Before starting to study the timer, let's define the basic concept of "frequency". In simple terms, this is the number of repetitions per second. This means that if you clap your palms 2 times in a second, the clap frequency will be equal to 2Hz. If for 3 times, then 3Hz.
Each microcontroller operates at a specific frequency. Most instructions are executed in one clock cycle, so the higher the frequency, the faster the microcontroller will run. If there is no clock source, then nothing will work accordingly. In the absence of an external clock source, most microcontrollers have their own internal clock. Usually they are tuned to it "from the factory".
The frequency of the internal source can change ("float") due to temperature, etc., therefore, it is considered unsuitable for serious projects, and we have just such 🙂 Therefore, a stable source of external frequency is used - a quartz resonator (quartz). One of the options for the quartz resonator:
Now, something about the timer. The timer runs at the same frequency as the microcontroller. Sometimes it can be too fast, so a prescaler is used that reduces the number of ticks by 8/64/256/1024 ... times. It all turns on programmatically.
Let's say we have chosen a 1024 prescaler, the microcontroller frequency is 8 MHz, so after the prescaler the timer frequency will become:
8,000,000 / 1,024 = 7813 Hz is the frequency at which our timer operates. In simple terms, the timer ticks 7813 times in one second.
Code execution can be linked to the number of ticks. This feature is not available for all timers, read the documentation for your stone. Let's say we want our code to execute every 0.5 seconds. In one second there are 7813 ticks, in half a second it is 2 times less - 3906. This value is entered into the comparison register, and with each tick it is checked whether the point is enough or not, like in an alarm clock, only very quickly.
But we have coincided these 2 values and what next? For this, there is such a useful thing as a coincidence interrupt. This means that if the timer and compare register match, your current program will stop. After that, a piece of code will be executed that is absolutely unrelated to the main program. Inside this section, you can write whatever you want and not worry that it will somehow affect the program, it will be executed only when the timer value coincides with the comparison register.
After the code inside the interrupt is executed, the program will resume from where it left off. Thus, you can periodically scan buttons, count the duration of pressing a button, measure the exact time intervals. A favorite question of beginners, how can I make an LED blink and do something else. So, timers and interrupts will help you with this.
Now we are ready to write our program. Therefore, we create a project using the project wizard. Let's attach the LCD right away, we already know how to do it).
Go to the Timers tab and take a closer look here:
Select the frequency 7813 and check the box next to Interrupt on: Compare A Match. Thus, we indicated that when the value matches, perform an interrupt (what was written above). We will interrupt once a second, i.e. we need to tick 7813 times, so convert 7813 to hex and get 1e85. This is what we write to the Comp A comparison register. Comp A comparison register is 16-bit, so we cannot write a number greater than 2 ^ 16 = 65536.
Generate, save, clean up our code. A new incomprehensible piece of code will appear
// Timer 1 output compare A interrupt service routine
interrupt void timer1_compa_isr (void)
{
This is the same interruption. It is inside these brackets that we can write the code that we would like to execute at certain intervals. We have one second. So it is logical to create a variable that we will increase 1 time per second, i.e. 1 time per interrupt. Therefore, we will initialize the variable int s = 0; and in the interrupt we will increase it from 0 to 59. The value of the variable will be displayed on the LCD. No tricks, everything is very simple.
The resulting code.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 | #include |
#include
Timers are another classic module found in almost all MCUs. It allows you to solve many problems, the most common of which is setting stable time intervals. The second most popular application is PWM generation (more on it later) at the MK output. Despite the fact that, as already mentioned, the use of timers is by no means limited to these tasks, only these two will be considered here as the most common.
The timer itself is a binary counter connected to the microcontroller clock system through an additional divider. Comparison units (there may be many of them) are connected to it, in turn, which are capable of performing various useful functions and generating interrupts, depending on the settings. In a simplified way, the timer device can be represented as follows:
Setting the timer, like all other peripherals, is done through its registers.
Generation of time intervals using a timer.
Interrupts.
As the name suggests, the main purpose of the compare blocks is to constantly compare the current timer value with the value specified in the OCRnX register. It has already been mentioned that register names often carry a deep sacred meaning - and comparison registers are no exception. So, n denotes the timer number, X - the letter (also a way of numbering, there can be many comparison blocks) of the comparison register. Thus, OCR1A can be understood as O utput C ompare R egister of 1 st timer, unit A... By the way, this will give a sophisticated embedder the opportunity to assume that perhaps there is a timer 0 and a comparison register B ...
