We assemble an adjustable power supply 0...30V / 5A.

Have you decided to assemble a power supply, but don’t know which circuit to choose? But indeed, on the Internet you can find many schematic diagrams of these devices. Well, in this article we will look at a power supply circuit implemented on a domestic element base; these components from which the circuit is assembled are quite widespread and not at all in short supply, and this is a big advantage of this option. The second advantage of this circuit is that the output voltage of the power supply is adjustable over a wide range, ranging from 0 to 30 Volts, while the output current can reach 5 Amps. And one more important point, this circuit has protection against overload and short circuit in the load. The circuit diagram is shown in the figure below:

Let's look at what nodes the circuit consists of:

A step-down transformer. Its power should be about 150 watts. For example, you can rewind the secondary windings of the TS-160 transformer, or use similar iron. When remaking the TS-160, the primary winding remains unchanged. The second winding is designed for a voltage of 28...30 Volts, and a current of at least 5...6 Amperes. The third winding should produce 5...6 Volts with a current of at least 1 Ampere.

Rectifier assembly. It consists of a diode bridge VD1...VD4, and a smoothing capacitance C1. The printed circuit board provides for the use of an imported diode assembly RS603 (RS602) for a current of 10 Amps, but you can also assemble a bridge from individual domestic diodes, for example, D242, although the dimensions of the device will naturally increase.

The KTs407 diode bridge and two integrated stabilizers 7805 and 7905 form the power supply unit for the control and protection unit. Instead of KTs407 you can put KTs402 or KTs405.

The protection is assembled on the KU101E thyristor, the VD9 LED indicates its status, and in case of overload and short circuit it lights up. Resistor R4 is installed as a current sensor; in the circuit it is designed for a current of 3 Amps; for 5 Amps it must be recalculated.

The regulating element is a powerful silicon transistor VT1 (KT827A). It must be installed on a radiator with a cooling area of ​​at least 1500 square meters. see. If difficulties arise in purchasing the KT827A, then instead you can install a pair of transistors connected according to the following diagram:

Resistor R7 regulates the minimum voltage of the power supply output. The potentiometer R13 handle is located on the front panel of the power supply and is an output voltage regulator. Rotate R14 to adjust the upper limit of the output voltage. R7 and R14 are multi-turn type SP5.

The pictures below show a version of the power supply circuit board:

The printed circuit board has dimensions of 110x75 mm.

Setting up the power supply:

The entire setup of the power supply comes down to setting the necessary limits for adjusting the output voltage, as well as the current value at which the protection will operate. As mentioned above, the protection current depends on the value of resistor R4.

To determine the output voltage regulation range, perform the following steps:

Set potentiometers R7 and R13 to the middle position.
Measuring Uout with a voltmeter. Using resistor R14, set the value to 15 Volts.
Turn resistor R13 to minimum, and use R7 to set the output to zero volts.
Now R13 to maximum, and using R14 set the output to 30 Volts. If necessary, instead of R14 (by measuring its readings), you can solder a constant resistance.

At this point, the setup is complete, if everything is assembled without mistakes and errors, the power supply will work “like a clock.” This is where we end the article, good luck with your repetition.

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

First, I’ll explain a little what it is and why.
Almost all radio amateurs use such a thing as a laboratory power supply in their work. Whether it's complex with software control or completely simple on the LM317, it still does almost the same thing, powers different loads while working with them.
Laboratory power supplies are divided into three main types.
With pulse stabilization.
With linear stabilization
Hybrid.

The first ones include a switching controlled power supply, or simply a switching power supply with a step-down PWM converter.
Advantages - high power with small dimensions, excellent efficiency.
Disadvantages - RF ripple, presence of capacious capacitors at the output

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

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

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

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

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

A little about packaging.
The designer arrived in a regular plastic bag, wrapped in soft material.
Inside, in an antistatic zip-lock bag, were all the necessary components, including the circuit board.

Everything inside was a mess, but nothing was damaged; the printed circuit board partially protected the radio components.

I won’t list everything that is included in the kit, it’s easier to do this later during the review, I’ll just say that I had enough of everything, even some left over.

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

The board coating, tinning, and the quality of the PCB itself is excellent.
I was only able to tear off a patch from the seal in one place, and that was after I tried to solder a non-original part (why, we will find out later).
In my opinion, this is the best thing for a beginner radio amateur; it will be difficult to spoil it.

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

The scheme is quite thoughtful, although not without its shortcomings, but I’ll tell you about them in the process.
Several main nodes are visible in the diagram; I separated them by color.
Green - voltage regulation and stabilization unit
Red - current regulation and stabilization unit
Purple - indicating unit for switching to current stabilization mode
Blue - reference voltage source.
Separately there are:
1. Input diode bridge and filter capacitor
2. Power control unit on transistors VT1 and VT2.
3. Protection on transistor VT3, turning off the output until the power supply to the operational amplifiers is normal
4. Fan power stabilizer, built on a 7824 chip.
5. R16, R19, C6, C7, VD3, VD4, VD5, unit for forming the negative pole of the power supply of operational amplifiers. Due to the presence of this unit, the power supply will not operate simply on direct current; it is the alternating current input from the transformer that is required.
6. C9 output capacitor, VD9, output protective diode.

First, I will describe the advantages and disadvantages of the circuit solution.
Pros -
It's nice to have a stabilizer to power the fan, but the fan needs 24 Volts.
I am very pleased with the presence of a power source of negative polarity; this greatly improves the operation of the power supply at currents and voltages close to zero.
Due to the presence of a source of negative polarity, protection was introduced into the circuit; as long as there is no voltage, the power supply output will be turned off.
The power supply contains a reference voltage source of 5.1 Volts, this made it possible not only to correctly regulate the output voltage and current (with this circuit, voltage and current are regulated from zero to maximum linearly, without “humps” and “dips” at extreme values), but also makes it possible to control external power supply, I simply change the control voltage.
The output capacitor has a very small capacitance, which allows you to safely test the LEDs; there will be no current surge until the output capacitor is discharged and the PSU enters current stabilization mode.
The output diode is necessary to protect the power supply from supplying reverse polarity voltage to its output. True, the diode is too weak, it is better to replace it with another one.

