Power supply 12V with your own hands. Homemade power supply: circuit

It's not difficult to make a 12V power supply with your own hands, but for this you need to learn a bit of theory. In particular, from which nodes the block is composed, for which each element of the product is responsible, the basic parameters of each. It is also important to know which transformers to use. If there is no suitable one, then it is possible to rewind the secondary winding independently to obtain the desired output voltage. It is not out of place to learn about the methods of etching printed circuit boards, as well as about the manufacture of the power supply enclosure.

Power Supply Components

The main element of any power supply is a step-down transformer. With its help, the voltage in the network (220 V) is reduced to 12 V. In the constructions considered below, it is possible to use both self-made transformers with rewound secondary winding and finished products without modernization. It is only necessary to take into account all the features and conduct a correct calculation of the wire cross-section and the number of turns.

The second element in importance is the rectifier. It is made of one, two or four semiconductor diodes. It all depends on the type of circuit on which the homemade power supply is assembled. For example, to realize the doubling of the voltage, two semiconductors should be used. For rectification without magnification, one is enough, but it is better to use a bridge circuit (all current ripples are smoothed out). After the rectifier, there must be an electrolytic capacitor. It is desirable to install a zener diode with suitable parameters, it allows the output to make a stable voltage.

What is a transformer

Transformers used for rectifiers have the following components:

1. A core (a magnetic core made of metal or a ferromagnet).
2. Networking (primary). It is powered by 220 volts.
3. Secondary winding (lowering). It is used to connect a rectifier.

Now about all the elements in more detail. The core can have any shape, but the most common are W-shaped and U-shaped. Less common are toroidal, but they have a different nature, more often used in inverters (voltage converters, for example, from 12 to 220 volts) than in conventional rectifying devices. The 12V 2A power supply is more suitable for use with a transformer having an U-shaped or U-shaped core.

Windings can be arranged as one on the other (first primary, and after secondary), on one frame, and on two coils. An example is a U-shaped transformer with two coils. On each of them, half of the primary and secondary windings are wound. When connecting a transformer, you need to connect the pins in series.

How to calculate the transformer

Suppose you decide to wind the secondary winding of the transformer yourself. To do this, you will need to know the value of the main parameter - the voltage, which can be removed from one turn. This is the easiest way to use it when making a transformer. It is much more difficult to calculate all the parameters if you want to wind not only the secondary but also the primary winding. It is necessary for this purpose to know the cross section of the magnetic circuit, its permeability and properties. If you calculate the power supply 12V 5A yourself, then this option is more accurate than adjusting to the ready parameters.

The primary winding is more difficult to wind than the secondary winding, since it can have several thousand turns of a thin wire. You can simplify the task and make a self-made power supply unit with a special machine.

To calculate the secondary winding, you need to wind 10 turns of the wire that you plan to use. Assemble the transformer and, observing the safety precautions, connect its primary winding to the mains. Measure voltage on the terminals of the secondary winding, divide the obtained value by 10. Now divide the number 12 by the obtained value. And get the number of turns needed to generate 12 volts. You can add a little to compensate for the voltage drop (enough to increase by 10%).

Power supply diodes

The choice of the semiconductor diodes used in the rectifier of the power supply unit depends directly on what values of the transformer parameters need to be obtained. The higher the current on the secondary winding, the more powerful the diodes should be used. Preference is given to those parts that are made on the basis of silicon. But do not take high-frequency, as they are not intended for use in rectifier devices. Their main purpose is to detect a high-frequency signal in radio receiving and transmitting devices.

The ideal solution for low-power power supplies is the use of diode assemblies, the 12V 5A power supply can be used to place them in a much smaller enclosure. Diode assemblies are a set of four semiconductor diodes. They are used exclusively for rectification of alternating current. Work with them is much more convenient, you do not need to make many connections, enough to put two voltages from the secondary winding of the transformer, and remove the remaining from the remaining one.

Stabilization of voltage

After making the transformer, be sure to measure the voltage at the terminals of its secondary winding. If it exceeds the value of 12 volts, then it is necessary to stabilize. Even the simplest 12V power supply will work badly without it. It should be noted that the supply voltage in the supply network is not constant. Connect the voltmeter to the outlet and measure at different times. For example, in the daytime it can jump up to 240 Volts, and in the evening it can drop to 180. Everything depends on the load on the power line.

If the voltage in the primary winding of the transformer changes, it will be unstable in the secondary. To compensate for this, you need to apply devices called voltage regulators. In our case it is possible to use zener diodes with a suitable value of the parameters (current and voltage). Zener sets, select the necessary elements before you make a 12V power supply.

There are also more "advanced" elements (such as KR142EN12), which are a set of several zener diodes and passive elements. Their characteristics are much better. Also there are foreign analogues of similar devices. It is necessary to get acquainted with these elements before 12V power supply you decide on your own.

