A simple flyback voltage converter. Half-bridge inverter in the charger. Diagram, description Charger on a field inverter diagram

The device consists of:
- network interference filter S8-T2-S12;
- pulse generator with counter on a digital chip DD1;
- push-pull semi bridge amplifier on field-effect transistors VT1,VT2;
- parametric power supply VD1-R10-C3-C4;
- output voltage stabilization circuits with optocoupler isolation of primary and secondary voltages (on VU1) and error signal amplifier (on a parallel stabilizer DA1);
- output voltage rectifier on diode assembly VD6;
- output filter L1-C7-C11.

Resistors R7 and R8 provide protection for field-effect transistor gates from excess charging currents of input capacitors. Fast diodes VD3 and VD4, placed parallel to the drain-source channels of transistors VT1 and VT2, protect channels from pulse currents reverse polarity appearing in the windings of transformer T1. Capacitor C6 between the drains of the transistors speeds up their switching. Capacitors C9 and C10 reduce the degree of interference when switching diodes of the rectifier bridge VD6.
Electronic protection of the device is implemented via a negative feedback circuit with the main amplifier on a parallel stabilizer DA1, loaded with an optocoupler VU1. When the output voltage is within normal limits, the parallel stabilizer DA1 covered, and the optocoupler LED VU1 open. The optocoupler transistor in the open state shunts the input R1 DD1, which allows the operation of the chip counters DD1.
An increase in the output voltage causes an increase in the level at control electrode 1 DA1. the parallel regulator opens and short-circuits the optocoupler LED VU1, it turns off. Phototransistor VU1 closes, input voltage R1 DD1 increases, which prevents the counter from operating. Resumption of work DD1 occurs when the output voltage drops to the set value
of great significance. In this way, the device is protected from overload and the output voltage is stabilized.
In the circuit, you can use factory transformers from push-pull converters of computer power supplies. Transformer T1 (159 W) is made on a K40x25x11 core. The primary winding contains 2 x35 turns of wire PEV 00.62 mm, secondary - 2 x7 turns of a harness of 4 MGTF wires with a cross section of 0.31 mm2. Throttle L1 made on a ring core K12x5x5 from

Flyback current converters - inverters consist of a powerful pulse commutator with a period equal to the amount open and closed states. Unlike push-pull converter they have fewer radio components, stabilization of the operating mode is carried out by optoelectronic feedback from the output voltage circuits to the generator control input, with a change in the duty cycle of the pulse - pulse-width conversion of the control signal.

Characteristic
Mains supply voltage, V__180-240
Output power, W______ 100
Output voltage, V______13.8
Output current max, A ________10
Generator frequency, kHz_____36
Weight, g_______________________360
Dimensions, mm___________120x70x60
Battery capacity, A*h__25-100

Adjustment of the output voltage of the converter - manual or automatic. The high-frequency transformers of the converter are implemented on ferrite cores.
The power of converters depends on the supply voltage, conversion frequency and magnetic properties of the transformer.
Using a field-effect transistor as a switch reduces control signal losses.
The current consumed by the primary winding of transformer T1 contains a rectangular component caused by the transfer of energy to the load, and a triangular component associated with the magnetization of the magnetic wire material.
The processes of storing energy and transferring it to the load in flyback converters are clearly separated. The battery charge voltage stabilization circuit uses pulse-frequency conversion of the error signal into a change in the output voltage at the load. The comparison circuit represents the input of external influence (modification) on the control voltage point of the inverter generator. Using this pin allows you to change its level to obtain modifications to the circuit. As the voltage increases, the duration of the pulses at the gate of the power switch decreases, and, consequently, the time the switch transistor remains in the open state decreases. The voltage on the secondary windings of the transformer also decreases and the secondary voltage of the inverter stabilizes. The charge current is regulated by pulse-width changes in the generator pulse duration at a constant frequency. The range of adjustment of the pulse duty cycle depends on the ratio of the resistance of the charge current regulator resistors. The inverter undergoes triple voltage conversion. AC voltage The electrical network is rectified by a powerful diode bridge and converted by an inverter into high-frequency voltage, which is supplied through a transformer, after rectification, to the load.
The accumulation of energy and its transfer to the load are separated in time, the maximum collector current of the key transistor does not depend on the load current.