Minuses.
The current-measuring shunt has too high a resistance, because of this, when operating with a load current of 3 Amps, about 4.5 Watts of heat are generated on it. The resistor is designed for 5 Watts, but the heating is very high.
The input diode bridge is made up of 3 Ampere diodes. It is good to have at least 5 Ampere diodes, since the current through the diodes in such a circuit is equal to 1.4 of the output, so in operation the current through them can be 4.2 Amperes, and the diodes themselves are designed for 3 Amperes. The only thing that makes the situation easier is that the pairs of diodes in the bridge work alternately, but this is still not entirely correct.
The big minus is that the Chinese engineers, when selecting operational amplifiers, chose an op-amp with a maximum voltage of 36 Volts, but did not think that the circuit had a negative voltage source and the input voltage in this version was limited to 31 Volts (36-5 = 31 ). With an input of 24 Volts AC, DC will be about 32-33 Volts.
Those. The op amps will operate in extreme mode (36 is the maximum, standard 30).

I'll talk more about the pros and cons, as well as about modernization later, but now I'll move on to the actual assembly.

First, let's lay out everything that is included in the kit. This will make assembly easier, and it will simply be clearer to see what has already been installed and what remains.

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

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

Having established the main quantity, I reached single resistors.
It may be more difficult here; you will have to deal with denominations more often.

I don’t solder the components right away, but simply bite them and bend the leads, and I bite them first and then bend them.
This is done very easily, the board is held in your left hand (if you are right-handed), and the component being installed is pressed at the same time.
We have side cutters in our right hand, we bite off the leads (sometimes even several components at once), and immediately bend the leads with the side edge of the side cutters.
This is all done very quickly, after a while it is already automatic.

Now we’ve reached the last small resistor, the value of the required one and what’s left are the same, which is not bad :)

Having installed the resistors, we move on to diodes and zener diodes.
There are four small diodes here, these are the popular 4148, two zener diodes of 5.1 Volts each, so it’s very difficult to get confused.
We also use it to form conclusions.

On the board, the cathode is indicated by a stripe, just like on diodes and zener diodes.

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

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

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

The main number of passive elements has been installed.

After that, we move on to installing operational amplifiers.
I would probably recommend buying sockets for them, but I soldered them as is.
On the board, as well as on the chip itself, the first pin is marked.
The remaining conclusions are counted counterclockwise.
The photo shows the place for the operational amplifier and how it should be installed.

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

That's it, now you can move on to soldering.
I use a very ordinary soldering iron with temperature control, but a regular soldering iron with a power of about 25-30 watts is quite sufficient.
Solder 1mm in diameter with flux. I specifically do not indicate the brand of solder, since the solder on the coil is not original (original coils weigh 1Kg), and few people will be familiar with its name.

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



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

The terminals of the transistors also need to be pre-formed; this must be done in such a way that the terminal does not become deformed near the base of the case (elders will remember the legendary KT315, whose terminals loved to break off).
I shape powerful components a little differently. Molding is done so that the component stands above the board, in which case less heat will transfer to the board and will not destroy it.

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

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

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

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

A couple of photos of the nearly soldered board. I won’t describe the installation of the terminal blocks and other components; it’s intuitive and can be seen from the photograph.
By the way, about the terminal blocks, the board has terminal blocks for connecting the input, output, and fan power.



I haven't washed the board yet, although I often do it at this stage.
This is due to the fact that there will still be a small part to finalize.

After the main assembly stage we are left with the following components.
Powerful transistor
Two variable resistors
Two connectors for board installation
Two connectors with wires, by the way the wires are very soft, but of small cross-section.
Three screws.

Initially, the manufacturer intended to place variable resistors on the board itself, but they are placed so inconveniently that I didn’t even bother to solder them and showed them just as an example.
They are very close and it will be extremely inconvenient to adjust, although it is possible.

But thank you for not forgetting to include the wires with connectors, it’s much more convenient.
In this form, the resistors can be placed on the front panel of the device, and the board can be installed in a convenient place.
At the same time, I soldered a powerful transistor. This is an ordinary bipolar transistor, but it has a maximum power dissipation of up to 100 Watts (naturally, when installed on a radiator).
There are three screws left, I don’t even understand where to use them, if in the corners of the board, then four are needed, if you are attaching a powerful transistor, then they are short, in general it’s a mystery.

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

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

First, I checked what the transformer outputs after rectification, as this determines the maximum output voltage.
I got about 25 Volts, not a lot. The capacity of the filter capacitor is 3300 μF, I would advise increasing it, but even in this form the device is quite functional.

Since for further testing it was necessary to use a normal radiator, I moved on to assembling the entire future structure, since the installation of the radiator depended on the intended design.
I decided to use the Igloo7200 radiator I had lying around. According to the manufacturer, such a radiator is capable of dissipating up to 90 watts of heat.

The device will use a Z2A housing based on a Polish-made idea, the price will be about $3.

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

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

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

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

The leads of the powerful transistor also need to be slightly molded so that they do not become deformed when the transistor is pressed against the radiator.

A small digression.
For some reason, the manufacturer thought of a place to install a rather small radiator, because of this, when installing a normal one, it turns out that the fan power stabilizer and the connector for connecting it get in the way.
I had to unsolder them, and seal the place where they were with tape so that there would be no connection to the radiator, since there is voltage on it.

I cut off the excess tape on the back side, otherwise it would turn out completely sloppy, we’ll do it according to Feng Shui :)

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

To set zero, I unscrewed both knobs to the extreme left position, turned off the load and set the output to zero. Now the output voltage will be regulated from zero.

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

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

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

After that, I started assembling the device itself as a whole.
I started by installing the radiator with the power supply board.
To do this, I marked the installation location of the fan and the power connector.
The hole was marked not quite round, with small “cuts” at the top and bottom, they are needed to increase the strength of the back panel after cutting the hole.
The biggest difficulty is usually holes of complex shape, for example, for a power connector.

A big hole is cut out of a big pile of small ones :)
A drill + a 1mm drill bit sometimes works wonders.
We drill holes, lots of holes. It may seem long and tedious. No, on the contrary, it is very fast, completely drilling a panel takes about 3 minutes.

After that, I usually set the drill a little larger, for example 1.2-1.3mm, and go through it like a cutter, I get a cut like this:

After this, we take a small knife in our hands and clean out the resulting holes, at the same time we trim the plastic a little if the hole is a little smaller. The plastic is quite soft, making it comfortable to work with.

The last stage of preparation is to drill the mounting holes; we can say that the main work on the back panel is finished.

