How to make a rectifier and a simple power supply. Do-it-yourself power supply Do-it-yourself laboratory power supply diagram

In the process of developing and repairing all kinds of electronic devices, various equipment is used. Among them, the regulated power supply circuit, used in many variants, is quite popular. These regulated units are known as laboratory power supplies and come in many variations.

Linear power supplies

The very first to appear were linear power supplies, which are still used today and belong to devices with traditional operating principles.

The main structural elements of these devices are a step-down transformer and an autotransformer. The conversion of alternating voltage to direct voltage is carried out using a rectifier. Most well-known models use rectifiers with one or four diodes connected to each other in the form.

Some models may have individual design features, but such schemes are used much less frequently and are intended for specific situations. In some devices, the circuit is supplemented with a special filter installed immediately behind the rectifier. The filter itself is a high-capacity capacitor. Sometimes linear power supplies are supplemented with voltage, high-frequency noise filters and other elements.

Among specialists involved in the repair and maintenance of electronics and radio equipment, the most popular are linear power supplies with possible voltage adjustment ranging from 0 to 30 volts and current from 0 to 5 amperes. As a rule, these are high-precision devices with easy and fine adjustments within the established ratings. Most of them are distinguished by a dual mode of operation, when a digital indicator simultaneously displays the values of output current and voltage. Many models are provided with protection against current overloads and short circuits.

Scheme and principle of operation of pulse power supplies

Today, increasing preference is given to switching type power supplies. The operating principle of these devices is completely different from that of linear equipment. In this case, the alternating voltage of the network with a frequency of 50 Hz is converted into high frequency voltage. It is transformed to the required parameters, after which it is straightened and filtered.

Direct conversion is performed using a powerful transistor operating in switch mode. Together with a pulse transformer, they form a high-frequency converter circuit. This device allows you to create a frequency in the range of 20-50 kHz, which in turn makes it possible to significantly reduce the dimensions of the pulse transformer. As a result, the power supply itself becomes light and compact.

The operating principle of the pulse unit can be seen in the diagram presented:

First, the voltage is supplied to the surge protector, after which it enters the rectifier. Here the voltage is rectified and filtered using a capacitor.
Next, through the primary winding W1, the voltage enters the collector of the transistor VT1, which is affected by a rectangular pulse. As a result, the transistor takes an open position and passes an increasing current through itself.
At the same time, the same current passes through the primary winding of the transformer, thereby causing an increase in the magnetic flux and the induction of self-induction emf in the secondary winding.

By changing the pulse duration upward, the voltage in the secondary circuit will also increase due to the greater amount of energy released. And, conversely, with a decrease in the pulse duration, a decrease in voltage will occur. Such manipulations allow you to adjust and stabilize the output voltage to the desired level. Pulses are generated and controlled using a PWM controller.

Adjustment and stabilization

In order to stabilize the output voltage, the PWM controller must receive information about the necessary parameters. This activity is performed using a feedback or tracking circuit.

This logic circuit works as follows: when the voltage decreases, it increases the pulse duration until the output voltage reaches the specified parameters. If the voltage increases, the reverse process occurs. Thus, the presented scheme can be considered a regulating and stabilizing element.

In switching power supplies, tracking circuits can be organized in two ways - direct and indirect. The method discussed above precisely belongs to the first option, since a secondary rectifier is directly used to relieve the feedback voltage. To remove the same voltage, in the indirect tracking version, an additional winding of the pulse transformer is used.

Pros and cons of different types of devices

Currently, pulse devices are gaining increasing popularity, actively displacing inconvenient and bulky linear devices from the electronic market. Despite this, each of these devices has its own advantages and disadvantages.

Pulse blocks have a high stabilizing coefficient and efficiency. They are distinguished by a wider range of input voltages and high power, compared to linear devices. Pulse devices do not respond at all to the quality of the supplied voltage and its frequency. They have small dimensions and weight, which makes them very convenient to transport and operate. The cost of such devices is affordable to almost all consumers.

However, the regulated switching power supply circuit has a number of noticeable disadvantages. First of all, this is impulse noise, which negatively affects electronic equipment. Complex circuits make the device less reliable. Because of this, it is not always possible to repair devices on your own.

