220 variable to 12 constant. How to get DC voltage from AC. Dual channel motor controller

Today we will try to figure out what the voltage of 12 volts is. Who is this monster? How hard does it bite? And in general, what is he capable of? Believe me, the fact that he is weaker than an ordinary monster with a voltage of 220 volts is a fairy tale. Interesting, let's go then.

Let's start with the history of occurrence. And the story is simple, the whole point is safety. After all, everything that is invented is done for two reasons. The first is laziness, as you know, it is the engine of progress. The second is the desire to protect ourselves, because we are often afraid of something. This is where the need for innovation comes in. After all, we are constantly frightened by the fact that you can’t stick your fingers into the socket - it will kill you. Although, if we stick our fingers into the socket, it is unlikely that something more terrible will happen to us than a slight shock. But many of us have children and pets at home. Children are curious people. Everything is always interesting to them, and a child is not a child if he crawled past the outlet. He must stick his fingers in there. But if he is shocked, then nothing good will definitely happen. It is clear that everything depends on the specific case, but it is better not to experiment. What if an animal gets into the socket? And it's good if your cat only burns his mustache and sits in shock under the bed for a couple of minutes. But things can get worse.

So, enough of the horror to catch up. 12 volts is a safe voltage that can solve a lot of problems at once. But unfortunately this voltage is not common in sockets, since electrical appliances are simply not made for it.

Let's go back to the origins. There are many rooms that are dangerous for electricity or have elevated level danger. Such rooms in your apartment include - kitchen, bathroom and other similar spaces. Imagine what kind of short circuit a 220 volt electric monster can arrange? The consequences may go far beyond our imagination. And believe me, they may not be limited to triggered security systems. 12 volts will definitely not arrange a catastrophe on a planetary or even apartment scale. In the worst case, the security systems will work or the transformer will burn out.

Now about where the 12 volt voltage came from. Such a voltage is in most cases used for lighting, and from there it originates. A few decades ago, halogen lamps for domestic use were invented. What is a halogen lamp? This is the same incandescent light bulb, but has a longer lifespan and is much smaller. What makes this possible? Due to the fact that the bulb of such a lamp is filled with a gas containing a halogen, such as iodine. The filament in such an environment wears out much more slowly. So it turns out that such a lamp works twice as long, with a size of one-fourth of the usual one. But what about 12 volts? And besides. Someone conducted experiments and realized that at this voltage the filament is subject to much less destructive effects of electric current. And this means that it can be heated to a higher temperature and, therefore, get more light. Add to this almost absolute safety for wet rooms. It turns out a very cool way of wiring and lighting.

But do not rush, as with any free cheese, there are also mousetraps here. They are in a transformer. And since the voltage in the rest of the apartment is 220 volts, we will definitely need it, we can’t do without it. And an extra element in the power supply network, as you know, reduces its reliability. But the only thing that a transformer can be dangerous for is that it will simply burn out. Let's now move on to describing the network itself, how it is built and what is needed for this.

By itself, a network with a voltage of 12 volts begins with a transformer. It is he who converts the usual 220 volts to 12. But the transformer must be selected wisely. We will not go into particular devices of the transformer itself. I will say one thing, the transformer must be of suitable power. This means that for a start it is worth understanding how many lamps there will be, what is their total power. It is worth adding 40 percent of the margin to the obtained value, and you will get the desired transformer power. Otherwise, the transformer can fail very quickly, and this is not good.

After you have chosen a transformer, you should think about fixtures and lamps. There is nothing unusual in the lamps, many lamps are universal, but before buying, just in case, it is worth clarifying. But with lamps, things are a little more complicated. They are divided into lamps that operate on 220 volts, and those that operate on 12. And if 220-watt lamps from 12 volts simply do not work, flashes will begin in the reverse order. Overvoltage may cause the lamp to explode. Therefore, just check the markings, and everything, as they say, will be a bunch. Lamps rated at 12 volts are usually more expensive. Just because it is safer, there is no other constructive and cardinal difference in the design.

If he talks about the connecting link of the lamps and the transformer - the wire, then it can be anything. But a huge plus is that you can use small wires. Since with such a voltage of the network, overheating is almost impossible. There are special wires, they are sold in stores, but any small wire will do. Now you know everything.

