DIY high-frequency voltage converter. Voltage converter circuit

From a 12V car battery. In this case, it converts the 12 volts of the car battery into +- 35 volts. To reduce the size of the device, the conversion occurs at an increased frequency. In a voltage converter, the frequency is 50 kHz. The converter provides bipolar ULF power supply with a maximum power of about 200W. Mostly imported components were chosen for the circuit, since they are now easier to obtain. The circuit uses the TL494 chip as a pulse-width modulator. The TL494 generator is common in many UPS circuits; for example, you can unsolder it from an AT or ATX. Power field-effect IRFZ44N were chosen as switching transistors. To discharge the capacitances of the gates of field-effect transistors, buffer transistors KT961 and KT639 are used.

Schematic diagram of a voltage converter 12 - 2x35 volts to power a powerful UMZCH.

The voltage converter works as follows. A pulse generator with a frequency of about 30-50 KHz is assembled on a TL494; pulses in antiphase are supplied to the fast charging and discharging circuits of gate capacitors, which form pulses with a short rise and fall. The generated pulses arrive at the gates of control transistors, the drains of which are connected to the transformer. Inductive surge suppression circuits are included in parallel with its windings to eliminate the possibility of transistor breakdown due to excess voltage. The rectifier has nothing special, a regular diode bridge and a capacitive filter with an anti-interference choke. The control unit on the TL494 chip starts working immediately. It is not critical to the parts used. At pins 9 and 10 there should be rectangular pulses, shifted in time.

The voltage converter is assembled on a printed circuit board made of single-sided foil fiberglass. The layout of the printed circuit board significantly affects the RF interference at the output of the converter and, accordingly, at the output. Designing your own signet requires knowledge. It may be better to find a ready-made signet. I can say about my signet that it is fully functional and has a minimum of interference, although it can be done better.

The circuit used resistors of the MLT type - 0.125, with the exception of those whose power is indicated on the circuit, trimming resistors - any suitable in size and location of the terminals, preferably they should be type A. The rectifier diodes are installed on a small radiator. Driver transistors do not need radiators. Powerful field-effect transistors are installed through mica spacers on a large radiator; if necessary, a cooler is added. The winding data of the transformer and chokes are indicated in the diagram.

The transformer must be wound very efficiently, the operation of everything depends on this. The winding of the transformer must be done as tightly as possible to the core and the turns should be distributed evenly throughout the entire ring. The primary winding is 4 turns along the entire magnetic circuit with a bundle of 10 wires with a diameter of 1.6 mm, after which we divide the bundle in half. The end of one is connected to the beginning of the other half-winding. Secondary - 16 turns of a bundle of 4 wires with a diameter of 1.2 mm, then divided in half. You can take the wires of a different diameter and change the number of cores, so that the cross-section remains the same.

But all these figures are given approximately, since special accuracy of the output voltages is not required. Well, you will have not +-35, but 31 volts, so what? The magnetic core can be wrapped with a layer of varnished cloth so as not to damage the wire insulation during winding. We also lay a layer of insulation between the windings to prevent short circuits. The output of the transformer should be trapezoidal pulses. The choke is made on ferrite from the computer power supply, 10 turns of PEL-1 wire. It is better to install rectifier diodes with a low voltage drop - Schottky.

When setting up the converter, first turn it on through a 12V car lamp with a power of several tens of watts, this will save the circuit from burning out if there are errors in the installation. Measurements of the converter output voltages must be made under load. By rotating the trimmer resistor slider we set the voltage we need; usually it is regulated within the range of 20V - 40V. Material provided by alpha and qwert390.

Discuss the article VOLTAGE CONVERTER DIAGRAM

Why do you need to make a converter for a 3-phase electric motor yourself, and how to make it yourself? To protect the environment, rules are being created everywhere that recommend that manufacturers of electrical devices make products that will save electrical energy. This can often be achieved by properly controlling the speed of the electric motor. A frequency converter easily solves this problem.

Various names: inverter, frequency current changer, frequency-controlled drive mechanism. Today, such devices are made by various factories, but many craftsmen make no worse ones with their own hands.

How I made my own frequency converter

I also made an asynchronous drive for my friend. He needed a drive for the sawmill, powerful and good. Since I loved working with electronics, I immediately offered him the following circuit:

I used a three-phase bridge on transistors with feedback diodes that were available. The control was carried out through the HCPL 3120 optodriver with a PIC16F628A microcontroller. I soldered a quenching capacitance at the entrance so that the electrolytes were charged smoothly. Then I soldered the shunt relay. I also installed a current protection trigger against short circuit and overload. For control I installed two buttons and a switch for reverse rotation.

I assembled the power part using a wall-mounted installation.

I connected the resistors in parallel at 270 kOhm using gate pass capacitors and soldered them behind the board. My board is shown in the external view:

View of this board of mine from the other side:

To connect the supply voltage, I assembled a power supply that operates on pulses, flyback. Here is a diagram of this power supply:

How did I program the microcontroller? Simple blinkers did not pose any problem for me. The result was constants in the form of a matrix, which my controller worked on. The frequency and voltage were specified by these values. I checked the entire operation scheme on a low-power fan motor, 200 W. My design looked like this:

Initial experiments gave good results. Then I modified the program. I revved up the 4 kW engine and went to assemble the sawmill controls.

