High-quality laboratory power supply with your own hands. How to make a rectifier and a simple power supply

Hi all. Today is the final review, assembly of a laboratory linear power supply. Today there is a lot of locksmith work, hull manufacturing and final assembly. The review is posted on the DIY or DIY blog, I hope I don’t distract anyone here and don’t bother anyone to amuse my eyes with the charms of Lena and Igor))). Anyone who is interested in homemade products and radio engineering - Welcome !!!
ATTENTION: A lot of letters and photos! Traffic!

Welcome radio amateur and homemade lover! To begin with, let's remember the assembly steps for a laboratory linear power supply. It is not directly related to this review, therefore it is placed under the spoiler:

Assembly steps

Assembly of the power module. Board, heatsink, power transistor, 2 variable multi-turn resistors and a green transformer (from the Eighties®) As suggested by the wise kirich, I independently assembled a circuit that the Chinese sell in the form of a constructor for assembling a power supply. At first I was upset, but then I decided that, apparently, the circuit is good, since the Chinese are copying it ... At the same time, the children's sores of this circuit (which were completely copied by the Chinese) got out, without replacing the microcircuits with more "high-voltage ones", you cannot apply to the input more than 22 volts of alternating voltage ... And a few smaller problems that our forum users suggested to me, for which many thanks to them. Recently future engineer "Anna Sun"offered getting rid of the transformer. Of course, everyone can upgrade their PSU in any way, you can put a pulser as a power source. But any pulser (maybe except for resonant ones) has a lot of noise at the output, and this interference will partially go to the LabBP output ... And if there are impulsive interference, then (IMHO) this is not LabBP.Therefore, I will not get rid of the "green transformer".


Since this is a linear power supply, it has a characteristic and significant drawback, all excess energy is released on the power transistor. For example, we apply 24V AC voltage to the input, which after rectification and smoothing will turn into 32-33V. If you connect a powerful load to the output that consumes 3A at a voltage of 5V, all the remaining power (28V at a current of 3A), which is 84W, will be dissipated in the power transistor, turning into heat. One way to prevent this problem, and increase efficiency accordingly, is to install a manual or automatic winding switching module. This module has been reviewed in:

For the convenience of working with the power supply and the ability to instantly turn off the load, an additional relay module was introduced into the circuit, which allows you to turn the load on or off. It was dedicated to this.


Unfortunately, due to the lack of the necessary relays (normally closed), this module did not work correctly, therefore it will be replaced by another module, on a D-trigger, which allows you to turn the load on or off with a single button.

Briefly tell about the new module. The scheme is quite well-known (sent to me in PM):


I slightly modified it to fit my needs and collected the following board:


On the back side:


This time there were no problems. Everything works very clearly and is controlled by one button. When power is applied, the 13th output of the microcircuit is always a logical zero, the transistor (2n5551) is closed and the relay is de-energized - accordingly, the load is not connected. When the button is pressed, a logical unit appears at the output of the microcircuit, the transistor opens and the relay is activated by connecting the load. Pressing the button again returns the chip to its original state.

What is the power supply without a voltage and current indicator? Therefore, I tried to make an ampervoltmeter myself. In principle, it turned out to be a good device, but it has some non-linearity in the range from 0 to 3.2A. This error will not affect in any way when using this meter, say, in a car battery charger, but it is unacceptable for a Laboratory PSU, therefore, I will replace this module with Chinese precision panel boards and displays with 5 digits ... And the module I assembled will find application in some other do-it-yourselfer.


Finally, higher-voltage microcircuits arrived from China, which I told you about in. And now you can apply 24V AC to the input without fear that it will break through the microcircuits ...

Now it's up to the "small", to make the case and assemble all the blocks together, which I will do in this final review on this topic.
Looking for a ready-made case, I did not find anything suitable. The Chinese have good boxes, but, unfortunately, their price, and especially ...

The “toad” didn’t allow me to give the Chinese 60 bucks, and it’s stupid to give that kind of money for the case, you can add a little more and buy it. At least the case will come out of this Bp good.

Therefore, I went to the construction market and bought 3 meters of aluminum corner. With it, the frame of the device will be assembled.
Preparing the details right size. We draw the blanks and cut the corners with a cutting disc. .



Then lay out the blanks of the top and bottom panels to figure out what happens.


Trying to place modules inside


The assembly goes on countersunk screws (under the head with a countersink, a hole is drilled so that the screw head does not protrude above the corner), and nuts on the reverse side. Slowly, the outlines of the frame of the power supply appear:


And now the frame is assembled ... Not very even, especially in the corners, but I think that the painting will hide all the bumps:


Dimensions of the frame under the spoiler:

Dimension measurement

Unfortunately, there is little free time, because locksmith work is progressing slowly. In the evenings, in a week, I made a front panel from a sheet of aluminum and a socket for the power input and fuse.






