Scheme of a pulse generator with a transformer. A simple source of short pulses is not inferior to expensive laboratory equipment. Advantages and disadvantages

Pulse generators are designed to receive pulses of a certain shape and duration. They are used in many circuits and devices. And also they are used in measuring equipment for adjustment and repair of various digital devices. Square waveforms are great for testing digital circuits, while triangular waveforms can be useful for sweep or sweep generators.

The generator generates a single rectangular pulse at the push of a button. The circuit is assembled on logical elements, which is based on a conventional RS flip-flop, thanks to which the possibility of penetration of bounce pulses of the button contacts to the counter is also excluded.

In the position of the button contacts, as shown in the diagram, a high level voltage will be present at the first output, and at the second output of a low level or logic zero, when the button is pressed, the trigger state will change to the opposite. This generator is perfect for testing the operation of various counters.

In this circuit, a single pulse is formed, the duration of which does not depend on the duration of the input pulse. Such a generator is used in a wide variety of ways: to simulate the input signals of digital devices, when checking the performance of circuits based on digital microcircuits, the need to apply a certain number of pulses to some device under test with visual control of processes, etc.

As soon as the circuit is powered on, the capacitor C1 starts charging and the relay is activated, opening the power supply circuit with its front contacts, but the relay will not turn off immediately, but with a delay, since the discharge current of the capacitor C1 will flow through its winding. When the rear contacts of the relay are closed again, a new cycle will begin. The switching frequency of the electromagnetic relay depends on the capacitance of the capacitor C1 and the resistor R1.

You can use almost any relay, I took it. Such a generator can be used, for example, to switch Christmas tree garlands and other effects. The disadvantage of this circuit is the use of a large capacitor.

Another oscillator circuit on a relay, with a principle of operation similar to the previous circuit, but unlike it, the repetition rate is 1 Hz with a smaller capacitor capacitance. At the moment the generator is turned on, capacitor C1 begins to charge, then the zener diode opens and relay K1 is activated. The capacitor begins to discharge through the resistor and the composite transistor. After a short period of time, the relay turns off and a new generator cycle begins.

In the pulse generator, in Figure A, three AND-NOT logic elements and a unipolar transistor VT1 are used. Depending on the values ​​of the capacitor C1 and resistors R2 and R3, pulses are generated at output 8 with a frequency of 0.1 - up to 1 MHz. Such a huge range is explained by the use of a field effect transistor in the circuit, which made it possible to use megaohm resistors R2 and R3. Using them, you can also change the duty cycle of the pulses: the resistor R2 sets the duration of the high level, and R3 - the duration of the low level voltage. VT1, you can take any of the KP302, KP303 series. - K155LA3.

If you use CMOS chips instead of K155LA3, for example K561LN2, you can make a wide-range pulse generator without using a field effect transistor in the circuit. The diagram of this generator is shown in Figure B. To expand the number of generated frequencies, the capacitance of the timing circuit capacitor is selected by switch S1. The frequency range of this generator is 1Hz to 10kHz.

The last figure shows a pulse generator circuit in which the possibility of adjusting the duty cycle is incorporated. For those who have forgotten, we recall. The pulse duty cycle is the ratio of the repetition period (T) to the duration (t):

The duty cycle at the output of the circuit can be set from 1 to several thousand, using the resistor R1. The transistor operating in the key mode is designed to amplify power pulses

If there is a need for a highly stable pulse generator, then it is necessary to use quartz at the appropriate frequency.

The generator circuit shown in the figure is capable of generating rectangular and sawtooth pulses. The master oscillator is made on the logic elements DD 1.1-DD1.3 of the K561LN2 digital microcircuit. Resistor R2 paired with capacitor C2 form a differentiating circuit, which at the output of DD1.5 generates short pulses with a duration of 1 μs. An adjustable current stabilizer is assembled on a field effect transistor and resistor R4. From its output, a current flows charging capacitor C3 and the voltage across it increases linearly. At the moment of receipt of a short positive pulse, the transistor VT1 opens, and the capacitor C3 is discharged. Thereby forming a sawtooth voltage on its plates. With a variable resistor, you can adjust the capacitor charge current and the slope of the sawtooth voltage pulse, as well as its amplitude.

A variant of the oscillator circuit on two operational amplifiers

The circuit is built using two op-amps of the LM741 type. The first op amp is used to generate a rectangular shape, and the second one generates a triangular one. The generator circuit is built as follows:

In the first LM741, feedback (OS) is connected to the inverting input from the output of the amplifier, made on resistor R1 and capacitor C2, and the OS also goes to the non-inverting input, but through a voltage divider, based on resistors R2 and R5. The output of the first op-amp is directly connected to the inverting input of the second LM741 through the resistance R4. This second op amp, together with R4 and C1, form an integrator circuit. Its non-inverting input is grounded. Both op amps are supplied with +Vcc and -Vee supply voltages, as usual on the seventh and fourth pins.

The scheme works as follows. Assume that initially there is +Vcc at the output of U1. Then the capacitance C2 starts charging through the resistor R1. At a certain point in time, the voltage at C2 will exceed the level at the non-inverting input, which is calculated using the formula below:

V 1 \u003d (R 2 / (R 2 + R 5)) × V o \u003d (10 / 20) × V o \u003d 0.5 × V o

The output signal V 1 becomes -Vee. So, the capacitor starts to discharge through the resistor R1. When the voltage across the capacitance becomes less than the voltage given by the formula, the output signal will again be + Vcc. Thus, the cycle is repeated, and thanks to this, rectangular pulses are generated with a time period determined by an RC circuit consisting of resistance R1 and capacitor C2. These square-shaped formations are also input signals to the integrator circuit, which converts them into a triangular shape. When the output of op-amp U1 is +Vcc, capacitance C1 is charged to its maximum level and produces a positive, rising slope of the triangle at the output of op-amp U2. And, accordingly, if there is -Vee at the output of the first op-amp, then a negative, downward slope will be formed. That is, we get a triangular wave at the output of the second op-amp.

