Pulse generators are devices that are capable of creating waves of a certain shape. The clock frequency in this case depends on many factors. The main purpose of generators is considered to be the synchronization of processes in electrical appliances. Thus, the user has the opportunity to configure various digital equipment.
Examples include clocks and timers. The main element of devices of this type is considered to be an adapter. Additionally, capacitors and resistors along with diodes are installed in the generators. The main parameters of devices include the indicator of oscillation excitation and negative resistance.
Generators with inverters
You can make a pulse generator with your own hands using inverters at home. To do this, you will need a capacitorless adapter. It is best to use field resistors. Their impulse transmission parameter is at a fairly high level. Capacitors for the device must be selected based on the power of the adapter. If its output voltage is 2 V, then the minimum should be at 4 pF. Additionally, it is important to monitor the negative resistance parameter. On average, it must fluctuate around 8 ohms.
Rectangular pulse model with regulator
Today, a square pulse generator with regulators is quite common. In order for the user to be able to adjust the maximum frequency of the device, it is necessary to use a modulator. Manufacturers present them on the market in rotary and push-button types. In this case, it is best to go with the first option. All this will allow you to fine-tune the settings and not be afraid of a failure in the system.
The modulator is installed in the square pulse generator directly on the adapter. In this case, soldering must be done very carefully. First of all, you should thoroughly clean all contacts. If we consider capacitorless adapters, their outputs are on the top side. Additionally, there are analog adapters, which are often available with a protective cover. In this situation, it must be removed.
In order for the device to have high throughput, resistors must be installed in pairs. The oscillation excitation parameter in this case must be at the level. As the main problem, the rectangular pulse generator (the diagram is shown below) has a sharp increase in operating temperature. In this case, you should check the negative resistance of the capacitorless adapter.
Overlapping pulse generator
To make a pulse generator with your own hands, it is best to use an analog adapter. In this case, it is not necessary to use regulators. This is due to the fact that the level of negative resistance can exceed 5 ohms. As a result, the resistors are subject to quite a large load. Capacitors for the device are selected with a capacity of at least 4 ohms. In turn, the adapter is connected to them only by output contacts. The main problem with the pulse generator is the asymmetry of oscillations, which occurs due to overloading of the resistors.
Symmetrical pulse device
It is possible to make a simple pulse generator of this type only using inverters. In such a situation, it is best to select an adapter of the analog type. It costs much less on the market than the capacitorless modification. Additionally, it is important to pay attention to the type of resistors. Many experts advise choosing quartz models for the generator. However, their throughput is quite low. As a result, the oscillation excitation parameter will never exceed 4 ms. Plus, there is the risk of the adapter overheating.
Considering all of the above, it is more advisable to use field-effect resistors. in this case it will depend on their location on the board. If you choose the option when they are installed in front of the adapter, in this case the excitation rate of oscillations can reach up to 5 ms. In the opposite situation, you can’t count on good results. You can check the operation of the pulse generator by simply connecting a 20 V power supply. As a result, the level of negative resistance should be around 3 ohms.
To keep the risk of overheating to a minimum, it is additionally important to use only capacitive capacitors. The regulator can be installed in such a device. If we consider rotary modifications, then the modulator of the PPR2 series is suitable as an option. According to its characteristics, it is quite reliable today.
Generator with trigger
A trigger is a device that is responsible for transmitting a signal. Today they are sold unidirectional or bidirectional. For the generator, only the first option is suitable. The above element is installed near the adapter. In this case, soldering should be done only after thoroughly cleaning all contacts.
You can even choose an analog adapter directly. The load in this case will be small, and the level of negative resistance with successful assembly will not exceed 5 Ohms. The parameter for excitation of oscillations with a trigger is on average 5 ms. The main problem the pulse generator has is this: increased sensitivity. As a result, these devices are not capable of operating with a power supply higher than 20 V.
increased load?
Let's pay attention to the microcircuits. Pulse generators of this type involve the use of a powerful inductor. Additionally, only an analog adapter should be selected. In this case, it is necessary to achieve high system throughput. For this purpose, capacitors are used only of the capacitive type. At a minimum, they must be able to withstand a negative resistance of 5 ohms.
A wide variety of resistors are suitable for the device. If you choose them of a closed type, then it is necessary to provide for them a separate contact. If you decide to use field-effect resistors, the phase change in this case will take quite a long time. Thyristors are practically useless for such devices.
Models with quartz stabilization
The pulse generator circuit of this type provides for the use of only a capacitorless adapter. All this is necessary to ensure that the excitation rate of oscillations is at least at the level of 4 ms. All this will also reduce thermal losses. Capacitors for the device are selected based on the level of negative resistance. Additionally, the type of power supply must be taken into account. If we consider pulsed models, their output current level is on average around 30 V. All this can ultimately lead to overheating of the capacitors.
