Generator based on NE555 timer. Frequency controlled pulse generator Ramp pulse generator for 555

An electrical impulse is a short-term surge in voltage or current. That is, this is an event in the circuit in which the voltage sharply increases several times, and then just as sharply drops to its original value. The most obvious example is the electrical impulse that makes our heart beat. The largest number of impulses occurs in the nerve cells of the brain and spinal cord. We think and solve lessons thanks to electrical impulses! What about electronics? In electronics, pulses are used everywhere. For example, in microcontrollers or even in full-fledged processors of a home computer, electrical impulses set the rhythm of its operation. They are also called clock pulses, or sync pulses. Sometimes the performance of computers is compared precisely using clock speed values. All data inside electronic devices is also transmitted using pulses. Our Internet, wired and wireless, cellular communications and even the TV remote control all use a pulse signal. Let's try to complete several tasks and understand from our own experience the features of generating electrical impulses. Let's start by getting to know their important characteristics.

1. Period and duty cycle of the pulse signal

Let's imagine that we are preparing for the New Year and we just need to make a blinking garland. Since we don’t know how to make it blink on its own, we’ll make a garland with a button. We will press the button ourselves, thereby connecting the garland circuit to the power source and causing the light bulbs to light up. The schematic diagram of a manually controlled garland will look like this:

Appearance layout

We assemble the circuit and conduct a small test. Let's try to control the garland according to a simple algorithm:

press the button;
wait 1 second;
release the button;
wait 2 seconds;
go to point 1.

This is a batch process algorithm. By pressing the button according to the algorithm, we thereby generate a real pulse signal! Let's depict its time diagram on the graph.

For a given signal, we can determine the repetition period and frequency. Repetition period (T)- this is the period of time during which the garland returns to its original state. This segment is clearly visible in the figure; it is equal to three seconds. The reciprocal of the repetition period is called frequency of the periodic signal (F). The signal frequency is measured in Hertz. In our case: F = 1/T = 1/3 = 0.33 Hz The repetition period can be divided into two parts: when the garland is lit and when it is not lit. The length of time during which the garland is lit is called pulse duration (t). Now comes the fun part! The ratio of the repetition period (T) to the pulse duration (t) is called duty cycle. S = T/t The duty cycle of our signal is S = 3/1 = 3. The duty cycle is a dimensionless quantity. In English-language literature, another term has been adopted - duty cycle. This is the reciprocal of the duty cycle. D = 1 / S = t / T In the case of our garland, the fill factor is: D = 1 / 3 = 0.33(3) ≈ 33% This option is more clear. D = 33% means that a third of the period is occupied by the impulse. And, for example, with D = 50%, the duration of the high signal level at the timer output will be equal to the duration of the low level.

2. Generating a pulse signal using a 555 chip

Now let’s try to replace the person and the button, because we don’t want to turn the garland on and off every 3 seconds throughout the holiday. As an automatic pulse generator, we use a very well-known microcircuit of the 555 family. The 555 microcircuit is a generator of single or periodic pulses with specified characteristics. In another way, this class of microcircuits is called timers. There are different modifications of the 555 timer, developed by different companies: KR1006VI1, NE555, TLC555, TLC551, LMC555. As a rule, they all have the same set of pins.

Manufacturers also distinguish two modes of timer operation: single-shot and multivibrator. The second mode is suitable for us; it is in this mode that the timer will continuously generate pulses with the specified parameters. For example, let's connect one LED to the 555 timer. Moreover, we use the option when the positive terminal of the LED is connected to the power supply, and the ground to the timer. Later it will be clear why we do this.

Schematic diagram

Layout appearance

Note. Capacitor C2 may not be used in the circuit. This circuit has three unrated components: resistors Ra and Rb, and capacitor C1 (hereinafter simply C). The fact is that it is with the help of these elements that the characteristics of the generated pulse signal we need are adjusted. This is done using simple formulas taken from the technical documentation for the microcircuit. T = 1/F = 0.693*(Ra + 2*Rb)*C; (1) t = 0.693*(Ra + Rb)*C; (2) Ra = T*1.44*(2*D-1)/C; (3) Rb = T*1.44*(1-D)/C. (4) Here F is the signal frequency; T—pulse period; t is its duration; Ra and Rb are the required resistances. Based on these formulas, the fill factor cannot be less than 50% (otherwise we will get a negative resistance value). What a news! What should we do with the garland? Indeed, according to our formulation, the duty cycle of the pulse signal must certainly be 33%. There are two ways to get around this limitation. The first method is to use a different timer connection scheme. There are more complex circuits that allow you to vary the parameter D over the entire range from 0 to 100%. The second method does not require modification of the circuit. We simply invert the output of the timer! Actually, in the scheme proposed above, we have already done this. Let us remember that we connected the cathode of the LED to the output of the timer. In this circuit, the LED will light up when the timer output is low. If so, then we need to adjust the resistances Ra and Rb of the circuit so that the duty cycle D is equal to 66.6%. Considering that T = 3 sec, and D = 0.66, we get: Ra = 3*1.44*(2*0.66 - 1)/0.0001 = 13824 Ohm Rb = 3*1.44*(1-D)/0.0001 = 14688 Ohm At in fact, if we use more accurate values of D, we get Ra = Rb = 14400 Ohms. It is unlikely that we will find a resistor with such a value. Most likely we will need to put several resistors in series, for example: one resistor for 10 KOhm and 4 pieces for 1 KOhm. For greater accuracy, we can add two more 200 Ohm resistors. The result should be something like this:

This circuit uses 15KΩ resistors.

3. Connecting a group of LEDs to a 555 timer

Now that we have learned how to set the desired rhythm, let's assemble a small garland. In the new scheme, five LEDs will turn on for 0.5 seconds every second. For such a rhythm, Ra = 0, Rb = 7.2 kOhm. That is, instead of resistor Ra we can put a jumper. The output of the 555 IC is too weak to light 5 LEDs at the same time. But in a real garland there can be 15, 20 or more of them. To solve this problem, we use a bipolar transistor operating in electronic key mode. Let's take the most common NPN transistor 2N2222. You can also use an N-channel field-effect transistor, for example 2N7000, in this circuit. Our LEDs will require a current-setting resistor. The total current of five parallel-connected LEDs should be equal to I = 20 mA*5 = 100 mA. The supply voltage for the entire circuit is 9 Volts. On the red LED the voltage drops by 2 Volts. Thus, Ohm's law in this section of the circuit looks like: 100 mA = (9V-2V)/R; hence R2 = 7V/0.1A = 70 Ohm. Let's round the resistance to 100 Ohms, which can be obtained by connecting two 200 Ohm resistors in parallel. Or you can even leave one 200 Ohm resistor, the LEDs will just burn a little dimmer.

Schematic diagram

Layout appearance

Note. Capacitor C2 may not be used in the circuit. We assemble the circuit, connect the battery and observe the result. If everything works as it should, we’ll consolidate our knowledge by making some fun devices.

Tasks

Sound generator. In the garland circuit, replace the group of LEDs with a piezo speaker. Increase the sound frequency, for example, to 100 Hz. If you raise the frequency to 15 kHz, you can repel mosquitoes!
Railway traffic light. Connect two LEDs to the timer so that one is connected to the timer by the cathode, and the second by the anode. Set the pulse frequency to 1 Hz.

Conclusion

As already mentioned, the 555 timer is a very popular chip. This is because most electronic devices are characterized by periodic processes. Any sound is a periodic process. The PWM signal that controls the motor speed is also periodic, and with a varying duty cycle. And as already mentioned, the operation of any microcontroller and processor is based on a clock signal that has a very precise frequency. In the next lesson we will make a binary clock using a timer and a binary counter. It will be a little more difficult, but more interesting! Measurement technique

NE555 generator with frequency control

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

Description NE555

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

The functional diagram looks like this.

Rice. 1. Functional diagram

Can operate in one of two main modes:

1.Multivibrator (monostable);

2.Pulse generator.

We are only interested in the last option.

Simple generator on NE555

The simplest diagram is presented below.

Rice. 2. NE555 generator circuit

Rice. 3. Output voltage graph

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

f = 1 / (0.693*С*(R1 + 2*R2)),

Accordingly, the formula for the full period is:

t = 0.693*С*(R1 + 2*R2).

The pulse time (t1) is calculated as follows:

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

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

t2 = 0.693 * R * 2 * C

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

Adjustable frequency generator on NE555

The simplest option is to redesign the unregulated generator circuit.

Rice. 4. Generator circuit

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

Another option for an adjustable oscillator on a 555 timer.

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

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

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

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

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

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

Another variation with regulation.

Rice. 6. Scheme regulated generator

IC1 is an NE555N timer.

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

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

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

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

The circuit requires bipolar power supply!

Publication date: 21.02.2018

Readers' opinions

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

555 - analog integrated circuit, universal timer - a device for generating (generating) single and repeating pulses with stable timing characteristics. It is used to build various generators, modulators, time relays, threshold devices and other components of electronic equipment. Examples of the use of a timer microcircuit include functions for restoring a digital signal distorted in communication lines, bounce filters, on-off controllers in automatic control systems, pulse converters of electricity, pulse-width control devices, timers, etc.

