Making a 12V power supply with your own hands is not difficult, but for this you need to learn a little theory. In particular, which nodes the block consists of, for which each element of the product is responsible, the main parameters of each. It is also important to know which transformers to use. If there is no suitable one, then you can rewind the secondary winding yourself to obtain the desired output voltage. It will be useful to learn about the etching methods of printed circuit boards, as well as about the manufacture of the power supply housing.
Power Supply Components
The main element of any power supply is a step-down transformer. With its help, the voltage in the network (220 Volts) decreases to 12 V. In the designs discussed below, you can use both home-made transformers with rewound secondary winding and finished products, without modernization. It is only necessary to take into account all the features and conduct the 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 that the home-made power supply is going to. For example, to implement voltage doubling , two semiconductors must be used. For straightening without magnification, one is enough, but it is better to use a bridge circuit (all current ripples are smoothed). An electrolytic capacitor is required after the rectifier. It is desirable to install a zener diode with suitable parameters, it allows you to make a stable voltage at the output.
What is a transformer?
The transformers used for rectifiers have the following components:
- Core (magnetic core made of metal or a ferromagnet).
- Network winding (primary). It is powered by 220 volts.
- Secondary winding (step-down). Used to connect the rectifier.
Now about all the elements in more detail. The core can be of any shape, but the most common are U-shaped and U-shaped. Toroidal are less common, but their specificity is different, they are more often used in inverters (voltage converters, for example, from 12 to 220 Volts) than in conventional rectifier devices. The power supply unit 12V 2A is more expedient to do using a transformer having a W-shaped or U-shaped core.
The windings can be located both on top of each other (first primary, and then secondary), on one frame, and on two coils. An example is a transformer with a U-shaped core, on which there are two coils. Each of them produced half of the primary and secondary windings. When connecting a transformer, it is required to connect the terminals 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 find out the value of the main parameter - the voltage, which can be removed from one turn. This is the easiest way that you can use in the manufacture of the transformer. It is much more difficult to calculate all the parameters if you need to win not only the secondary, but also the primary winding. It is necessary for this to know the cross section of the magnetic circuit, its permeability and properties. If you calculate the 12V 5A power supply yourself, then this option is more accurate than adapting to the ready-made parameters.
It is more difficult to wind the primary winding than the secondary, since it can contain several thousand turns of thin wire. You can simplify the task and make a home-made power supply unit using a special machine.
To calculate the secondary winding, you need to wind 10 turns with the wire that you plan to use. Assemble the transformer and, observing safety precautions, connect its primary winding to the network. Measure the voltage at the terminals of the secondary winding, divide the resulting value by 10. Now, divide the number 12 by the obtained value. And you get the number of turns necessary to generate 12 volts. You can add a little to compensate for the voltage drop (enough to increase by 10%).
Diodes for power supply
The choice of semiconductor diodes used in the rectifier of the power supply directly depends on what values ββof the parameters of the transformer must be obtained. The greater the current strength on the secondary winding, the more powerful the diodes must be used. Preference should be given to those parts that are made on the basis of silicon. But do not take high-frequency ones, as they are not intended for use in rectifier devices. Their main purpose is the detection of a high-frequency signal in radio receivers and transmitting devices.
The ideal solution for low-power power supplies is the use of diode assemblies, the 12V 5A power supply with their help can be placed in a much smaller case. Diode arrays are a collection of four semiconductor diodes. They are used exclusively for AC rectification. It is much more convenient to work with them, you do not need to make many connections, it is enough to apply voltage from the secondary winding of the transformer to two conclusions, and remove the constant from the remaining ones.
Voltage stabilization
After manufacturing the transformer, be sure to measure the voltage at the terminals of its secondary winding. If it exceeds the value of 12 volts, it is necessary to carry out stabilization. Even the simplest 12V power supply will not work well without this. It should be noted that in the mains voltage is not constant. Connect the voltmeter to a power outlet and take measurements at different times. So, for example, during the day it can jump up to 240 volts, and in the evening it can even drop to 180 volts. It all depends on the load on the power line.
If the voltage changes in the primary winding of the transformer, then it will be unstable in the secondary as well. To compensate for this, devices called voltage stabilizers must be used. In our case, you can use zener diodes with a suitable value of the parameters (current and voltage). A lot of zener diodes, select the necessary elements before making a 12V power supply.