To avoid such problems, many experts advise installing zener diodes. They are soldered directly onto the adapter. To do this, you need to clean all contacts and check the cathode voltage. Auxiliary adapters for such generators are also used. In this situation they play the role of a dial-up transceiver. As a result, the oscillation excitation parameter increases to 6 ms.
Generators with capacitors PP2
Setting up a high-voltage pulse generator with capacitors of this type is quite simple. Finding elements for such devices on the market is not a problem. However, it is important to choose a high-quality microcircuit. Many people purchase multi-channel modifications for this purpose. However, they are quite expensive in the store compared to regular types.
Transistors for generators are most suitable unijunction ones. In this case, the negative resistance parameter should not exceed 7 Ohms. In such a situation, one can hope for the stability of the system. To increase the sensitivity of the device, many advise using zener diodes. However, triggers are used extremely rarely. This is due to the fact that the throughput of the model is significantly reduced. The main problem with capacitors is considered to be amplification of the limiting frequency.
As a result, the phase change occurs with a large margin. To set up the process properly, you must first configure the adapter. If the negative resistance level is at 5 ohms, then the maximum frequency of the device should be approximately 40 Hz. As a result, the load on the resistors is removed.
Models with PP5 capacitors
A high-voltage pulse generator with the specified capacitors can be found quite often. Moreover, it can be used even with 15 V power supplies. Its throughput depends on the type of adapter. In this case, it is important to decide on resistors. If you select field models, then it is more advisable to install the adapter of the capacitorless type. In this case, the negative resistance parameter will be around 3 ohms.
Zener diodes are used quite often in this case. This is due to a sharp decrease in the level of the limiting frequency. In order to level it, zener diodes are ideal. They are usually installed near the output port. In turn, it is best to solder resistors near the adapter. The indicator of oscillatory excitation depends on the capacitance of the capacitors. Considering 3 pF models, note that the above parameter will never exceed 6 ms.
Main generator problems
The main problem with devices with PP5 capacitors is considered to be increased sensitivity. At the same time, thermal indicators are also at a low level. Due to this, there is often a need to use a trigger. However, in this case it is still necessary to measure the output voltage. If it exceeds 15 V with a block of 20 V, then the trigger can significantly improve the operation of the system.
Devices on MKM25 regulators
The pulse generator circuit with this regulator includes only closed-type resistors. In this case, microcircuits can even be used in the PPR1 series. In this case, only two capacitors are required. The level of negative resistance directly depends on the conductivity of the elements. If the capacitor capacitance is less than 4 pF, then the negative resistance can even increase to 5 ohms.
To solve this problem, it is necessary to use zener diodes. In this case, the regulator is installed on the pulse generator near the analog adapter. The output contacts must be thoroughly cleaned. You should also check the threshold voltage of the cathode itself. If it exceeds 5 V, then an adjustable pulse generator can be connected to two contacts.
- Tutorial
Good afternoon, dear Khabrovsk residents.
This post will be a little unusual.
In it I will tell you how to make a simple and fairly powerful high-voltage generator (280,000 volts). I took the Marx Generator circuit as a basis. The peculiarity of my scheme is that I recalculated it for accessible and inexpensive parts. In addition, the circuit itself is easy to repeat (it took me 15 minutes to assemble it), does not require configuration and starts the first time. In my opinion, it is much simpler than a Tesla transformer or a Cockroft-Walton voltage multiplier.
Operating principle
Immediately after switching on, the capacitors begin to charge. In my case, up to 35 kilovolts. As soon as the voltage reaches the breakdown threshold of one of the arresters, the capacitors through the arrester will be connected in series, which will lead to a doubling of the voltage on the capacitors connected to this arrester. Because of this, the remaining spark gaps are triggered almost instantly, and the voltage on the capacitors adds up. I used 12 steps, which means the voltage should be multiplied by 12 (12 x 35 = 420). 420 kilovolts are almost half-meter discharges. But in practice, taking into account all the losses, the resulting discharges were 28 cm long. The losses were due to corona discharges.
About details:
The circuit itself is simple, consisting of capacitors, resistors and arresters. You will also need a power source. Since all the parts are high-voltage, the question arises, where can I get them? Now, first things first:1 - resistors
Resistors needed are 100 kOhm, 5 watt, 50,000 volt.I tried many factory resistors, but none could withstand such voltage - the arc would break through the top of the case and nothing would work. Careful googling yielded an unexpected answer: the craftsmen who assembled the Marx generator for voltages of more than 100,000 volts used complex liquid resistors, the Marx generator on liquid resistors, or used a lot of stages. I wanted something simpler and made resistors from wood.