Conclusion: Low-voltage lighting is a huge plus for domestic use, and for some industrial facilities. You understand that safety is paramount. It is also a huge and undoubted advantage that you can make such wiring yourself in your bathroom or kitchen. Agree, the article does not describe more than one complex process. Even a child can cope with many of these processes, but it is better not to entrust them with this.

Let's first clarify what we mean by "constant voltage". As Wikipedia tells us, a constant voltage (it is also a constant current) is such a current, the parameters, properties and direction of which do not change with time. Direct current flows in only one direction and for it the frequency is zero.

Oscillogram direct current we considered in the article Oscilloscope. Operating Basics :

As you remember, horizontally on the chart we have time(X-axis), and vertically voltage(Y axis).

In order to convert a single-phase alternating voltage of one value into a single-phase alternating voltage of a smaller (possibly larger) value, we use a simple single-phase transformer. And in order to convert into a constant pulsating voltage, after the transformer, we connected the Diode bridge. The output received a constant pulsating voltage. But with such tension, as they say, you can't change the weather.

But what about us from a pulsating constant voltage

get the most real constant voltage?

To do this, we need only one radio component: capacitor. And this is how it should be connected to the diode bridge:

This circuit uses an important property of a capacitor: to charge and discharge. A capacitor with a small capacitance charges quickly and discharges quickly. Therefore, in order to get an almost straight line on the waveform, we must insert a decent capacitor.

The dependence of ripple on the capacitance of the capacitor

Let's consider in practice why we need to install a large capacitor. In the photo below we have three capacitors of different capacities:

Let's consider the first one. We measure its face value using our LC - meter. Its capacitance is 25.5 nanofarads or 0.025 microfarads.

We cling it to the diode bridge according to the scheme above

And we cling to the oscilloscope:

Let's look at the waveform:

As you can see, the pulsations still remain.

Well, let's take a larger capacitor.

We get 0.226 microfarads.

We cling to the diode bridge in the same way as the first capacitor, we take readings from it.

And here is the oscillogram

Not…almost, but still not the same. The ripples are still visible.

We take our third capacitor. Its capacitance is 330 microfarads. Even my LC meter will not be able to measure it, since I have a limit on it of 200 microfarads.

We hook it to the diode bridge and take an oscillogram from it.

And here she is

Here you go. It's quite another matter!

So, let's make some conclusions:

- the larger the capacitance of the capacitor at the output of the circuit, the better. But do not abuse the capacity! Since in this case our device will be very large, because capacitors of large capacities are usually very large. And the initial charge current will be huge, which can lead to an overload of the supply circuit.

- the lower the load at the output of such a power supply, the greater the ripple amplitude will be. They fight this with the help of, and also use integrated voltage regulators, which give out the purest constant voltage.

How to choose radio elements for a rectifier

Let's return to our question at the beginning of the article. How to get a direct current of 12 volts at the output for your needs? First you need to choose a transformer so that it gives out ... 12 volts at the output? But they didn't guess! From the secondary winding of the transformer, we will receive.

where

U D - operating voltage, V

U max - maximum voltage, V

Therefore, in order to get 12 volts of direct voltage, the output of the transformer must be 12/1.41=8.5 volts of alternating voltage. Now here is the order. In order to obtain such a voltage on the transformer, we must add or decrease the windings of the transformer. Formula. Then we select diodes. We select diodes based on the maximum current strength in the circuit. We are looking for suitable diodes according to datasheets ( technical descriptions to radio elements). We insert a capacitor with a decent capacity. We select it based on the fact that the constant voltage on it does not exceed that which is written on its marking. The simplest constant voltage source is ready to use!

By the way, I got a 17 volt DC voltage source, since the transformer has 12 volts at the output (multiply 12 by 1.41).

And finally, to better remember:

Electricity- this is a directed or ordered movement of charged particles: electrons in metals, ions in electrolytes, and electrons and ions in gases. Electric current can be both direct and variable.

