Pulse voltage removal from a charged capacitor circuit. ¡ — Experiments with capacitors

Laboratory work No. 6

STUDYING THE PROCESS OF CHARGING AND DISCHARGING A CAPACITOR

GOAL OF THE WORK

Study of the processes of charging and discharging capacitors in R.C.- circuits, familiarization with the operation of devices used in pulsed electronic technology.

THEORETICAL BASIS OF WORK

Let's consider the diagram shown in Fig. 1. The circuit includes a direct current source, an active resistance and a capacitor, in which we will consider the charge and discharge processes. We will analyze these processes separately.

Capacitor discharge.

Let first a current source e be connected to a capacitor C through a resistance R. Then the capacitor will charge as shown in Fig. 1. Let's move key K from position 1 to position 2. As a result, the capacitor is charged to voltage e, will begin to discharge through resistance R. Considering the current positive when it is directed from the positively charged plate of the capacitor to the negatively charged one, we can write

https://pandia.ru/text/78/025/images/image003_47.gif" width="69 height=25" height="25">, , (1)

Where i– instantaneous value of current in the circuit, the minus sign of which indicates that the appearance of current in the circuit i associated with a decrease in charge q on the capacitor;

q And WITH– instantaneous values of charge and voltage on the capacitor.

Obviously, the first two expressions represent the definitions of current and electrical capacity, respectively, and the last is Ohm's law for a section of the circuit.

From the last two relations we express the current strength i in the following way:

https://pandia.ru/text/78/025/images/image006_31.gif" width="113" height="53 src=">. (2)

18. Why is there no DC source in this installation as shown in the circuit diagram?

19. Is it possible to use a sinusoidal voltage generator or a sawtooth voltage generator in this installation?

20. What frequency and duration of pulses should the generator produce?

21. Why is active resistance needed in this circuit? R? What should its size be?

22. What types of capacitors and resistors can be used in this installation?

23. What values can capacitance and resistance have in this circuit?

24. Why is oscilloscope signal synchronization needed?

25. How do you achieve the optimal appearance of the signal on the oscilloscope screen? What adjustments apply?

26. What is the difference between the charge and discharge circuits of a capacitor?

27. What measurements need to be taken to determine the capacitance of the capacitor in R.C.-chains?

28. How to evaluate measurement errors during operation of the installation?

29. How to improve the accuracy of determining relaxation time R.C.-chains?

30. Name ways to improve the accuracy of determining the capacitance of a capacitor.

High-voltage, low-power generators are widely used in flaw detection, to power portable charged particle accelerators, X-ray and cathode ray tubes, photomultiplier tubes, and ionizing radiation detectors. In addition, they are also used for electric pulse destruction of solids, production of ultrafine powders, synthesis of new materials, as spark leak detectors, for launching gas-discharge light sources, in electric-discharge diagnostics of materials and products, obtaining gas-discharge photographs using the S. D. Kirlian method , testing the quality of high-voltage insulation. In everyday life, such devices are used as power sources for electronic ultrafine and radioactive dust collectors, electronic ignition systems, for electroeffluvial chandeliers (A.L. Chizhevsky chandeliers), aeroionizers, medical devices, gas lighters, electric fences, electric shock guns etc. .

Conventionally, we include devices that generate voltages above 1 kV as high-voltage generators.

The generator of high-voltage pulses using a resonant transformer (Fig. 11.1) is made according to the classical scheme using a gas spark gap RB-3.

Capacitor C2 is charged with a pulsating voltage through diode VD1 and resistor R1 to the breakdown voltage of the gas spark gap. As a result of breakdown of the gas gap of the spark gap, the capacitor is discharged onto the primary winding of the transformer, after which the process is repeated. As a result, damped high-voltage pulses with an amplitude of up to 3...20 kV are formed at the output of transformer T1.

To protect the output winding of the transformer from overvoltage, a spark gap made in the form of electrodes with an adjustable air gap is connected in parallel to it.

Rice. 11.1. Circuit of a high-voltage pulse generator using a gas spark gap

Rice. 11.2. Circuit of a high-voltage pulse generator with voltage doubling

Transformer T1 of the pulse generator (Fig. 11.1) is made on an open ferrite core M400NN-3 with a diameter of 8 and a length of 100 mm. The primary (low-voltage) winding of the transformer contains 20 turns of 0.75 mm MGShV wire with a winding pitch of 5...6 mm. The secondary winding contains 2400 turns of ordinary winding of PEV-2 wire 0.04 mm. The primary winding is wound on top of the secondary winding through a 2x0.05 mm polytetrafluoroethylene (fluoroplastic) gasket. The secondary winding of the transformer must be reliably isolated from the primary.

An embodiment of a high-voltage pulse generator using a resonant transformer is shown in Fig. 11.2. In this generator circuit there is galvanic isolation from the supply network. The mains voltage is supplied to the intermediate (step-up) transformer T1. The voltage removed from the secondary winding of the network transformer is supplied to a rectifier operating according to a voltage doubling circuit.

As a result of the operation of such a rectifier, a positive voltage equal to V2L/„ appears on the upper plate of the capacitor C2 relative to the neutral wire, where is the voltage on the secondary winding of the power transformer.

A corresponding voltage of the opposite sign is formed at capacitor C1. As a result, the voltage on the plates of the capacitor SZ will be equal to 2 V2L/„.

The charging rate of capacitors C1 and C2 (C1=C2) is determined by the value of resistance R1.

When the voltage on the plates of capacitor SZ is equal to the breakdown voltage of the gas gap FV1, a breakdown of its gas gap will occur, capacitor SZ and, accordingly, capacitors C1 and C2 will be discharged, and periodic damped oscillations will occur in the secondary winding of transformer T2. After discharging the capacitors and turning off the spark gap, the process of charging and subsequent discharging the capacitors to the primary winding of transformer T2 will be repeated again.

A high-voltage generator used to obtain photographs in a gas discharge, as well as to collect ultrafine and radioactive dust (Fig. 11.3) consists of a voltage doubler, a relaxation pulse generator and a step-up resonant transformer.

The voltage doubler is made using diodes VD1, VD2 and capacitors C1, C2. The charging chain is formed by capacitors C1 - C3 and resistor R1. A 350 V gas spark gap is connected in parallel to capacitors C1 - SZ with the primary winding of step-up transformer T1 connected in series.

As soon as the DC voltage level on capacitors C1 - SZ exceeds the breakdown voltage of the spark gap, the capacitors are discharged through the winding of the step-up transformer and as a result a high-voltage pulse is formed. The circuit elements are selected so that the pulse formation frequency is about 1 Hz. Capacitor C4 is designed to protect the output terminal of the device from mains voltage.

The output voltage of the device is entirely determined by the properties of the transformer used and can reach 15 kV. High voltage transformer for output

Rice. 11.3. Circuit of a high voltage pulse generator using a gas spark gap or dinistors

voltage of the order of ^0 kV is made on a dielectric tube with an outer diameter of 8 and a length of 150 mm; a copper electrode with a diameter of 1.5 mm is located inside. The secondary winding contains 3...4 thousand turns of PELSHO 0.12 wire, wound turn to turn in 10...13 layers (winding width 70 mm) and impregnated with EF-2 glue with interlayer insulation made of polytetrafluoroethylene. The primary winding contains 20 turns of PEV 0.75 wire passed through a polyvinyl chloride cambric.

As such a transformer, you can also use a modified horizontal scan output transformer of a TV; transformers for electronic lighters, flash lamps, ignition coils, etc.

The R-350 gas discharger can be replaced by a switchable chain of dinistors of the KN102 type (Fig. 11.3, right), which will allow the output voltage to be changed stepwise. To evenly distribute the voltage across the dinistors, resistors of the same value with a resistance of 300...510 kOhm are connected in parallel to each of them.

A variant of the circuit of a high-voltage generator using a gas-filled device - a thyratron - as a threshold-switching element is shown in Fig. 11.4.

Rice. 11.4. High voltage pulse generator circuit using a thyratron

flares up. Capacitor C2 is discharged through the primary winding of transformer T1, the thyratron goes out, the capacitor begins to charge again, etc.

An automobile ignition coil is used as transformer T1.

Instead of the VL1 MTX-90 thyratron, you can turn on one or more KN102 type dinistors. The amplitude of the voltage can be adjusted by the number of switched on dinistors.

The design of a high-voltage converter using a thyratron switch is described in the work. Note that other types of gas-filled devices can be used to discharge a capacitor.

More promising is the use of semiconductor switching devices in modern high-voltage generators. Their advantages are clearly expressed: high repeatability of parameters, lower cost and dimensions, high reliability.