The pulse generator in the first circuit is built on the TL494 chip, which is great for setting up any electronic circuits. The peculiarity of this circuit is that the amplitude of the output pulses can be equal to the supply voltage of the circuit, and the microcircuit is capable of operating up to 41 V, because it is not just that it can be found in power supplies for personal computers.

You can download the PCB layout from the link above.

The pulse repetition rate can be changed by switch S2 and a variable resistor RV1, resistor RV2 is used to adjust the duty cycle. Switch SA1 is designed to change the operating modes of the generator from in-phase to anti-phase. Resistor R3 should cover the frequency range, and the duty cycle adjustment range is regulated by the selection of R1, R2

Capacitors C1-4 from 1000 pF to 10 uF. Transistors any high-frequency KT972

A selection of circuits and designs of generators of rectangular pulses. The amplitude of the generated signal in such generators is very stable and close to the supply voltage. But the shape of the oscillations is very far from sinusoidal - the signal is pulsed, and the duration of the pulses and pauses between them is easily adjustable. It is easy to give pulses the appearance of a meander when the duration of the pulse is equal to the duration of the pause between them

It generates powerful short single pulses that set the input or output of any digital element to a logic level opposite to the existing one. The pulse duration is chosen so as not to disable the element, the output of which is connected to the tested input. This makes it possible not to disturb the electrical connection of the tested element with the rest.

The pulse current generator (PGG) is designed for the primary conversion of electrical energy. Includes 50 Hz alternating current electrical network, high-voltage transformer, rectifier, current-limiting device, protection equipment. In GIT, charging and discharging circuits are distinguished, which are interconnected by a capacitor bank. The PCG, which is a power source, is connected to the process unit through a discharge circuit.

Pulse generators are characterized by the following main parameters: voltage across the capacitor bank u, the electric capacity of the battery C, the energy stored in the capacitors W n, energy in impulse W0 pulse repetition rate υ.

The purpose of the charging circuit is to charge the capacitor bank to a predetermined voltage. The circuit includes a current-limiting device, a step-up transformer and a high-voltage rectifier. To rectify the charging current, selenium or silicon pillars are used. With a high-voltage transformer, the initial supply voltage of 380/220 V is increased to (2-70) 10 3 V.

In the scheme L - C - D we have ή 3 > 50%.

When using generators of pulsed currents, energy losses are significant at the stage of discharge formation. This disadvantage is devoid of a common system that combines generators of pulsed currents and voltages (Fig. 30). In this system, the breakdown of the forming gap is produced at the expense of the energy of the capacitor bank of the voltage generator, which creates a conductive channel in the main working gap and ensures the release of the main discharge energy in the discharge gap of the pulse current generator.

The ratio of electrical voltages and capacitances characteristic of such a system is: » at where index 1 corresponds to the voltage generator, and index 2 to the current generator. So, for example

The energy and weight and size indicators of the generator significantly depend on the high-voltage transformer and rectifier. The efficiency of the charger-rectifier increases when high-voltage silicon pillars are used. Rectifiers have high characteristic indicators - specific

volume from 0.03 to 0.28 m 3 /kW and a specific gravity of 25-151 kg/kW.

In electropulse installations, single blocks are also used, including a transformer and a rectifier, which reduces the main dimensions and simplifies the switching network.

Pulse capacitors are designed to store electrical energy. High-voltage pulse capacitors must have an increased specific energy capacity, low internal inductance and low resistance at high discharge currents, and the ability to withstand multiple charge-discharge cycles. The main technical data of pulse capacitors are given below.

Voltage (nominal), kV .................................... 5-50

Capacity (nominal), uF. . ...................................0.5-800

Discharge frequency, number of pulses/min.......................1-780

Discharge current, kA ............................................... .................0.5-300

Energy intensity, J/kg....................................... .......4.3-30

Resource, number of impulses .............................................. .10 e - 3 10 7

One of the main characteristics of pulse capacitors, which affects the size of the battery and the electric pulse installation as a whole, is the indicator of specific volumetric energy consumption

(3.23)

where E n- accumulated energy; V to is the volume of the condenser.

For existing capacitors ω with= 20 -g 70 kJ/m 3 , which determines the increased size of the storage. So the battery capacity for E n\u003d 100 kJ is 1.5-5.0 m 3. In the storage units of installations, capacitors are connected into batteries, which ensures the summation of their electrical capacitance, which is 100-8000 microfarads.

High-voltage switches are used for instantaneous release of electrical energy accumulated in a capacitor bank in a technological unit. High-voltage switches (arresters) "perform two functions: they turn off the discharge circuit

from the drive when it is charging; instantly include the drive in the load circuit.

Various design schemes of arresters and types of switches corresponding to these schemes are possible: air, vacuum, gas-filled, contact disc, ignitron and trigatron, with a solid dielectric.

The main requirements for the switches are as follows - to withstand high-voltage operating voltage without breakdown, to have low inductance and low resistance, to provide a given current pulse repetition rate.

In laboratory electropulse installations, mainly air-type arresters are used, which provide high-energy switching with a long service life and have a relatively simple design scheme (Fig. 31).