Linear or transformer units are still used today due to the simple and reliable design of all models. They can be easily repaired using inexpensive spare parts and do not create interference in the surrounding area.

The drop in demand for these products is primarily due to their large weight and overall dimensions, which create inconvenience during handling and transportation. The design itself is characterized by high metal consumption. The stability of the output voltage is inversely related to the efficiency of the device.

Thanks to the wide range, it is possible to choose one or another device for specific purposes. For use in certain conditions, specialists can independently manufacture a power supply according to a given circuit with all the necessary parameters.

Adjustable power supply: how to make it yourself

Before assembly, you need to take into account all the factors that can help or, conversely, hinder the work. Any power supply consists of a transformer, converter, indicator with ammeter and voltmeter, transistor and other parts, without which the device cannot operate. It is necessary to think in advance about protection against strong and weak currents in order to avoid emergency situations. If connected, soldered or installed incorrectly, the equipment may simply burn out.

The typical diagram shown in the figure is designed for a universal type of assembly and can be assembled even by a novice specialist. All parts are available, assembled simply and quickly, and further customization is simple.

The finished device must meet certain requirements that you need to know in advance. Regulation and stabilization of the output is provided in the range from 3 to 24 volts, with a minimum current load of 2 amperes. In addition, an unregulated 12 or 24 V output device with a high current load is provided. The first output is equipped with an integral stabilizer, and the second - behind the diode bridge, bypassing the stabilizing element.

A typical design consists of a powerful transformer, a capacitor, a stabilizer chip, strapping and other elements of a specific circuit. The power supply is assembled in a prescribed sequence, all actions are performed in a certain order.

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If you are looking for a simple and reliable linear power supply circuit, then this article is just for you. Here you will find complete instructions for assembling and setting up this power supply. The author of this homemade product is Roman (YouTube channel “Open Frime TV”).

First, a little background. Quite recently, the author was remodeling his workplace and wanted to install a linear unit as a third power supply, since sometimes he has to assemble circuits that cannot tolerate voltage ripple. And as we know, the linear unit has almost completely no voltage ripple at the output.

Until this moment, the author was not very interested in linear blocks, and somehow he did not particularly delve into this topic. When the idea to build such a block came, Roman immediately opened everyone’s favorite and widely known video hosting site YouTube. As a result, after a lengthy search, the author was able to identify 2 schemes for himself. The author of the first is AKA KASYAN (author of the YouTube channel of the same name), and the second circuit is built on op-amps.

But since opamps can operate at voltages up to 32V, the output voltage accordingly could not exceed this limit, which means this circuit is no longer needed.

Okay, we can put together a diagram from Kasyan, but even here we were disappointed. This scheme is afraid of static. This manifested itself as an explosion of transistors if you touched the output contacts.

This happened several times. And then the author decided to leave this scheme alone. You will say that the Internet is full of linear power supply circuits.

Yes, this is undoubtedly true, but only these two schemes mentioned above had normally routed signets, which could simply be downloaded. Everything else is either without seals or assembled by hanging installation. And we (radio amateurs) are accustomed to the fact that everything is served on a silver platter.

The author decided to create a normal signet. The board turned out to be quite compact. After testing this scheme, surprisingly it performed well.

With such simplicity, the author liked it so much that he even decided to make a kit from this board. To do this, you need to convert the signet into a Gerber file (a file with the extension .gbr, which is a design of a printed circuit board for the subsequent production of photo masks on various equipment). Then you need to send the boards for manufacturing.

And now, a couple of weeks after ordering, we receive our long-awaited boards. Having opened the parcel and taken a closer look at the boards, we can make sure that everything turned out to be of very high quality and beautiful.

So, let's solder this board and check its operation. There are not so many components for installation; soldering takes about 20 minutes, no more.

We're done with soldering. We make the first switch on. And here we are in for a little disappointment. This board was not without its problems. They manifested themselves in the fact that when the potentiometer knob is rotated to the left, the voltage and current increase, and when rotated to the right, a decrease occurs.

