Schematic diagram of the pulse generator. Calculation of pulse generators

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

Initial data:

· Type of technological process and its characteristics;

· Constructive use of the discharge circuit;

· Characteristics of supply voltage;

· Parameters of the electric pulse, etc.

Calculation sequence:

The sequence of the calculation 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 constant (alternating) voltage, an auto-generator, a rectifier, a discharge circuit, a high-voltage transformer, a load (Figure 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 - autogenerator; 3 - rectifier; 4 - smoothing filter; 5 - discharge circuit with a high-voltage transformer; 6 - load.

Calculation of the converter (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 400Hz.

The output voltage of the converter is selected from the conditions for increasing the stability of the generator frequency and to obtain good linearity of the output voltage pulses, i.e. U n \u003e\u003e U on dash, usually U n \u003d 2U on dash.

The frequency of the output voltage is set on the basis of the conditions for optimum performance of the master oscillator of the voltage converter.

The values \u200b\u200bof P 0 and U 0 make it possible to use the KY102 series dinistor VS in the generator circuit.

As a transistor VT, we use MP26B, for which the limiting modes are as follows: U kbm \u003d 70V, I KM \u003d 0.4A, I bm \u003d 0.015A, U kbm \u003d 1V.

We offer the transformer core made of electrical steel. We accept B M \u003d 0.7T, η \u003d 0.75, 25s.

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

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

Collector current of the transistor

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

AND.

Base current:

I bm \u003d 1.2 · 0.003 \u003d 0.0036A.

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

Resistor resistance in the voltage divider circuit:

Ohm; (2.79)

Ohm.

We accept the nearest standard values \u200b\u200bof the resistances of the resistors R 1 \u003d 13000 Ohm, R 2 \u003d 110 Ohm.

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:

Fig 2.15. Principled electrical circuit pulse generator: a - converter;

b - pulse generator

We choose a core Ш8 × 8, for which S c \u003d 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 capacity VC1:

Diameter of wires of windings of transformer TV1:

We choose 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.

Figure: 2.16. Calculation scheme of the pulse generator

Calculation of pulse generators (Fig.2.16)

We accept the voltage at the generator input equal to the voltage at the converter output U 0 \u003d 300 V. Pulse frequency f \u003d 1… 2 Hz. Pulse voltage amplitude is not more than 10 kV. The amount of electricity in a pulse is no more than 0.003 Cl. Pulse duration up to 0.1 s.

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

Direct resistance to direct current of the diode R dd \u003d 3.3 Ohm and thyristor R td \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. Its resistance:

Ohm, (2.90)

where U p is the voltage across the charging capacitor VC2 at the beginning of the discharge, its value is equal to U off. In this case, the condition R 1 \u003e\u003e R 2 (20 · 10 3 \u003e\u003e 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 VC2:

. (2.93)

Capacitance VC2 for frequency f \u003d 1 Hz:

F

And for a frequency of 2 Hz:

C 2 \u003d 36 · 10 -6 F.

Amplitude of the current in the charging circuit of the capacitor VC2

, (2.94)

Amplitude of the current in the charging circuit of the capacitor VC2:

, (2.95)

Pulse energy:

J. (2.96)

Maximum amount of electricity per 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 is the efficiency of a low-power transformer.

Cross-sectional area of \u200b\u200bthe transformer core:

The number of turns of each transformer winding per

vit / B. (2.100)

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

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.

Diameter of wires in windings (2.85):

mm;

mm.

We select 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 fig. 2.16.

Given: U c \u003d 300 V AC 400 Hz, C \u003d 36 10 -6 F, R d.p \u003d 10 Ohm, R tp \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.

Impedance of the capacitance charge circuit VC2:

The charge current is:

AND.

Pulse generators are designed to produce pulses of a certain shape and duration. They are used in many circuits and devices. They are also used in measuring technology for setting up and repairing various digital devices. Square waveforms are great for testing digital circuitry, while triangular waveforms can be useful for sweep or sweep oscillators.

The generator generates a single rectangular pulse by pressing a button. The circuit is assembled on logical elements based on a regular RS-trigger, thanks to which it also excludes the possibility of penetration of bounce pulses of the button contacts to the counter.