Arresters of this type have a number of significant drawbacks that limit their use: the influence of the surface state and the state of atmospheric air (dust content, humidity, pressure) on the stability of the reproducible pulse; nitrogen oxides are formed that affect humans; powerful high-frequency sound pressure is generated.

In industrial mobile installations, mechanical poppet switches have become widespread (see Fig. 31, a). Arresters of this type are simple in electrical circuit and design, reliable during transportation and operation in areas with rugged terrain, but require regular cleaning of the surface of disc elements. I

The electropulse installation also includes control units for the pulse generator and the technological process, protection and interlock systems, auxiliary systems that provide mechanization and automation of processes in the technological unit.

The control unit includes electric circuits for starting, blocking and a circuit for generating a synchronization pulse.

The interlock system is used for “instantaneous disconnection of high voltage. The control system consists of a voltmeter and a kipovoltmeter, indicating, respectively, the voltage of the network and on the capacitor bank, of indicator lamps, sound signals, and a frequency meter.

Technological node

The technological node is designed to convert electrical energy into other types of energy and to transfer the converted energy to the processing object.

With regard to the specifics of the discharge-pulse technology of rock destruction, the technological unit includes: a working discharge chamber, a working body in the form of an electrode system or an electro-hydraulic fuse, a device for inlet and outlet of the working fluid, and a device for moving electrodes or an exploding conductor (Fig. 32). The working discharge chamber is filled with a working fluid or a special dielectric composition.

Discharge (working) chambers are divided into open and closed, buried and surface, stationary, mixed and remote. Chambers can be disposable and reusable; vertical, horizontal and inclined. The type and shape of the working chamber must ensure the maximum release of the accumulated electrical energy, the maximum to l.d. converting this energy into mechanical, transferring this energy to the processing object or to its specified zone.

The working technological body is intended for the direct conversion of electrical energy into mechanical energy and for the input of this energy into the working environment, and through it - to the processing object. The type of the working body depends on the type of electric discharge in the liquid used in this technological process - with the free formation of the discharge, electrode systems are rational (Fig. 33, a); with an initiated discharge - an electro-hydraulic fuse with an exploding conductor (Fig. 33.6).

The working body experiences dynamic loads, the action of an electromagnetic field and ultraviolet radiation, as well as the influence of the working fluid.

The electrode system is used for free discharge formation. According to the constructive factor, rod linear and coaxial systems are distinguished. The simplest in execution are linear (opposing or parallel) systems with combinations of electrode shapes tip - tip and tip - plane. The disadvantages of linear systems are their significant inductance (1-10 μH) and non-directional action.

More perfect coaxial systems have a small intrinsic inductance and high efficiency. conversion of stored electrical energy into plasma energy. The disadvantage of coaxial systems is their low reliability and fragility. The electrode system is technologically advanced and highly productive due to the high frequency of the process of creating mechanical loading forces.

According to the number of repeated discharges, systems of single and multiple action are distinguished. Repetitive systems are more economical and productive. The amount of energy converted by the electrode system also affects the design and durability.

In the mining industry, electrode systems designed for a pulse repetition rate of 1-12 per minute have received greater use. During an electrical discharge, due to thermal processes, erosion of the electrodes occurs, the intensity of which depends on the material of the electrodes and the working fluid, as well as on the amount of energy released in

discharge channel. The working part of the electrodes is made of steel St3 or St45; the diameter of the protruding part must be more than 8 mm with a length of at least 12 mm. In the electrode zone, the melting point of iron is reached in 10 -6 s, and the boiling point in 5 10 -6 s.

The intense destruction of the electrode caused by this is accompanied by the formation of plasma jets (vapors and liquid drops of metal). The weakened zone of the electrode is the insulating layer at the border of the output of the rod - current lead and water.

The main requirements for the electrode system are: high efficiency of electrical energy conversion, high

operational and technological indicators, cost-effective durability. The electrodes made of an alloy of copper, tungsten carbide and nickel have the highest erosion resistance.

The surface area of ​​the cathode should exceed the area of ​​the anode by 60–100 times, which, in combination with the supply of a positive voltage pulse to the anode, will ensure a reduction in energy losses at the stage of discharge formation and increase the efficiency. systems. Rational insulation material - fiberglass, vacuum rubber, polyethylene.

An electro-hydraulic fuse is used for an initiated discharge, it perceives dynamic loads, the impact of high-current fields and working fluid, which leads to the destruction of the body, insulation and electrode.

In an electro-hydraulic fuse, the positive electrode is isolated from the body; an exploding conductor is installed between the electrode and the grounded body, which acts as a negative electrode.

Depending on the technological tasks to be solved, conductors made of copper, aluminum, tungsten are used; conductor dimensions within diameter 0.25-2 mm, length 60-300 mm. The design of an electro-hydraulic fuse must ensure the concentration of energy in the required direction and the formation of a cylindrical shock wave front, as well as the manufacturability of operations for installing and replacing an exploding conductor.

To fulfill part of these requirements, it is necessary that the body of the electro-hydraulic fuse serve as a rigid barrier to the propagating wave front.

This is ensured by the use of special cumulative recesses in the fuse body and a certain combination of the linear dimensions of the body and conductor. Thus, the diameter of the body of the fuse must be 60 times or more greater than the diameter of the exploding conductor.

In recent years, new design schemes and special devices have been developed that increase the efficiency of the action of the working bodies, ensuring the direction of the action on the object of processing the generated waves and hydroflow.

