An inverter with a power supply below 12 volts. Power supply on mains transformer

Of course, this device is extremely primitive and is more like a warm-up for the mind. For more stable operation, it needs to be supplemented with a simple control circuit that maintains the shutdown threshold much more accurately:

Read also: DIY 220 V electric air compressor

Threshold adjustment is carried out by selecting the resistor R3.

We suggest watching a video on the topic

Inverter Fault Detection

The listed simple circuits have two most common faults - either there is no voltage at the output of the transformer, or it is too low.

Understanding how to make 220 from 12 volts allows you to independently make a converter to obtain a standard mains voltage.

To make a device with a high-quality sinusoid at the output, all electrical engineering requirements must be taken into account.

When is a voltage converter needed?

In a domestic environment, this device ensures the smooth operation of devices such as a gas boiler, refrigerator, TV and other complex electrical equipment if it is impossible to use a centralized supply of electrical energy at 220 V.

Features of the influence of parameters on electrical devices:

• the amplitude of the applied voltage affects the engine speed, and the gross rotation speed in the asynchronous type motor directly depends on the indicators of the supply network;
• household appliances of the heating type operate at operating current rates proportional to the voltage level, but a significant part of such products are not designed for operation in non-standard voltage conditions;
• household electrical appliances often need a voltage that is different from the network parameters with strictly defined, stable amplitude indicators, therefore, the normal operation of some devices is possible only when a voltage converter is used.

12-220 V voltage boost converter circuit

Especially often the device is used in households with an autonomous heating system, where imported gas equipment with electronic control and monitoring is installed as a heating device. The performance of such devices depends entirely on the availability of an uninterrupted voltage of 220 V and 50 Hz with a correct sine wave.

The scope of the voltage converter is very wide, including field conditions, operation of yachts and cars, summer cottages without mains power supply, and so on.

Electricity meters are different in the number of phases, tariffs and other parameters. - read the recommendations of experts.

The principle of operation of LED lamps and tips for repairing faulty bulbs with your own hands are described.

You can familiarize yourself with the rules for installing electricity meters.

Varieties of converters 12 to 220 volts

Inverters are devices that allow you to convert direct current values, including 12 V, into alternating current with or without a change in voltage level. As a rule, such devices are generators of periodic voltage close to the shape of a sinusoid.

All currently manufactured DC / DC voltage converters can be represented:

• voltage regulators;
• voltage level converters;
• linear stabilizers.

Homemade converter

Purely theoretically, any current values \u200b\u200bcan be obtained at the output, adjustable from zero point to maximum values. Most often, a standard battery is used as a 12V DC source. Converters existing today differ in several parameters.

Depending on the type of the resulting sinusoid:

• Devices created with a sinusoid of a normal or constant form are characterized by functioning without deviations and adherence to all operating parameters with a high level of accuracy. Such devices are used to connect any electrical appliances that operate under 220 V.
• Devices created with a modified sinusoid are characterized by slight deviations in the voltage value. Such features are not capable of negatively impacting the performance of standard household appliances. However, such equipment is not used to connect devices belonging to the category of complex measuring or medical equipment.

Depending on the power indicators:

• converters with a power of up to 100 W are not designed for too high loads, therefore they are the best option for powering a charger for a simple household appliance;
• converters with power ranging from 100 W to 1.5 kW. This type of device is mainly used to power simple appliances connected to a household power supply;
• converters with a power of more than 1.5 kW allow you to supply power to such rather powerful household appliances, including a microwave oven, irons and large multicooker.

• compact-type devices, characterized by unpretentiousness to the power source, and operating under voltage conditions of 12-50 V;
• stationary type devices with a pure sinus and issuing low voltage 12-36V;
• portable type automotive devices characterized by operation in certain devices.

When choosing a model of a voltage indicator converter, it is recommended to purchase a device that has a certain power reserve.

Voltage converters from 12 to 220 V output standard indicators that correspond to the main characteristics of a home electrical network, therefore they are compatible with almost any household appliances.