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 low-level or logical zero output, when the button is pressed, the trigger state will change to the opposite. This generator is perfect for checking 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 options: to simulate input signals of digital devices, when checking the operability of circuits based on digital microcircuits, the need to supply a certain number of pulses to some device under test with visual control of processes, etc.

As soon as the power supply of the circuit is turned on, the capacitor C1 starts charging and the relay operates, 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 close 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. Such a generator can be used, for example, to switch Christmas tree lights and other effects. The disadvantage of this circuit is the use of a large capacitor.

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

In the pulse generator, in Figure A, three logical elements NAND and a unipolar transistor VT1 are used. Depending on the values \u200b\u200bof the capacitor C1 and the resistors R2 and R3 at the output 8, pulses are generated 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 megohm resistors R2 and R3. With the help of them, you can also change the duty cycle of the pulses: resistor R2 sets the duration of the high level, and R3 sets the duration of the low level voltage. VT1 can be taken from any of the KP302, KP303 series. - K155LA3.

If you use CMOS microcircuits instead of K155LA3, for example K561LN2, you can make a wide-range pulse generator without using a field-effect transistor in the circuit. The circuit 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 up to 10 kHz.

The last figure shows the circuit of the pulse generator in which the possibility of adjusting the duty cycle is incorporated. For those who have forgotten, recall. The 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 the 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 producing rectangular and sawtooth pulses. The master generator is made on the logic elements DD 1.1-DD1.3 of the digital microcircuit K561LN2. Resistor R2 paired with capacitor C2 form a differentiating circuit, which at the output 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. A charging capacitor C3 flows from its output 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. Thus, forming a sawtooth stress on its plates. A variable resistor 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 LM741 type op amps. The first op amp is used to generate a rectangular shape, and the second one generates a triangular shape. The generator circuit is structured as follows:

In the first LM741, the inverting input from the amplifier output is connected feedback (OS) made on resistor R1 and capacitor C2, and the OS also goes to the non-inverting input, but already 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 R4. This second op-amp together with R4 and C1 form the integrator circuit. Its non-inverting input is grounded. Both op amps are supplied with supply voltages + Vcc and –Vee, as usual on the seventh and fourth pins.

The scheme works as follows. Suppose initially there is + Vcc at the U1 output. Then the capacitance C2 begins to charge through the resistor R1. At a certain point in time, the voltage on 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 V 1 output will become –Vee. So, the capacitor begins to discharge through the resistor R1. When the voltage across the capacitance falls below the formula voltage, the output will again be + Vcc. Thus, the cycle repeats, and due to this, rectangular pulses are generated with a period of time determined by an RC network consisting of a resistance R1 and a capacitor C2. These rectangular formations are also input signals to the integrator circuit, which converts them to a triangular form. When the output of op amp U1 is + Vcc, C1 is charged to its maximum level and produces a positive, upward triangle slope at the output of op amp U2. And, accordingly, if at the output of the first OS there is -Vee, then a negative, descending 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 microcircuit, 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 the power supplies of personal computers.

You can download the PCB layout from the link above.

The pulse repetition rate can be changed by switch S2 and 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 antiphase. Resistor R3 should cover the frequency range, and the duty cycle adjustment range is adjusted by selecting R1, R2

C1-4 capacitors from 1000 pF to 10 μF. Any high-frequency transistors KT972

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 oscillation form 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 impulses the form of a meander when the pulse duration is equal to the pause duration between them

It generates powerful short single pulses that set the opposite logic level at the input or output of any digital element. The pulse duration is chosen so as not to damage 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.

And finally, hands got around. After assembling small coils, I decided to swing at a new circuit, more serious and difficult to set up and work with. Let's move from words to deeds. The complete diagram looks like this:

Works on the principle of an auto-generator. The chopper kicks the driver UCC27425 and the process begins. The driver gives a pulse to the GDT (Gate Drive Transformator - literally: the transformer that controls the gates) with the GDT there are 2 secondary windings included in antiphase. Such inclusion provides alternate opening of transistors. During the opening, the transistor pumps current through itself and a 4.7 μF capacitor. At this moment, a discharge is formed on the coil, and the signal goes through the OS to the driver. The driver changes the direction of the current in the GDT and the transistors change (which was open - closes, and the second opens). And this process is repeated as long as there is a signal from the breaker.