During installation, my friend and I accidentally had a short circuit and the protection was triggered; we checked its operation. The 2 kW 1500 rpm motor sawed boards with ease. Now the program is still being finalized to boost the engine above its nominal value. Characteristics: frequency from 2 to 50 hertz in steps of 1.5 hertz, synchronous frequency, constantly changing, run-up from 1500 to 3500 hertz, scalar type U/F control, motor power up to 5 kW.

Hold down the RUN button and accelerate the engine. Let go, the frequency remains at the same level. When the LED lights up, the drive is ready to start.

How to make an inverter yourself?

Along with the production of factory inverters, amateurs make them themselves, with their own hands. There is nothing complicated here. Such a frequency converter converts one phase and turns it into three phases. An electric motor with a similar frequency range is used at home; its power will not be lost.

The rectification block in the circuit is located at the beginning. Next come those that cut off current variables. To manufacture these inverters, IGBT transistors are used.

Thyristors are the future, although they have been used in the present for a long time. A purchased frequency switch based on bipolar transistors is expensive and is rarely used (servo drives, metal cutting). These drives such as conveyors and conveyors, rotary machines, water pumping stations, climate control systems are most of from the entire use of factory devices, where it is better to use frequency converters to control electric motors with squirrel-cage armatures and you can control the engine speed if you apply potential, changing the frequency up to 50 hertz.

Let's give simple examples frequency converters that pulled powerful electric motors of diesel locomotives and electric trains, which included many freight platform cars, large stations with 600-volt pumps, supplying urban areas drinking water. Obviously, these strong electric motors are not suitable for bipolar transistors. Therefore, active thyristors of the GTO, GCT, IGCT and SGCT types are used. They convert from direct current to a three-phase current network with good power. However, there are simple circuits using simple thyristors that are closed by the reverse cathode current. Such thyristors will not operate in PWM mode; they are well used in direct control of electric motors, without a constant current. Frequency converters based on thyristors in stagnant times were used for motors on DC. Siemens invented a technology that transformed the industry beyond recognition.

The cost of all parts of a homemade inverter is significantly lower than the price of a factory device.

Such homemade devices are well suited for electric motors with a power of up to 0.75 kW.

What is the inverter intended for - its operating principle

The inverter acts on the rotation speed of asynchronous motors. Motors convert electricity into mechanical movement. Rotational movement converted into mechanical movements. This creates great convenience. Asynchronous motors are very popular in many aspects of people's lives.

The speed of the electric motor can be changed by other devices. But they have many shortcomings. They are difficult to use, expensive, work with poor quality, and the adjustment range is small.

For a three-phase motor, this problem is easily solved. Everyone knows that using frequency converters to change the rotation speed is the best and most correct method. Such a device provides soft starting and braking, and also controls many processes occurring in the motor. In this case, emergency situations are eliminated.

To smoothly and quickly regulate engine operation, experts have developed a special electrical diagram. The use of a frequency generator makes it possible to operate the engine without interruption, economically. Its efficiency reaches 98%. This occurs by increasing the switching frequency. Mechanical devices cannot perform such functions.

How to regulate the speed of an inverter?

How can a frequency generator change an electric motor? First, he changes the mains voltage. Next, the required voltage amplitude and frequency are obtained from it and supplied to the electric motor.

The speed control interval run-up by the converter is large. You can change the rotation of the motor in the other direction. To prevent the engine from failing, you need to take into account the data from its characteristics, permissible speed, power.

What does the control drive consist of?

Frequency circuit diagram.

It consists of three links:

1. a rectifier that provides a direct current potential when connected to the electrical network. The network may or may not be managed;
2. a filter element that smoothes the output voltage (capacitance is used);
3. an inverter that produces the desired frequency potential, the outermost link near the electric motor.

Frequency control mode

They are divided into types of engine speed control:

1. (no connection from the reverse side);
2. vector control mode (there is or is no connection from the reverse side).

In the first case, the stator is controlled with its magnetic field. Vector control takes into account the action of the rotor and stator magnet fields, improving torque at different rotation speeds. This is the main difference between their control modes.

The vector method is more accurate and efficient. It is more expensive to maintain. It is more suitable for specialists with good professional skills and knowledge. The scalar type control method is the easiest to use. It is used with output parameters that do not require special precision adjustment.

How to connect an inverter with delta and star?

When we bought an inverter at an inexpensive price, the need arises: connecting it to the electric motor ourselves without specialists. First you need to install for security circuit breaker for de-energizing. If a short circuit occurs in the phases, the entire system will shut down.

You can connect the motor with a star or triangle.

When the regulation drive is with one phase, the contacts of the electric motor are connected in a triangle. Then power will not be lost. The power of this frequency converter will be no more than 3 kW.

Three-phase inverters are technically the most modern. They are powered by factory three-phase networks and connected by a star.

To limit the starting current and reduce the starting torque when starting an electric motor over 5 kW, you can use the delta and star connection method.