Output voltage waveform

Electronic devices in the form of converters or inverters differ depending on the waveform in the output voltage:

• Modified variant, represented by a smooth sinusoid, modified to a trapezoidal, rectangular or even triangular shape. Such devices are characterized by a limited area of \u200b\u200buse and are suitable for consumers represented by lighting and heating devices. In order to operate equipment with an inductive load, the inverter power must have a significant headroom due to the high inrush current.
• A variant of the "pure" sinusoid are used in power supply of any type of load, and also allow to ensure reliable and stable operation of highly sensitive equipment. A significant part of inverters of this type have charger built-in type, due to which it is used as an uninterruptible power supply.
• Hybrid option suitable for providing electrical circuits designed to support multiple power supplies. The device has the ability to use a certain type of priority energy source or use several options at once in order to charge the battery.

Self-made voltage converter 12-220

When choosing a device, you should pay attention to the availability of alternative energy sources, which allows you to quickly recoup the purchased, rather expensive equipment.

The purchased device must have optimal rated power, protection against overheating and short circuits, a passive and active cooling system, as well as sufficient efficiency for functioning.

Transformer devices

Transformer-type converters are devices based on two winding systems. Devices of this type are characterized by a change in inductive coupling when exposed to the input displacement.

In this case, one winding system is connected to an alternating current source with voltage, and the second winding, in this case, is used as an output.

Automotive voltage converter 12-220 V

Any transformer is designed to perform such basic functions as measurement and protection. Especially in demand are modern transformer devices of the converting type, designed to perform a circuit for doubling or tripling the frequency of the supply voltage.

In the industrial area and in everyday life, modern devices that allow controlling the input / output current and transforming variable indicators into constant parameters, as well as those capable of distributing voltage, are in great demand.

Construction of a conventional step-up voltage converter from 12 to 220

Nevertheless, you need to take into account some of the disadvantages of such partings. The main disadvantages of voltage converters are represented by the susceptibility of many models of such devices to high humidity indicators, often very impressive in size and relatively high cost, therefore, the choice of an inverter must be approached very carefully.

Video on the topic

When using low-power household appliances, there is often a need for a voltage converter from 12 to 220 volts. This can be a laptop, a charger for a mobile phone or tablet, or even a TV set with LED elements.

When is a voltage converter needed?

1. Long-term failure of centralized power supply.
2. Emergency power supply to the gas boiler electronics.
3. Lack of a 220 volt household network (remote garden area, garage cooperative).
4. Car.
5. Tourist parking (if possible, take a 12 volt battery with you).

In all these cases, it is enough to have a charged battery, and you will be able to fully use the mains electrical equipment.

note

Important! The power consumption of the device should not exceed several hundred watts. More powerful devices will quickly drain the battery used as a donor.

For the sake of fairness, we note that for use in a car, there are power supplies and chargers that are connected to the 12 volt on-board network. They are made in the form of a connector connected to the cigarette lighter socket.

However, if you have multiple gadgets, you will have to splurge on buying the same number of charges. And having one converter from 12 to 220 - you will provide complete versatility of connection.

There is a wide range of off-the-shelf converters on sale. The power ranges from 150 W to several kilowatts. Of course, for each consumer power, it is necessary to select the appropriate battery.

It is also necessary to carefully read the technical specifications - often, for advertising purposes, manufacturers indicate on the packaging the peak power that the converter can withstand only a few seconds. Working power is typically 25% - 30% lower.

Varieties of converters 12 to 220 volts

For the right choice, check out the main types of voltage converters on the electrical goods market:

Output voltage waveform

Devices are classified into pure sine and modified sine. The difference in waveform can be seen in the illustration.