So, comparison blocks can generate interrupts every time the timer value matches (by the way, it is in the register TCNTn — T imer / C ou NT er # n) with a given number. The reader should already be familiar with the concept of an interrupt, but just in case, let's refresh it in memory, and at the same time we'll talk about how to describe it in C. So, the above means that as soon as the described event occurs, the processor will save the number of the current command in stack and goes to the execution of specially defined code, and then returns back. Everything happens in much the same way as when calling a regular function, only it is called at the hardware level. Such functions are declared using a macro declared in avr / interrupt.h (ISR — « I nterrupt S ervice R outine "," interrupt handler "):
ISR (< имя вектора прерывания> ) { / * interrupt handling code * / }
Each interrupt (of course, there are many of them) corresponds to the so-called. interrupt vector is a constant also declared in avr / interrupt. For example, an interrupt handler that matches the timer value with the value of the OCR1A register will look like this:
ISR (TIMER1_COMPA_vect) ( / * handler code * / }
Undoubtedly, the discerning reader has already guessed how vector names are formed. However, a complete list of these constants can be found in the documentation for avr-libc (a library of standard functions for AVR-GCC).
Datasheet (from the English datasheet) - a file of technical documentation, a description of a specific device (microcircuit, transistor, etc.). Contains all information about the characteristics and application of the component. Almost always in PDF format. Usually googled like “<название компонента>pdf ".
The last three bits control the prescaler mentioned at the very beginning (the rest are not of interest to us yet):
Let's configure the timer so that interrupts occur twice a second. Let's choose a prescaler 64; to do this, set bits CS11 and CS10:
TCCR1B = (1< < CS11) | (1 < < CS10) ;
Then the counting frequency will be 8MHz / 64 = 125KHz, i.e. every 8μS one will be added to the TCNT1 value. We want interruptions to occur with a period of 500ms. Obviously, during this time the timer will count up to a value of 500mS / 8mkS = 62500, or 0xF424. Timer 1 is 16-bit, so it's okay.
OCR1A = 0xF424;
It is clear that in the event that the calculated value exceeds the bit width of the timer, the choice of a larger prescaler is required. The author leaves the derivation of a simple formula for calculating the number that must be loaded into the timer to obtain the desired interrupt frequency for a given processor frequency and prescaler.
It remains only to enable the coincidence interrupt - the bit in the TIMSK1 register is responsible for it:
The following is written about him:
So, we set the desired value:
TIMSK1 = (1< < OCIE1A) ;
In addition, it should be remembered that before using interrupts, they must be globally enabled by calling the function sei ()... To globally disable interrupts, use the function cli ()... These functions set / clear a bit I in the register SREG by controlling the very possibility of using a mechanism such as interrupts. Registers like TIMSKn are nothing more than local settings for a particular module.
As already mentioned, an interrupt can occur at any time, interrupting the program anywhere. However, there are times when this is undesirable. The mechanism of global prohibition / permission of interrupts allows to solve this problem.
So, the program, blinking LED, using interrupts can be rewritten as follows:
# include< avr/io.h ># include< avr/interrupt.h >ISR (TIMER1_COMPA_vect) (TCNT1 = 0; if (PORTB & (1< < PB0) ) PORTB& = ~ (1 < < PB0) ; else PORTB| = (1 < < PB0) ; } void main (void ) { DDRB= 0xFF ; PORTB= 0 ; OCR1A= 0xF424 ; TIMSK1= (1 < < OCIE1A) ; TCCR1B= (1 < < CS11) | (1 < < CS10) ; sei() ; while (1 ) ; }It can be seen that now, in the intervals between LED switching, the processor is absolutely free to perform other tasks, while in the first example it was busy with useless counting clock cycles (the _delay_xx () functions work this way). Thus, interrupts allow you to organize primitive multitasking.
PWM generation using a timer.
With certain settings, the comparison blocks allow you to organize the hardware generation of a PWM signal on the MK legs, designated as OСnX:
PWM (PWM) - NS irot- AND pulse M modulation ( P ulse W idth M odulation). A PWM signal is a sequence of rectangular pulses with varying duration:
For PWM, two related characteristics are introduced - the duty cycle (D) and the duty cycle - the reciprocal of the duty cycle. The duty cycle is the ratio of the pulse time to the period duration:
The fill factor is often expressed as a percentage, but decimal fractions are also common.