Definition of direct electric current, its sources

D.C(DC, in English Direct Current) is an electric current whose properties and direction do not change over time. Direct current and voltage are indicated in the form of a short horizontal dash or two parallel ones, one of which is dashed.

DC is used in cars and at home, in numerous electronic devices: laptops, computers, TVs, etc. The measured electric current from the socket is converted into direct current using a power supply or a voltage transformer with a rectifier.

Any power tool, device or device powered by batteries is also a consumer of direct current, because a battery or battery is only a source of direct current, which, if necessary, is converted into alternating current using special converters (inverters).

How AC works

Alternating current(AC in English Alternating Current) is an electric current that changes in magnitude and direction over time. On electrical appliances, it is conventionally indicated by a segment of the sinusoid "~".
Sometimes, after the sinusoid, the characteristics of the alternating current can be indicated - frequency, voltage, number of phases.

Alternating current can be either single or three-phase, for which the instantaneous values of current and voltage change according to a harmonic law.

Main characteristics alternating current - the effective value of the voltage and frequency.

note, as in the left graph for a single-phase current, the direction and magnitude of the voltage change with a transition to zero over a period of time T, and in the second graph for a three-phase current, there is a shift of three sinusoids by one third of the period. On the right graph, phase 1 is indicated by the letter "a", and the second by the letter "b". It is well known that the home socket is 220 volts. But few people know that this is the effective value of the alternating voltage, but the amplitude or maximum value will be greater by the root of two, that is, it will be equal to 311 volts.

Thus, if for direct current the voltage magnitude and direction do not change over time, then for alternating current, the voltage is constantly changing in magnitude and direction (a graph below zero is the opposite direction).

And so we approached to the concept of frequency- this is the ratio of the number of complete cycles (periods) to the unit of time of a periodically changing electric current. Measured in hertz. In our country and in Europe, the frequency is 50 Hertz, in the USA it is 60 Hz.

What does the frequency of 50 Hertz mean? It means that we have an alternating current changing its direction to the opposite and back (segment T- on the graph) 50 times per second!

AC sources are all sockets in the house and everything that is connected directly by wires or cables to the electrical panel. Many people have a question: why is there no direct current in the outlet? The answer is simple. In AC networks, the voltage value is easily and with minimal losses converted to the required level using a transformer in any volume. The voltage must be increased in order to be able to transmit electricity over long distances with the least losses on an industrial scale.
From the power plant, where there are powerful electric generators, a voltage of 330,000-220,000 comes out, then near our house at a transformer substation it is converted from a value of 10,000 Volts to a three-phase voltage of 380 Volts, which comes into apartment house, and a single-phase voltage comes to our apartment, because between the voltage is 220 V, and between opposite phases in the electrical panel is 380 volts.

And one more important advantage of alternating voltage is that asynchronous AC motors are structurally simpler and work much more reliably than DC motors.

How to make alternating current direct

For consumers operating on direct current, alternating current is converted using rectifiers.

DC to AC converter

If there are no difficulties with converting alternating current to direct current, then with the reverse conversion everything is much more complicated. For this at home inverter is used- This is a generator of periodic voltage from a constant, in shape close to a sinusoid.

The voltage of 12 volts is used to power a large number of electrical appliances: receivers and radios, amplifiers, laptops, screwdrivers, LED strips, and more. Often they run on batteries or power supplies, but when one or the other fails, the question arises before the user: “How to get 12 volts AC”? We will talk about this further, providing an overview of the most rational ways.

We get 12 volts from 220

The most common task is to get 12 volts from a 220V household electrical network. This can be done in several ways:

Step down the voltage without a transformer.
Use a 50 Hz mains transformer.
Use a switching power supply, possibly paired with a switching or linear converter.

