The 12 volt DC power supply consists of three main parts:
- A step-down transformer from a conventional input alternating voltage of 220 V. At its output there will be the same sinusoidal voltage, only reduced to approximately 16 volts at idle - without load.
- Rectifier in the form of a diode bridge. It “cuts off” the lower half-sine waves and puts them up, that is, the resulting voltage varies from 0 to the same 16 volts, but in the positive region.
- A high-capacity electrolytic capacitor that smooths out the half-sine voltage, making it approach a straight line at 16 volts. This smoothing is better, the larger the capacitor capacity.
The simplest thing you need to obtain a constant voltage capable of powering devices designed for 12 volts - light bulbs, LED strips and other low-voltage equipment.
A step-down transformer can be taken from an old computer power supply or simply bought in a store so as not to bother with windings and rewinding. However, in order to ultimately reach the desired 12 volts of voltage with a working load, you need to take a transformer that lowers the volts to 16.
For the bridge, you can take four 1N4001 rectifier diodes, designed for the voltage range we need or similar.
The capacitor must have a capacity of at least 480 µF. For good output voltage quality, you can use more, 1,000 µF or higher, but this is not at all necessary to power lighting devices. The operating voltage range of the capacitor is needed, say, up to 25 volts.
Device layout
If we want to make a decent device that we won’t be ashamed to attach later as a permanent power supply, say, for a chain of LEDs, we need to start with a transformer, a board for mounting electronic components and a box where all this will be fixed and connected. When choosing a box, it is important to consider that the electrical circuits heat up during operation. Therefore, it is good to find a box that is suitable in size and with holes for ventilation. You can buy it in a store or take a case from a computer power supply. The latter option may be cumbersome, but as a simplification you can leave the existing transformer in it, even along with the cooling fan.
On the transformer we are interested in the low-voltage winding. If it reduces the voltage from 220 V to 16 V, this is an ideal case. If not, you'll have to rewind it. After rewinding and checking the voltage at the output of the transformer, it can be mounted on the circuit board. And immediately think about how the circuit board will be attached inside the box. It has mounting holes for this.
Further installation steps will take place on this mounting board, which means that it must be sufficient in area, length and allow the possible installation of radiators on diodes, transistors or a microcircuit, which must still fit into the selected box.
We assemble the diode bridge on the circuit board, you should get such a diamond of four diodes. Moreover, the left and right pairs consist equally of diodes connected in series, and both pairs are parallel to each other. One end of each diode is marked with a stripe - this is indicated by a plus. First we solder the diodes in pairs to each other. In series - this means the plus of the first is connected to the minus of the second. The free ends of the pair will also turn out - plus and minus. Connecting pairs in parallel means soldering both pluses of the pairs and both minuses. Now we have the output contacts of the bridge - plus and minus. Or they can be called poles - upper and lower.
The remaining two poles - left and right - are used as input contacts, they are supplied with alternating voltage from the secondary winding of the step-down transformer. And the diodes will supply a pulsating voltage of constant sign to the bridge outputs.
If you now connect a capacitor in parallel with the output of the bridge, observing the polarity - to the plus of the bridge - plus of the capacitor, it will begin to smooth out the voltage, and as well as its capacitance is large. 1,000 uF will be enough, and even 470 uF is used.
Attention! An electrolytic capacitor is an unsafe device. If it is connected incorrectly, if voltage is applied to it outside the operating range, or if it is overheated, it may explode. At the same time, all its internal contents scatter around the area - tatters of the case, metal foil and splashes of electrolyte. Which is very dangerous.
Well, here we have the simplest (if not primitive) power supply for devices with a voltage of 12 V DC, that is, direct current.
Problems with a simple power supply with a load
The resistance drawn on the diagram is the equivalent of the load. The load must be such that the current supplying it, with an applied voltage of 12 V, does not exceed 1 A. You can calculate the load power and resistance using the formulas.
Where does the resistance R = 12 Ohm, and the power P = 12 watts come from? This means that if the power is more than 12 watts and the resistance is less than 12 ohms, then our circuit will begin to work with overload, will get very hot and will quickly burn out. There are several ways to solve the problem:
- Stabilize the output voltage so that when the load resistance changes, the current does not exceed the maximum permissible value or when there are sudden current surges in the load network - for example, when some devices are turned on - the peak current values are cut to the nominal value. Such phenomena occur when the power supply powers radio-electronic devices - radios, etc.