Inverter 12V / 220V is a necessary thing on the farm. Sometimes it is simply necessary: \u200b\u200bthe network, for example, disappeared, but the phone is discharged and there is meat in the refrigerator. Demand determines the offer: for ready-made models for 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 nowadays is an option available to everyone who knows how to solder: assembling it from a ready-made set of components will cost three to four times cheaper + a little work and metal from scrap at hand. If there is for automobile rechargeable batteries (AKB), you can meet in general in 300-500 rubles. And if you also have the initial radio amateur skills, then, rummaging through the storehouses, 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: globally

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

1. Make a ready-made block with Avito, Ebay or AliExpress in a case with a heat sink. Searched by request "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. Collect the same from the set: printed circuit board + "scatter" component. It is purchased in the same place, but diy is added to the request, which means for self-assembly. The price is still approx. 1.5 times lower. You need initial skills in electronics: use a multimeter, knowledge of the wiring (pinouts) of the outputs 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 which current of which section the wires are needed;
3. Adapt a computer uninterruptible power supply (UPS, UPS) for the inverter. A used UPS without a standard battery can be found for 300-500 rubles. You don't need any skills - the auto battery is simply connected to the UPS. But you will have to charge it separately, see also below;
4. Choose a conversion method, a scheme (see below) in accordance with your needs and the availability of parts, calculate and assemble completely independently. Perhaps completely for nothing, but in addition to basic electronic skills, you will need the ability to use some special measuring instruments (also see below) and make the simplest engineering calculations.

From a ready-made module

Assembly methods according to PP. 1 and 2 are actually not that simple. The cases of ready-made factory inverters also serve as heat sinks for powerful transistor switches inside. If you take a "semi-finished product" or "scatter", then there will be no case for them: with the current cost of electronics, manual labor and non-ferrous metals, the difference in prices is explained 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 place of installation of the keys should be from 4 mm, and the area for each key should be from 50 sq. see for each kW of output power; with blowing from a computer fan-cooler for 12 V 110-130 mA - from 30 sq. cm * kW * key.

For example, the set (module) contains 2 keys (you can see them, 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 is needed 1.5 kW. This means that you need a radiator of 150 sq. see. In addition to him, there are also installation kits for keys: insulating heat-conducting gaskets and accessories for fastening screws - insulating cups and washers. If the module is with thermal protection (there will be some kind of wick - a thermal sensor) sticking out between the keys, then a little thermal paste to glue it to the radiator. Wires - of course, see below.

From UPS (UPS)

An inverter 12V DC / 220V AC 50 Hz, to which you can connect any devices within the permissible power, is made from a computer UPS quite simply: standard wires to "your" battery are replaced with long ones with clamps for the car battery terminals. The cross-section of the wires 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 may arise - with it, and it is more expensive and more necessary than the converter.

The UPS also uses lead-acid batteries. Today it is the only widely available secondary chemical power source capable of regularly delivering large currents (extracurrents) 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, not widely circulated, and their resource by household standards is negligible - approx. 150 cycles.

The discharge of acidic batteries is clearly monitored by the voltage on the bank, and the UPS controller will not allow the "foreign" battery to over discharge. But in standard UPS batteries, the electrolyte is gel, and in car batteries, it is liquid. The charge modes in both cases are significantly different: currents such as through a liquid cannot be passed through the gel, and in a liquid electrolyte with a too low charge current, the mobility of ions will be low and they will not all return to their places in the electrodes. As a result, the UPS will chronically undercharge the car battery, it will soon sulfate and become completely unusable. Therefore, a battery charger is needed in the kit for the inverter on the UPS. You can do it yourself, but that's another topic.

Battery and power

The suitability of the converter for a particular purpose also depends on the battery. The step-up voltage inverter does not take energy for consumers from the "dark matter" of the universe, black holes, the spirit of the saint, or from somewhere else just like that. Only - from the battery. And from it, he will take the power given to consumers, divided by the efficiency of the converter itself.

If you see on the case of a branded inverter "6800W" or more - believe your eyes. Modern electronics makes it possible to fit more powerful devices in the volume of a cigarette pack. But, let's say we need a load power of 1000 W, and we have a conventional 12 V 60 A / h car battery at our disposal. Typical inverter efficiency is 0.8. This means that he will take approx. 100 A. Such a current also requires wires with a cross section of 5 sq. mm (see above), but this is not the main thing here.

