C7 = 10uF/50V electrolytic
C8 = 330pF ceramic
C9 = 100pF ceramic
D1, D2, D3, D4 = 1N5402,3,4 diode 2A - RAX GI837U
D5, D6 = 1N4148
D7, D8 = 5.6V Zener
D9, D10 = 1N4148
D11 = 1N4001 diode 1A
Q1 = BC548, NPN transistor or BC547
Q2 = 2N2219 NPN transistor - (Replace with KT961A- everything is working)
Q3 = BC557, PNP transistor or BC327
Q4 = 2N3055 NPN power transistor ( replace with KT 827A)
U1, U2, U3 = TL081, op. amplifier
D12 = LED diode

As a result, I assembled a laboratory power supply myself, but in practice I encountered something that I considered necessary to correct. Well, first of all, this is a power transistor Q4 = 2N3055 it is needed in urgently cross it out and forget it. I don’t know about other devices, but it is not suitable for this regulated power supply. The fact is that this type transistors fail instantly when there is a short circuit and the current of 3 amperes does not draw at all!!! I didn’t know what was wrong until I changed it to our native Soviet one KT 827 A. After installing it on the radiator, I didn’t know any grief and never returned to this issue.

As for the rest of the circuitry and parts, there are no difficulties. With the exception of the transformer, we had to wind it. Well, this is purely out of greed, half a bucket of them is in the corner - don’t buy it =))

Well, in order not to break the good old tradition, I am posting the result of my work to the general public 🙂 I had to play around with the column, but overall it turned out not bad:

The front panel itself - I moved the potentiometers to the left side, on the right side there was an ammeter and a voltmeter + a red LED to indicate the current limit.

The next photo shows the rear view. Here I wanted to show how to install a cooler with a radiator from motherboard. A power transistor is placed on the back side of this radiator.

Here it is, the KT 827 A power transistor. Mounted on the rear wall. I had to drill holes for the legs, lubricate all contact parts with heat-conducting paste and secure them with nuts.

Here they are....the insides! Actually everything is in a heap!

Slightly larger inside the body

Front panel on the other side

Taking a closer look, you can see how the power transistor and transformer are mounted.

Power supply board on top; Here I cheated and packed low-power transistors at the bottom of the board. They are not visible here, so don't be surprised if you don't find them.

Here is the transformer. I rewound it to 25 volts of the TVS-250 output voltage. Rough, sour, not aesthetically pleasing, but everything works like a clock =) I didn’t use the second part. Left room for creativity.

Somehow like this. A little creativity and patience. The unit has been working great for 2 years now. To write this article I had to disassemble it and reassemble it. It's just awful! But everything is for you, dear readers!

Designs from our readers!

The master whose device was described in the first part, having set out to make a power supply with regulation, did not complicate things for himself and simply used boards that were lying idle. The second option involves the use of an even more common material - an adjustment has been added to the usual block, perhaps this is a very promising solution in terms of simplicity, given that the necessary characteristics will not be lost and even the most experienced radio amateur can implement the idea with his own hands. As a bonus, there are two more options simple circuits with all the detailed explanations for beginners. So, there are 4 ways for you to choose from.

We'll tell you how to make an adjustable power supply from an unnecessary computer board. The master took the computer board and cut out the block that powers the RAM.
This is what he looks like.

Let's decide which parts need to be taken and which ones not, in order to cut off what is needed so that the board has all the components of the power supply. Typically, a pulse unit for supplying current to a computer consists of a microcircuit, a PWM controller, key transistors, an output inductor and an output capacitor, and an input capacitor. For some reason, the board also has an input choke. He left him too. Key transistors - maybe two, three. There is a seat for 3 transistors, but it is not used in the circuit.

The PWM controller chip itself may look like this. Here she is under a magnifying glass.

It may look like a square with small pins on all sides. This is a typical PWM controller on a laptop board.

This is what a switching power supply looks like on a video card.

