In one of mine, I showed how to make a good power supply yourself and complained about why good power supplies are rarely found on sale. I liked this power supply just from the picture, but since the picture can be deceiving, I decided to take a closer look and test it.
The review will include a description, photos, tests and analysis of a small design error.
Continue reading below the cut.
My readers probably remember the review “12 Volt 5 Ampere power supply or how it could be done.” This power supply reminded me of the one I made at the end of the review :)
But tests and checks are of course good, but I’ll start, as always, with how it drove and how it arrived.
More than one power supply arrived, I’ll tell you about the second product another time, I think it will be no less interesting. I drove quickly and got there along the track in 8 days.
But there was a complaint about the packaging, but since not everyone likes packaging, I’ll hide a few photos under the spoiler.
Package
The order arrived in a regular gray bag, wrapped in foam tape. 
It was this packaging that I had complaints about. The packer simply folded my two bags, wrapped them with tape and taped them together, but the edges were left open.
As a result, the bags and the roll of tape traveled separately. It was very lucky that the trip was short and they were packed in separate bags, otherwise they could have broken through the packaging with their radiators and crawled out. 
The board was packed in a familiar antistatic bag, with an equally familiar sticker. 
Brief characteristics:
Input voltage 85-265 Volts
Output voltage - 12 Volts
Load current - 6 Amperes nominal, 8 Amps maximum.
Output power - 100 Watts (maximum)
The dimensions of the board are not very large, 107x57x30mm. 
There is a drawing with more accurate dimensions, I think it will be useful. 
The board itself looks very neat, completely matches the photo in the store, which pleasantly surprised me. 
The board has quite large heatsinks, and the board itself is made in an open design, i.e. It is intended for installation in some device and does not have its own housing.
I took it for a reason, but for business :) I have an idea to remake one of my devices, but since I was not sure of the quality of this power supply, I decided to order and try only that one first, so there will be a continuation. Well, at least I hope so. 
The board contains an input filter, an inrush current limiter and a screwless terminal block for the 220 Volt input.
The power transformer has a DC12V-8 sticker.
The output winding of the transformer is wound in 5 wires 
The soldering is very neat, the leads are bitten off quite briefly, nothing sticks out, the flux is completely washed away. There are no missing components.
The board is two-layer with double-sided mounting.
But there is a small note: only one mounting pin is soldered on each of the radiators.
In my opinion this is not very good. What prevented us from soldering both is unclear.
Moreover, in the photo of the store everything is absolutely exactly the same.
I would like to note that the output voltage is measured at a point as close as possible to the output connector, which is a plus and affects the accuracy of holding the output voltage. 
A closer look at the main components of the board.
Installed PWM controller CR6842S, which is a complete analogue of the more famous controller
Almost all installed resistors are accurate, no worse than 1%, as indicated by the four-digit marking. 
Power transistor 600 Volt 20 Ampere, 0.19 Ohm manufactured by Infineon.
Another minor note: the mounting screw was tightened too much and it pressed in the insulating sleeve. The transistor remained isolated from the radiator, and the radiator itself was isolated from other components, but the impression was somewhat spoiled.
The transistor is isolated from the radiator by a mica plate.
Let me digress a little, in the photo you can see a small electrolytic capacitor, judging by the soldering it was either soldered in later or replaced, this did not affect the performance in any way (or almost in no way).
The fact is that if the load changes sharply from zero to 4 Amps or more, the power supply may turn off for 0.5 seconds. I would advise replacing this electrolyte with something like 47µFx50 V.
If such modes are not planned, then you can leave it as is. 
Output diode assembly 100 Volt 2x20 Ampere manufactured by ST.
The radiator is actually smooth, that’s how it looks in the photo :) 
You can also see a pair of output capacitors 1000 µF x 35 Volt, an output filter choke and an LED indicating the power supply is turned on.
Here the connector has already been installed with a regular screw connector.
Although, as for me, connectors are generally superfluous for an embedded board. 
The output capacitors are installed with a good voltage margin, which is very good.
Along the way, I checked the capacitance and ESR of these capacitors, and it turned out just as good.
The device showed the total capacitance and ESR, if recalculated for each separately, it will be approximately 1050 μF and 30 mOhm.
The capacitors are hardly branded, but the characteristics are quite normal, I was pleased with the operating voltage of 35 Volts. I usually use 25 Volt capacitors in my power supplies. 
