Good day forum users and guests of the site radio circuits! Wanting to assemble a decent, but not too expensive and cool power supply, so that everything was in it and it didn’t cost anything, . As a result, 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 has high repeatability. This scheme has already been considered on the site, but with the help of colleagues, we managed to improve it somewhat.

I assembled this circuit in its original form and ran into one unpleasant moment. When adjusting the current, I can’t set 0.1 A - a minimum of 1.5 A at R6 0.22 Ohm. When I increased the resistance of R6 to 1.2 Ohm, the short-circuit current turned out to be at least 0.5 A. But now R6 began to heat up quickly and strongly. Then I used a little refinement and got a much wider current adjustment. 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 voltage drop of the resistor, a drop in the B-E transition is added and this additional voltage allows you to open T5 earlier, and as a result, limit the current earlier.

On the basis of this proposal, he conducted successful tests and eventually received a simple laboratory PSU. I post a photo of my laboratory power supply with three outputs, where:

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

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

Many of us have accumulated various power supplies from laptops, printers or monitors with a voltage of +12, +19, +22. These are excellent power supplies with protection against both short circuit and overheating. Whereas in home, amateur radio practice, an adjustable, stabilized source is constantly required. If it is not advisable to make changes to the circuit of existing power supplies, then a very simple prefix to such a unit will come to the rescue.

It will take

To assemble an amateur set-top box with smooth adjustment of the output voltage, we need:

• - assembly box;
• - two sockets with an internal diameter of 5.2 mm;
• - potentiometer 10 kOhm;
• - two fixed resistors 22 kOhm each;
• - panel.

The article will consist of several finished parts, each of which will describe in detail the steps, features and pitfalls of the components used.

Step-down DC-DC converter on the lm2596 chip

The lm2596 chip on which the module is implemented is good in that it has overheat protection and short circuit protection, but it has several features.
Look at the typical option for turning it on, in this case, the output fixed voltage revision chip +5 volts, but, for the essence, this is not important:

Maintaining a stable voltage level is ensured by connecting the feedback output of the fourth (Feed Back) leg of the microcircuit, connected directly to the stabilized voltage output.
In the particular module under consideration, an edition of the microcircuit with a variable output voltage is used, but the principle of regulating the output voltage is the same:

A resistive divider R1-R2 is connected to the output of the module with the upper trimmer resistor R1 turned on, introducing resistance, which, the output voltage of the microcircuit can be changed. In this module R1 = 10 kΩ R2 = 0.3 kΩ. The bad thing is that the adjustment is not smooth and is carried out only at the last 5-6 turns of the tuning resistor.
To implement a smooth adjustment of the output voltage, radio amateurs exclude the resistor R2, and change the tuning resistor R1 to a variable one. The schema looks like this:

And right here, a serious problem arises. The fact is, during the operation of the variable resistor, sooner or later, the contact (its attachment to the resistive shoe) of the middle output is broken and output 4 (Feed Back) of the microcircuit is (albeit for a millisecond) in the air. This leads to instant failure of the microcircuit.
The situation is just as bad when conductors are used to connect a variable resistor - the resistor turns out to be remote - this can also contribute to loss of contact. Therefore, the regular resistive divider R1 and R2 should be unsoldered, and instead of it, two permanent ones should be soldered directly on the board - this solves the problem of losing contact with the variable resistor in any case. The variable resistor itself should be soldered to the soldered terminals.
In the diagram, R1= 22 kΩ and R2=22 kΩ, and R3=10 kΩ.

On a real circuit. R2 was the resistance corresponding to its marking, but R1 surprised me, although it was marked 10 kOhm in fact, its nominal resistance turned out to be 2 kOhm.

Remove R2 and put a drop of solder in its place. Remove resistor R1 and flip the board over:

Solder two new R1 and R2 resistors as shown in the photo. As you can see, the future conductors of the variable resistor R3 will be connected to the three points of the divider.
That's it, put the module aside.
Next up is a panel ammeter.