Car enthusiasts know: drove the starter for 20 minutes - buy a new battery. True, the new machines have time limits for its operation, so they may not know. And not everyone knows for sure that the starter of a passenger car, after spinning, 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 discharge of the battery, then ours will completely drain in 15 minutes. So choose or design your converter based on the capabilities of the battery on hand.

Note: This implies a huge advantage of 12/220 V converters based on computer UPSs - their controller will not let the battery 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. 120W, 230W and 400W resp. For 10 min. load (for example, for powering an electric tool), it can be increased by 2.5 times, but after that the ABK must rest for at least 20 minutes.

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

What will happen at the exit?

With rare exceptions (see below), voltage converters for the sake of reducing the mass and dimensions of the device operate at increased frequencies from hundreds of Hz to units and tens of kHz. A current of such a frequency will not be accepted by any consumer, and the losses of its energy in ordinary wiring will be enormous. Therefore, inverters 12-200 are built for the output voltage trace. species:

• Constant rectified 220 V (220V AC). Suitable for powering telephone chargers, most power sources (IP) tablets, incandescent lamps, fluorescent housekeepers and LEDs. For power from 150-250 W, they are perfect for hand-held power tools: the power consumption at direct current decreases slightly, and the torque increases. Not suitable for switching power supplies (UPS) TVs, computers, laptops, microwaves, etc. with a power of more than 40-50 W: in these there is necessarily a so-called. a starting node, for the normal operation of which the mains voltage must periodically pass through zero. Unsuitable and dangerous for devices with power transformers on iron and AC electric motors: stationary power tools, refrigerators, air conditioners, most of Hi-Fi audio, food processors, some vacuum cleaners, coffee makers, coffee grinders and microwave ovens (for the latter, due to the presence of a rotation motor table).
• Modified sinusoidal (see below) - suitable for any consumer, except Hi-Fi audio from UPS, other devices with 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.

Sinus or pseudosine?

In order to increase efficiency, voltage conversion is carried out not only at higher frequencies, but also by multipolar pulses. However, it is impossible to supply power to many consumer devices with a sequence of heteropolar rectangular pulses (the so-called meander): large surges at the fronts of the meander with even a little reactive load will lead to large energy losses and can cause a consumer malfunction. However, it is also impossible to design a converter for sinusodal current - the efficiency does 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. 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 tightened (the meander fronts on the screen of the cathode-ray oscilloscope are often not visible at all). Due to this, consumers with iron-based transformers or noticeable reactivity (asynchronous electric motors) "understand" the pseudo-sinusoid "as real" and work as if nothing had happened; Hi-Fi audio with a network transformer on the hardware can be powered by a modified sine wave. In addition, the modified sinusoid can be smoothed out to "almost real" by fairly simple methods, the differences from which are barely noticeable on the oscilloscope on the oscilloscope; converters of the "Pure sine" type are not much more expensive than conventional ones, on the right in fig.

However, it is undesirable to start devices with capricious analog nodes and UPS from a modified sinusoid. The latter are highly undesirable. The fact is that the middle area of \u200b\u200bthe modified sinusoid is not pure zero voltage. The UPS startup unit from the modified sine wave does not work clearly and the entire UPS may not exit from startup mode to operating. The user sees it first as ugly glitches, and then smoke comes out of the device, as in a joke. Therefore, the devices in the UPS must be powered by Pure Sine inverters.

We make the inverter ourselves

So, it is still 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 norms for fluctuations in the frequency of the power supply network are 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" from the rated speed. The latter is very dangerous for refrigerators and air conditioners; they can fail irreparably due to depressurization. But there is no need to buy, rent or beg for a time accurate and multifunctional electronic frequency counter - we do not need its accuracy. Either an electromechanical resonant frequency meter (item 1 in the figure), or a pointer of any system, item. 2:

They are both inexpensive, sold on the Internet, and in large cities in special electrical 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 frequency of the network in the house - the counter does not respond to their connection to the network.