The value of PWM for the national economy lies in the fact that the effective voltage value of such a signal is directly proportional to the duty cycle:
- with this integral, the manual looks more solid; dependence is expressed by the following formula:
U avg - average voltage value (here - it is also effective);
D is the fill factor;
U p-p - pulse amplitude.
Thus, PWM is a simple way to obtain an analog signal using a microcontroller - for this, such a sequence of pulses must be applied to a low-pass filter (which, by the way, is the physical embodiment of the integral written above).
The most common PWM mode is the so-called. Fast PWM (you can read about other modes directly in the documentation), so let's consider it. In this case, the comparison blocks work as follows: when the timer is reset, the OCnX output goes high; as soon as the timer counts down to the number written in the OCRnX, the OCnX is put into a low-level state. All this is repeated with a counter overflow period. It turns out that the output pulse width depends on the OCRnX value, and the output frequency is equal to the clock frequency of the timer divided by its maximum value. The figure from the datasheet explains what was said:
An inverse mode is also possible, in which the OCnX state is changed in the reverse order, which is convenient in practice.
Setting up a comparison unit for generating PWM.
Here again the documentation will help us. So, first you need to switch the comparison unit to the PWM generation mode and select the output of interest from the available ones. These settings are available in the TCCR0A register:
We are interested in the WGMxx and COMnXn bits. The following is said about them:
That is, we are interested in the bits WGM00 and WGM01 - Fast PWM mode,
and also COM0A1 - non-inverting PWM on OC0A pin. Configuring:
TCCR0A = (1< < COM0A1) | (1 < < WGM01) | (1 < < WGM00) ;
Naturally, in addition, the selected leg must be configured for output using the DDR register of the corresponding port.
OCR0A = 128;
Finally, enable the timer by selecting the divisor. Everything is the same here:
Usually the highest possible frequency is chosen for PWM (in order to obtain the maximum quality of the output signal). That is, it is advisable to set the minimum divisor value:
TCCR0B = (1< < CS00) ;
At this point, the PWM tuning is complete, and you can see the signal on the selected leg.
As mentioned above, PWM is an easy way to get an analog signal using an MCU. For example, you can organize a smooth blinking of the LED (in this case, the observer's eye plays the role of an integrator-low-pass filter, so that the LED can be connected to the MK leg through a conventional resistor).
Some points in this example require clarification.
The list of included files contains a mysterious stdint.h- types with an explicitly specified bit depth are declared in this file, for example
uint8_t — u nsigned 8
-bit int eger t ype
uint16_t — u nsigned 16
-bit int eger t ype
uint32_t — u nsigned 32
-bit int eger t ype
int8_t- signed 8
-bit int eger t ype
etc. These types contribute to the consistency and readability of the program. In addition, it is guaranteed that when the code is ported, the bit depth of the data remains specified. And by the way, uint8_t is much faster to write than unsigned char.
Modifier volatile means that the compiler is not allowed to optimize the given variable. For example, if you compile the following example:
void main (void) (unsigned char i = 0; while (1) (i + +;))then examine the disassembled code, you can find that in fact no variable has been created, and the program is an empty loop. This happened because the optimizer considered the variable unused and did not include it in the resulting code. If a variable declared in this way were used, for example, in an interrupt, such a liberty of the optimizer would cause the program to malfunction. Application volatile eliminates this behavior.
#includeEven a novice radio amateur can independently make a transformer from 220 to 12 volts. This device belongs to AC machines, the principle of operation remotely resembles an asynchronous motor. Of course, you can buy a ready-made transformer, but why spend money, especially when you have enough steel for the core and wire for the coils on hand? It remains only to study a little theory and you can start making the device.
How to choose materials
When manufacturing a step-down transformer from 220 to 12 Volts, it is important to use high-quality materials - this will ensure high reliability of the device, which you will subsequently assemble on it. It should be noted that the transformer allows for isolation from the network, therefore it is allowed to install it to power incandescent lamps and other devices that are located in rooms with high humidity (showers, basements, etc.). When making your own coil frame, you need to use durable cardboard or textolite.