- Use special protection circuits that would turn off the power supply if the load current exceeds.
- Use more powerful power supplies or power supplies with more power reserves.
The figure below shows the development of the previous simple circuit by including a 12-volt stabilizer LM7812 at the output of the microcircuit.
This is already better, but the maximum load current of such a stabilized power supply unit should still not exceed 1 A.
High Power Power Supply
The power supply can be made more powerful by adding several powerful stages using TIP2955 Darlington transistors to the circuit. One stage will provide an increase in load current of 5 A, six composite transistors connected in parallel will provide a load current of 30 A.
A circuit with this kind of power output requires adequate cooling. Transistors must be provided with heat sinks. You may also need an additional cooling fan. In addition, you can protect yourself with fuses (not shown in the diagram).
The figure shows the connection of one composite Darlington transistor, which makes it possible to increase the output current to 5 amperes. You can increase it further by connecting new cascades in parallel with the specified one.
Attention! One of the main disasters in electrical circuits is a sudden short circuit in the load. In this case, as a rule, a current of gigantic power arises, which burns everything in its path. In this case, it is difficult to come up with such a powerful power supply that can withstand this. Then protection circuits are used, ranging from fuses to complex circuits with automatic shutdown on integrated circuits.
When you assemble any electronic homemade product, you need a power supply to test it. There is a wide variety of ready-made solutions on the market. Beautifully designed, have many functions. There are also many kits for DIY production. I'm not even talking about the Chinese with their trading platforms. I bought step-down converter module boards on Aliexpress, so I decided to make them on it. The voltage is regulated, there is enough current. The unit is based on a module from China, as well as radio components that were in my workshop (they had been lying around for a long time and were waiting in the wings). The unit regulates from 1.5 volts to the maximum (it all depends on the rectifier used to the adjustment board.
Description of components
I have a 17.9 Volt transformer with a current of 1.7 Ampere. It is installed in the housing, which means there is no need to select the latter. The winding is quite thick, I think it will handle 2 Amps. Instead of a transformer, you can use a switching power supply for a laptop, but then you also need a housing for the remaining components.
The AC rectifier will be a diode bridge, which can also be assembled from four diodes. An electrolytic capacitor will smooth out the ripples; I have 2200 microfarads and an operating voltage of 35 volts. I used it used, it was in stock.
I will regulate the output voltage. There are a wide variety of them on the market. It provides good stabilization and is quite reliable.
To conveniently adjust the output voltage, I will use a 4.7 kOhm adjustment resistor. The board has 10 kOhm installed, but I’ll install whatever I had. The resistor is from the early 90s. With this rating, adjustment is ensured smoothly. I also picked up a handle for it, also from a shaggy age.
The output voltage indicator is . It has three wires. Two wires power the voltmeter (red and black), and the third (blue) is measuring. You can combine red and blue together. Then the voltmeter will be powered from the output voltage of the unit, that is, the indication will light up from 4 volts. Agree, it’s not convenient, so I’ll feed it separately, more on that later.
To power the voltmeter, I will use a domestic 12-volt voltage stabilizer chip. This will ensure that the voltmeter indicator operates at a minimum. The voltmeter is powered through the red plus and black minus. The measurement is carried out through the black minus and blue plus output of the block.
My terminals are domestic. They have holes for banana plugs and holes for clamping wires. Similar . I also selected wires with lugs.
Power supply assembly
Everything is assembled according to a simple sketched diagram.
The diode bridge must be soldered to the transformer. I bent it for comfortable installation. A capacitor was soldered to the output of the bridge. It turned out not to go beyond the height dimensions.
I screwed the power supply arm of the voltmeter to the transformer. In principle, it does not heat up, and so it stands in its place and does not bother anyone.
I removed a resistor on the regulator board and soldered two wires under the remote resistor. I also soldered wires under the output terminals.