Well, “in order not to run twice,” I checked the input electrolyte.
It says 82uF 400 Volts 105 degrees.
Capacitance is almost normal, ESR is normal.
Capacitor manufacturer Taicon. 
And of course I drew a diagram of this power supply. Most components are numbered according to the printed circuit board. 
To test the power supply I prepared this bunch of different things :)
Nothing unusual:
Load resistors 3 pieces 10 Ohms and one set giving a total of 3 Ohms (5 pieces of 15 Ohms connected in parallel) + fan.
Multimeter
Non-contact thermometer
Oscilloscope
All kinds of connectors and wires. 
Power supply testing
The testing process involved progressively increasing the load, and after each increase in load I waited about 15 minutes, then measured the temperature of the main components and moved on to the next step of increasing the load.
The oscilloscope divider was in the 1:1 position all this time.
1. Idle mode. Voltage 12.29 Volts.
2. One 10 Ohm resistor is connected. The voltage drops slightly to 12.28 Volts. 
1. 2 10 Ohm resistors are connected, voltage 12.28 Volts.
2. 3 10 Ohm resistors are connected, voltage 12.27 Volts. 
1. Connected to a 3 Ohm resistance set + fan, voltage 12.27 Volts
2. Set 3 Ohm + 10 Ohm resistor, voltage 12.27 Volts.
A small note: when connecting a load of more than 4 amperes, the power supply may turn off for 0.5 seconds and then turn on again. This only happens when moving from idle mode; even a small load removes this effect completely. 
1. Set of 3 Ohms + 2 resistors 10 Ohms, voltage 12.27 Volts.
2. Maximum load mode, set 3 Ohm + 3 resistors 10 Ohm, voltage 12.27 Volts. 
As I wrote above, during the testing process I measured the temperatures of various components.
Temperatures measured:
Power transistor
Transformer
Output diode
The first according to the output capacitor circuit.
For more accurate readings, the temperature of the transistor and diode assembly itself, and not their radiators, was measured.
With a load power of 80 Watts, I measured the temperature twice, the second measurement was after an additional 10 minute warm-up. 
Summary:
pros
High quality build
Quite high quality components with a reserve.
Compliance with the stated parameters.
Excellent accuracy of output voltage stabilization
I don't see any need for improvement.
Low price.
Minuses
Note on packaging (minus the store)
One mounting contact on the radiator is not soldered.
My opinion.
To be honest, I already liked this power supply from the outside in the photo of the store, and I already had some confidence in what I would get in the end, but it’s one thing to see, and another thing to try.
The power supply left positive emotions and is perfect for being built into some kind of homemade device.
Of course, there are some downsides, but they are very small compared to the advantages.
The power supply for review was provided by banggood.
I hope that my review will be useful.
Of course, you can say that I am praising the product, but I can say that I have been working on power supplies for about 15 years, during this time I have collected more than 1000 units, how many I have repaired and remade, I have lost count. That’s why I can’t not praise a normal thing. I've seen better things, especially industrial power supplies, but the price tag is different.
You can also consider such a power supply, but with less power.
A small note to Chinese engineers
The power supply showed very good results, but there is a small remark about the design, or rather about the printed circuit board.
The routing of some circuits is not done correctly, and if it were done correctly, the ripple level could be further reduced.
I'll show you with an example.
1. How it is done in the power supply, this section can be seen on the board, I simplified it a little for clarity.
2. How can this be done better without moving components on the board?
3. how to do it even better, but with moving components.
The fact is that in power circuits it is undesirable to have areas where current can flow in two directions, as this increases the level of interference.
The current must flow in only one direction.
In the original version, the capacitor charging current first flows along the same tracks, then the discharge current flows through them. 
The power supply is quite simple to manufacture, if you understand a little the theoretical part and understand how it works. Everything is not as difficult as it seems. What a 12-volt power supply consists of, with photos and examples, as well as a description of its elements and operating principle are further in the article.
Basic elements and principle of operation of power supplies
The main part is a step-down transformer, and in its absence with necessary parameters, then the secondary winding is rewound manually and the required output voltage is obtained. By means of a transformer, the voltage of the 220 volt network is reduced to 12, which goes further to the consumer.
There is no fundamental difference between standard devices and those with a rewound secondary winding; the main thing is to correctly calculate the cross-section of the wire and the number of turns on the winding.