It is best to wind GDT on an imported ring - Epcos N80. The windings are wound in a 1: 1: 1 or 1: 2: 2 ratio. On average, about 7-8 turns, if desired, you can calculate. Consider the RD chain in the gates of power transistors. This chain provides Dead Time. This is the time when both transistors are off. That is, one transistor has already closed, and the second has not yet managed to open. The principle is this: the transistor smoothly opens through the resistor and quickly discharges through the diode. The oscillogram looks like this:

If you do not provide dead time, then it may turn out that both transistors will be open and then a power explosion is provided.

Move on. OS (feedback) is made in this case in the form of CT (current transformer). TT is wound on an Epcos N80 ferrite ring for at least 50 turns. The lower end of the secondary winding is pulled through the ring, which is grounded. Thus, the high current from the secondary winding turns into a sufficient potential on the CT. Further, the current from the CT goes to the capacitor (smooths out interference), Schottky diodes (only pass one half-cycle) and the LED (acts as a zener diode and visualizes generation). For the generation to be, it is also necessary to observe the phrasing of the transformer. If there is no generation or very weak - you just need to turn the TT.

Let's consider the breaker separately. Of course I sweated with the breaker. Collected pieces of 5 different ... Some are puffy from high-frequency current, others do not work as it should. Next, I'll tell you about all the breakers that I did. Perhaps I'll start with the very first - on TL494... The scheme is standard. Possibility of independent adjustment of frequency and duty cycle. The circuit below can generate from 0 to 800-900 Hz by replacing 1 μF with a 4.7 μF capacitor. The duty cycle is from 0 to 50. What you need! However, there is one BUT. This PWM controller is very sensitive to RF current and various fields from the coil. In general, when connected to the coil, the breaker simply did not work, either all at 0 or CW mode. Escaping partially helped, but did not completely solve the problem.

The next breaker was assembled on UC3843 very often found in IIP, especially ATX, from there, in fact, he took it. The circuit is also not bad and is not inferior TL494 by parameters. Here you can adjust the frequency from 0 to 1 kHz and the duty cycle from 0 to 100%. That was fine with me too. But again, these pickups from the coil ruined everything. Even shielding didn't help at all here. I had to refuse, although I assembled it well on the board ...

I thought of returning to oak and reliable, but little functional 555 ... I decided to start with a burst interrupter. The essence of an interrupter is that it interrupts itself. One microcircuit (U1) sets the frequency, the other (2) the duration, and the third (U3) the operating time of the first two. Everything would be fine if it were not for the small pulse duration with U2. This breaker is sharpened for DRSSTC and can work with SSTC, but I did not like it - the discharges are thin, but fluffy. Then there were several attempts to increase the duration, but they were unsuccessful.

Generator diagrams for 555

Then I decided to change the schematic diagram and make an independent duration on the capacitor, diode and resistor. Many may find this scheme absurd and silly, but it works. The principle is this: the signal to the driver goes until the capacitor is charged (I think no one will argue with this). NE555 generates a signal, it goes through a resistor and a capacitor, while if the resistance of the resistor is 0 Ohm, then it goes only through the capacitor and the duration is maximum (how much capacity is enough), regardless of the generator duty cycle. The resistor limits the charging time, i.e. the greater the resistance, the less time the impulse will take. The driver receives a signal with a shorter duration, but the same frequency. The capacitor is discharged quickly through a resistor (which goes to ground 1k) and a diode.

Pros and cons

pros : Frequency independent duty cycle adjustment, SSTC will never go to CW mode if breaker burns.

Minuses : the duty cycle cannot be increased "infinitely much", such as by UC3843, it is limited by the capacitance of the capacitor and the duty cycle of the generator itself (it cannot be more than the duty cycle of the generator). The current flows through the capacitor smoothly.

