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High voltage pulse generator circuit. Pulse current generator Electrical circuit of the pulse generator

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

The generator generates a single rectangular pulse by pressing a button. The circuit is assembled on logical elements based on a regular RS trigger, which also eliminates the possibility of bouncing pulses from the button contacts reaching the counter.

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

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

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

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

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

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

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

The last figure shows the circuit of the pulse generator, which includes the ability to adjust the duty cycle. For those who have forgotten, let us remind you. The duty cycle of pulses is the ratio of the repetition period (T) to the duration (t):

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

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

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

Variant of an oscillator circuit using two operational amplifiers

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

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

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

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

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

The pulse generator in the first circuit is built on the TL494 microcircuit, perfect for setting up any electronic circuits. The peculiarity of this circuit is that the amplitude of the output pulses can be equal to the supply voltage of the circuit, and the microcircuit is capable of operating up to 41 V, because it is not for nothing that it can be found in power supplies of personal computers.

You can download the PCB layout from the link above.

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

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

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

Generates powerful short single pulses that set a logical level opposite to the existing one at the input or output of any digital element. The pulse duration is chosen so as not to damage the element whose output is connected to the input under test. This makes it possible not to disrupt the electrical connection of the element under test with the rest.

Schema and theories of action

As shown in Fig. 3.2, the current-limiting transformer T1 is connected to the bridge rectifier D1-D4 and charges the external storage capacitor C through the overvoltage protection resistor R18. An external storage capacitor is connected between the discharge ground and the spark gap electrode G1. The load in this project is not connected as standard, but between the discharge ground and the spark gap electrode G2. Note that the load is complex, usually highly inductive (not in all cases) with little resistance from the Load inductor wire. The spark gap electrodes G1 and G2 are located at a distance 1.2-1.5 times greater than the breakdown distance at a given voltage.

The third trigger electrode TE1 is discharged by a short high-voltage pulse of low energy into G2, creating a voltage peak that ionizes

Rice. 3.2. Schematic diagram of a pulse generator

Note:

Special note regarding diodes D14, D15. The polarity can be reversed to produce a greater trigger effect with low impedance loads, as is the case with can warping devices, wire exploding devices, plasma weapons, etc.

Attention! If the load impedance is too high, energy can be directed back through the diodes and transformer T2 and cause these components to fail.

Note that the circuit ground and common wire are isolated from each other.

The discharge ground is connected to the chassis and ground through the green wire of the power cord.

To ensure greater safety, it is recommended to use non-latching buttons as the S3 switch, which is only activated when pressed.

If the device is located in a location where unauthorized personnel have access, it is recommended to use a key switch as S4.

a gap between G1 and G2, which leads to the discharge of the energy accumulated in the external capacitive storage device into a load with complex resistance.

The charge voltage of the external capacitive storage device is set by the resistive divider circuit R17, which also produces a signal for the voltmeter Ml. The charge voltage is set by a variable control resistor R8 connected in series with R17. This control signal sets the turn-off level of comparator II, which sets the DC bias of transistor Q1. In turn, Q1 controls the relay, which turns the relay off. The contacts of the de-energized relay RE1 remove the power supply to the primary winding T1. When R8 is set to a given value, it automatically maintains a certain voltage level in external capacitive storage devices. The S3 safety button provides the ability to manually delay the charge of the external capacitor.

The red LED LA1 lights up when the power is turned on. The yellow LED LA2 lights up when the charge reaches the set value.

The trigger electrode circuit is a special capacitive discharge (CD) system, where the energy of capacitor C6 is directed to the primary winding of pulse transformer T2. A sequence of positive high voltage pulses is generated on the secondary winding T2, which is supplied to capacitors C8 and C9 through decoupling diodes D14 and D15. These high voltage DC pulses cause ionization in the gaps by discharge through the trigger electrode TE1. At the input of this circuit there is a voltage doubler consisting of capacitors C4, C5 and diodes D8 and D9. Start switch S1 supplies energy to the circuit, causing the spark gap to immediately operate. The silicon triode thyristor SCR removes the charge from C6, the unlocking current to the SCR is supplied by the DIAC dinistor, the bias to which is set by the variable resistance R14 and the capacitor C7.