50 Hz from computer

In most cases, power supply of 220 V 50 Hz is required by consumers who are not particularly powerful, up to 250-350 W. Then the basis of the 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 sells it on the cheap. The power delivered to the load will be approx. 0.7 times 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 check on a load of incandescent lamps. Withstood 2 hours - it is capable of delivering such power for a long time. How to make an inverter 12V DC / 220V AC 50Hz 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 more power is needed. Then the choice of key elements becomes important: they must switch large currents with the least switching losses, be reliable and affordable. In this respect, bipolar transistors and thyristors in this field of application are surely a thing of the past.

The second revolution in the inverter business is associated with the emergence of powerful field-effect transistors ("field workers") so-called. vertical structure. However, they turned over all the power supply technology for low-power devices: it is becoming more and more difficult to find a transformer on iron in the "household".

The best high-power field workers for voltage converters are insulated gate and induced channel (MOSFET), eg. IFR3205, left in 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. MOSFET analogs with built-in channel, eg. IFRZ44, give lower efficiency, but are much cheaper. A couple of these or others allows you to bring the power in the load to approx. 600 watts; both can be paralleled without problems (on the right in the figure), which allows you to build inverters for power up to 3 kW.

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

TL494

The third element that made it possible to bring the voltage converters to their present 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 bipolar, which allows you to control pairs of keys. The reference conversion frequency is set by one RC circuit, the parameters of which can be changed over a wide range.

When the constant is enough

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

Video: single transistor boost converter

Already to power 2-3 LED bulbs, more power is needed. The efficiency of blocking generators when trying to "squeeze" it drops sharply, and one has 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 key, the self-induction EMF of one of the transformer windings is used together with a timing circuit. In the second, the step-up transformer itself is the frequency setting element due to its own time constant; its value is determined mainly by the phenomenon of self-induction. Therefore, those and other inverters are sometimes called self-induction converters. Their efficiency, as a rule, is not higher than 0.6-0.65, but, firstly, the circuit is simple and does not require adjustment. Secondly, the output voltage is trapezoidal rather than meander; "Demanding" consumers "understand" it as a modified sinusoid. The disadvantage is that field switches are practically inapplicable in such converters, because often fail from 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 failed 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 its photo (see the picture on the right) is not ferrite at all. It looks more like the old carbonyl, oxidized from the outside from time to 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 \u200b\u200b0.7-1.2 sq. cm. The primary winding should then contain 7 turns of wire with a diameter of 0.6-0.8 mm copper, and the secondary 57-58 turns of wire 0.3-0.32 mm. This is for straightening with doubling, see below. For "clean" 220 V - 230-235 turns of wire 0.2-0.25. In this case, this inverter, when replacing KT814 with KT818, will give 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 sq. cm.

On pos. 2 shows a diagram of an "antediluvian" converter 12-220 with separate feedback windings. It is not so archaic. First, the output voltage under load is a rounded trapezoid with no overshoot. It's even better than a modified sine wave. Secondly, this converter can be designed for power up to 300-350 W and a frequency of 50 Hz without any alterations in the circuit, then a rectifier is not needed, you just need to put VT1 and VT2 on radiators from 250 kV. see each. Thirdly, it protects the battery: when overloaded, the conversion frequency drops, the power delivered decreases, and if you load even more, the generation is disrupted. That is, to avoid over-discharge of the battery, no automation is required.

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

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

This "omnivorous" 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 comparison with the typical calculated values \u200b\u200bof induction in steel magnetic circuits is caused by a sharp increase in the switching losses of non-sinusoidal currents with its increase. Therefore, no more than 100-120 W can be removed from the core of the power transformer of the old 270 W "coffin" TV in this 50 Hz converter. But - there is no fish and cancer.