On the latter, I do not know how the driver reacts (smooth charging). On the one hand, the driver can also smoothly open the transistors and they will heat up more. On the other hand UCC27425 - digital microcircuit. For her there is only a log. 0 and log. 1. So while the voltage is above the threshold - UCC works, as soon as it falls below the minimum - it does not work. In this case, everything works normally, and the transistors open completely.

Let's move from theory to practice

I assembled a Tesla generator in a case from ATX. Power supply capacitor 1000 microfarad 400v. Diode bridge from the same ATX at 8A 600V. I put a 10 W 4.7 ohm resistor in front of the bridge. This ensures smooth charging of the capacitor. To power the driver, I installed a 220-12V transformer and also a stabilizer with a 1800 uF capacitor.

I screwed the diode bridges onto the radiator for convenience and for heat dissipation, although they hardly get warm.

I assembled the breaker almost with a canopy, took a piece of PCB and cut out the tracks with a clerical knife.

The power unit was assembled on a small radiator with a fan; later it turned out that this radiator is quite enough for cooling. The driver mounted it over the power pack through a thick piece of cardboard. Below is a photo of an almost assembled design of a Tesla generator, but being tested, measured the temperature of the power one under various modes (you can see a regular room thermometer, stuck to the power one on thermoplastic).

The toroid of the coil is assembled from a corrugated plastic pipe with a diameter of 50 mm and pasted over with aluminum tape. The secondary winding itself is wound on a 110 mm pipe 20 cm high with a 0.22 mm wire about 1000 turns. The primary winding contains as many as 12 turns, made with a margin in order to reduce the current through the power section. I did it with 6 turns at the beginning, the result is almost the same, but I think it's not worth risking transistors for a couple of extra inches of discharge. The frame of the primary is an ordinary flower pot. From the beginning I thought that it would not break through if the secondary housing is wrapped with tape, and the primary housing is over the tape. But alas, it pierced ... Of course, it also pierced in the pot, but here the scotch tape helped to solve the problem. In general, the finished structure looks like this:

Well, a few pictures with a discharge

Now everything seems to be.

A few more tips: do not try to plug the coil into the network right away, not the fact that it will work immediately. Constantly monitor the power temperature, it can bang when overheated. Do not wind too high-frequency secondary, transistors 50b60 can work at a maximum of 150 kHz on the datasheet, in fact a little more. Check the breakers, the life of the coil depends on them. Find the maximum frequency and duty cycle at which the power temperature is stable for a long time. Too large a toroid can also damage the power unit.

SSTC video

P.S. Power transistors used IRGP50B60PD1PBF. Project files. Good luck, I was with you [) eNiS!

Discuss the article TESLA GENERATOR

The current pulse generator (PCG) is designed to generate repetitive current impulses that reproduce the electrohydraulic effect. The circuit diagrams of the GIT were proposed back in the 1950s and have not undergone significant changes over the years, but their component equipment and the level of automation have significantly improved. Modern PCGs are designed to operate in a wide range of voltage (5-100 kV), capacitance (0.1-10,000 μF), stored energy of the storage device (10-106 J), pulse repetition rate (0.1-100 Hz).

The above parameters cover most of the modes in which electro-hydraulic installations for various purposes operate.

The choice of the GIT scheme is determined in accordance with the purpose of specific electro-hydraulic devices. Each generator circuit includes the following main blocks: power supply - transformer with rectifier; energy storage - capacitor; switching device - forming (air) gap; load - working spark gap. In addition, the PCG circuits include a current-limiting element (this can be resistance, capacitance, inductance, or their combined combinations). The PCG circuits can have several forming and working spark gaps and energy storage devices. Power supply of the PCG is carried out, as a rule, from the AC mains of industrial frequency and voltage.

GIT works as follows. Electric energy through the current-limiting element and the power supply enters the energy storage capacitor. The energy stored in the capacitor with the help of a switching device - an air forming gap - is impulsively transmitted to the working gap in the liquid (or other medium), where the electric energy of the storage unit is released, resulting in an electrohydraulic shock. In this case, the shape and duration of the current pulse passing through the discharge circuit of the PCG depend both on the parameters of the charging circuit and on the parameters of the discharge circuit, including the working spark gap. If, for single impulses of special PCGs, the parameters of the charging circuit (power supply) circuit do not have a significant effect on the general energy indicators of electrohydraulic installations for various purposes, then in industrial PCGs the efficiency of the charging circuit significantly affects the efficiency of the electrohydraulic installation.