The 12 V step-down voltage transformer TZ powers the control circuit, which also includes relay RE1. If the system does not have 12 V, it can only be started by activating RE1 manually. The diode rectifier D10-D13 rectifies the 12 V AC voltage, which is then filtered by the capacitive filter C1. Resistor R5 decouples power for control through the zener diode Z3, Z4, which is necessary for stable operation of the comparator circuit. Power for energy storage comes from the 115 VAC mains, with fuse F1 activated, and the 115 VAC mains is turned on by switch S4.

Comment

In our lab at Information Unlimited, the energy storage equipment includes 10 racks of oil-filled capacitors. Each rack houses 50 32uF 4500V capacitors connected in parallel to achieve a total capacitance of 1600uF or about 13000J at 4000V per rack. All 10 racks connected in parallel provide 130,000 J. At these energy levels, it is very important to properly connect and assemble the system with the required location and thickness of wires to produce pulses with power of hundreds of megawatts. To protect personnel from dangerous voltage, explosion shields are installed around storage racks.

The charging time for one stand is about 10 minutes. With this charge, using 10 racks would be impractical because it would take almost 2 hours to charge them. We use a 10,000 V, 1 A current charging system that can charge all 10 racks of oil capacitors to store 130,000 J of energy in 1 min . This high voltage charger is available upon special order.

Device pre-assembly procedure

This section assumes that you are familiar with basic tools and have sufficient assembly experience. The pulse generator is assembled on a metal chassis 25.4 × 43.2 × 3.8 cm, made of galvanized iron 1.54 mm thick (22 gauge). It uses an RMS transformer with a current limit of 6500 V, 20 mA. It is necessary to follow the given drawing as accurately as possible. You can use a more powerful transformer, then you will have to change the size of the device. We propose to connect in parallel up to 4 previously used transformers; to get a charging current of 80 mA. A voltmeter and controls are installed on the front panel. It is recommended to replace S4 with a key switch if the device is located in an area where unauthorized personnel have access.

When assembling the device, follow the following sequence of actions:

1. If you purchased a kit, lay out and identify all components and structural parts.

2. Cut a board from the blank with a 0.25 cm grid perforation and dimensions of 15.9 x 10.8 cm (6.25 x 4.25 inches).

Rice. 3.3. Pulse generator circuit board

Note:

The dotted line shows the connections on the back of the board. Large black dots indicate holes in the board that are used to install components and connections between them.

3. Insert the elements as shown in the figure. 3.3, and solder them to the terminals of the elements, to those contact pads where it is necessary, as you move from the lower left edge to the right. The dotted line shows the wire connections on the back of the board according to the circuit diagram. Avoid wire bridges, potential shorts and cold soldering as these will inevitably cause problems. Solder joints should be shiny and smooth, but not spherical.

4. Connect the circuit board with wires to the following points (see Fig. 3.3):

– to chassis ground with #18 vinyl-insulated wire, 20 cm long;

– with TE1 high voltage wire 20 kV, 10 cm long;

– with resistor R18, vinyl insulated wire #18 20 cm long;

– with anodes D3 and D4 with vinyl insulated wire #18 30 cm long (circuit ground);

– with TZ (2) 12 V DC with #22 vinyl insulated wire, 20 cm long;

– with a voltmeter M1 (2) with a #22 vinyl insulated wire 20 cm long. Check all connections, components, the location of all diodes, semiconductor elements, electrolytic capacitors CI, C2, C4, C5, C7. Check the quality of solder joints, potential short circuits, and the presence of cold solder joints. Solder joints should be smooth and shiny, but not spherical. Check this carefully before turning on the device.

