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 excitation of oscillations 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 rectangular 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.

Pulse generators are an important component of many radio-electronic devices. The simplest pulse generator (multivibrator) can be obtained from a two-stage ULF (Fig. 6.1). To do this, simply connect the amplifier's input to its output. The operating frequency of such a generator is determined by the values ​​of R1C1, R3C2 and the supply voltage. In Fig. 6.2, 6.3 show multivibrator circuits obtained by simply rearranging the elements (parts) of the circuit shown in Fig. 6.1. It follows that the same simple diagram can be depicted in different ways.

Practical examples of using a multivibrator are shown in Fig. 6.4, 6.5.

In Fig. Figure 6.4 shows a generator circuit that allows you to smoothly redistribute the duration or brightness of the LEDs connected as a load in the collector circuit. By rotating the R3 potentiometer knob, you can control the ratio of the durations of the LEDs of the left and right branches. If you increase the capacitance of capacitors C1 and C2, the generation frequency will decrease and the LEDs will begin to blink. As the capacitance of these capacitors decreases, the generation frequency increases, the flickering of the LEDs will merge into a continuous glow, the brightness of which will depend on the position of the potentiometer R3 knob. Based on such a circuit design, various useful structures can be assembled, for example, a brightness control for an LED flashlight; toy with blinking eyes; a device for smoothly changing the spectral composition of the radiation source (multi-colored LEDs or miniature light bulbs and a light-summing screen).

The variable frequency generator (Fig. 6.5) designed by V. Tsibulsky allows you to obtain sound that smoothly changes over time in frequency [R 5/85-54]. When the generator is turned on, its frequency increases from 300 to 3000 Hz in 6 seconds (with a capacitor capacity of SZ 500 μF). Changing the capacitance of this capacitor in one direction or another accelerates or, conversely, slows down the rate of change in frequency. You can smoothly change this speed with variable resistance R6. In order for this generator to act as a siren, or to be used as a sweeping frequency generator, it is possible to provide a circuit for forced periodic discharge of the SZ capacitor. Such experiments can be recommended for independent expansion of knowledge in the field of pulse technology.

A controlled square pulse generator is shown in Fig. 6.6 [R 10/76-60]. The generator is also a two-stage amplifier covered by positive feedback. To simplify the generator circuit, it is enough to connect the emitters of the transistors with a capacitor. The capacitance of this capacitor determines the operating frequency of generation. In this circuit, a varicap is used as a voltage-controlled capacitance to control the generation frequency. An increase in the blocking voltage on the varicap leads to a decrease in its capacity. Accordingly, as shown in Fig. 6.7, the operating frequency of generation increases.

The varicap, as an experiment and to study the operating principle of this semiconductor device, can be replaced with a simple diode. It should be taken into account that germanium point diodes (for example, D9) have a very small initial capacitance (of the order of several pF), and, accordingly, provide a small change in this capacitance depending on the applied voltage. Silicon diodes, especially power diodes designed for high current, as well as zener diodes, have an initial capacity of 100... 1000 pF, so they can often be used instead of varicaps. Pn junctions of transistors can also be used as varicaps, see also Chapter 2.

To control the operation, the signal from the generator (Fig. 6.6) can be applied to the input of the frequency meter and the tuning limits of the generator can be checked when the control voltage changes, as well as when changing a varicap or its analogue. It is recommended that the results obtained (control voltage values ​​and generation frequency) when using different types of varicaps be entered into a table and displayed on a graph (see, for example, Fig. 6.7). Note that the stability of generators based on RC elements is low.

In Fig. 6.8, 6.9 show typical circuits of light and sound pulse generators made on transistors of various conductivity types. Generators are operational in a wide range of supply voltages. The first of them produces short flashes of light with a frequency of one Hz, the second produces pulses of sound frequency. Accordingly, the first generator can be used as a beacon, a light metronome, the second - as a sound generator, the oscillation frequency of which depends on the position of the potentiometer R1. These generators can be combined into a single unit. To do this, it is enough to turn on one of the generators as a load of the other, or in parallel with it. For example, instead of a chain of LEDs HL1, R2 or in parallel with it (Fig. 6.8), you can turn on the generator according to the circuit in Fig. 6.9. The result will be a periodic sound or light and sound signaling device.

The pulse generator (Fig. 6.10), made on a composite transistor (p-p-p and p-p-p), does not contain capacitors (a piezoceramic emitter BF1 is used as a frequency-setting capacitor). The generator operates at a voltage from 1 to 10 B and consumes a current from 0.4 to 5 mA. To increase the sound volume of a piezoceramic emitter, it is tuned to the resonant frequency by selecting resistor R1.

In Fig. Figure 6.11 shows a rather original generator of relaxation oscillations, made on a bipolar avalanche transistor.

The generator contains as an active element a transistor of the K101KT1A microcircuit with inverse switching in the mode with a “broken” base. The avalanche transistor can be replaced with its analogue (see Fig. 2.1).