The use of reactive current-limiting elements in PCG circuits is due to their ability to accumulate and then release energy into the electrical circuit, which ultimately increases the efficiency.

The electrical efficiency of the charging circuit is a simple and reliable circuit in operation (a PCG with a limiting active charging resistance (Fig. 3.1, a) is very low (30-35%), since the capacitors are charged in it by pulsating voltage and current. voltage regulators (magnetic amplifier, saturation choke), it is possible to achieve a linear change in the current-voltage characteristic of the capacitive storage charge and thereby create conditions under which energy losses in the charging circuit will be minimal, and the overall efficiency of the PCG can be brought to 90%.

To increase the total power when using the simplest PCG circuit, in addition to the possible use of a more powerful transformer, it is sometimes advisable to use a PCG that has three single-phase transformers, the primary circuits of which are connected by a "star" or "triangle" and are powered from a three-phase network. The voltage from their secondary windings is fed to separate capacitors, which work through a rotating forming-gap for one common working spark gap in the liquid (Fig. 3.1, b) [- |]. .4

When designing and developing a PCG of electrohydraulic installations, the use of the resonant mode of charging a capacitive storage from an AC source without a rectifier is of considerable interest. The electrical efficiency of resonant circuits is very high (up to 95%), and when they are used, an automatic significant increase in the operating voltage occurs. It is advisable to use resonant circuits when operating at high frequencies (up to 100 Hz), but this requires special capacitors designed to operate on alternating current. When using these circuits, it is necessary to observe the well-known resonance condition

W \u003d 1 / L [HS,

Where is the co-frequency of the forcing EMF; L-circuit inductance; C is the capacity of the circuit.

A single-phase resonant PCG (Figure 3.1, c) can have a total electrical efficiency in excess of 90%. The PCG allows obtaining a stable frequency of alternation of discharges, which is optimally equal to either a single or double frequency of the supply current (i.e., 50 and 100 Hz, respectively) when powered by a current of industrial frequency. The use of the circuit is most rational (. With a power of the supply transformer of 15-30 kW. A synchronizer is introduced into the discharge circuit of the circuit - an air-forming gap, between the balls of which there is a rotation

A wobbling disc with a contact that triggers the forming gap when the contact passes between the balls. In this case, the rotation of the disk is synchronized with the moments of voltage peaks.

The diagram of a three-phase resonant PCG (Fig. 3.1, d) includes "a three-phase step-up transformer, each winding on the high side of which works as a single-phase resonant circuit n ^ one common for all or three independent working spark gaps with a common synchronizer for three forming gaps This circuit allows you to obtain a frequency of alternation of discharges equal to three or six times the frequency of the supply current (ie, 150 or 300 Hz, respectively) when operating at industrial frequency. The circuit is recommended for operation at a PCG power of 50 kW or more. The three-phase PCG circuit is more economical, since the charging time of a capacitive storage (of the same power) is less than when using a single-phase PCG circuit. However, a further increase in the rectifier power will be advisable "only up to a certain limit.

It is possible to increase the efficiency of the process of charging the capacitive storage of the PCG by using various circuits with a filter capacity. The PCG circuit with a filter capacitance and an inductive charging circuit of a working capacitance (Fig. 3.1, (3) allows you to obtain practically any pulse alternation frequency when operating on small (up to 0.1 ^ μF) capacities and has an overall electrical efficiency of about 85%. This is achieved by the fact that the filter capacitance operates in an incomplete discharge mode (up to 20%), and the working capacitance is charged through an inductive circuit - a choke with a low active resistance - during one half-period in an oscillatory mode, set by the rotation of the disk at the first forming gap. In this case, the filter capacity exceeds the working capacity by 15-20 times.

The rotating disks of the forming spark gaps sit on the same shaft and therefore the frequency of the alternating discharges can be varied within a very wide range, which is as much as possible limited only by the power of the supply transformer. This circuit can use 35-50 kV transformers as it doubles the voltage. The circuit can also be connected directly to the high-voltage network.