We draw future holes for the Voltmeter and Ammeter. The seat should be 45.5mm by 26.5mm
We glue the landing holes with masking tape:


And with a cutting disc, using a dremel, we make cuts (adhesive tape is needed so as not to go beyond the dimensions of the sockets and not to spoil the panel with scratches) Dremel quickly copes with aluminum, but it takes 3-4 per hole

Again there was a hitch, corny, the cutting discs for the dremel ran out, the search in all the shops in Almaty did not lead to anything, so I had to wait for the discs from China ... Fortunately, they came quickly in 15 days. Then the work went more fun and faster ...
Sawed holes with a dremel digital indicators, and processed with a file.


We put a green transformer on the "corners"


We try on a radiator with a power transistor. It will be isolated from the case, since a transistor is installed on the radiator in the TO-3 case, and there it is difficult to isolate the transistor collector from the case. The radiator will be behind a decorative grille with a cooling fan.




I processed the front panel with sandpaper on a bar. I decided to try on everything that will be fixed on it. It turns out like this:


Two digital meters, a load enable button, two multi-turn potentiometers, output terminals, and a current limit LED holder. Didn't you forget something?


On the back of the front panel.
We disassemble everything and paint the frame of the power supply unit with black paint from a can.


Bolted to the back wall decorative grille(bought at the car market, anodized aluminum for tuning the air intake of the radiator 2000 tenge (6.13USD))


So it happened, the view from the back of the power supply housing.


We put a fan to blow the radiator with a power transistor. I attached it with plastic black clamps, it holds well, appearance does not suffer, they are almost invisible.


We return the plastic base of the frame to its place with the power transformer already installed.


We mark the places of fastening of the radiator. The radiator is isolated from the body of the device, because on it the voltage is equal to the voltage on the collector of the power transistor. I think that it will be well blown by a fan, which will significantly reduce the temperature of the radiator. The fan will be controlled by a circuit that reads information from a sensor (thermistor) mounted on a radiator. Thus, the fan will not “thresh” into an empty one, but will turn on when it reaches certain temperature on the heatsink of the power transistor.


We attach the front panel in place, see what happens.


There are a lot of decorative grilles left, so I decided to try to make a U-shaped cover for the power supply case (in the manner of computer cases), if I don’t like it, I’ll change it to something else.


Front view. While the grille is "baited" and is not yet firmly attached to the frame.


It seems to work well. The grille is strong enough, you can safely put something on top, but it’s not even worth talking about the quality of ventilation inside the case, the ventilation will be just excellent, compared to closed cases.

Well, let's continue with the build. We connect a digital ammeter. Important: do not step on my rake, do not use a regular connector, just solder directly to the connector pins. Otherwise, it will be in place of the current in Amperes, show the weather on Mars.


The wires for connecting the ammeter, and all other auxiliary devices, should be as short as possible.
Between the output terminals (plus or minus) I installed a socket made of foil textolite. It is very convenient to draw insulating grooves in copper foil to create platforms for connecting all auxiliary devices (ammeter, voltmeter, load disconnection board, etc.)

The main board is installed next to the heatsink of the output transistor.

The winding switching board is installed above the transformer, which made it possible to significantly reduce the length of the wire loop.

It's time to assemble the module additional food for winding switching module, ammeter, voltmeter, etc.
Since we have a linear - analog PSU, we will also use the option on a transformer, no switching power supplies. :-)
Etching the board:


Soldering the details:


We test, put brass “legs” and embed the module into the case:

Well, all the blocks are built in (except for the fan control module, which will be made later) and installed in their places. The wires are connected, the fuse is inserted. You can carry out the first inclusion. We overshadow ourselves with the cross, close our eyes and give nourishment ...
There is no boom and white smoke - it’s already good ... It seems that nothing is heating up at idle ... We press the load switch button - the green LED lights up and the relay clicks. Everything seems to be fine so far. You can start testing.

As the saying goes, "soon a fairy tale is told, but not soon the deed is done." Pitfalls surfaced again. The transformer winding switching module does not work correctly with the power module. At the switching voltage from the first winding to the next, a voltage jump occurs, i.e. when 6.4V is reached, a jump occurs up to 10.2V. Then, of course, you can reduce the voltage, but this is not the point. At first I thought that the problem was in the power supply of the microcircuits, since their power is also from the windings power transformer, and increases accordingly with each subsequent connected winding. Therefore, I tried to power the microcircuits from a separate power source. But it did not help.
Therefore, there are 2 options: 1. Completely redo the circuit. 2. Refuse the automatic winding switching module. I'll start with option 2. I can’t stay completely without switching the windings, because I don’t like the option of putting up with the stove, so I’ll put a toggle switch that allows you to choose the voltage supplied to the PSU input from 2 options 12V or 24V. This is of course a "half-measure", but better than nothing at all.
At the same time, I decided to change the ammeter to another similar one, but with a green glow of the numbers, since the red numbers of the ammeter glow rather weakly and are hard to see in sunlight. Here's what happened:


It seems so much better. It is also possible that I will replace the voltmeter with another one, because. 5 digits in the voltmeter is clearly redundant, 2 digits after the decimal point is enough. I have replacement options, so there will be no problems.