Step down voltage without transformer

You can convert the voltage from 220 Volts to 12 without a transformer in 3 ways:

Lower the voltage with a ballast capacitor. Universal way used to power low power electronics such as LED lamps and to charge small batteries such as flashlights. The disadvantage is the low cosine Phi of the circuit and low reliability, but this does not prevent it from being widely used in cheap electrical appliances.
Lower the voltage (limit the current) with a resistor. The method is not very good, but it has the right to exist, it is suitable to power some very weak load, such as an LED. Its main disadvantage is the release of a large amount of active power in the form of heat on the resistor.
Use an autotransformer or choke with similar winding logic.

quenching capacitor

Before proceeding with the consideration of this scheme, it is first worth saying about the conditions that you must comply with:

The power supply is not universal, so it is calculated and used only to work with one known device.
All external elements of the power supply, such as regulators, if you use additional components for the circuit, must be insulated, and plastic caps are put on the metal knobs of the potentiometers. Do not touch the power supply board and the output voltage wires unless a load is connected to them or if the circuit does not have a zener diode or regulator for low DC voltage.

However, such a scheme is unlikely to kill you, but the blow electric shock you can get.

The circuit is shown in the figure below:

R1 - needed to discharge the quenching capacitor, C1 - the main element that quenches the capacitor, R2 - limits the currents when the circuit is turned on, VD1 - diode bridge, VD2 - zener diode for the desired voltage, for 12 volts suitable: D814D, KS207V, 1N4742A. You can also use a linear converter.

Or an enhanced version of the first scheme:

The value of the quenching capacitor is calculated by the formula:

C (uF) \u003d 3200 * I (load) / √ (U input²-U output²)

C(µF) = 3200*I(load)/√Uinput

But you can also use calculators, they are available online or in the form of a PC program, for example, as an option from Vadim Goncharuk, you can search the Internet.

Capacitors should be like this - film:

Or like this:

It makes no sense to consider the rest of the listed methods, because. lowering the voltage from 220 to 12 volts with a resistor is not effective due to the large heat generation (the dimensions and power of the resistor will be appropriate), and winding the inductor with a tap from a certain turn to get 12 volts is impractical due to labor costs and dimensions.

Power supply on a network transformer

Classic and reliable circuit, ideal for powering audio amplifiers, such as speakers and radio tape recorders. Subject to the installation of a normal filter capacitor, which will provide the required level of ripple.

In addition, you can install a 12 volt stabilizer, such as KREN or L7812 or any other for the desired voltage. Without it, the output voltage will change according to power surges in the network and will be equal to:

Uout=Uin*Ktr

Ktr - transformation coefficient.

It is worth noting here that the output voltage after the diode bridge should be 2-3 volts more than the PSU output voltage - 12V, but not more than 30V, it is limited by the technical characteristics of the stabilizer, and the efficiency depends on the voltage difference between input and output.

The transformer must supply 12-15V AC. It is worth noting that the rectified and smoothed voltage will be 1.41 times the input voltage. It will be close to the amplitude value of the input sinusoid.

I also want to add an adjustable power supply circuit to the LM317. With it, you can get any voltage from 1.1 V to the value of the rectified voltage from the transformer.

12 volts from 24 volts or other increased direct voltage

To lower the DC voltage from 24 Volts to 12 Volts, you can use a linear or switching regulator. Such a need may arise if you need to power a 12 V load from the on-board network of a bus or truck with a voltage of 24 V. In addition, you will receive a stabilized voltage in the car's network, which often changes. Even in cars and motorcycles with an on-board network of 12 V, it reaches 14.7 V with the engine running. Therefore, this circuit can also be used to power LED strips and LEDs on vehicles.

The circuit with a linear stabilizer was mentioned in the previous paragraph.

You can connect a load with current up to 1-1.5A to it. To amplify the current, you can use a pass transistor, but the output voltage may drop slightly - by 0.5V.

Similarly, you can use LDO-stabilizers, these are the same linear voltage regulators, but with a low voltage drop, such as AMS-1117-12v.

Or pulse analogs like AMSR-7812Z, AMSR1-7812-NZ.

Connection diagrams are similar to L7812 and Krenkam. Also, these options are suitable for lowering the voltage from the power supply from the laptop.

It is more efficient to use pulse step-down voltage converters, for example, based on the LM2596 IC. The board has contact pads In (input +) and (- Out output), respectively. On sale you can find a version with a fixed output voltage and with an adjustable one, as in the photo above on the right side you see a blue multi-turn potentiometer.

12 volts from 5 volts or other reduced voltage

You can get 12V from 5V, for example, from a USB port or charger for mobile phone, can also be used with now popular lithium batteries with a voltage of 3.7-4.2V.