Next, the current goes to the rectifier. Consists of semiconductors, such as diodes. A diode bridge, in different circuits, can consist of one, two or four diodes. After the rectifier, the current flows to the capacitor; it is also desirable to include a zener diode with the appropriate characteristics in the circuit to produce a stable voltage.
Transformer
The transformer consists of a core made of a ferromagnetic material, as well as primary and secondary windings. 220 volts comes to the primary winding, and from the secondary, in this case, 12 are removed, going to the rectifier. Cores in this type Power supplies are mostly made in W- and U-shapes.
The arrangement of the windings is allowed either one on top of the other on a common coil, or separately. For example, a U-shaped core has a pair of coils, each of which has half of the windings wound on it. When connecting a transformer, the terminals are connected in series.
How to correctly calculate the number of turns
When rewinding the secondary coil, you need to know what voltage the turn corresponds to. If you do not plan to rewind the primary winding, there is no need to calculate either the cross-section of the wire or its properties. The problem with the primary winding is large quantities turns of thin wire from which it consists.
To calculate the secondary winding, make 10 turns and connect the transformer to the network. Measure the voltage at the terminals, then divide it by 10, after which 12 is divided by the resulting number. The result will be the required number of turns, and it is recommended to increase it by 10% to compensate for the voltage drop.
Diodes
The choice of diodes is determined by the current strength on the secondary winding. Silicon semiconductors are suitable for these purposes, but not high-frequency ones, since they are designed to perform other tasks.
To make the device compact, good decision There will be the use of diode assemblies of four elements. Two terminals are supplied with power from the transformer, and rectified current is removed from the other two terminals.
After the diode bridge, it is strongly recommended to provide a zener diode with suitable parameters in the circuit, since during the day it is far from a fact that the input voltage will be a stable 220 volts. If you apply more voltage to the primary winding, then the output will also be more than 12 volts.
Frame
It is very convenient to make the housing for the power supply from aluminum. First, a frame is assembled from corners, which is then sheathed with aluminum plates. There are at least two advantages of this solution - firstly, aluminum is easy to work with, and secondly, it conducts heat very well, which will protect the power supply from overheating.
If you don’t want to assemble the frame yourself, you can borrow it from an old microwave. This solution has certain advantages - light weight, aesthetic appearance and spaciousness.
Printed circuit board for power supply
It is made of foil-coated PCB, for which the metal is treated with hydrochloric acid or battery electrolyte.
Work is carried out using rubber gloves and taking precautions. The metal is washed with a soda solution and an image of a printed circuit board is applied. There are special computer programs to create such images.
The board is etched by immersing it in a solution of ferric chloride or a mixture of copper sulfate and salt.
Installation of elements
At the end of etching, the board is rinsed, the protection is removed from the tracks and degreased. Using a very thin drill, holes are drilled in the board for the elements. Then the elements are inserted into the holes and soldered to the tracks, after which the tracks are tinned with tin.
Photo of a homemade 12 volt power supply
Those beginners who are just starting to study electronics are in a hurry to build something supernatural, like microbugs for wiretapping, a laser cutter from a DVD drive, and so on... and so on... What about assembling a power supply with an adjustable output voltage? This power supply is an essential item in every electronics enthusiast's workshop.
Where to start assembling the power supply?
First, you need to decide on the required characteristics that the future power supply will satisfy. The main parameters of the power supply are the maximum current ( Imax), which it can supply to the load (powered device) and the output voltage ( U out), which will be at the output of the power supply. It’s also worth deciding what kind of power supply we need: adjustable or unregulated.
Adjustable power supply is a power supply whose output voltage can be changed, for example, from 3 to 12 volts. If we need 5 volts - we turned the regulator knob - we got 5 volts at the output, we need 3 volts - we turned it again - we got 3 volts at the output.
An unregulated power supply is a power supply with a fixed output voltage - it cannot be changed. For example, the well-known and widely used “Electronics” power supply D2-27 is unregulated and has an output voltage of 12 volts. Also unregulated power supplies are all kinds of chargers for cell phones, adapters for modems and routers. All of them, as a rule, are designed for one output voltage: 5, 9, 10 or 12 volts.
It is clear that for a novice radio amateur it is the regulated power supply that is of greatest interest. It can power a huge number of both homemade and industrial devices designed for different supply voltages.