Below we will consider generators of high-voltage pulses using semiconductor switching devices (dinistors, thyristors, bipolar and field-effect transistors).

A completely equivalent, but low-current analogue of gas dischargers are dinistors.

In Fig. Figure 11.5 shows the electrical circuit of a generator made using dinistors. The structure of the generator is completely similar to those described earlier (Fig. 11.1, 11.4). The main difference is the replacement of the gas discharger with a chain of dinistors connected in series.

Rice. 11.5. Circuit of a high-voltage pulse generator using dinistors

Rice. 11.6. Circuit of a high-voltage pulse generator with a bridge rectifier

It should be noted that the efficiency of such an analogue and switched currents are noticeably lower than that of the prototype, however, dinistors are more affordable and more durable.

A somewhat complicated version of the high-voltage pulse generator is shown in Fig. 11.6. The mains voltage is supplied to the bridge rectifier using diodes VD1 - VD4. The rectified voltage is smoothed out by capacitor C1. This capacitor generates a constant voltage of about 300 V, which is used to power a relaxation generator composed of elements R3, C2, VD5 and VD6. Its load is the primary winding of transformer T1. Pulses with an amplitude of approximately 5 kBv\ repetition frequency up to 800 Hz are removed from the secondary winding.

The chain of dinistors must be designed for a switching voltage of about 200 V. Here you can use dinistors of the KN102 or D228 type. It should be taken into account that the switching voltage of dinistors of type KN102A, D228A is 20 V; KN102B, D228B - 28 V; KN102V, D228V - 40 V;

KN102G, D228G - 56 V; KN102D, D228D - 80 V; KN102E - 75 V; KN102Zh, D228Zh - 120 V; KN102I, D228I - 150 B.

As a T1 transformer in the above devices, a modified line transformer from a black and white TV can be used. Its high-voltage winding is left, the rest is removed and a low-voltage (primary) winding is wound instead - 15...30 turns of PEV wire with a diameter of 0.5...0.8 mm.

When choosing the number of turns of the primary winding, the number of turns of the secondary winding should be taken into account. It is also necessary to keep in mind that the value of the output voltage of the high-voltage pulse generator depends to a greater extent on the adjustment of the transformer circuits to resonance rather than on the ratio of the number of turns of the windings.

The characteristics of some types of horizontal scanning television transformers are given in table 11.1.

Table 11.1. Parameters of high-voltage windings of unified horizontal television transformers

Transformer type	Number of turns	R windings, Ohm
TVS-A, TVS-B





TVS-110, TVS-110M




Transformer type	Number of turns	R windings, Oi





TVS-90LTs2, TVS-90LTs2-1





TVS-110PTs15
TVS-110PTs16, TVS-11RPTs18

Rice. 11.7. Electrical circuit of a high-voltage pulse generator

In Fig. Figure 11.7 shows a diagram of a two-stage high-voltage pulse generator published on one of the sites, in which a thyristor is used as a switching element. In turn, a gas-discharge device - a neon lamp (chain HL1, HL2) was chosen as a threshold element that determines the repetition frequency of high-voltage pulses and triggers the thyristor.

When supply voltage is applied, the pulse generator, made on the basis of transistor VT1 (2N2219A - KT630G), produces a voltage of about 150 V. This voltage is rectified by diode VD1 and charges capacitor C2.

After the voltage on capacitor C2 precedes the ignition voltage of neon lamps HL1, HL2, the capacitor will be discharged through the current-limiting resistor R2 to the control electrode of thyristor VS1, and the thyristor will be unlocked. The discharge current of capacitor C2 will create electrical oscillations in the primary winding of transformer 12.

The thyristor switching voltage can be adjusted by selecting neon lamps with different ignition voltages. You can change the thyristor turn-on voltage stepwise by switching the number of neon lamps connected in series (or dinistors replacing them).

Rice. 11.8. Diagram of electrical processes on the electrodes of semiconductor devices (to Fig. 11.7)

The voltage diagram at the base of transistor VT1 and at the anode of the thyristor is shown in Fig. 11.8. As follows from the presented diagrams, the blocking generator pulses have a duration of approximately 8 ms. Capacitor C2 is charged exponentially in accordance with the action of pulses taken from the secondary winding of transformer T1.

Pulses with a voltage of approximately 4.5 kV are formed at the output of the generator. The output transformer for low-frequency amplifiers is used as transformer T1. As a high-voltage transformer T2, a transformer from a photo flash or a recycled (see above) horizontal scanning television transformer was used.

The diagram of another version of the generator using a neon lamp as a threshold element is shown in Fig. 11.9.

Rice. 11.9. Electrical circuit of a generator with a threshold element on a neon lamp

The relaxation generator in it is made on elements R1, VD1, C1, HL1, VS1. It operates with positive half-cycles of the mains voltage, when capacitor 01 is charged to the switching voltage of the threshold element on the neon lamp HL1 and thyristor VS1. Diode VD2 dampens self-induction pulses of the primary winding of step-up transformer T1 and allows you to adjust the output voltage of the generator. The output voltage reaches 9 kV. The neon lamp also serves as an indicator that the device is connected to the network.

The high-voltage transformer is wound on a piece of rod with a diameter of 8 and a length of 60 mm made of M400NN ferrite. First, the primary winding is placed - 30 turns of PELSHO 0.38 wire, and then the secondary winding - 5500 turns of PELSHO 0.05 or larger diameter. Between the windings and every 800... 1000 turns of the secondary winding, an insulation layer of polyvinyl chloride insulating tape is laid.

In the generator, it is possible to introduce discrete multi-stage adjustment of the output voltage by switching neon lamps or dinistors in a series circuit (Fig. 11.10). In the first version, two stages of regulation are provided, in the second - up to ten or more (when using KN102A dinistors with a switching voltage of 20 V).

Rice. 11.10. Electrical circuit of the threshold element

Rice. 11.11. Electrical circuit of a high voltage generator with a diode threshold element

A simple high-voltage generator (Fig. 11.11) allows you to obtain output pulses with an amplitude of up to 10.

The control element of the device switches with a frequency of 50 Hz (at one half-wave of the mains voltage). The diode VD1 D219A Shch220, D223) operating at reverse bias in avalanche breakdown mode was used as a threshold element.

When the avalanche breakdown voltage at the semiconductor junction of the diode exceeds the avalanche breakdown voltage, the diode transitions to a conducting state. The voltage from the charged capacitor C2 is supplied to the control electrode of the thyristor VS1. After turning on the thyristor, capacitor C2 is discharged into the winding of transformer T1.

Transformer T1 does not have a core. It is made on a reel with a diameter of 8 mm from polymethylmethacrylate or polytetrachlorethylene and contains three spaced sections 9 mm wide. The step-up winding contains 3×1000 turns wound with PET, PEV-2 0.12 mm wire. After winding, the winding must be soaked in paraffin. 2 - 3 layers of insulation are applied on top of the paraffin, after which the primary winding is wound - 3 × 10 turns of PEV-2 0.45 mm wire.

Thyristor VS1 can be replaced with another one for a voltage higher than 150 V. The avalanche diode can be replaced with a chain of dinistors (Fig. 11.10, 11.11 below).

The circuit of a low-power portable high-voltage pulse source with autonomous power supply from one galvanic element (Fig. 11.12) consists of two generators. The first is built on two low-power transistors, the second on a thyristor and a dinistor.

Rice. 11.12. Voltage generator circuit with low-voltage power supply and thyristor-dinistor key element

A cascade of transistors of different conductivities converts low-voltage direct voltage into high-voltage pulsed voltage. The timing chain in this generator is the elements C1 and R1. When the power is turned on, transistor VT1 opens, and the voltage drop across its collector opens transistor VT2. Capacitor C1, charging through resistor R1, reduces the base current of transistor VT2 so much that transistor VT1 comes out of saturation, and this leads to the closing of VT2. The transistors will be closed until capacitor C1 is discharged through the primary winding of transformer T1.

The increased pulse voltage removed from the secondary winding of transformer T1 is rectified by diode VD1 and supplied to capacitor C2 of the second generator with thyristor VS1 and dinistor VD2. In each positive half-cycle, storage capacitor C2 is charged to an amplitude voltage value equal to the switching voltage of dinistor VD2, i.e. up to 56 V (nominal pulse unlocking voltage for dinistor type KN102G).

The transition of the dinistor to the open state affects the control circuit of the thyristor VS1, which in turn also opens. Capacitor C2 is discharged through the thyristor and the primary winding of transformer T2, after which the dinistor and thyristor close again and the next capacitor charge begins - the switching cycle is repeated.