Mark holes on the case for everything that will be on the front panel. I cut holes for a voltmeter and one terminal. I install the resistor and the second terminal at the junction of the box. When assembling the box, everything will be fixed by compressing both halves.
The terminal and voltmeter are installed.
This is how it turned out to install the second terminal and the adjusting resistor. I made a cutout for the resistor key.
Cut out a window for the switch. We assemble the housing and close it. All that remains is to wire the switch and the regulated power supply is ready for use.
This is how the regulated power supply turned out. This design is simple and can be repeated by anyone. The parts are not rare.
Good luck with making everyone!
Details
Diode bridge at the input 1n4007 or a ready-made diode assembly designed for a current of at least 1 A and a reverse voltage of 1000 V.Resistor R1 is at least two watts, or 5 watts 24 kOhm, resistor R2 R3 R4 with a power of 0.25 watts.
Electrolytic capacitor on the high side 400 volts 47 uF.
Output 35 volts 470 – 1000 uF. Film filter capacitors designed for a voltage of at least 250 V 0.1 - 0.33 µF. Capacitor C5 – 1 nF. Ceramic, ceramic capacitor C6 220 nF, film capacitor C7 220 nF 400 V. Transistor VT1 VT2 N IRF840, transformer from an old computer power supply, diode bridge at the output full of four ultra-fast HER308 diodes or other similar ones.
In the archive you can download the circuit and board:
(downloads: 1555)
The printed circuit board is made on a piece of foil-coated single-sided fiberglass laminate using the LUT method. For ease of connecting power and connecting output voltage, the board has screw terminal blocks.
12 V switching power supply circuit
The advantage of this circuit is that this circuit is very popular of its kind and is repeated by many radio amateurs as their first switching power supply and efficiency and times more, not to mention size. The circuit is powered from a mains voltage of 220 volts; at the input there is a filter which consists of a choke and two film capacitors designed for a voltage of at least 250 - 300 volts with a capacity of 0.1 to 0.33 μF; they can be taken from a computer power supply.
In my case there is no filter, but it is advisable to install it. Next, the voltage is supplied to a diode bridge designed for a reverse voltage of at least 400 Volts and a current of at least 1 Ampere. You can also supply a ready-made diode assembly. Next in the diagram there is a smoothing capacitor with an operating voltage of 400 V, since the amplitude value of the mains voltage is around 300 V. The capacitance of this capacitor is selected as follows, 1 μF per 1 Watt of power, since I am not going to pump large currents out of this block, then in my case, the capacitor is 47 uF, although such a circuit can pump out hundreds of watts. The power supply for the microcircuit is taken from the alternating voltage, here a power source is arranged, resistor R1, which provides current damping, it is advisable to set it to a more powerful one of at least two watts since it is heated, then the voltage is rectified by just one diode and goes to a smoothing capacitor and then to the microcircuit. Pin 1 of the microcircuit is plus power and pin 4 is minus power.
You can assemble a separate power source for it and supply it with 15 V according to the polarity. In our case, the microcircuit operates at a frequency of 47 - 48 kHz. For this frequency, an RC circuit is organized consisting of a 15 kohm resistor R2 and a 1 nF film or ceramic capacitor. With this arrangement of parts, the microcircuit will work correctly and produce rectangular pulses at its outputs, which are supplied to the gates of powerful field switches through resistors R3 R4, their ratings can deviate from 10 to 40 Ohms. Transistors must be installed N channel, in my case they are IRF840 with a drain-source operating voltage of 500 V and a maximum drain current at a temperature of 25 degrees of 8 A and a maximum power dissipation of 125 Watts. Next in the circuit there is a pulse transformer, after it there is a full-fledged rectifier made of four diodes of the HER308 brand, ordinary diodes will not work here since they will not be able to operate at high frequencies, so we install ultra-fast diodes and after the bridge the voltage is already supplied to the output capacitor 35 Volt 1000 μF , it is possible and 470 uF, especially large capacitances in switching power supplies are not required.
