How to make a pulse generator from a horn. Signal generator: DIY function generator

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-oscillatory mode, the generator has two states of quasi-equilibrium 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 frequency of which are determined mainly only by the parameters of the generator. The main requirement for such generators is high frequency stability of self-oscillations. Meanwhile, as a result of changes in supply voltages, replacement and aging of elements, 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 take place in the circuit. One process is associated with the flow of the capacitor recharge current from the power supply 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 .

	Capacitor charging process is exponential in nature with a time constant . Therefore, the capacitor charging time , as well as the rise time of the collector voltage , i.e. the duration of the pulse front . During this time the capacitor charging up to voltage .Due to capacitor overcharging base voltage transistor VT2 growing, but for now transistor VT2 closed and the transistor VT1

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 VT2 closes. Capacitor is charged to a voltage
, and the capacitor almost empty(
). This corresponds to the time , from which the consideration of processes in the scheme 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 .

Let us assume that at the moment of time (Fig. 6.20) voltage , A . If the current through the capacitor does not leak, then the voltage on it , and at the element input LE1 . A capacitor charging current flows in the circuit from LE1 through a resistor . Input voltage LE2 as the capacitor charges is decreasing, but for now ,LE2 is at zero at the output.

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.

Multivibrator on operational amplifier has two feedback circuits (Fig. 6.22). The feedback circuit of the non-inverting input is formed by two resistors ( And ) and therefore . Feedback on the inverting input is formed by a chain ,

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
.

We will consider the processes occurring in the multivibrator, starting from the moment of time (Fig. 6.23) when the output voltage is positive ( ). In this case, the capacitor as a result of processes occurring at previous moments of time, it is charged in such a way that a negative voltage is applied to the inverting input.

A positive voltage is applied to the non-inverting input
. 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).

	One feedback branch, as in a multivibrator, is formed by a capacitor and resistor ; the other is a resistor , included in the common circuit of the emitters of both transistors. Thanks to this inclusion of the resistor base-emitter voltage

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.

Let us assume that at the moment of time (Fig. 6.26) a pulse is received at the input of the circuit, the amplitude of which is sufficient to open the transistor VT1 . As a result, the process of opening the transistor begins in the circuit VT1 accompanied by an increase in collector current and a decrease in collector voltage .

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 .

In this case, the self-excitation condition is satisfied, the regenerative process develops and the circuit goes into a quasi-stable state. Transistor VT1 turns out to be in a closed state, because due to the charge on the capacitor A negative voltage is applied to its base. Transistor VT2 remains open even after the end of the input signal, since the collector potential of the transistor VT1 when it closed, it increased, and the voltage at the base increased accordingly VT2 .

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.

In order for the circuit to be in a stable state, the control input LE1 voltage must be applied (Fig. 6.30). Under this condition LE2 is in state “1”, and LE1– in state “0”. Any other combination of element states is not stable. In this state, the circuit on the resistor there is some voltage drop, which is caused by the current LE2, flowing in

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 decrease
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 .

When reaches the value , the diode opens VD, and at this point the process of changing the voltage at the inverting input stops. The circuit appears to be in a stable state. Pulse duration determined by the exponential process of capacitor charging with time constant from voltage before , is equal .

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).

	Positive feedback in the circuit is manifested in the fact that with an increase in current in the primary (collector) winding of the transformer, i.e., the collector current of the transistor ( ), a voltage of such polarity is induced in the secondary (base) winding that the base potential increases. And, conversely, when

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:
.

When submitted at the time to the base of the unlocking pulse transistor (Fig. 6.34) the current increases , the transistor switches to active mode and a collector current appears . Increment of the collector current by the amount leads to an increase in voltage on the primary winding of the transformer , subsequent growth of the reduced

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.