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

Almost at the very beginning I mentioned revision.
I'll work on it a little.
To begin with, I decided to replace the original diodes in the input diode bridge with Schottky diodes; for this I bought four 31DQ06 pieces. and then I repeated the mistake of the board developers, by inertia buying diodes for the same current, but it was necessary for a higher one. But still, the heating of the diodes will be less, since the drop on Schottky diodes is less than on conventional ones.
Secondly, I decided to replace the shunt. I was not satisfied not only with the fact that it heats up like an iron, but also with the fact that it drops about 1.5 Volts, which can be used (in the sense of a load). To do this, I took two domestic 0.27 Ohm 1% resistors (this will also improve stability). Why the developers didn’t do this is unclear, the price of the solution is absolutely the same as in the version with native 0.47 Ohm resistors.
Well, rather as an addition, I decided to replace the original 3300 µF filter capacitor with a higher quality and capacitive Capxon 10000 µF...

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

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

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

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

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

Several stages of preparing the front panel.
1. Draw a full-size layout of the front panel (I use the usual Sprint Layout). The advantage of using identical housings is that preparing a new panel is very simple, since the required dimensions are already known.
We attach the printout to the front panel and drill marking holes with a diameter of 1 mm in the corners of the square/rectangular holes. Use the same drill to drill the centers of the remaining holes.
2. Using the resulting holes, we mark the cutting locations. We change the tool to a thin disk cutter.
3. We cut straight lines, clearly in size at the front, a little larger at the back, so that the cut is as complete as possible.
4. Break out the cut pieces of plastic. I usually don't throw them away because they can still be useful.

In the same way as preparing the back panel, we process the resulting holes using a knife.
I recommend drilling large-diameter holes with a cone drill; it does not “bite” the plastic.

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

As I wrote above, for the display I decided to use the board left over from one of the previous reviews. In general, this is a very bad solution, but for a temporary option it is more than suitable, I will explain why later.
We unsolder the indicators and connectors from the board, call the old indicators and the new ones.
I wrote out the pinout of both indicators so as not to get confused.
In the native version, four-digit indicators were used, I used three-digit ones. since it didn’t fit into my window anymore. But since the fourth digit is needed only to display the letter A or U, their loss is not critical.
I placed the LED indicating the current limit mode between the indicators.

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

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

The resulting front panel design.

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

But I decided to install better current and voltage control resistors than those suggested by the manufacturer.
The original ones are quite high quality and run smoothly, but these are ordinary resistors and, in my opinion, a laboratory power supply should be able to more accurately adjust the output voltage and current.
Even when I was thinking about ordering a power supply board, I saw them in the store and ordered them for review, especially since they had the same rating.

In general, I usually use other resistors for such purposes; they combine two resistors inside themselves for rough and smooth adjustment, but lately I can’t find them on sale.
Does anyone know their imported analogues?

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

New resistors compared to the original ones, the size is certainly impressive.
Along the way, I shortened the wires to the resistors a little, this should improve noise immunity.

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

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

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

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

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

Back view.
Attentive readers have probably noticed that the fan is positioned in such a way that it blows hot air out of the case, rather than pumping cold air between the fins of the radiator.
I decided to do this because the radiator is slightly smaller in height than the case, and to prevent hot air from getting inside, I installed the fan in reverse. This, of course, significantly reduces the efficiency of heat removal, but allows for a little ventilation of the space inside the power supply.
Additionally, I would recommend making several holes at the bottom of the lower half of the body, but this is more of an addition.

After all the alterations, I ended up with a slightly less current than in the original version, and was about 3.35 Amperes.

So, I’ll try to describe the pros and cons of this board.
pros
Excellent workmanship.
Almost correct circuit design of the device.
A complete set of parts for assembling the power supply stabilizer board
Well suited for beginner radio amateurs.
In its minimal form, it additionally requires only a transformer and a radiator; in a more advanced form, it also requires an ampere-voltmeter.
Fully functional after assembly, although with some nuances.
No capacitive capacitors at the power supply output, safe when testing LEDs, etc.

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

My opinion. During the assembly process, I got the impression that the circuit was designed by two different people, one applied the correct regulation principle, reference voltage source, negative voltage source, protection. The second one incorrectly selected the shunt, operational amplifiers and diode bridge for this purpose.
I really liked the circuit design of the device, and in the modification section, I first wanted to replace the operational amplifiers, I even bought microcircuits with a maximum operating voltage of 40 Volts, but then I changed my mind about modifications. but otherwise the solution is quite correct, the adjustment is smooth and linear. Of course there is heating, you can’t live without it. In general, as for me, this is a very good and useful constructor for a beginning radio amateur.
Surely there will be people who will write that it is easier to buy a ready-made one, but I think that assembling it yourself is both more interesting (probably this is the most important thing) and more useful. In addition, many people quite easily have at home a transformer and a radiator from an old processor, and some kind of box.

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

That's probably all. Perhaps I’ll remember something else and add something, but I’m more looking forward to comments with questions.
We also plan to devote several more reviews to designers for beginner radio amateurs; perhaps someone will have suggestions regarding certain designers.

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

Single-polar laboratory power supply 0-30V/0-3A with “coarse” and “smooth” adjustments of the output voltage, adjustment of the output current (current limitation) and indication of the operating mode - voltage adjustment or activation of current limitation. The IRLZ44N field-effect transistor is used as a regulating element.

Finally, I etched and drilled holes in the LBP board to make sure that the circuit was working - everything worked almost immediately ;-(... The boards will be manufactured with a mask and markings in two versions: LBP with DC voltage supply - without a rectifier bridge and a variable resistor " smoothly" to adjust the output voltage, LPS powered by AC voltage - a rectifier bridge is installed on the board and a variable resistor is provided to adjust the output voltage "smoothly", but otherwise everything remains unchanged. If a diode bridge is not needed (an external one will be used), then on the board you just need to install jumpers instead. Both diagrams are shown below. Buy printed circuit boards, assembly kits, assemble and use ;-)

Specifications:

Input voltage (for diode bridge board): 7...32V AC

Input voltage (for board without diode bridge): 9...45V DC

Load current: 0-3A (with indication of current limit mode activation)

Output voltage instability: no more than 1%

Brief description of the design:

For a single-polar power supply, two printed circuit boards with dimensions of 62x59 mm and 92x59 mm have been developed. A photo of the printed circuit boards is shown below. The printed circuit boards have holes with a diameter of 3 mm. At the top of the board, for attaching the radiator, and at the bottom, for attaching the board itself to the power supply case. The regulating transistor must be installed on a large ;-) radiator with a surface area of ​​at least300 cm sq. Transistor Q1 is needed fix with heat-conducting paste and, if necessary, using insulating heat-conducting substrates. Variable resistors for adjusting current and voltage can be secured to the front panel of the power supply directly using standard nuts.