Let's return to the transformer, it can be found on the boards of computer power supplies, it is not difficult to identify it; in the photo you can see the largest one, and that is what we need. To rewind such a transformer, you need to loosen the glue that glues the halves of the ferrite together; to do this, take a soldering iron or a soldering iron and slowly warm up the transformer, you can put it in boiling water for a few minutes and carefully separate the halves of the core. We wind up all the basic windings, and we will wind our own. Based on the fact that I need to get a voltage of around 12-14 Volts at the output, the primary winding of the transformer contains 47 turns of 0.6 mm wire in two cores, we make insulation between the windings with ordinary tape, the secondary winding contains 4 turns of the same wire in 7 cores . It is IMPORTANT to wind in one direction, insulate each layer with tape, marking the beginning and end of the windings, otherwise nothing will work, and if it does, then the unit will not be able to deliver all the power.
Block check
Well, now let's test our power supply, since my version is completely working, I immediately connect it to the network without a safety lamp.Let's check the output voltage as we see it is around 12 - 13 V and does not fluctuate much due to voltage drops in the network.
As a load, a 12 V car lamp with a power of 50 Watts flows a current of 4 A. If such a unit is supplemented with current and voltage regulation, and an input electrolyte of a larger capacity is supplied, then you can safely assemble a car charger and a laboratory power supply.
Before starting the power supply, you need to check the entire installation and connect it to the network through a 100-watt incandescent safety lamp; if the lamp burns at full intensity, then look for errors when installing the snot; the flux has not been washed off or some component is faulty, etc. When assembled correctly, the lamp should be slightly flash and go out, this tells us that the input capacitor is charged and there are no errors in the installation. Therefore, before installing components on the board, they must be checked, even if they are new. Another important point after startup is that the voltage on the microcircuit between pins 1 and 4 must be at least 15 V. If this is not the case, you need to select the value of resistor R2.
DC power supplies are needed not only by radio amateurs. They have a very wide scope of application, and therefore most home craftsmen use them to one degree or another. This article describes the main types of voltage converters, their characteristic differences and applications, and how to make a simple power supply with your own hands.
Doing it yourself will save you a lot of money. Once you understand the device and operating principle, you can easily repair this device.
Areas of use
These devices have a very wide range of applications. Let's look at the main uses. To save battery life, low-voltage power tools are connected to homemade power supplies. Such devices are used for connecting LED lighting devices, installing lighting in rooms with high humidity and danger of electric shock, and for many other purposes not directly related to radio electronics.
Device classification
Most power supplies convert AC mains voltage of 220 volts into DC voltage of a given value. Moreover, the device is characterized by a large list of operating parameters that must be taken into account when purchasing or designing.
The main operating parameters are output current, voltage and the ability to stabilize and adjust the output voltage. All these converters are classified into two large groups according to the conversion method: analog and pulse devices. These groups of power supplies have strong differences and are easily distinguished from the photo at first glance.
Previously, only analog devices were produced. In them, voltage conversion is carried out using a transformer. Collecting such a source is not difficult. Its scheme is quite simple. It consists of a step-down transformer, a diode bridge and a stabilizing capacitor.
Diodes convert AC voltage to DC voltage. The capacitor further smoothes it out. The disadvantage of such devices is their large dimensions and weight.
A 250-watt transformer weighs several kilograms. In addition, the voltage at the output of such devices can change due to external factors. Therefore, to stabilize the output parameters in such devices, special elements are added to the electronic circuit.
High-power power supplies are manufactured using transformers. It is advisable to use such devices for charging car batteries or for connecting electric drills to save the life of lithium batteries.
The advantage of such a device is the galvanic isolation between the two windings (with the exception of autotransformers). The primary winding connected to the high voltage network has no physical contact with the secondary winding. A reduced voltage is generated on it.
Energy transfer is carried out using an alternating current magnetic field in the metal core of the transformer. If you have minimal knowledge in radio electronics, it is easier to assemble a classic adjustable power supply using a transformer with your own hands.
With the development of electronic technology, it has become possible to produce cheaper semiconductor voltage converters. They are very compact, light in weight and have a very low price. Thanks to this, they became market leaders. Every apartment uses several different power supplies.
Unfortunately, most modern devices do not have galvanic isolation from the power supply. Because of this, quite often people die who use the device while charging a cell phone or other equipment and at the same time take a bath or wash their face.