In the PCG circuit with a filter tank (Fig. 3.1, e), the alternate connection of the working and filter containers to the working spark gap in the liquid is carried out using one rotating spark gap - the forming gap. However, during the operation of such a PCG, the operation of the rotating spark gap begins at a lower voltage (when the balls approach each other) and ends with a greater (when the balls are removed) than is specified by the minimum distance between the spark gap balls. This leads to instability of the main parameter

Discharges - .voltage, and, consequently, to a decrease in the reliability of the generator.

To increase the reliability of the PCG operation by ensuring the specified stability of the discharge parameters, a rotating switching device is included in the PCG circuit with a filter capacity - a disk with sliding contacts for alternate preliminary currentless switching on and off of the charging and discharge circuits.

When voltage is applied to the generator circuit, the filter capacitance is initially charged. Then, a rotating contact without current (and therefore without sparking) closes the circuit, a potential difference arises on the balls of the forming spark gap, a breakdown occurs and the working capacitor is charged to the voltage of the filter capacitance. After this, the current in the circuit disappears and the contacts are opened again without sparking by the rotation of the disk.Then, the rotating disk (also without current and sparking) closes the contacts of the discharge circuit and the voltage of the working capacitor is applied to the forming discharge, its breakdown occurs, as well as the breakdown of the working spark gap in the liquid. In this case, the working capacitor is discharged, the current in the discharge circuit stops and, therefore, the contacts can be opened again by rotating the disk without sparking destroying them.

The use of a PCG of this type makes it possible to obtain stable parameters of stationary spherical arresters and to close and open the circuits of the charging and discharge circuits in a no-current mode, thereby improving all indicators and reliability of the generator of the power plant.

A power supply scheme for electrohydraulic installations was also developed, which allows the most rational use of electrical energy (with a minimum of possible losses). In the known electrohydraulic devices, the working chamber is grounded and therefore part of the energy after the breakdown of the working spark gap in the liquid is practically lost, dissipating on the ground. In addition, with each discharge of the working capacitor, a small (up to 10% of the initial) charge remains on its plates.

Experience has shown that any electro-hydraulic device can effectively operate according to a scheme in which the energy stored on one capacitor C1, passing through the forming gap of the FP, enters the working spark gap of the RP, where most of it is spent on performing the useful work of the electro-hydraulic shock. The remaining unused energy goes to the second uncharged capacitor C2, where it is stored for later use (Fig. 3.2). After that, the energy of the recharged to the required
the value of the potential of the second capacitor C2, passing through the forming gap of the FP, is discharged to the working spark gap of the RP, and the newly unused part of it now falls on the first capacitor of the CS, etc.

The alternate connection of each of the capacitors, either to the charging or to the discharge circuit, is performed by the switch / 7, in which the conductive plates A and B, separated by a dielectric, are alternately connected to the contacts 1-4 of the charging and discharge circuits.

The requirements for pulse generators (PIs) include the need to achieve high efficiency. In addition, they are determined by the properties of the interelectrode gap (IEP) - a sharply nonlinear element of the electrical circuit.

Stability of current pulses - the constancy of their duration depends on the constancy of the properties of the gap and the steepness of the leading edge of the voltage pulse. The greater this slope, the more stable the current pulses. Hence, another requirement for pulse generators follows - a high degree of steepness of the leading edge of the voltage pulse.

The supply of energy pulses to the interelectrode gap during EDM can be carried out according to the structural diagram shown in Fig. 1, a.

Fig. 1 Block diagrams of the power supply for the EDM installation and timing diagrams of voltage and current

During the time τ and the switch K is closed and the power source gives the load (MEM) power P and, which is n times greater than the average power over the pulse repetition period T.

The power of the power supply must be equal to P and \u003d I m * U m, where I m and U m are the amplitude values \u200b\u200bof voltage and current during the pulse. It is consumed only in the time interval τ and.

If we neglect the losses in the energy storage device, then the energy given off by the storage device in the MEM will be A \u003d P and * τ and, and the power of the source is P \u003d A / T \u003d P and * τ and / T \u003d P and / n, i.e. when introduced into the block diagram of the energy storage, the power of the source can be reduced by a factor of n.