We put the switch and connect the wires to it. We check.
With the switch in the "down" position - the maximum voltage without load was about 16V

When the switch is up, the maximum voltage available for this transformer is 34V (no load)

Now the handles, for a long time I did not come up with options and found plastic dowels of a suitable diameter, both internal and external.


We cut off the tube of the required length and put it on the rods of variable resistors:


Then we put on the handles and fix them with screws. Since the dowel tube is quite soft, the handle is fixed very well, it takes considerable effort to rip it off.

The review is very large. Therefore, I will not take your time and briefly test the Laboratory Power Supply.
We already looked at interference with an oscilloscope in the first review, and since then nothing has changed in circuitry.
Therefore, we check the minimum voltage, the adjustment knob is in the leftmost position:

Now the maximum current

1A current limit

Maximum current limit, current adjustment knob in the far right position:

That's all my dear radio killers and sympathizers ... Thanks to everyone who read to the end. The device turned out to be brutal, heavy and, I hope, reliable. See you on the air!

UPD: Oscillograms at the output of the power supply when the voltage is turned on:


And turn off the voltage:

UPD2: Friends from the Soldering Iron forum gave an idea on how to start the winding switching module with minimal alterations to the circuit. Thank you all for your interest, I will finish the device. Therefore, to be continued. Add to favorites Liked +72 +134

A rectifier is a device for converting AC voltage to DC. It is one of the most common parts in electrical appliances, ranging from hair dryers to all types of power supplies with DC output voltage. There is different schemes rectifiers and each of them copes with its task to a certain extent. In this article we will talk about how to make a single-phase rectifier, and why you need it.

Definition

A rectifier is a device that converts AC to DC. The word "constant" is not entirely correct, the fact is that at the output of the rectifier, in the sinusoidal alternating voltage circuit, in any case, there will be an unstabilized pulsating voltage. In simple words: constant in sign but varying in magnitude.

There are two types of rectifiers:

half wave. It rectifies only one half-wave of the input voltage. Strong ripples and low relative to the input voltage are characteristic.

full wave. Accordingly, two half-waves are straightened. The ripple is lower, the voltage is higher than at the rectifier input - these are the two main characteristics.

What does stabilized and unstabilized voltage mean?

A stabilized voltage is a voltage that does not change in magnitude regardless of either the load or the input voltage surges. For transformer power supplies, this is especially important, because the output voltage depends on the input voltage and differs from it by Ktransformation times.

Unstabilized voltage - varies depending on surges in the supply network and load characteristics. With such a power supply, due to drawdowns, the connected devices may malfunction or be completely inoperable and fail.

Output voltage

The main values ​​\u200b\u200bof alternating voltage are the amplitude and effective value. When they say “in the 220V network,” they mean the current voltage.

If they talk about the amplitude value, then they mean how many volts are from zero to the top point of the half-wave of the sinusoid.

Omitting the theory and a number of formulas, we can say that 1.41 times less than the amplitude. Or:

The amplitude voltage in the 220V network is:

The first scheme is more common. It consists of a diode bridge - interconnected by a "square", and a load is connected to its shoulders. The bridge type rectifier is assembled according to the diagram below:

It can be connected directly to a 220V network, as done in, or to the secondary windings of a mains (50 Hz) transformer. Diode bridges according to this scheme can be assembled from discrete (separate) diodes or you can use a ready-made assembly of a diode bridge in a single package.

The second circuit - a mid-point rectifier cannot be connected directly to the network. Its meaning is to use a transformer with a tap from the middle.

In essence, these are two half-wave rectifiers connected to the ends of the secondary winding, the load is connected with one contact to the junction point of the diodes, and the second - to the tap from the middle of the windings.

Its advantage over the first circuit is a smaller number of semiconductor diodes. And the disadvantage is the use of a transformer with a midpoint or, as they also call it, a tap from the middle. They are less common than conventional non-tapped secondary transformers.

Ripple smoothing

Power supply with pulsating voltage is unacceptable for a number of consumers, for example, light sources and audio equipment. Moreover, the permissible light pulsations are regulated in state and industry regulations.

To smooth out ripples, they use a parallel-mounted capacitor, an LC filter, various P- and G-filters ...

But the most common and simplest option is a capacitor installed in parallel with the load. Its disadvantage is that in order to reduce ripples on a very powerful load, it will be necessary to install capacitors of a very large capacity - tens of thousands of microfarads.

Its principle of operation is that the capacitor is charged, its voltage reaches an amplitude, the supply voltage after the point of maximum amplitude begins to decrease, from that moment the load is powered by the capacitor. The capacitor discharges depending on the resistance of the load (or its equivalent resistance if it is not resistive). The larger the capacitance of the capacitor, the smaller the ripple will be when compared with a capacitor with a smaller capacitance connected to the same load.