When the stator is turned on, a star circuit is used, and if the engine speed is normal, then they switch to the triangle version. But this is used when there is a possibility of connecting in two circuits.

We note that in the star-delta version there will always be large current drops. When switching to the second scheme, the engine speed will decrease significantly. To restore the rotation speed, the current must be increased.

Frequency switches for motors with power up to 8 kW are widely used.

Application of new generation inverters

Modern ones are made using devices such as microcontrollers. This significantly improves the functions of inverters in control and monitoring algorithms from the point of view of operational safety.

Frequency generators have been successfully used in the following areas of production:

• in water supply, heat supply when changing the pump supply speed of cold and hot water supply;
• in factory conditions of mechanical engineering;
• in light and textile industries;
• in energy and fuel production;
• for sewerage and well pumps;
• in technological processes for control automation.

To control and monitor frequency drivers, the device manufacturer offers a created program that will always communicate with the controller via a port, will show the status on the monitor and will allow control. The data is documented by an exchange protocol and is used by users who create control programs for electronic equipment and controllers.

Data is exchanged in three stages:

1. Identification.
2. Initialization.
3. Management and control.

The cost of uninterruptible voltage power supplies depends on whether it contains a frequency converter. Such devices are the future. The economic and energy sectors will develop faster thanks to new modern devices.

A 12V/220V inverter is a necessary thing on a household. Sometimes it’s simply necessary: ​​the network, for example, has disappeared, and the phone is dead and there’s meat in the refrigerator. Demand determines supply: for ready-made models of 1 kW or more, from which you can power any electrical appliances, you will have to pay somewhere from $150. Possibly over $300. However, making a voltage converter with your own hands in our time is accessible to anyone who knows how to solder: assembling it from a ready-made set of components will cost three to four times less + a little work and metal from scrap trash. If there is one for car batteries, you can generally spend 300-500 rubles. And if you also have basic amateur radio skills, then, after rummaging through the stash, it is quite possible to make a 12V DC/220V AC 50Hz inverter for 500-1200 W for nothing. Let's consider the possible options.

Options: Global

A 12-220 V voltage converter to power a load up to 1000 W or more can generally be made independently in the following ways (in order of increasing costs):

1. Place a ready-made unit in a case with a heat sink from Avito, Ebay or AliExpress. Search for "inverter 220" or "inverter 12/220"; you can immediately add the required power. It will cost approx. half the price of the same factory one. No electrical skills required, but - see below;
2. Assemble the same one from the kit: printed circuit board + “scattered” components. It can be purchased there, but diy is added to the request, which means self-assembly. Price still approx. 1.5 times lower. You need basic skills in radio electronics: using a multimeter, knowledge of the wiring (pinouts) of the terminals of active elements or the ability to look for them, the rules for including polar components (diodes, electrolytic capacitors) in the circuit and the ability to determine what current and what cross-section wires are needed;
3. Adapt a computer uninterruptible power supply (UPS, UPS) to the inverter. A working used UPS without a standard battery can be found for 300-500 rubles. You don’t need any skills - you simply connect the car battery to the UPS. But you will have to charge it separately, also see below;
4. Choose a conversion method, a diagram (see below) in accordance with your needs and the availability of parts, calculate and assemble completely yourself. It may be completely free, but in addition to basic electronic skills, you will need the ability to use some special measuring instruments (also see below) and perform simple engineering calculations.

From a finished module

Assembly methods according to paragraphs. 1 and 2 are actually not that simple. The housings of ready-made factory inverters also serve as heat sinks for powerful transistor switches inside. If you take a “semi-finished product” or “loose”, then there will be no housing for them: given the current cost of electronics, manual labor and non-ferrous metals, the difference in prices is explained precisely by the absence of the second and, possibly, the third. That is, you will have to make a radiator for powerful keys yourself or look for a ready-made aluminum one. Its thickness at the location where the keys are installed should be at least 4 mm, and the area for each key should be at least 50 square meters. see for each kW of power output; with blowing from a 12 V computer fan-cooler 110-130 mA – from 30 sq. cm*kW*key.

For example, there are 2 keys in a set (module) (they can be seen, they stick out from the board, see on the left in the figure); modules with keys on the radiator (on the right in the figure) are more expensive and are designed for a certain, usually not very high power. There is no cooler, the power required is 1.5 kW. This means you need a radiator of 150 sq. see. In addition to this, there are also installation kits for keys: insulating heat-conducting gaskets and fittings for mounting screws - insulating cups and washers. If the module has thermal protection (there will be some other piece sticking out between the keys - a thermal sensor), then a little thermal paste to glue it to the radiator. Wires - of course, see below.

From UPS

The 12V DC/220V AC 50Hz inverter, to which you can connect any devices within the permissible power limit, is made from a computer UPS quite simply: the standard wires to “your” battery are replaced with long ones with clamps for the car battery terminals. The wire cross-section is calculated based on the permissible current density of 20-25 A/sq. mm, see also below. But because of a non-standard battery, problems can arise - with it, and it is more expensive and more necessary than a converter.

