Circuits of master RF oscillators for use in radio transmitters

Blocking generator: operating principle

Devices of this type are used to create signals with high duty cycle that are rarely repeated. They use a transformer, which is included in the feedback circuit. The presence of galvanic isolation at the output allows the formation of high-voltage pulses. This feature is used to power line scanning units and Tesla coils.

What does a blocking generator look like?

A simple generator blocking circuit can be assembled without difficulty at home.

Principle of operation

The diagram shown below will help you understand the functioning of the blocking generator.

Schematic diagram of a typical generator

The following list shows the main stages of work:

• After applying voltage through resistor R1, capacitor C is charged. The completion time of this process is determined by the parameters of these elements.

The amount of current is limited by the resistance of the circuit, and the voltage at the capacitor terminals does not have time to reach its maximum.

• As soon as it reaches a certain value, the transistor will begin to open. The current begins to flow through the circuit: transformer winding – collector – emitter. At this stage, the voltage reaches its maximum almost instantly and the current increases relatively slowly.
• It induces an EMF in the transformer winding connected to the base, which further increases the voltage and opens the transistor. This process ends when the transformer core is saturated (the material is not capable of conducting a magnetic field of a certain intensity). It will also stop when the base current increases, until the saturation threshold of the semiconductor device.
• The transistor turns off. Charging of capacitor C begins. The inductance of the transformer winding produces an emf in the direction opposite to the original one. This speeds up the closing of the transistor.

The principle of operation of a blocking generator is easier to understand with the help of timing diagrams, which illustrate the change in electrical parameters in individual parts of the circuit.

Current and voltage diagrams

These drawings must be studied in conjunction with the following drawing, which shows another circuit diagram of a blocking generator.

Generator blocking circuit

The figure above does not show a specific load (designation Rн). The diode performs damping functions. It prevents voltage surges that could damage the transistor.

The stages described above are clearly visible in the diagrams. Below are the features that are characteristic of the second scheme:

• The t combination marks the moment when the voltage at the base of the transistor is not enough to open it.
• The time interval t – t1 indicates the period of gradual opening of the transistor. At the end point, saturation has occurred, so changing the base current does not affect the pulse shape.
• However, the capacitor discharge occurs. Therefore, there is a gradual decrease in the base current.
• Since the load on the collector has inductive characteristics, the current Ic does not decrease. The duration of this period is determined by the parameters of the transformer core.
• The pulse cutoff begins at point t2. The current created by induction decreases, which provokes a gradual closing of the transistor switch. The figures show when current appears in the opposite direction. This process intensifies the discharge of the capacitor. The closing speed of the transistor increases, and the cutoff becomes steep (formed in a short time).
• Point t3 indicates the moment the transistor gate is completely closed. After it, the appearance of oscillatory processes is permissible. To block them, a diode is installed in this circuit.

Starting the device

Before starting the generator, you need to double-check that its connections are correct so that you don’t end up with a rather expensive pile of transistors labeled “Burnt.”

It is advisable to carry out the first start-up with control of the current consumption. This current can be limited to a safe level by using a 2-10 Ohm resistor in the generator power circuit (collector or drain of the modulating transistor). The operation of the generator can be checked with various devices: a search receiver, a scanner, a frequency meter, or simply an energy-saving lamp. HF radiation with a power of more than 3-5 W makes it glow.

HF currents easily heat some materials that come into contact with them, including biological tissues. So, be careful, you can get a thermal burn by touching exposed resonators (especially when operating generators with powerful transistors). Even a small generator based on the MRF284 transistor, with a power of only about 2 watts, easily burns the skin of your hands, as you can see in this video:

With some experience and sufficient generator power, at the end of the resonator, you can ignite the so-called. “torch” is a small plasma ball that will be powered by RF energy from the generator. To do this, simply bring a lit match to the tip of the resonator.

T.N. "torch" at the end of the resonator.

In addition, it is possible to ignite an RF discharge between the resonators. In some cases, the discharge resembles a tiny ball of lightning moving chaotically along the entire length of the resonator. You can see what it looks like below. The current consumption increases somewhat and many terrestrial television channels “go out” throughout the house))).

Plasma arc between the resonators of the RF generator on the MRF284 transistor

Calculation

The principle of operation of the blocking generator is clear. Below is a calculation that will help you choose the right transistor of the second circuit diagram.

For the example, the following initial parameters were used:

• frequency (F) – 40 kHz;
• duty cycle (C) – 0.25;
• amplitude (AM) – 6 V;
• resistance Rng (load) – 30 Ohm;
• voltage at the output of the power source (PS) – 300 V.

The permissible base-collector voltage should be from 1.5 to 2 times greater than NP. For this example - from 450 to 600 V.

The collector current ( Ik ) is determined by the formula:

Ik must be equal to or greater than ((3...5)*AM*CTF)/ Rng.

KTF is a coefficient that takes into account the features of energy transformation (collector - load windings):

Thus, the permissible collector current must be greater than the following values:

((3…5)*6*0,024)/ 30 = 0,0144…0,024.

The maximum frequency (Chmax, kHz) is calculated using the following formula:

Hmax≥(5…8) * H = (5…8) * 40 = 200…320.

Based on the data obtained, the type of transistor is determined.