Such devices include passive reflective surfaces, electrodes with complex geometry, generators of divergent waves. There are also devices for pulling an exploding conductor, which complicates the design of the fuse, but increases the manufacturability of the process.

To directly convert the energy of an electric discharge into the energy of a compression pulse, special electroexplosive cartridges are used (Fig. 34).

The working fluid filling the technological unit plays a very significant role in the process of electric discharge. It is in the liquid that the discharge is reproduced with the direct conversion of electrical energy into mechanical energy.

Ionization is observed in the liquid, as well as gas evolution of unreacted oxygen and hydrogen (up to 0.5 10 -6 m 3 /kJ), the liquid is involved in the movement of the propagating wave front, which forms a hydroflow in the technological unit capable of performing mechanical work.

Water (technical, marine, distilled) and aqueous electrolytes are used as a working fluid; hydrocarbon (kerosene, glycerin, transformer oil) and silicone (polymethylsiloxane) liquids, as well as special dielectric, liquid and solid compositions. Industrial water, the specific electrical conductivity of which is (1-10) Sm / m, has received greater use.

The electrical conductivity of the liquid significantly affects the amount of energy required for the formation of the discharge, since it determines the magnitude of the breakdown voltage and the speed of the streamers. The minimum tension at which streamers appear is estimated at 3.6 10 3 V/mm.

The electrical conductivity values ​​(S/m) of some fluids used to fill the process unit are shown below.

Service water (tap) .............................................................. ............(1-10) 10 -2

Sea water................................................ .............................................1-10

Distilled water................................................ ...............................4.3 -10 -4

Glycerol................................................. ................................................. ..6.4 10 -6

It can be seen that dielectric liquids have low ionic conductivity. The specific electrical resistance of the liquid (R W) also determines the magnitude of the electrical efficiency. and depends on the amount of energy introduced per unit volume of the working fluid. So, for water, the parameter p w decreases with an increase to values ​​of 500-1000 kJ / ; with a further increase in W 0, the parameter p w stabilizes within 10-25 Ohm-m.

An electric discharge in a liquid also depends on the density of the working liquid - with an increase in density, the overvoltage peak and the steepness of the current decay decrease. To increase the voltage of the discharge circuit, and, accordingly, the magnitude of the breakdown voltage, working fluids with low specific conductivity should be used (for example, technical water).

The use of liquids with higher conductivity facilitates the formation of sliding discharges; increases energy losses at the stage of channel formation and reduces the amplitude of the shock wave.

Viscous compositions are also used as a working fluid (spindle oil - 70%, aluminum powder - 20%, chalk - 10%), which increases the amplitude of the shock wave by 20-25% and reduces energy losses.

As a dielectric, a metallized dielectric filament and paper tapes impregnated with an electrolyte are also used. The introduction of a solid dielectric reduces the total energy consumption for breakdown (4-5 times), reduces the required number of streamers (4-6 times), reduces thermal radiation and ultraviolet radiation. The introduction of solid particles of conductive additives into the working fluid flow is used instead of exploding conductors.

The task of the calculation is to determine the structure of the electrical circuit, select the element base, determine the parameters of the electrical circuit of pulse generators.

Initial data:

type of technological process and its characteristics;

constructive use of the discharge circuit;

characteristics of the supply voltage;

parameters of the electrical impulse, etc.

Calculation sequence:

The calculation sequence depends on the structure of the electrical circuit of the generator, which consists in whole or in part of the following elements: a source of direct (alternating) voltage, an autogenerator, a rectifier, a discharge circuit, a high-voltage transformer, a load (Fig. 2.14).

calculation of the voltage converter (Fig. 2.15, a);

calculation of the actual pulse generator (Fig. 2.16).

2.14. Complete block diagram of the pulse generator: 1 - voltage source; 2 - self-oscillator; 3 - rectifier; 4 - smoothing filter; 5 - discharge circuit with a high-voltage transformer; 6 - load.

Converter calculation (Fig. 2.15 a). Supply voltage U n \u003d 12V DC. We select the output voltage of the converter U 0 \u003d 300V at a load current J 0 \u003d 0.001 A, output power P 0 \u003d 0.3 W, frequency f 0 \u003d 400 Hz.

The output voltage of the converter is selected from the conditions for increasing the frequency stability of the generator and to obtain good linearity of the output voltage pulses, i.e. U n >> U incl. dash, usually U n =2U incl. dash.

The frequency of the output voltage is set from the conditions of optimal performance of the master oscillator of the voltage converter.

The values ​​of P 0 and U 0 make it possible to use the KY102 series dynistor VS in the generator circuit.

As a transistor VT, we use MP26B, for which the limit modes are as follows: U kbm = 70V, I KM = 0.4A, I bm = 0.015A, U kbm = 1V.

We offer the transformer core made of electrical steel. We accept V M = 0.7 T, η = 0.75, 25 s.

We check the suitability of the performed transformer for operation in the converter circuit according to the conditions:

U kbm ≥2.5U n ; I km ≥1.2I kn; I bm ≥1.2I bn. (2.77)

transistor collector current

Collector current maximum:

According to the output collector characteristics of the MP26B transistor for a given collector current β st \u003d 30, therefore, the base saturation current

BUT.

Base current:

I bm \u003d 1.2 0.003 \u003d 0.0036A.

Therefore, the MP26B transistor, according to condition (2.78), is suitable for the designed circuit.

The resistance of the resistors in the voltage divider circuit:

Om,; (2.79)

Ohm.

We accept the nearest standard values ​​of the resistances of the resistors R 1 =13000 ohms, R 2 =110 ohms.