5. The spark gap is assembled as follows (Fig. 3.4):

– make the base BASE1 from a sheet of galvanized iron 1.4 mm thick (20 gauge) and dimensions 11.4 x 5 cm (4.75 x 2 inches);

– Make two BRKT1 brackets from 1.4 mm thick (20 gauge) galvanized iron sheet, each measuring 6.4 x 3.2 cm (2.5 x 1.25 in.). Fold the edge into a 1.9 cm visor;

– Make two BLK1 blocks from polyvinyl chloride (PVC) or similar material, 1.9 cm thick and 2.5 x 3.2 cm (1 x 1.25 in.) in size. They must have good insulating properties;

– make a BLK2 block from Teflon. It must withstand the high voltage trigger pulse;

– carefully solder the COL1 flanges to the BRK1 brackets. Adjust the fixture to ensure precise alignment of the tungsten electrodes after assembling the unit. At this point you will have to use a propane gas blowtorch, etc.;

– grind off the sharp ends of the eight screws. This is necessary to prevent the PVC material from breaking due to corona discharge generated at the sharp ends at high voltage;

– pre-assemble the parts, drill the necessary holes in them for assembly. Follow the picture for correct placement;

Rice. 3.4. Spark gap and ignition device

Note:

The spark gap is the heart of the system, and it is there that the energy accumulated by the capacitors over the entire charge period is quickly released into the load in the form of a high-power pulse. It is very important that all connections are able to withstand high currents and high discharge voltages.

The device shown here is designed for the HEP90 and is capable of switching at up to 3000 J of energy (when pulsed correctly), which is usually sufficient for efficient experimentation with mass transfer devices, can bending, wire exploding, magnetism and other similar projects.

A high energy switch capable of operating at 20,000J of energy can be supplied upon special order. Both switches use a high voltage trigger pulse that is dependent on the high line load impedance. This is usually not a problem for moderately inductive loads, but can be a problem for low inductance loads. This problem can be solved by placing some ferrite or ring cores in these lines. The cores react very strongly to the triggering pulse, but during the main discharge they reach saturation.

The design of the spark gap must take into account the mechanical forces that arise as a result of the action of strong magnetic fields. This is very important when working with physical energy and will require additional means to reduce inductance and resistance.

Attention! When conducting experiments, a screen must be installed around the device to protect the operator from possible fragments if the device breaks down.

For reliable starting, the starting gap must be set depending on the charge voltage. The gap should be located at least 0.6 cm from the bracket. If the switching is unstable, you need to experiment with this value.

– attach the large block lugs LUG1 to each side of the BRKT1 brackets. The connection must be made carefully, since the pulse current reaches kiloamperes;

– temporarily set the main gap to 0.16 cm and the trigger gap to 0.32 cm.

Procedure for final assembly of the device

The following are the final assembly steps:

1. Make the chassis and panel as shown in Fig. 3.5. It would be wise to make a square hole in the panel to accommodate a voltmeter before making the panel. The voltmeter that is used requires a 10 cm square hole. Other, smaller holes can be determined from the drawing and drilled after connecting the chassis and panel.

Note:

Make a front panel from 1.54 cm (22 gauge) galvanized iron sheet measuring 53.34 x 21.59 cm (21 x 8.5 in). Bend 5 cm on each side to connect to the chassis, as shown in the figure. Make a hole for the voltmeter.

Make a chassis from 1.54 cm (22 gauge) galvanized iron measuring 55.88 x 27.9 cm (22 x 15 in.). Fold 5 cm on each side and make a 1.25 cm canopy. The overall size will be (25x43x5cm) with a 1.25 cm canopy along the bottom of the chassis.

Make smaller holes and holes for connections as you proceed.

The visor going to the attached part of the chassis is not shown in the figure.

Rice. 3.5. Drawing for making the chassis

2. Try on the control panel and drill the necessary holes for controls, indicators, etc. Pay attention to the insulating material between the chassis and parts of the device, see fig. 3.6 part PLATE1. This can be achieved by using a small amount of RTV room temperature silicone adhesive sealant. Drill the appropriate holes as you work, checking for correct placement and dimensions.

Rice. 3.6. General view of the assembled device

Note:

Wires are shown slightly elongated to ensure clarity of images and connections.

The dotted lines show the components and connections located under the chassis.