It is recommended to use domestic-made wires, they are much stronger than their Chinese counterparts, they have better insulation. You can use a wire from old transformers, as long as there is no damage to the insulation. To isolate the layers from each other, you can use both plain paper (preferably thin) and FUM tape, which is used in plumbing. But for the insulation of the windings, it is recommended to use a fabric impregnated with varnish. On top of the windings, it is imperative to apply insulation - varnish cloth or cable paper.
How to calculate?
Now that all the materials are ready, you can calculate the transformer from 220 to 12 volts (for a lamp or any other household appliance). In order to calculate the number of turns of the primary winding, you need to use the formula:
N = (40..60) / S.
S is the cross-sectional area of the magnetic circuit, the unit of measurement is sq. see In the numerator there is a constant - it depends on the quality of the core metal. Its value can range from 40 to 60.
Calculation by example
Let's say we have the following parameters:
- The window is 53 mm high and 19 mm wide.
- The frame is made of PCB.
- Upper and lower cheeks: 50 mm, frame 17.5 mm, therefore the window measures 50 x 17.5 mm.
Next, you need to calculate the diameter of the wires. Let's say you need the power to be 170 watts. In this case, the current on the mains winding will be 0.78 A (we divide the power by the voltage). In the design, the current density is equal to 2 A / sq. mm. With this data, you can calculate that you need to use a wire with a diameter of 0.72 mm. It is allowed to use 0.5 mm, 0.35 mm, but the current will be less.
From this we can conclude that to power radio equipment on lamps, for example, you need to wind 950-1000 turns for a high-voltage winding. For heating - 11-15 turns (the wire only needs to be used with a larger diameter, depending on the number of lamps). But all these parameters can be found empirically, which will be discussed further.
Calculation of the primary winding
When making a transformer with your own hands from 220 to 12 volts, you need to correctly calculate the primary (network) winding. And only after that you can start doing the rest. If you incorrectly make the calculation as primary, then the device will start to warm up, hum a lot, it will be inconvenient to use it, and even dangerous. Let's say a wire with a cross section of 0.35 mm is used for winding. One layer will fit 115 turns (50 / (0.9 x 0.39)). The number of layers is also easy to calculate. To do this, it is enough to divide the total number of turns by how many fit in one layer: 1000/115 = 8.69.
Now you can calculate the height of the frame together with the windings. The primary has eight full layers, plus insulation (0.1 mm thick): 8 x (0.1 + 0.74) = 6.7 mm. To avoid high-frequency interference, the mains winding is shielded from the rest. For the screen, you can use a simple wire - wind one layer, insulate it and connect the ends to the body. Foil is also allowed (of course, it must be strong). In general, the primary winding of our transformer will be 7.22mm.
A simple way to calculate secondary windings
And now about how to calculate the secondary windings, if the primary is already available or ready. You can use such a 220-volt transformer for LED strips, just be sure to install a voltage stabilizer. Otherwise, the brightness will be inconsistent. So what do you need to calculate? A few meters of wire and only, wind a certain number of turns over the primary winding. Let's say you wound 10 (and you don't need more, that's enough).
Next, you need to assemble the transformer and connect the primary winding to the network through a circuit breaker (for safety net). Connect a voltmeter to the secondary winding and click the machine. See what voltage value the device shows (for example, it showed 5 V). Therefore, each turn produces exactly 0.5 V. And now you just focus on what voltage you need to get (in our case, it is 12 V). Two turns are 1 volt of voltage. And 12 V is 24 turns. But it is recommended to take a small margin - about 25% (which is 6 turns). No one canceled the voltage loss, so the 12 V secondary winding should contain 30 turns of wire.
How to make a coil frame
It is extremely important in the manufacture of the frame to achieve the complete absence of sharp corners, otherwise the wire may be damaged, an interturn short circuit will appear. On the cheeks, you need to take the places to which the output contacts from the windings will be attached. After the final assembly of the frame, it is necessary to round off all sharp edges with a file.
Plates made of transformer steel should fit into the holes as tightly as possible, free play is not allowed. For winding thin wires, you can use a special device with a manual or electric drive. And thick wires must be wound exclusively by hand without additional devices.
Rectifier unit
By itself, the transformer 220 for 12 Volts will not give out direct current, you need to use additional devices. These are rectifier, filter and stabilizer. The first is performed on one or more diodes. The most popular scheme is bridge. It has a lot of advantages, among the main ones - minimal voltage losses and high quality of the output current. But it is allowed to use other rectifier circuits.