Parameters of a suitable conditional device:

• maximum collector-base voltage (NCV) – 620 V;
• maximum base-emitter voltage (NBE) – 8 V$
• maximum collector current (Ik) – 0.03 A;
• collector-base current (Ikb) – 12 µA;
• maximum frequency (Chmax) – 1000 kHz;
• base resistance (Rb) – 250 Ohm.

Calculation and practice allow you to assemble a blocking generator with your own hands

To create a blocking generator correctly, you need to know theory and practice, and be able to make calculations.

Powerful ultrasonic generator

This circuit can produce an ultrasonic signal of several watts using a piezoelectric tweeter or other type of transducer. The operating frequency is from 18,000 to 40,000 Hz, it can be changed by selecting the capacitance of capacitor C1. At large capacitance values, a signal will be generated in the audio range, which allows the circuit to be used in alarms and other devices. In this case, the tweeter can be replaced with a regular loudspeaker.

The circuit consumes several hundred milliamps from a 9 or 12 V power supply. Batteries are recommended for short-term operation only.

You can use this device to scare away dogs and other animals by installing it near garbage collection areas, etc.

Ultrasonic operating mode is achieved with capacitance C1 from 470 to 2200 pF. An audio signal requires a capacitance in the range of 0.01-0.012 µF.

The schematic diagram of a powerful ultrasonic generator is shown in the figure; the list of elements is given in the table.

Powerful ultrasonic generator. All transistors must be mounted on radiators

Field-effect transistor generator

The operating principle of this device does not differ from the options discussed above. But changes have been made to the scheme that significantly increase energy efficiency, reliability and durability.

Field-effect transistor generator blocking circuit

Recommendations for proper assembly of the product:

• The domestic transistors and diodes indicated in the drawing can be replaced with similar imported semiconductor devices with suitable electrical characteristics.
• Resistance R2 is selected so that the voltage at C1 in idle mode does not exceed 450 V. This setting will prevent breakdown of the semiconductor junction of the VT transistor
• To avoid damaging the device, it should not be turned on without load.
• Resistance R6 performs protective functions. Its presence allows you to disconnect the generator from the network when the circuit breaker S is open

Blocking generator

In this article I will tell you about what a blocking generator is .

A blocking generator is a pulse generator of relatively short duration and long period. It works thanks to transformer feedback. Because of its simplicity, the blocking generator is widely used in compact voltage converters (for example, this circuit can be found in every second electronic lighter circuit).

This is a blocking generator (one of many variations of this scheme):

As you can see, it is really easy to assemble. The most difficult part in it is the transformer. But first things first.

1) Operating principle

First, winding 2 acts as a “resistor”, i.e. a current flows through it and the resistor, which begins to open the transistor. Opening the transistor leads to the appearance of a current in winding 1, and this in turn leads to the appearance of voltage on winding 2, i.e. the voltage at the base of the transistor increases further, it opens even more, and this happens until the core or transistor enters saturation. When this happens, the current through winding 1 begins to decrease, therefore the voltage on winding 2 changes polarity, which leads to the closing of the transistor. That's it, the cycle is closed!

2) Details

Transformer winding 1 is usually 2 times larger than winding 2, and the number of turns and wire diameter are selected depending on the voltage on winding 3 and the current through it.

The resistor is usually taken within the range of 1 kOhm - 4.7 kOhm.

Almost any transistor will do.

3) Test

First, let's assemble a basic generator circuit. This is the transformer from the ballast of an energy-saving lamp:

On it I first wound winding 2 (18 turns with 0.4 mm wire)

I insulated it (ordinary electrical tape will do)

And then I wound winding 1 (36 turns with the same wire as the 2nd one)

And finally, I inserted the core and secured it with the same electrical tape

At this point the transformer is ready.

I chose a powerful transistor: KT805, because the winding has only 36 turns of not the thinnest wire (low resistance).

Blocking generator is the simplest transformer. for charging gauss capacitors

• 2 Pages
• 1

• You cannot create a new topic
• You can't reply to the topic

#1 Fan_TOM_AS

• Group: Users
• Posts: 817
• Registration: 08 August 10

Many people who decide to assemble a Gauss stop at the issue of a converter; there are tons of circuits on the Internet, but this one is as simple as two fingers, uncritical of details, cannot fail; almost all the parts live in the old TV

Actually the scheme itself is nothing complicated. you will need such details as: my core is TOR (in TV there are U-shaped fuel assemblies, they are also suitable) there is also PM. R.M. ETD. Sh. U. and TeDe and TePe

Next you need a transistor (you can also find them on TVs)

I used the imported NPN 13007 and the Soviet PNP kt837. The circuit works with both transistors, you just need to change the power polarity and deploy the electrolyte. varnished wire for winding the transformer, thicker and thinner (I have 1mm and 0.56mm)

Blocking generator. Blocking generator calculation

Good day to all! In the last article, I talked about multivibrators, which are designed to generate rectangular pulses. But for this same purpose, another type of generator is used, which is called a blocking generator. In general, a blocking generator is a regenerative device (pulse generator) based on a single-stage amplifier, in which feedback is created by a pulse transformer.

To assemble a radio-electronic device, you can pre-make a DIY KIT kit using the link.