This happened because the author placed the resistors for this board on wires (for subsequent installation on the case) and there, without any problems, it was possible to change the direction of rotation simply by changing the side contacts. Well, okay, but everything else works as expected.

But nevertheless, the author corrected the signet, now when the potentiometer is rotated to the right, the voltage increases, everything is as it should be. So you can safely download and repeat this design (the archive with this printed circuit board is in the description under the original video of the author, you must follow the SOURCE link at the end of the article).

Now let's move on to a detailed examination of the circuit and the board itself. You can see the diagram on your screens.

This power supply is equipped with a voltage and current regulator, as well as a short circuit protection system, which is simply necessary in such units.

Imagine for a moment what happens during a short circuit when the input voltage is 36V. It turns out that all the voltage is dissipated on the power transistor, which, of course, is unlikely to withstand such abuse.

Protection can be configured here. Using this tuning resistor, we set any operating current.

A 12V protection switch is installed here, and the input voltage can reach 40V. Therefore, it was necessary to obtain a voltage of 12V.

This can be implemented using a parametric stabilizer using a transistor and a zener diode. The zener diode is 13V, since there is a voltage drop across the collector-emitter transitions of the two transistors.

So, now you can start testing this linear power supply. We supply a voltage of 40V from the laboratory power supply. On the load we hang a light bulb designed for a voltage of 36V, with a power of 100W.

Then we begin to slowly rotate the variable resistor.

As you can see, the voltage regulation works perfectly. Now let's try to regulate the current.

As you can see, when the second resistor rotates, the current decreases, which means that the circuit is operating normally.
Since this is a linear unit and all the “extra” voltage turns into heat, it needs a fairly large radiator. Radiators from a computer processor have proven themselves to be excellent for these purposes. Such radiators have a large dissipation area, and if they are also equipped with a fan, then you can, in principle, completely forget about overheating of the transistor.

Hello everyone. This article is a companion piece to the video. We will look at a powerful laboratory power supply, which is not yet fully completed, but functions very well.

The laboratory source is single-channel, completely linear, with digital display, current protection, although there is also an output current limitation.

The power supply can provide an output voltage from zero to 20 volts and a current from zero to 7.5-8 Amps, but more is possible, at least 15, at least 20 A, and the voltage can be up to 30 Volts, but my option has a limitation due to with transformer.

Regarding stability and ripples, it is very stable, the video shows that the voltage at a current of 7 Amperes does not drop even by 0.1 V, and the ripples at currents of 6-7 Amperes are about 3-5 mV! in class it can compete with industrial professional power supplies for a couple of hundred dollars.

At a current of 5-6 Amps, the ripple is only 50-60 millivolts; budget Chinese industrial-style power supplies have the same ripples, but at currents of only 1-1.5 amperes, that is, our unit is much more stable and can compete in class with samples for a couple of hundred dollars

Despite the fact that the side is linear, it has high efficiency, it has an automatic winding switching system, which will reduce power losses on transistors at low output voltages and high current.

This system is built on the basis of two relays and a simple control circuit, but later I removed the board, since the relays, despite the declared current of more than 10 Amps, could not cope, I had to buy powerful 30 Ampere relays, but I have not yet made a board for them, but without a system The switching unit works great.

By the way, with the switching system, the unit will not need active cooling; a huge radiator at the rear will be enough.

The case is from an industrial network stabilizer, the stabilizer was bought new, from the store, just for the sake of the case.

I left only a voltmeter, a power switch, a fuse and a built-in socket.

There are two LEDs under the voltmeter, one shows that the stabilizer board is receiving power, the second, red, shows that the unit is operating in current stabilization mode.

The display is digital, designed by a good friend of mine. This is a personalized indicator, as evidenced by the greeting, you will find the firmware with the board at the end of the article, and below is the indicator diagram

But essentially this is a volt/ampere wattmeter, there are three buttons under the display that will allow you to set the protection current and save the value, the maximum current is 10 Amps. The protection is relay, the relay is again weak, and at high currents there is quite a strong heating of the contacts.