Note: if there is a steel magnetic circuit of a deliberately oversized section, do not squeeze power out of it! Let the induction be less 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 according to the scheme with parallel voltage doubling (item 3 in the figure with the diagrams): the components for it will cost less, and the power loss on non-sinusoidal current will be less than in the bridge one. Capacitors must be taken "power", designed for high reactive power (with the designation PE or W). If you put "sound" without these letters, they can simply explode.

50 Hz? It's very easy!

A simple 50 Hz inverter (pos. 4 in the figure above with diagrams) is an interesting design. Some types of typical power transformers have their own time constant close to 10 ms, i.e. half a period of 50 Hz. By correcting it with time-setting resistors, which will simultaneously be the limiters of the control current of the switches, it is possible to obtain at the output a smoothed 50 Hz square wave without complex shaping circuits. Transformers TP, TPP, VT for 50-120 W are suitable, but not all. It may be necessary to change the resistor values \u200b\u200band / or connect capacitors in parallel to them by 1-22 nF. If the conversion frequency is still far from 50 Hz, it is useless to disassemble and rewind the transformer: the magnetic core glued with ferromagnetic glue will fluff up, and the parameters of the transformer will deteriorate sharply.

This inverter is a weekend cottage converter. He will not plant the battery of the car for the same reasons as the previous one. But it's enough to light a house with a veranda lED lamps and a TV or vibrating pump in the well. The conversion frequency of an adjusted inverter when the load current changes from 0 to maximum does not go beyond the technical standard for power supply networks.

The windings of the original transformer are separated as follows. In typical power transformers, there is an even number of secondary windings for 12 or 6 V. Two of them are "deposited", and the rest are soldered in parallel into groups of an equal number of windings in each. Further, the groups are connected in series so that 2 half-windings of 12 V each are obtained, 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 a step-up winding. An additive to it is needed, because the voltage drop across the keys from 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 to normal.

DC from IC

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

A diagram of a simple converter 12 V DC / 220 V DC for 500-600 W is shown in Fig.:

Its main purpose is to power handheld 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 a ferrite with a cross section of 2-2.5 square meters. cm; the core of a power transformer from a computer UPS will do. 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 battery discharge control, 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 can) - stop, turn off! Has dropped to 1.75 V per can (10.5 V whole battery) - this is already sulfation!

How to wind a transformer on a ring

On the quality characteristics the inverter, in particular, its efficiency is rather strongly influenced by the stray field of its transformer. The principal solution for its reduction has long been known: the primary winding, which "pumps" the magnetic circuit with energy, is placed close to it; secondary above it in decreasing order of their power. But technology is such a thing that the theoretical principles in concrete constructions sometimes have to be turned inside out. One of Murphy's laws says approx. so: if the piece of iron doesn't want to work as it should, try to do the opposite in it. This fully applies to a high-frequency transformer on a ferrite ring magnetic core with windings of a relatively thick rigid wire. The transformer of the voltage converter is wound on the ferrite ring as follows:

• The magnetic core is isolated and, with the help of the winding shuttle, a secondary boost winding is wound on it, laying the turns as tightly as possible, pos. 1 in the figure:

• The "secondary" is tightly covered with tape, pos 2.
• Prepare 2 identical wire harnesses for the primary winding: wind the number of turns of half of the low-voltage winding with a thin unusable wire, remove it, measure the length, cut off the required number of sections of the winding wire with a margin and collect them into bundles.
• The secondary winding is additionally insulated until a relatively flat surface is obtained.
• They wind the "primary" with 2 bundles at once, placing the wires of the bundles with tape and evenly distributing the turns over the core, pos. 3.
• The ends of the harnesses are called out and the beginning of one is connected to the end of the other, this will be the middle point of the winding.