In this article I will talk about building a generator on this chip. As written above, we already know that the microcircuit generates repeating pulses with stable time characteristics, this is what we need.

Switching circuit in astable mode. The figure below shows this.

Since we have a pulse generator, we must know their approximate frequency. Which we calculate using the formula.

The values of R1 and R2 are substituted in Ohms, C - in Farads, the frequency is obtained in Hertz.
The time between the beginning of each next pulse is called a period and is designated by the letter t. It consists of the duration of the pulse itself - t1 and the interval between pulses - t2. t = t1+t2.

Frequency and period are inverse concepts and the relationship between them is as follows:
f = 1/t.
t1 and t2, of course, can and should also be calculated. Like this:
t1 = 0.693(R1+R2)C;
t2 = 0.693R2C;

Done with the theory like this Let's start practicing.

I developed a simple diagram with details accessible to everyone.

I'll tell you about its features. As many have already understood, switch S2 is used to switch the operating frequency. The KT805 transistor is used to amplify the signal (installed on a small radiator). Resistor R4 is used to regulate the output signal current. The chip itself serves as a generator. We change the duty cycle and frequency of operating pulses with resistors R3 and R2. The diode serves to increase the duty cycle (can be omitted altogether). There is also a shunt and an operation indicator; an LED with a built-in current limiter is used for it (you can use a regular LED by limiting the current with a 1 kOhm resistor). Actually, that’s all, then I’ll show you what a working device looks like.

Top view, visible operating frequency switches.

I have attached a reminder below.

These trimming resistors regulate the duty cycle and frequency (their designation is visible on the memo).

On the side is the power switch and signal output.

List of radioelements

Designation	Type	Denomination	Quantity	My notepad
IC1	Programmable timer and oscillator	NE555	1	To notepad
T1	Bipolar transistor	KT805A	1	To notepad
D1	Rectifier diode	1N4148	1	To notepad
C1	Capacitor	1 nF	1	To notepad
C2	Capacitor	100 nF	1	To notepad
C3	Capacitor	1000 nF	1	To notepad
C4	Electrolytic capacitor	100 µF	1	To notepad
R1	Resistor	500 Ohm	1

In amateur radio practice there is often a need to use a sinusoidal oscillation generator. You can find a wide variety of applications for it. Let's look at how to create a sinusoidal signal generator on a Wien bridge with a stable amplitude and frequency.

The article describes the development of a sinusoidal signal generator circuit. You can also generate the desired frequency programmatically:

The most convenient, from the point of view of assembly and adjustment, version of a sinusoidal signal generator is a generator built on a Wien bridge, using a modern Operational Amplifier (OP-Amp).

Bridge of Wine

The Wien bridge itself is a bandpass filter consisting of two. It emphasizes the central frequency and suppresses other frequencies.

The bridge was invented by Max Wien back in 1891. On a schematic diagram, the Wien bridge itself is usually depicted as follows:

Picture borrowed from Wikipedia

The Wien bridge has an output voltage to input voltage ratio b=1/3 . This is an important point, because this coefficient determines the conditions for stable generation. But more on that later

How to calculate frequency

Autogenerators and inductance meters are often built on the Wien Bridge. In order not to complicate your life, they usually use R1=R2=R And C1=C2=C . Thanks to this, the formula can be simplified. The fundamental frequency of the bridge is calculated from the ratio:

f=1/2πRC

Almost any filter can be thought of as a frequency-dependent voltage divider. Therefore, when choosing the values of the resistor and capacitor, it is desirable that at the resonant frequency the complex resistance of the capacitor (Z) is equal to, or at least of the same order of magnitude as, the resistance of the resistor.

Zc=1/ωC=1/2πνC

Where ω (omega) - cyclic frequency, ν (nu) - linear frequency, ω=2πν

Wien bridge and operational amplifier

The Wien bridge itself is not a signal generator. For generation to occur, it must be placed in the positive feedback circuit of the operational amplifier. Such a self-oscillator can also be built using a transistor. But using an op-amp will clearly simplify life and give better performance.

Gain factor of three

The Wien bridge has a transmittance b=1/3 . Therefore, the condition for generation is that the op-amp must provide a gain of three. In this case, the product of the transmission coefficients of the Wien bridge and the gain of the op-amp will give 1. And stable generation of the given frequency will occur.

If the world were ideal, then by setting the required gain with resistors in the negative feedback circuit, we would get a ready-made generator.