UPS also uses lead-acid batteries. This is today the only widely available secondary chemical power source capable of regularly delivering large currents (extra currents) without being completely “killed” in 10-15 charge-discharge cycles. In aviation, silver-zinc batteries are used, which are even more powerful, but they are monstrously expensive, are not widely available, and their service life is negligible by everyday standards - approx. 150 cycles.

The discharge of acid batteries is clearly monitored by the voltage on the bank, and the UPS controller will not allow the “foreign” battery to be discharged beyond measure. But in standard UPS batteries the electrolyte is gel, while in car batteries it is liquid. The charging modes in both cases are significantly different: the same currents cannot be passed through the gel as through a liquid, and in a liquid electrolyte, if the charge current is too low, the mobility of the ions will be low and not all of them will return to their places in the electrodes. As a result, the UPS will chronically undercharge the car battery; it will soon become sulfated and become completely unusable. Therefore, in the kit for the inverter on the UPS you need Charger for batteries. You can make it yourself, but that's another topic.

Battery and power

The suitability of the converter for a particular purpose also depends on the battery. A boost voltage inverter does not take energy for consumers from the “dark matter” of the Universe, black holes, the holy spirit, or anywhere else just like that. Only from the battery. And from it he will take the power supplied to consumers, divided by the efficiency of the converter itself.

If you see “6800W” or more on the body of a branded inverter, believe your eyes. Modern electronics make it possible to fit even more powerful devices into the volume of a cigarette pack. But let’s say we need a load power of 1000 W, and we have a regular 12 V 60 A/h car battery at our disposal. Typical efficiency value inverter – 0.8. This means it will take approx. 100 A. For such a current, wires with a cross-section of 5 square meters are also needed. mm (see above), but that’s not the main thing here.

Car enthusiasts know: if you run the starter for 20 minutes, buy a new battery. True, new machines have time limiters for its operation, so perhaps they don’t know. And certainly not everyone knows that the starter of a car, once spun up, takes a current of approx. 75 A (within 0.1-0.2 s at startup - up to 600 A). The simplest calculation - and it turns out that if the inverter does not have automatic equipment that limits the battery discharge, then ours will run out completely in 15 minutes. So choose or design your converter taking into account the capabilities of the existing battery.

Note: This implies a huge advantage of 12/220 V converters based on computer UPSs - their controller will not allow the battery to drain completely.

The service life of acid batteries does not noticeably decrease if they are discharged with a 2-hour current (12 A for 60 A/h, 24 A for 120 A/h and 42 A for 210 A/h). Taking into account the conversion efficiency, this gives a permissible long-term load power of approx. 120 W, 230 W and 400 W respectively. For 10 min. load (for example, to power a power tool), it can be increased by 2.5 times, but after this the ABC must rest for at least 20 minutes.

Overall, the result is not entirely bad. Of the ordinary household power tools, only the grinder can take 1000-1300 W. The rest, as a rule, cost up to 400 W, and screwdrivers up to 250 W. A refrigerator from a 12 V 60 A/h battery will work through an inverter for 1.5-5 hours; quite enough to take the necessary measures. Therefore, making a 1 kW converter for a 60 A/h battery makes sense.

What will be the output?

In order to reduce the weight and size of the device, with rare exceptions (see below), voltage converters operate at increased frequencies from hundreds of Hz to units and tens of kHz. No consumer will accept a current of such frequency, and the loss of its energy in conventional wiring will be enormous. Therefore, inverters 12-200 are built for the following output voltage. types:

• Constant rectified 220 V (220V AC). Suitable for powering telephone chargers, most power supplies (PS) for tablets, incandescent lamps, fluorescent housekeepers and LED lamps. With a power of 150-250 W, they are perfect for hand-held power tools: the DC power they consume is slightly reduced, and the torque increases. Not suitable for switching power supplies (UPS) of TVs, computers, laptops, microwave ovens, etc. with a power of more than 40-50 W: these necessarily have the so-called. a starting unit, for the normal operation of which the mains voltage must periodically pass through zero. Unsuitable and dangerous for devices with iron-based power transformers and electric motors alternating current: stationary power tools, refrigerators, air conditioners, most Hi-Fi audio, food processors, some vacuum cleaners, coffee makers, coffee grinders and microwave ovens (for the latter - due to the presence of a table rotation motor).
• Modified sine wave (see below) - suitable for any consumers, except for Hi-Fi audio with a UPS, other devices with a UPS from 40-50 W (see above) and, often local security systems, home weather stations, etc. with sensitive analog sensors.
• Pure sinusoidal - suitable without restrictions, except for power, for any electricity consumers.

Sine or pseudosine?

In order to increase efficiency, voltage conversion is carried out not only at higher frequencies, but also with heteropolar pulses. However, powering many consumer devices with a sequence of different polarity rectangular pulses(the so-called meander) is impossible: large surges on the meander fronts with even a slightly reactive load will lead to large energy losses and can cause a consumer malfunction. However, it is also impossible to design the converter for sinusodal current - the efficiency will not exceed approx. 0.6.