Pulses with an amplitude of several kilovolts are removed from the secondary winding of transformer T2. The frequency of spark discharges is approximately 20 Hz, but it is much less than the frequency of the pulses taken from the secondary winding of transformer T1. This happens because capacitor C2 is charged to the dinistor switching voltage not in one, but in several positive half-cycles. The capacitance value of this capacitor determines the power and duration of the output discharge pulses. The average value of the discharge current that is safe for the dinistor and the control electrode of the thyristor is selected based on the capacitance of this capacitor and the magnitude of the pulse voltage supplying the cascade. To do this, the capacitance of capacitor C2 should be approximately 1 µF.

Transformer T1 is made on a ring ferrite magnetic core of type K10x6x5. It has 540 turns of PEV-2 0.1 wire with a grounded tap after the 20th turn. The beginning of its winding is connected to transistor VT2, the end to diode VD1. Transformer T2 is wound on a coil with a ferrite or permalloy core with a diameter of 10 mm and a length of 30 mm. A coil with an outer diameter of 30 mm and a width of 10 mm is wound with PEV-2 0.1 mm wire until the frame is completely filled. Before winding is completed, a grounded tap is made, and the last row of wire of 30...40 turns is wound turn to turn over an insulating layer of varnished cloth.

Transformer T2 during winding must be impregnated with insulating varnish or BF-2 glue, then thoroughly dried.

Instead of VT1 and VT2, you can use any low-power transistors capable of operating in pulse mode. Thyristor KU101E can be replaced with KU101G. Power source - galvanic cells with a voltage of no more than 1.5 V, for example, 312, 314, 316, 326, 336, 343, 373, or nickel-cadmium disk batteries type D-0.26D, D-0.55S and so on.

A thyristor generator of high-voltage pulses with mains power is shown in Fig. 11.13.

Rice. 11.13. Electrical circuit of a high-voltage pulse generator with a capacitive energy storage device and a thyristor-based switch

During the positive half-cycle of the mains voltage, capacitor C1 is charged through resistor R1, diode VD1 and the primary winding of transformer T1. Thyristor VS1 is closed in this case, since there is no current through its control electrode (the voltage drop across diode VD2 in the forward direction is small compared to the voltage required to open the thyristor).

During a negative half-cycle, diodes VD1 and VD2 close. A voltage drop is formed at the cathode of the thyristor relative to the control electrode (minus - at the cathode, plus - at the control electrode), a current appears in the control electrode circuit, and the thyristor opens. At this moment, capacitor C1 is discharged through the primary winding of the transformer. A high voltage pulse appears in the secondary winding. And so - every period of mains voltage.

At the output of the device, bipolar high-voltage pulses are formed (since when the capacitor is discharged, damped oscillations occur in the primary winding circuit).

Resistor R1 can be composed of three parallel-connected MLT-2 resistors with a resistance of 3 kOhm.

Diodes VD1 and VD2 must be designed for a current of at least 300 mA and a reverse voltage of at least 400 V (VD1) and 100 B (VD2). Capacitor C1 type MBM for a voltage of at least 400 V. Its capacity - fractions of a few microfarads - is selected experimentally. Thyristor VS1 type KU201K, KU201L, KU202K - KU202N. Transformer T1 - ignition coil B2B (6 B) from a motorcycle or car.

The device can use a horizontal scanning television transformer TVS-110L6, TVS-110LA, TVS-110AM.

A fairly typical circuit of a high-voltage pulse generator with a capacitive energy storage device is shown in Fig. 11.14.

Rice. 11.14. Scheme of a thyristor high-voltage pulse generator with a capacitive energy storage

The generator contains a quenching capacitor C1, a diode rectifier bridge VD1 - VD4, a thyristor switch VS1 and a control circuit. When the device is turned on, capacitors C2 and S3 are charged, thyristor VS1 is still closed and does not conduct current. The maximum voltage on capacitor C2 is limited by the zener diode VD5 with a value of 9 B. During the charging of capacitor C2 through resistor R2, the voltage on potentiometer R3 and, accordingly, on the control transition of thyristor VS1 increases to a certain value, after which the thyristor switches to a conducting state, and capacitor SZ through Thyristor VS1 is discharged through the primary (low-voltage) winding of transformer T1, generating a high-voltage pulse. After this, the thyristor closes and the process begins again. Potentiometer R3 sets the response threshold of thyristor VS1.

The pulse repetition rate is 100 Hz. An automobile ignition coil can be used as a high-voltage transformer. In this case, the output voltage of the device will reach 30...35 kV. The thyristor generator of high-voltage pulses (Fig. 11.15) is controlled by voltage pulses taken from a relaxation generator made on dinistor VD1. The operating frequency of the control pulse generator (15...25 Hz) is determined by the value of resistance R2 and the capacitance of capacitor C1.

Rice. 11.15. Electrical circuit of a thyristor high-voltage pulse generator with pulse control

The relaxation generator is connected to the thyristor switch through a pulse transformer T1 type MIT-4. A high-frequency transformer from the Iskra-2 darsonvalization apparatus is used as the output transformer T2. The voltage at the device output can reach 20...25 kV.

In Fig. Figure 11.16 shows an option for supplying control pulses to thyristor VS1.

The voltage converter (Fig. 11.17), developed in Bulgaria, contains two stages. In the first of them, the load of the key element, made on the transistor VT1, is the winding of the transformer T1. Rectangular control pulses periodically turn on/off the switch on transistor VT1, thereby connecting/disconnecting the primary winding of the transformer.

Rice. 11.16. Thyristor switch control option

Rice. 11.17. Electrical circuit of a two-stage high-voltage pulse generator

An increased voltage is induced in the secondary winding, proportional to the transformation ratio. This voltage is rectified by diode VD1 and charges capacitor C2, which is connected to the primary (low-voltage) winding of the high-voltage transformer T2 and thyristor VS1. The operation of the thyristor is controlled by voltage pulses taken from the additional winding of transformer T1 through a chain of elements that correct the shape of the pulse.

As a result, the thyristor periodically turns on/off. Capacitor C2 is discharged onto the primary winding of the high-voltage transformer.

Generator of high-voltage pulses, Fig. 11.18, contains a generator based on a unijunction transistor as a control element.

The mains voltage is rectified by the diode bridge VD1 - VD4. Smoothes out rectified voltage ripples

Rice. 11.18. Circuit of a high-voltage pulse generator with a control element based on a unijunction transistor

capacitor C1, the charge current of the capacitor at the moment the device is connected to the network is limited by resistor R1. Through resistor R4, capacitor S3 is charged. At the same time, a pulse generator based on a unijunction transistor VT1 comes into operation. Its “trigger” capacitor C2 is charged through resistors R3 and R6 from a parametric stabilizer (ballast resistor R2 and zener diodes VD5, VD6). As soon as the voltage on capacitor 02 reaches a certain value, transistor VT1 switches, and an opening pulse is sent to the control transition of thyristor VS1.

Capacitor 03 is discharged through thyristor VS1 to the primary winding of transformer T1. A high voltage pulse is formed on its secondary winding. The repetition rate of these pulses is determined by the frequency of the generator, which, in turn, depends on the parameters of the chain R3, R6 and 02. The tuning resistor R6 can change the output voltage of the generator by approximately 1.5 times. In this case, the pulse frequency is regulated within the range of 250... 1000 Hz. In addition, the output voltage changes when selecting resistor R4 (ranging from 5 to 30 kOhm.

It is advisable to use paper capacitors (01 and 03 - for a rated voltage of at least 400 V); The diode bridge must be designed for the same voltage. Instead of what is indicated in the diagram, you can use the T10-50 thyristor or, in extreme cases, KU202N. Zener diodes VD5, VD6 should provide a total stabilization voltage of about 18 B.

The transformer is made on the basis of TVS-110P2 from black and white TVs. All primary windings are removed and 70 turns of PEL or PEV wire with a diameter of 0.5...0.8 mm are wound onto the vacant space.

Electrical circuit of a high voltage pulse generator, Fig. 11.19, consists of a diode-capacitor voltage multiplier (diodes VD1, VD2, capacitors C1 - C4). Its output produces a constant voltage of approximately 600 V.

Rice. 11.19. Circuit of a high-voltage pulse generator with a mains voltage doubler and a trigger pulse generator based on a unijunction transistor

A unijunction transistor VT1 type KT117A is used as a threshold element of the device. The voltage at one of its bases is stabilized by a parametric stabilizer based on a VD3 zener diode of type KS515A (stabilization voltage 15 B). Through resistor R4, capacitor C5 is charged, and when the voltage at the control electrode of transistor VT1 exceeds the voltage at its base, VT1 switches to a conducting state, and capacitor C5 is discharged to the control electrode of thyristor VS1.