There are more βadvancedβ elements (type 14212), which are a set of several zener diodes and passive elements. Their characteristics are much better. There are also foreign analogues of such devices. You need to become familiar with these elements before making 12V power supply you decide for yourself.
Features of switching power supplies
Power supplies of this type are widely used in personal computers. They have two voltage values ββat the output: 12 Volts - for powering the drives of drives, 5 Volts - for the functioning of microprocessors and other devices. The difference from simple power supplies is that the output signal is not constant, but pulsed - in shape it looks like rectangles. In the first period of time, the signal appears, in the second it is zero.
There are also differences in the scheme of the device. For normal operation, a self-made switching power supply unit needs to rectify the mains voltage without first lowering its value (there is no transformer at the input). You can use switching power supplies as independent devices, as well as their upgraded analogues - rechargeable batteries. As a result, you can get the simplest uninterruptible, and its power will depend on the parameters of the power supply and the type of batteries used.
How to get uninterrupted power?
It is enough to connect the power supply in parallel with 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 operation of the carβs power supply. And when you disconnect the uninterrupted power supply unit 12V from a network, there is a supply of voltage to all equipment from the battery.
But there are cases when it is necessary to obtain a network voltage of 220 volts at the output, for example, to power personal computers. In this case, it will be necessary to introduce an inverter into the circuit - a device that converts a DC voltage of 12 Volts to AC 220. The circuit is more complicated than a simple power supply, but it can be assembled.
Filtering and clipping a variable component
Filters occupy an important place in rectifier technology. Take a look at the 12V power supply, the circuit of which is the most common. It consists of a diode bridge, capacitor, resistance. Filters cut off all unnecessary harmonics, leaving a constant voltage at the output of the power supply. For example, the simplest filter is an electrolytic capacitor with a large capacity. If you look at his work at constant and alternating voltages, then his principle of functioning becomes clear.
In the first case, it has a certain resistance and in the equivalent circuit it can be replaced by a constant resistor. This is relevant for calculations according to Kirchhoff's theorems.
In the second case (when AC flows), the capacitor becomes a conductor. In other words, it can be replaced with a jumper that has no resistance. She 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 flow of current. Only constant voltage will remain. In addition, for a quick discharge of capacitors, the assembled 12V power supply unit with its own hands must be equipped with a resistor with high resistance (3-5 MΞ©) at the output.
Body manufacture
For the manufacture of the power supply housing, aluminum corners and plates are ideal. First you need to make a kind of skeleton of the structure, which can subsequently be sheathed with sheets of aluminum of a suitable shape. To reduce the weight of the power supply, thinner metal can be used as casing. To make a 12V power supply unit yourself from such improvised materials is not difficult.
A microwave enclosure is ideal. Firstly, the metal is quite thin and light. Secondly, if you do everything carefully, the paintwork will not be damaged, so the appearance will remain attractive. Thirdly, the size of the casing of the microwave oven is quite large, which allows you to make almost any body.
PCB manufacturing
Prepare foil textolite, for this, treat the metal layer with a solution of hydrochloric acid. If not, then you can use the electrolyte, poured into the batteries of cars. This procedure will degrease the surface. Work in rubber gloves to prevent solutions from getting on your skin, because you can get a severe burn. Then rinse with water and soda (soap can be used to neutralize acid). And you can apply a picture of the printed circuit board.
You can make a drawing using a special program for computers, as well as manually. If you are manufacturing a conventional 12V 2A power supply rather than a switching power supply, then the number of elements is minimal. Then, when applying the drawing, you can do without modeling programs, it is enough to apply it on the surface of the foil with a permanent marker. It is advisable to make two or three layers, allowing the previous one to dry. Good results can give the use of varnish (for example, for nails). True, the picture may come out uneven due to the brush.
How to etch a board
Place the prepared and dried circuit board in a solution of ferric chloride. Its saturation should be such that copper corrodes 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, then try to heat the solution. To do this, collect water in a container, place a jar of solution in it (do not forget that it is advisable to store it in plastic or glass containers) and heat over low heat. Warm water will heat the solution of ferric chloride.
If you have a lot of time or do not have 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 this method is that the power supply board is etched very slowly; it will take almost a day for all copper to completely disappear from the surface of the PCB. But for want of a better one, you can use this option.
Component Installation
After the etching procedure, you will need to rinse the board, clean the protective layer of the track, degrease them. Mark the location of all elements, drill holes for them. More than 1.2 mm drill should not be used. 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., tin them. A self-made 12V power supply with tinning of mounting tracks will last you much longer.