A schematic diagram of an electric discharge plant, which ensures operation with energy storage devices, is shown in Fig. 1, b.

During the pause P and * τ and the switch K is in position 1, and through the current limiter, the drive consumes power P / n from the power source. At the same time, the storage device stores energy A \u003d P and * τ and, which, when switching the switch K for the pulse time τ and in position 2, gives off power P and \u003d A / τ and.

Working according to this scheme makes it possible to transform the power of the source P \u003d P and / n into power that is consumed under load.

Pulse generators are distinguished by the principle of operation, design and pulse parameters. GIs are conditionally subdivided into dependent, limited-dependent and independent. In the first of them, the parameters of the generated pulses are determined by the physical state of the interelectrode gap. In independent generators, pulses are not associated with the state of the IEP.

Electric energy in the storage device can be stored in the form of an electric field of a capacitor or an electromagnetic field of an inductive coil. Also used are combined storage devices containing active resistances, capacitance and inductance - relaxation generators (Fig. 2).

Fig. 2 Schematic diagrams of relaxation generators for EEE installations

In the process of their discharge, the energy stored in the reactive elements of the circuit (capacitor or inductive coil) is consumed.

RC-pulse generator (Fig. 2, a) consists of a series-connected power supply G, key TO, current-limiting resistance R 1 and a storage capacitor C 1connected in parallel with the IEP.

Capacitive storage is charged from a power source through a limiting resistance R 1 due to which the winding current is much less than the pulse current I and. The capacitor charging current is determined from the ratio i 1 \u003d (dUc / dτ) * С. Capacitor voltage where U co is the initial voltage across the capacitor at the moment τ \u003d 0. By the end of charging the voltage U c will be equal to the voltage of the power supply. Discharge occurs within time τ \u003d T/n... In the case of a large pulse duty cycle, the average value of the discharge current during the passage of the pulse τ and in n times the charging current, therefore the capacitive storage is essentially a current transformer.

In an inductive storage, the rate of rise of the current in the inductance is determined by its value and the applied voltage. Required current I and can be obtained at low values \u200b\u200bof the voltage drop across the inductance U to<

In the processes of electrical discharge machining, generators with a capacitive storage are more widely used, since an inductive storage is inferior to a capacitive storage in terms of energy indicators.

Pulse circuit LC-generator is shown in fig. 2, b. The charging current flows to the capacitor FROM from power source G through the vibrator winding L... First it pulls the anchor I AM electromagnetic vibrator and increases the interelectrode gap by raising the tool electrode.

By the end of the capacitor charging, the current through the vibrator winding gradually decreases, the electromagnetic force holding the vibrator armature weakens and the electrodes begin to approach each other, reducing the IEP. After the breakdown of the IED and the passage of the current pulse, the cycle of the generator is repeated. The pulse frequency is determined by the ratio L and C in the generator circuit.

Generators made according to this scheme have high efficiency and productivity.

Introduction to the charging circuit of the RC inductor generator (go to the generator RLC) increases the efficiency of the generator, since in this case the current-limiting resistance decreases. RLC-generators (Fig. 2, c) operate at a lower voltage than RC-generators, since in the presence of resonance between L and FROM the voltage across the storage capacitor turns out to be greater than the power supply voltage.

Charging circuit transient equation RLC-generator has the form

From this equation it follows that the charge of a capacitor can occur exponentially or according to an oscillatory law.

The oscillatory process occurs when. In this operating mode of the charging circuit, the voltage across the capacitor at the end of the charging period τ zar is equal to almost double the EMF.

In fact, the maximum voltage up to which the capacitor can be charged depends on the ratio R 1 / (2L 1).

EEE also applies SS- a pulse generator, in which a capacitor C 1 is used as a current-limiting element. Such a generator has a higher efficiency compared to LC- a generator with an electromagnetic vibrator. Frequency properties SS- generators are determined mainly by the frequency characteristics of the rectifier diodes IN.

The main disadvantage of relaxation generators is the connection between the frequency of current pulses and the physical state of the IEP. It can be eliminated if a controlled switch is introduced into the discharge circuit, which at a given time would connect a storage capacitor to the IEP.