A quiet, but significant revolution in this industry occurred when microcircuits were developed specifically for voltage inverters, forming the so-called. a modified sinusoid (on the left in the figure), although it would be more correct to call it pseudo-, meta-, quasi-, etc. sinusoid. The current shape of the modified sinusoid is stepped, and the pulse fronts are prolonged (the meander fronts are often not visible at all on the screen of a cathode-ray oscilloscope). Thanks to this, consumers with transformers on iron or noticeable reactivity (asynchronous electric motors) “understand” the pseudosine wave “as real” and work as if nothing had happened; Hi-Fi audio with a network transformer on hardware can be powered with a modified sine wave. In addition, a modified sinusoid can be smoothed out in fairly simple ways to an “almost real” one, the differences from a pure one on an oscilloscope are barely noticeable by eye; Converters of the “Pure Sine” type are not much more expensive than conventional ones, on the right in Fig.

However, it is not advisable to run devices with capricious analog components and UPSs from a modified sine wave. The latter are extremely undesirable. The fact is that the middle platform of the modified sinusoid is not a pure zero voltage. The UPS starting unit from a modified sine wave does not operate clearly and the entire UPS may not exit the startup mode into operating mode. The user sees this at first as ugly glitches, and then smoke comes out of the device, as in the joke. Therefore, the devices in the UPS must be powered from Pure Sine inverters.

We make the inverter ourselves

So, for now it is clear that it is best to make an inverter for an output of 220 V 50 Hz, although we will also remember about the AC output. In the first case, to control the frequency you will need a frequency meter: the norm for fluctuations in the frequency of the power supply network is 48-53 Hz. AC electric motors are especially sensitive to its deviations: when the frequency of the supply voltage reaches the tolerance limits, they heat up and “go away” from the rated speed. The latter is very dangerous for refrigerators and air conditioners; they can irreparably fail due to depressurization. But we don’t need to buy, rent, or beg for a loan an accurate and multifunctional electronic frequency meter - we don’t need its accuracy. Either an electromechanical resonant frequency meter (pos. 1 in the figure) or a pointer of any system, pos. 2:

Both are inexpensive, sold on the Internet, and in large cities in electrical specialty stores. An old resonant frequency meter can be found at the iron market, and one or the other, after setting up the inverter, is very suitable for monitoring the network frequency in the house - the meter does not respond to connecting them to the network.

50 Hz from computer

In most cases, 220 V 50 Hz power is required by consumers that are not particularly powerful, up to 250-350 W. Then the basis for a 12/220 V 50 Hz converter can be a UPS from an old computer - if, of course, one is lying around in the trash or someone is selling it cheap. The power delivered to the load will be approx. 0.7 from the rated UPS. For example, if “250W” is written on its body, then devices up to 150-170 W can be connected without fear. You need more - you must first test it on a load of incandescent lamps. It lasted 2 hours – it can deliver such power for a long time. How to make a 12V DC/220V AC 50Hz inverter from a computer power supply, see the video below.

Video: a simple 12-220 converter from a computer power supply

Keys

Let's say there is no computer UPS or you need more power. Then the choice of key elements becomes important: they must switch high currents with minimal switching losses, be reliable and affordable. In this regard, bipolar transistors and thyristors are confidently becoming a thing of the past in this area of ​​application.

The second revolution in the inverter business is associated with the advent of powerful field-effect transistors (“field transistors”), the so-called. vertical structure. However, they have revolutionized the entire technology of power supply for low-power devices: it is becoming increasingly difficult to find a transformer on iron in household appliances.

The best of the high-power field devices for voltage converters are insulated gate induced channel (MOSFET), e.g. IFR3205, left in the figure:

Due to the negligible switching power, the efficiency of an inverter with a DC output on such transistors can reach 0.95, and with an AC 50 Hz output 0.85-0.87. Analogues of MOSFET with a built-in channel, e.g. IFRZ44, give lower efficiency, but are much cheaper. A pair of one or the other allows you to bring the power in the load to approx. 600 W; both can be paralleled without problems (on the right in the figure), which makes it possible to build inverters with a power of up to 3 kW.

Note: The power loss of switching switches with a built-in channel when operating on a significantly reactive load (for example, an asynchronous electric motor) can reach 1.5 W per switch. Keys with an induced channel are free from this drawback.

TL494

The third element that made it possible to bring voltage converters to their current state is the specialized TL494 microcircuit and its analogues. All of them are a pulse-width modulation (PWM) controller that generates a modified sine wave signal at the outputs. The outputs are multi-polar, which allows you to control pairs of keys. The reference conversion frequency is set by a single RC circuit, the parameters of which can be changed within wide limits.

When is a permanent job enough?

The circle of 220 V DC consumers is limited, but it is they who need an autonomous power supply not only in emergency situations. For example, when working with power tools on the road or in the far corner of your own site. Or is it always present, say, at the emergency lighting of the entrance to the house, hallway, corridor, local area from solar battery, during the day recharging the battery. The third typical case is charging your phone on the go from the cigarette lighter. Here the output power is needed very little, so the inverter can be made with just 1 transistor according to the relaxation generator circuit, see next. video clip.