The resistor R in the base circuit of the transistor regulates the output power of the generator, its resistance is 0.5 ... 1 kOhm.

Cross-section of the core of the transformer TV1:

Figure 2.15. Schematic diagram of the pulse generator: a - converter;

b - pulse generator

We choose the core Ш8×8, for which S c =0.52·10 -4 m2.

The number of turns in the windings of the transformer TV1:

Vit.; (2.81)

vit.; (2.82)

vit. (2.83)

Filter capacitor capacitance VC1:

The diameter of the wires of the windings of the transformer TV1:

We select the standard wire diameters d 1 \u003d 0.2 mm, d 2 \u003d mm, d 3 \u003d 0.12 mm.

Taking into account the thickness of the enamel insulation d 1 \u003d 0.23 mm, d 2 \u003d 0.08 mm, d 3 \u003d 0.145 mm.

Rice. 2.16. Calculation scheme of the pulse generator

Calculation of pulse generators (Fig. 2.16)

We take the voltage at the input of the generator equal to the voltage at the output of the converter U 0 = 300 V. The pulse frequency f = 1 ... 2 Hz. The pulse voltage amplitude is not more than 10 kV. The amount of electricity in the pulse is not more than 0.003 C. Pulse duration up to 0.1 s.

We select a diode VD type D226B (U arr = 400 V, I pr \u003d 0.3 A, U pr \u003d 1 V) and a thyristor of the KN102I type (U on = 150 V, I pr t = 0.2 A, U pr \u003d 1 .5 V, I on = 0.005 A, I off = 0.015 A, τ on = 0.5 10 -6 s τ off = 40 10 -6 s).

The direct resistance to direct current of the diode R d.pr \u003d 3.3 Ohm and the thyristor R t.pr \u003d 7.5 Ohm.

Pulse repetition period for a given frequency range:

. (2.86)

The resistance of the charging circuit R 3 must be such that

Ohm. (2.88)

Then R 3 \u003d R 1 + R d.pr \u003d 20 10 3 + 3.3 \u003d 20003.3 Ohm.

Charge current:

A. (2.89)

Resistor R 2 limits the discharge current to a safe value. His resistance:

Ohm, (2.90)

where U p is the voltage on the charging capacitor VC2 at the beginning of the discharge, its value is equal to U off. In this case, the condition R 1 >>R 2 (20·10 3 >>750) must be observed.

Discharge circuit resistance:

R p \u003d R 2 R t. pr \u003d 750 + 7.5 \u003d 757.5 Ohm.

The conditions for stable inclusion (2.91, 2.92) are satisfied.

, , (2.91)

, . (2.92)

Capacitor capacitance VC2:

. (2.93)

Capacitance VC2 for frequency f=1 Hz:

F

And for a frequency of 2 Hz:

C 2 \u003d 36 10 -6 F.

The amplitude of the current in the charge circuit of the capacitor VC2

, (2.94)

The amplitude of the current in the charge circuit of the capacitor VC2:

, (2.95)

Pulse energy:

J. (2.96)

The maximum amount of electricity in a pulse:

q m \u003d I p τ p \u003d I p R p C 2 \u003d 0.064 757.5 72 10 -6 \u003d 0.003 C (2.97)

does not exceed the specified value.

Let's calculate the parameters of the output transformer TV2.

Estimated transformer power:

Tue, (2.98)

where η t \u003d 0.7 ... 0.8 - the efficiency of a low-power transformer.

Sectional area of ​​the transformer core:

The number of turns of each transformer winding per

vit/V. (2.100)

The number of turns in the windings of the transformer TV2:

W 4 \u003d 150 N \u003d 150 16.7 \u003d 2505 vit.; (2.101)

W 5 \u003d 10000 16.7 \u003d 167 10 3 vit.

Wire diameter in windings (2.85):

mm;

mm.

We choose the standard diameters of wires with enameled insulation d 4 \u003d 0.2 mm, d 5 \u003d 0.04 mm.

Example. Determine the voltage and currents in the circuit of fig. 2.16.

Given: U c \u003d 300 V AC 400 Hz, C \u003d 36 10 -6 F, R d.pr \u003d 10 Ohm, R t.pr \u003d 2.3 Ohm, L w \u003d 50 mH, R 1 \u003d 20 kOhm , R 2 \u003d 750 Ohm.

Capacitor voltage at the time of charging:

, (2.102)

where τ st \u003d 2 10 4 36 10 -6 \u003d 0.72 s.

The impedance of the charge circuit of the capacitance VC2:

The charge current is:

BUT.

Scheme 1

The generator has been designed to use a minimum number of commonly available electronic components, with good repeatability and sufficient reliability. The oscillator option (circuit 1) is assembled on the basis of the widely used UC3525 (U1) PWM controller, which controls the Q4-Q7 field-effect transistor bridge circuit. If the lower switches of each of the half-bridges operating in antiphase are controlled directly by the outputs of the 11/14 U2 microcircuit, then bootstrap cascades on transistors Q2, Q3 are used as upper-side drivers. Such stages are widely used in most modern IC drivers and are fairly well documented in the power electronics literature. The input voltage is AC or DC (~24~220V/30-320V), supplied to the input of the diode bridge (or bypassing it in the case of a DC voltage supply), feeds the power part of the circuit. To prevent a large starting current, a thermistor Vr1 (5A / 5Ohm) is included in the power circuit break. The control part of the circuit can be powered from any source with an output voltage of +15/+25V and a current of 0.5A or more. The parametric voltage regulator on transistor Q1 can have an output voltage from +9 to +18V (depending on the type of power switches used, for example), but in some cases you can do without this stabilizer if an external power source with the necessary parameters is already stabilized. The UC3525 microcircuit was not chosen by chance - the ability to generate a pulse sequence from several tens of hertz to 500 kHz and sufficiently powerful outputs (0.5A). At least the TL494 microcircuits could not function at a frequency of less than 250 Hz in a push-pull mode (in a single-cycle mode - no problem) - the internal logic failed and the pulse sequence, as well as their duration, became chaotic.