The main purpose of blocking generators is to create powerful short pulses with steep edges and high duty cycle. Currently they are used in switching power supplies as master oscillators

Just like a multivibrator, a blocking oscillator can operate in the following modes: self-oscillating, standby, synchronization and frequency division, but the most common are self-oscillating and standby modes.

Generator designs. Circuit examples

A device without a generator is either not capable of anything at all, or is designed to be connected to another (which most likely contains a generator). It is no exaggeration to say that generators are as necessary a device in electronics as a regulated DC power supply.

Depending on the specific application, the generator may simply be used as a source of regular pulses (a "clock" in a digital system). It may be required to be stable and accurate (such as a time reference in a frequency meter), adjustable (such as a local oscillator in a transmitter or receiver), or capable of producing exactly the same waveform (such as the horizontal scan generator of an oscilloscope).

Self-oscillating blocking oscillator

As mentioned above, a self-oscillating blocking oscillator is the most common. Let's look at its design and operating principle based on the simplest circuit shown below

The simplest circuit of a self-oscillating blocking oscillator.

The simplest blocking oscillator consists of a transistor VT1 in a common-emitter circuit, a feedback transformer T1, a damping circuit in the form of a diode VD1, a timing chain R2C1, a base resistor R1 and a load resistance Rн.

Let's consider the operation of the blocking generator based on the timing diagrams of its operation, which are presented below

Timing diagrams of the blocking generator.

First stage ( formation of the pulse front

) begins at time t, that is, at the moment the power is turned on or at the end of the period of the previous pulse. At this moment, the transistor is locked, and capacitor C1 begins to charge through resistor R2. As capacitor C1 charges, the voltage UBE at the base of transistor VT1 increases, which leads to a gradual opening of the transistor and an increase in the collector current IC. An increasing collector current leads to the formation of an EMF in the transformer and an increasing voltage and current is formed at its terminals in proportion to the collector current of transistor VT1. This stage ends at time t1, when the transistor has completely entered saturation mode.

Second stage ( formation of the top of the impulse

) starts at time t1. After transistor VT1 has entered saturation mode, it is little affected by the current flowing through the base of the transistor, so the increase in the pulse amplitude stops and a flat top of the pulse begins to form. During this period of time, the voltage at the transformer terminals practically does not change, so the voltage at the collector does not change, but since capacitor C1 is discharged, the voltage at the base of transistor VT1 decreases, and therefore the base current Ib. As the base current Ib decreases, the collector current IC begins to decrease, but due to the inductive nature of the collector load, the magnetizing current of the transformer begins to increase, and, consequently, the collector current of the transistor VT1, as a result, the voltage on the collector remains constant for some time, which depends on the parameters of the transformer T1.

Third stage ( pulse cut formation

) starts at time t2. At this time, the bias current decreases and transistor VT1 begins to close under the influence of the decreasing base current Ib, due to the discharge of capacitor C1. When the transistor is completely closed, the collector current will decrease to almost zero and the potential at the terminals of transformer T1 will also decrease, but as a result, a current will arise in the windings of the transformer that is opposite to the collector current IC and, accordingly, to the base current Ib, which will lead to an even faster discharge of the capacitor and the formation of a negative voltage surge on base. A negative voltage pulse based on transistor VT1 will discharge the capacitor even faster, which will reduce the duration of the pulse cutoff compared to the front.

Fourth stage ( recovery

) starts at time t3. At this time, the transistor is in a completely closed state. During this period of time, the energy stored in the third stage of the blocking generator is dissipated in the capacitor and transformer. During this period of time, some oscillatory processes may occur in the transformer (voltage change to the UK max level), which is generally undesirable, therefore, to prevent this, various damping circuits are connected in parallel with the collector winding of the transformer; in this case, this role is played by the diode VD1.

Push-pull generator for the lazy

The simplest generator circuit I've ever seen:

In this circuit one can easily see the similarity with a multivibrator. I'll tell you more - this is a multivibrator. Only instead of delay circuits on a capacitor and resistor (RC circuit), inductors are used here. Resistor R1 sets the current through the transistors. In addition, without it, generation simply will not work.

Generation mechanism:

Let's say VT1 opens, collector current VT1 flows through L1. Accordingly, VT2 is closed, and the opening base current VT1 flows through L2. But since the resistance of the coils is 100...1000 times less than the resistance of resistor R1, then by the time the transistor is fully opened, the voltage across them drops to a very small value, and the transistor closes. But! Since before closing the transistor, a large collector current flowed through L1, at the moment of closing there is a voltage surge (self-induction emf), which is supplied to the base of VT2 and opens it. Everything starts over again, only with a different generator arm. And so on…

This generator has only one advantage - ease of manufacture. The rest are cons.

Since it does not have a clear timing link (oscillating circuit or RC circuit), it is very difficult to calculate the frequency of such a generator. It will depend on the properties of the transistors used, the supply voltage, temperature, etc. In general, it is better not to use this generator for serious things. However, in the microwave range it is used quite often.

Calculation of a blocking oscillator in self-oscillating mode

Like any electronic circuit, the operating parameters of the blocking generator completely depend on the values ​​of the elements that make up the circuit, so for the calculation it is necessary to set the circuit parameters.

To calculate a blocking oscillator, the following output characteristics of the circuit are usually specified: pulse amplitude Um, pulse period T, pulse duration τi, load resistance RH.