In simple words: the slower the capacitor discharges, the less ripple.

The discharge rate of the capacitor depends on the current drawn by the load. It can be determined by the time constant formula:

where R is the load resistance and C is the capacitance of the smoothing capacitor.

Thus, from a fully charged state to a fully discharged capacitor, it will be discharged in 3-5 t. It charges at the same rate if the charge occurs through a resistor, so in our case it does not matter.

It follows from this that in order to achieve an acceptable level of ripple (it is determined by the requirements of the load on the power source), a capacitance is needed that will be discharged in a time many times greater than t. Since the resistances of most loads are relatively small, a large capacitance is needed, therefore, in order to smooth out ripples at the output of the rectifier, they are used, they are also called polar or polarized.

Please note that it is highly not recommended to confuse the polarity of an electrolytic capacitor, because this is fraught with its failure and even explosion. Modern capacitors are protected from explosion - they have a stamping in the form of a cross on the top cover, along which the case will simply crack. But a jet of smoke will come out of the condenser, it will be bad if it gets into your eyes.

The capacitance is calculated based on what ripple factor needs to be provided. If expressed plain language, then the ripple coefficient shows by what percentage the voltage sags (pulses).

C=3200*In/Un*Kp,

Where In is the load current, Un is the load voltage, Kn is the ripple factor.

For most types of equipment, the ripple factor is taken as 0.01-0.001. Additionally, it is desirable to install as large a capacitance as possible to filter out high-frequency interference.

How to make a power supply with your own hands?

The simplest DC power supply consists of three elements:

1. Transformer;

3. Capacitor.

This is an unregulated DC power supply with a smoothing capacitor. The voltage at its output is greater than the AC voltage secondary winding. This means that if you have a 220/12 transformer (primary at 220V and secondary at 12V), then you will get 15-17V DC at the output. This value depends on the capacitance of the smoothing capacitor. This circuit can be used to power any load, if it does not matter to it that the voltage can “float” with changes in the mains voltage.

A capacitor has two main characteristics - capacitance and voltage. We figured out how to select the capacitance, but not with the selection of voltage. The voltage of the capacitor must exceed the amplitude voltage at the output of the rectifier by at least half. If the actual voltage on the capacitor plates exceeds the nominal voltage, there is a high probability of its failure.

Old Soviet capacitors were made with a good voltage margin, but now everyone uses cheap electrolytes from China, where in best case there is a small margin, and in the worst case, it will not withstand the specified rated voltage. So don't skimp on reliability.

A stabilized power supply differs from the previous one only in the presence of a voltage (or current) stabilizer. The simplest option- use L78xx or others, such as domestic ROOL.

So you can get any voltage, the only condition when using such stabilizers is that the voltage to the stabilizer must exceed the stabilized (output) value by at least 1.5V. Consider what is written in the 12V datasheet of the L7812 stabilizer:

The input voltage should not exceed 35V, for stabilizers from 5 to 12V, and 40V for stabilizers at 20-24V.

The input voltage should exceed the output voltage by 2-2.5V.

Those. for a stabilized 12V power supply with an L7812 series stabilizer, it is necessary that the rectified voltage lies within 14.5-35V to avoid drawdowns, it would be an ideal solution to use a transformer with a 12V secondary winding.

But the output current is quite modest - only 1.5A, it can be amplified using a pass transistor. If you have , you can use this scheme:

It shows only the connection of a linear stabilizer. The "left" part of the circuit with a transformer and a rectifier is omitted.

If you have NPN transistors like KT803 / KT805 / KT808, then this one will do:

It is worth noting that in the second circuit, the output voltage will be less than the stabilization voltage by 0.6V - this is a drop at the emitter-base junction, we wrote more about this. To compensate for this drop, a diode D1 was introduced into the circuit.

It is possible to install two linear stabilizers in parallel, but it is not necessary! Due to possible deviations in manufacturing, the load will be unevenly distributed and one of them may burn out because of this.

Install both the transistor and the linear regulator on a heatsink, preferably on separate heatsinks. They get very hot.

Regulated power supplies

The simplest adjustable power supply can be made with an adjustable linear stabilizer LM317, its current is also up to 1.5 A, you can amplify the circuit with a pass transistor, as described above.

Here is a more visual diagram for assembling an adjustable power supply.

With a thyristor regulator in the primary winding, essentially the same regulated power supply.

By the way, a similar scheme regulates the welding current:

Conclusion

A rectifier is used in power supplies to produce direct current from alternating current. Without his participation, it will not be possible to power a DC load, for example led strip or radio.

Also used in a variety of car battery chargers, there are a number of circuits using a transformer with a group of taps from the primary winding, which are switched by a jack switch, and only a diode bridge is installed in the secondary winding. The switch is installed on the high voltage side, since the current is several times lower there and its contacts will not burn from this.

According to the diagrams from the article, you can assemble the simplest power supply for both permanent job with some kind of device, and for testing their electronic homemade products.