When the thyristor is turned on, the chain of capacitors C1 - C4, charged to a voltage of about 600...620 B, is discharged into the low-voltage winding of step-up transformer T1. After this, the thyristor turns off, the charge-discharge processes are repeated with a frequency determined by the constant R4C5. Resistor R2 limits the short circuit current when the thyristor is turned on and at the same time is an element of the charging circuit of capacitors C1 - C4.

The converter circuit (Fig. 11.20) and its simplified version (Fig. 11.21) is divided into the following components: network suppression filter (interference filter); electronic regulator; high voltage transformer.

Rice. 11.20. Electrical circuit of a high voltage generator with a surge protector

Rice. 11.21. Electrical circuit of a high voltage generator with a surge protector

Scheme in Fig. 11.20 works as follows. The capacitor SZ is charged through the diode rectifier VD1 and resistor R2 to the amplitude value of the network voltage (310 B). This voltage passes through the primary winding of transformer T1 to the anode of thyristor VS1. Along the other branch (R1, VD2 and C2), capacitor C2 is slowly charged. When, during its charging, the breakdown voltage of dinistor VD4 is reached (within 25...35 B), capacitor C2 is discharged through the control electrode of thyristor VS1 and opens it.

Capacitor SZ is almost instantly discharged through the open thyristor VS1 and the primary winding of the transformer

T1. The pulsed changing current induces a high voltage in the secondary winding T1, the magnitude of which can exceed 10 kV. After the discharge of the capacitor SZ, the thyristor VS1 closes and the process repeats.

A television transformer is used as a high-voltage transformer, from which the primary winding is removed. For the new primary winding, a winding wire with a diameter of 0.8 mm is used. Number of turns - 25.

For the manufacture of barrier filter inductors L1, L2, high-frequency ferrite cores are best suited, for example, 600NN with a diameter of 8 mm and a length of 20 mm, each having approximately 20 turns of winding wire with a diameter of 0.6...0.8 mm.

Rice. 11.22. Electrical circuit of a two-stage high-voltage generator with a field-effect transistor control element

A two-stage high-voltage generator (author - Andres Estaban de la Plaza) contains a transformer pulse generator, a rectifier, a timing RC circuit, a key element on a thyristor (triac), a high-voltage resonant transformer and a thyristor operation control circuit (Fig. 11.22).

An analogue of the TIP41 transistor is KT819A.

A low-voltage transformer voltage converter with cross-feedback, assembled on transistors VT1 and VT2, produces pulses with a repetition frequency of 850 Hz. To facilitate operation when large currents flow, transistors VT1 and VT2 are installed on radiators made of copper or aluminum.

The output voltage removed from the secondary winding of transformer T1 of the low-voltage converter is rectified by the diode bridge VD1 - VD4 and charges capacitors S3 and C4 through resistor R5.

The thyristor switching threshold is controlled by a voltage regulator, which includes a field-effect transistor VT3.

Further, the operation of the converter does not differ significantly from the previously described processes: periodic charging/discharging of capacitors occurs on the low-voltage winding of the transformer, and damped electrical oscillations are generated. The output voltage of the converter, when used at the output as a step-up transformer of an ignition coil from a car, reaches 40...60 kV at a resonant frequency of approximately 5 kHz.

Transformer T1 (output horizontal scan transformer) contains 2×50 turns of wire with a diameter of 1.0 mm, wound bifilarly. The secondary winding contains 1000 turns with a diameter of 0.20...0.32 mm.

Note that modern bipolar and field-effect transistors can be used as controlled key elements.

High-voltage, low-power generators are widely used in flaw detection, to power portable charged particle accelerators, X-ray and cathode ray tubes, photomultiplier tubes, and ionizing radiation detectors. In addition, they are also used for electric pulse destruction of solids, production of ultrafine powders, synthesis of new materials, as spark leak detectors, for launching gas-discharge light sources, in electric-discharge diagnostics of materials and products, obtaining gas-discharge photographs using the S. D. Kirlian method , testing the quality of high-voltage insulation. In everyday life, such devices are used as power sources for electronic traps of ultrafine and radioactive dust, electronic ignition systems, for electroeffluvial chandeliers (chandeliers by A. L. Chizhevsky), aeroionizers, medical devices (D'Arsonval, franklization, ultratonotherapy devices ), gas lighters, electric fences, electric stun guns, etc.

Conventionally, we classify as high-voltage generators devices that generate voltages above 1 kV.

The high-voltage pulse generator using a resonant transformer (Fig. 11.1) is made according to the classical scheme using a gas spark gap RB-3.

To protect the output winding of the transformer from overvoltage, a spark gap made in the form of electrodes with an adjustable air gap is connected in parallel to it.

Rice. 11.1. Circuit of a high-voltage pulse generator using a gas spark gap.

Rice. 11.2. Circuit of a high-voltage pulse generator with voltage doubling.

Transformer T1 of the pulse generator (Fig. 11.1) is made on an open ferrite core M400NN-3 with a diameter of 8 and a length of 100 mm. The primary (low-voltage) winding of the transformer contains 20 turns of MGShV wire 0.75 mm with a winding pitch of 5...6 mm. The secondary winding contains 2400 turns of ordinary winding of PEV-2 wire 0.04 mm. The primary winding is wound over the secondary winding through a 2x0.05 mm polytetrafluoroethylene (fluoroplastic) gasket. The secondary winding of the transformer must be reliably isolated from the primary.

As a result of the operation of such a rectifier, a positive voltage appears on the upper plate of capacitor C2 relative to the neutral wire, equal to the square root of 2Uii, where Uii is the voltage on the secondary winding of the power transformer.

A corresponding voltage of the opposite sign is formed at capacitor C1. As a result, the voltage on the plates of the capacitor SZ will be equal to 2 square roots of 2Uii.

The charging rate of capacitors C1 and C2 (C1=C2) is determined by the value of resistance R1.

The voltage doubler is made using diodes VD1, VD2 and capacitors C1, C2. The charging circuit is formed by capacitors C1 SZ and resistor R1. A 350 V gas spark gap is connected in parallel to capacitors C1 SZ with the primary winding of step-up transformer T1 connected in series.

As soon as the DC voltage level on capacitors C1 SZ exceeds the breakdown voltage of the spark gap, the capacitors are discharged through the winding of the step-up transformer and as a result a high-voltage pulse is formed. The circuit elements are selected so that the pulse formation frequency is about 1 Hz. Capacitor C4 is designed to protect the output terminal of the device from mains voltage.

Rice. 11.3. Circuit of a high voltage pulse generator using a gas spark gap or dinistors.

The output voltage of the device is entirely determined by the properties of the transformer used and can reach 15 kV. A high-voltage transformer with an output voltage of about 10 kV is made on a dielectric tube with an outer diameter of 8 and a length of 150 mm; a copper electrode with a diameter of 1.5 mm is located inside. The secondary winding contains 3...4 thousand turns of PELSHO 0.12 wire, wound turn to turn in 10...13 layers (winding width 70 mm) and impregnated with BF-2 glue with interlayer insulation made of polytetrafluoroethylene. The primary winding contains 20 turns of PEV 0.75 wire passed through a polyvinyl chloride cambric.

As such a transformer, you can also use a modified horizontal scan output transformer of a TV; transformers for electronic lighters, flash lamps, ignition coils, etc.

A variant of the high-voltage generator circuit using a gas-filled device, a thyratron, as a threshold-switching element is shown in Fig. 11.4.

Rice. 11.4. Circuit of a high voltage pulse generator using a thyratron.

The mains voltage is rectified by diode VD1. The rectified voltage is smoothed by capacitor C1 and supplied to the charging circuit R1, C2. As soon as the voltage on capacitor C2 reaches the ignition voltage of thyratron VL1, it flashes. Capacitor C2 is discharged through the primary winding of transformer T1, the thyratron goes out, the capacitor begins to charge again, etc.

An automobile ignition coil is used as transformer T1.

Instead of the VL1 MTX-90 thyratron, you can turn on one or more KN102 type dinistors. The amplitude of the high voltage can be adjusted by the number of included dinistors.

The design of a high-voltage converter using a thyratron switch is described in the work. Note that other types of gas-filled devices can be used to discharge a capacitor.

Below we will consider high-voltage pulse generators using semiconductor switching devices (dinistors, thyristors, bipolar and field-effect transistors).

A completely equivalent, but low-current analogue of gas dischargers are dinistors.

In Fig. Figure 11.5 shows the electrical circuit of a generator made on dinistors. The structure of the generator is completely similar to those described earlier (Fig. 11.1, 11.4). The main difference is the replacement of the gas discharger with a chain of dinistors connected in series.