The frequency of the pulse sequence is adjusted by a variable resistor R1, the pulse duration is adjusted using R4. The initial duration of the "dead time" is set by the resistor R3.

Scheme 2

The generator shown in diagram 2 is a complete analogue of the previous circuit and has practically no circuit differences. However, the domestic K1156EU2 chip (a complete analogue of the UC3825) used in this generator is capable of operating at higher frequencies (almost up to 1 MHz), the output stages have a greater load capacity (up to 1.5A). In addition, it has a minor difference in pinout compared to UC3525. So, the "clock" capacitor is connected to pin 6 (5 - for the 3525 chip), the timing resistor is connected to pin 5 (6 - for the 3525 chip). If pin 9 of the UC3525 is the output of the error amplifier, then in the UC3825 this pin acts as the input of the "current" limiter. However, all the details are in the datasheet for these microcircuits. It should be noted, however, that the K1156EU2 is less stable at frequencies below 200 Hz and requires more careful layout and mandatory blocking of its supply circuits with relatively large capacitors. If these conditions are ignored, the smooth adjustment of the pulse duration near their time maximum may be disturbed. The described feature manifested itself, however, only when assembling on a breadboard. After assembling the generator on the printed circuit board, this problem did not appear.

Both circuits are easily scalable in power by using either more powerful transistors or by connecting them in parallel (for each of the switches), as well as by changing the supply voltage of the power switches. It is desirable to "plant" all power components on radiators. Up to a power of 100W, adhesive-based heatsinks were used, designed for installation on memory chips in video cards (output switches and a stabilizer transistor). Within half an hour of operation at a frequency of 10 kHz with a maximum duration of output pulses, at a supply voltage of the keys (31N20 transistors were used) + 28 V to a load of about 100 W (two 12 V / 50 W lamps connected in series), the temperature of the power switches did not exceed 35 degrees Celsius.

To build the above circuits, ready-made circuit solutions were used, which I only rechecked and supplemented during prototyping. For generator circuits, printed circuit boards were designed and manufactured. Figure 1 and Figure 2 show the boards of the first variant of the generator circuit, Figure 3, Figure 4 - images of the board for the second circuit.

Both circuits at the time of this writing were tested at frequencies from 40Hz to 200kHz with various active and inductive loads (up to 100W), at constant input supply voltages from 23 to 100V, with output transistors IRFZ46, IRF1407, IRF3710, IRF540, IRF4427, 31N20 , IRF3205. Instead of bipolar transistors Q2, Q3, it is recommended to install (especially for operation at frequencies above 1 kHz) field-effect transistors such as IRF630, IRF720 and the like with a current of 2A and an operating voltage of 350V. In this case, the value of the resistor R7 can vary from 47 ohms (over 500 Hz) to 1k.

Component ratings indicated through a slash - for frequencies above 1 kHz / for frequencies up to 1 kHz, except for resistors R10, R11, not indicated in the circuit diagram, but for which there are mounting places on the boards, jumpers can be installed instead of these resistors.

Generators do not require adjustment and, with error-free installation and serviceable components, they start working immediately after power is applied to the control circuit and output transistors. The required frequency range is determined by the capacitance of the capacitor C1. The component ratings and positions for both circuits are the same.

Figure 5 shows the assembled generator boards.

List of radio elements

Designation	Type	Denomination	Quantity	Note	Score	My notepad
R1	Resistor	100 kOhm	1			To notepad
R2	Resistor	3.3 kOhm	1			To notepad
R3	Resistor	22/100	1			To notepad
R4	Resistor	10 kOhm	1			To notepad
R5	Resistor	33/100	1			To notepad
R8, R9	Resistor	51/3k3	2			To notepad
R10, R11	Resistor	0.47	2			To notepad
C1	Capacitor	1nF/0.33uF	1			To notepad
C2	Capacitor	0.1u	1			To notepad
C3		1000uFX35V	1			To notepad
C4	electrolytic capacitor	100uF/25V	1			To notepad
C5	electrolytic capacitor	220uF/25V	1			To notepad
C6, C7	electrolytic capacitor	47uF50V	2			To notepad
C8, C9	Capacitor	330uF	2			To notepad
C10, C11	electrolytic capacitor	120uF/400V	2			To notepad
D2, D3, D6, D7	rectifier diode	FR207	4			To notepad
Q2, Q3	bipolar transistor

All the high voltage generators discussed above had a capacitor as an energy storage device. Of no less interest are devices that use inductance as such an element.

In the overwhelming majority of designs of this kind of converters of the early years, they contained a mechanical inductance switch. The disadvantages of such a circuit solution are obvious: these are increased wear of contact pairs, the need for their periodic cleaning and adjustment, and a high level of interference.

With the advent of modern byutro-operating electronic switches, the design of voltage converters with a switched inductive energy storage has become noticeably simpler and more competitive.

The basis of one of the simplest high-voltage generators (Fig. 12.1) is inductive energy storage.