Since at present blocking generators are very often used as master oscillators for switching power supplies, as an example we will calculate the simplest circuit on the basis of which a switching power supply can be created.

Let's set the following parameters for calculation: pulse frequency F = 50 kHz, pulse duty cycle Q = 0.3, output pulse amplitude Um = 5 V, load resistance RH = 25 Ohm, circuit supply voltage EK = 310 V (rectified mains voltage).

1. The first stage of the calculation is to determine the type of transistor as the main element of the circuit. The transistor is selected according to the following parameters: maximum permissible voltage UCBmax, maximum permissible collector current ICmax and limiting frequency fh21e.

where nH is the transformation coefficient from the collector winding to the load winding.

Let's take IC = 0.02 A

Transistor MJE13001 satisfies these parameters

with the following characteristics:

• transistor type: NPN
  ;
• UCBmax = 600 V;
• UBEmax = 7 V;
• ICmax = 0.2 A;
• ICBO = 10 µA;
• fh21e = 8 MHz;
• h21e = 5…30;
• rb ≈ 200 Ohm.

2. Determine the value of resistance R1

Let's take the value R1 = 390 Ohm.

3.Calculate the parameters of the pulse transformer. Transformation ratio for output winding nH

Controlled blocking generator circuit

_________________ Wisdom (experience and endurance) comes with age. All your troubles and problems are due to lack of knowledge. A smart person will learn from a fool, but Albert Einstein will not help a fool and the GDP will not save him. and the Ministry of Emergency Situations is late and yet now Fools and Tolerants die on Fridays!

_________________ Who is covered in MEAVE, how will you wash yourself off? “Juhan, Thor! You are ready to fight! (Reverse)

JLCPCB, only $2 per PCB prototype! Any colour!

Register and receive two coupons for $5 each: https://jlcpcb.com/cwc

There is a circuit for powering an LED from one battery:

Tell me, is it possible to power this from two batteries in series? To reduce the current consumption from one battery (so the battery will last longer). The fact is that the voltage for the LED is approximately 2.8 volts, but new batteries give 3.2 v and discharge to 1.5 v. Will the blocking generator work in this case and how effectively?

_________________ () I only solder with a copper tip. _/_ . . Should I join the sect of TS100 lovers?

PCB Assembly from $30 + FREE Shipping Worldwide + Stencil

I did it according to this scheme.

The transistor used was germanium - GT311I. Its measured gain (h21e) is about 40. The LEDs begin to glow at 0.28 V, the current consumed from the battery is = 3 mA. 0.28 V - 3.00 mA 0.50 V - 17.9 mA. 0.75 V - 31.0 mA. 1.00 V - 42.3 mA. 1.25 V - 51.7 mA. 1.50 V - 59.2 mA. I tried the KT315B, but it needs about 0.4-0.45 V to start working. A germanium transistor is more suitable in this regard.

In the tests, a power supply was used instead of a battery. Resistor 680 Ohm. I determined the resistance using the selection method - set it to 1.5 V on the power supply and reduced the resistance until generation failed. After that, I added a little resistance until it worked stable. The result was maximum brightness with minimal energy consumption.

The transformer was wound on the first ferrite ring that came across (about 21x12x6, I didn’t measure it exactly before winding) with a 0.35 mm wire, in two wires, turn to turn until filled (

50 turns of primary and the same number of secondary windings). L1 = 1477 µH. L2 = 1477 µH.

I also added a Schottky diode (SS24 - Multicomp Schottky Diode, 2 A, 40 V, SMB) and a 470 μFx35V capacitor (see diagram).

I installed a “GP Super” battery with U = 1.12 V, I don’t remember the short-circuit current, about 0.3-0.4 A. The flashlight worked for 62 hours on this already dead battery. At the end, the voltage on the battery was U = 0.249 V. It barely smoldered. Not bad. I turned it off, the voltage on the battery began to increase (to 0.26-0.27 V), turned it on - it caught fire and the voltage immediately began to drop. Even at 0.25 V it ignites confidently. Great!

We invite everyone to attend a webinar on October 13, 2022 on artificial intelligence, machine learning and solutions for their implementation from Microchip. Modern environments for deep learning of neural networks make it possible, without detailed study of the subject, to deploy an artificial neural network (ANN) not only on high-performance microprocessors and FPGAs, but also on 32-bit microcontrollers. And thanks to Microchip’s wide portfolio, which includes a range of components from microcontrollers and sensors to FPGAs, high-speed transmission and storage of information, it is possible to solve the entire range of problems that arise when training, verifying and deploying an ANN model.

Types of digital generators

In this article I want to give a brief overview of different frequency generation methods, but first I will tell you a few words about myself. This is my first article. I am a graduate student at the Moscow Energy Institute. Studied in the specialty “Metrology standardization and certification”. This article was written primarily for myself, in order to understand what available methods of generating a signal are, and since I did not find a summary of the information in one place, I decided to do it myself and publish it here. All this is done for self-educational purposes. I will be happy to receive comments on the text, essence and style in personal mail, and I will answer all your questions in the comments. I tried to write the article in the most accessible and simple language possible. So the types, or rather even methods, of generating a sinusoidal (and generally analog) signal. The first of these is called direct digital synthesis, or Direct Digital Synthesis.