Rice. 11.5. Circuit of a high-voltage pulse generator using dinistors.

Rice. 11.6. Circuit of a high-voltage pulse generator with a bridge rectifier.

It should be noted that the efficiency of such an analogue and switched currents are noticeably lower than that of the prototype, however, dinistors are more affordable and more durable.

A somewhat complicated version of the high-voltage pulse generator is shown in Fig. 11.6. The mains voltage is supplied to a bridge rectifier using diodes VD1 VD4. The rectified voltage is smoothed out by capacitor C1. This capacitor generates a constant voltage of about 300 V, which is used to power a relaxation generator composed of elements R3, C2, VD5 and VD6. Its load is the primary winding of transformer T1. Pulses with an amplitude of approximately 5 kV and a repetition frequency of up to 800 Hz are removed from the secondary winding.

A modified line transformer from a black-and-white TV can be used as a T1 transformer in the above devices. Its high-voltage winding is left, the rest are removed and instead a low-voltage (primary) winding is wound 15...30 turns of PEV wire with a diameter of 0.5...0.8 mm.

The characteristics of some types of horizontal scanning television transformers are given in Table 11.1.

Table 11.1. Parameters of high-voltage windings of unified horizontal television transformers.

Transformer type	Number of turns	R windings, Ohm
TVS-A, TVS-B





TVS-110, TVS-110M

Transformer type	Number of turns	R windings, Ohm





TVS-90LTs2, TVS-90LTs2-1





TVS-110PTs15
TVS-110PTs16, TVS-110PTs18

Rice. 11.7. Electrical circuit of a high-voltage pulse generator.

In Fig. Figure 11.7 shows a diagram of a two-stage high-voltage pulse generator published on one of the sites, in which a thyristor is used as a switching element. In turn, a gas-discharge device neon lamp (chain HL1, HL2) was chosen as a threshold element that determines the repetition rate of high-voltage pulses and triggers the thyristor.

When supply voltage is applied, the pulse generator, made on the basis of transistor VT1 (2N2219A KT630G), produces a voltage of about 150 V. This voltage is rectified by diode VD1 and charges capacitor C2.

After the voltage on capacitor C2 exceeds the ignition voltage of neon lamps HL1, HL2, the capacitor will be discharged through the current-limiting resistor R2 to the control electrode of thyristor VS1, and the thyristor will be unlocked. The discharge current of capacitor C2 will create electrical oscillations in the primary winding of transformer T2.

Rice. 11.8. Diagram of electrical processes on the electrodes of semiconductor devices (to Fig. 11.7).

Pulses with a voltage of approximately 4.5 kV are formed at the output of the generator. The output transformer for low-frequency amplifiers is used as transformer T1. As

High-voltage transformer T2 uses a transformer from a photo flash or a recycled (see above) horizontal scanning television transformer.

The diagram of another version of the generator using a neon lamp as a threshold element is shown in Fig. 11.9.

Rice. 11.9. Electrical circuit of a generator with a threshold element on a neon lamp.

The relaxation generator in it is made on elements R1, VD1, C1, HL1, VS1. It operates at positive line voltage cycles, when capacitor C1 is charged to the switching voltage of the threshold element on the neon lamp HL1 and thyristor VS1. Diode VD2 dampens self-induction pulses of the primary winding of step-up transformer T1 and allows you to increase the output voltage of the generator. The output voltage reaches 9 kV. The neon lamp also serves as an indicator that the device is connected to the network.

The high-voltage transformer is wound on a piece of rod with a diameter of 8 and a length of 60 mm made of M400NN ferrite. First, a primary winding of 30 turns of PELSHO 0.38 wire is placed, and then a secondary winding of 5500 turns of PELSHO 0.05 or larger diameter is placed. Between the windings and every 800... 1000 turns of the secondary winding, an insulation layer of polyvinyl chloride insulating tape is laid.

Rice. 11.10. Electrical circuit of the threshold element.

Rice. 11.11. Electrical circuit of a high voltage generator with a diode threshold element.

A simple high-voltage generator (Fig. 11.11) allows you to obtain output pulses with an amplitude of up to 10 kV.

The control element of the device switches with a frequency of 50 Hz (at one half-wave of the mains voltage). The diode VD1 D219A (D220, D223) operating under reverse bias in avalanche breakdown mode was used as a threshold element.

Transformer T1 does not have a core. It is made on a reel with a diameter of 8 mm from polymethyl methacrylate or polytetrachlorethylene and contains three spaced sections with a width of

9 mm. The step-up winding contains 3x1000 turns, wound with PET, PEV-2 0.12 mm wire. After winding, the winding must be soaked in paraffin. 2 x 3 layers of insulation are applied on top of the paraffin, after which the primary winding is wound with 3 x 10 turns of PEV-2 0.45 mm wire.

Thyristor VS1 can be replaced with another one for a voltage higher than 150 V. The avalanche diode can be replaced with a chain of dinistors (Fig. 11.10, 11.11 below).

Rice. 11.12. Voltage generator circuit with low-voltage power supply and thyristor-dinistor key element.

The storage capacitor C2 is charged to an amplitude voltage value equal to the switching voltage of the dinistor VD2, i.e. up to 56 V (nominal pulse unlocking voltage for dinistor type KN102G).

Transformer T1 is made on a ring ferrite magnetic core of type K10x6x5. It has 540 turns of PEV-2 0.1 wire with a grounded tap after the 20th turn. The beginning of its winding is connected to transistor VT2, the end is connected to diode VD1. Transformer T2 is wound on a coil with a ferrite or permalloy core with a diameter of 10 mm and a length of 30 mm. A coil with an outer diameter of 30 mm and a width of 10 mm is wound with PEV-2 0.1 mm wire until the frame is completely filled. Before winding is completed, a grounded tap is made, and the last row of wire of 30...40 turns is wound turn to turn over an insulating layer of varnished cloth.

The T2 transformer must be impregnated with insulating varnish or BF-2 glue during winding, then thoroughly dried.

Instead of VT1 and VT2, you can use any low-power transistors capable of operating in pulse mode. Thyristor KU101E can be replaced with KU101G. Power source galvanic cells with a voltage of no more than 1.5 V, for example, 312, 314, 316, 326, 336, 343, 373, or nickel-cadmium disk batteries type D-0.26D, D-0.55S and so on.

A thyristor generator of high-voltage pulses with mains power is shown in Fig. 11.13.

Rice. 11.13. Electrical circuit of a high-voltage pulse generator with a capacitive energy storage device and a thyristor switch.

During a negative half-cycle, diodes VD1 and VD2 close. A voltage drop is formed at the cathode of the thyristor relative to the control electrode (minus at the cathode, plus at the control electrode), a current appears in the control electrode circuit, and the thyristor opens. At this moment, capacitor C1 is discharged through the primary winding of the transformer. A high voltage pulse appears in the secondary winding. And so on every period of mains voltage.

At the output of the device, bipolar high-voltage pulses are formed (since damped oscillations occur when the capacitor is discharged in the primary winding circuit).

Resistor R1 can be composed of three parallel-connected MLT-2 resistors with a resistance of 3 kOhm.

Diodes VD1 and VD2 must be designed for a current of at least 300 mA and a reverse voltage of at least 400 V (VD1) and 100 B (VD2). Capacitor C1 of the MBM type for a voltage of at least 400 V. Its capacitance (a fraction of a unit of microfarad) is selected experimentally. Thyristor VS1 type KU201K, KU201L, KU202K KU202N. Transformators B2B ignition coil (6 V) from a motorcycle or car.

The device can use a horizontal scanning television transformer TVS-110L6, TVS-1 YULA, TVS-110AM.

A fairly typical circuit of a high-voltage pulse generator with a capacitive energy storage device is shown in Fig. 11.14.

Rice. 11.14. Scheme of a thyristor generator of high-voltage pulses with a capacitive energy storage device.

The generator contains a quenching capacitor C1, a diode rectifier bridge VD1 VD4, a thyristor switch VS1 and a control circuit. When the device is turned on, capacitors C2 and S3 are charged, thyristor VS1 is still closed and does not conduct current. The maximum voltage on capacitor C2 is limited by a zener diode VD5 of 9V. In the process of charging capacitor C2 through resistor R2, the voltage at potentiometer R3 and, accordingly, at the control transition of thyristor VS1 increases to a certain value, after which the thyristor switches to a conducting state, and capacitor SZ through thyristor VS1 is discharged through the primary (low-voltage) winding of transformer T1, generating a high voltage pulse. After this, the thyristor closes and the process begins again. Potentiometer R3 sets the response threshold of thyristor VS1.