The circuits do not have high efficiency, but they produce a stabilized voltage without much ripple, you should check the capacitance of the capacitors and calculate for a specific load. They are perfect for low-power audio amplifiers, and will not create additional background. An adjustable power supply will be useful for motorists and auto electricians to test the generator voltage regulator relay.

An adjustable power supply is used in all areas of electronics, and if it is improved with short-circuit protection or a current stabilizer on two transistors, then you will get an almost full-fledged laboratory power supply.

The master, whose device description is in the first part, having set himself the goal of making an adjustable power supply, did not complicate his business and simply used boards that were idle. The second option involves the use of an even more common material - to regular block adjustment was added, perhaps this is a very promising solution in terms of simplicity, despite the fact that desired characteristics will not be lost and you can realize the idea with your own hands, even for not the most experienced radio amateur. As a bonus, there are two more options at all simple circuits with all detailed explanations for beginners. So there are 4 options for you to choose from.

We will tell you how to make an adjustable power supply from an unnecessary computer board. The master took the computer board and sawed out the block that feeds the RAM.
This is how he looks.

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

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

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

It looks like a switching power supply on a video card.

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

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

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

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

Using the tester in continuity mode and focusing on the circuit, I soldered the wires. Also using the tester, I found the 6th output of the PWM controller and resistors rang from it feedback. The resistor was rfb, it was soldered out and instead of it, a 10 kilo-ohm trimming resistor was soldered from the output to regulate the output voltage, I also found out by calling that the power of the PWM controller is directly connected to the input power line. This means that it will not be possible to apply more than 12 volts to the input, so as not to burn the PWM controller.

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

Soldered the plug for the input voltage, voltage indicator and output wires. We connect an external power supply of 12 volts. The indicator lights up. Already set to 9.2 volts. Let's try to adjust the power supply with a screwdriver.

It's time to check out what the power supply is capable of. Took wooden block and a homemade wire-wound resistor made of nichrome wire. Its resistance is low and, together with the tester probes, is 1.7 ohms. We turn on the multimeter in ammeter mode, connect it in series with the resistor. See what happens - the resistor glows red, the output voltage barely changes, and the current is about 4 amps.

Previously, the master has already made similar power supplies. One is cut out by hand from the laptop board.

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

How to make a regulating PSU from a regular one, from a printer

We will talk about the canon printer power supply, inkjet. They are left unused for a lot of people. This is essentially a separate device, the printer is held on by a latch.
Its characteristics: 24 volts, 0.7 amperes.

I needed a power supply for a homemade drill. It's just right for the power. But there is one caveat - if you connect it like that, we get only 7 volts at the output. Triple output, connector and we get only 7 volts. How to get 24 volts?
How to get 24 volts without disassembling the block?
Well, the simplest is to close the plus with an average output and get 24 volts.
Let's try to do it. We connect the power supply to the network 220. We take the device and try to measure it. Connect and see the output of 7 volts.
It does not have a central connector. If we take and connect to two at the same time, we see a voltage of 24 volts. This is the easiest way to make sure that this power supply, without disassembling, gives out 24 volts.

Required homemade regulator so that the voltage can be regulated within certain limits. 10 volts to max. This is easy to do. What is needed for this? First, open the power supply itself. It is usually glued on. How to open it so as not to damage the case. You don't have to poke or poke anything. We take a piece of wood more massive or there is a rubber mallet. We put it on a hard surface and peel along the seam. The glue comes off. Then they sounded good on all sides. Miraculously, the glue comes off and everything opens up. Inside we see the power supply.

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

If we apply voltage, then this transistor opens and 2.5 volts appear on the resistive divider, which are necessary for the operation of the zener diode. And the output appears 24 volts. This is the easiest option. How to start it, you can still - is to throw out the transistor q51 and put a jumper instead of the resistor r 57 and that's it. When we turn it on, the output is always 24 volts continuously.

How to make an adjustment?

You can change the voltage, make it 12 volts. But in particular the master, it is not necessary. It needs to be adjustable. How to do? We discard this transistor and instead of a 57 by 38 kilo-ohm resistor we put an adjustable one. There is an old Soviet one for 3.3 kilo-ohms. You can put from 4.7 to 10, which is. Only the minimum voltage to which it can lower it depends on this resistor. 3.3 is very low and not needed. The motors are planned to be supplied at 24 volts. And just from 10 volts to 24 is normal. Who needs a different voltage, you can use a large resistance trimmer.
Let's go, let's drink. We take a soldering iron, hair dryer. Soldered the transistor and resistor.

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

Such an option turned out. Installed a variable resistor. The handle turned out to be an adjustable power supply - quite convenient.

Video channel "Tekhnar".

It is easy to find such power supplies in China. I came across an interesting store that sells used power supplies from various printers, laptops and netbooks. They disassemble and sell the boards themselves, fully serviceable for different voltages and currents. The biggest plus is that they dismantle branded equipment and all power supplies are of high quality, with good details, all have filters.
Photos - different power supplies, cost a penny, almost a freebie.