A sinusoidal signal is, in fact, a solution to the equation Y= Sin(X), with a linearly varying value of the argument X. To receive a digital signal from the microcontroller, we need to feed the function values ​​to a digital-to-analog converter (DAC). This means that to obtain a sinusoidal signal, we need to know the values ​​of the Y function for each value of the argument X (in fact, X determines the value of the signal phase). It is possible to calculate all the function values ​​directly in the microcontroller, but to ensure high accuracy of the calculated values, a high-performance processor or floating point module is required. Calculating values ​​in a microcontroller can take a long time, so to ensure quick calculations, they take ready-made function values ​​and load them into memory. To ensure smoothness of the output signal, to reduce the error associated with the nonlinearity of the characteristic of the digital-to-analog converter, as many sine values ​​as possible are needed. Thus, there will be ready-made sine samples in memory. In order for these samples to turn into a sine, they need to be somehow stretched in time so that each sample is fed to the DAC a certain period of time after the previous one. This requires a reference frequency generator. Such a generator will produce pulses of constant duty cycle. These pulses, in the simplest case, arrive at the counter, and the counter, in turn, outputs a sequence of increasing codes. The code at the counter output will point to the address of the next sample in memory (ROM). The ROM, according to the codes, produces at its output the function values ​​contained in the memory at these addresses, which are transferred to the DAC and the output of the DAC will be a sine wave with an ideal frequency. The sine frequency will correspond to the frequency of the clock generator. To ensure frequency tuning, you need to somehow regulate the frequency of the reference oscillator. In the simplest case, a frequency divider is placed between the meter and the generator. Such a divider allows you to change the frequency within certain limits. The tuning limit depends on the adder capacity and the frequency of the reference oscillator. In this case, restructuring will only be possible by certain values, since division is only possible by numbers that are multiples of 2.

The simplest circuit of such a generator is shown in Figure 1. It includes a reference frequency generator (G). Divider into which the frequency code (division coefficient), counter (CT), ROM, DAC and filter are loaded. The filter in this case is necessary in order to smooth the digital signal at the output. A DAC is a digital device that only outputs a certain signal level. The lower the sampling frequency, the more pronounced the step characteristic of the output signal. In order to remove the error introduced by the sampling frequency, a signal filter is applied at the output. In the simplest case, this is a simple RC chain, but it is necessary to take into account the speed characteristics of the DAC, since the useful signal can be filtered out at high frequencies.

Here we consider the simplest DDS scheme. Many elements in it can be replaced and modified. For example, if you replace the meter with a more complex device, the so-called. phase accumulator, then we will have more possibilities, such as frequency tuning without phase shift or, for example, the ability to use a quarter of the period of sine values, instead of the full period, but such complications will not be considered within the scope of this article.

Currently, DDS are implemented as separate chips. In such a microcircuit it is enough to load the parameters of the desired signal and connect the reference frequency generator, and at the output we will get a digital sinusoid, which we only need to filter with the given parameters. Such generators allow you to obtain frequencies up to 1.4 GHz. They, in turn, have one drawback. Direct digital synthesis generators are most often used as frequency generators, so the amplitude of the output signal is not stable.

Another way to generate a sine wave signal using a controller is the PWM + passive RC filter method. PWM – pulse width modulation. It allows, by adjusting the duty cycle of the pulses, to obtain the desired constant signal amplitude. The wider the pulse, the higher the output voltage on the filter. The voltage can be changed from zero to supply voltage. Thus, if you set a specific program to regulate the duty cycle of the pulses, you can get a signal of any shape at the output, including a sinusoidal one. In the simplest case, the circuit is shown in Figure 2.

Such a generator is cheap, and most importantly, the most easily implemented way to convert a digital signal to analog using a microcontroller. It does not require special chips or any complex circuit solutions. The only thing that is necessary when creating such a generator is to calculate the output filter for a given cutoff frequency so that it does not cut off the useful signal. True, it is impossible to achieve high metrological characteristics with such a generator, since it is difficult to achieve a low harmonic distortion coefficient. Low levels of harmonic distortion can be achieved using another generator option.

The third version of the generator is based on a circuit called the “Wien bridge”. The essence of this circuit is that an amplifier with two RC circuits in feedback is used. One serial and one parallel. The circuit of such a generator is shown in Figure 3. For this circuit, it is necessary to take into account that the elements in the RC circuit must be strictly identical. Otherwise the circuit will not be stable. To reduce these effects, various tricks are used, such as automatic gain control and other tricks. In the simplest case, automatic control is carried out by some nonlinear element, for example a light bulb. But tuning such a generator in frequency is difficult. It is necessary to use variable capacitors, which complicates the circuit by an order of magnitude. This method is good, but mainly for generating a specific frequency, or a frequency with a small adjustment range.

There are different options and modifications of the above schemes. In addition to these circuits, there are analog solutions that were not described here due to inconsistency with the topic of the article. In conclusion, I want to say that each scheme must be selected and its possible implementation must be worked out depending on the task that needs to be completed. My challenge is to create a precision sine wave generator that can simultaneously produce a highly stable sine wave signal and add higher order harmonics to the signal. To accomplish this task, the best solution would be to calculate the values ​​of the sine function directly in the microcontroller and transfer the values ​​to the DAC. Such an implementation will allow me to take into account the shortcomings of each scheme and work out the technical implementation required specifically for my task. You can simultaneously make a stable amplitude, remove harmonic distortion introduced by the circuit feature and get a fairly stable generator. And the final errors will depend only on which elements are selected and what degree of simplification of the algorithm is taken. Thus, while the basic structure remains unchanged, it is possible to obtain a flexible solution to a certain class of problems.