The power supply for the processor looks exactly the same. We see a PWM controller and several processor power channels. 3 transistors in this case. Choke and capacitor. This is one channel.
Three transistors, a choke, a capacitor - the second channel. Channel 3. And two more channels for other purposes.
You know what a PWM controller looks like, look at its markings under a magnifying glass, look for a datasheet on the Internet, download pdf file and look at the diagram so as not to confuse anything.
In the diagram we see a PWM controller, but the pins are marked and numbered along the edges.

Transistors are designated. This is the throttle. This is an output capacitor and an input capacitor. The input voltage ranges from 1.5 to 19 volts, but the supply voltage to the PWM controller should be from 5 volts to 12 volts. That is, it may turn out that a separate power source is required to power the PWM controller. All the wiring, resistors and capacitors, don’t be alarmed. You don't need to know this. Everything is on the board; you do not assemble a PWM controller, but use a ready-made one. You only need to know 2 resistors - they set the output voltage.

Resistor divider. Its whole point is to reduce the signal from the output to about 1 volt and apply feedback to the input of the PWM controller. In short, by changing the value of the resistors, we can regulate the output voltage. In the case shown, instead of a feedback resistor, the master installed a 10 kilo-ohm tuning resistor. This was sufficient to regulate the output voltage from 1 volt to approximately 12 volts. Unfortunately, this is not possible on all PWM controllers. For example, on PWM controllers of processors and video cards, in order to be able to adjust the voltage, the possibility of overclocking, the output voltage is supplied by software via a multi-channel bus. The only way to change the output voltage of such a PWM controller is by using jumpers.

So, knowing what a PWM controller looks like and the elements that are needed, we can already cut out the power supply. But this must be done carefully, since there are tracks around the PWM controller that may be needed. For example, you can see that the track goes from the base of the transistor to the PWM controller. It was difficult to save it; I had to carefully cut out the board.

Using the tester in dial mode and focusing on the diagram, I soldered the wires. Also using the tester, I found pin 6 of the PWM controller and the feedback resistors rang from it. The resistor was located in the rfb, it was removed and instead of it, a 10 kilo-ohm tuning resistor was soldered from the output to regulate the output voltage; I also found out by calling that the power supply of the PWM controller is directly connected to the input power line. This means that you cannot supply more than 12 volts to the input, so as not to burn out the PWM controller.

Let's see what the power supply looks like in operation

I soldered the input voltage plug, voltage indicator and output wires. Connecting external power supply 12 volts. The indicator lights up. It was already set to 9.2 volts. Let's try to adjust the power supply with a screwdriver.

It's time to check out what the power supply is capable of. Took it wooden block and a homemade wirewound resistor made from nichrome wire. Its resistance is low and, together with the tester probes, is 1.7 Ohms. We turn the multimeter into ammeter mode and connect it in series with the resistor. See what happens - the resistor heats up to red, the output voltage remains virtually unchanged, and the current is about 4 amperes.

The master had already made similar power supplies before. One is cut out with your own hands from a laptop board.

This is the so called standby voltage. Two sources of 3.3 volts and 5 volts. I made a case for it on a 3D printer. You can also look at the article where I made a similar adjustable power supply, also cut from a laptop board (https://electro-repair.livejournal.com/3645.html). This is also a PWM power controller for RAM.

How to make a regulating power supply from a regular printer

We will talk about the power supply for a Canon inkjet printer. Many people have them idle. This is essentially a separate device, held in the printer by a latch.
Its characteristics: 24 volts, 0.7 amperes.

I needed a power supply for a homemade drill. It's just right in terms of power. But there is one caveat - if you connect it like this, the output will only get 7 volts. Triple output, connector and we get only 7 volts. How to get 24 volts?
How to get 24 volts without disassembling the unit?
Well, the simplest one is to close the plus with the middle output and we get 24 volts.
Let's try to do it. We connect the power supply to the 220 network. We take the device and try to measure it. Let's connect and see 7 volts at the output.
Its central connector is not used. If we take it and connect it to two at the same time, the voltage is 24 volts. This is the easiest way to ensure that this power supply produces 24 volts without disassembling it.