Devices (Fig. 6.11) are often used to convert the measured parameter (light intensity, temperature, pressure, humidity, etc.) into frequency using resistive or capacitive sensors.

When the generator is operating, a capacitor connected in parallel to the active element is charged from the power source through a resistor. When the voltage on the capacitor reaches the breakdown voltage of the active element (avalanche transistor, dinistor, or similar element), the capacitor is discharged into the load resistance, after which the process is repeated with a frequency determined by the constant of the RC circuit. Resistor R1 limits the maximum current through the transistor, preventing its thermal breakdown. The timing circuit of the generator (R1C1) determines the operating range of generation frequencies. Headphones are used as an indicator of sound vibrations for quality control of generator operation. To quantify the frequency, a frequency meter or pulse counter can be connected to the generator output.

The device is operational in a wide range of parameters: R1 from 10 to 100 kOhm (and even up to 10 MOhm), C1 - from 100 pF to 1000 μF, supply voltage from 8 to 300 V. The current consumed by the device usually does not exceed one mA. It is possible for the generator to operate in standby mode: when the base of the transistor is shorted to ground (common bus), generation is interrupted. The converter-generator (Fig. 6.11) can also be used in the mode of a touch key, a simple Rx and Cx meter, a tunable wide-range pulse generator, etc.

Pulse generators (Fig. 6.12, 6.13) are also made on avalanche transistors of the K101KT1 microcircuit of the p-p-p type or K162KT1 of the p-p-p type, dinistors, or their analogues (see Fig. 2.1). The generators operate at a supply voltage above 9 B and produce a triangular voltage. The output signal is taken from one of the terminals of the capacitor. The input resistance of the cascade following the generator (load resistance) must be tens of times greater than the value of resistance R1 (or R2). A low-resistance load (up to 1 kOhm) can be connected to the collector circuit of one of the generator transistors.

Quite simple and often encountered in practice pulse generators (blocking generators) using inductive feedback are shown in Fig. 6.14 [A. With. USSR 728214], 6.15 and 6.16. Such generators are usually operational over a wide range of supply voltage changes. When assembling blocking generators, it is necessary to observe the phasing of the terminals: if the “polarity” of the winding is connected incorrectly, the generator will not work.

Such generators can be used when testing transformers for the presence of interturn short circuits (see Chapter 32): such defects cannot be detected by any other method.

Literature: Shustov M.A. Practical circuit design (Book 1), 2003

Rectangular pulse generators are widely used in radio engineering, television, automatic control systems and computer technology.

To obtain rectangular pulses with steep edges, devices are widely used whose operating principle is based on the use of electronic amplifiers with positive feedback. These devices include so-called relaxation oscillators - multivibrators, blocking oscillators. These generators can operate in one of the following modes: standby, self-oscillating, synchronizing and frequency division.

In standby mode, the generator has one stable equilibrium state. An external trigger pulse causes an abrupt transition of the waiting generator to a new state, which is not stable. In this state, called quasi-equilibrium, or temporarily stable, relatively slow processes occur in the generator circuit, which ultimately lead to a reverse jump, after which a stable initial state is established. The duration of the quasi-equilibrium state, which determines the duration of the generated rectangular pulse, depends on the parameters of the generator circuit. The main requirements for waiting generators are the stability of the duration of the generated pulse and the stability of its initial state. Waiting generators are used, first of all, to obtain a certain time interval, the beginning and end of which are fixed, respectively, by the front and fall of the generated rectangular pulse, as well as to expand pulses, to divide the pulse repetition rate and other purposes.

In the self-oscillating mode, the generator has two quasi-equilibrium states and does not have a single stable state. In this mode, without any external influence, the generator sequentially jumps from one state of quasi-equilibrium to another. In this case, pulses are generated, the amplitude, duration and repetition rate of which are determined mainly only by the parameters of the generator. The main requirement for such generators is high stability of the frequency of self-oscillations. Meanwhile, as a result of changes in supply voltages, replacement and aging of elements, and the influence of other factors (temperature, humidity, interference, etc.), the stability of the frequency of self-oscillations of the generator is usually low.

In synchronization or frequency division mode, the repetition rate of the generated pulses is determined by the frequency of the external synchronizing voltage (sinusoidal or pulsed) supplied to the generator circuit. The pulse repetition frequency is equal to or a multiple of the synchronizing voltage frequency.

A generator of periodically repeating relaxation-type rectangular pulses is called a multivibrator.

The multivibrator circuit can be implemented both on discrete elements and in integrated design.

Multivibrator based on discrete elements. This multivibrator uses two amplification stages covered by feedback. One feedback leg is formed by a capacitor and a resistor , and the other - And (Fig. 6.16).

states and ensures the generation of periodically repeating pulses, the shape of which is close to rectangular.