Next you need to decide on the power supply circuit. The circuit should be simple, easy to repeat by beginning radio amateurs. Here it is better to stick to a circuit with a conventional power transformer. Why? Because finding a suitable transformer is quite easy both in radio markets and in old consumer electronics. Making a switching power supply is more difficult. For pulse block power supply, it is necessary to manufacture quite a lot of winding parts, such as a high-frequency transformer, filter chokes, etc. Also, switching power supplies contain more electronic components than conventional power supplies with a power transformer.
So, the circuit of the regulated power supply proposed for repetition is shown in the picture (click to enlarge).
Power supply parameters:
Output voltage ( U out) – from 3.3...9 V;
Maximum load current ( Imax) – 0.5 A;
The maximum amplitude of output voltage ripple is 30 mV;
Overcurrent protection;
Protection against overvoltage at the output;
High efficiency.
It is possible to modify the power supply to increase the output voltage.
The circuit diagram of the power supply consists of three parts: a transformer, a rectifier and a stabilizer.
Transformer. Transformer T1 reduces the alternating mains voltage (220-250 volts), which is supplied to the primary winding of the transformer (I), to a voltage of 12-20 volts, which is removed from the secondary winding of the transformer (II). Also, “part-time”, the transformer serves as a galvanic isolation between the electrical network and the powered device. This is a very important function. If the transformer suddenly fails for any reason (voltage surge, etc.), then the mains voltage will not be able to reach the secondary winding and, therefore, the powered device. As you know, the primary and secondary windings of a transformer are reliably isolated from each other. This circumstance reduces the risk of electric shock.
Rectifier. From the secondary winding of power transformer T1, a reduced alternating voltage of 12-20 volts is supplied to the rectifier. This is already a classic. The rectifier consists of a diode bridge VD1, which rectifies alternating voltage from the secondary winding of the transformer (II). To smooth out voltage ripples, after the rectifier bridge there is an electrolytic capacitor C3 with a capacity of 2200 microfarads.
Adjustable pulse stabilizer.
The pulse stabilizer circuit is assembled on a fairly well-known and affordable DC/DC converter microcircuit - MC34063.
To make it clear. The MC34063 chip is a specialized PWM controller designed for pulsed DC/DC converters. This chip is the core of the adjustable switching regulator used in this power supply.
The MC34063 chip is equipped with an overload protection unit and short circuit in the load circuit. The output transistor built into the microcircuit is capable of delivering up to 1.5 amperes of current to the load. Based on a specialized microcircuit, the MC34063 can be assembled as step-up ( Step-Up), and downward ( Step-Down) DC/DC converters. It is also possible to build adjustable pulse stabilizers.
Features of pulse stabilizers.
By the way, switching stabilizers have a higher efficiency compared to stabilizers based on KR142EN series microcircuits ( CRANKS), LM78xx, LM317, etc. And although power supplies based on these microcircuits are very simple to assemble, they are less economical and require the installation of a cooling radiator.
The MC34063 chip does not require a cooling radiator. It is worth noting that this chip can often be found in devices that operate autonomously or use backup power. The use of a switching stabilizer increases the efficiency of the device, and, consequently, reduces power consumption from the battery or battery. Due to this it increases offline time operation of the device from a backup power source.
I think it’s now clear why a pulse stabilizer is good.
Parts and electronic components.
Now a little about the parts that will be required to assemble the power supply.
Power transformers TS-10-3M1 and TP114-163M
A TS-10-3M1 transformer with an output voltage of about 15 volts is also suitable. You can find a suitable transformer in radio parts stores and radio markets, the main thing is that it meets the specified parameters.
Chip MC34063 . The MC34063 is available in DIP-8 (PDIP-8) for conventional through-hole mount and SO-8 (SOIC-8) for surface mount. Naturally, in the SOIC-8 package the chip is smaller in size, and the distance between the pins is about 1.27 mm. Therefore, make printed circuit board for a microcircuit in the SOIC-8 package is more difficult, especially for those who have only recently begun to master the technology of producing printed circuit boards. Therefore, it is better to take the MC34063 chip in a DIP package, which is larger in size, and the distance between the pins in such a package is 2.5 mm. It will be easier to make a printed circuit board for a DIP-8 package.