3. Try on the remaining parts (see Fig. 3.6) and drill all the holes necessary for installation and placement. Pay attention to the fuse holders FH1 /FS1 and the insulation of the input power cord BU2. They are located on the underside of the chassis and are shown with dotted lines.

4. Provide sufficient space for high voltage components: transformer output terminals, high voltage diodes and resistor R18. Please note that the high voltage diodes are installed on the plastic board using double-sided RTV tape.

5. Reinstall the control panel. Secure the circuit board with a few pieces of tape coated with RTV adhesive once you are sure everything is fine.

6. Make all connections. Please note the use of wire nuts when connecting terminals T1 and T2.

Preliminary electrical tests

To perform preliminary electrical tests, follow these steps:

1. Short-circuit the output terminals of the transformer using a high-voltage wire with a clamp.

2. Remove the fuse and install a 60 W barretor in the fuse holder as a ballast for the testing period.

3. Set switch S4 (see Fig. 3.7) to the off state, move the axis of the switch combined with variable resistance R8/S2 to the “off” position, set variable resistances R14 and R19 to the middle position and turn on the device to a 115 V AC network by plugging the COl power cord into the electrical outlet.

4. Turn the axis of the combined switch with variable resistance R8 until it turns on and watch the lamps LA1 and LA2 light up.

5. Press the charge button S3 and make sure that the RE1 relay is turned on (a clicking sound is heard) and the LA2 lamp is extinguished for the time that the S3 button is pressed.

6. Turn on S4 and press S3, notice that the barreter, turned on in accordance with point 2, burns at full heat.

7. Press the "Start" button S1 and observe the flash between the trigger electrode TE1 and the main discharge gap between G1 and G2. Please pay

Rice. 3.7. Front panel and controls

Please note that the variable resistance axis is set to the average value, but by turning the axis clockwise you can increase the discharge.

Basic tests

To carry out the tests, follow these steps:

1. Unplug the power cord and turn off S2 and S4.

2. Connect a 30uF, 4kV capacitor and a 5kOhm, 50W resistor as C and R as shown in Fig. 3.6.

3. Remove the ballast lamp and insert a 2A fuse.

4. Set the pilot gap to 0.32 cm and the main gap to 0.16 cm.

5. Connect a high-precision voltmeter through an external capacitor.

6. Turn on the device and turn on S2 and S4. Press button S3 and ensure that the external capacitor is charged to 1 kV before RE1 turns off. Note that in normal condition LA2 is on and off only for the duration of the charge cycle. When the set charge is reached, the LA2 LED turns on again, indicating that the system is ready.

7. Turn R8/S2 30° clockwise and notice that the voltage reaches a higher value before charging stops.

8. Press button S1 and observe the instantaneous powerful arc in the main gap that occurs when energy is directed to the external load.

9. Charge the device to 2500 V, measuring the voltage using an external voltmeter connected through a capacitor. Adjust R19 so that the front panel voltmeter reads 2.5 at full scale 5. Make a mark on the front panel so you know where the voltage is 2500 V. The front panel meter now reads the charge voltage with reasonable accuracy when the external voltmeter. Repeat step 8, observing a strong arc as the discharge occurs. Repeat charge and discharge cycles at different voltages to become familiar with the operation of the device.

This completes the verification and calibration of the device. Further operations will require additional equipment, depending on the project in which you are experimenting.

Useful mathematical relationships for bottom equipment

System storage energy:

The ideal current rise is achieved in LC systems. Use a factor of 0.75 when using oil capacitors and lower values for photo- and electrolytic capacitors. Time to reach peak current at 1 A cycle:

Magnetic flux

A = area of the coil face in m2; Le = distance between poles in m; M = mass in kg. Force:

Acceleration: Speed:

where t is the time to reach the peak current.

The generator, depending on the voltage of the power source, produces high-voltage pulses with an amplitude of up to 25 kV. It can be powered by a 6V galvanic battery (four A-type cells), a 6...12V battery, a car's on-board power supply, or a laboratory power supply up to 15V. The range of applications is quite wide: electric fences on an animal farm, a gas lighter, an electroshock protective device, etc. In the manufacture of such devices, the greatest difficulties are caused by a high-voltage transformer.