A conventional electrolytic capacitor is used as filters, which allows you to get rid of the residuals of the variable component of the output current. A zener diode installed at the output allows you to keep the voltage at the same level. In this case, even if there are ripples in the 220 V network and in the secondary winding at the output of the rectifier, the voltage will always have the same value. This is good for the devices that connect to it.
As you know, a voltage of 220 or 380 V passes through household power grids. Usually this is exactly what is required for this or that equipment. However, some electrical appliances cannot operate at such high rates, and safety is not in the last place here. In this case, a special device is used - a step-down transformer 220 for 12 volts, which allows you to provide the required voltage. Today we will talk about the types of such devices, the principle of operation and purpose. It is worth considering the possibility of self-assembly of the step-down transformer circuit at home.
Read in the article:
Step-down transformer 220 to 12 volts: applications
Today, many household appliances require undervoltage. These are modern TVs, personal computers and laptops, various gadgets. However, these devices are either supplied with a transformer, called a power supply, or it is built into the device. Lighting is a separate issue. Halogen or LED lamps (especially those installed in rooms with high humidity) require a separate voltage reducing device. This is due to safety requirements, although economy plays an important role.
Important! When purchasing a transformer for 12 volt LED lamps for a bathroom, you need to pay attention to the IP protection class. The device must be splash-proof to prevent short circuits and damage. For a living room or bedroom, this requirement is irrelevant.
The principle of operation of the transformer: general information
All such devices, regardless of type, do the same job. A voltage is applied to the transformer, which is reduced using coils or certain electronic components to the desired value. Such devices can be step-down (the output voltage is less than the input) or step-up (the output voltage is higher than the input). For domestic needs, step-up transformers are irrelevant, because 220 V is enough for the operation of all electrical appliances.
Consider the types of transformers used today in everyday life.
Separation of voltage reducing devices by type
Transformers are divided by design features into 2 types:
- Toroidal, or electromagnetic- an outdated version with large dimensions and lower efficiency (COP). This type is practically not used for domestic needs;
- electronic (pulse) devices- compact, lightweight, with a high percentage of efficiency tending to 100%.
Despite the fact that the former are gradually being replaced by the latter in all areas, it would be a mistake not to consider them.
Toroidal transformer 220 for 12 volts: device, circuit
A fairly simple device, consisting of two coils with different numbers of turns, mounted on a single steel core. The change in voltage at the output depends on the difference in turns. According to the laws of physics, any conductor through which an electric current flows creates an electromagnetic field around itself, which is amplified when the wire is wound into a coil. Thus, the current flowing through the primary coil (to which voltage is applied) creates a strong electromagnetic field, which is transmitted through the steel core to the secondary coil, from which the voltage is removed.
Important! Without an iron core, such a device will not work, even if the secondary coil is wound directly onto the primary. Moreover, such an attempt will lead to burnout of the primary coil wire.
Below is a diagram of the simplest toroidal transformer.
Household electronic voltage reducing device
The circuit of an electronic transformer 220 for 12 volts is more complex, however, its principle of operation is the same. A small ferrite ring with windings acts as a steel core with a large number of turns. The main work is performed by thyristors (dinistors), various limiting resistors and transistors. A detailed diagram can be found below.
Pulse step-down devices have a number of advantages over electromagnetic ones:
- small dimensions and weight;
- high efficiency;
- minimal heating, which is completely invisible with proper ventilation;
- long service life.
Important! Despite all the advantages of impulse devices, they have one drawback - such a transformer cannot be connected to the network without load. In the event of such an activation, the device quickly burns out.
Specifications: what to look out for
There are 3 main parameters that you should pay attention to. It:
- the value of the input voltage (220 or 380 V). In the case of household lighting, you should choose a device with an indicator of 220 V;
- output voltage- must correspond to 12 V;
- power. This indicator is calculated from the total load that the luminaires will create. For example, if you plan to connect 9 lamps of 15 W each, then the power of the transformer should be 150 W.
Expert opinion
Design Engineer ES, EM, EO (power supply, electrical equipment, interior lighting) ASP North-West LLC
Ask a specialist“You shouldn't buy a step-down device with a large power reserve. This will lead not only to unnecessary purchase costs, but also to a shorter service life. The optimal margin is 10-15% ”.