Note on power supply diagrams:

After assembling and testing the power supply by the buyer, it was noticed that when the power supply is disconnected from the network with a small load or no load, there is a slight decrease in voltage, and then its surge to 12-15V and then a decrease to zero. As it turned out, this is due to the fact that the voltage turning off the field-effect transistor disappears before the filter capacitor CF discharges. When checking the power supply under load with a powerful lamp, this was not noticed (for obvious reasons). To eliminate the voltage surge, it is necessary to connect an electrolytic capacitor C5 470 μFx6.3V from pin 8 m/sx to the common wire (soldered on top of the microcircuit between pins 8 and 11) - see diagrams.

Circuit operation:

The voltage stabilization circuit is assembled on U1.3 and U1.4. A differential cascade is assembled at U1.4, amplifying the voltage of the feedback divider formed by resistors R14 and R15. The amplified signal is sent to comparator U1.3, which compares the output voltage with the reference voltage generated by stabilizer U2 and potentiometer RV2. The resulting voltage difference is fed to transistor Q2, which controls the control element Q1. The current is limited by the comparator U1.1, which compares the voltage drop across the shunt R16 with the reference generated by the potentiometer RV1. When the specified threshold is exceeded, U1.1 changes the reference voltage for comparator U1.3, which leads to a proportional change in the output voltage. The operational amplifier U1.2 houses an indication unit for the operating mode of the device. When the voltage at output U1.1 drops below the voltage generated by the divider R2 and R3, LED D1 lights up, signaling that the circuit has switched to current stabilization mode.

Note:

If the device operates from a supply voltage below 23V, the zener diode D3 must be replaced with a jumper. It is also possible to power the low-current part of the circuit from a separate source by applying a voltage of 9-35V directly to the input of the stabilizer U3 and removing the zener diode D3.

VOLTMETERS And AMPERMETERS with seven-segment LEDindicators



Posted These are not Chinese measuring instruments! Made in Donetsk

Quickly made videos of the power supply in action can be viewed using the links below. One video shows testing of a digital voltmeter on an inexpensive specialized m/sx ICL7107.

The cost of a printed circuit board measuring 62x59 mm for two variable resistors - temporarily out of stock

PCB cost sizesand 92x59 mm for three variable resistors - temporarily out of stock

Cost of a kit for assembling a power supply (with a board for two resistors, handles included)

Cost of a kit for assembling a power supply (with a board for three resistors, handles included) temporarily out of stock

Brief description, diagram and list of kit parts and

Thank you for your attention! Good luck to everyone, peace, goodness, 73!

For a radio amateur's home laboratory. The basis of the power supply circuit is the TLC2272 operational amplifier. The circuit allows you to smoothly change the output voltage in the range from 0 to 30 volts, as well as control the load current limit.

Power supply 30 volts - description

The output voltage from the transformer is supplied to the diode bridge. The rectified voltage of 38 volts is smoothed by capacitor C1 and supplied to a parametric stabilizer consisting of transistor VT1, diode VD5, capacitor C2 and resistors R1, R2. Through this stabilizer, the operational stabilizer DA1 is powered. Diode VD5 () is an adjustable voltage stabilizer.

The DA1.1 operational amplifier houses the power supply control unit, and the DA1.2 element contains a short circuit protection and load current limiting unit. LED HL1 is a short circuit indicator. Setting up the power source.

First, adjust the supply voltage of the operational amplifier DA1 (for this, before turning on the device, the operational amplifier must be removed from the socket). The setting consists of selecting the resistance of resistor R2, at which the voltage at the emitter of transistor VT1 will be around 6.5 volts. After this, DA1 can be installed back on the board.

Material: ABS + metal + acrylic lenses. LED lights...

Next, the variable resistor R15 is moved to the lower position according to the diagram (i.e. 0 Volt). By selecting the resistance of resistor R6, a reference voltage of 2.5 volts is set at the top terminal of the variable resistor R15 according to the circuit. Then the variable resistor R15 is moved to the upper position in the circuit and the maximum voltage (i.e. 30 volts) is set with the trimming resistor R10.

Details. Trimmer resistors - SP5. Any transformer Tr1 with a power of at least 100 watts. Transistor VT1 - any silicon medium power transistor with Uk of at least 50 V.

Attention! Since the circuit elements are under mains voltage, electrical safety measures should be observed when setting up the device.

  1. Acceptable simplifications
  2. About computer power supplies
  3. Get to work!
  4. About power supply repair
  5. A couple of impulses
  6. For dessert

Making a power supply with your own hands makes sense not only for enthusiastic radio amateurs. A homemade power supply unit (PSU) will create convenience and save a considerable amount in the following cases:

  • To power low-voltage power tools, to save the life of an expensive rechargeable battery;
  • For electrification of premises that are particularly dangerous in terms of the degree of electric shock: basements, garages, sheds, etc. When powered by alternating current, a large amount of it in low-voltage wiring can create interference with household appliances and electronics;
  • In design and creativity for precise, safe and waste-free cutting of foam plastic, foam rubber, low-melting plastics with heated nichrome;
  • In lighting design, the use of special power supplies will extend the life of the LED strip and obtain stable lighting effects. Powering underwater illuminators of a fountain, pond, etc. from a household electrical network is generally unacceptable;
  • For charging phones, smartphones, tablets, laptops away from stable power sources;
  • For electroacupuncture;
  • And many other purposes not directly related to electronics.

Acceptable simplifications

Professional power supplies are designed to power any kind of load, incl. reactive. Possible consumers include precision equipment. The pro-BP must maintain the specified voltage with the highest accuracy for an indefinitely long time, and its design, protection and automation must allow operation by unqualified personnel in difficult conditions, for example. biologists to power their instruments in a greenhouse or on an expedition.

An amateur laboratory power supply is free from these limitations and therefore can be significantly simplified while maintaining quality indicators sufficient for personal use. Further, through also simple improvements, it is possible to obtain a special-purpose power supply from it. What are we going to do now?

Abbreviations

  1. KZ – short circuit.
  2. XX – idle speed, i.e. sudden disconnection of the load (consumer) or a break in its circuit.
  3. VS – voltage stabilization coefficient. It is equal to the ratio of the change in input voltage (in % or times) to the same output voltage at a constant current consumption. Eg. The network voltage dropped completely, from 245 to 185V. Relative to the norm of 220V, this will be 27%. If the VS of the power supply is 100, the output voltage will change by 0.27%, which, with its value of 12V, will give a drift of 0.033V. More than acceptable for amateur practice.
  4. IPN is a source of unstabilized primary voltage. This can be an iron transformer with a rectifier or a pulsed network voltage inverter (VIN).
  5. IIN - operate at a higher (8-100 kHz) frequency, which allows the use of lightweight compact ferrite transformers with windings of several to several dozen turns, but they are not without drawbacks, see below.