Even if successfully manufactured, it is not reliable and often fails due to dampness or due to breakdown of the insulation between the coils. An attempt to make a high-voltage generator based on a diode voltage multiplier also does not always give a positive result.

The easiest way is to use a ready-made high-voltage transformer - a car ignition coil from a car with a classic ignition system. This transformer is highly reliable and can operate even in the most unfavorable field conditions. The ignition coil design is designed for tough operation in all weather conditions.

The schematic diagram of the generator is shown in the figure. An asymmetrical multivibrator is made on transistors VT1 and VT2; it produces pulses with a frequency of about 500 Hz. These pulses flow through the collector load of transistor VT2 - the primary winding of the ignition coil. As a result, an alternating pulsed high-voltage voltage is induced in its secondary winding, which has a significantly larger number of turns.

This voltage is supplied to the spark gap, if it is a self-defense device or a gas lighter, or to an electric fence. In this case, voltage is supplied to the fence from the central terminal of the ignition coil (from the terminal from which voltage is supplied to the distributor and spark plugs), and the common plus of the circuit must be grounded.

If the generator will be used as a means of self-defense, it is most convenient to make it in the form of a stick. Take a plastic or metal tube of such a diameter that the ignition coil with its metal body is tightly inserted into it. In the remaining space of the pipe, place batteries and transistors. S1 in this case is the instrument button. The upper part of the reel body will have to be redone.

It is most convenient to take an old-style plug for a 220V network, with screw-out contacts. The hole for the wire in it must be drilled so that the part of the ignition coil with a high-voltage contact fits tightly into it. Then you need to remove the mounting wires from this contact and from the general plus of the circuit and, along the very edges of the plug, bring them to the pin contacts of the plug.

Then this plug must be coated with epoxy glue in the drilled hole for the wire and pressed tightly onto the plastic body of the high-voltage contact of the coil. You need to screw discharge petals under the pin contacts of the plug, the distance between which should be about 15 mm.

The ignition coil can be anything from a contact ignition system (not suitable for electronic ignition), preferably imported - it is smaller in size and operating.

The setting consists of selecting the value of R1 so that there is a reliable electrical discharge between the discharge petals.

Rectangular pulse generators are used in many amateur radio devices: electronic meters, slot machines, and they are most widely used when setting up digital equipment. We bring to your attention a selection of circuits and designs of rectangular pulse generators

The amplitude of the generated signal in such generators is very stable and close to the supply voltage. But the shape of the oscillations is very far from sinusoidal - the signal is pulsed, and the duration of the pulses and pauses between them is easily adjustable. Pulses can easily be given the appearance of a meander when the duration of the pulse is equal to the duration of the pause between them.

The main and widespread type of relaxation generator is a symmetrical multivibrator with two transistors, the circuit of which is shown in the figure below. In it, two standard amplifier stages on transistors VT1 and VT2 are connected in a series chain, that is, the output of one stage is connected to the input of the other through separating capacitors C1 and C2. They also determine the frequency of the generated oscillations F, or more precisely, their period T. Let me remind you that the period and frequency are related by the simple relation

If the circuit is symmetrical and the ratings of the parts in both stages are the same, then the output voltage has a meander shape.

The generator works like this: immediately after switching on, while capacitors C1 and C2 are not charged, the transistors find themselves in a “linear” amplification mode, when some small base current is set by resistors R1 and R2, it determines the collector current Vst times greater, and the voltage on the collectors is somewhat less than the power supply voltage due to the voltage drop across the load resistors R3 and R4. In this case, the slightest changes in the collector voltage (at least due to thermal fluctuations) of one transistor are transmitted through capacitors C1 and C2 to the base circuit of the other.

Let's assume that the collector voltage VT1 has dropped slightly. This change is transmitted through capacitor C2 to the base circuit VT2 and slightly blocks it. The collector voltage VT2 increases, and this change is transmitted by capacitor C1 to the base VT1, it is unlocked, its collector current increases, and the collector voltage decreases even more. The process occurs like an avalanche and very quickly.

