Power supply (12 volts) with your hands. Power supply circuit for 12 volts

The 12-volt power supply will allow powering almost any home appliances, including even a laptop. Note that the input voltage of the notebook is 19 Volts. But it will work fine if we carry out the washing from 12. True, the maximum current is 10 Amps. Only to such a value consumption is very rare, the average holds at a level of 2-4 Amperes. The only thing that should be taken into account is that when you replace the standard power source with a self-made one, you will not be able to use the built-in battery. But all the same, 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 - from the used wire in the secondary winding of the transformer. About how to choose it, will be told a little lower. For yourself, you must decide in advance for what purposes you plan to use a 12-volt power supply. If you need to power low-power equipment - navigators, LEDs, and so on, then quite enough at the output of 2-3 Amps. And then this will be a lot.

But if you plan to use it to carry out more serious actions - for example, to charge the car's battery pack , then it will take 6-8 amperes at the output. The charging current must be ten times less than the capacity of the battery - this requirement is necessarily taken into account. If there is a need to connect devices whose supply voltage is significantly different from 12 volts, then it is more reasonable to set the adjustment.

How to choose a transformer

The first element is a voltage converter. The transformer facilitates the conversion of an alternating voltage of 220 volts into the same in amplitude, only with a value much less. At least you need less value. For powerful power supplies, a transformer of the TS-270 type can be used as a basis. It has high power, even there are 4 windings, which give out 6.3 volts each. They were used to power the radiolamp. Without much difficulty from it you can make a power supply 12 Volt 12 Ampere, which can even charge the car battery.

But if you are not completely satisfied with its windings, then you can remove all the secondary ones, leaving 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 gives 6.3 Volts. Now just divide 6.3 by the number of turns. And you get the voltage value, which can be removed from one turn of the wire. It remains only to calculate how much to wind the turns to get 12.5-13 volts output. It will be even better if the output is 1-2 volts voltage higher than required.

Manufacture of rectifier

What is a rectifier and what is it for? This device is based on semiconductor diodes, which is a converter. With its help, the alternating current becomes permanent. To analyze the operation of the rectifier cascade, the oscilloscope is better used. If you see a sinusoid in front of the diodes, then after them there will be a practically even line. But small pieces of the sinusoid will still remain. Get rid of them afterwards.

The choice of diodes should be taken with maximum seriousness. If a 12 volt power supply is used as a battery charger, then items with a reverse current of up to 10 amperes are required. If they intend to supply power to low-current consumers, then it will be sufficient to build the bridge assembly. Here it is worth dwelling. Preference is given to the rectifier circuit, assembled by the type of bridge - from four diodes. If applied to a single semiconductor (half-wave circuit), then the efficiency of the power supply unit is reduced by almost half.

Filter unit

Now, when the output has a constant voltage, it is necessary that the circuit of the 12 V power supply unit be slightly improved. For this purpose, you need to use filters. It is enough to use the LC-chain to power household appliances. It is worth discussing it in more detail. To the positive output of the rectifier cascade is connected inductance - throttle. The 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 throttle, an electrolytic capacitor is connected to the plus. The second output is connected to the common wire (minus). The essence of the work of the electrolytic capacitor is that it allows you to get rid of the whole variable component of the current. Remember, at the output of the rectifier there were small pieces of a sinusoid? That's it, it's necessary to get rid of it, otherwise the 12 V 12 amp power supply will interfere with the device connected to it. For example, a radio or radio receiver will emit a strong buzz.

Stabilization of output voltage

To implement the stabilization of the output voltage, one can use only one semiconductor element. It can be like a zener diode with a working voltage of 12 volts, and more modern and perfect assemblies such as LM317, LM7812. The latter are designed to stabilize the voltage at the level of 12 volts. Therefore, even if the output of the rectifier cascade is 15 volts, after stabilization there will be only 12. Everything else goes into heat. And this means that it is extremely important to install a stabilizer on the radiator.

Voltage regulation 0-12 Volts

For greater versatility of the device it is worth using an uncomplicated circuit that can be built in a few minutes. This can be implemented using the previously mentioned assembly LM317. Only the difference from the switching circuit in the stabilization mode will be small. In the wire break, which goes to minus, a variable resistor of 5 kΩ is switched on. Between the output of the assembly and the variable resistor, a resistance of about 220 Ohm is included. And between the input and output of the stabilizer, reverse-voltage protection is a semiconductor diode. Thus, the 12-volt power supply unit, assembled by its own hands, turns into a multifunctional device. Now it remains only to assemble it and scale the scale. And it is possible and at all to put an electronic voltmeter on the output and look at the current voltage value.