Features of switching power supplies

Power supplies of this type are widely used in personal computers. They have two voltage values at the output: 12 volts - to power the drive drives, 5 volts - for the operation of microprocessors and other devices. The difference from simple power supplies is that the output signal is not constant, and the pulse signal is similar in shape to the rectangles. In the first period of time, the signal appears, in the second it is zero.

There are also differences in the device layout. For normal operation, a homemade switching power supply requires straightening the mains voltage without first reducing its value (there is no transformer at the input). Use pulse power supplies can be both stand-alone devices, and their upgraded analogs - rechargeable batteries. As a result, you can get the simplest uninterruptible power, and its power will depend on the parameters of the power supply unit and the type of batteries used.

How to get uninterrupted power?

The power supply should be connected in parallel to the battery so that when the power is turned off, all devices continue to operate in normal mode. When the network is connected, the power supply unit charges the battery, the principle is similar to the work of the electric power supply of the car. And when the uninterruptible power supply 12V is disconnected from the mains, voltage is applied to all equipment from the battery.

But there are cases when it is necessary to get the output voltage of 220 volts, for example, for powering personal computers. In this case, it is necessary to introduce a device into the inverter circuit, which converts a DC voltage of 12 volts into an AC 220. The circuit proves to be more complicated than a simple power supply, but it can be assembled.

Filtering and clipping of the variable component

An important place in rectifying technology is occupied by filters. Look at the 12V power supply, the circuit of which is most common. It consists of a diode bridge, a capacitor, and a resistance. The filters cut off any excess harmonics, leaving a constant voltage at the output of the power supply. For example, the simplest filter is an electrolytic capacitor with a large capacitance. If you look at its work under constant and variable stresses, then its principle of functioning becomes clear.

In the first case, it has a certain resistance and in the replacement circuit it can be replaced by a constant resistor. This is actual for carrying out calculations based on Kirchhoff's theorems.

In the second case (when an alternating current flows), the capacitor becomes a conductor. In other words, it can be replaced by a jumper that does not have resistance. It will connect both outputs. With a more detailed study, you can see that the variable component will go away, because the outputs are closed during the current flow. There will be only a constant voltage. In addition, for the rapid discharge of capacitors, the 12V power supply to be assembled by the hands must be equipped with a resistor with a high resistance (3-5 MOhm) at the output.

Making the case

For the manufacture of the power supply housing, aluminum corners and plates are ideal. First you need to make a kind of skeleton structure, which can then be sewn with aluminum sheets of a suitable shape. To reduce the weight of the power supply, you can use a thinner metal as the skin. To make a power supply 12V with your own hands from such improvised materials is not difficult.

Ideally fit the body from the microwave. First, the metal is thin and light enough. Secondly, if you do everything neatly, then the paintwork will not be damaged, so the appearance will remain attractive. Thirdly, the size of the skin of the microwave oven is quite large, which makes it possible to make almost any case.

PCB Manufacturing

Prepare the foil-shaped textolite, for this process the metal layer with a solution of hydrochloric acid. If there is no such, then it is possible to use electrolyte, which is poured into car batteries. This procedure will degrease the surface. Work in rubber gloves to avoid getting solutions on the skin, because you can get a severe burn. After this, rinse with water with the addition of soda (soap can be used to neutralize the acid). And you can print a printed circuit board.

You can make a drawing either with the help of a special program for computers, or manually. If you are manufacturing a conventional 12V 2A power supply, not a power supply, the number of elements is minimal. Then, when drawing a drawing, you can do without modeling software, just apply it to the surface of the foil with a permanent marker. It is advisable to make two or three layers, letting the previous dry. Not bad results can give the application of varnish (for example, for nails). True, the drawing may come out uneven because of the brush.

How to etch the board

Prepared and dried board put in a solution of ferric chloride. Its saturation should be such that copper is consumed as quickly as possible. If the process is slow, it is recommended to increase the concentration of ferric chloride in water. If this does not help, try to heat the solution. To do this, put water in the container, install a jar of solution in it (do not forget that it is desirable to store it in a plastic or glass container) and heat it over low heat. Warm water will heat the ferric chloride solution.

If you have a lot of time or there is no ferric chloride, then use a mixture of salt and copper sulfate. The board is prepared in a similar way, after which it is placed in the solution. The disadvantage of the method is that the power supply board is etched very slowly, it will take almost a day for the complete disappearance of all copper from the textolite surface. But for lack of the best, you can use this option.

Assembly of components

After the etching procedure, you will need to rinse the board, clean the protective layer of the track, and degrease them. Mark the location of all the elements, drill the holes for them. More 1.2mm drill bit is not worth using. Install all the elements and solder them to the tracks. After this, it is necessary to cover all the tracks with a layer of tin, i.e., to make them tin. The manufactured power supply 12V with your own hands with the tinning of the mounting tracks will last you much longer.