If you are interested in any material on a similar topic, or in general something in the field of measuring instruments and their design, then I could try to write some material to cover your question in a simpler and more understandable way

Sources:

1. DDS: direct digital frequency synthesis. Author: Ridiko L.I. [Electronic resource]: Article – https://www.digit-el.com/files/articles/dds.pdf – 12/25/2013

2. Test signal generator with a low level of harmonics on the Wien bridge [Electronic resource]: Article - https://myelectrons.ru/wien-bridge-oscillator-low-thd/ - 12/26/2013

Controlled blocking generator circuit

The blocking oscillator is a single-stage relaxation generator of short-term pulses with strong inductive positive feedback created by a pulse transformer. The pulses generated by the blocking generator have a large rise and fall steepness and are close to rectangular in shape. The pulse duration can range from several tens of ns to several hundreds of microseconds. Typically, the blocking generator operates in high duty cycle mode, i.e., the duration of the pulses is much less than their repetition period. The duty cycle can be from several hundred to tens of thousands. The transistor on which the blocking generator is assembled opens only for the duration of the pulse generation, and is closed the rest of the time. Therefore, with a large duty cycle, the time during which the transistor is open is much less than the time during which it is closed. The thermal regime of the transistor depends on the average power dissipated at the collector. Due to the high duty cycle in the blocking oscillator, very high power can be obtained during low and medium power pulses.

With a high duty cycle, the blocking oscillator operates very economically, since the transistor consumes energy from the power source only during a short pulse formation time. Just like a multivibrator, a blocking oscillator can operate in self-oscillating, standby, and synchronization modes.

Blocking generators can be assembled using transistors connected in a circuit with an OE or in a circuit with an OB. The circuit with OE is used more often, since it allows one to obtain a better shape of the generated pulses (shorter rise time), although the circuit with OB is more stable with respect to changes in the parameters of the transistor.

The blocking oscillator circuit is shown in Figure 3.3.1

Figure 3.3.1 Blocking oscillator

The operation of the blocking generator can be divided into two stages. In the first stage, which occupies most of the oscillation period, the transistor is closed, and in the second, the transistor is open and a pulse is formed. The closed state of the transistor in the first stage is maintained by the voltage on capacitor C1, charged by the base current during the generation of the previous pulse. In the first stage, the condenser is slowly discharged through the high resistance of the resistor R1, creating a potential close to zero at the base of the transistor VT1 and it remains closed.

When the voltage at the base reaches the opening threshold of the transistor, it opens and current begins to flow through the collector winding I of transformer T. In this case, a voltage is induced in the base winding II, the polarity of which must be such that it creates a positive potential at the base. If windings I and II are connected incorrectly, the blocking oscillator will not generate. It means that the ends of one of the windings, no matter which one, must be swapped.

The positive voltage that arises in the base winding will lead to a further increase in the collector current and thereby to a further increase in the positive voltage at the base, etc. An avalanche-like process of increasing the collector current and voltage at the base develops. As the collector current increases, there is a sharp drop in voltage across the collector.

Pulse generators (injection field-effect transistors, negavaristors)

Pulse generators based on analogues of injection field-effect transistors (IFT), known since 1973, are one of the simplest generators operating in a wide range of supply voltages [Рл 4/97-33].

In Fig. 8.1, 8.2 show diagrams of analogues of IPT p- and p-structures, made on the basis of jointly connected field-effect and bipolar transistors [Рл 4/97-33].

Rice. 8.1

Rice. 8.2

At low bias based on the IPT analogue, the collector current of the bipolar transistor is small. When the voltage at the base increases, an abrupt change in the state of the IPT occurs. The base-emitter transition resistance of the IPT analog goes from a non-conducting state to a conducting state, and the collector current increases sharply. The device can be converted into a relaxation pulse generator (RPG) if a capacitor is connected parallel to the emitter-base transition of the IPT analogue.

Figure 8.3 shows a diagram of a controlled RGI of audio frequencies using an analogue of the IPT. A piezoceramic buzzer is used as a timing capacitor for the generator. A change in resistance in the IPT base circuit from 24 to 510 kOhm at IPT = 9 V causes a change in the generation frequency from 1100 to 200 Hz, while the current consumed by the device decreases from 240 to 20 μA. The generator operates in the supply voltage range from 3 to 10 V,

Rice. 8.3

Rice. 8.4

The generator according to the circuit in Fig. is less economical. 8.4, which can operate in the supply voltage range from 1 to 10 B. A timing circuit (R1, C1) is connected to the control electrode of the IPT analogue. The TK-67 (TM-2V) telephone capsule was used as the RGI load. The generation frequency of the DGI is 2.7 kHz at ipit = 9 6, and the current consumption is 10 mA.

Infra-low frequency generators can also be made based on an analogue of the IPT, for example, an economical light flash generator (Fig. 8.5). With the ratings indicated in the diagram, the generation frequency is 2 Hz. Since the generated pulses are quite short, the current consumed by the device is small and ranges from 20 to 120 μA. Maximum current through

The LED is limited by the high internal resistance of the bipolar transistor, which is part of the IPT analogue. To reduce the initial amplitude of the current pulse through the LED and transistor, a resistor with a resistance of 200...620 Ohms can be connected to this circuit.