    6. So, we calculated, for example, for a bridge rectifier, 4 + 4 + 2.5 = 10.5 V extra. We add it to the required output voltage of the power supply unit; let it be 12V, and divide by 1.414, we get 22.5/1.414 = 15.9 or 16V, this will be the lowest permissible voltage of the secondary winding. If TP is factory-made, we take 18V from the standard range.

    Now the secondary current comes into play, which, naturally, is equal to the maximum load current. Let us say we need 3A; multiply by 18V, it will be 54W. We have obtained the overall power Tr, Pg, and we will find the nameplate power P by dividing Pg by the efficiency Tr?, which depends on Pg:

    • up to 10W, ? = 0.6.
    • 10-20 W, ? = 0.7.
    • 20-40 W, ? = 0.75.
    • 40-60 W, ? = 0.8.
    • 60-80 W, ? = 0.85.
    • 80-120 W, ? = 0.9.
    • from 120 W, ? = 0.95.

    In our case, there will be P = 54/0.8 = 67.5 W, but there is no such standard value, so you will have to take 80 W. In order to get 12Vx3A = 36W at the output. A steam locomotive, and that's all. It’s time to learn how to calculate and wind the “trances” yourself. Moreover, in the USSR, methods for calculating transformers on iron were developed that make it possible, without loss of reliability, to squeeze 600 W out of a core, which, when calculated according to amateur radio reference books, is capable of producing only 250 W. "Iron Trance" is not as stupid as it seems.

    SNN

    The rectified voltage needs to be stabilized and, most often, regulated. If the load is more powerful than 30-40 W, short-circuit protection is also necessary, otherwise a malfunction of the power supply may cause a network failure. SNN does all this together.

    Simple reference

    It is better for a beginner not to immediately go into high power, but to make a simple, highly stable 12V ELV for testing according to the circuit in Fig. 2. It can then be used as a source of reference voltage (its exact value is set by R5), for checking devices, or as a high-quality ELV ION. The maximum load current of this circuit is only 40mA, but the VSC on the antediluvian GT403 and the equally ancient K140UD1 is more than 1000, and when replacing VT1 with a medium-power silicon one and DA1 on any of the modern op-amps it will exceed 2000 and even 2500. The load current will also increase to 150 -200 mA, which is already useful.

    0-30

    The next stage is a power supply with voltage regulation. The previous one was done according to the so-called. compensating comparison circuit, but it is difficult to convert one to a high current. We will make a new SNN based on an emitter follower (EF), in which the RE and CU are combined in just one transistor. The KSN will be somewhere around 80-150, but this will be enough for an amateur. But the SNN on the ED allows, without any special tricks, to obtain an output current of up to 10A or more, as much as the Tr will give and the RE will withstand.

    The circuit of a simple 0-30V power supply is shown in pos. 1 Fig. 3. IPN for it is a ready-made transformer such as TPP or TS for 40-60 W with a secondary winding for 2x24V. Rectifier type 2PS with diodes rated at 3-5A or more (KD202, KD213, D242, etc.). VT1 is installed on a radiator with an area of ​​50 square meters or more. cm; An old PC processor will work very well. Under such conditions, this ELV is not afraid of a short circuit, only VT1 and Tr will heat up, so a 0.5A fuse in the primary winding circuit of Tr is enough for protection.

    Pos. Figure 2 shows how convenient a power supply on an electric power supply is for an amateur: there is a 5A power supply circuit with adjustment from 12 to 36 V. This power supply can supply 10A to the load if there is a 400W 36V power supply. Its first feature is the integrated SNN K142EN8 (preferably with index B) acts in an unusual role as a control unit: to its own 12V output is added, partially or completely, all 24V, the voltage from the ION to R1, R2, VD5, VD6. Capacitors C2 and C3 prevent excitation on HF DA1 operating in an unusual mode.

    The next point is the short circuit protection device (PD) on R3, VT2, R4. If the voltage drop across R4 exceeds approximately 0.7V, VT2 will open, close the base circuit of VT1 to the common wire, it will close and disconnect the load from the voltage. R3 is needed so that the extra current does not damage DA1 when the ultrasound is triggered. There is no need to increase its denomination, because when the ultrasound is triggered, you need to securely lock VT1.

    And the last thing is the seemingly excessive capacitance of the output filter capacitor C4. In this case it is safe, because The maximum collector current of VT1 of 25A ensures its charge when turned on. But this ELV can supply a current of up to 30A to the load within 50-70 ms, so this simple power supply is suitable for powering low-voltage power tools: its starting current does not exceed this value. You just need to make (at least from plexiglass) a contact block-shoe with a cable, put on the heel of the handle, and let the “Akumych” rest and save resources before leaving.

    About cooling

    Let's say in this circuit the output is 12V with a maximum of 5A. This is just the average power of a jigsaw, but, unlike a drill or screwdriver, it takes it all the time. At C1 it stays at about 45V, i.e. on RE VT1 it remains somewhere around 33V at a current of 5A. Power dissipation is more than 150 W, even more than 160, if you consider that VD1-VD4 also needs to be cooled. It is clear from this that any powerful adjustable power supply must be equipped with a very effective cooling system.

    A finned/needle radiator using natural convection does not solve the problem: calculations show that a dissipating surface of 2000 sq. m. is needed. see and the thickness of the radiator body (the plate from which the fins or needles extend) is from 16 mm. To own this much aluminum in a shaped product was and remains a dream in a crystal castle for an amateur. A CPU cooler with airflow is also not suitable; it is designed for less power.

    One of the options for the home craftsman is an aluminum plate with a thickness of 6 mm and dimensions of 150x250 mm with holes of increasing diameter drilled along the radii from the installation site of the cooled element in a checkerboard pattern. It will also serve as the rear wall of the power supply housing, as in Fig. 4.

    An indispensable condition for the effectiveness of such a cooler is a weak, but continuous flow of air through the perforations from the outside to the inside. To do this, install a low-power exhaust fan in the housing (preferably at the top). A computer with a diameter of 76 mm or more is suitable, for example. add. HDD cooler or video card. It is connected to pins 2 and 8 of DA1, there is always 12V.

    Note: In fact, a radical way to overcome this problem is a secondary winding Tr with taps for 18, 27 and 36V. The primary voltage is switched depending on which tool is being used.