Simple block with adjustment

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

Homemade regulated block on one transistor

What is the simplest regulated power supply you can make yourself? This can be done on the lm317 chip. She already with herself is almost a power supply. On it, you can make both a voltage-adjustable power supply and a flow. This video tutorial shows a device with voltage regulation. The master found a simple scheme. Input voltage maximum 40 volts. Output from 1.2 to 37 volts. Maximum output current 1.5 amps.

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


Let's start assembling

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

Everything is regulated. We set 3 volts and add current. On the power supply, we will set the restrictions only more. Move the toggle switch to the top position. Now 0.5 amps. The microcircuit began to warm up. Nothing to do without a heat sink. I found some kind of plate, not for long, but enough. Let's try again. There is a drawdown. But the block works. Voltage regulation is in progress. We can insert a credit for this scheme.

Radioblog video. Solderer video blog.

Adjustable voltage source from 5 to 12 volts

Continuing with our guide to converting an ATX PSU to a desktop power supply, one very good addition to this is the LM317T positive voltage regulator.

The LM317T is an adjustable 3-pin positive voltage regulator capable of supplying a variety of DC voltage outputs other than a +5V or +12V DC voltage source, or as an AC output voltage from a few volts up to some maximum value, all with currents around 1. 5 amps.

With a little extra circuitry added to the power supply output, we can have a desktop power supply capable of operating over a range of fixed or variable voltages, both positive and negative in nature. This is actually much easier than you might think, since the transformer, rectification and smoothing have already been done by the PSU beforehand, and all we have to do is connect our extra circuit to the +12 Volt yellow wire output. But first, let's consider a fixed output voltage.

Fixed 9V power supply

There is a wide variety of three-pole voltage regulators in the standard TO-220 package, with the most popular fixed voltage regulator being the 78xx series positive regulators, which range from the very common 7805 +5V fixed voltage regulator to the 7824, +24V fixed voltage regulator. There is also a series of 79xx fixed negative voltage regulators that provide an additional negative voltage of -5 to -24 volts, but in this tutorial we will only use positive types 78xx .

The fixed 3-pin regulator is useful in applications where a regulated output is not required, making the output power supply simple but very flexible as the output voltage only depends on the regulator selected. They are called 3-pin voltage regulators because they only have three terminals to connect to and that's it. Entrance , General and Exit .

The input voltage for the regulator will be a +12V yellow wire from the power supply (or a separate transformer power supply) that is connected between the input and common terminals. Stabilized +9 volts is taken through the output and common as shown.

Voltage regulator circuit

So let's say we want to get a +9V output from our desktop power supply, then all we have to do is connect a +9V voltage regulator to yellow wire+12V. Since the power supply has already done the rectification and smoothing to +12V output, only additional components are required: a capacitor at the input and another at the output.

These additional capacitors contribute to the stability of the regulator and can range from 100nF to 330nF. An additional 100uF output capacitor helps to smooth out the characteristic ripple for a good transient response. This large capacitor placed at the output of the power supply circuit is commonly referred to as the "smoothing capacitor".

These series regulators 78xx give a maximum output current of about 1.5 A at fixed stabilized voltages of 5, 6, 8, 9, 12, 15, 18 and 24 V, respectively. But what if we want the output voltage to be +9V but only have the 7805 regulator, +5V?. The +5V output of the 7805 refers to the "ground, Gnd" or "0V" terminal.

If we were to increase this voltage on pin 2 from 4V to 4V, the output would also increase by another 4V, assuming sufficient input voltage. Then, by placing a small 4V (nearest preferred value of 4.3V) Zener diode between the regulator pin 2 and ground, we can cause the 7805 5V regulator to generate a +9V output as shown in the figure.

Increasing the output voltage

So how does it work. The 4.3V zener requires about 5mA of reverse bias current to maintain the output with a regulator drawing about 0.5mA. This total current of 5.5 mA is supplied through resistor "R1" from output pin 3.

So the resistor value needed for the 7805 regulator would be R = 5V / 5.5mA = 910 ohms. The feedback diode D1, connected across the input and output terminals, is for protection and prevents reverse bias of the regulator when the input power is turned off and the output power remains on or active for a short period of time due to the large inductance. load such as a solenoid or motor.

We can then use 3-pin voltage regulators and a suitable zener diode to get various fixed output voltages from our previous power supply ranging from +5V to +12V. But we can improve this design by replacing the DC voltage regulator with an AC voltage regulator such as LM317T .

AC voltage source

The LM317T is a fully adjustable 3-pin positive voltage regulator capable of delivering a 1.5A output voltage ranging from 1.25V to just over 30V. By using the ratio of two resistances, one fixed and the other variable (or both fixed), we can set the output voltage to the desired level with a corresponding input voltage ranging from 3 to 40 volts.