Video: boost converter on one transistor

Already for 2-3 meals LED light bulbs need more power. When trying to “squeeze” it, the efficiency of blocking generators drops sharply, and you have to switch to circuits with separate timing elements or full internal inductive feedback; they are the most economical and contain the least number of components. In the first case, to switch one switch, the self-induction EMF of one of the transformer windings is used together with a timing circuit. In the second, the frequency-setting element is the step-up transformer itself due to its own time constant; its value is determined primarily by the phenomenon of self-induction. Therefore, both inverters are sometimes called self-induction converters. Their efficiency, as a rule, is no higher than 0.6-0.65, but, firstly, the circuit is simple and does not require adjustment. Secondly, the output voltage is more trapezoidal than square wave; “demanding” consumers “understand” it as a modified sine wave. Disadvantage: field switches in such converters are practically inapplicable, because often fail due to voltage surges on the primary winding during switching.

An example of a circuit with external timing elements is given in pos. 1 pic:

The author of the design was unable to squeeze more than 11 W out of it, but apparently, he confused ferrite with carbonyl iron. In any case, the armored (cup) magnetic circuit in his own photo (see figure on the right) is in no way ferrite. It looks more like an old carbonyl one, oxidized on the outside with time, see fig. on right. It is better to wind the transformer for this inverter on a ferrite ring with a ferrite cross-sectional area of ​​0.7-1.2 square meters. cm. The primary winding should then contain 7 turns of wire with a copper diameter of 0.6-0.8 mm, and the secondary winding should contain 57-58 turns of wire 0.3-0.32 mm. This is for straightening with doubling, see below. For “pure” 220 V - 230-235 turns of wire 0.2-0.25. In this case, when replacing KT814 with KT818, this inverter will deliver power up to 25-30 W, which is enough for 3-4 LED lamps. When replacing KT814 with KT626, the load power will be approx. 15 W, but the efficiency will increase. In both cases, the key radiator is from 50 square meters. cm.

At pos. Figure 2 shows a diagram of the “antediluvian” converter 12-220 with separate feedback windings. It's not that archaic. First, the output voltage under load is trapezoidal with rounded fractures and no spikes. It's even better than a modified sine wave. Secondly, this converter can be designed without any modifications in the circuit for a power of up to 300-350 W and a frequency of 50 Hz, then a rectifier is not needed, you just need to install VT1 and VT2 on radiators from 250 kW. see each. Thirdly, it protects the battery: when overloaded, the conversion frequency drops, the output power decreases, and if you load it even more, the generation stops. That is, to avoid over-discharging the battery, no automation is required.

The procedure for calculating this inverter is given in the scan in Fig.:

The key quantities in it are the conversion frequency and the working induction in the magnetic circuit. The conversion frequency is selected based on the material of the available core and the required power:

This “omnivorousness” of ferrite is explained by the fact that its hysteresis loop is rectangular and the working induction is equal to the saturation induction. The decrease in the calculated values ​​of induction in steel magnetic cores compared to typical values ​​is caused by a sharp increase in switching losses of non-sinusoidal currents as it increases. Therefore from the core power transformer of an old 270 W “coffin” TV in this 50 Hz converter it will be possible to remove no more than 100-120 W. But - without fish, there is cancer in fish.

Note: If you have a steel magnetic core with a deliberately oversized cross-section, do not squeeze the power out of it! Let the induction be better - the efficiency of the converter will increase, and the shape of the output voltage will improve.

Straightening

It is better to rectify the output voltage of these inverters using a circuit with parallel voltage doubling (item 3 in the figure with diagrams): the components for it will cost less, and the power losses on a non-sinusoidal current will be less than in a bridge. Capacitors should be taken “power”, designed for large reactive power(designated PE or W). If you put “sound” ones without these letters, they may simply explode.

50 Hz? It's very simple!

A simple 50 Hz inverter (item 4 in the figure above with diagrams) is an interesting design. For some types of standard power transformers, the intrinsic time constant is close to 10 ms, i.e. half a period of 50 Hz. By adjusting it with timing resistors, which will also act as limiters of the switch control current, you can immediately obtain a smoothed 50 Hz square wave at the output without complex formation circuits. Transformers TP, TPP, TN for 50-120 W are suitable, but not just any kind. You may have to change the resistor values ​​and/or connect 1-22 nF capacitors in parallel with them. If the conversion frequency is still far from 50 Hz, it is useless to disassemble and rewind the transformer: the magnetic circuit glued with ferromagnetic glue will fluff up, and the parameters of the transformer will deteriorate sharply.

This inverter is a weekend dacha converter. It will not drain the car battery for the same reasons as the previous one. But it’s enough to illuminate a house with a veranda LED lamps and a TV or vibration pump in the well. The conversion frequency of the adjusted inverter when the load current changes from 0 to maximum does not go beyond the technical norms for power supply networks.

The windings of the original transformer are routed like this. In typical power transformers, there is an even number of secondary windings for 12 or 6 V. Two of them are “set aside”, and the rest are soldered in parallel into groups of an equal number of windings in each. Next, the groups are connected in series so that you get 2 half-windings of 12 V each, this will be a low-voltage (primary) winding with a midpoint. Of the remaining low-voltage windings, one is connected in series with the 220 V mains winding; this will be the step-up winding. An additive is needed because... The voltage drop across switches made of bipolar composite transistors, together with its losses in the transformer, can reach 2.5-3 V, and the output voltage will be underestimated. Additional winding will bring it up to normal.