Note: on electric schematic diagrams the beginning of the windings, if it matters, 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 output of the inverter, suitable for connecting any household electricity consumers, and even that would not hurt to "smooth" it. The simplest of them is the good old transformer on iron, it “iron” well due to its electrical inertia. True, finding a magnetic core with more than 500 W is becoming increasingly difficult. Such an isolation transformer is switched on to the low-voltage output of the inverter, and the 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 such a 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 is used in all further calculations. So it is necessary to take into account the so-called. form factor of non-sinusoidal voltage Kf; sinusoid Kf \u003d 1.
• The step-up winding is calculated first as a mains winding for 220 V for a given power (or determined by the parameters of the magnetic circuit and the value of the operating induction). Then the found number of its turns is multiplied by 1.08 for power 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 secondary for a voltage of 14.5 V for bipolar keys or with a built-in channel and at 13.2 V for keys with an induced channel.

Examples of circuit solutions of converters 12-200 V 50 Hz with an isolating transformer are given in Fig.:

On the one on the left, the keys are controlled by a master oscillator on the so-called. A "soft" multivibrator, it already generates a meander with collapsed fronts and smoothed fractures, so no additional smoothing measures are required. The frequency instability of a soft multivibrator is higher than that of a conventional one, therefore a potentiometer P is needed to adjust it. Keys on KP904 from old trash or IRFZ44 allow 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 generator on the TL494 (on the right in the figure) keeps the frequency iron in all imaginable inconceivable operating conditions. For a more efficient smoothing of the pseudosine wave, 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 in acute resonance, but their amplitudes do not increase significantly. Technically, this can be solved simply: a smoothing capacitor is connected to the step-up winding, the capacitance value of which is selected according to the best form of current (not voltage!) Under load. To control the current shape, a 0.1-0.5 Ohm resistor is included in the load circuit for a power of 0.03-0.1 of the nominal, to which an oscilloscope with a closed input is connected. The smoothing capacitance does not reduce the efficiency of the inverter, but it is impossible to use the computer programs to simulate the low frequency oscilloscope for tuning, since the input of the sound card used in them is not designed for an amplitude of 220x1.4 \u003d 310 V! Keys and powers are the same as before. case.

A more perfect circuit of the 12-200 V 50 Hz converter is given in Fig.:

It uses complex composite keys. To improve the quality of the output voltage, it uses the fact that the emitter of planar-epitaxial bipolar transistors is doped much more strongly than the base and collector. When TL494 gives a closing potential, for example, to the base of VT3, its collector current will stop, but due to the resorption of the space charge of the emitter, it will slow down the blocking of T1 and the voltage surges from the EMF of self-induction Tr will be absorbed by the 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. it is impossible to use paired powerful keys in this circuit - the spread in the magnitude of the gate charge of the MOSFET transistors is quite significant and the switching of the keys will be fuzzy, 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 in 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 inductor magnetic circuit must not be shorted! Establishing the circuit is a rather painstaking business and requires a lot of experience: you need to select L1, R11 and C5 according to the best form of the output current under load, as in the previous. case. On the other hand, the Hi-Fi powered by this converter remains “high-fi” for the most discerning ear.

Is it possible without a transformer?

Already a winding wire for a powerful 50 Hz transformer will cost a pretty penny. More or less magnetic cores are available from "coffin" transformers up to 270 W overall, 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, in which the eddy current losses are large at non-sinusoidal voltage on the windings. It is generally problematic to find an SHL magnetic core made of a thin tape capable of delivering more than 350 W at an induction of 0.7 T, it will be expensive, and the entire converter will turn out to be huge and unmanageable. UPS transformers are not designed for frequent operation in a long-term mode - they heat up and their magnetic circuits in inverters degrade pretty soon - 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 junk - KP904, etc.

The bridge is powered by a constant 220 V DC from a simple 12-220 inverter with rectification. The shoulders of the bridge open in pairs in a crosswise direction, 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 from specials. IC with optocoupler decoupling, but in amateur conditions, both can be replaced with an additional low-power inverter 12 V DC - 12 V 50 Hz, operating on a small transformer on iron, see fig. The magnetic circuit for it can be taken from a Chinese bazaar low-power power transformer. Due to its electrical inertia, the output voltage quality is even better than the modified sine wave.