Voltammeter DSN-VC288

The DSN-VC288 is not suitable for assembling a laboratory power supply, since the minimum current that can be measured with it is 10 mA.
But the ammeter is great for assembling an amateur design, and therefore, I will use it.
The view from the back is like this:

Pay attention to the location of the connectors and accessible adjustment elements, and especially to the height of the current measurement connector:

Since the case I chose for this homemade product does not have sufficient height, I had to bite off the metal pins of the DSN-VC288 current connector, and solder the attached thick conductors onto the pins directly. Before soldering, make a loop at the ends of the wires, and put each one on each pin, solder - for reliability:

Scheme

Schematic diagram of the connection DSN-VC288 and lm2596

Left side of DSN-VC288:

• - black thin wire is not connected to anything, insulate its end;
• - yellow thin connect to the positive output of the module lm2596 - LOAD "PLUS";
• - red thin connect to the positive input of the lm2596 module.

Right side of DSN-VC288:

• - connect the black thick one to the negative output of the lm2596 module;

Final assembly of the block

The mounting box I used was 85 x 58 x 33 mm.:

After marking with a pencil, a dremel disk, I cut out a window for the DSN-VC288 to fit the inner rim of the device. At the same time, at first I sawed through the diagonals, and then sawed off individual sectors along the perimeter of the marked rectangle. You will have to work with a flat file, gradually fitting the window under the inner side of the DSN-VC288:

In these photos, the lid is not transparent. I decided to use transparent later, but it doesn't matter, except for transparency, they are exactly the same.
Also, mark the hole for the threaded collar of the variable resistor:

Please note that the mounting ears of the base half of the box are cut off. And on the microcircuit itself, it makes sense to stick a small radiator. I had ready-made ones at hand, but it’s not difficult to cut out a similar one from a radiator, for example, an old video card. I cut a similar one for installing a laptop chip on the PCH, nothing complicated =)

Mounting ears would interfere with the installation of these 5.2mm jacks:

In the end, you should get exactly this:
In this case, the input socket is on the left, the output is on the right:

Examination

Power up the console and look at the display. Depending on the position of the axis of the variable resistor, the device may show different volts, but the current should be zero. If this is not the case, then the device will have to be calibrated. Although, I read many times that this has already been done by the plant, and nothing will have to be done from us, but still.
But first, pay attention to the upper left corner of the DSN-VC288 board, two metalized holes are designed to set the device to zero.

So, if without load the device shows a certain current, then:

• - turn off the console;
• - securely close these two contacts with tweezers;
• - turn on the console;
• - remove the tweezers;
• - disconnect our set-top box from the power supply, and connect it again.

Load tests

I don’t have a powerful resistor, but there was a piece of a nichrome spiral:

In the cold state, the resistance was about 15 ohms, in the hot state, about 17 ohms.
On the video, you can see the tests of the resulting set-top box just for such a load, I compared the current with a model device. The power supply was taken at 12 volts from a long-disappeared laptop. Also on the video you can see the range of adjustable voltage at the output of the set-top box.

Outcome

• - the prefix is ​​​​not afraid of a short circuit;
• - not afraid of overheating;
• - not afraid of an open circuit of the adjusting resistor, when it breaks, the voltage automatically drops to a safe level below one and a half volts;
• - the prefix will also easily withstand if the input and output are reversed when connected - this happened;
• - there is an application for any external power supply from 7 volts to 30 volts maximum.

Somehow recently, on the Internet, I came across one circuit of a very simple power supply with the ability to adjust the voltage. It was possible to regulate the voltage from 1 Volt to 36 Volts, depending on the output voltage on the secondary winding of the transformer.

Take a close look at the LM317T in the circuit itself! The third leg (3) of the microcircuit clings to the capacitor C1, that is, the third leg is the INPUT, and the second leg (2) clings to the capacitor C2 and a 200 Ohm resistor and is the OUTPUT.