    And yet the UPS

    The described power supply for the workshop is good and very reliable, but it’s hard to carry it with you on trips. This is where a computer power supply will fit in: the power tool is insensitive to most of its shortcomings. Some modification most often comes down to installing an output (closest to the load) electrolytic capacitor of large capacity for the purpose described above. There are a lot of recipes for converting computer power supplies for power tools (mainly screwdrivers, which are not very powerful, but very useful) in RuNet; one of the methods is shown in the video below, for a 12V tool.

    Video: 12V power supply from a computer

    With 18V tools it’s even easier: for the same power they consume less current. A much more affordable ignition device (ballast) from a 40 W or more energy saving lamp may be useful here; it can be completely placed in the case of a bad battery, and only the cable with the power plug will remain outside. How to make a power supply for an 18V screwdriver from ballast from a burnt housekeeper, see the following video.

    Video: 18V power supply for a screwdriver

    High class

    But let’s return to SNN on ES; their capabilities are far from being exhausted. In Fig. 5 – bipolar powerful power supply with 0-30 V regulation, suitable for Hi-Fi audio equipment and other fastidious consumers. The output voltage is set using one knob (R8), and the symmetry of the channels is maintained automatically at any voltage value and any load current. A pedant-formalist may turn gray before his eyes when he sees this circuit, but the author has had such a power supply working properly for about 30 years.

    The main stumbling block during its creation was?r = ?u/?i, where?u and?i are small instantaneous increments of voltage and current, respectively. To develop and set up high-quality equipment, it is necessary that?r does not exceed 0.05-0.07 Ohm. Simply, ?r determines the ability of the power supply to instantly respond to surges in current consumption.

    For SNN on EP?r is equal to that of ION, i.e. Zener diode divided by current transfer coefficient? RE. But for powerful transistors? at a large collector current it drops sharply, and the ?r of the zener diode ranges from a few to tens of ohms. Here, in order to compensate for the voltage drop across the RE and reduce the temperature drift of the output voltage, we had to assemble a whole chain of them in half with diodes: VD8-VD10. Therefore, the reference voltage from the ION is removed through an additional ED on VT1, is it? multiplied by? RE.

    The next feature of this design is short circuit protection. The simplest one, described above, does not fit into a bipolar circuit in any way, so the protection problem is solved according to the principle “there is no trick against scrap”: there is no protective module as such, but there is redundancy in the parameters of powerful elements - KT825 and KT827 at 25A and KD2997A at 30A. T2 is not capable of providing such a current, and while it warms up, FU1 and/or FU2 will have time to burn out.

    Note: It is not necessary to indicate blown fuses on miniature incandescent lamps. It’s just that at that time LEDs were still quite scarce, and there were several handfuls of SMOKs in the stash.

    It remains to protect the RE from the extra discharge currents of the pulsation filter C3, C4 during a short circuit. To do this, they are connected through low-resistance limiting resistors. In this case, pulsations may appear in the circuit with a period equal to the time constant R(3,4)C(3,4). They are prevented by C5, C6 of smaller capacity. Their extra currents are no longer dangerous for RE: the charge drains faster than the crystals of the powerful KT825/827 heat up.

    Output symmetry is ensured by op-amp DA1. The RE of the negative channel VT2 is opened by current through R6. As soon as the minus of the output exceeds the plus in modulus, it will slightly open VT3, which will close VT2 and the absolute values ​​of the output voltages will be equal. Operational control over the symmetry of the output is carried out using a dial gauge with a zero in the middle of the scale P1 (its appearance is shown in the inset), and adjustment, if necessary, is carried out by R11.

    The last highlight is the output filter C9-C12, L1, L2. This design is necessary to absorb possible HF interference from the load, so as not to rack your brain: the prototype is buggy or the power supply is “wobbly”. With electrolytic capacitors alone, shunted with ceramics, there is no complete certainty here; the large self-inductance of the “electrolytes” interferes. And chokes L1, L2 divide the “return” of the load across the spectrum, and to each their own.

    This power supply unit, unlike the previous ones, requires some adjustment:

    1. Connect a load of 1-2 A at 30V;
    2. R8 is set to maximum, in the highest position according to the diagram;
    3. Using a reference voltmeter (any digital multimeter will do now) and R11, the channel voltages are set to be equal in absolute value. Maybe, if the op-amp does not have the ability to balance, you will have to select R10 or R12;
    4. Use the R14 trimmer to set P1 exactly to zero.

    About power supply repair

    PSUs fail more often than other electronic devices: they take the first blow of network surges, and they also get a lot from the load. Even if you do not intend to make your own power supply, a UPS can be found, in addition to a computer, in a microwave oven, washing machine, and other household appliances. The ability to diagnose a power supply and knowledge of the basics of electrical safety will make it possible, if not to fix the fault yourself, then to competently bargain on the price with repairmen. Therefore, let's look at how a power supply is diagnosed and repaired, especially with an IIN, because over 80% of failures are their share.

    Saturation and draft

    First of all, about some effects, without understanding which it is impossible to work with a UPS. The first of them is the saturation of ferromagnets. They are not capable of absorbing energies of more than a certain value, depending on the properties of the material. Hobbyists rarely encounter saturation on iron; it can be magnetized to several Tesla (Tesla, a unit of measurement of magnetic induction). When calculating iron transformers, the induction is taken to be 0.7-1.7 Tesla. Ferrites can withstand only 0.15-0.35 T, their hysteresis loop is “more rectangular”, and operate at higher frequencies, so their probability of “jumping into saturation” is orders of magnitude higher.

    If the magnetic circuit is saturated, the induction in it no longer grows and the EMF of the secondary windings disappears, even if the primary has already melted (remember school physics?). Now turn off the primary current. The magnetic field in soft magnetic materials (hard magnetic materials are permanent magnets) cannot exist stationary, like an electric charge or water in a tank. It will begin to dissipate, the induction will drop, and an EMF of the opposite polarity relative to the original polarity will be induced in all windings. This effect is quite widely used in IIN.

    Unlike saturation, through current in semiconductor devices (simply draft) is an absolutely harmful phenomenon. It arises due to the formation/resorption of space charges in the p and n regions; for bipolar transistors - mainly in the base. Field-effect transistors and Schottky diodes are practically free from drafts.

    For example, when voltage is applied/removed to a diode, it conducts current in both directions until the charges are collected/dissolved. That is why the voltage loss on the diodes in rectifiers is more than 0.7V: at the moment of switching, part of the charge of the filter capacitor has time to flow through the winding. In a parallel doubling rectifier, the draft flows through both diodes at once.