Rice. 8.5

Rice. 8.6

Due to the high efficiency and extreme simplicity of RGIs, it is advisable to use them in electronic equipment to indicate the on state (supply voltage).

In Fig. Figure 8.6 shows a diagram of an audio pulse generator. When R1 = 910 Ohm, C1 = 1 μF and changing the supply voltage from 2 to 10 B, the generation frequency changes from 5 to 500 Hz with an increase in current consumption from 3 to 6 mA.

The pulse generator shown in Fig. 8.7, differs in the connection of a timing capacitor. The generator produces fairly stable sinusoidal oscillations: the generation frequency varies from 644 to 639 Hz when the supply voltage changes from 3 to 10 B, and the current consumption is from 4 to 5.5 mA.

Rice. 8.7

Rice. 8.8

Rice. 8.9

In Fig. 8.8 and 8.9 show the possibility of using generators based on IPT as a portable low-power voltage converter. Such devices can be used to supply increased voltages to controlled semiconductor capacitors - varicaps. The converter (Fig. 8.8) operates at 1)pit = 3...10 V (the upper voltage value is determined by the type of semiconductor devices used) and allows you to obtain 11out = 2 (11pit-1).

The converter (Fig. 8.9) is loaded onto a high-frequency oscillatory circuit. When using an inductor from the intermediate frequency filter of the VEF radio receiver (inductance 260 μH), the generator operates at a frequency of 140...200 kHz in the supply voltage range from 1.5 to 10 V. This generator can be used to create a portable metal detector, see, for example , rice. 21.1, 21.6.

When selecting resistance in the base circuit (Fig. 8.9), the current consumed by the generator, the output voltage and the shape of the generated signal (up to sinusoidal) change. At 11pit = 0.7 V, a voltage of 5 V was obtained at the output of the device (R1 = 750 Ohm, 1POTR = 20 mA). With an increase in the supply voltage to 1 V, the output voltage reaches 20 V, and at 2 V it reaches 27 V (current consumption - 50 mA). The efficiency of the converter increases with increasing resistance in the base circuit.

In Fig. 8.10 and 8.11 show circuits of generators based on analogues of the IPT p-structure. As follows from a comparison of the circuits (see, for example, Fig. 8.9 and 8.10 and Fig. 8.4 and 8.11), the methods for connecting analogues of IPT p- and p-structures are identical to the methods for connecting bipolar transistors p-p-p and p-p-p types (changing the polarity of the power source). When the capacitance of the capacitor (Fig. 8.11) changes from zero (capacitance of the installation and semiconductor junctions) to 0.33 μF, the generation frequency changes from 3.5 kHz to 200 Hz.

Rice. 8.10

Rice. 8.11

The device (Fig. 8.11) can be used as a wide-range pulse generator, a simple electric musical instrument, a capacitor capacitance meter, monitoring changes in the capacitance of capacitor sensors, varicaps, etc.

The sound-light pulse signaling device - beeper - is designed to indicate the switching on of components and blocks of radio-electronic equipment. The beeper (Fig. 8.12) is made on an analogue of an injection field-effect transistor (transistors VT1, VT2) [Рл 2/01-18]. When turned on, the beeper generates attention-grabbing short synchronized sound and light signals. The value of resistor R1 determines the duration of the sound burst; R2 - pauses between them. Capacitor C1 is an element of the timing circuit; C2 - provides the characteristic “coloring” of the generated sound signal. A TK-67 telephone capsule or a TM-2B microtelephone was used as a sound emitter. The average current consumed by the device is 1.5 mA at a supply voltage of 6... 15 6. If the LED indicator (HL1) is excluded from the circuit, the beeper will begin to operate at a supply voltage of 4 V.

Rice. 8.12

All the devices discussed in this chapter are made on so-called non-gavaristors - devices that have a section of negative dynamic resistance on the current-voltage characteristic. If shown in Fig. 8.1 - 8.12 circuits were implemented on analogues of the IPT (S-shaped current-voltage characteristic), then the generator circuits shown below (Fig. 8.13 - 8.17) demonstrate the possibility of using other types of structures (non-gavaristors) to generate electrical oscillations. These structures (the combination of elements included in them) may have a fundamentally different structure, but they are intended to perform similar tasks and have a common property: an S- or N-shaped type of current-voltage characteristic.

The sound generator (Fig. 8.13) is assembled on an analogue of a lambda diode and has as a load a low-frequency oscillatory circuit consisting of an electromagnetic capsule TM-2B (inductance) and capacitor C1. The generator produces oscillations that are close to sinusoidal in shape and consumes a current of up to 0.4 mA at a supply voltage of 1.5...2.5 V. If an additional high-frequency oscillatory circuit is connected in series with the generator load, the device will turn into a high-frequency signal generator with the possibility of modulation by low-frequency vibrations.

Rice. 8.13

Rice. 8.14

The generators (Fig. 8.14, 8.15) are very similar in construction. To excite these generators (set the operating point at which the generation process begins), the selection of resistive elements will be required: R1 (Fig. 8.14) and R2 (Fig. 8.15).