With the help of a transformer from a mains voltage of 220 volts, we get 25 volts, no more. Less is possible, more is not. Then we straighten the whole thing with a diode bridge and smooth out the ripples with the help of capacitor C1. All this is described in detail in the article how to get a constant voltage from an alternating voltage. And here is our most important trump card in the power supply - a highly stable voltage regulator chip LM317T. At the time of this writing, the price of this microcircuit was around 14 rubles. Even cheaper than a loaf of white bread.

Description of the microcircuit

LM317T is a voltage regulator. If the transformer produces up to 27-28 volts on the secondary winding, then we can easily regulate the voltage from 1.2 to 37 volts, but I would not raise the bar for more than 25 volts at the output of the transformer.

The microcircuit can be executed in the TO-220 package:

or in D2 Pack

It can pass a maximum current of 1.5 amps through itself, which is enough to power your electronic gadgets without a voltage drop. That is, we can give out a voltage of 36 Volts at a load current of up to 1.5 Amperes, and at the same time, our microcircuit will still give out 36 Volts as well - this, of course, ideally. In reality, fractions of a volt will drop, which is not very critical. With a large current in the load, it is more expedient to put this microcircuit on a radiator.

In order to assemble the circuit, we will also need a 6.8 Kilo-ohm variable resistor, maybe even 10 Ki-ohm, as well as a 200 Ohm fixed resistor, preferably from 1 watt. Well, at the output we put a capacitor of 100 microfarads. Absolutely simple scheme!

Assembly in hardware

Previously, I had a very bad power supply still on transistors. I thought why not redo it? Here is the result ;-)

Here we see the GBU606 imported diode bridge. It is designed for current up to 6 amperes, which is more than enough for our power supply, since it will deliver a maximum of 1.5 amperes to the load. I put the LM-ku on the radiator using KPT-8 paste to improve heat transfer. Well, everything else, I think, is familiar to you.

And here is the antediluvian transformer, which gives me a voltage of 12 volts on the secondary winding.

We carefully pack all this into the case and remove the wires.

So what do you think? ;-)

The minimum voltage I got was 1.25 Volts, and the maximum voltage was 15 Volts.

I put any voltage, in this case the most common 12 Volts and 5 Volts

Everything works with a bang!

This power supply is very convenient for adjusting the speed of a mini drill, which is used for drilling boards.

Analogues on Aliexpress

By the way, on Ali you can immediately find a ready-made set of this block without a transformer.

Too lazy to collect? You can take a ready-made 5 Ampere for less than $ 2:

You can view by this link.

If 5 Amperes is not enough, then you can look at 8 Amperes. It will be enough even for the most seasoned electronics engineer:

In most modern electronic devices, analog (transformer) power supplies are practically not used; they have been replaced by pulse voltage converters. To understand why this happened, it is necessary to consider the design features, as well as the strengths and weaknesses of these devices. We will also talk about the purpose of the main components of pulsed sources, we will give a simple implementation example that can be assembled by hand.

Design features and principle of operation

Of the several ways to convert voltage to power electronic components, two of the most widely used can be distinguished:

1. Analog, the main element of which is a step-down transformer, in addition to the main function, it also provides galvanic isolation.
2. impulse principle.

Let's take a look at the difference between these two options.

PSU based on power transformer

Consider a simplified block diagram of this device. As can be seen from the figure, a step-down transformer is installed at the input, with its help the amplitude of the supply voltage is converted, for example, from 220 V we get 15 V. The next block is a rectifier, its task is to convert the sinusoidal current into a pulsed one (the harmonic is shown above the symbolic image). For this purpose, rectifier semiconductor elements (diodes) connected in a bridge circuit are used. Their principle of operation can be found on our website.