    A draft of transistors causes a voltage surge on the collector, which can damage the device or, if a load is connected, damage it through extra current. But even without that, a transistor draft increases dynamic energy losses, like a diode draft, and reduces the efficiency of the device. Powerful field-effect transistors are almost not susceptible to it, because do not accumulate charge in the base due to its absence, and therefore switch very quickly and smoothly. “Almost”, because their source-gate circuits are protected from reverse voltage by Schottky diodes, which are slightly, but through.

    TIN types

    UPS trace their origins to the blocking generator, pos. 1 in Fig. 6. When turned on, Uin VT1 is slightly opened by current through Rb, current flows through winding Wk. It cannot instantly grow to the limit (remember school physics again); an emf is induced in the base Wb and load winding Wn. From Wb, through Sb, it forces the unlocking of VT1. No current flows through Wn yet and VD1 does not start up.

    When the magnetic circuit is saturated, the currents in Wb and Wn stop. Then, due to the dissipation (resorption) of energy, the induction drops, an EMF of the opposite polarity is induced in the windings, and the reverse voltage Wb instantly locks (blocks) VT1, saving it from overheating and thermal breakdown. Therefore, such a scheme is called a blocking generator, or simply blocking. Rk and Sk cut off HF interference, of which blocking produces more than enough. Now some useful power can be removed from Wn, but only through the 1P rectifier. This phase continues until the Sat is completely recharged or until the stored magnetic energy is exhausted.

    This power, however, is small, up to 10W. If you try to take more, VT1 will burn out from a strong draft before it locks. Since Tp is saturated, the blocking efficiency is no good: more than half of the energy stored in the magnetic circuit flies away to warm other worlds. True, due to the same saturation, blocking to some extent stabilizes the duration and amplitude of its pulses, and its circuit is very simple. Therefore, blocking-based TINs are often used in cheap phone chargers.

    Note: the value of Sb largely, but not completely, as they write in amateur reference books, determines the pulse repetition period. The value of its capacitance must be linked to the properties and dimensions of the magnetic circuit and the speed of the transistor.

    Blocking at one time gave rise to line scan TVs with cathode ray tubes (CRT), and it gave birth to an INN with a damper diode, pos. 2. Here the control unit, based on signals from Wb and the DSP feedback circuit, forcibly opens/locks VT1 before Tr is saturated. When VT1 is locked, the reverse current Wk is closed through the same damper diode VD1. This is the working phase: already greater than in blocking, part of the energy is removed into the load. It’s big because when it’s completely saturated, all the extra energy flies away, but here there’s not enough of that extra. In this way it is possible to remove power up to several tens of watts. However, since the control unit cannot operate until Tr has approached saturation, the transistor still shows through strongly, the dynamic losses are large and the efficiency of the circuit leaves much more to be desired.

    The IIN with a damper is still alive in televisions and CRT displays, since in them the IIN and the horizontal scan output are combined: the power transistor and Tr are common. This greatly reduces production costs. But, frankly speaking, an IIN with a damper is fundamentally stunted: the transistor and transformer are forced to work all the time on the verge of failure. The engineers who managed to bring this circuit to acceptable reliability deserve the deepest respect, but it is strongly not recommended to stick a soldering iron in there except for professionals who have undergone professional training and have the appropriate experience.

    The push-pull INN with a separate feedback transformer is most widely used, because has the best quality indicators and reliability. However, in terms of RF interference, it also sins terribly in comparison with “analog” power supplies (with transformers on hardware and SNN). Currently, this scheme exists in many modifications; powerful bipolar transistors in it are almost completely replaced by field-effect ones controlled by special devices. IC, but the principle of operation remains unchanged. It is illustrated by the original diagram, pos. 3.

    The limiting device (LD) limits the charging current of the capacitors of the input filter Sfvkh1(2). Their large size is an indispensable condition for the operation of the device, because During one operating cycle, a small fraction of the stored energy is taken from them. Roughly speaking, they play the role of a water tank or air receiver. When charging “short”, the extra charge current can exceed 100A for a time of up to 100 ms. Rc1 and Rc2 with a resistance of the order of MOhm are needed to balance the filter voltage, because the slightest imbalance of his shoulders is unacceptable.

    When Sfvkh1(2) are charged, the ultrasonic trigger device generates a trigger pulse that opens one of the arms (which one does not matter) of the inverter VT1 VT2. A current flows through the winding Wk of a large power transformer Tr2 and the magnetic energy from its core through the winding Wn is almost completely spent on rectification and on the load.

    A small part of the energy Tr2, determined by the value of Rogr, is removed from the winding Woc1 and supplied to the winding Woc2 of a small basic feedback transformer Tr1. It quickly saturates, the open arm closes and, due to dissipation in Tr2, the previously closed one opens, as described for blocking, and the cycle repeats.

    In essence, a push-pull IIN is 2 blockers “pushing” each other. Since the powerful Tr2 is not saturated, the draft VT1 VT2 is small, completely “sinks” into the magnetic circuit Tr2 and ultimately goes into the load. Therefore, a two-stroke IPP can be built with a power of up to several kW.

    It's worse if he ends up in XX mode. Then, during the half cycle, Tr2 will have time to saturate itself and a strong draft will burn both VT1 and VT2 at once. However, now there are power ferrites on sale for induction up to 0.6 Tesla, but they are expensive and degrade from accidental magnetization reversal. Ferrites with a capacity of more than 1 Tesla are being developed, but in order for IINs to achieve “iron” reliability, at least 2.5 Tesla is needed.

    Diagnostic technique

    When troubleshooting an “analog” power supply, if it is “stupidly silent,” first check the fuses, then the protection, RE and ION, if it has transistors. They ring normally - we move on element by element, as described below.

    In the IIN, if it “starts up” and immediately “stalls out”, they first check the control unit. The current in it is limited by a powerful low-resistance resistor, then shunted by an optothyristor. If the “resistor” is apparently burnt, replace it and the optocoupler. Other elements of the control device fail extremely rarely.

    If the IIN is “silent, like a fish on ice,” the diagnosis also begins with the OU (maybe the “rezik” has completely burned out). Then - ultrasound. Cheap models use transistors in avalanche breakdown mode, which is far from being very reliable.

    The next stage in any power supply is electrolytes. Fracture of the housing and leakage of electrolyte are not nearly as common as they write on the RuNet, but loss of capacity occurs much more often than failure of active elements. Electrolytic capacitors are checked with a multimeter capable of measuring capacitance. Below the nominal value by 20% or more - we lower the “dead” into the sludge and install a new, good one.

    Then there are the active elements. You probably know how to dial diodes and transistors. But there are 2 tricks here. The first is that if a Schottky diode or zener diode is called by a tester with a 12V battery, then the device may show a breakdown, although the diode is quite good. It is better to call these components using a pointer device with a 1.5-3 V battery.