The LM317T AC Voltage Regulator also has built-in current limiting and thermal shutdown features, making it short circuit resistant and ideal for any low voltage or home desktop power supply.

The output voltage of the LM317T is determined by the ratio of the two feedback resistors R1 and R2, which form a potential divider network at the output terminal as shown below.

LM317T AC voltage regulator

The voltage across the feedback resistor R1 is a constant reference voltage of 1.25 V, V ref, generated between the "output" and "regulation" terminals. The control terminal current is 100µA DC. Since the reference voltage across resistor R1 is DC, the DC current I will flow through another resistor R2, resulting in an output voltage of:

Then any current flowing through resistor R1 also flows through resistor R2 (ignoring the very small current on the control terminal), with the sum of the voltage drops across R1 and R2 equal to the output voltage Vout . Obviously, the input voltage Vin must be at least 2.5 V higher than the required output voltage to power the regulator.

In addition, the LM317T has very good load regulation, provided that the minimum load current exceeds 10 mA. So in order to maintain a constant reference voltage of 1.25V, the minimum value of the feedback resistor R1 must be 1.25V / 10mA = 120 ohms and this value can vary from 120 ohms to 1000 ohms with typical values ​​of R 1 being approximately 220 Ω to 240 ohms for good stability.

If we know the value of the required output voltage, Vout, and the feedback resistor R1 is, say, 240 ohms, then we can calculate the value of the resistor R2 from the equation above. For example, our original output voltage of 9V would give a resistive value for R2:

R1. ((Vout / 1.25) -1) = 240. ((9 / 1.25) -1) = 1488 ohms

or 1500 ohms (1 kOhm) to the nearest preferred value.

Of course, in practice, resistors R1 and R2 are usually replaced by a potentiometer to generate an AC voltage source, or by several switched preset resistors if several fixed output voltages are required.

But in order to reduce the math required to calculate the value of resistor R2, each time we need a certain voltage, we can use standard resistance tables as shown below, which give us the output voltage of the regulators for various ratios of resistors R1 and R2 with using resistance values ​​E24 ,

The ratio of resistances R1 to R2

By changing the potentiometer resistor R2 to 2 kΩ, we can control the output voltage range of our desktop power supply from about 1.25 volts to a maximum output voltage of 10.75 (12-1.25) volts. Then our final modified AC power circuit is shown below.

AC power circuit

We can improve our basic voltage regulator circuit a bit by connecting an ammeter and a voltmeter to the output terminals. These instruments will visually display the current and voltage at the output of the AC voltage regulator. If desired, a fast-acting fuse can also be included in the design to ensure additional protection against short circuit, as shown in the figure.

Disadvantages of LM317T

One of the major disadvantages of using the LM317T as part of an AC power supply circuit for voltage regulation is that up to 2.5 volts is dropped or wasted as heat through the regulator. So, for example, if the required output voltage must be +9 volts, then the input voltage must be as much as 12 volts or more if the output voltage is to remain stable under maximum load conditions. This voltage drop across the regulator is called "dropout". Also due to this voltage drop, some form of heatsink is required to keep the regulator cool.

Fortunately, low-dropout AC voltage regulators are available, such as National Semiconductor's "LM2941T" low-dropout voltage regulator, which has low voltage shutdowns as low as 0.9 V at maximum load. This low voltage drop comes at a cost, as this device is only capable of delivering 1.0 amps with an AC voltage output of 5 to 20 volts. However, we can use this device to get an output voltage of around 11.1V, just below the input voltage.

So to sum it up, our desktop power supply we made from an old PC power supply in the previous study guide, can be converted to provide an AC voltage source using the LM317T to regulate the voltage. By connecting the input of this device through the yellow output wire +12V of the power supply, we can have a fixed voltage of +5V, +12V and a variable output voltage in the range of 2 to 10 volts with a maximum output current of 1.5A.

I watch a lot of videos on repairing various electronics and often the video begins with the phrase "connect the board to the LBP and ...".
In general, the LBP is a useful and cool thing, it just stands like an airplane wing, and I don’t need precision in fractions of a millivolt for crafts, it’s enough to replace a bunch of Chinese PSUs of dubious quality, and be able to determine how much power the device needs without fear of burning something lost PSU, we connect and increase the voltage until it works (routers, switches, laptops), and the so-called "Troubleshooting using the LBP method" is also a handy thing (this is when there is a short circuit on the board, but you will understand which of the thousands of SMD elements the hell has struck, to the inputs LBP clings with a current limit of 1A and a hot element is searched for by touch - heating = breakdown).

But because of the toad, I could not afford such a luxury, but while crawling along Pikabu I came across an interesting post that says how to assemble the PSU of your dreams from shit and sticks of Chinese modules.
After digging more on this topic, I found a bunch more videos on how to collect such a miracle Once Two.
Anyone can assemble such a craft, and the cost is not so expensive compared to ready-made solutions.
By the way, there is a whole album where people show off their crafts.
I ordered everything and started to wait.

