Voltage Adjustable Power Supply: Specifications

Novice hams often make voltage -controlled power supplies . This is a very necessary device, since without it the equipment will not be able to work. But you need to take into account that for the operation of the equipment, different voltages may be required - from 1.5 to 30 V. And I do not want to make a new power supply each time, to wind transformers. It is much easier to make one, but universal, which can be used in any homemade product.

PC power supply

In the event that you have a desktop power supply, you can use it. To do this, perform the following manipulations:

1. Remove the top cover.
2. Next, using a soldering iron, remove all excess wires. It is necessary to leave 1-2 wires of each color.
3. Connect the green wire (it’s the only one in the bundle) to the black (body). You can simply install a jumper on the board.
4. To make a power supply unit with voltage regulation with your own hands, it is necessary to measure at each terminal.
5. Connect the wires to the appropriate sockets or to the switch.

Such a power supply allows you to get several voltages - 3, 3V, 5V, 12V. This is quite enough for the full operation of most devices. Even for charging mobile phones, you can use such a unit.

The easiest way

The easiest way is to make a power supply with stepwise regulation of the output voltage. Surely you have seen these more than once. They have a switch to several positions, each of which corresponds to a certain voltage value. Is it reliable? As a laboratory power supply with voltage regulation, such a device may not work for long.

The reason is a very small current at the output, and it is unlikely to connect a powerful load. Even a running meter of an LED strip will glow with low brightness. In order not to use large toggle switches or switches in homemade products, you can install several sockets on the front panel of the device. Plugs will be inserted into them. The main thing is to correctly sign all the sockets so as not to burn the equipment.

How to make a transformer

To create such a unit, you will need to make a transformer yourself - rewind the secondary winding. And be sure to calculate the voltage per revolution. To do this, proceed as follows:

1. Completely remove the secondary winding, if any.
2. Winding 10 turns of wire and assemble the magnetic core of the transformer.
3. Connect the transformer to the mains and measure the voltage on the secondary winding.

For example, you found that you can remove 1 V. from 10 turns. Therefore, you need to wind exactly 300 turns for a 30 V output voltage. But what if you need multiple voltages? To do this, make bends from the corresponding turns.

Rectifier

A rectifier is a part of a power supply unit that allows you to convert alternating voltage into direct voltage. It is made of semiconductor diodes. There are several types of switching schemes:

1. Half wave - only one semiconductor is used. Very low efficiency. The circuit can be used to power the equipment for a short time. In addition, structures of this type have a high level of interference.
2. Half-wave - two diodes are used. Efficiency is slightly higher than the previous one, but far from ideal.
3. Doubling voltage - consists of capacitors and diodes. It allows you to increase the voltage, but the current decreases.
4. Bridge - contains four semiconductors. The efficiency of the circuit is very high, so it is used in almost all devices.

It should be noted that there are various bridge assemblies. No need to check the circuit and connect the diodes - just apply alternating voltage to the device, and remove the direct voltage from it.

Filter and stabilization unit

This is exactly what can be called the part of the circuit in which electrolytic capacitors, resistors and chokes are installed. The latter allows you to get rid of the possible appearance of high frequency currents. The capacitor is necessary in order to remove the DC component in direct current. If you are manufacturing a laboratory power supply with voltage and current adjustment, you need to make sure that all parameters are stable at the output. How to do it?

Zener diodes are used for this - these are devices that equalize the voltage value. Moreover, there are semiconductor and vacuum devices. In any case, when the voltage is exceeded, its excess is converted into heat. Therefore, it is necessary to ensure good cooling of the device. You can even install a fan for cooling. In order for the capacitor to discharge faster after shutdown, a constant resistor is installed at the output.

Voltage regulation unit

You can make such a device on transistors or special assemblies. Very often in amateur radio practice products like LM317T are used. In order to make a device based on it, you need to have the following details:

1. Direct assembly of the LM317T.
2. Diode bridge (or 4 identical diodes).
3. Two electrolytic capacitors - 1000 and 100 microfarads. Voltage not less than 50 V.
4. Constant impedance 200 ohms.
5. 6.8 kΩ variable resistor.

A variable resistor is used to adjust the output voltage. If you have digital devices - a voltmeter and an ammeter, then you can install them at the output of the power supply. Note that the latter is included in the wire break (for example, positive). A voltmeter is connected with plus and minus. After the final assembly, you can not do graduation on the front panel.

The transformer for the design can be borrowed from any household appliances. It is desirable that he have sufficient power. Good results are shown by a TVK or TVZ transformer (output frame scan and sound of tube TVs, respectively). The primary winding is designed for connection to a 220 V household network. It is quite possible that the secondary will have to be rewound. It is advisable to use a wire with a maximum cross section. This will allow you to give out more current, as a result - you can connect any equipment without any problems.