Chandelier transformer: selection criteria
Choosing such equipment, you should pay attention not only to the technical characteristics, but also to the possibility of placement. If you plan to install a stretch or suspended ceiling, there will be no questions. But in the absence of those, everything becomes a little more complicated. You can choose a fairly compact device that fits in a junction box, but it should be borne in mind that small dimensions also mean less power, which may not be enough if there are a lot of consumers. If a standard transformer in the chandelier is out of order, then everything is simple - we dismantle it and get an identical one. And what to do if it is decided to change incandescent lamps to halogen or LED, now we will analyze in more detail.
Let's consider an option. It is planned to install 8 30W halogen lamps. We make calculations: 8 × 30 + 10% = 264 W. Paying attention to the line of capacities offered by the manufacturer, you can see that the closest indicator in the big direction is a 12 volt 300 watt transformer. This is what you should get. Below you can see the diagram of an electronic transformer for 12 V halogen lamps.
How to connect a step-down transformer 220 / 12V
There is a certain procedure for connecting a step-down transformer. First, consumers are connected to the secondary winding, and only then voltage is applied to the primary. Installation is carried out according to the scheme, which is contained in the technical documentation. Grounding can be connected in various ways. If the body of the device is metal, then it can also be grounded. Below are photos of different types of transformers.
Very important! All work related to electrical installation is carried out exclusively with the voltage removed. Remember that electric shock is dangerous to life and health.
If you plan to connect LED lamps, then you need to purchase a transformer with a built-in rectifier or separately include a diode bridge in the circuit, which will provide the constant voltage necessary for the stable operation of the light diodes.
How to check a 220 to 12V step-down transformer using a multimeter
If you have a step-down transformer, and you do not know if it works, and what is its output voltage, you can use a multimeter. However, it should be understood that an incorrect check can damage the meter. Let's analyze the algorithm of actions:
- We find visually the primary and secondary and secondary windings. This is easy to do. The primary cores are always thinner.
- We set the AC indicator to the minimum with the multimeter switch (usually 200 V).
- We apply voltage to the primary winding.
- We take readings from the secondary winding. If there are more than two contacts, we check them alternately. It is possible that, in addition to 12 V, the transformer is capable of delivering 24 and 36 V.
How to make a 220 to 12V transformer with your own hands
For self-manufacturing of a step-down transformer, you will need the following materials:
- a core that can be taken from an old TV;
- varnished cloth;
- thick cardboard;
- boards and wooden blocks;
- steel bar;
- glue and saws.
First, let's look at the option of making the simplest wire winding machine.
| Illustration | Action being performed |
 | This is the simplest way to wind a wire around a spool. The diagram clearly shows how it can be assembled. However, there are also more convenient devices that will speed up the process. |
 | Using an ordinary vise, a steel rod and a bend (hand drill), you can assemble a winding device that will save time and effort. |
 | Another must-have device. Old coils are often used to make a transformer. It is such a machine, together with one of the previous devices, that will allow you to neatly rewind the wire from one coil to another. |
Now you should consider making a cardboard frame, directly onto which the wire will be wound.
| Illustration | Action being performed |
 | The dimensions of the frame are measured according to the core (it should fit inside rather tightly). Based on the fact that the core can be either conventional plates or notched, we suggest that the reader familiarize himself with both options. |
 | We make a pattern according to the size, which is glued together. Any glue can be used for fixing, but it is better to give preference to waterproof. The best option would be epoxy. |
 | And here you can see the ratio of the dimensions of the prefabricated frame, which is more difficult to manufacture, but more reliable and does not require gluing. Remember that non-compliance with the parameters can lead to unstable operation of the transformer. |
When everything you need is ready, you can start winding itself. This work also has its own nuances that should be taken into account.