This is a non-inverting amplifier and its gain is determined by the relation:K=1+R2/R1

But alas, the world is not ideal. ... In practice, it turns out that to start generation it is necessary that at the very initial moment the coefficient. the gain was slightly more than 3, and then for stable generation it was maintained at 3.

If the gain is less than 3, the generator will stall; if it is more, then the signal, upon reaching the supply voltage, will begin to distort and saturation will occur.

When saturated, the output will maintain a voltage close to one of the supply voltages. And random chaotic switching between supply voltages will occur.

Therefore, when building a generator on a Wien bridge, they resort to using a nonlinear element in the negative feedback circuit that regulates the gain. In this case, the generator will balance itself and maintain generation at the same level.

Amplitude stabilization on an incandescent lamp

In the most classic version of the generator on the Wien bridge at the op-amp, a miniature low-voltage incandescent lamp is used, which is installed instead of a resistor.

When such a generator is turned on, at the first moment, the lamp spiral is cold and its resistance is low. This helps to start the generator (K>3). Then, as it heats up, the resistance of the spiral increases and the gain decreases until it reaches equilibrium (K=3).

The positive feedback circuit in which the Wien bridge was placed remains unchanged. The general circuit diagram of the generator is as follows:

Positive feedback elements of the op amp determine the generation frequency. And the elements of negative feedback are reinforcement.

The idea of using a light bulb as a control element is very interesting and is still used today. But, alas, the light bulb has a number of disadvantages:

selection of a light bulb and a current-limiting resistor R* is required.
With regular use of the generator, the life of the light bulb is usually limited to several months
The control properties of the light bulb depend on the temperature in the room.

Another interesting option is to use a directly heated thermistor. Essentially, the idea is the same, but instead of a light bulb filament, a thermistor is used. The problem is that you first need to find it and again select it and current-limiting resistors.

Amplitude stabilization on LEDs

An effective method for stabilizing the amplitude of the output voltage of a sinusoidal signal generator is to use op-amp LEDs in the negative feedback circuit ( VD1 And VD2 ).

The main gain is set by resistors R3 And R4 . The remaining elements ( R5 , R6 and LEDs) adjust the gain within a small range, keeping the output stable. Resistor R5 you can adjust the output voltage in the range of approximately 5-10 volts.

In the additional OS circuit it is advisable to use low-resistance resistors ( R5 And R6 ). This will allow significant current (up to 5mA) to pass through the LEDs and they will be in optimal mode. They will even glow a little :-)

In the diagram shown above, the Wien bridge elements are designed to generate at a frequency of 400 Hz, however they can be easily recalculated for any other frequency using the formulas presented at the beginning of the article.

Quality of generation and elements used

It is important that the operational amplifier can provide the current necessary for generation and have sufficient frequency bandwidth. Using the popular TL062 and TL072 as op amps gave very sad results at a generation frequency of 100 kHz. The signal shape could hardly be called a sinusoidal; it was more like a triangular signal. Using TDA 2320 gave even worse results.

But the NE5532 showed its excellent side, producing an output signal very similar to a sinusoidal one. LM833 also coped with the task perfectly. So it is NE5532 and LM833 that are recommended for use as affordable and common high-quality op-amps. Although, with a decrease in frequency, the rest of the op-amps will feel much better.

The accuracy of the generation frequency directly depends on the accuracy of the elements of the frequency-dependent circuit. And in this case, it is important not only that the value of the element corresponds to the inscription on it. More precise parts have better stability of values with temperature changes.

In the author's version, a resistor of type C2-13 ±0.5% and mica capacitors with an accuracy of ±2% were used. The use of resistors of this type is due to the low dependence of their resistance on temperature. Mica capacitors also have little dependence on temperature and have a low TKE.

Cons of LEDs

It's worth focusing on LEDs separately. Their use in a sine generator circuit is caused by the magnitude of the voltage drop, which usually lies in the range of 1.2-1.5 volts. This allows you to obtain a fairly high output voltage.

After implementing the circuit on a breadboard, it turned out that due to the variation in LED parameters, the fronts of the sine wave at the generator output are not symmetrical. It's a little noticeable even in the above photo. In addition, there were slight distortions in the shape of the generated sine, caused by the insufficient operating speed of the LEDs for a generation frequency of 100 kHz.

4148 diodes instead of LEDs

The LEDs have been replaced with the beloved 4148 diodes. These are affordable, high-speed signal diodes with switching speeds of less than 4 ns. At the same time, the circuit remained fully operational, not a trace remained of the problems described above, and the sinusoid acquired an ideal appearance.

In the following diagram, the elements of the wine bridge are designed for a generation frequency of 100 kHz. Also, the variable resistor R5 was replaced with constant ones, but more on that later.