Structure schematic diagram
The circuit of a single-cycle pulse-width converter (Fig. 1) includes: a pulse generator on an analog timer DA1 with a pulse-width load current regulator R1, a power switch on a field-effect transistor VT1 with external circuits for protection against switching interference, circuits for protection against overvoltage on the load with galvanic separation of high and low voltage circuits by optocoupler DA3, circuits protecting the field-effect transistor from exceeding switching currents on an analog voltage stabilizer parallel type DA2, network rectifier with limiting the inrush currents of the filter capacitor charge and limiting impulse noise.

Description of the operation of circuit elements
The rectangular pulse generator is made on an analog timer DA1. The microcircuit includes: two comparators, an internal trigger, an output amplifier to increase the load capacity, and an open-collector key discharge transistor. The generation frequency is set by an external RC circuit. The circuit provides an option for adjusting the duty cycle of pulses at a constant frequency.
The comparators switch the internal trigger when the threshold voltage level on capacitor C2 is reached at 1/3 and 2/3 Un.
Timer output 4 DA1 - reset input, used to return output 3 DA1 to zero state, regardless of the state of other inputs, not used in this circuit.
Pin 5 DA1 - control voltage pin, allows direct access to the divider point of the upper comparator. The circuit is used to obtain modifications of the rectangular pulse generation mode in order to stabilize the output voltage.
Pin 7 of DA1 is connected to the internal discharge transistor of the analog timer and is used to discharge the internal capacitance of the field-effect transistor VT1. affecting the locking speed.
The voltage inverter consists of a powerful key transistor VT1 and transformer T1. To protect the transistor from breakdown by pulsed currents and voltages arising during the conversion process, the transistor and transformer are “tied together” with diode-resistor-capacitor circuits.
Exceeding the voltage level on resistor R10 of the source circuit additionally leads to the opening of the parallel stabilizer DA2 and shunting of the transistor gate during overloads.
The transformer in the inverter is factory-made, from outdated computer power supplies. The transformer is selected based on the required overall power, which is equal to the sum of the power of all loads.
Formulas for calculating the cross-section of the rod and the number of turns of the windings can be taken from. The difficulty is not in the calculations, but in the lack of appropriate ferrite and dimensions; it was not possible to disassemble and rewind the factory transformer without breaking the ferrite. The number of turns and their cross-section practically fits the calculations. With a load current of 10 A and a secondary winding voltage at no-load of at least 18 V, 250 W transformers with a window area of ​​15 mm2 and a core of about 10 mm2 are suitable. The gap in such transformers consists of a thin layer of glue, that is, it is practically absent, and its introduction, due to a decrease in magnetic permeability, will require almost doubling the winding turns.
Single-ended converters are used in low-power current sources when the load is of a changing nature, which is quite suitable in this situation.
The conversion frequency of the inverter plays a major role in the maximum power of the device; when it increases tenfold, the power of the transformer, without changing the ferrite and windings, increases almost fourfold.
When designing a charger, you should adhere to the operating frequency of the transformer, taking into account the characteristics of the transistor switch. The factory design of the transformers has the primary and secondary windings arranged in layers to ensure good magnetic coupling and reduce leakage inductance; additionally, electrostatic screens made of bronze copper are laid between the sections of the windings.
The windings of high-frequency transformers are made of stranded wire to reduce the “surface” effect.
You should not disassemble a single transformer to clarify the location and number of turns, because it will not be possible to reassemble it correctly into the reverse state. It is better to experiment without disassembling, and running the circuit will give considerable experience. Before turning on any hastily assembled circuit, put on armor-piercing goggles or connect a 220 V light bulb in series to the network; in the event of an accidental short circuit in any circuit, the fuses in the power filters explode with the release of everything they consist of . Even factory assembly of converter circuits often leads to breakdown of the working transistor and possible fire of the devices.
The reasons are adequate: the parameters of the transistor are underestimated or impulse noise from household electrical appliances exceed the capabilities of the filters.