The next block performs two functions: it smoothes the voltage (a capacitor of the appropriate capacity is used for this purpose) and stabilizes it. The latter is necessary so that the voltage does not “fall through” with increasing load.

The given block diagram is greatly simplified, as a rule, this type of source has an input filter and protective circuits, but this is not essential for explaining the operation of the device.

All the disadvantages of the above option are directly or indirectly related to the main structural element - the transformer. First, its weight and dimensions limit miniaturization. In order not to be unfounded, we give as an example a 220/12 V step-down transformer with a rated power of 250 W. The weight of such a unit is about 4 kilograms, dimensions are 125x124x89 mm. You can imagine how much a laptop charger based on it would weigh.

Secondly, the price of such devices sometimes many times exceeds the total cost of other components.

Impulse devices

As can be seen from the block diagram shown in Figure 3, the principle of operation of these devices differs significantly from analog converters, first of all, by the absence of an input step-down transformer.

Figure 3. Structural diagram of a switching power supply

Consider the algorithm of such a source:

• Power is supplied to the surge protector, its task is to minimize network interference, both incoming and outgoing, resulting from operation.
• Next, a unit for converting a sinusoidal voltage into a pulsed constant and a smoothing filter come into operation.
• At the next stage, an inverter is connected to the process, its task is to form rectangular high-frequency signals. Feedback to the inverter is carried out through the control unit.
• The next block is IT, it is necessary for automatic generator mode, supply voltage to the circuits, protection, controller control, as well as the load. In addition, the task of IT is to provide galvanic isolation between high and low voltage circuits.

Unlike a step-down transformer, the core of this device is made of ferrimagnetic materials, this contributes to the reliable transmission of RF signals, which can be in the range of 20-100 kHz. A characteristic feature of IT is that when it is connected, it is critical to turn on the beginning and end of the windings. The small dimensions of this device make it possible to manufacture devices of miniature size, as an example, we can cite the electronic piping (ballast) of an LED or energy-saving lamp.

• Next, the output rectifier comes into operation, since it operates with a high-frequency voltage, the process requires high-speed semiconductor elements, therefore, Schottky diodes are used for this purpose.
• At the final phase, smoothing is performed on an advantageous filter, after which the voltage is applied to the load.

Now, as promised, we will consider the principle of operation of the main element of this device - the inverter.

How does an inverter work?

RF modulation can be done in three ways:

• frequency-pulse;
• phase-pulse;
• pulse width.

In practice, the latter option is used. This is due both to the simplicity of execution and the fact that PWM has a constant communication frequency, unlike the other two modulation methods. A block diagram describing the operation of the controller is shown below.

The device operation algorithm is as follows:

The master frequency generator generates a series of rectangular signals, the frequency of which corresponds to the reference one. Based on this signal, U P of a sawtooth shape is formed, which is fed to the input of the comparator K PWM. The second input of this device is supplied with the signal U US coming from the control amplifier. The signal generated by this amplifier corresponds to the proportional difference between U P (reference voltage) and U PC (control signal from the feedback circuit). That is, the control signal U US, in fact, is a mismatch voltage with a level that depends both on the current on the load and on the voltage on it (U OUT).

This implementation method allows you to organize a closed circuit that allows you to control the output voltage, that is, in fact, we are talking about a linear-discrete functional unit. At its output, pulses are formed, with a duration depending on the difference between the reference and control signal. Based on it, a voltage is created to control the key transistor of the inverter.

The process of stabilization of the output voltage is carried out by monitoring its level, when it changes, the voltage of the regulating signal U PC changes proportionally, which leads to an increase or decrease in the duration between pulses.

As a result, there is a change in the power of the secondary circuits, which ensures the stabilization of the output voltage.

To ensure safety, galvanic isolation between the supply network and the feedback is required. As a rule, optocouplers are used for this purpose.