The basis was a pulsed power supply unit 24V 6A (the same as in the soldering station, but about it next time)

The voltage and current regulation will go through such a converter - a limiter.

Well, the indicator is up to 100 volts.

In principle, this is enough for the circuit to work, but I decided to make a full-fledged device and bought more:

Power connectors for cable "eight"

Front panel banana plugs and 10K multi-turn resistors for smooth adjustment.
And I also found drills, bolts, nuts, hot-melt glue in the nearest construction store and tore out a CD drive from the old system unit.

To begin with, I collected everything on the table and tested it, the circuit is not complicated, I took it

I know that these are screenshots from YouTube, but I'm too lazy to download videos and cut frames from there, the essence of this will not change, but I could not find the source images now.

The pinout of my indicator was found in Google.


I assembled and connected the light bulb for the load, it works, I need to assemble it into a case, I have an old CD drive as the case (probably also a working one, but I think it’s time for this standard to rest) the drive is old, because the metal is thick and durable, the front panels are made of plugs from the system.

I figured out what and where it would fit in the case, and the assembly began.

I marked out the places for the components, drilled holes, painted the cork from the balloon and inserted the bolts.

Under all the elements, I glued the plastic from the packaging of the headphones to avoid a possible short circuit to the case, and under the DC-DC converters for USB power and cooling I also put a thermal pad (by making a cutout in the plastic under it, after cutting off all protruding legs, I took the thermal pad itself from the drive, it cooled the motor driver).

From the inside, I screwed one nut at a time and cut a washer from a plastic container on top to raise the pallets above the body.

I soldered all the wires, since there is no faith in the clamps, they can loosen up and start heating up.

To blow through the hottest elements (Voltage Regulator), I installed 2 40mm 12V fans in the side wall, since the PSU does not heat up all the time, but only under load, I don’t really want to constantly listen to the howl of not the quietest fans (yes, I took the cheapest fans, and they make noise strongly) to control the cooling, I ordered such a temperature control module, the thing is simple and super useful, you can both cool and heat, it’s easy to set up. Here is the instruction.

I set it to about 40 degrees, as the hottest point was taken by the radiator of the converter.

In order not to drive excess air, I set about 8 volts on the cooling power converter.
As a result, something like this turned out, inside the place in bulk, you can add some kind of load resistor.

Already under the final view I ordered twisters, I had to cut off 5mm of the resistor shaft and put 2 plastic washers with inside so that the handles are close to the body.

And that we have a completely suitable PSU, with an additional USB output that can give 3A to charge the tablet.

This is how the PSU looks already on rubber legs (3M Bumpon Self-Adhesive) paired with a soldering station.

I am pleased with the result, it turned out to be quite a powerful power supply unit with smooth adjustment and at the same time light and portable, I sometimes work on the road and carrying a factory LBP with a toroidal transformer is not a thrill at all, but here it fits quite easily in a backpack.

About how I did soldering station I'll tell you next time.

I recently came across a curious circuit diagram of a simple but pretty good entry-level power supply capable of delivering 0-24 V at a current of up to 5 amperes. The power supply provides protection, that is, limiting the maximum current in case of overload. The attached archive contains a printed circuit board and a document that describes the settings for this unit, and a link to the author's website. Please read the description carefully before assembling.

Here is a photo of my PSU version, a view of the finished board, and you can see how to roughly apply the case from an old computer ATX. The adjustment is made 0-20 V 1.5 A. Capacitor C4 for such a current is set to 100 uF 35 V.

At short circuit the maximum limited current is issued and the LED lights up, brought the limiter resistor to the front panel.

Power supply indicator

I conducted an audit, found a couple of simple M68501 arrowheads for this PSU. I spent half a day creating a screen for it, but still drew it and fine-tuned it to the required output voltages.

The resistance of the indicator head used and the applied resistor are indicated in the attached file on the indicator. I spread the front panel of the block, if anyone needs a case from an ATX power supply to remake, it will be easier to rearrange the inscriptions and add something than to create from scratch. If other voltages are required, the scale can simply be recalibrated, this will be easier. Here is the finished view of the regulated power supply:

Film - self-adhesive type "bamboo". The indicator has a backlight Green colour. Red LED Attention indicates that the overload protection has been activated.

Additions from BFG5000

The maximum limiting current can be made more than 10 A. On the cooler - a roll of 12 volts plus a temperature speed controller - from 40 degrees it starts to increase speed. The circuit error does not particularly affect the operation, but judging by the measurements during a short circuit, an increase in the transmitted power appears.

The power transistor installed 2n3055, everything else is also foreign analogues, except for BC548 - I installed KT3102. It turned out really indestructible BP. For beginner radio amateurs, that's it.

The output capacitor is set to 100 uF, the voltage does not jump, the adjustment is smooth and without visible delays. I set the calculation as indicated by the author: 100 microfarads of capacity per 1 A of current. The authors: Igoran and BFG5000.

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