| Illustration | Action being performed |
 | The wire should unwind from the "donor" coil from above, and, on the contrary, should be wound from the bottom up. The distance between the coils should not be less than a meter. Hold the wire with your right hand and rotate with your left. |
 | Outputs for different voltage values are sealed using insulating gaskets. They can be made from a wound wire or a flexible lead can be soldered to it, which is more convenient. The place of the adhesion is insulated without fail. The lead is passed through a hole in the cheek and fixed. In order not to get confused later (if there are several conclusions), it is better to immediately mark it. |
 | The fixing insulating pads are glued, however, even in this case, additional fixation is necessary. |
 | The figure shows how the fixing insulating gaskets are clamped with the wound wire. It is important to do everything according to the instructions - only in this case you can hope for a positive result. Remember that the turns of the wire must fit snugly together to ensure a stable magnetic field for the coil. |
Calculation of the number of turns of the primary and secondary winding
The main work in the manufacture of a transformer can be called the calculation of the number of turns of the primary and secondary winding. On average, for a converter of 90-150 W, the number of turns per 1 V is taken into account, equal to 50 Hz / 10 = 5. The total number is calculated by the formulas:
- W1 = 220 × 5 = 1100;
- W2 = 12 × 5 = 60.
We get the required number of turns of the primary winding - 1100, and the secondary - 60.
Prices for transformers 220 to 12 volts
Consider at what price you can buy 220-volt transformers on the Russian market. Prices are as of April 2018.
| Photo | Brand | Power, W | Average cost (as of April 2018), rubles |
 | Feron | 60 | 150 |
 | TRA54 | 200 | 500 |
 | TRA110 | 250 | 375 |
 | Pondtech | 75 | 4200 |
 | Relco | 250 | 4100 |
As you can see, the price range is quite large. It depends on the brand and the quality of the components, which means you should not think that the step-down transformer costs 150 rubles. will work for a long time.
Let's sum up
Before purchasing a step-down transformer for a home, it is important to calculate all the parameters. You should not take this carelessly, because the durability of the converter depends on the correctness of the calculations. If you decide to make such a device yourself, then you need to treat the calculations even more carefully. If, of course, the home craftsman expects to use a ready-made converter.
A car voltage inverter is sometimes incredibly useful, but most of the products in stores either have a quality fault, or they do not suit in terms of power, and are not cheap at the same time. But after all, the inverter circuit consists of the simplest parts, therefore we offer instructions for assembling a voltage converter with our own hands.
Inverter housing
The first thing to consider is the loss of electricity conversion, released in the form of heat on the keys of the circuit. On average, this value is 2-5% of the nominal power of the device, but this indicator tends to grow due to improper selection or aging of components.
The removal of heat from semiconductor elements is of key importance: transistors are very sensitive to overheating and this is expressed in the rapid degradation of the latter and, probably, their complete failure. For this reason, the base for the case should be a heat sink - an aluminum radiator.
Of the radiator profiles, the usual "comb" with a width of 80-120 mm and a length of about 300-400 mm is well suited. shields of field-effect transistors are fastened to the flat part of the profile with screws - metal spots on their back surface. But even with this, not everything is simple: there should be no electrical contact between the screens of all the transistors of the circuit, therefore the radiator and fasteners are insulated with mica films and cardboard washers, while a thermal interface is applied on both sides of the dielectric gasket with a metal-containing paste.
Determining the load and purchasing components
It is extremely important to understand why an inverter is not just a voltage transformer, and also why there is such a diverse list of such devices. First of all, remember that by connecting the transformer to a direct current source, you will not get anything at the output: the current in the battery does not change polarity, therefore, the phenomenon of electromagnetic induction in the transformer is absent as such.
The first part of the inverter circuit is an input multivibrator that simulates the oscillations of the network for making a transformation. It is usually assembled on two bipolar transistors that can swing power switches (for example, IRFZ44, IRF1010NPBF or more powerful - IRF1404ZPBF), for which the most important parameter is the maximum permissible current. It can reach several hundred amperes, but in general, you just need to multiply the current value by the battery voltage to get an approximate number of watts of output power without taking into account losses.
Simple converter based on multivibrator and power field switches IRFZ44
The frequency of the multivibrator is not constant, calculating and stabilizing it is a waste of time. Instead, the current at the output of the transformer is converted back to constant current by means of a diode bridge. Such an inverter can be suitable for powering purely active loads - incandescent lamps or electric heaters, stoves.
On the basis of the resulting base, you can collect other circuits that differ in the frequency and purity of the output signal. The selection of components for the high-voltage part of the circuit is easier to make: the currents here are not so high, in some cases the assembly of the output multivibrator and filter can be replaced with a pair of microcircuits with the appropriate strapping. Capacitors for the load network should be electrolytic, and for circuits with a low signal level - mica.