Chokes. Chokes L1 and L2 can be made independently. To do this, you will need two ring magnetic cores made of 2000HM ferrite, size K17.5 x 8.2 x 5 mm. The standard size is deciphered as follows: 17.5 mm. – outer diameter of the ring; 8.2 mm. - inner diameter; a 5 mm. – height of the ring magnetic circuit. To wind the choke you will need a PEV-2 wire with a cross section of 0.56 mm. 40 turns of such wire must be wound on each ring. The turns of the wire should be distributed evenly over the ferrite ring. Before winding, the ferrite rings must be wrapped in varnished cloth. If you don’t have varnished fabric at hand, you can wrap the ring with three layers of tape. It is worth remembering that ferrite rings may already be painted - covered with a layer of paint. In this case, there is no need to wrap the rings with varnished cloth.
In addition to homemade chokes, you can also use ready-made ones. In this case, the process of assembling the power supply will speed up. For example, as chokes L1, L2 you can use the following surface-mount inductors (SMD - inductor).
As you can see, on the top of their case the inductance value is indicated - 331, which stands for 330 microhenry (330 μH). Also, ready-made chokes with radial leads for conventional installation in holes are suitable as L1, L2. This is what they look like.
The amount of inductance on them is marked either with a color code or with a number. For the power supply, inductances marked 331 (i.e. 330 μH) are suitable. Taking into account the tolerance of ±20%, which is allowed for elements of household electrical equipment, chokes with an inductance of 264 - 396 μH are also suitable. Any inductor or inductor is designed for a certain direct current. As a rule, it maximum value (I DC max) is indicated in the datasheet for the throttle itself. But this value is not indicated on the body itself. In this case, you can approximately determine the value of the maximum permissible current through the inductor based on the cross-section of the wire with which it is wound. As already mentioned, to independently manufacture chokes L1, L2, you need a wire with a cross-section of 0.56 mm.
Throttle L3 is homemade. To make it, you need a magnetic core made of ferrite. 400HH or 600HH with a diameter of 10 mm. You can find this in antique radios. There it is used as a magnetic antenna. You need to break off a piece 11 mm long from the magnetic circuit. This is quite easy to do; ferrite breaks easily. You can simply tightly clamp the required section with pliers and break off the excess magnetic circuit. You can also clamp the magnetic core in a vice, and then sharply hit the magnetic core. If you fail to carefully break the magnetic circuit the first time, you can repeat the operation.
Then the resulting piece of magnetic circuit must be wrapped with a layer of paper tape or varnished cloth. Next, we wind 6 turns of PEV-2 wire folded in half with a cross-section of 0.56 mm onto the magnetic circuit. To prevent the wire from unwinding, wrap it with tape on top. Those wire leads from which winding of the inductor began are subsequently soldered into the circuit in the place where the points are shown in image L3. These points indicate the beginning of winding the coils with wire.
Additions.
Depending on your needs, you can make certain changes to the design.
For example, instead of a VD3 zener diode type 1N5348 (stabilization voltage - 11 volts), you can install a protective diode - a suppressor - in the circuit 1.5KE10CA.
A suppressor is a powerful protective diode, its functions are similar to a zener diode, however, its main role is in electronic circuits– protective. The purpose of the suppressor is to suppress high-voltage pulse noise. The suppressor has high performance and is able to dampen powerful impulses.
Unlike the 1N5348 zener diode, the 1.5KE10CA suppressor has a high response speed, which will undoubtedly affect the performance of the protection.
In technical literature and among radio amateurs, a suppressor can be called differently: protective diode, limiting zener diode, TVS diode, voltage limiter, limiting diode. Suppressors can often be found in switching power supplies - there they serve as protection against overvoltage of the powered circuit in the event of faults in the switching power supply.
You can learn about the purpose and parameters of protective diodes from the article about suppressor.
Suppressor 1.5KE10 C A has a letter WITH in the name and is bidirectional - the polarity of its installation in the circuit does not matter.
If there is a need for a power supply with a fixed output voltage, then the variable resistor R2 is not installed, but replaced with a wire jumper. The required output voltage is selected using a constant resistor R3. Its resistance is calculated using the formula:
Uout = 1.25 * (1+R4/R3)
After the transformations, we obtain a formula that is more convenient for calculations:
R3 = (1.25 * R4)/(U out – 1.25)
If you use this formula, then for U out = 12 volts you will need a resistor R3 with a resistance of about 0.42 kOhm (420 Ohm). When calculating, the value of R4 is taken in kilo-ohms (3.6 kOhm). The result for resistor R3 is also obtained in kilo-ohms.