In a multivibrator, both transistors can be in the active mode for a very short time, since as a result of positive feedback, the circuit jumps into a state where one transistor is open and the other is closed.

Let us assume for definiteness that at the moment of time transistor VT1 open and saturated, and the transistor VT2 closed (Fig. 6.17). Capacitor Due to the current flowing in the circuit at previous times, it is charged to a certain voltage. The polarity of this voltage is such that to the base of the transistor VT2 a negative voltage is applied relative to the emitter and VT2 closed. Since one transistor is closed, and the other is open and saturated, the self-excitation condition is not satisfied in the circuit, since the gain coefficients of the stages
.

In this state, two processes occur in the circuit. One process is associated with the flow of capacitor recharge current from the power source through the resistor circuit – open transistor VT1 .The second process is due to the charge of the capacitor through a resistor
and the base circuit of the transistor VT1 , resulting in voltage at the collector of the transistor VT2 increases (Fig. 6.17). Since the resistor included in the base circuit of the transistor has a higher resistance than the collector resistor (
), capacitor charging time less time to recharge the capacitor .

open because its base is connected to the positive pole of the power supply through a resistor .

Basic
and collector
transistor voltage VT1 however, they do not change. This state of the circuit is called quasi-stable.

At a moment in time as the capacitor recharges, the voltage at the base of the transistor VT2 reaches the opening voltage and the transistor VT2 switches to active operating mode, for which
. When opening VT2 collector current increases and decreases accordingly
. Decrease
causes a decrease in the base current of the transistor VT1 , which, in turn, leads to a decrease in the collector current . Current reduction accompanied by an increase in the base current of the transistor VT2 , since the current flowing through the resistor
, branches into the base of the transistor VT2 And
.

After the transistor VT1 exits the saturation mode, the self-excitation condition is satisfied in the circuit:
. In this case, the process of switching the circuit proceeds like an avalanche and ends when the transistor VT2 goes into saturation mode, and the transistor VT1 – to cut-off mode.

Subsequently, the almost discharged capacitor (
) is charged from a power source through a resistor circuit
– basic circuit of an open transistor VT2 according to exponential law with time constant
. As a result, over time
the voltage across the capacitor increases before
and the front of the collector voltage is formed
transistor VT1 .

Transistor off state VT1 ensured by the fact that initially charged to voltage capacitor through an open transistor VT2 connected to the base-emitter gap of the transistor VT1 , which maintains a negative voltage at its base. Over time, the blocking voltage at the base changes as the capacitor recharged through the resistor circuit – open transistor VT2 . At a moment in time transistor base voltage VT1 reaches the value
and it opens.

In the circuit, the self-excitation condition is again satisfied and a regenerative process develops, as a result of which the transistor VT1 goes into saturation mode, and VT2 closes. Capacitor turns out to be charged to voltage
, and the capacitor almost empty(
). This corresponds to a moment in time , from which the consideration of processes in the circuit began. This completes the full cycle of operation of the multivibrator, since in the future the processes in the circuit are repeated.

As follows from the timing diagram (Fig. 6.17), in a multivibrator, periodically repeating rectangular pulses can be removed from the collectors of both transistors. In the case when the load is connected to the collector of the transistor VT2 , pulse duration determined by the process of recharging the capacitor , and the duration of the pause – the process of recharging the capacitor .

Capacitor recharge circuit contains one reactive element, therefore, where
;
;.

Thus, .

Recharge process ends at the moment of time , When
. Consequently, the duration of the positive pulse of the collector voltage of the transistor VT2 is determined by the formula:

.

In the case when the multivibrator is made on germanium transistors, the formula is simplified, since
.

Capacitor recharging process , which determines the duration of the pause between transistor collector voltage pulses VT2 , proceeds in the same equivalent circuit and under the same conditions as the process of recharging the capacitor , only with a different time constant:
. Therefore, the formula for calculating similar to the formula for calculating :

.

Typically, in a multivibrator, the pulse duration and pause duration are adjusted by changing the resistance of the resistors And .

The duration of the fronts depends on the opening time of the transistors and is determined by the charging time of the capacitor through the collector resistor of the same arm
. When calculating a multivibrator, it is necessary to satisfy the condition of saturation of an open transistor
. For transistor VT2 excluding current
capacitor recharge current
. Therefore, for the transistor VT1 saturation condition
, and for a transistor VT2 -
.

Frequency of generated pulses
. The main obstacle to increasing the pulse generation frequency is the long pulse rise time. Reducing the duration of the pulse front by reducing the resistance of the collector resistors can lead to failure of the saturation condition.

With a high degree of saturation in the considered multivibrator circuit, cases are possible when, after turning on, both transistors are saturated and there are no oscillations. This corresponds to a strict self-excitation mode. To prevent this, you should select an open transistor operating mode near the saturation limit in order to maintain sufficient gain in the feedback circuit, and also use special multivibrator circuits.