If safety precautions are followed, there is no danger to a person. These devices are quite low in cost and when they break down, they often do not try to repair them, but purchase a new device. However, if you understand the circuits and operating principles of switching power supplies, you can easily both repair such a power supply and assemble a new device.
Switching power supplies
Let's look at the design and operating principle of switching power supplies. In such devices, the alternating mains voltage is converted into high-frequency voltage at the input. To transform high-frequency currents, it is not large transformers that are required, but miniature electromagnetic coils. Therefore, such converters easily fit into small housings. For example, they can easily be placed in the plastic socket of an energy-saving lamp.
The layout of such a power supply in a small device does not cause any problems. For reliable operation, it is necessary to provide the possibility of cooling the heating elements of the electronic circuit on special metal radiators. The converted voltage is rectified using high-speed diodes and smoothed at the output filter.
The disadvantage of such devices is the inevitable presence of high-frequency interference at the output of the converter, despite the presence of special filters. In addition, pulsed devices use special output voltage stabilization circuits.
The switching power supply can be purchased as a separate unit, ready for installation in the device. You can also assemble this device yourself using widely available diagrams and instructions for assembling power supplies.
It should be taken into account that self-assembly may be more expensive than a purchased product purchased online in the Asian market. This may be due to the fact that electronic components are sold at a higher markup than the manufacturer's markup in China for the assembly of the product and its delivery. In any case, having understood the structure of such devices, it will be possible not only to assemble such a device yourself, but also, if necessary, to repair it. Such skills will be very useful.
If you want to save money, you can use switching power supplies from personal computers. Often, a faulty personal computer contains a working unit. They require minimal modification before use.
Such power supplies have idle protection. They must be under load at all times. Therefore, in order to avoid shutdown, a constant resistance is included in the load. Such modernized units are used primarily to power household power tools.
DIY photo of power supplies
Switching power supplies are often used by radio amateurs in homemade designs. With relatively small dimensions, they can provide high output power. With the use of a pulse circuit, it became possible to obtain output power from several hundred to several thousand watts. Moreover, the dimensions of the pulse transformer itself are no larger than a matchbox.
Switching power supplies - operating principle and features
The main feature of pulsed power supplies is their increased operating frequency, which is hundreds of times higher than the network frequency of 50 Hz. At high frequencies with a minimum number of turns in the windings, high voltage can be obtained. For example, to obtain 12 Volts of output voltage at a current of 1 Ampere (in the case of a mains transformer), you need to wind 5 turns of wire with a cross-section of approximately 0.6–0.7 mm.
If we talk about a pulse transformer, the master circuit of which operates at a frequency of 65 kHz, then to obtain 12 Volts with a current of 1A, it is enough to wind only 3 turns with a wire of 0.25–0.3 mm. That is why many electronics manufacturers use a switching power supply.
However, despite the fact that such units are much cheaper, more compact, have high power and light weight, they have electronic filling, and therefore are less reliable when compared with a network transformer. It is very simple to prove their unreliability - take any switching power supply without protection and short-circuit the output terminals. At best, the unit will fail, at worst, it will explode and no fuse will save the unit.
Practice shows that the fuse in a switching power supply burns out last, first of all the power switches and the master oscillator fly out, then all parts of the circuit one by one.
Switching power supplies have a number of protections both at the input and output, but they do not always save. In order to limit the current surge when starting the circuit, almost all SMPS with a power of more than 50 Watts use a thermistor, which is located at the input of the circuits.
Let's now look at the TOP 3 best switching power supply circuits that you can assemble with your own hands.
Simple DIY switching power supply
Let's look at how to make the simplest miniature switching power supply. Any novice radio amateur can create a device according to the presented scheme. It is not only compact, but also operates over a wide range of supply voltages.
A homemade switching power supply has a relatively low power, within 2 Watts, but it is literally indestructible and is not afraid of even long-term short circuits.
Circuit diagram of a simple switching power supply
The power supply is a low-power switching power supply of the self-oscillator type, assembled with just one transistor. The autogenerator is powered from the network through a current-limiting resistor R1 and a half-wave rectifier in the form of a diode VD1.