To more accurately set the output voltage U out, you can install a trimming resistor instead of R2 and set the required voltage using the voltmeter more accurately.
It should be taken into account that a zener diode or suppressor should be installed with a stabilization voltage 1...2 volts higher than the calculated output voltage ( U out) power supply. So, for a power supply with a maximum output voltage equal to, for example, 5 volts, a 1.5KE suppressor should be installed 6V8 CA or similar.
Manufacturing of printed circuit board.
A printed circuit board for the power supply can be made different ways. Two methods for making printed circuit boards at home have already been discussed on the pages of the site.
The fastest and most comfortable way is to make a printed circuit board using a printed circuit board marker. Marker used Edding 792. He showed himself at his best. By the way, the signet for this power supply was made with just this marker.
The second method is suitable for those who have a lot of patience and a steady hand. This is a technology for making a printed circuit board using a correction pencil. This is a fairly simple and affordable technology that will be useful to those who could not find a marker for printed circuit boards, but do not know how to make boards with LUT or do not have a suitable printer.
The third method is similar to the second, only it uses tsaponlak - How to make a printed circuit board using tsaponlak?
In general, there is plenty to choose from.
Setting up and checking the power supply.
To check the functionality of the power supply, you first need to turn it on, of course. If there are no sparks, smoke or pops (this is quite possible), then the power supply is most likely working. At first, keep some distance from him. If you made a mistake when installing electrolytic capacitors or set them to a lower operating voltage, they can “pop” and explode. This is accompanied by electrolyte splashing in all directions through the protective valve on the body. So take your time. You can read more about electrolytic capacitors. Don’t be lazy to read this – it will come in handy more than once.
Attention! The power transformer is under high voltage during operation! Don't put your fingers near it! Don't forget about safety rules. If you need to change something in the circuit, then first completely disconnect the power supply from the mains, and then do it. There is no other way - be careful!
At the end of this whole story, I want to show you a finished power supply that I made with my own hands.
Yes, it does not yet have a housing, a voltmeter and other “goodies” that make it easier to work with such a device. But, despite this, it works and has already managed to burn out an awesome three-color flashing LED because of its stupid owner, who loves to twist the voltage regulator recklessly. I wish you, novice radio amateurs, to collect something similar!
A rectifier is a device for converting alternating voltage to direct voltage. This is one of the most common parts in electrical appliances, from hair dryers to all types of power supplies with output voltage direct current. There are different rectifier circuits 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 it is needed.
Definition
A rectifier is a device designed to convert alternating current into direct current. 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. Characterized by strong ripples and low voltage relative to the input.
Full wave. Accordingly, two half-waves are rectified. The ripple is lower, the voltage is higher than at the rectifier input - these are two main characteristics.
What does stabilized and unstabilized voltage mean?
Stabilized is a voltage that does not change in value regardless of the load or 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 - changes depending on surges in the supply network and load characteristics. With such a power supply, due to drawdowns, the connected devices may malfunction or become completely inoperable and fail.
Output voltage
The main quantities of alternating voltage are amplitude and effective value. When they say “in a 220V network,” they mean the effective voltage.
If we talk about the amplitude value, then we mean how many volts from zero to the top point of the half-wave of a sine wave.
Omitting the theory and a number of formulas, we can say that it is 1.41 times less than the amplitude. Or:
The amplitude voltage in a 220V network is equal to:
The first scheme is more common. It consists of a diode bridge - connected to each other 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 network (50 Hz) transformer. Diode bridges according to this scheme can be assembled from discrete (individual) diodes or use a ready-made diode bridge assembly in a single housing.
The second circuit - a midpoint rectifier cannot be connected directly to the network. Its meaning is to use a transformer with a tap from the middle.
At its core, these are two half-wave rectifiers connected to the ends of the secondary winding; the load is connected with one contact to the diode connection point, and the second to the tap from the middle of the windings.
Its advantage over the first circuit is the smaller number of semiconductor diodes. 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 transformers with a secondary winding without taps.
Ripple Smoothing
Power supply with pulsating voltage is unacceptable for a number of consumers, for example, light sources and audio equipment. Moreover, permissible light pulsations are regulated in state and industry regulations.