Strengths and weaknesses of impulse sources

If we compare analog and pulse devices of the same power, then the latter will have the following advantages:

• Small size and weight, due to the absence of a low-frequency step-down transformer and control elements that require heat dissipation using large radiators. Through the use of high-frequency signal conversion technology, it is possible to reduce the capacitance of the capacitors used in the filters, which allows the installation of smaller elements.
• Higher efficiency, since the main losses are caused only by transients, while in analog circuits a lot of energy is constantly lost during electromagnetic conversion. The result speaks for itself, an increase in efficiency up to 95-98%.
• Lower cost due to the use of less powerful semiconductor elements.
• Wider input voltage range. This type of equipment is not demanding on frequency and amplitude, therefore, connection to networks of various standards is allowed.
• Availability of reliable protection against short circuit, overload and other emergency situations.

The disadvantages of impulse technology include:

The presence of RF interference, this is a consequence of the operation of the high-frequency converter. Such a factor requires the installation of a filter that suppresses interference. Unfortunately, its operation is not always efficient, which imposes some restrictions on the use of devices of this type in high-precision equipment.

Special requirements for the load, it should not be reduced or increased. As soon as the current level exceeds the upper or lower threshold, the output voltage characteristics will begin to differ significantly from the standard ones. As a rule, manufacturers (recently even Chinese) provide for such situations and install appropriate protection in their products.

Scope of application

Almost all modern electronics is powered by blocks of this type, as an example we can give:

We assemble a pulsed power supply unit with our own hands

Consider a simple power supply circuit, where the above principle of operation is applied.

Designations:

• Resistors: R1 - 100 Ohm, R2 - from 150 kOhm to 300 kOhm (selected), R3 - 1 kOhm.
• Capacitances: C1 and C2 - 0.01 uF x 630 V, C3 -22 uF x 450 V, C4 - 0.22 uF x 400 V, C5 - 6800 -15000 pF (selected), 012 uF, C6 - 10 uF x 50 V, C7 - 220 uF x 25 V, C8 - 22 uF x 25 V.
• Diodes: VD1-4 - KD258V, VD5 and VD7 - KD510A, VD6 - KS156A, VD8-11 - KD258A.
• Transistor VT1 - KT872A.
• Voltage stabilizer D1 - chip KR142 with index EH5 - EH8 (depending on the required output voltage).
• Transformer T1 - a w-shaped ferrite core with dimensions of 5x5 is used. The primary winding is wound with 600 turns of wire Ø 0.1 mm, the secondary (terminals 3-4) contains 44 turns Ø 0.25 mm, and the last - 5 turns Ø 0.1 mm.
• Fuse FU1 - 0.25A.

The setting is reduced to the selection of R2 and C5 ratings, which provide excitation of the generator at an input voltage of 185-240 V.

For two voltages (+5 and +12 V) is shown in fig. 1:

The stabilizer provides two voltages at the output: 5 V, at a current of 0.75 A; 12 V at about 200 mA. The main voltage generated by the switching regulator is +5 volts. The second voltage is obtained due to the autotransformer winding II of the transformer T1.

The article "Laboratory power supply", was published in the journal for 1980 No. 11. According to the original source, in the 80s, an operating power supply was manufactured, which is still working.

The main benefits of laboratory nutrition are:

Wide range of output voltages (0... ±40 V);

Possibility of smooth adjustment of tension in the shoulders both separately and symmetrically;

The boost circuit can be implemented on the controller of the MC33063A / MC34063A pulse converter, or their Russian counterpart KR1156EU5R / KF1156EU5T. The MC33063A/MC34063A microcircuits differ from each other only in the case type, i.e. DIP-8 or SO8 respectively. Input voltage from 3 to 40 volts.

In this circuit, the output of the converter is 28 volts, with an input voltage of 12 volts, the load current will be 175 milliamps.

Another voltage value at the booster output can be obtained by changing the ratio R1 / R2 according to the formula:

V out \u003d 1.25 x (1 + R2 / R1).

For implementation, apart from