The pulse generator is used for laboratory research when developing and setting up electronic devices. The generator operates in a voltage range from 7 to 41 volts and has a high load capacity depending on the output transistor. The amplitude of the output pulses can be equal to the value of the supply voltage of the microcircuit, up to the limiting value of the supply voltage of this microcircuit +41 V. Its basis is known to everyone, often used in.

Analogues TL494 are microcircuits KA7500 and its domestic clone - KR1114EU4 .

Parameter limit values:

Supply voltage 41V
Amplifier input voltage (Vcc+0.3)V
Collector output voltage 41V
Collector output current 250mA
Total power dissipation in continuous mode 1W
Operating temperature range environment:
-c suffix L -25..85С
-with suffix С.0..70С
Storage temperature range -65…+150С

Schematic diagram of the device

Square pulse generator circuit

Generator printed circuit board TL494 and other files are in a separate .

Frequency adjustment is carried out by switch S2 (roughly) and resistor RV1 (smoothly), the duty cycle is adjusted by resistor RV2. Switch SA1 changes the generator operating modes from in-phase (single-cycle) to anti-phase (two-cycle). Resistor R3 selects the most optimal frequency range to cover; the duty cycle adjustment range can be selected using resistors R1, R2.

Pulse generator parts

Capacitors C1-C4 of the timing circuit are selected for the required frequency range and their capacity can be from 10 microfarads for the infra-low subrange to 1000 picofarads for the highest frequency.

With an average current limit of 200 mA, the circuit is able to charge the gate fairly quickly, but
It is impossible to discharge it with the transistor turned off. Discharging the gate using a grounded resistor is also unsatisfactorily slow. For these purposes, an independent complementary repeater is used.

• Read: "How to make it from a computer."

Transistors are selected at any HF with a low saturation voltage and sufficient current reserve. For example KT972+973. If there is no need for powerful outputs, the complementary repeater can be eliminated. In the absence of a second construction resistor of 20 kOm, two constant resistors of 10 kOm were used, providing a duty cycle within 50%. The author of the project is Alexander Terentyev.

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, voltage will be present at the first output high level, and at the second output 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.

Scheme 1

The generator was designed to use a minimum number of commonly available electronic components, with good repeatability and reasonable reliability. The generator version (circuit 1) is assembled on the basis of the widely used PWM controller UC3525 (U1), which controls a bridge circuit based on field-effect transistors Q4-Q7. If the lower switches of each of the half-bridges operating in antiphase are controlled directly by the outputs of the 11/14 U2 microcircuit, then booster cascades on transistors Q2, Q3 are used as drivers of the upper arm. Such stages are widely used in most modern microcircuit drivers and are quite well described in the literature on power electronics. The input voltage, alternating or direct (~24~220V/30-320V), supplied to the input of the diode bridge (or bypassing it in the case of DC voltage), powers the power part of the circuit. To prevent a large starting current, thermistor Vr1 (5A/5Ohm) is connected to the power supply circuit. The control part of the circuit can be powered from any source with an output voltage of +15/+25V and a current of 0.5A. The parametric voltage stabilizer on transistor Q1 can have an output voltage from +9 to +18V (depending on the type of power switches used, for example), but in some cases you can do without this stabilizer if an external power source with the necessary parameters is already stabilized. The UC3525 microcircuit was not chosen by chance - it has the ability to generate a pulse sequence from several tens of hertz to 500 kHz and quite powerful outputs (0.5A). At the very least, the TL494 microcircuits could not function at a frequency of less than 250 Hz in push-pull mode (in single-cycle mode - no problem) - the internal logic malfunctioned and the sequence of pulses, as well as their duration, became chaotic.

The frequency of the pulse sequence is adjusted using variable resistor R1, and the pulse duration is adjusted using R4. The initial duration of the "dead time" is set by resistor R3.