DC from the chip

The efficiency of the described converters does not exceed 0.8, and the frequency varies noticeably depending on the load current. The maximum load power is less than 400 W, so it’s time to think about modern circuit solutions.

The circuit of a simple converter 12 V DC/220 V DC for 500-600 W is shown in the figure:

Its main purpose is to power hand-held power tools. Such a load is not demanding on the quality of the supplied voltage, so the keys are taken cheaper; IFRZ46, 48 are also suitable. The transformer is wound on ferrite with a cross-section of 2-2.5 square meters. cm; A power transformer core from a computer UPS is suitable. Primary winding - 2x5 turns of a bundle of 5-6 winding wires with a copper diameter of 0.7-0.8 mm (see below); secondary - 80 turns of the same wire. No adjustment is required, but there is no monitoring of battery discharge, so during operation you need to attach a multimeter to its terminals and do not forget to look at it (the same applies to all other homemade voltage inverters). If the voltage drops to 10.8 V (1.8 V per cell) - stop, turn off! It dropped to 1.75 V per cell (10.5 V for the entire battery) - this is already sulfation!

How to wind a transformer on a ring

The quality characteristics of the inverter, in particular its efficiency, are quite strongly influenced by the stray field of its transformer. The fundamental solution to reduce it has long been known: the primary winding, which “pumps” the magnetic circuit with energy, is placed close to it; secondary ones above it in descending order of their power. But technology is such a thing that theoretical principles in specific designs sometimes have to be turned inside out. One of Murphy's laws states approx. so: if the piece of hardware still doesn’t want to work as it should, try doing the opposite in it. This fully applies to a high-frequency transformer on a ferrite ring magnetic core with windings made of relatively thick rigid wire. Wind the voltage converter transformer on a ferrite ring like this:

• The magnetic circuit is insulated and, using a winding shuttle, a secondary step-up winding is wound onto it, laying the turns as tightly as possible, pos. 1 in Fig.:

• Tightly wrap the secondary part with tape, pos. 2.
• Prepare 2 identical wire harnesses for the primary winding: wind the number of turns of half the low-voltage winding with a thin unusable wire, remove it, measure the length, cut off the required number of winding wire segments with a reserve and assemble them into bundles.
• Additionally, the secondary winding is insulated until a relatively flat surface is obtained.
• Wind the “primary” with 2 bundles at once, arranging the wires of the bundles with tape and evenly distributing the turns over the core, pos. 3.
• Call the ends of the bundles and connect the beginning of one to the end of the other, this will be the middle point of the winding.

Note: on electric circuit diagrams the beginnings of the windings, if relevant, are indicated by a dot.

50 Hz smoothed

A modified sine wave from a PWM controller is not the only way to get 50 Hz at the inverter output, suitable for connecting any household electricity consumers, and it wouldn’t hurt to “smooth” that too. The simplest of them is the good old iron transformer; it “irons” well due to its electrical inertia. True, it is becoming increasingly difficult to find a magnetic core rated at more than 500 W. Such an isolation transformer is switched on to the low-voltage output of the inverter, and a load is connected to its step-up winding. By the way, most computer UPSs are built according to this scheme, so they are quite suitable for this purpose. If you wind the transformer yourself, then it is calculated similarly to the power one, but with a trace. features:

• The initially determined value of the working induction is divided by 1.1 and applied in all further calculations. This is necessary in order to take into account the so-called. non-sinusoidal voltage shape factor Kf; for a sinusoid Kf=1.
• The step-up winding is first calculated as a 220 V mains winding for a given power (or determined by the parameters of the magnetic circuit and the value of the working induction). Then the found number of turns is multiplied by 1.08 for powers up to 150 W, by 1.05 for powers of 150-400 W and by 1.02 for powers of 400-1300 W.
• Half of the low-voltage winding is calculated as a secondary voltage of 14.5 V for bipolar switches or with a built-in channel and 13.2 V for switches with an induced channel.

Examples of circuit solutions for 12-200 V 50 Hz converters with an isolation transformer are shown in the figure:

On the one on the left, the keys are controlled by the so-called master oscillator. a “soft” multivibrator, it already generates a meander in blocked fronts and smoothed fractures, so no additional smoothing measures are required. The instability of the frequency of a soft multivibrator is higher than that of a regular one, so to adjust it you need a potentiometer P. With keys on the KT827, you can remove power up to 200 W (radiators from 200 sq. cm without blowing). Keys on KP904 from old junk or IRFZ44 allow you to increase it to 350 W; single on IRF3205 up to 600 W, and paired on them up to 1000 W.

An inverter 12-220 V 50 Hz with a master oscillator on TL494 (on the right in the figure) maintains the frequency firmly in all conceivable operating conditions. To more effectively smooth out a pseudosinusoid, the so-called phenomenon is used. indifferent resonance, in which the phase relationships of currents and voltages in the oscillatory circuit become the same as with acute resonance, but their amplitudes do not increase noticeably. Technically, this can be solved simply: a smoothing capacitor is connected to the boost winding, the capacitance value of which is selected according to the best shape of the current (not voltage!) under load. To control the shape of the current, a 0.1-0.5 Ohm resistor is connected to the load circuit at a power of 0.03-0.1 of the rated value, to which an oscilloscope with a closed input is connected. The smoothing capacitance does not reduce the efficiency of the inverter, but can be used for tuning computer programs oscilloscope low-frequency simulation is not possible, because the input of the sound card they use is not designed for an amplitude of 220x1.4 = 310 V! The keys and powers are the same as before. case.