If the pulse duration equal to duration , which is usually achieved at , then such a multivibrator is called symmetrical.

The rise time of the pulses generated by the multivibrator can be significantly reduced if diodes are additionally introduced into the circuit (Fig. 6.18).

When, for example, a transistor turns off VT2 and the collector voltage begins to increase, then to the diode VD2 reverse voltage is applied, it closes and thereby turns off the charging capacitor from the collector of the transistor VT2 . As a result, the capacitor charge current no longer flows through the resistor , and through a resistor . Consequently, the duration of the front pulse of the collector voltage
is now determined only by the process of closing the transistor VT2 . A diode works the same way. VD1 when charging a capacitor .

Although in such a circuit the rise time is significantly reduced, the charging time of the capacitors, which limits the duty cycle of the pulses, remains virtually unchanged. Time constants
And
cannot be reduced by reducing . Resistor in the open state of the transistor, it is connected through an open diode in parallel with the resistor .As a result, when
The power consumption of the circuit increases.

Multivibrator on integrated circuits(Fig. 6.19). The simplest circuit contains two inverting logic elements LE1 And LE2, two timing chains
And
and diodes VD1 , VD2 .

At a moment in time
and at the exit LE2
. As a result, at the entrance LE1 through a capacitor , which is charged to voltage
, voltage is applied and LE1 goes to zero state
. Since the output voltage LE1 decreased, then the capacitor starts to discharge. As a result, the resistor a voltage of negative polarity will arise, the diode will open VD2 and capacitor will quickly discharge to voltage
. After this process is completed, the input voltage LE2
.

At the same time, the capacitor is charging in the circuit. and over time the input voltage LE1 decreases. When at a point in time voltage
,
,
. The processes begin to repeat themselves. The capacitor charges again , and the capacitor discharges through an open diode VD1 . Since the resistance of the open diode is much less than the resistance of the resistors , And , capacitor discharge And occurs faster than their charge.

Input voltage LE1 in the time interval
determined by the capacitor charging process :, Where
;
– output resistance of the logic element in the one state;
;
, where
. When
, the formation of the pulse at the output of the element ends LE2, therefore, the pulse duration

.

The duration of the pause between pulses (time interval from before ) is determined by the process of charging the capacitor , That's why

.

The duration of the front of the generated pulses is determined by the switching time of the logic elements.

In the time diagram (Fig. 6.20), the amplitude of the output pulses does not change:
, since during its construction the output resistance of the logic element was not taken into account. Taking into account the finiteness of this output resistance, the amplitude of the pulses will change.

The disadvantage of the considered simplest multivibrator circuit based on logic elements is the hard self-excitation mode and the associated possible absence of an oscillatory mode of operation. This drawback of the circuit can be eliminated if you additionally introduce an AND logical element (Fig. 6.21).

When the multivibrator generates pulses, the output LE3
, because the
. However, due to the strict self-excitation mode, it is possible that when the power supply voltage is turned on, due to the low rate of voltage rise, the charging current of the capacitors And turns out to be small. In this case, the voltage drop across the resistors And may be less than threshold
and both elements( LE1 And LE2) will find themselves in a state where the voltages at their outputs
. With this combination of input signals at the output of the element LE3 tension will arise
, which through a resistor supplied to the element input LE2. Because
, That LE2 is transferred to the zero state and the circuit begins to generate pulses.

To build rectangular pulse generators, along with discrete elements and LEs in an integrated design, operational amplifiers are used.

therefore the voltage at the inverting input
depends not only on the voltage at the output of the amplifier, but is also a function of time, since
.

The non-inverting input has a positive voltage
. Voltage
remains constant, and the voltage at the inverting input
increases over time, tending to the level
, since the process of recharging the capacitor takes place in the circuit .

However, for now
, the state of the amplifier determines the voltage at the non-inverting input and the output level is maintained
.

At a moment in time The voltages at the inputs of the operational amplifier become equal to:
. Further slight increase
leads to the fact that the differential (difference) voltage at the inverting input of the amplifier
turns out to be positive, so the output voltage decreases sharply and becomes negative
. Since the voltage at the output of the operational amplifier has changed polarity, the capacitor subsequently recharges and the voltage on it, as well as the voltage at the inverting input, tend to
.

At a moment in time again
and then the differential (difference) voltage at the amplifier input
becomes negative. Since it acts on the inverting input, the voltage at the output of the amplifier jumps again to the value
. The voltage at the non-inverting input also changes abruptly
. Capacitor , which by the time charged to a negative voltage, recharges again and the voltage at the inverting input increases, tending to
. Since in this case
, then the voltage at the amplifier output remains constant. As follows from the time diagram (Fig. 6.23), at the moment of time the full cycle of operation of the circuit ends and in the future the processes in it are repeated. Thus, periodically repeating rectangular pulses are generated at the output of the circuit, the amplitude of which at
equal to
. Pulse duration (time interval
) is determined by the time it takes to recharge the capacitor according to the exponential law from
before
with time constant
, Where
– output impedance of the operational amplifier. Because during the pause (interval
) the capacitor is recharged under exactly the same conditions as during the formation of pulses, then
. Hence, the circuit works as a symmetrical multivibrator.

occurs with time constant
. With a negative output voltage (
) diode open VD2 and the capacitor recharge time constant , which determines the duration of the pause,
.