Transformer of a simple switching power supply
A pulse transformer has three windings, a collector or primary winding, a base winding and a secondary winding.
An important point is the winding of the transformer - both the printed circuit board and the diagram indicate the beginning of the windings, so there should be no problems. We borrowed the number of turns of the windings from a transformer for charging cell phones, since the circuit diagram is almost the same, the number of windings is the same.
First we wind the primary winding, which consists of 200 turns, the wire cross-section is from 0.08 to 0.1 mm. Then we put insulation and use the same wire to wind the base winding, which contains from 5 to 10 turns.
We wind the output winding on top, the number of turns depends on what voltage is needed. On average, it turns out to be about 1 Volt per turn.
Video about testing this power supply:
Do-it-yourself stabilized switching power supply on SG3525
Let's take a step-by-step look at how to make a stabilized power supply using the SG3525 chip. Let's immediately talk about the advantages of this scheme. The first and most important thing is stabilization of the output voltage. There is also a soft start, short circuit protection and self-recording.
First, let's look at the device diagram.
Beginners will immediately pay attention to 2 transformers. In the circuit, one of them is power, and the second is for galvanic isolation.
Don't think that this will make the scheme more complicated. On the contrary, everything becomes simpler, safer and cheaper. For example, if you install a driver at the output of a microcircuit, then it needs a harness.
Let's look further. This circuit implements microstart and self-powering.
This is a very productive solution, it eliminates the need for a standby power supply. Indeed, making a power supply for a power supply is not a very good idea, but this solution is simply ideal.
Everything works as follows: the capacitor is charged from a constant voltage and when its voltage exceeds a given level, this block opens and discharges the capacitor to the circuit.
Its energy is quite enough to start the microcircuit, and as soon as it starts, the voltage from the secondary winding begins to power the microcircuit itself. You also need to add this output resistor to the microstart; it serves as a load.
Without this resistor the unit will not start. This resistor is different for each voltage and must be calculated based on considerations such that at the rated output voltage, 1 W of power is dissipated on it.
We calculate the resistance of the resistor:
R = U squared/P
R = 24 squared/1
R = 576/1 = 560 Ohm.
There is also a soft start on the diagram. It is implemented using this capacitor.
And current protection, which in the event of a short circuit will begin to reduce the PWM width.
The frequency of this power supply is changed using this resistor and connector.
Now let's talk about the most important thing - stabilizing the output voltage. These elements are responsible for it:
As you can see, 2 zener diodes are installed here. With their help you can get any output voltage.
Calculation of voltage stabilization:
U out = 2 + U stab1 + U stab2
U out = 2 + 11 + 11 = 24V
Possible error +- 0.5 V.
For stabilization to work correctly, you need a voltage reserve in the transformer, otherwise, when the input voltage decreases, the microcircuit simply will not be able to produce the required voltage. Therefore, when calculating a transformer, you should click on this button and the program will automatically add voltage to you on the secondary winding for reserve.
Now we can move on to looking at the printed circuit board. As you can see, everything here is quite compact. We also see a place for the transformer, it is toroidal. Without any problems, it can be replaced with an W-shaped one.
The optocoupler and zener diodes are located near the microcircuit, and not at the output.
Well, there was nowhere to put them on the way out. If you don't like it, make your own PCB layout.
You may ask, why not increase the fee and make everything normal? The answer is as follows: this was done so that it would be cheaper to order the board in production, since boards larger than 100 square meters. mm are much more expensive.
Well, now it’s time to assemble the circuit. Everything is standard here. We solder without any problems. We wind the transformer and install it.
Check the output voltage. If it is present, then you can already connect it to the network.
First, let's check the output voltage. As you can see, the unit is designed for a voltage of 24V, but it turned out a little less due to the spread of the zener diodes.
This error is not critical.
Now let's check the most important thing - stabilization. To do this, take a 24V lamp with a power of 100W and connect it to the load.
As you can see, the voltage did not sag and the block withstood without problems. You can load it even more.
Video about this switching power supply:
We reviewed the TOP 3 best switching power supply circuits. Based on them, you can assemble a simple power supply, devices on TL494 and SG3525. Step-by-step photos and videos will help you understand all installation issues.