As a result, transistor VT1 is completely open, its collector voltage will be no more than 0.05...0.1 V, and VT2 is completely locked, and its collector voltage is equal to the supply voltage. Now we need to wait until capacitors C1 and C2 are recharged and transistor VT2 is slightly opened by the current flowing through bias resistor R2. The avalanche-like process will go in the opposite direction and will lead to the complete opening of transistor VT2 and the complete closing of VT1. Now you need to wait another half-period needed to recharge the capacitors.

The recharging time is determined by the supply voltage, the current through resistors Rl, R2 and the capacitance of capacitors Cl, C2. In this case, they talk about the “time constant” of the chains Rl, C1 and R2, C2, approximately corresponding to the period of oscillations. Indeed, the product of resistance in ohms and capacitance in farads gives the time in seconds. For the values indicated in the diagram of Figure 1 (360 kOhm and 4700 pF), the time constant is about 1.7 milliseconds, which indicates that the multivibrator frequency will lie in the audio range of the order of hundreds of hertz. The frequency increases with increasing supply voltage and decreasing the ratings of Rl, C1 and R2, C2.

The described generator is very unpretentious: you can use almost any transistors in it and change the values of the elements within a wide range. You can connect high-impedance telephones to its outputs to hear sound vibrations, or even a loudspeaker - a dynamic head with a step-down transformer, for example, a subscriber broadcast loudspeaker. This way you can organize, for example, a sound generator for learning Morse code. The telegraph key is placed in the power circuit, in series with the battery.

Since two antiphase outputs of a multivibrator are rarely needed in amateur radio practice, the author set out to design a simpler and more economical generator containing fewer elements. What happened is shown in the following figure. Here two transistors with different types of conductivity are used - p-p-p and p-n-p. They open simultaneously, the collector current of the first transistor serves as the base current of the second.

Together, the transistors also form a two-stage amplifier, covered by the PIC through the chain R2, C1. When the transistors are turned off, the voltage at the collector VT2 (output 1 V) drops to zero, this drop is transmitted through the PIC chain to the base of VT1 and completely turns it off. When capacitor C1 is charged to approximately 0.5 V on the left plate, transistor VT1 will open slightly, current will flow through it, causing even more current to transistor VT2; The output voltage will begin to rise. This increase is transmitted to the base of VT1, causing it to open even more. The above-described avalanche-like process occurs, completely unlocking both transistors. After some time required to recharge C1, transistor VT1 will close, since the current through the high-value resistor R1 is insufficient to fully open it, and the avalanche-like process will develop in the opposite direction.

The duty cycle of the generated pulses, that is, the ratio of pulse durations and pauses, is regulated by the selection of resistors R1 and R2, and the oscillation frequency by the selection of capacitance C1. Stable generation at the selected supply voltage is achieved by selecting resistor R5. It can also regulate the output voltage within certain limits. So, for example, with the ratings indicated in the diagram and a supply voltage of 2.5 V (two alkaline disk batteries), the generation frequency was 1 kHz, and the output voltage was exactly 1 V. The current consumed from the battery was about 0.2 mA, which indicates very high efficiency of the generator.

The load of the generator R3, R4 is made in the form of a divider by 10, so that a lower signal voltage can be removed, in this case 0.1 V. An even lower voltage (adjustable) is removed from the variable resistor R4 motor. This adjustment can be useful if you need to determine or compare the sensitivity of phones, test a highly sensitive ULF by applying a small signal to its input, and so on. If such tasks are not set, resistor R4 can be replaced with a constant one or another divider link (0.01 V) can be made by adding another 27 Ohm resistor at the bottom.

A rectangular signal with steep edges contains a wide range of frequencies - in addition to the fundamental frequency F, also its odd harmonics 3F, 5F, 7F and so on, up to the radio frequency range. Therefore, the generator can be used to test not only audio equipment, but also radio receivers. Of course, the amplitude of harmonics decreases as their frequency increases, but a sufficiently sensitive receiver allows you to listen to them in the entire range of long and medium waves.