A standby multivibrator or monovibrator has one stable state and provides the generation of rectangular pulses when short trigger pulses are applied to the input of the circuit.

Single vibrator based on discrete elements consists of two amplification stages covered by positive feedback (Fig. 6.25).

transistor VT1 depends on the collector current of the transistor VT2 . This circuit is called an emitter-coupled single-vibrator. The circuit parameters are calculated in such a way that in the initial state, in the absence of input pulses, the transistor VT2 was open and rich, and VT1 was in cutoff mode. This state of the circuit, which is stable, is ensured when the following conditions are met:
.

Let us assume that the monovibrator is in a stable state. Then the currents and voltages in the circuit will be constant. Transistor base VT2 through a resistor connected to the positive pole of the power supply, which, in principle, ensures the open state of the transistor. To calculate the collector
and basic currents we have a system of equations

.

Having determined from here the currents
And , we write the saturation condition in the form:

.

Considering that
And
, the resulting expression is significantly simplified:
.

On a resistor due to the flow of currents ,
voltage drop is created
. As a result, the potential difference between the base and emitter of the transistor VT1 is determined by the expression:

If the condition is met in the circuit
, then the transistor VT1 closed. Capacitor at the same time charged to voltage. The polarity of the voltage across the capacitor is shown in Fig. 6.25.

When the transistor VT1 opens, capacitor turns out to be connected to the base-emitter region of the transistor VT2 such that the base potential becomes negative and the transistor VT2 goes into cut-off mode. The circuit switching process is avalanche-like in nature, since at this time the self-excitation condition is satisfied in the circuit. The switching time of the circuit is determined by the duration of the transistor switching processes VT1 and turn off the transistor VT2 and is a fraction of a microsecond.

When the transistor turns off VT2 through a resistor collector and base currents stop flowing VT2 . As a result, the transistor VT1 remains open even after the end of the input pulse. At this time on the resistor voltage drops
.

State of the circuit when the transistor VT1 open and VT2 closed and quasi-stable. Capacitor through a resistor , open transistor VT1 and resistor turns out to be connected to the power source in such a way that the voltage on it has opposite polarity. A capacitor recharging current flows in the circuit , and the voltage across it, and therefore at the base of the transistor VT2 strives for a positive level.

Voltage change
is exponential in nature: where
. Initial voltage at the base of the transistor VT2 determined by the voltage to which the capacitor is initially charged and residual voltage on the open transistor:

The limiting voltage value to which the voltage at the base of the transistor tends VT2 , .

It is taken into account here that through a resistor not only the capacitor recharging current flows , but also current open transistor VT1 . Hence, .

At a moment in time voltage
reaches release voltage
and transistor VT2 opens. Appearing collector current creates an additional voltage drop across the resistor , which leads to a decrease in voltage
. This causes a decrease in the base and collector currents and a corresponding increase in voltage
. Positive increment of transistor collector voltage VT1 through a capacitor transmitted to the base circuit of the transistor VT2 and contributes to an even greater increase in its collector current . A regenerative process again develops in the circuit, ending with the transistor VT1 closes and the transistor VT2 goes into saturation mode. This completes the process of generating an impulse. The pulse duration is determined by putting
: .

After the end of the pulse, the capacitor is charged in the circuit. through a circuit consisting of resistors
,and emitter circuit of an open transistor VT2 . At the initial moment, the base current transistor VT2 equal to the sum of the capacitor charge currents : current , limited by the resistance of the resistor
, and the current flowing through the resistor . As the capacitor charges current the base current of the transistor decreases and accordingly decreases VT2 , tending to a stationary value determined by the resistor . As a result, at the moment the transistor opens VT2 voltage drop across resistor turns out to be greater than the stationary value, which leads to an increase in the negative voltage at the base of the transistor VT1 . When the voltage across the capacitor reaches
the circuit returns to its original state. Duration of the capacitor recharging process , which is called the recovery stage, is determined by the relation.

Minimum repetition period of one-shot pulses
, and the maximum frequency
. If the interval between input pulses is less , then the capacitor will not have time to recharge and this will lead to a change in the duration of the generated pulses.

The amplitude of the generated pulses is determined by the voltage difference across the transistor collector VT2 in closed and open states.

A one-shot can be implemented on the basis of a multivibrator, if one feedback branch is made not capacitive, but resistor and a voltage source is introduced
(Fig. 6.27). Such a circuit is called a single-vibrator with collector-base connections.