A more advanced 12-200 V 50 Hz converter circuit is shown in Fig.:

It uses complex compound keys. To improve the quality of the output voltage, it uses the fact that the emitter of planar epitaxial bipolar transistors is heavily doped stronger than the base and collector. When TL494 applies a closing potential, for example, to the base of VT3, its collector current will stop, but due to the resorption of the emitter space charge, it will slow down the closing of T1 and voltage surges from the self-induction emf Tr will be absorbed by circuits L1 and R11C5; they will “tilt” the fronts more. The output power of the inverter is determined by the overall power Tr, but not more than 600 W, because It is impossible to use paired powerful switches in this circuit - the spread in the value of the gate charge of MOSFET transistors is quite significant and the switching of the switches will be unclear, which is why the shape of the output voltage may even worsen.

Choke L1 is 5-6 turns of wire with a diameter of 2.4 mm on copper, wound on a piece of ferrite rod with a diameter of 8-10 m and a length of 30-40 mm with a pitch of 3.5-4 mm. The throttle magnetic circuit must not be short-circuited! Setting up a circuit is quite a painstaking task and requires a lot of experience: you need to select L1, R11 and C5 according to the best shape of the output current under load, as in the previous one. case. But Hi-Fi, powered from this converter, remains “hi-fi” to the most demanding ears.

Is it possible without a transformer?

Already the winding wire for a powerful 50 Hz transformer will cost a pretty penny. Magnetic cores from “coffin” transformers up to 270 W overall are more or less available, but in an inverter you cannot squeeze more than 120-150 W out of this, and the efficiency will be 0.7 at best, because “coffin” magnetic cores are wound from a thick tape, the eddy current losses in which are large at non-sinusoidal voltage on the windings. Finding an SL magnetic core made of a thin strip capable of delivering more than 350 W at an induction of 0.7 Tesla is generally problematic, it will be expensive, and the entire converter will be huge and heavy-lifting. UPS transformers are not designed for frequent operation in long-term mode - they heat up and their magnetic circuits in inverters degrade quite quickly - the magnetic properties deteriorate greatly, the power of the converter drops. Is there a way out?

Yes, and this solution is often used in branded converters. This is an electric bridge made of keys on high-voltage power field effect transistors with a breakdown voltage of 400 V and a drain current of more than 5 A. Suitable from the primary circuits of computer UPSs, and from old trash - KP904, etc.

The bridge is powered by a constant 220 V DC from a simple 12-220 inverter with rectification. The arms of the bridge open in pairs, crosswise, alternately, and the current in the load included in the diagonal of the bridge changes direction; The control circuits of all keys are galvanically separated. IN industrial structures the keys are controlled by special IC with optocoupler isolation, but in amateur conditions both can be replaced with an additional low-power inverter 12 V DC - 12 V 50 Hz, powered by a small transformer on hardware, see fig. The magnetic core for it can be taken from a Chinese market low-power power transformer. Due to its electrical inertia, the quality of the output voltage is even better than a modified sine wave.

From a AA battery, but then I thought that they would have to be changed too. I wanted to power the converter from batteries. This is a larger capacity compared to standard crowns, and the costs are lower.

I found a diagram online and assembled the device. Impressed. Without load it consumes about 0.2 mA, and the efficiency reaches, as it was written there, up to 94%. I tried to power the device from 1.5 V - I didn’t like the output voltage, and I was too lazy to rewind the transformer. Therefore, I took a battery from a mobile phone, it is flat, the capacity for a multimeter is good, and the shape is also good.

I did not install 1000 uF capacitors; I installed ceramics and 120 nF film in parallel. They didn't have much impact on the work. The transistor was taken from an old Soviet one. Here you need to install germanium transistors, then the minimum supply voltage will decrease. The source says that work starts at 0.4 volts and continues right up to 0.2 volts. It turns out that you can power the device even from potatoes, lemon and other things.

I installed a 10 V zener diode in parallel with the output to protect the multimeter from power surges. The transformer was wound on a ferrite ring. Winding data: 10 turns of 0.5 mm and 50 turns of 0.1 mm wire - I tried turn to turn, but it turned out as always. If the converter does not work, we swap the secondary outputs, which is what I did after the first start-up, even though the circuit produced a voltage slightly higher than the input voltage.

Capacitor C1, 80 nF, can be changed from 1 to 100 nF, it affects the output voltage and, accordingly, the efficiency.

Video of converter operation

It is clear that this simplest voltage converter can be used not only to obtain 9 volts at the output, and not only to power a multimeter - its scope of application is very wide, including for LED flashlights. Author of the design BFG5000.

Discuss the article THE SIMPLE VOLTAGE CONVERTER