The pulse generator (Fig. 8.16) is made according to the circuit of a symmetrical multivibrator, but the transistors are turned on inversely (in the “wrong” polarity of the supply voltages) and with a “broken” DC base. Despite such an exotic and unconventional inclusion, damage to the semiconductor elements does not occur. The power dissipated by semiconductor junctions is extremely low, since high-resistance resistors are included in the transistor load circuit. Bipolar avalanche transistors usually operate in this mode; see, for example, diagrams for the practical use of such generators (Fig. 20.6, 20.7)

Rice. 8.15

Rice. 8.16

Rice. 8.17

In Fig. Figure 8.17 shows a pulse generator circuit made on a thyristor (B.E. Alginin). The generator operates in the audio frequency range (not higher than a few kHz) and has a fairly high output power. The thyristor can be replaced with its analogue (Fig. 2.2).

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

TV Service

IP repair. Division into a blocking generator and a control circuit. The power supply based on discrete elements (transistors) is designed schematically in two parts: 1) a self-oscillator (blocking generator), 2) a device for controlling the operation of the self-generator (control circuit, KU switch and R limit). M50.jpg The autogenerator ensures the generation of pulse voltages at the TPI, and the device controls the output voltages of the power source and regulates the operation of the autogenerator when they change. The self-oscillator is usually made on: a) a powerful output transistor, b) a TPI winding operating in POS (Positive Feedback) mode, c) resistance Rst and capacitance Csv, connected in series between the POS winding and the base of the transistor d) bias resistance Rcm, switched on between Upit+ (rectified mains voltage) and the base of the transistor. e) a diode that ensures a constant unlocking current at the base of the transistor and shunts the RC circuit in the forward direction. The POS winding, Rst and Cst form a pulse of a certain shape based on the transistor. The diode forms a positive bias at the base of the transistor, thereby providing the necessary swing on the TPI windings. Rcm is used for the initial start of the autogenerator.

The idea of ​​a repair technique. Disconnect the blocking generator from the control circuit and some of the loads on the secondary windings of the power supply, check its functionality, if necessary, repair it, and then connect the control circuit, loads, etc. in several stages. at the same time check the functionality and, if necessary, repair. But if you simply turn on the autogenerator, the power supply will immediately go into overdrive and the key transistor will fail. Also, if there are defects in the generator itself, the key transistor may also fail. Therefore, you need to check in two modes. All loads in the secondary power supply are switched off, with the exception of the diode and capacitance at B+, and a lamp of usually 220 volts 60 watts is connected in parallel to this capacitance. Then the control circuit and its power supply are turned off and a 220 volt 100 watt lamp is connected to the gap between the mains capacitor and the TPI winding. M50_2-2.jpg IP is turned on. Both lamps should light up and the IP should not make any extraneous sounds. If the lamp on B+ does not light up or the IP crackles, squeals, etc., then the blocking generator needs to be repaired. If normal, then the capacitor-TPI connection is restored and a 100-watt lamp is soldered in instead of the fuse. It is advisable to select lamps in such a way that the voltage at B+ is as close to optimal as possible. For the network, a set of lamps 200 watt, 150 watt, 100 watt, for the load 100 watt, 60 watt, 40 watt. If you don’t know which llamas are optimal for a given power supply, then it’s better to start with a 100-watt network and a 100-watt load. An increase in the power of the llama in the network circuit increases B+, an increase in power in the load decreases. After checking the functionality of the blocking generator in the second mode, the control circuit, loads, etc. are connected in series. At the same time, the functionality is checked and, if necessary, repaired.

For example, the repair method for IP chassis M50.

M50_PS.jpg Voltage at the working power supply: B+112 volts Q801 K 5.1v, E 9.7v, B 9.2v, Q802 K 0.0v, E 2.0v, B?, Q803 K 1.6v, E 0, 2c, B 0.4c.

The repair begins with checking the functionality of the generator. The following parts are unsoldered from one end: R831, R832, ​​R831A, L804 (secondary IP) D805, D807, C810 (autogenerator control device). A 60-watt lamp is soldered parallel to C827 (B+) and between C806 and the 3rd leg of a 100-watt TPI.

M50_PS_2-2.jpg We connect the IP to the network. The IP must operate without any extraneous sounds (screaming, whistling, etc.). At B+ 64 volts. If there is no startup or extraneous sounds are produced by the TPI, then the blocking generator needs to be repaired. If normal, then the junction between the mains capacitor and TPI is restored and a 100-watt lamp is soldered in instead of the fuse. The operation of the blocking generator in this mode is checked. There should be 112 volts at B+ on the 82 volt mains capacitor. D805 and D807 are soldered back in. The following voltages should be Q801 K 10.0v, E 10.0v, B 9.4v, Q802, K 0.6v, E 3.1v, B 2.8v, Q803 K 3.3v, E 0.6v, B 0 ,6c. If there are large voltage deviations, we repair the control device. If normal, then solder back the C810, unsolder the lamp between the mains capacitor and the TPI and restore the connection at this point. After switching on, the voltage on B+ should be +112 volts. If necessary, adjust VR801. Then the lamp with B+ is unsoldered and R831, R832, ​​R831A, L804 are soldered back. And the operation of the TV is checked and, if necessary, other units are repaired.

Thank you for your help in preparing the material viktor_ramb and Admin.