If we are talking about power supplies, you can also intervene in the internal circuit, edit the reference voltage source, but for this you need to have certain knowledge in electronics. But you can make it easier and get 12V using a boost converter, for example, based on the XL6009 IC. On sale there are options with a fixed output of 12V or regulated with adjustment in the range from 3.2 to 30V. Output current - 3A.

It is sold on a finished board, and there are marks on it with the purpose of the pins - input and output. Another option is to use the MT3608 LM2977, which boosts up to 24V and can withstand the output current up to 2A. Also in the photo, the signatures for the contact pads are clearly visible.

How to get 12V from improvised means

The easiest way to get a voltage of 12V is to connect 8 1.5V AA batteries in series.

Or use a ready-made 12V battery marked 23AE or 27A, these are used in remote controls. Inside it is a selection of small "pills" that you see in the photo.

We considered a set of options for getting 12V at home. Each of them has its pros and cons, varying degrees of efficiency, reliability and efficiency. Which option is better to use, you must choose on your own based on your capabilities and needs.

It is also worth noting that we did not consider one of the options. You can also get 12 volts from an ATX computer power supply. To run it without a PC, you need to close the green wire to any of the black ones. 12 volts are on the yellow wire. Typically, the power of a 12V line is several hundred watts and a current of tens of amperes.

Now you know how to get 12 volts from 220 or other available values. Finally, we recommend watching a useful video

On simple mechanisms, it is convenient to install analog current regulators. For example, they can change the speed of rotation of the motor shaft. From the technical side, it is easy to make such a regulator (you will need to install one transistor). Applicable for adjusting the independent speed of motors in robotics and power supplies. The two most common types of regulators are single-channel and dual-channel.

Video #1. Single channel controller in action. Changes the speed of rotation of the motor shaft by turning the knob of the variable resistor.

Video #2. Increasing the speed of rotation of the motor shaft during the operation of a single-channel regulator. The increase in the number of revolutions from the minimum to the maximum value when the variable resistor knob is rotated.

Video number 3. Dual channel controller in action. Independent setting of the speed of rotation of the motor shafts based on tuning resistors.

Video number 4. The voltage at the output of the regulator is measured with a digital multimeter. The resulting value is equal to the battery voltage, from which 0.6 volts have been subtracted (the difference occurs due to the voltage drop across the transistor junction). When using a 9.55 volt battery, a change from 0 to 8.9 volts is recorded.

Functions and main characteristics

The load current of a single-channel (photo. 1) and two-channel (photo. 2) regulators does not exceed 1.5 A. Therefore, to increase the load capacity, the KT815A transistor is replaced with a KT972A transistor. The pin numbering for these transistors is the same (e-k-b). But the KT972A model is operable with currents up to 4A.

Single channel motor controller

The device controls one motor, powered by a voltage in the range from 2 to 12 volts.

Device design

The main design elements of the regulator are shown in the photo. 3. The device consists of five components: two variable resistance resistors with a resistance of 10 kOhm (No. 1) and 1 kOhm (No. 2), a transistor model KT815A (No. 3), a pair of two-section screw terminal blocks for connecting the motor (No. 4) and battery input (No. 5).

Note 1. Screw terminals are not required. With the help of a thin installation stranded wire, you can connect the motor and power supply directly.

Principle of operation

The operating procedure of the motor controller is described by the wiring diagram (Fig. 1). Given the polarity, a constant voltage is applied to the XT1 connector. A light bulb or a motor is connected to the XT2 connector. At the input, a variable resistor R1 is turned on, the rotation of its knob changes the potential at the middle output as opposed to the minus of the battery. Through the current limiter R2, the middle output is connected to the base output of the transistor VT1. In this case, the transistor is connected according to the regular current circuit. The positive potential at the base output is increased by moving up the middle output from the smooth rotation of the variable resistor knob. There is an increase in current, which is due to a decrease in the resistance of the collector-emitter junction in the transistor VT1. The potential will decrease if the situation is reversed.

Circuit diagram

Materials and details

A printed circuit board measuring 20x30 mm is required, made of a sheet of fiberglass laminated on one side (permissible thickness 1-1.5 mm). Table 1 lists the radio components.