Rice. 11.15. Electrical circuit of a thyristor high-voltage pulse generator with pulse control.

In Fig. Figure 11.16 shows an option for supplying control pulses to thyristor VS1.

Rice. 11.16. Option for controlling a thyristor switch.

Rice. 11.17. Electrical circuit of a two-stage high-voltage pulse generator.

An increased voltage is induced in the secondary winding, proportional to the transformation ratio. This voltage is rectified by diode VD1 and charges capacitor C2, which is connected to the primary (low-voltage) winding of high-voltage transformer T2 and thyristor VS1. The operation of the thyristor is controlled by voltage pulses taken from the additional winding of transformer T1 through a chain of elements that correct the shape of the pulse.

As a result, the thyristor periodically turns on/off. Capacitor C2 is discharged onto the primary winding of the high-voltage transformer.

High-voltage pulse generator, fig. 11.18, contains a generator based on a unijunction transistor as a control element.

Rice. 11.18. Circuit of a high-voltage pulse generator with a control element based on a unijunction transistor.

The mains voltage is rectified by the diode bridge VD1 VD4. The ripples of the rectified voltage are smoothed out by capacitor C1; the charging current of the capacitor at the moment the device is connected to the network is limited by resistor R1. Through resistor R4, capacitor S3 is charged. At the same time, a pulse generator based on a unijunction transistor VT1 comes into operation. Its “trigger” capacitor C2 is charged through resistors R3 and R6 from a parametric stabilizer (ballast resistor R2 and zener diodes VD5, VD6). As soon as the voltage on capacitor C2 reaches a certain value, transistor VT1 switches, and an opening pulse is sent to the control transition of thyristor VS1.

Capacitor SZ is discharged through thyristor VS1 to the primary winding of transformer T1. A high voltage pulse is formed on its secondary winding. The repetition rate of these pulses is determined by the frequency of the generator, which, in turn, depends on the parameters of the chain R3, R6 and C2. Using the tuning resistor R6, you can change the output voltage of the generator by about 1.5 times. In this case, the pulse frequency is regulated within the range of 250... 1000 Hz. In addition, the output voltage changes when selecting resistor R4 (ranging from 5 to 30 kOhm).

It is advisable to use paper capacitors (C1 and SZ for a rated voltage of at least 400 V); The diode bridge must be designed for the same voltage. Instead of what is indicated in the diagram, you can use the T10-50 thyristor or, in extreme cases, KU202N. Zener diodes VD5, VD6 should provide a total stabilization voltage of about 18 V.

The transformer is made on the basis of TVS-110P2 from black and white televisions. All primary windings are removed and 70 turns of PEL or PEV wire with a diameter of 0.5...0.8 mm are wound onto the vacant space.

Electrical circuit of a high voltage pulse generator, Fig. 11.19, consists of a diode-capacitor voltage multiplier (diodes VD1, VD2, capacitors C1 C4). Its output produces a constant voltage of approximately 600 V.

Rice. 11.19. Circuit of a high-voltage pulse generator with a mains voltage doubler and a trigger pulse generator based on a unijunction transistor.

When the thyristor is turned on, the chain of capacitors C1 C4, charged to a voltage of about 600...620 V, is discharged into the low-voltage winding of the step-up transformer T1. After this, the thyristor turns off, the charge-discharge processes are repeated with a frequency determined by the constant R4C5. Resistor R2 limits the short circuit current when the thyristor is turned on and at the same time is an element of the charging circuit of capacitors C1 C4.

Rice. 11.20. Electrical circuit of a high voltage generator with a surge protector.

Rice. 11.21. Electrical circuit of a high voltage generator with a surge protector.

Scheme in Fig. 11.20 works as follows. The capacitor SZ is charged through the diode rectifier VD1 and resistor R2 to the amplitude value of the network voltage (310 V). This voltage passes through the primary winding of transformer T1 to the anode of thyristor VS1. Along the other branch (R1, VD2 and C2), capacitor C2 is slowly charged. When, during its charging, the breakdown voltage of dinistor VD4 is reached (within 25...35 V), capacitor C2 is discharged through the control electrode of thyristor VS1 and opens it.

Capacitor SZ is almost instantly discharged through the open thyristor VS1 and the primary winding of transformer T1. The pulsed changing current induces a high voltage in the secondary winding T1, the value of which can exceed 10 kV. After the discharge of the capacitor SZ, the thyristor VS1 closes and the process repeats.

Rice. 11.22. Electrical circuit of a two-stage high-voltage generator with a field-effect transistor control element.

A two-stage high-voltage generator (author Andres Estaban de la Plaza) contains a transformer pulse generator, a rectifier, a timing RC circuit, a key element on a thyristor (triac), a high-voltage resonant transformer and a thyristor operation control circuit (Fig. 11.22).

Analogue of transistor TIP41 KT819A.

The output voltage removed from the secondary winding of transformer T1 of the low-voltage converter is rectified by the diode bridge VD1 VD4 and charges capacitors S3 and C4 through resistor R5.

The thyristor switching threshold is controlled by a voltage regulator, which includes a field-effect transistor VTZ.

Transformer T1 (output horizontal scan transformer) contains 2x50 turns of wire with a diameter of 1.0 mm, wound bifilarly. The secondary winding contains 1000 turns with a diameter of 0.20...0.32 mm.

Note that modern bipolar and field-effect transistors can be used as controlled key elements.

We recently dealt with , now let's get down to it capacitors.

Capacitor- is a device for storing charge and energy of an electric field. Structurally, it is a “sandwich” of two conductors and a dielectric, which can be a vacuum, gas, liquid, organic or inorganic solid. The first domestic capacitors (glass jars with shot, covered with foil) were made in 1752 by M. Lomonosov and G. Richman.

What could be interesting about a capacitor? When starting to work on this article, I thought that I could collect and briefly present everything about this primitive part. But as I got to know the capacitor, I was surprised to realize that I couldn’t tell even a hundredth part of all the secrets and wonders hidden in it...

The capacitor is already more than 250 years old, but it does not even think of becoming obsolete.. In addition, 1 kg of “ordinary just capacitors” stores less energy than a kilogram of batteries or fuel cells, but is capable of releasing it faster than they do, while developing more power. - When a capacitor is quickly discharged, a high-power pulse can be obtained, for example, in photoflashes, optically pumped pulsed lasers and colliders. There are capacitors in almost any device, so if you don’t have new capacitors, you can remove them from there for experiments.

Capacitor charge is the absolute value of the charge of one of its plates. It is measured in coulombs and is proportional to the number of extra (-) or missing (+) electrons. To collect a charge of 1 coulomb, you will need 6241509647120420000 electrons. There are about the same number of them in a hydrogen bubble the size of a match head.

Since the ability to accumulate charges at the electrode is limited by their mutual repulsion, their transfer to the electrode cannot be endless. Like any storage device, a capacitor has a very specific capacity. That's what it's called - electrical capacitance. It is measured in farads and for a flat capacitor with plates of area S(each), located at a distance d, the capacity is equalSε 0 ε / d (atS >> d), Where ε - relative dielectric constant, andε 0 =8,85418781762039 * 10 -12 .

The capacitance of the capacitor is also equal to q/U, Where q- charge of the positive plate, U- tension between plates. The capacitance depends on the geometry of the capacitor and the dielectric constant of the dielectric, and does not depend on the charge of the plates.

In a charged conductor, the charges try to scatter from each other as far as possible and therefore are not in the thickness of the capacitor, but in the surface layer of the metal, like a film of gasoline on the surface of water. If two conductors form a capacitor, then these excess charges collect opposite each other. Therefore, almost the entire electric field of the capacitor is concentrated between its plates.

On each plate, charges are distributed so as to be away from neighbors. And they are located quite spaciously: in an air capacitor with a distance between the plates of 1 mm, charged up to 120 V, the average distance between electrons is more than 400 nanometers, which is thousands of times greater than the distance between atoms (0.1-0.3 nm), and This means that for millions of surface atoms there is only one extra (or missing) electron.

If reduce the distance between the plates, then the attractive forces will increase, and at the same voltage the charges on the plates will be able to “get along” more closely. Capacity will increase capacitor. This is what the unsuspecting professor at Leiden University, van Musschenbroeck, did. He replaced the thick-walled bottle of the world's first condenser (created by the German priest von Kleist in 1745) with a thin glass jar. He charged it and touched it, and when he woke up two days later, he said that he would not agree to repeat the experiment, even if they promised the French kingdom for it.