To the base of the transistor VT2 negative voltage is applied and it is closed. Capacitor charged to voltage
. In the case of germanium transistors
.

Capacitor , acting as a boost capacitor, is charged to voltage
. This state of the circuit is stable.

When applied to the base of the transistor VT2 unlocking pulse (Fig. 6.28), the processes of opening the transistor begin to take place in the circuit VT2 and closing the transistor VT1 .

When switching the circuit, the front of the output pulse is formed, which is usually removed from the collector of the transistor VT1 . Subsequently, the circuit undergoes a process of recharging the capacitor .Voltage on it
, and therefore the voltage at the base transistor VT1 changes according to exponential law
,Where
.

When at a point in time the base voltage reaches
, transistor VT1 opens, voltage on its collector
the transistor decreases and turns off VT2 . In this case, a cutoff of the output pulse is formed. We obtain the pulse duration if we put
:

.

Because
, That . Slice duration
.

Subsequently, a capacitor charging current flows in the circuit through a resistor
and the base circuit of the open transistor VT1 . The duration of this process, which determines the recovery time of the circuit,
.

The amplitude of the output pulses in such a one-shot circuit is almost equal to the voltage of the power source.

One-shot logic gate. To implement a one-shot on logical elements, AND-NOT elements are usually used. The block diagram of such a one-shot device includes two elements ( LE1 And LE2) and timing chain
(Fig. 6.29). Inputs LE2 combined and it works as an inverter. Exit LE2 connected to one of the inputs LE1, and a control signal is supplied to its other input.

its input circuit. The circuit generates a rectangular pulse with a short-term decrease (time ) input voltage
. After a time interval equal to
(not shown in Fig. 6.29), at the output LE1 the voltage will increase. This voltage surge across the capacitor passed to the input LE2. Element LE2 switches to state “0”. Thus, at the input 1 LE1 after an interval of time
tension begins to take effect
and this element will remain in the state of one, even if after time
voltage
will again become equal to logical “1”. For normal operation of the circuit, it is necessary that the input pulse duration
.

As the capacitor charges output current LE1 decreases. Accordingly, the voltage drop by :
. At the same time, the voltage increases slightly
, striving for tension
, which when switching LE1 in state “1” there was less
due to the voltage drop across the output resistance LE1. This circuit state is temporarily stable.

At a moment in time voltage
reaches the threshold
and element LE2 switches to state “1”. To input 1 LE1 signal is given
and it switches to the log state. "0". In this case, the capacitor , which is in the time interval from before charged, begins to discharge through the output resistance LE1 and diode VD1 . After time has passed , determined by the capacitor discharge process , the circuit returns to its original state.

Thus, the output LE2 a rectangular pulse is generated. Its duration, depending on the time of reduction
before
, is determined by the relation
, Where
– output impedance LE1 in state "1". Circuit recovery time , where
– output impedance LE1 in state "0"; – internal resistance of the diode in the open state.

and the voltage at the inverting input is small:
, Where
voltage drop across the diode in the open state. The voltage at the non-inverting input is also constant:
, and since
, then the output voltage is maintained constant
.

When submitted at the time input pulse of positive polarity amplitude
the voltage at the non-inverting input becomes greater than the voltage at the inverting input and the output voltage suddenly becomes equal to
. At the same time, the voltage at the non-inverting input also increases abruptly to
. At the same time the diode VD closes, capacitor begins to charge and the positive voltage increases at the inverting input (Fig. 6.32). Bye
voltage is maintained at the output
. At a moment in time at
the polarity of the output voltage changes and the voltage at the non-inverting input takes on its original value, and the voltage begins to decrease as the capacitor discharges .

Because
, That
.

The recovery time of the circuit is determined by the duration of the capacitor discharge process from
before
and taking into account the accepted assumptions
.

Generators based on operational amplifiers provide the formation of pulses with an amplitude of up to tens of volts; The duration of the rises depends on the frequency band of the operational amplifier and can be a fraction of a microsecond.

A blocking oscillator is a relaxation-type pulse generator in the form of a single-stage amplifier with positive feedback created using a transformer. The blocking oscillator can operate in standby and self-oscillating modes.

Standby mode blocking-generator When operating in standby mode, the circuit has a single stable state and generates rectangular pulses when trigger pulses are received at the input. The stable state of the blocking oscillator on a germanium transistor is achieved by including a bias source in the base circuit. When using a silicon transistor, no bias source is required because the transistor is closed at zero base voltage (Figure 6.33).

the base voltage decreases. Such a connection is realized by appropriately connecting the beginning of the transformer windings (shown by dots in Fig. 6.33).

In most cases, the transformer has a third (load) winding to which the load is connected .

The voltages on the windings of the transformer and the currents flowing in them are related to each other as follows:
,
,
,
Where
,
– transformation coefficients;
– number of turns of the primary, secondary and load windings, respectively.