I broke off two even branches of a damp tree on the street (dry ones do not conduct current) and turned on the first branch instead of a group of resistors to the right of the capacitors, the second branch instead of a group of resistors to the left of the capacitors. It turned out to be two branches with many conclusions at equal distances. I made conclusions by winding bare wire over branches. Experience shows that such resistors can withstand voltages of tens of megavolts (10,000,000 volts)
2 - capacitors
Everything is simpler here. I took capacitors that were the cheapest on the radio market - K15-4, 470 pF, 30 kV (aka greensheets). They were used in tube TVs, so now you can buy them at a disassembly site or ask for them for free. They withstand a voltage of 35 kilovolts well, not a single one has broken through.3 - power supply
I just couldn’t bring myself to assemble a separate circuit to power my Marx generator. Because the other day my neighbor gave me an old TV “Electron TC-451”. The anode of the kinescope in color televisions uses a constant voltage of about 27,000 volts. I disconnected the high-voltage wire (suction cup) from the anode of the kinescope and decided to check what kind of arc would be produced from this voltage.Having played a lot with the arc, I came to the conclusion that the circuit in the TV is quite stable, can easily withstand overloads, and in the event of a short circuit, the protection is triggered and nothing burns out. The circuit in the TV has a power reserve and I managed to overclock it from 27 to 35 kilovolts. To do this, I twisted the R2 trimmer in the TV power module so that the horizontal power supply rose from 125 to 150 volts, which in turn led to an increase in the anode voltage to 35 kilovolts. When you try to increase the voltage even more, the KT838A transistor breaks through in the horizontal scan of the TV, so you need to not overdo it.
Build process
Using copper wire, I screwed the capacitors to tree branches. There must be a distance of 37 mm between the capacitors, otherwise an unwanted breakdown may occur. I bent the free ends of the wire so that there was 30 mm between them - these will be the arresters.It's better to see once than to hear 100 times. Watch the video where I showed in detail the assembly process and operation of the generator:
Safety precautions
Particular care must be taken, since the circuit operates at a constant voltage and a discharge from even one capacitor will most likely be fatal. When turning on the circuit, you need to be at a sufficient distance because electricity penetrates 20 cm or even more through the air. After each shutdown, you must always discharge all capacitors (even those in the TV) with a well-grounded wire.It is better to remove all electronics from the room where the experiments will be carried out. The discharges create powerful electromagnetic pulses. The phone, keyboard and monitor that are shown in my video are out of order and can no longer be repaired! Even in the next room my gas boiler turned off.
You need to protect your hearing. The noise from the discharges is similar to gunshots, then it makes your ears ring.
The first thing you feel when you turn it on is how the air in the room is electrified. The electric field intensity is so high that it is felt by every hair of the body.
The corona discharge is clearly visible. Beautiful bluish glow around parts and wires.
There is always a slight electric shock, sometimes you don’t even understand why: you touched the door - a spark jumped, you wanted to take the scissors - the scissors shot. In the dark, I noticed that sparks were jumping between various metal objects that were not connected to the generator: in a briefcase with a tool, sparks were jumping between screwdrivers, pliers, and a soldering iron.
The lights light up on their own, without wires.
The whole house smells like ozone, like after a thunderstorm.
Conclusion
All parts will cost about 50 UAH ($5), this is an old TV and capacitors. Now I am developing a fundamentally new scheme with the goal of obtaining meter discharges without special costs. You ask: what is the application of this scheme? I will answer that there are applications, but they need to be discussed in another topic.That's all for me, be careful when working with high voltage.
Powerful high voltage generator (Kirlian apparatus), 220/40000 volts
The generator produces voltages up to 40,000 V and even higher, which can be applied to the electrodes described in previous projects.
It may be necessary to use a thicker glass or plastic plate in the electrode to avoid serious electrical shock. Although the circuit is powerful, its output current is low, reducing the risk of fatal shock if it comes into contact with any parts of the device.
However, you should be extremely careful when handling it, as the possibility of electric shock cannot be ruled out.
Attention! High voltages are dangerous. Be extremely careful when working with this circuit. It is advisable to have experience with such devices.
You can use the generator in experiments with Kirlian photography (electrophotography) and other paranormal experiments, such as those involving plasma or ionization.
The circuit uses conventional components and has an output power of about 20 W.
Below are some characteristics of the device:
- power supply voltage - 117 V or 220/240 V (AC mains);
- output voltage - up to 40 kV (depending on the high-voltage transformer);
- output power - from 5 to 25 W (depending on the components used);
- number of transistors - 1;
- operating frequency - from 2 to 15 kHz.