Converter noise reduction circuits. Troubles in the operation of a field-effect transistor arise from the action of interelectrode feed-through capacitors; when the transistor is turned off, they delay transient processes. The transistor is turned on by applying a rectangular pulse from output 3 of the timer generator DA1 through resistor R5 to the gate, turning off -low level at pin 7 DA1. Directly connecting the gate to the timer, without resistor R5, will lead to a critical input current pulse, which can overload not only the timer chip, but also break through the electrostatic junction between the gate and the drain-source circuit (in the literature it is recommended to solder field-effect transistors with the soldering iron turned off and with shorted terminals of the transistor, from possible breakdown by static electricity).
The absence of resistor R7 in the circuit is also undesirable; it reduces the input voltage at the gate and discharges the input capacitance of the transistor with a small turn-off potential on resistor R10.
To speed up the discharge of the internal capacitance of the field-effect transistor, bypassing the gate resistor, a diode is installed by reverse connection; in this analog timer circuit, instead of an external discharge diode, a discharge timer transistor is used, the opening of which occurs with the switching of the state of the internal trigger, at zero voltage at output 3 DA1.
The transistor is mounted on a radiator with dimensions of 50*50*10 mm.
The T2 inductor is a winding of ten turns of PEV copper wire with a cross section of 4x0.5 mm with a ferrite rod with a diameter of 4 mm.
Transformer T1 is used from AT/ATX power supplies of type R320. AR-420X, the primary winding contains 38-42 turns of wire with a diameter of 0.8 mm, the secondary - 2x7.5 turns with a cross-section of 4x0.31 mm - installed power 250 W.
The inverter power circuits are made on a pulse diode bridge
VD8 with increased load characteristics and filter capacitor C5.
The inverter is powered directly from the network, without galvanic isolation.
Mains voltage fluctuations are compensated by negative feedback circuits with galvanic separation of secondary and primary, life-threatening voltage.
The charge of the filter capacitor is limited by resistor RT1, this protects the diode bridge VD8 from damage by critical currents. Pulse current through field-effect transistor the inverter is limited by resistor R14.
Battery charging circuits. These include a rectifier based on a high-frequency diode assembly VD7. To equalize the charge current, the filter includes capacitors C9, C11 and a choke on transformer T2. In the absence of rectified voltage on the secondary winding of transformer T1, with the inverter current flowing forward, the voltage across the load is maintained by the energy accumulated in the inductor of transformer T2 and the filter capacitor. When the key is closed, the energy accumulated in transformer T1 is transferred to the secondary winding and accumulated in the filter capacitors and inductor for subsequent transmission to the load.
The load current is monitored using a PA1 galvanometer with an internal 10 A shunt.
Possible interference accompanying the switching of diode VD7 is eliminated by capacitor C11.
Voltage stabilization circuits. Permanent output voltage The converter must be compared with a reference voltage and generate a mismatch error voltage. The voltage stabilization circuit consists of a bridge with resistors RK1, R9 and an optocoupler diode DA3. Increasing the voltage at the rectifier output causes the optocoupler diode to conduct, which opens the optocoupler transistor with a gain depending on the element used.
A change (decrease) in the voltage at pin 5 of the DA1 timer leads to a change in the frequency of the output pulses towards an increase, while the duty cycle of the pulses does not change.
The output pulse duration is reduced. This will reduce the average charging current.
As the output voltage decreases, the reverse process occurs.
The capacitor SZ eliminates the influence of impulse noise from the converter on the operation of the generator. The thermistor RK1 in the circuit for stabilizing the output voltage during heating allows you to influence the output voltage towards a decrease; the thermistor type MMT-1 is attached through an insulating gasket to the radiator of the transistor.
Current stabilization circuits. Current stabilization is performed using an analogue of the parallel stabilizer-timer DA2. An increase in current in the drain-source circuit of the field-effect transistor leads to a voltage drop across resistor R10 in the source circuit VT1, which is supplied through resistor R8 to control electrode 1 DA2 of the analog stabilizer. When the voltage threshold at the stabilizer input is above 2.5 V, timer DA2 opens and bypasses the gate of the field-effect transistor by supplying a negative voltage relative to the gate, the process of energy accumulation in the transformer will be interrupted. The value of the limited current will be less than the maximum permissible, which will not damage the key transistor. The transistor closes regardless of the state of the generator output, and the current in the source circuit stops.