The duration of the transistor switching process is so short that during this time the magnetizing current practically does not increase (
). Therefore, the current equation when analyzing the transient process of turning on a transistor is simplified:
.

base current
and the actual current flowing in the base circuit of the transistor,
.

Thus, the initial change in base current
as a result of processes occurring in the circuit, leads to a further change in this current
, and if
, then the process of changing currents and voltages has an avalanche-like character. Consequently, the condition for self-excitation of the blocking oscillator:
.

In the absence of load (
) this condition is simplified:
. Because
, then the self-excitation condition in the blocking generator is satisfied quite easily.

The process of opening the transistor, accompanied by the formation of a pulse front, ends when it goes into saturation mode. In this case, the self-excitation condition ceases to be satisfied and the top of the pulse is subsequently formed. Since the transistor is saturated:
, then voltage is applied to the primary winding of the transformer
and reduced base current
, as well as load current
, turn out to be constant. The magnetizing current during the formation of the pulse apex can be determined from the equation
, from where, under zero initial conditions, we obtain
.

Thus, the magnetizing current in the blocking generator, when the transistor is saturated, increases in time according to a linear law. In accordance with the current equation, the collector current of the transistor also increases according to a linear law
.

Over time, the transistor's saturation level decreases as the base current remains constant.
, and the collector current increases. At some point in time, the collector current increases so much that the transistor switches from saturation mode to active mode and the self-excitation condition of the blocking oscillator begins to be fulfilled again. It is obvious that the duration of the pulse apex is determined by the time during which the transistor is in saturation mode. The boundary of the saturation mode corresponds to the condition
. Hence,
.

From here we get the formula for calculating the duration of the pulse apex:

.

Magnetizing current
during the formation of the top of the pulse, it also increases at the moment of the end of this process, i.e., when
, reaches the value
.

Since the voltage of the power source is applied to the primary winding of the pulse transformer when the top of the pulse is formed , then the amplitude of the pulse on the load
.

When the transistor switches to active mode, the collector current decreases
. A voltage is induced in the secondary winding, leading to a decrease in base voltage and current, which in turn causes a further decrease in the collector current. A regenerative process develops in the circuit, as a result of which the transistor goes into cutoff mode and a pulse cutoff is formed.

The avalanche-like process of closing the transistor has such a short duration that the magnetizing current during this time practically does not change and remains equal
. Consequently, by the time the transistor closes in inductance energy stored
. This energy is dissipated only in the load , since the collector and base circuits of the closed transistor are open. In this case, the magnetizing current decreases exponentially:
, Where
– time constant. Flowing through a resistor the current creates a reverse voltage surge across it, the amplitude of which is
, which is also accompanied by a voltage surge at the base and collector of the closed transistor
. Using the previously found relation for
, we get:

,

.

The process of dissipation of energy stored in a pulse transformer, which determines the recovery time of the circuit , ends after a time interval
, after which the circuit returns to its original state. Additional collector voltage surge
may be significant. Therefore, in the blocking generator circuit, measures are taken to reduce the value
, for which a damping circuit consisting of a diode is connected parallel to the load or in the primary winding VD1 and resistor , whose resistance
(Fig. 6.33). When a pulse is formed, the diode is closed, since a voltage of reverse polarity is applied to it, and the damping circuit does not affect the processes in the circuit. When a voltage surge occurs in the primary winding when the transistor is turned off, a forward voltage is applied to the diode, it opens and current flows through the resistor . Because
, then the collector voltage surge
and reverse voltage surge on are significantly reduced. However, this increases the recovery time:
.

A resistor is not always connected in series with the diode , and then the amplitude of the burst turns out to be minimal, but its duration increases.

impulses. We will consider the processes occurring in the circuit, starting from the moment of time , when the voltage on the capacitor reaches the value
and the transistor will open (Fig. 6.36).

Since the voltage on the secondary (base) winding remains constant during the formation of the top of the pulse
, then as the capacitor charges, the base current decreases exponentially
, Where
– resistance of the base-emitter region of the saturated transistor;
– time constant.

In accordance with the current equation, the collector current of the transistor is determined by the expression
.

From the above relations it follows that in a self-oscillating blocking oscillator, during the formation of the top of the pulse, both the base and collector currents change. As can be seen, the base current decreases over time. The collector current, in principle, can both increase and decrease. It all depends on the relationship between the first two terms of the last expression. But even if the collector current decreases, it is slower than the base current. Therefore, when the base current of the transistor decreases, a moment in time occurs , when the transistor comes out of saturation mode and the process of forming the top of the pulse ends. Thus, the duration of the top of the pulse is determined by the relation
. Then we can write the current equation for the moment of completion of the formation of the top of the pulse:

.

After some transformations we have
. The resulting transcendental equation can be simplified under the condition
. Using the exponential series expansion and limiting ourselves to the first two terms
, we obtain a formula for calculating the duration of the pulse apex
, Where
.