To smooth out ripples, they use a parallel-installed 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 to reduce ripple on a very powerful load, you will have to install very large capacitors - tens of thousands of microfarads.
Its operating principle is that the capacitor is charged, its voltage reaches amplitude, the supply voltage after the point of maximum amplitude begins to decrease, from this 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 greater the capacitance of the capacitor, the smaller the ripple will be when compared with a capacitor with a lower 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 consumed by the load. It can be determined using 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 completely discharged state, the capacitor will be discharged in 3-5 t. It charges at the same speed if the charge occurs through a resistor, so in our case it does not matter.
It follows that in order to achieve an acceptable level of ripple (it is determined by the load requirements for the power source), you need a capacitance that will be discharged in a time several times greater than t. Since the resistance of most loads is 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 can lead to its failure and even explosion. Modern capacitors are protected from explosion - they have a cross-shaped stamping on the top cover, along which the case will simply crack. But a stream of smoke will come out of the condenser; it will be bad if it gets into your eyes.
The capacitance is calculated based on the ripple factor that needs to be ensured. To put it simply in simple language, then the ripple coefficient shows by what percentage the voltage sags (pulsates).
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 coefficient is taken to be 0.01-0.001. Additionally, it is advisable to install as large a capacity 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 alternating voltage on the secondary winding. This means that if you have a 220/12 transformer (the primary is 220V and the secondary is 12V), then at the output you will get 15-17V constant. 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” when the supply voltage changes.
A capacitor has two main characteristics - capacitance and voltage. We figured out how to select the capacitance, but not how to select the voltage. The capacitor voltage must exceed the amplitude voltage at the rectifier output 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 reserve, but now everyone uses cheap electrolytes from China, where at best there is a small reserve, and at worst it will not withstand the specified rated voltage. Therefore, do not skimp on reliability.
The stabilized power supply differs from the previous one only by the presence of a voltage (or current) stabilizer. The simplest option- use L78xx or others, such as the domestic KREN.
This way 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. Let's look at what is written in the datasheet of the 12V stabilizer L7812:
The input voltage should not exceed 35V, for stabilizers from 5 to 12V, and 40V for stabilizers 20-24V.
The input voltage must exceed the output voltage by 2-2.5V.
Those. for a stabilized 12V power supply with a stabilizer of the L7812 series, it is necessary that the rectified voltage lies in the range of 14.5-35V, in order to avoid sags, 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 the transformer and 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 0.6V less than the stabilization voltage - this is a drop at the emitter-base transition, we wrote more about this. To compensate for this drop, diode D1 was introduced into the circuit.
It is possible to install two linear stabilizers in parallel, but this is not necessary! Due to possible deviations during manufacturing, the load will be distributed unevenly and one of them may burn out because of this.
Install both the transistor and the linear stabilizer on the radiator, preferably on different radiators. 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 is used to regulate the welding current:
Conclusion
A rectifier is used in power supplies to produce direct current from alternating current. Without its participation, it will not be possible to power a DC load, for example LED strip or radio.
Also used in a variety of chargers For car batteries, there are a number of circuits using a transformer with a group of taps from the primary winding, which are switched by a switch, and only diode bridge. The switch is installed on the high voltage side, since the current there is several times lower and its contacts will not burn from this.
Using the diagrams from the article, you can assemble a simple power supply both for constant operation with some device and for testing your electronic homemade products.
The circuits are not characterized by high efficiency, but they produce a stabilized voltage without much ripple; the capacitance of the capacitors should be checked and calculated for a specific load. They are perfect for low-power audio amplifiers and will not create additional background noise. An adjustable power supply will be useful for car enthusiasts and auto electricians to test the generator voltage regulator relay.
A regulated 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, you will get an almost complete laboratory block nutrition.
A 12 Volt power supply will allow you to power almost any household appliance, including even a laptop. Please note that the laptop input is supplied with voltage up to 19 Volts. But it will work great if powered from 12. However, the maximum current is 10 Amperes. Only consumption reaches this value very rarely, the average remains at the level of 2-4 Amperes. The only thing you should take into account is that when replacing a standard one with a homemade one, you will not be able to use the built-in battery. But still, a 12-volt power supply is ideal even for such a device.