If you place a dielectric between the plates, they will polarize it, that is, they will attract the opposite charges of which it consists. This will have the same effect as if the plates were brought closer. A dielectric with a high relative dielectric constant can be considered as a good transporter of the electric field. But no conveyor is perfect, so no matter what wonderful dielectric we add on top of the existing one, the capacitance of the capacitor will only decrease. You can increase the capacitance only if you add a dielectric (or better yet, a conductor) instead of already existing but having a smaller ε.

There are almost no free charges in dielectrics. All of them are fixed either in a crystal lattice or in molecules - polar (representing dipoles) or not. If there is no external field, the dielectric is unpolarized, dipoles and free charges are scattered chaotically and the dielectric has no field of its own. in an electric field it is polarized: the dipoles are oriented along the field. Since there are a lot of molecular dipoles, when they are oriented, the pros and cons of neighboring dipoles inside the dielectric compensate each other. Only surface charges remain uncompensated - on one surface - one, on the other - another. Free charges in the external field also drift and separate.

In this case, different polarization processes occur at different speeds. One thing is the displacement of electron shells, which occurs almost instantly, another thing is the rotation of molecules, especially large ones, and the third is the migration of free charges. The last two processes obviously depend on temperature, and in liquids they occur much more quickly than in solids. If the dielectric is heated, dipole rotations and charge migration will accelerate. If the field is turned off, the depolarization of the dielectric does not occur instantly either. It remains polarized for some time until thermal motion scatters the molecules into their original chaotic state. Therefore, for capacitors where the polarity is switched at high frequencies, only non-polar dielectrics are suitable: fluoroplastic, polypropylene.

If you disassemble a charged capacitor and then reassemble it (with plastic tweezers), the energy will not go anywhere, and the LED will be able to blink. It will even blink if you connect it to a capacitor in a disassembled state. This is understandable - during disassembly, the charge did not disappear from the plates, and the voltage even increased, since the capacity decreased and now the plates are literally bursting with charges. Wait, how did this tension increase, because then the energy will also increase? That’s right, we imparted mechanical energy to the system, overcoming the Coulomb attraction of the plates. Actually, this is the trick of electrification by friction - to hook electrons at a distance of the order of the size of atoms and drag them to a macroscopic distance, thereby increasing the voltage from several volts (and this is the voltage in chemical bonds) to tens and hundreds of thousands of volts. Now it’s clear why a synthetic jacket does not generate electric shock when you wear it, but only when you take it off? Wait, why not up to billions? A decimeter is a billion times larger than an angstrom, on which we snatched electrons? Yes, because the work of moving a charge in an electric field is equal to the integral Eq over d and this same E weakens quadratically with distance. And if on the entire decimeter between the jacket and the nose there was the same field as inside the molecules, then a billion volts would click on the nose.

Let's check this phenomenon - an increase in voltage when stretching the capacitor - experimentally. I wrote a simple program inVisual Basic to receive data from our PMK018 controllerand displaying them on the screen. In general, we take two 200x150 mm plates of textolite, covered on one side with foil, and solder the wires going to the measuring module. Then we put a dielectric - a sheet of paper - on one of them and cover it with the second plate. The plates do not fit tightly, so we will press them on top with the body of the pen (if you press with your hand, you can create interference).

The measurement circuit is simple: potentiometerR1 sets the voltage (in our case it is 3 volts) applied to the capacitor, and the buttonS1 serves to supply it to the capacitor, or not to supply it.

So, let's press and release the button - we will see the graph shown on the left. The capacitor quickly discharges through the oscilloscope input. Now let's try to relieve the pressure on the plates during the discharge - we will see a voltage peak on the graph (right). This is exactly the desired effect. At the same time, the distance between the capacitor plates increases, the capacitance decreases, and therefore the capacitor begins to discharge even faster.

Here I seriously thought... It seems that we are on the verge of a great invention... After all, if when moving the plates apart, the voltage on them increases, but the charge remains the same, then you can take two capacitors, on one you push the plates apart on them, and at the point of maximum expansion transfer charge to a stationary capacitor. Then return the plates to their place and repeat the same thing in reverse, moving the other capacitor apart. In theory, the voltage on both capacitors will increase with each cycle by a certain number of times. Great idea for a power generator! It will be possible to create new designs for windmills, turbines and all that! So, great... for convenience, you can place all this on two disks rotating in opposite directions.... oh, what is this... ugh, this is a school electric machine! :(

It did not take root as a generator, since it is inconvenient to deal with such voltages. But at the nanoscale, everything can change. Magnetic phenomena in nanostructures are many times weaker than electric ones, and the electric fields there, as we have already seen, are enormous, so a molecular electrophoric machine can become very popular.

Capacitor as an energy store

It is very easy to make sure that energy is stored in the smallest capacitor. To do this, we need a transparent red LED and a constant current source (a 9-volt battery will do, but if the rated voltage of the capacitor allows, it is better to take a larger one). The experiment consists of charging a capacitor, and then connecting an LED to it (don’t forget about the polarity), and watching it blink. In a dark room, a flash is visible even from capacitors of tens of picofarads. Some hundred million electrons emit one hundred million photons. However, this is not the limit, because the human eye can notice much weaker light. I just haven’t found any less capacitive capacitors. If the count goes to thousands of microfarads, spare the LED, and instead short the capacitor to a metal object to see a spark - obvious evidence of the presence of energy in the capacitor.

The energy of a charged capacitor behaves in many ways like potential mechanical energy - the energy of a compressed spring, a weight raised to a height, or a water tank (and the energy of an inductor, on the contrary, is similar to kinetic energy). The ability of a capacitor to store energy has long been used to ensure continuous operation of devices during short-term drops in supply voltage - from watches to trams.

The capacitor is also used to store "almost eternal" energy generated by shaking, vibration, sound, detecting radio waves or power grid radiation. Little by little, the accumulated energy from such weak sources over time allows wireless sensors and other electronic devices to operate for some time. This principle is the basis of an eternal “finger-type” battery for devices with modest power consumption (like TV remote controls). Its body contains a capacitor with a capacity of 500 millifarads and a generator that feeds it with oscillations at a frequency of 4-8 hertz with free power from 10 to 180 milliwatts. Generators based on piezoelectric nanowires are being developed that are capable of directing the energy of such weak vibrations as heartbeats, shoe soles hitting the ground, and vibrations of technical equipment into a capacitor.

Another source of free energy is inhibition. Usually, when a vehicle brakes, energy turns into heat, but it can be stored and then used during acceleration. This problem is especially acute for public transport, which slows down and accelerates at every stop, which leads to significant fuel consumption and air pollution from exhaust emissions. In the Saratov region in 2010, the Elton company created the Ecobus - an experimental minibus with unusual motor-wheel electric motors and supercapacitors - braking energy storage devices, reducing energy consumption by 40%. It uses materials developed in the Energia-Buran project, in particular carbon foil. In general, thanks to the scientific school created back in the USSR, Russia is one of the world leaders in the development and production of electrochemical capacitors. For example, Elton products have been exported abroad since 1998, and recently the production of these products began in the USA under a license from a Russian company.

The capacity of one modern capacitor (2 farads, photo on the left) is thousands of times greater than the capacity of the entire globe. They are capable of storing an electrical charge of 40 Coulombs!

They are used, as a rule, in car audio systems to reduce the peak load on the car's electrical wiring (during moments of powerful bass hits) and, due to the huge capacitance of the capacitor, suppress all high-frequency interference in the on-board network.

But this Soviet “grandfather’s chest” for electrons (photo on the right) is not so capacious, but can withstand a voltage of 40,000 volts (note the porcelain cups that protect all these volts from breakdown on the capacitor body). This is very convenient for an “electromagnetic bomb”, in which a capacitor is discharged onto a copper tube, which at the same moment is compressed from the outside by an explosion. The result is a very powerful electromagnetic pulse that disables radio equipment. By the way, during a nuclear explosion, unlike a normal one, an electromagnetic pulse is also released, which once again emphasizes the similarity of the uranium nucleus to a capacitor. By the way, such a capacitor can be directly charged with static electricity from a comb, but of course it will take a long time to charge to full voltage. But it will be possible to repeat van Musschenbroeck’s sad experience in a very aggravated version.