A variant of the converter with a frequency generator on K561TM2 microcircuits in the primary circuit
It is also worth noting that in order to increase the final power, it is not at all necessary to purchase more powerful and heat-resistant components of the primary multivibrator. The problem can be solved by increasing the number of converter circuits connected in parallel, but each of them will require its own transformer.
Option with parallel connection of circuits
Fighting for a sine wave - disassembling typical circuits
Voltage inverters are used today everywhere, both by motorists who want to use household appliances far from home, and by residents of autonomous homes powered by solar energy. And in general, we can say that the width of the spectrum of current collectors that can be connected to it directly depends on the complexity of the converter device.
Unfortunately, a pure "sine" is present only in the main power grid, it is very, very difficult to achieve the conversion of direct current into it. But in most cases this is not required. To connect electric motors (from drills to coffee grinders), a pulsating current with a frequency of 50 to 100 hertz is sufficient without smoothing.
ESL, LED lamps and all kinds of current generators (power supplies, chargers) are more critical to the choice of frequency, since it is at 50 Hz that their operation scheme is based. In such cases, microcircuits, called a pulse generator, should be included in the secondary vibrator. They can switch a small load directly, or act as a "conductor" for a series of power switches of the inverter output circuit.
But even such a cunning plan will not work if you plan to use the inverter to provide stable power supply to networks with a mass of dissimilar consumers, including asynchronous electrical machines. Here, pure "sine" is very important and only digitally controlled frequency converters can do this.
Transformer: pick up or yourself
For the assembly of the inverter, we are missing only one circuit element that performs the transformation of low voltage to high voltage. You can use transformers from power supplies of personal computers and old UPSs, their windings are just designed for the transformation of 12 / 24-250 V and vice versa, it remains only to correctly determine the conclusions.
And yet it is better to wind the transformer with your own hands, since the ferrite rings make it possible to do it yourself and with any parameters. Ferrite has excellent electromagnetic conductivity, which means that transformation losses will be minimal even if the wire is hand wound and not tight. In addition, you can easily calculate the required number of turns and the thickness of the wire using calculators available on the network.
Before winding the core ring, you need to prepare - remove the sharp edges with a file and wrap tightly with an insulator - fiberglass impregnated with epoxy glue. This is followed by the winding of the primary winding from a thick copper wire of the calculated cross-section. After dialing the required number of turns, they must be evenly distributed over the surface of the ring at equal intervals. The winding leads are connected according to the diagram and insulated with heat shrinkage.
The primary winding is covered with two layers of polyester tape, then the high-voltage secondary winding and another layer of insulation are wound. An important point - you need to wind the "secondary" in the opposite direction, otherwise the transformer will not work. Finally, a semiconductor thermal fuse must be soldered to one of the taps, the current and operating temperature of which are determined by the parameters of the secondary winding wire (the fuse case must be tightly tied to the transformer). The top of the transformer is wrapped with two layers of vinyl insulation without an adhesive backing, the end is fixed with a tie or cyanoacrylate glue.
Installation of radioelements
It remains to assemble the device. Since there are not so many components in the circuit, they can be placed not on the printed circuit board, but by surface mounting with attachment to the radiator, that is, to the device body. We solder to the pin legs with a mono-core copper wire of a sufficiently large cross-section, then the junction is reinforced with 5-7 turns of thin transformer wire and a small amount of POS-61 solder. After the connection has cooled down, it is insulated with a thin heat shrink tube.
High power circuits with complex secondary circuits may require a printed circuit board with transistors in a row at the edge for free attachment to the heatsink. For the manufacture of a seal, glass fiber laminate with a foil thickness of at least 50 microns is suitable, but if the coating is thinner, reinforce the low voltage circuits with copper wire jumpers.
Making a printed circuit board at home is easy today - the Sprint-Layout program allows you to draw clipping stencils for circuits of any complexity, including for double-sided boards. The resulting image is printed by a laser printer on high-quality photo paper. Then the stencil is applied to the cleaned and defatted copper, ironed, the paper is washed off with water. The technology received the name "laser-ironing" (LUT) and is described in the network in sufficient detail.
You can etch the remains of copper with ferric chloride, electrolyte or even table salt, there are plenty of ways. After etching, the stuck toner must be washed off, the mounting holes must be drilled with a 1 mm drill, and the soldering iron (submerged-arc) walked along all the tracks to tin the copper of the contact pads and improve the channel conductivity.