Required homemade regulator so that the voltage can be adjusted within certain limits. From 10 volts to maximum. It's easy to do. What is needed for this? First, open the power supply itself. It is usually glued. How to open it without damaging the case. There is no need to pick or pry anything. We take a piece of wood that is heavier or have a rubber mallet. Place it on a hard surface and tap along the seam. The glue comes off. Then they tapped thoroughly on all sides. Miraculously, the glue comes off and everything opens up. Inside we see the power supply.

We'll get the payment. Such power supplies can be easily converted to the desired voltage and can also be made adjustable. On the reverse side, if we turn it over, there is an adjustable zener diode tl431. On the other hand, we will see the middle contact goes to the base of transistor q51.

If we apply voltage, then this transistor opens and 2.5 volts appears at the resistive divider, which is needed for the zener diode to operate. And 24 volts appears at the output. This is the simplest option. Another way to start it is to throw away transistor q51 and put a jumper instead of resistor r 57 and that’s it. When we turn it on, the output is always 24 volts continuously.

How to make the adjustment?

You can change the voltage, make it 12 volts. But in particular, the master does not need this. You need to make it adjustable. How to do it? We throw away this transistor and replace the 57 by 38 kilo-ohm resistor with an adjustable one. There is an old Soviet one with 3.3 kilo-ohms. You can put from 4.7 to 10, which is what it is. Only the minimum voltage to which it can lower it depends on this resistor. 3.3 is very low and not necessary. The engines are planned to be supplied at 24 volts. And just from 10 volts to 24 is normal. If you need a different voltage, you can use a high-resistance tuning resistor.
Let's get started, let's solder. Take a soldering iron and hair dryer. I removed the transistor and resistor.

We soldered the variable resistor and will try to turn it on. We applied 220 volts, we see 7 volts on our device and begin to rotate the variable resistor. The voltage has risen to 24 volts and we rotate it smoothly and smoothly, it drops - 17-15-14, that is, it decreases to 7 volts. In particular, it is installed on 3.3 rooms. And our rework turned out to be quite successful. That is, for purposes from 7 to 24 volts, voltage regulation is quite acceptable.

This option worked out. I installed a variable resistor. The handle turns out to be an adjustable power supply - quite convenient.

Video of the channel “Technician”.

Such power supplies are easy to find in China. I came across an interesting store that sells used power supplies from various printers, laptops and netbooks. They disassemble and sell the boards themselves, fully functional different voltages and currents. The biggest plus is that they disassemble branded equipment and all power supplies are of high quality, with good parts, all have filters.
The photos are of different power supplies, they cost pennies, practically a freebie.

Simple block with adjustment

Simple option homemade device for powering regulated devices. The scheme is popular, it is widespread on the Internet and has shown its effectiveness. But there are also limitations, which are shown in the video along with all the instructions for making a regulated power supply.

Homemade regulated unit on one transistor

What is the simplest regulated power supply you can make yourself? This can be done on the lm317 chip. It almost represents a power supply itself. It can be used to make both a voltage- and flow-regulated power supply. This video tutorial shows a device with voltage regulation. The master found a simple scheme. Input voltage maximum 40 volts. Output from 1.2 to 37 volts. Maximum output current 1.5 amperes.

Without a heat sink, without a radiator, the maximum power can be only 1 watt. And with a radiator 10 watts. List of radio components.


Let's start assembling

Let's connect an electronic load to the output of the device. Let's see how well it holds current. We set it to minimum. 7.7 volts, 30 milliamps.

Everything is regulated. Let's set it to 3 volts and add current. We’ll only set larger restrictions on the power supply. We move the toggle switch to the upper position. Now it's 0.5 ampere. The microcircuit began to warm up. There is nothing to do without a heat sink. I found some kind of plate, not for long, but enough. Let's try again. There is a drawdown. But the block works. Voltage adjustment is in progress. We can insert a test into this scheme.

Radioblogful video. Soldering video blog.