Scheme 2

The generator shown in Diagram 2 is a complete analogue of the previous circuit and has virtually no circuit differences. However, the domestic K1156EU2 microcircuit (a complete analogue of the UC3825), used in this generator, is capable of operating at higher frequencies (almost up to 1 MHz), the output stages have a higher load capacity (up to 1.5A). In addition, it has a minor difference in pinout compared to the UC3525. So, the “clock” capacitor is connected to pin 6 (5 for the 3525 chip), the timing resistor is connected to pin 5 (6 for the 3525 chip). If pin 9 of the UC3525 chip is the output of the error amplifier, then in the UC3825 chip this pin functions as the input of the “current” limiter. However, all the details are in the datasheet for these microcircuits. It is worth noting, however, that the K1156EU2 is less stable at frequencies below 200 Hz and requires a more careful layout and mandatory blocking of its power circuits with relatively large capacitance capacitors. If these conditions are ignored, the smoothness of the pulse duration adjustment near their temporary maximum may be disrupted. The described feature appeared, however, only when assembled on a breadboard. After assembling the generator on the printed circuit board, this problem did not appear.

Both circuits are easily scalable in power by using either more powerful transistors or by connecting them in parallel (for each of the switches), as well as by changing the supply voltage of the power switches. It is advisable to “mount” all power components on radiators. Up to a power of 100W, radiators with an adhesive base were used, designed for installation on memory chips in video cards (output switches and stabilizer transistor). Within half an hour of operation at a frequency of 10 kHz with a maximum duration of output pulses, with a switch supply voltage (31N20 transistors were used) +28V for a load of about 100W (two series-connected 12V/50W lamps), the temperature of the power switches did not exceed 35 degrees Celsius.

To construct the above circuits, ready-made circuit solutions were used, which I only double-checked and supplemented during prototyping. Printed circuit boards were designed and manufactured for the generator circuits. Figure 1 and Figure 2 show the boards of the first version of the generator circuit, Figure 3, Figure 4 show the board images for the second circuit.

At the time of writing, both circuits were tested in operation at frequencies from 40Hz to 200kHz with various active and inductive loads (up to 100W), at constant input supply voltages from 23 to 100V, with output transistors IRFZ46, IRF1407, IRF3710, IRF540, IRF4427, 31N20 ,IRF3205. Instead of bipolar transistors Q2, Q3, it is recommended to install (especially for operation at frequencies above 1 kHz) field-effect transistors, such as IRF630, IRF720 and the like with a current of 2A and an operating voltage of 350V. In this case, the value of resistor R7 can vary from 47 Ohm (over 500 Hz) to 1 k.

Component ratings are indicated through a slash - for frequencies above 1 kHz / for frequencies up to 1 kHz, except for resistors R10, R11, not indicated in the circuit diagram, but for which there are mounting locations on the boards - jumpers can be installed instead of these resistors.

The generators do not require configuration and, with error-free installation and serviceable components, begin to work immediately after power is applied to the control circuit and output transistors. The required frequency range is determined by the capacitance of capacitor C1. The component values ​​and positions for both circuits are the same.

Figure 5 shows the assembled generator boards.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
R1	Resistor	100 kOhm	1			To notepad
R2	Resistor	3.3 kOhm	1			To notepad
R3	Resistor	22/100	1			To notepad
R4	Resistor	10 kOhm	1			To notepad
R5	Resistor	33/100	1			To notepad
R8, R9	Resistor	51/3k3	2			To notepad
R10, R11	Resistor	0.47	2			To notepad
C1	Capacitor	1nF/0.33uF	1			To notepad
C2	Capacitor	0.1u	1			To notepad
C3		1000uFX35V	1			To notepad
C4	Electrolytic capacitor	100uF/25V	1			To notepad
C5	Electrolytic capacitor	220uF/25V	1			To notepad
C6, C7	Electrolytic capacitor	47uF50V	2			To notepad
C8, C9	Capacitor	330 µF	2			To notepad
C10, C11	Electrolytic capacitor	120uF/400V	2			To notepad
D2, D3, D6, D7	Rectifier diode	FR207	4			To notepad
Q2, Q3	bipolar transistor

The purpose of these devices is clear from the name. With their help, they create impulses that have certain parameters. If necessary, you can purchase a device made using factory technologies. But this article will discuss the circuit diagrams and do-it-yourself assembly technologies. This knowledge will be useful for solving various practical problems.