It is a ring of two inverters. The functions of the first of them are performed by transistor VT2, at the input of which an emitter follower on transistor VT1 is connected. This is done to increase the input resistance of the first inverter, making it possible to generate low frequencies with a relatively small capacitance of capacitor C7. At the output of the generator, element DD1.2 is included, which acts as a buffer element that improves the matching of the generator output with the circuit under test.

In series with the timing capacitor (the required capacitance value is selected by switch SA1), resistor R1 is connected, by changing the resistance of which the output frequency of the generator is regulated. To adjust the duty cycle of the output signal (the ratio of the pulse period to its duration), resistor R2 is introduced into the circuit.

The device generates pulses of positive polarity with a frequency of 0.1 Hz...1 MHz and a duty cycle of 2...500. The frequency range of the generator is divided into 7 subranges: 0.1...1, 1.10, 10...100, 100 ...1000 Hz and 1...10, 10...100, 100...1000 kHz, which are set by switch SA1.

The circuit can use silicon low-power transistors with a gain of at least 50 (for example, KT312, KT342, etc.), integrated circuits K155LNZ, K155LN5.

The rectangular pulse generator on the microcontroller in this circuit will be an excellent addition to your home measurement laboratory.

A feature of this oscillator circuit is a fixed number of frequencies, 31 to be exact. And it can be used in various digital circuit solutions where it is necessary to change the oscillator frequencies automatically or using five switches.

The choice of one frequency or another is carried out by sending a five-bit binary code at the input of the microcontroller.

The circuit is assembled on one of the most common microcontrollers, Attiny2313. A frequency divider with an adjustable division ratio is built in software, using the frequency of a quartz oscillator as a reference.

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

Initial data:

· type of technological process and its characteristics;

· constructive use of the discharge circuit;

· supply voltage characteristics;

· electrical impulse parameters, etc.

Calculation sequence:

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

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

· calculation of the pulse generator itself (Fig. 2.16).

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

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

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

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

The values of P 0 and U 0 allow the use of a VS dinistor of the KY102 series in the generator circuit.

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

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

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

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

Transistor collector current

Maximum collector current:

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

Base current:

I bm =1.2·0.003=0.0036A.

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

Resistor resistance in the voltage divider circuit:

Om; (2.79)

Ohm.

We accept the nearest standard values of resistor resistances R 1 = 13000 Ohm, R 2 = 110 Ohm.

Resistor R in the base circuit of the transistor regulates the output power of the generator; its resistance is taken to be 0.5...1 kOhm.

Transformer core cross-section TV1:

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

b – pulse generator

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

Number of turns in the windings of transformer TV1:

Vit.; (2.81)

vit.; (2.82)

vit. (2.83)

Filter capacitor capacity VC1:

Diameter of wires of transformer windings TV1:

We select standard wire diameters d 1 = 0.2 mm, d 2 = mm, d 3 = 0.12 mm.

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

Rice. 2.16. Design diagram of the pulse generator

Calculation of pulse generators (Fig. 2.16)

We take the voltage at the generator input equal to the voltage at the output of the converter U 0 = 300 V. Pulse frequency f = 1...2 Hz. The pulse voltage amplitude is no more than 10 kV. The amount of electricity per pulse is not more than 0.003 C. Pulse duration up to 0.1 s.

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

Direct resistance to direct current of the diode R d.pr = 3.3 Ohm and thyristor R t.pr = 7.5 Ohm.

Pulse repetition period for a given frequency range:

. (2.86)

The charging circuit resistance R 3 must be such that

Ohm. (2.88)

Then R 3 =R 1 +R d.pr =20·10 3 +3.3=20003.3 Ohm.

Charge current:

A. (2.89)

Resistor R2 limits the discharge current to a safe value. Its resistance:

Ohm, (2.90)

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

Discharge circuit resistance:

R p = R 2 R t. pr = 750 + 7.5 = 757.5 Ohm.

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

, , (2.91)