During the formation of the top of the pulse due to the flow of the base current of the transistor, the voltage on the capacitor changes and by the time the transistor closes it becomes equal
. Substituting the value into this expression
and integrating, we get:

.

When the transistor switches to the active operating mode, the self-excitation condition begins to be fulfilled again and an avalanche-like process of its closing occurs in the circuit. As in the standby blocking generator, after the transistor is closed, the process of dissipation of the energy stored in the transformer occurs, accompanied by the appearance of surges in the collector and base voltages. After this process is completed, the transistor continues to be in the off state due to the fact that the negative voltage of the charged capacitor is applied to the base . This voltage does not remain constant, since in the closed state of the transistor through the capacitor and resistor recharge current flows from the power source . Therefore, as the capacitor recharges the voltage at the base of the transistor increases exponentially
, Where
.

When the base voltage reaches
, the transistor opens and the pulse formation process begins again. Thus, the duration of the pause , determined by the time the transistor is in the off state, can be calculated if we put
. Then we get
.For a blocking oscillator on a germanium transistor, the resulting formula is simplified, since
.

Blocking generators have a high efficiency, since practically no current is consumed from the power source during the pause between pulses. Compared to multivibrators and monovibrators, they allow you to obtain a higher duty cycle and shorter pulse duration. An important advantage of blocking generators is the ability to obtain pulses whose amplitude is greater than the power source voltage. To do this, it is enough that the transformation ratio of the third (load) winding
. In a blocking generator, if there are several load windings, it is possible to carry out galvanic isolation between the loads and receive pulses of different polarities.

The blocking oscillator circuit is not implemented in an integrated design due to the presence of a pulse transformer.

NE555 generator with frequency control

By the way, the NE555 microcontroller was developed back in 1971 and is so successful that it is used even today. There are many analogs, more functional models, modifications, etc., but the original chip is still relevant.

Description NE555

The microcircuit is an integrated timer. Currently produced primarily in DIP packages (previously there were round metal versions).

The functional diagram looks like this.

Rice. 1. Functional diagram

Can operate in one of two main modes:

1.Multivibrator (monostable);

2.Pulse generator.

We are only interested in the last option.

Simple generator on NE555

The simplest diagram is presented below.

Rice. 2. NE555 generator circuit

Rice. 3. Output voltage graph

Thus, the calculation of the oscillation frequency (with period t on the graph) will be performed based on the following formula:

f = 1 / (0.693*C*(R1 + 2*R2)),

Accordingly, the formula for the full period is:

t = 0.693*С*(R1 + 2*R2).

The pulse time (t1) is calculated as follows:

t1 = 0.693 * (R1 + R2) * C,

then the gap between pulses (t2) is like this:

t2 = 0.693 * R * 2 * C

By changing the values ​​of the resistors and capacitor, you can obtain the required frequency with a given pulse duration and pause between them.

Adjustable frequency generator on NE555

The simplest option is to redesign the unregulated generator circuit.

Rice. 4. Generator circuit

Here the second resistor is replaced with two adjustable ones connected with back-to-back diodes.

Another option for an adjustable oscillator on a 555 timer.

Rice. 5. Circuit of an adjustable oscillator on a 555 timer

Here, by switching the switch position (by turning on the desired capacitor), you can change the adjustable frequency range:

• 3-153 Hz;
• 437-21000 Hz;
• 1.9-95 kHz.

The switch in front of diode D1 increases the duty cycle; it doesn’t even need to be used in the circuit (during its operation, the frequency range may change slightly).

It is best to mount the transistor on a heat sink (even a small one).

The duty cycle and frequency are controlled by variable resistors R3 and R2.

Another variation with regulation.

Rice. 6. Scheme regulated generator

IC1 is an NE555N timer.

The transistor is a high-voltage field-effect transistor (to minimize the heating effect even at high currents).

A slightly more complex circuit that works with a larger number of control ranges.

Rice. 7. Circuit operating with a large number of control ranges

All details are already indicated on the diagram. It is regulated by turning on one of the ranges (on capacitors C1-C5) and potentiometers P1 (responsible for frequency), P4 (responsible for amplitude).

The circuit requires bipolar power supply!

Publication date: 21.02.2018

Readers' opinions

• Valentin / 06.16.2019 - 18:53
  Under Fig. 3 in the formula for the duration of the pause between pulses, remove the extra asterisk and bring the formula to the form t2=0.693×R2×C
• shadi abusalim / 03.09.2018 - 13:55
  Please help you use the electronic circuit using the built-in 555 To adjust the pulse width and control it, to add control to the flash, extinguish and light the lamp in the same circle The frequency of the circuit should be up to 500KHz There is a circle located on the site similar but mail fluctuates slightly [email protected] The current and frequency are controlled by the variable resistors R3 and R2. Another variation with regulation. Fig. 6. Scheme of the regulated 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.

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.