Assembly order
The inverter board measuring 110x65 mm (Fig. 2) is mounted in a suitable BP-1 type housing, on the outer side of which a galvanometer, switch, and fuse are mounted. The connection between the device and the battery is made with a stranded wire with a cross-section of 2 mm. For technologies for charging and restoring batteries, see in detail.

Circuit adjustment
The device should be connected to the network through a limiter in the form of a network light bulb. The setup begins by checking the supply voltages of the generator microcircuit and the inverter transistor. The presence of rectangular pulses at output 3 of DA1 will be indicated by the LED indicator HL1. Instead of a load, you should connect a 12/24 V light bulb from the car, the glow of the light bulb will indicate the process of current conversion in the inverter, the weak glow of the mains light confirms the normal operation of the converter, with a light load the current in the primary winding should not exceed 200 mA.
The secondary voltage level is pre-set by trimming resistor R9 with the resistor R1 slider in the middle position.
The charge current depends on the duty cycle of the generator pulse, the state of which depends on the position of the resistor R1 slider.
In the right position of the engine, the charging time of capacitor C2 is minimal, and the discharging time is maximum, the pulse arriving at the key transistor VT1 is very short, and the average current in the load is minimal. In the right position of the engine, the pulse duration is maximum, as is the battery charging current.
After a short switching time, it is necessary to check the thermal conditions of the radio components.
Due to the impossibility of changing the parameters of the transformer, the required parameters of the power source can only be adjusted by changing the frequency of the generator (capacitor C2), the duty cycle of the R1 pulses, the terminals of the secondary winding of the transformer, or by completely replacing the transformer.
Upon completion of the adjustment work and running the circuit over time, the mains and load lamps are removed, the circuit is restored and switched on for charging the batteries.
Pay attention to the operating mode of the circuits feedback by current and voltage.

The circuit is fundamentally different from the design of its predecessor - the welding transformer. The basis of the design of the previous welding machines there was a step-down transformer, which made them bulky and heavy. Modern welding inverters, thanks to the use of advanced developments in their production, are lightweight and compact devices characterized by wide functionality.

The main element electrical diagram any welding inverter is a pulse converter that produces high-frequency current. It is thanks to this that the use of an inverter makes it possible to easily ignite the welding arc and maintain it in a stable state throughout the welding process. The welding inverter circuit, depending on the model, may have certain features, but the principle of its operation, which will be discussed below, remains unchanged.

What types of inverters are available on the modern market?

For certain type welding, you should choose the right inverter equipment, each type of which has a specific electrical circuit and, accordingly, special technical characteristics and functionality.

Inverters produced by modern manufacturers can be used equally successfully both in industrial enterprises and in everyday life. Developers are constantly improving the electrical circuit diagrams of inverter devices, which allows them to be equipped with new functions and improve them specifications.

Inverter devices as the main equipment are widely used to perform the following technological operations:

• consumable and non-consumable electrodes;
• welding using semi-automatic and automatic technologies;
• plasma cutting, etc.

In addition, inverter machines are the most efficient type of equipment used for welding aluminum, stainless steel and other difficult-to-weld metals. Welding inverters, regardless of the features of their electrical circuit, allow you to obtain high-quality, reliable and neat welds made using any technology. At the same time, what is important is that the compact and not too heavy inverter machine, if necessary, can be easily moved at any time to the place where welding work will be performed.

What does the design of a welding inverter include?

The welding inverter circuit, which determines its technical characteristics and functionality, includes the following required elements, How:

• a unit that provides electrical power to the power part of the device (it consists of a rectifier, a capacitive filter and a nonlinear charging circuit);
• power part, made on the basis of a single-cycle converter (this part of the electrical circuit also includes a power transformer, a secondary rectifier and an output choke);
• power supply unit for elements of the low-current part of the electrical circuit of the inverter apparatus;
• PWM controller, which includes a current transformer and a load current sensor;
• a block responsible for thermal protection and control of cooling fans (this block of the circuit diagram includes inverter fans and temperature sensors);
• controls and indications.

How does a welding inverter work?

The formation of a high current, with the help of which an electric arc is created to melt the edges of the parts being joined and the filler material, is what any welding machine is designed for. For the same purposes, an inverter apparatus is also needed, which allows the generation of welding current with a wide range of characteristics.

In its simplest form, the principle looks like this.

• Alternating current with a frequency of 50 Hz from a regular electrical network is supplied to the rectifier, where it is converted into direct current.
• After the rectifier, the direct current is smoothed using a special filter.
• From the filter, direct current flows directly to the inverter, whose task is to convert it again into alternating current, but at a higher frequency.
• After this, using a transformer, the voltage of the alternating high-frequency current is reduced, which makes it possible to increase its strength.

In order to understand the importance of each element of the electrical circuit diagram of an inverter device, it is worth considering its operation in more detail.

Processes occurring in the electrical circuit of a welding inverter

The circuit allows you to increase the current frequency from the standard 50 Hz to 60–80 kHz. Due to the fact that high-frequency current is subject to regulation at the output of such a device, compact transformers can be effectively used for this. An increase in the frequency of the current occurs in that part of the inverter electrical circuit where the circuit with powerful power transistors is located. As you know, only direct current is supplied to transistors, which is why a rectifier is needed at the input of the device.