There are power terminals at the bottom and a fuse at the output. By the way, foolproof protection is implemented here; if you use the power supply as a charger and accidentally reverse the polarity of the connection, the diode will open, burning the fuse.

Now about the scheme. This is a very popular variation based on three op-amps, the Chinese are also churning them out en masse, in this source it is the Chinese board that is used, but with major changes.

Here is the diagram that I got, with what was changed highlighted in red.

Let's start with the diode bridge. The bridge is full-wave, made on 4 powerful dual Schottky diodes type SBL4030, 40 volts 30 amperes, diodes in TO-247 package.

There are two diodes in one case, I paralleled them, and as a result I got a bridge on which there is a very small voltage drop, and therefore losses, at maximum currents, “that bridge is barely warm, but despite this the diodes are installed on an aluminum heat sink, represented by a massive plate The diodes are isolated from the radiator with a mica gasket.

A separate board was created for this node.

Next is the power part. The original circuit is only 3 Amperes, but a modified one can easily give out 8 Amps in this situation. There are already two keys. These are powerful composite transistors 2SD2083 with a collector current of 25 Amps. It would be appropriate to replace it with KT827, they are cooler.
The keys are essentially parallelized; in the emitter circuit there are equalizing resistors of 0.05 Ohm 10 watts, or rather, for each transistor, 2 resistors of 5 watts 0.1 Ohm are used in parallel.

Both keys are installed on a massive radiator, their substrates are isolated from the radiator; this can not be done, since the collectors are common, but the radiator is screwed to the body, and any short circuit can have disastrous consequences.

The smoothing capacitors after the rectifier have a total capacitance of about 13,000 µF and are connected in parallel.
The current shunt and the specified capacitors are located on the same printed circuit board.

A fixed resistor was added on top (in the diagram) of the variable resistor responsible for regulating the voltage. The fact is that when power is supplied (say 20 Volts) from the transformer, we get some drop on the diode rectifier, but then the capacitors are charged to the amplitude value (about 28 Volts), that is, at the output of the power supply the maximum voltage will be greater than the voltage supplied transformer. Therefore, when connecting a load to the output of the block, there will be a large drawdown, this is unpleasant. The task of the previously indicated resistor is to limit the voltage to 20 Volts, that is, even if you turn the variable to maximum, it is impossible to set more than 20 Volts at the output.

The transformer is a converted TS-180, provides an alternating voltage of about 22 volts and a current of at least 8 A, there are 9 and 15 volt taps for the switching circuit. Unfortunately, there was no normal winding wire at hand, so new windings were wound with mounting, stranded copper wire 2.5 sq. mm. Such a wire has thick insulation, so it was impossible to wind the winding to a voltage of more than 20-22V (this takes into account the fact that I left the original filament windings at 6.8V, and connected the new one in parallel with them).

Hello dear friends. In my next article, I decided to show how a power supply with voltage and current regulation was assembled. I saw the diagram in Aka’s video and decided to make myself the same device. There was no printed circuit board with the video, I drew it myself, it will be below. At first, I simply assembled the circuit using a surface-mounted installation, but for some reason it didn’t work for me the first time, I probably mixed up the transistor terminals, so I assembled it again, but now it just couldn’t help but work.
Here is a diagram of the device.

The circuit is quite simple and does not require adjustment; all the parts can be found in an old TV. But I didn’t disassemble the TV, since I had all these parts, well, let’s not deviate from the topic. I drew the PCB in the Sprint-Layout_5.0 program. and transferred it to the board.

But for some reason it didn’t go well for me and I had to finish drawing it with a permanent marker. Next I threw it into the etching solution.

When my board was etched, I washed it thoroughly with water; if you don’t wash it with water, it will be sticky. I dried it, removed the toner with a solvent and this is what happened.

The thing I don't like is drilling holes in the board. Now the most interesting and easy part begins - tinning the board.

After tinning, we need to remove everything that is left of the flux, let's do it with a solvent, just wipe our board. Now we take the parts, I found them in advance and insert them into the printed circuit board according to the diagram.

That's all, you can rejoice, the circuit is assembled. Here is the PCB

And also, in my photo there is no output capacitor, I didn’t install it because I couldn’t find it.