To power the EEE devices, there are static pulse generators that regulate time and energy parameters in a wide range in the absence of storage elements. They easily form rectangular and unipolar pulses. By the way they are generated, they are divided into generators with independent excitation, autogenerators and inverters.

Structurally, they are mainly based on transistor or thyristor devices.

The block diagram of a wide-range pulse generator is shown in Fig. 2.3.

Fig. 3 Block diagram of a wide-range transistor pulse generator

It includes a power supply, power units, the number of which can be equal to six, with a separating diode VD, an ignition unit, a master oscillator, a power preamplifier, a working gap (MEP), a short circuit protection unit. The power blocks and the ignition block include power transistors operating in the key mode and switching synchronously from the master generator. When the transistors are turned on, a low-power pulse is supplied from the ignition unit. It contributes to the breakdown of the gap and the formation of a low-voltage discharge. Before breakdown, the isolation diode D is closed. After breakdown, the voltage across the gap drops to 40-25 V, diode D opens and a current pulse passes through the gap, the value of which is determined by the number of power units connected in parallel. Their synchronous shutdown interrupts the discharge. In the event of a short circuit in the electrode gap of the MEP, all transistors of the power units are turned off. The supply of pulses to the IEP resumes after the elimination of the short circuit.

For EEE of metals using high-energy pulses with a frequency of 50-100 Hz, static pulse generators are used - industrial frequency transformers with a valve.

Energy pulses with a duration of up to milliseconds are obtained using pulse generators, which, according to the principle of operation, are divided into commutator and inductor generators.

The magnetic commutator generator (MCG) includes an alternating-pole magnetic system on a stator and an armature winding. The armature winding on its circumference is unevenly distributed on narrow parts under the poles, of which the ICG is much larger than that of conventional machines, due to which the generator current frequency increases. When the generator armature rotates in its winding, located in a narrow section opposite the poles of the inductor, a symmetrical pulse EMF is induced at the moment of its passage through the alternating-pole inductor.

The unipolarization of pulses is carried out using a collector (commutator) located on the same shaft with the armature, consisting of two systems of segments with brushes superimposed on them. The presence of pauses between pulses facilitates commutation, since the transition of brushes from one segment system to another occurs at the moment of the absence of voltage in the armature winding.

The machine inductor pulse generator (MTI) is a brushless electric machine that generates an alternating voltage of increased frequency. Its main feature is the absence of a rotating pole system, which is replaced by a gear inductor. The armature winding and excitation are located on the generator stator. Variable magnetic flux occurs due to a change in the resistance of the magnetic circuit of the generator, due to the gearing of the rotating inductor.

Due to the use of a gear inductor, an asymmetrical AC voltage curve with different amplitudes of half-waves of positive and negative polarity is obtained. With a sufficiently small amplitude of the reverse voltage half-wave, the IEP breakdown occurs only with voltage pulses of straight polarity, as a result of which the current pulses will always be unipolar.

Industrial power supplies for EEE installations.

Thyristor pulse generator of TG-250-0.15M type is designed to convert three-phase alternating current of industrial frequency into a pulse current with a frequency of 150 Hz with adjustable duty cycle. It is used as a power source with technological current for electric discharge machines models 4723, 4A724, 4D723, 4D26.

The maximum productivity of the machine when powered by a thyristor pulse generator is 4000 mm 3 / min in the case of processing steel 45 with a copper tool and 3500 mm 3 / min when processing with a graphite tool.

The pulse generator includes blocks of valves, ignition, control, flow and resistance regulator, as well as transformers and inductive ballasts. The valve block is assembled according to the scheme of a three-phase semi-controlled bridge on diodes and thyristors. The ignition unit, synchronously with the power ones, generates high-voltage pulses with an amplitude of 400-500 V, which break through the erosion gap and form a low-voltage discharge. For automatic maintenance of the working distance of the erosion gap, a feed control unit with voltage feedback is provided. Structurally, the pulse generator is made in the form of a double-sided service metal cabinet. Compulsory air cooling.

Manufacturer - Software "Transformer", Zaporozhye.