What does the G5-54 pulse generator look like?

Necessity

When you press a key on an electric musical instrument, electromagnetic vibrations are amplified and sent to the loudspeaker. A sound of a certain tone is heard. In this case, a sinusoidal signal generator is used.

For the coordinated operation of memory, processors, and other computer components, precise synchronization is necessary. A sample signal with a constant frequency is created by a clock generator.

To check the operation of meters and other electronic devices, and to identify malfunctions, single pulses with the necessary parameters are used. Such problems are solved using special generators. A regular manual switch will not work, since it will not be able to provide a specific signal shape.

Output parameters

Before choosing one scheme or another, it is necessary to clearly formulate the purpose of the project. The following figure shows an enlarged view of a typical square wave.

Square pulse circuit

Its shape is not ideal:

• The tension increases gradually. The duration of the front is taken into account. This parameter is determined by the time during which the pulse grows from 10 to 90% of the amplitude value.
• After the maximum surge and return to the original value, oscillations occur.
• The top is not flat. Therefore, the duration of the pulse signal is measured on a conventional line, which is drawn 10% below the maximum value.

Also, to determine the parameters of the future circuit, the concept of duty cycle is used. This parameter is calculated using the following formula:

• S is the duty cycle;
• T – pulse repetition period;
• t – pulse duration.

If the duty cycle is low, it is difficult to detect a short-term signal. This provokes failures in information transmission systems. If the time distribution of highs and lows is the same, the parameter will be equal to two. Such a signal is called a meander.

Square wave and basic pulse parameters

For simplicity, only rectangular pulse generators will be considered in the following.

Schematic diagrams

Using the following examples, you can understand the operating principles of the simplest devices of this class.

Square Pulse Generator Circuits

The first circuit is designed to generate single rectangular pulses. It is created on two logic elements, which are connected to perform the functions of an RS type flip-flop. If the button is in the indicated position, the third leg of the microcircuit will have high voltage, and the sixth leg will have low voltage. When pressed, the levels will change, but contact bounce and corresponding distortion of the output signal will not occur. Since operation requires external influence (in this case, manual control), this device does not belong to the group of self-generators.

A simple generator, but performing its functions independently, is shown in the second half of the figure. When power is applied through the resistor, the capacitor is charged. The relay does not operate immediately, since after the contact is broken, the flow of current through the winding for some time is ensured by the charge of the capacitor. Once the circuit is closed, this process is repeated repeatedly until the power is turned off.

By changing the resistance and capacitor values, you can observe the corresponding transformations in frequency and other signal parameters on an oscilloscope. It will not be difficult to create such a square wave generator with your own hands.

In order to expand the frequency range, the following circuit is useful:

Generator with variable pulse parameters

To implement a plan, two logical elements are not enough. But it’s not difficult to choose one suitable microcircuit (for example, in the K564 series).

Signal parameters that can be changed by manual adjustment, other important parameters

Circuit diagram element	Purpose and features
VT1	This field effect transistor is used so that high resistance resistors can be used in the feedback circuit.
C1	The permissible capacitance of the capacitor is from 1 to 2 µF.
R2	The resistance value determines the duration of the upper parts of the pulses.
R3	This resistor sets the duration of the lower parts.

To ensure the stability of the frequency of rectangular signals, circuits based on quartz elements are used:

Video. IN DIY high-voltage pulse generator

To make it easier to assemble a pulse generator of a certain frequency with your own hands, it is better to use a universal circuit board. It will be useful for experiments with different electrical circuits. Once you have acquired the skills and relevant knowledge, it will not be difficult to create the ideal device to successfully solve a specific problem.