Note 2. The variable resistor required for the device can be of any production, it is important to observe the current resistance values \u200b\u200bfor it indicated in table 1.

Note 3. To adjust currents above 1.5A, the KT815G transistor is replaced with a more powerful KT972A (with a maximum current of 4A). In this case, the printed circuit board pattern does not need to be changed, since the pin assignment for both transistors is identical.

Assembly process

For further work, you need to download the archive file located at the end of the article, unzip it and print it. A regulator drawing is printed on glossy paper (file), and an installation drawing (file) is printed on a white office sheet (A4 format).

Next, the drawing of the circuit board (No. 1 in the photo. 4) is glued to the current-carrying tracks on the opposite side of the printed circuit board (No. 2 in the photo. 4). It is necessary to make holes (No. 3 in the photo. 14) on the installation drawing in the seats. The assembly drawing is attached to the printed circuit board with dry glue, while the holes must match. Photo.5 shows the pinout of the KT815 transistor.

The input and output of the terminal blocks-sockets are marked in white. A voltage source is connected to the terminal block through the clip. A fully assembled single-channel regulator is shown in the photo. The power supply (9 volt battery) is connected at the final stage of assembly. Now you can adjust the speed of rotation of the shaft using the motor, for this you need to smoothly rotate the variable resistor adjustment knob.

To test the device, you need to print a disk drawing from the archive. Next, you need to stick this drawing (No. 1) on thick and thin cardboard paper (No. 2). Then, with the help of scissors, a disk (No. 3) is cut out.

The resulting workpiece is turned over (No. 1) and a square of black electrical tape (No. 2) is attached to the center for better adhesion of the surface of the motor shaft to the disk. You need to make a hole (No. 3) as shown in the image. Then the disk is installed on the motor shaft and you can start testing. The single-channel motor controller is ready!

Dual channel motor controller

Used to independently control a pair of motors at the same time. Power is supplied from a voltage in the range from 2 to 12 volts. The load current is rated up to 1.5A per channel.

Device design

The main components of the design are shown in photo.10 and include: two trimmers for adjusting the 2nd channel (No. 1) and the 1st channel (No. 2), three two-section screw terminal blocks for output to the 2nd motor (No. 3), for the exit to the 1st motor (No. 4) and for the entrance (No. 5).

Note.1 Installation of screw terminals is optional. With the help of a thin installation stranded wire, you can connect the motor and power supply directly.

Principle of operation

The circuit of the two-channel controller is identical to the electrical circuit of the single-channel controller. Consists of two parts (Fig. 2). The main difference: the variable resistance resistor is replaced by a tuning resistor. The speed of rotation of the shafts is set in advance.

Note.2. To quickly adjust the speed of rotation of the motors, the tuning resistors are replaced with a mounting wire with variable resistance resistors with the resistance values \u200b\u200bspecified in the diagram.

Materials and details

You will need a printed circuit board 30x30 mm in size, made of a sheet of fiberglass laminated on one side with a thickness of 1-1.5 mm. Table 2 lists the radio components.

Assembly process

After downloading the archive file located at the end of the article, you need to unzip it and print it. A drawing of a regulator for thermal transfer (termo2 file) is printed on glossy paper, and an installation drawing (montag2 file) is printed on a white office sheet (A4 format).

The circuit board drawing is glued to the current-carrying tracks on the opposite side of the printed circuit board. Holes are formed on the installation drawing in the seats. The assembly drawing is attached to the printed circuit board with dry glue, while the holes must match. The pinout of the KT815 transistor is being made. To check, temporarily connect inputs 1 and 2 with a mounting wire.

Any of the inputs is connected to the power supply pole (the example shows a 9 volt battery). The minus of the power source is attached to the center of the terminal block. It is important to remember: the black wire is “-”, and the red one is “+”.

The motors must be connected to two terminal blocks, and the desired speed must also be set. After successful tests, you need to remove the temporary connection of the inputs and install the device on the robot model. The two-channel motor controller is ready!

In the presented necessary schemes and drawings for work. The emitters of the transistors are marked with red arrows.