Operating principle
The diagram shown in Fig. 2.63, consists of a single-transistor generator, the operating frequency of which is determined by capacitors C3 and C4 and the inductance of the primary winding of the high-voltage transformer.
Rice. 2.63 Kirlian apparatus
The project uses a high-power silicon npn transistor. To remove heat, it should be mounted on a sufficiently large radiator.
Resistors R1 and R2 determine the output power by setting the transistor current. Its operating point is set by resistor R3. Depending on the characteristics of the transistor, it is necessary to experimentally select the value of resistor R3 (it should be in the range of 270...470 Ohms).
The horizontal output transformer of the TV (horizontal transformer) with a ferrite core is used as a high-voltage transformer, which also determines the operating frequency. The primary winding consists of 20...40 turns of ordinary insulated wire. A very high voltage is generated on the secondary winding, which you will use in experiments.
The power supply is very simple; it is a full-wave rectifier with a step-down transformer. It is recommended to use a transformer with secondary windings providing voltages of 20...25 V and currents of 3...5 A.
Assembly
The list of elements is given in table. 2.13. Since the assembly requirements are not very strict, in Fig. Figure 2.64 shows the installation method using a mounting block. It contains small parts, such as resistors and capacitors, interconnected by hinged mounting.
Table 2.13. List of elements
Large parts, such as a transformer, are screwed directly to the housing.
It is better to make the body plastic or wood.
Rice. 2.64. Device installation
The high-voltage transformer can be removed from a non-working black-and-white or color TV. If possible, use a TV with a diagonal of 21 inches or larger: the larger the kinescope, the greater the voltage the TV’s line transformer should generate.
Resistors R1 and R2 - wirewound C1 - any capacitor with a nominal value of 1500...4700 µF.
The generator produces high-voltage pulses with a frequency of 400 Hz, following in bursts with a duration of 0.05 seconds. and a repetition rate of 4 Hz. The pulses have a range of 18-25 kV. The current consumed by the generator from a source with a voltage of 6... 15 V is not more than 0.5A. Most high-voltage generators developed by radio amateurs are based on high-voltage multipliers or homemade high-voltage transformers.
In both cases, the reliability of the device is low. Multiplier diodes are easily broken, and making a high-quality multi-turn high-voltage coil in amateur conditions is very difficult and time-consuming.
In this regard, of great interest is the use of a ready-made factory high-voltage coil in such a generator - an ignition coil from a car with a contact ignition system. These coils, despite the large number of turns and the high voltage they generate, are highly resistant to humidity and temperature changes and are most suitable for work in field conditions.
The schematic diagram of a generator based on a standard ignition coil from a VAZ - B115 car is shown in the figure above.
Operating principle of a pulsed high-voltage generator:
The output stage is made on transistors VT1 and VT2 according to a circuit reminiscent of the output stage circuit of a transistor ignition system. VT2 operates in key mode and interrupts the current flowing through the coil, as a result, oscillations appear in the circuit consisting of the low-resistance winding of the coil and C5, which induce a high-voltage pulse in the high-resistance winding.
In order to ensure the most economical mode and at the same time maintain the efficiency of the generator, a pulse signal is received at the input of the output stage, consisting of bursts of 0.05 seconds duration, following with a frequency of 4 Hz, which contain pulses with a frequency of 400 Hz.
This signal is generated by a generator on chips D1 and D2. Elements D1.1 and D1.2 contain a multivibrator that generates pulses with a frequency of 400 Hz. These pulses, through the key device on D2.1 and the buffer stage on D2.2 and D2.3, are supplied to the VT1 base.
But their arrival is interrupted by a multivibrator on D1.3 and D1.4, which produces pulses that follow at a frequency of 4 Hz. Resistors R3 and R2 are selected in such a way that the duration of the positive half-cycle at which D2.1 opens is 0.05 seconds.
Diode D246 can be replaced with D243, KD213. The KT838 transistor can be replaced with KT812. Ignition coil - any high-resistance coil, from the classic ignition system of VAZ, Moskvich, Volga cars.
Setting:
The repetition rate of high-voltage pulses can be set by selecting R2.
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 collectors 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.
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 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.
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 taken 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 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.
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 12 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 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.
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 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.
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 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.
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 V.
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 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.
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, 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.
The thyristor switching voltage can be adjusted by selecting neon lamps with different ignition voltages. You can change the thyristor switch-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
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.
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 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.
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 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).
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 every positive half-cycle
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).
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 the transistor VT2, the end to the 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 etc.
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 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 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.
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. 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.
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 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.
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 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.
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, 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).
Analogue of transistor TIP41 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 VTZ.
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 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.