Rice. 12.1. Electric circuit of a high-voltage generator based on an inductive energy storage

The rectangular pulse generator is assembled on a 555 microcircuit (KR1006VI1). Pulse parameters are regulated by potentiometers R2 and R3. The frequency of the control pulses also depends on the capacitance of the time-setting capacitor 01. The pulses from the generator output are fed through the resistor R5 to the base of the key (switching) element - a powerful transistor VT1.

This transistor, in accordance with the duration and frequency of the control pulses, switches the primary winding of the transformer T1.

As a result, high voltage pulses are formed at the output of the converter. To protect the transistor VT1 (2N3055 - KT819GM) from breakdown, it is advisable to connect a diode in parallel with the emitter - collector junction, for example, of the KD226 type (cathode to collector).

The high-voltage generator (Fig. 12.2), developed in Bulgaria, also contains a master square-wave generator on a 555 chip (K1006VI1). The pulse frequency is continuously adjustable by resistor R2 from 85 to 100 Hz. These pulses are fed through RC chains to key elements on transistors VT1 and VT2. Zener diodes VD3 and VD4 protect transistors from damage when operating on an inductive load.

Rice. 12.2. Scheme of a high voltage generator based on an inductive energy storage

The high voltage generator (Fig. 12.2) can be used either independently - to obtain high voltage (usually up to 1 ... 2 kV), or as an intermediate stage of "pumping" other converters.

Transistors BD139 can be replaced by KT943V.

For many years, powerful bipolar transistors have been used as key elements of converters with an inductive energy storage. Their shortcomings are obvious: the residual voltages on the open key are quite high, as a result, energy losses, overheating of transistors.

With the improvement of field-effect transistors, the latter began to push aside bipolar transistors in power supply circuits and voltage converters.

For modern high-power field-effect transistors, the open-key resistance can reach ten ... one hundredth of an ohm, and the operating voltage can reach 1 ... 2 kV.

On fig. 12.3 shows the electrical circuit of the voltage converter, the output stage of which is made on a MOSFET field effect transistor. To match the generator with a field effect transistor, a bipolar transistor with a high transfer coefficient is included.

Electrical circuit of a high-voltage pulse generator with a key field-effect transistor

The master oscillator is assembled on a /SMO/7-chip CD4049 according to a typical scheme. Both the output stages themselves and the stages for generating control signals, shown in Fig. 12.1 - 12.3 ff are interchangeable and may be used in any combination.

The output stage of the high voltage generator of the electronic ignition system designed by P. Bryantsev (Fig. 12.4) is made on a modern domestic element base.

When control pulses are applied to the input of the circuit, transistors VT1 and VT2 open for a short time. As a result, the inductor is briefly connected to the source

Rice. 12.4. Scheme of the output stage of the high voltage generator P. Bryantsev on a composite transistor

Rice. 12.5. Circuit diagram of a high voltage generator with a master oscillator based on Schmitt triggers

nutrition. Capacitor C2 smooths out the peak of the voltage pulse. The resistive divider (R3 and R5) limits and stabilizes the maximum voltage at the collector of the transistor VT2.

The ignition coil B115 was used as a transformer T1. Its main parameters are: Ri=1.6 Ohm, \

The following two schemes of high-voltage voltage generators using inductive energy storage devices (Fig. 12.5, 12.6) were developed by Andres Estaban de la Plaza.

The first of the devices contains a master square-wave generator, an intermediate and output stage, and a high-voltage transformer.

Electrical circuit of a high voltage generator with a master oscillator based on an operational amplifier

The master oscillator is based on a Schmitt trigger (KMO/7-chip type 4093). Using a Schmitt trigger instead of NOT gates (see, for example, Fig. 12.3) allows you to get pulses with steeper fronts, and, therefore, reduce energy losses on key elements.

Matching KMO / 7-elements with a power transistor VT2 is carried out by a preamplifier on a transistor VT1. The output transformer T1 is switched by a power bipolar transistor VT2. This transistor is mounted on a heat sink plate.

The pulse frequency of the generator is changed in steps by the switch SA1. The ratio between the pulse duration and pause and the pulse repetition rate are smoothly regulated by potentiometers R1 and R2.

Switch SA2 turns on / off the resistor R6, connected in series with the primary winding of the step-up transformer. Thus, the output power of the converter is regulated stepwise.

The operating frequency of the generator in its five subbands is adjustable within 0.6 ... 8.5 kHz; 1.5…20 kHz; 5.3…66 kHz; A3…MO kHz; 43…>200 kHz.

The primary winding of the transformer T1, wound on a core from a horizontal-scan transformer, has 40 turns with a diameter of 1.0 mm. The output voltage of the converter at frequencies below 5 kHz is 20 kV, in the frequency range of 50 ... 70 kHz, the output voltage drops to 5 ... 10 / St.

The output power of the high-frequency signal of the device can reach up to 30 watts. In this regard, when using this design, for example, for gas discharge photography, special measures must be taken to limit the output current.

Vyuokoltny generator, fig. 12.6 has a more complex design.

Its master oscillator is made on an operational amplifier DA1 (CA3140). To power the master oscillator and the buffer stage (DDI type 4049 chip), a 12 S voltage regulator is used on a DA2 type 7812 integrated circuit.

The terminal cascade on complementary transistors VT1 and VT2 ensures the operation of the final stage - on a powerful transistor VT3.

The duration/pause ratio is controlled by potentiometer R7, and the pulse frequency by potentiometer R4.

The generation frequency can be changed in steps - by switching the capacitance of the capacitor C1. The initial generation frequency is close to 20 kHz.