If you simply rub a pen (comb, balloon, synthetic underwear, etc.) on your hair, the LED will not light up. This is because the excess (taken from the hair) electrons are captive, each at their own point on the surface of the plastic. Therefore, even if we hit some electron with the output of the LED, others will not be able to rush after it and create the current necessary for the LED to glow noticeably to the naked eye. It’s another matter if you transfer the charges from the pen to the capacitor. To do this, take the capacitor by one terminal and rub the pen in turn, first on your hair, then on the free terminal of the capacitor. Why rub? To maximize the harvest of electrons from the entire surface of the pen! Let's repeat this cycle several times and connect an LED to the capacitor. It will blink, and only if the polarity is observed. So the capacitor became a bridge between the worlds of “static” and “ordinary” electricity :)

I took a high-voltage capacitor for this experiment, fearing a breakdown of the low-voltage one, but it turned out that this was an unnecessary precaution. When the charge supply is limited, the voltage across the capacitor can be much less than the power supply voltage. A capacitor can convert high voltage to low voltage. For example, static high-voltage electricity - into ordinary electricity. In fact, is there a difference: charging a capacitor with one microcoulomb from a source with a voltage of 1 V or 1000 V? If this capacitor is so capacious that a charge of 1 µC on it does not increase the voltage above the voltage of a one-volt power source (i.e. its capacitance is higher than 1 µF), then there is no difference. It’s just that if you don’t forcefully limit the pendants, then more of them will want to come running from a high-willed source. And the thermal power released at the terminals of the capacitor will be greater (and the amount of heat is the same, it will just be released faster, which is why the power is greater).

In general, apparently, any capacitor with a capacity of no more than 100 nf is suitable for this experiment. You can do more, but you will need to charge it for a long time to get enough voltage for the LED. But if the leakage currents in the capacitor are small, the LED will burn longer. You might think about using this principle to create a device for recharging a cell phone by rubbing it against your hair during a conversation :)

An excellent high voltage capacitor is a screwdriver. In this case, its handle serves as a dielectric, and the metal rod and human hand serve as plates. We know that a fountain pen rubbed on hair attracts scraps of paper. If you rub a screwdriver on your hair, nothing will come of it - metal does not have the ability to take away electrons from proteins - it did not attract pieces of paper, and it did not. But if, as in the previous experiment, you rub it with a charged fountain pen, the screwdriver, due to its low capacity, quickly charges to a high voltage and pieces of paper begin to be attracted to it.

The LED also lights up from the screwdriver. It is impossible to capture a brief moment of his flash in a photo. But - let's remember the properties of the exponential - the extinction of the flash lasts a long time (by the standards of a camera shutter). And so we witnessed a unique linguistic-optical-mathematical phenomenon: the exhibitor was exposing the camera’s matrix!

However, why such difficulties - there is video recording. It shows that the LED flashes quite brightly:

When capacitors are charged to high voltages, the edge effect begins to play a role, which consists of the following. If a dielectric is placed in air between the plates and a gradually increasing voltage is applied to them, then at a certain voltage value a quiet discharge occurs at the edge of the plate, detectable by characteristic noise and glow in the dark. The magnitude of the critical voltage depends on the thickness of the plate, the sharpness of the edge, the type and thickness of the dielectric, etc. The thicker the dielectric, the higher the cr. For example, the higher the dielectric constant of a dielectric, the lower it is. To reduce the edge effect, the edges of the plate are embedded in a dielectric with high electrical strength, the dielectric gasket is thickened at the edges, the edges of the plates are rounded, and a zone with a gradually decreasing voltage is created at the edge of the plates by making the edges of the plates from a material with high resistance, reducing the voltage per one capacitor by dividing it into several series-connected ones.

That's why the founding fathers of electrostatics liked to have balls at the end of the electrodes. This, it turns out, is not a design feature, but a way to minimize the flow of charge into the air. There is nowhere else to go. If the curvature of some area on the surface of the ball is further reduced, then the curvature of neighboring areas will inevitably increase. And here, apparently, in our electrostatic affairs, it is not the average but the maximum curvature of the surface that is important, which is minimal, of course, for a ball.

Hmm.. but if the capacity of a body is the ability to accumulate charge, then it is probably very different for positive and negative charges…. Let's imagine a spherical capacitor in a vacuum... Let's charge it negatively from the heart, not sparing power plants and gigawatt-hours (that's what's good about a thought experiment!)... but at some point there will be so many excess electrons on this ball that they will simply start scattering around the entire vacuum, just not to be in such electronegative tightness. But this will not happen with a positive charge - electrons, no matter how few of them remain, will not fly away from the crystal lattice of the capacitor.

What happens, the positive capacitance is obviously much larger than the negative one? No! Because the electrons were actually there not for our pampering, but for connecting atoms, and without any noticeable share of them, the Coulomb repulsion of the positive ions of the crystal lattice would instantly smash the most armored capacitor into dust :)

In fact, without a secondary plate, the capacitance of the “solitary halves” of the capacitor is very small: the electrical capacitance of a single piece of wire with a diameter of 2 mm and a length of 1 m is approximately 10 pF, and the entire globe is 700 μF.

It is possible to construct an absolute standard of capacity by calculating its capacity using physical formulas based on accurate measurements of the dimensions of the plates. This is how the most precise capacitors in our country are made, which are located in two places. State standard GET 107-77 is located at FSUE SNIIM and consists of 4 unsupported coaxial-cylindrical capacitors, the capacitance of which is calculated with high accuracy using the speed of light and units of length and frequency, as well as a high-frequency capacitive comparator, which allows you to compare the capacitances of capacitors brought for verification with a standard (10 pf) with an error of less than 0 .01% in the frequency range 1-100 MHz (photo on the left).

In power electrical engineering, the first in the world to use a capacitor was Pavel Nikolaevich Yablochkov in 1877. He simplified and at the same time improved the Lomonosov capacitors, replacing shot and foil with liquid, and connecting the banks in parallel. He owns not only the invention of the innovative arc lamps that conquered Europe, but also a number of patents related to capacitors. Let's try to assemble a Yablochkov capacitor using salted water as a conducting liquid, and a glass jar of vegetables as a jar. The resulting capacity was 0.442 nf. If we replace the jar with a plastic bag, which has a larger area and many times less thickness, the capacity will increase to 85.7 nf. (First, fill the bag with water and check for leakage currents!) The capacitor works - it even allows you to blink the LED! It also successfully performs its functions in electronic circuits

The metal plates should fit as closely as possible to the dielectric, and it is necessary to avoid introducing an adhesive between the plate and the dielectric, which will cause additional losses on alternating current. Therefore, now mainly metal is used as plating, chemically or mechanically deposited on a dielectric (glass) or tightly pressed to it (mica).

Instead of mica, you can use a bunch of different dielectrics, whatever you like. Measurements (for dielectrics of equal thickness) showed that airε the smallest, for fluoroplastic it is larger, for silicone it is even larger, and for mica it is even larger, and in lead zirconate titanate it is simply huge. This is exactly how it should be according to science - after all, in fluoroplastic, electrons, one might say, are tightly chained to fluorocarbon chains and can only deviate slightly - there is nowhere for an electron to jump from atom to atom.

65 nanometers is the next goal of the Zelenograd plant Angstrem-T, which will cost 300-350 million euros. The company has already submitted an application for a preferential loan for the modernization of production technologies to Vnesheconombank (VEB), Vedomosti reported this week with reference to the chairman of the board of directors of the plant, Leonid Reiman. Now Angstrem-T is preparing to launch a production line for microcircuits with a 90nm topology. Payments on the previous VEB loan, for which it was purchased, will begin in mid-2017.

Beijing crashes Wall Street

Key American indices marked the first days of the New Year with a record drop; billionaire George Soros has already warned that the world is facing a repeat of the 2008 crisis.

The first Russian consumer processor Baikal-T1, priced at $60, is being launched into mass production

The Baikal Electronics company promises to launch into industrial production the Russian Baikal-T1 processor costing about $60 at the beginning of 2016. The devices will be in demand if the government creates this demand, market participants say.

MTS and Ericsson will jointly develop and implement 5G in Russia

Mobile TeleSystems PJSC and Ericsson have entered into cooperation agreements in the development and implementation of 5G technology in Russia. In pilot projects, including during the 2018 World Cup, MTS intends to test the developments of the Swedish vendor. At the beginning of next year, the operator will begin a dialogue with the Ministry of Telecom and Mass Communications on the formation of technical requirements for the fifth generation of mobile communications.

Sergey Chemezov: Rostec is already one of the ten largest engineering corporations in the world

The head of Rostec, Sergei Chemezov, in an interview with RBC, answered pressing questions: about the Platon system, the problems and prospects of AVTOVAZ, the interests of the State Corporation in the pharmaceutical business, spoke about international cooperation in the context of sanctions pressure, import substitution, reorganization, development strategy and new opportunities in difficult times.

Rostec is “fencing itself” and encroaching on the laurels of Samsung and General Electric

The Supervisory Board of Rostec approved the “Development Strategy until 2025”. The main objectives are to increase the share of high-tech civilian products and catch up with General Electric and Samsung in key financial indicators.