    The second is powerful field workers. Above (did you notice?) it is said that their I-Z are protected by diodes. Therefore, powerful field-effect transistors seem to sound like serviceable bipolar transistors, even if they are unusable if the channel is “burnt out” (degraded) not completely.

    Here, the only way available at home is to replace them with known good ones, both at once. If there is a burnt one left in the circuit, it will immediately pull a new working one with it. Electronics engineers joke that powerful field workers cannot live without each other. Another prof. joke – “replacement gay couple.” This means that the transistors of the IIN arms must be strictly of the same type.

    Finally, film and ceramic capacitors. They are characterized by internal breaks (found by the same tester that checks the “air conditioners”) and leakage or breakdown under voltage. To “catch” them, you need to assemble a simple circuit according to Fig. 7. Step-by-step testing of electrical capacitors for breakdown and leakage is carried out as follows:

    • We set on the tester, without connecting it anywhere, the smallest limit for measuring direct voltage (most often 0.2V or 200mV), detect and record the device’s own error;
    • We turn on the measurement limit of 20V;
    • We connect the suspicious capacitor to points 3-4, the tester to 5-6, and to 1-2 we apply a constant voltage of 24-48 V;
    • Switch the multimeter voltage limits down to the lowest;
    • If on any tester it shows anything other than 0000.00 (at the very least - something other than its own error), the capacitor being tested is not suitable.

    This is where the methodological part of the diagnosis ends and the creative part begins, where all the instructions are based on your own knowledge, experience and considerations.

    A couple of impulses

    UPSs are a special article due to their complexity and circuit diversity. Here, to begin with, we will look at a couple of samples using pulse width modulation (PWM), which allows us to obtain the best quality UPS. There are a lot of PWM circuits in RuNet, but PWM is not as scary as it is made out to be...

    For lighting design

    You can simply light the LED strip from any power supply described above, except for the one in Fig. 1, setting the required voltage. SNN with pos. 1 Fig. 3, it’s easy to make 3 of these, for channels R, G and B. But the durability and stability of the LEDs’ glow does not depend on the voltage applied to them, but on the current flowing through them. Therefore, a good power supply for LED strip should include a load current stabilizer; in technical terms - a stable current source (IST).

    One of the schemes for stabilizing the light strip current, which can be repeated by amateurs, is shown in Fig. 8. It is assembled on an integrated timer 555 (domestic analogue - K1006VI1). Provides a stable tape current from a power supply voltage of 9-15 V. The amount of stable current is determined by the formula I = 1/(2R6); in this case - 0.7A. The powerful transistor VT3 is necessarily a field-effect transistor; from a draft, due to the base charge, a bipolar PWM simply will not form. Inductor L1 is wound on a ferrite ring 2000NM K20x4x6 with a 5xPE 0.2 mm harness. Number of turns – 50. Diodes VD1, VD2 – any silicon RF (KD104, KD106); VT1 and VT2 – KT3107 or analogues. With KT361, etc. The input voltage and brightness control ranges will decrease.

    The circuit works like this: first, the time-setting capacitance C1 is charged through the R1VD1 circuit and discharged through VD2R3VT2, open, i.e. in saturation mode, through R1R5. The timer generates a sequence of pulses with the maximum frequency; more precisely - with a minimum duty cycle. The VT3 inertia-free switch generates powerful impulses, and its VD3C4C3L1 harness smooths them out to direct current.

    Note: The duty cycle of a series of pulses is the ratio of their repetition period to the pulse duration. If, for example, the pulse duration is 10 μs, and the interval between them is 100 μs, then the duty cycle will be 11.

    The current in the load increases, and the voltage drop across R6 opens VT1, i.e. transfers it from the cut-off (locking) mode to the active (reinforcing) mode. This creates a leakage circuit for the base of VT2 R2VT1+Upit and VT2 also goes into active mode. The discharge current C1 decreases, the discharge time increases, the duty cycle of the series increases and the average current value drops to the norm specified by R6. This is the essence of PWM. At minimum current, i.e. at maximum duty cycle, C1 is discharged through the VD2-R4-internal timer switch circuit.

    In the original design, the ability to quickly adjust the current and, accordingly, the brightness of the glow is not provided; There are no 0.68 ohm potentiometers. The easiest way to adjust the brightness is by connecting, after adjustment, a 3.3-10 kOhm potentiometer R* into the gap between R3 and the VT2 emitter, highlighted in brown. By moving its engine down the circuit, we will increase the discharge time of C4, the duty cycle and reduce the current. Another way is to bypass the base junction of VT2 by turning on a potentiometer of approximately 1 MOhm at points a and b (highlighted in red), less preferable, because the adjustment will be deeper, but rougher and sharper.

    Unfortunately, to set up this useful not only for IST light tapes, you need an oscilloscope:

    1. The minimum +Upit is supplied to the circuit.
    2. By selecting R1 (impulse) and R3 (pause) we achieve a duty cycle of 2, i.e. The pulse duration must be equal to the pause duration. You cannot give a duty cycle less than 2!
    3. Serve maximum +Upit.
    4. By selecting R4, the rated value of a stable current is achieved.

    For charging

    In Fig. 9 – diagram of the simplest ISN with PWM, suitable for charging a phone, smartphone, tablet (a laptop, unfortunately, will not work) from a homemade solar battery, wind generator, motorcycle or car battery, magneto flashlight “bug” and other low-power unstable random sources power supply See the diagram for the input voltage range, there is no error there. This ISN is indeed capable of producing an output voltage greater than the input. As in the previous one, here there is the effect of changing the polarity of the output relative to the input; this is generally a proprietary feature of PWM circuits. Let's hope that after reading the previous one carefully, you will understand the work of this tiny little thing yourself.

    Incidentally, about charging and charging

    Charging batteries is a very complex and delicate physical and chemical process, the violation of which reduces their service life several times or tens of times, i.e. number of charge-discharge cycles. The charger must, based on very small changes in battery voltage, calculate how much energy has been received and regulate the charging current accordingly according to a certain law. Therefore, the charger is by no means a power supply, and only batteries in devices with a built-in charge controller can be charged from ordinary power supplies: phones, smartphones, tablets, and certain models of digital cameras. And charging, which is a charger, is a subject for a separate discussion.

    For dessert

    About 3 years ago, a little-noticed but curious message flashed in the news: the number of transistors produced by the global electronics industry, including transistor structures in chips, exceeded the number of cereal grains grown in the entire history of mankind, except for rice. While nature is still ahead...