The primary winding of the modified horizontal transformer has 5 ... 10 turns, its inductance is approximately 0.5 mH. Protection of the output transistor against overvoltage is carried out by turning on the varistor R9 in parallel with this winding.

Transistor 2N2222 can be replaced with KT3117A, KT645; 2N3055 - on KT819GM; BD135 - on KT943A, BD136 - on KT626A, diodes 1N4148 - on KD521, KD503, etc. The DA2 microcircuit can be replaced with a domestic analogue - KR142EN8B (D); DDI - K561TL1.

The next type of high-voltage voltage generators are self-oscillating voltage converters with inductive feedback.

A pulse converter with self-excitation generates packets of high-frequency high-voltage oscillations (Fig. 12.7).

Rice. 12.7. Electric circuit of a pulse voltage converter with self-excitation

The autogenerator of high voltage pulses on the transistor VT1 receives * a feedback signal from the transformer T1 and has an ignition coil T2 as a load. The generation frequency is about 150 Hz. Capacitors C*, C2 and resistor R4 determine the mode of operation of the generator.

Transformer T1 is made on the magnetic circuit Ш 14×18. Winding I consists of 18 turns of PEV-2 wire 0.85 mm, wound in two wires, and II - of 72 turns of PELSHO wire 0.3 mm.

The VD2 zener diode is fixed in the center of a 40x40x4 mm duralumin radiator. This zener diode can be replaced by a chain of powerful zener diodes with a total stabilization voltage of 150 V. The VT1 transistor is also installed on a 50x50x4 mm radiator.

A resonant voltage converter with self-excitation is described in the work of E. V. Krylov (Fig. 12.8). It is made on a high-frequency powerful transistor VT1 type KT909A.

The converter transformer is made on a fluoroplastic frame with a diameter of 12 mm using a 150VCh ferrite rod with a size of 10 × 120 mm. Coil L1 contains 50 turns, L2 - 35 turns of LESHO wire 7 × 0.07 mm. The coils of the low-voltage half of the device have one turn of wire per

Rice. 12.8. Scheme of a resonant high-voltage generator with transformer feedback

fluoroplastic (polytetrafluoroethylene) insulation. They are wound over the L2 coil.

The output voltage of the converter is 1.5 kV (maximum - 2.5 kV). Conversion frequency - 2.5 MHz. Power consumption - 5 W. The output voltage of the device changes from 50 to 100% when the supply voltage increases from 8 to 24 V.

With a variable capacitor 04, the transformer is tuned to the resonant frequency. Resistor R2 sets the operating point of the transistor, regulates the level of positive feedback and the shape of the generated signals.

The converter is safe in operation - with a low-resistance load, the wave-frequency generation breaks down.

The following diagram of a high-voltage pulsed voltage source with a two-stage conversion is shown in fig. 12.9. The electrical circuit of its first stage is quite traditional and practically does not differ from the previously considered designs.

The difference between the device (Fig. 12.9) is the use of the second stage of increasing the voltage on the transformer. This significantly increases the reliability of the device, simplifies the design of transformers and provides effective isolation between the input and output of the device.

The T1 transformer is made on a W-shaped core made of transformer steel. The core cross section is

Rice. 12.9. Scheme of a high-voltage converter with transformer feedback and double transformer voltage conversion

16×16 mm. Collector windings I have 2 × 60 turns of wire with a diameter of 1.0 mm.

The feedback coils II contain 2x14 turns of 0.7mm diameter wire. The step-up winding III of the transformer T1, wound through several layers of interlayer insulation, has 20 ... 130 turns of wire with a diameter of 1.0 mm. The ignition coil of a car for 12 or 6 V was used as an output (high-voltage) transformer.

The generators of high voltage with inductive energy storage devices should also include the devices discussed below.

To obtain high-voltage nanosecond pulses, V. S. Belkin and G. I. Shulzhenko developed a shaper circuit based on drift diodes and saturable inductance with a single-cycle converter synchronized with the shaper, and also showed the possibility of combining the functions of the shaper switch and the converter.

The diagram of the converter synchronized with the shaper is shown in fig. 12.10; a variant of the shaper circuit with separate key elements is shown in Fig. 12.11, and the timing diagrams characterizing the operation of individual components of the shaper circuit are shown in fig. 12.12.

The master square-wave generator (Fig. 12.10) generates pulses that unlock the transistor key VT1

Rice. 12.10. Scheme of a high-voltage pulse shaper with a common key for the converter and shaper

Rice. 12.11. Fragment of the high-voltage pulse shaper circuit with separate keys

Rice. 12.12. Timing diagram of converter operation

for time 1n and locking for time \^ (Fig. 12.12). Their sum determines the pulse repetition period. During the time, a current I„ flows through the inductor L1. After the transistor is turned off, the current through the diode VD1 charges the storage capacitance of the shaper C1 to a voltage u^, the diode VD1 closes and cuts off the capacitor C1 from the power source.

Table 12.1 shows data on the possible use of semiconductor devices in the shaper of high-voltage pulses. The amplitude of the generated pulses is given for a low-resistance load of 50 Ohms.

Table 12.1. Selection of elements for high-voltage pulse shapers

Pulse duration, NS	Amplitude of the generated pulse, V
	KD204, KD226 (KT858, KT862)
		DL112-25(CT847)	DL122-40 (KP953)
		KD213 (KT847)	DL132-80 (KP953)

Bipolar pulse shapers based on serial diodes have an amplitude of each half-wave of 0.2 ... 1 kV for a matched load of 50 ... 75 Ohms with a total pulse duration of 4 ... 30 NS and a repetition rate of up to 20 kHz.