Schematic diagram of the factory welding inverter "Resanta" (click to enlarge)

Inverter circuit from German manufacturer FUBAG with a number of additional features (click to enlarge)

An example of a circuit diagram of a welding inverter for self-made(click to enlarge)

The electrical circuit diagram of the inverter device consists of two main parts: the power section and the control circuit. The first element of the power section of the circuit is a diode bridge. The task of such a bridge is precisely to convert alternating current into direct current.

In the direct current converted from alternating current in the diode bridge, pulses may occur that need to be smoothed out. To do this, a filter consisting of capacitors of predominantly electrolytic type is installed after the diode bridge. It is important to know that the voltage that comes out of the diode bridge is approximately 1.4 times greater than its value at the input. When converting AC to DC, rectifier diodes become very hot, which can seriously affect their performance.

To protect them, as well as other elements of the rectifier from overheating, radiators are used in this part of the electrical circuit. In addition, a thermal fuse is installed on the diode bridge itself, the task of which is to turn off the power supply if the diode bridge has heated up to a temperature exceeding 80–90 degrees.

High-frequency interference generated during operation of the inverter device can enter the electrical network. To prevent this from happening, an electromagnetic compatibility filter is installed in front of the rectifier block of the circuit. Such a filter consists of a choke and several capacitors.

The inverter itself, which converts direct current into alternating current, but with a much higher frequency, is assembled from transistors using an “oblique bridge” circuit. The switching frequency of transistors, due to which the alternating current is generated, can be tens or hundreds of kilohertz. The high-frequency alternating current thus obtained has a rectangular amplitude.

A voltage-reducing transformer installed behind the inverter unit allows you to obtain a current of sufficient strength at the output of the device so that you can effectively perform welding work with its help. In order to obtain direct current using an inverter apparatus, a powerful rectifier, also assembled on a diode bridge, is connected after the step-down transformer.

Inverter protection and control elements

Avoid influence negative factors Several elements in its circuit diagram allow the inverter to operate.

To ensure that transistors that convert direct current into alternating current do not burn out during their operation, special damping (RC) circuits are used. All electrical circuit blocks that operate under heavy load and become very hot are not only provided with forced cooling, but are also connected to temperature sensors that turn off their power if their heating temperature exceeds a critical value.

Due to the fact that the filter capacitors, after being charged, can produce a high current, which can burn the inverter transistors, the device must be provided with smooth start. For this purpose, stabilizers are used.

The circuit of any inverter has a PWM controller, which is responsible for controlling all elements of its electrical circuit. From the PWM controller, electrical signals are sent to a field-effect transistor, and from it to an isolation transformer, which simultaneously has two output windings. The PWM controller, through other elements of the electrical circuit, also supplies control signals to the power diodes and power transistors of the inverter unit. In order for the controller to effectively control all elements of the inverter's electrical circuit, it is also necessary to supply electrical signals to it.

To generate such signals it is used operational amplifier, the input of which is supplied with the output current generated in the inverter. If the values ​​of the latter diverge from the specified parameters, the operational amplifier generates a control signal to the controller. In addition, the operational amplifier receives signals from all protective circuits. This is necessary so that he can disconnect the inverter from the power supply at the moment when a critical situation arises in its electrical circuit.

Advantages and disadvantages of inverter-type welding machines

The devices that replaced the usual transformers have a number of significant advantages.

• Thanks to a completely different approach to the formation and regulation of welding current, the weight of such devices is only 5–12 kg, while welding transformers weigh 18–35 kg.
• Inverters have very high efficiency (about 90%). This is explained by the fact that they spend significantly less excess energy on heating components. Welding transformers, unlike inverter devices, get very hot.
• Inverters thanks to this high efficiency consume 2 times less electrical energy than conventional welding transformers.
• The high versatility of inverter machines is explained by the ability to regulate the welding current over a wide range with their help. Thanks to this, the same device can be used to weld parts made of different metals, as well as for its implementation using different technologies.
• Most modern inverter models are equipped with options that minimize the impact of welder errors on technological process. Such options, in particular, include “Anti-stick” and “Arc Force” (fast ignition).
• Exceptional stability of the voltage supplied to the welding arc is ensured by the automatic elements of the inverter electrical circuit. In this case, automation not only takes into account and smoothes out differences in input voltage, but also corrects even such interference as the attenuation of the welding arc due to strong wind.
• Welding using inverter equipment can be performed with any type of electrode.
• Some models of modern welding inverters have a programming function, which allows you to accurately and quickly configure their modes when performing a certain type of work.