Power supply parameters
The most important parameters of any power supply are the output voltage and current. Their values depend on one thing - the wire used in the secondary winding of the transformer. How to select it will be discussed below. For yourself, you must decide in advance for what purposes you plan to use the 12 Volt power supply. If you need to power low-power equipment - navigators, LEDs, etc., then an output of 2-3 Amps is quite sufficient. And then there will be a lot of this.
But if you plan to use it to carry out more serious actions - for example, charging a car, then you will need 6-8 Amperes at the output. The charging current must be ten times less than the battery capacity - this requirement must be taken into account. If there is a need to connect devices whose supply voltage differs significantly from 12 Volts, then it is wiser to set the adjustment.
How to choose a transformer
The first element is a voltage converter. The transformer helps convert an alternating voltage of 220 Volts into the same amplitude, only with a much smaller value. At the very least you need a smaller value. For powerful power supplies, you can take a transformer like TS-270 as a basis. It has high power, there are even 4 windings that produce 6.3 Volts each. They were used to power incandescent radio tubes. Without much difficulty, you can make a 12 Volt 12 Ampere power supply out of it, which can even charge a car battery.
But if you are not completely satisfied with its windings, then you can remove all the secondary ones and leave only the network one. And wind the wire. The problem is how to calculate the required number of turns. To do this, you can use a simple calculation scheme - count how many turns the secondary winding contains, which produces 6.3 Volts. Now just divide 6.3 by the number of turns. And you will get the amount of voltage that can be removed from one turn of wire. All that remains is to calculate how many turns need to be wound in order to get 12.5-13 Volts at the output. It will be even better if the output voltage is 1-2 Volts higher than required.
Making a rectifier
What is a rectifier and what is it for? This is a semiconductor diode device that is a converter. With its help it turns into a permanent one. To analyze the operation of the rectifier stage, it is more clear to use an oscilloscope. If you see a sinusoid in front of the diodes, then after them it will be almost straight line. But small pieces of the sinusoid will still remain. Get rid of them later.
The choice of diodes should be taken with the utmost seriousness. If a 12-volt power supply is used as a battery charger, then you will need to use elements with a reverse current of up to 10 Amps. If you intend to supply power to low-current consumers, then a bridge assembly will be quite sufficient. This is where it's worth stopping. Preference should be given to a rectifier circuit assembled as a bridge - consisting of four diodes. If used on one semiconductor (half-wave circuit), then the efficiency of the power supply is almost halved.
Filter block
Now that the output has a constant voltage, it is necessary that the 12 Volt power supply be slightly improved. For this purpose you need to use filters. To power household appliances, it is enough to use an LC circuit. It is worth talking about it in more detail. An inductance - a choke - is connected to the positive output of the rectifier stage. Current must pass through it; this is the first stage of filtration. Next comes the second - an electrolytic capacitor with a large capacity (several thousand microfarads).
After the choke, an electrolytic capacitor is connected to the positive. Its second pin is connected to the common wire (minus). The essence of the operation of an electrolytic capacitor is that it allows you to get rid of the entire alternating component of the current. Remember when there were small pieces of sine wave left at the output of the rectifier? This is exactly what you need to get rid of, otherwise the 12 Volt 12 Ampere power supply will interfere with the device connected to it. For example, a cassette player or radio will produce a strong hum.
Output voltage stabilization
To stabilize the output voltage, you can use just one semiconductor element. This can be either a zener diode with an operating voltage of 12 Volts, or more modern and advanced assemblies such as LM317, LM7812. The latter are designed to stabilize the voltage at 12 Volts. Consequently, even if the output of the rectifier stage is 15 Volts, after stabilization only 12 will remain. Everything else goes into heat. This means that it is extremely important to install a stabilizer on the radiator.
Voltage adjustment 0-12 Volts
For greater versatility of the device, you should use a simple circuit that can be built in a few minutes. This can be achieved using the previously mentioned LM317 assembly. Only the difference from the switching scheme in stabilization mode will be small. 5 kOhm is connected to the break in the wire that goes to minus. A resistance of about 220 Ohms is connected between the output of the assembly and the variable resistor. And between the input and output of the stabilizer, protection against reverse voltage is a semiconductor diode. Thus, a 12 Volt power supply, assembled with your own hands, turns into a multifunctional device. Now all that remains is to assemble it and calibrate the scale. Or you can even install an electronic voltmeter at the output, which can be used to view the current voltage value.