Unlike LEDs, the voltage drop across the p-n junction of conventional diodes is 0.6÷0.7 V, so the output voltage of the generator was about 2.5 V. To increase the output voltage, it is possible to connect several diodes in series, instead of one, for example like this:

However, increasing the number of nonlinear elements will make the generator more dependent on external temperature. For this reason, it was decided to abandon this approach and use one diode at a time.

Replacing a variable resistor with a constant one

Now about the tuning resistor. Initially, a 470 Ohm multi-turn trimmer resistor was used as resistor R5. It made it possible to precisely regulate the output voltage.

When building any generator, it is highly desirable to have an oscilloscope. Variable resistor R5 directly affects generation - both amplitude and stability.

For the presented circuit, generation is stable only in a small resistance range of this resistor. If the resistance ratio is greater than required, clipping begins, i.e. the sine wave will be clipped from above and below. If it is less, the shape of the sinusoid begins to distort, and with a further decrease, the generation stalls.

It also depends on the supply voltage used. The described circuit was originally assembled using an LM833 op-amp with a ±9V power supply. Then, without changing the circuit, the op amps were replaced with AD8616, and the supply voltage was changed to ±2.5V (the maximum for these op amps). As a result of this replacement, the sinusoid at the output was cut off. The selection of resistors gave values of 210 and 165 ohms, instead of 150 and 330, respectively.

How to choose resistors “by eye”

In principle, you can leave the tuning resistor. It all depends on the required accuracy and the generated frequency of the sinusoidal signal.

To make your own selection, you should first of all install a tuning resistor with a nominal value of 200-500 Ohms. By feeding the generator output signal to the oscilloscope and rotating the trimming resistor, reach the moment when the limitation begins.

Then, by lowering the amplitude, find the position in which the shape of the sinusoid will be the best. Now you can remove the trimmer, measure the resulting resistance values and solder the values as close as possible.

If you need a sinusoidal audio signal generator, you can do without an oscilloscope. To do this, again, it is better to reach the moment when the signal, by ear, begins to be distorted due to clipping, and then reduce the amplitude. You should turn it down until the distortion disappears, and then a little more. This is necessary because It is not always possible to detect distortions of even 10% by ear.

Additional reinforcement

The sine generator was assembled on a dual op-amp, and half of the microcircuit remained hanging in the air. Therefore, it is logical to use it under an adjustable voltage amplifier. This made it possible to move a variable resistor from the additional generator feedback circuit to the voltage amplifier stage to regulate the output voltage.

The use of an additional amplifier stage guarantees better matching of the generator output with the load. It was built according to the classical non-inverting amplifier circuit.

The indicated ratings allow you to change the gain from 2 to 5. If necessary, the ratings can be recalculated for the required task. The cascade gain is given by the relation:

K=1+R2/R1

Resistor R1 is the sum of variable and constant resistors connected in series. A constant resistor is needed so that at the minimum position of the variable resistor knob the gain does not go to infinity.

How to strengthen the output

The generator was intended to operate at a low-resistance load of several ohms. Of course, not a single low-power op-amp can produce the required current.

To increase power, a TDA2030 repeater was placed at the generator output. All the goodies of this use of this microcircuit are described in the article.

And this is what the circuit of the entire sinusoidal generator with a voltage amplifier and a repeater at the output looks like:

The sine generator on the Wien bridge can also be assembled on the TDA2030 itself as an op-amp. It all depends on the required accuracy and the selected generation frequency.

If there are no special requirements for the quality of generation and the required frequency does not exceed 80-100 kHz, but it is supposed to work with a low-impedance load, then this option is ideal for you.

Conclusion

A Wien bridge generator is not the only way to generate a sine wave. If you need high-precision frequency stabilization, it is better to look towards generators with a quartz resonator.

However, the described circuit is suitable for the vast majority of cases when it is required to obtain a stable sinusoidal signal, both in frequency and amplitude.

Generation is good, but how to accurately measure the magnitude of high-frequency alternating voltage? A scheme called . is perfect for this.

The material was prepared exclusively for the site

And finally, we got around to it. After assembling small coils, I decided to take a swing at a new circuit, more serious and complex to set up and operate. Let's move from words to action. The complete diagram looks like this:

It works on the principle of a self-generator. The breaker kicks the driver UCC27425 and the process begins. The driver supplies an impulse to the GDT (Gate Drive Transformator - literally: a transformer that controls the gates) with the GDT there are 2 secondary windings connected in antiphase. This connection ensures the alternating opening of the transistors. During opening, the transistor pumps current through itself and the 4.7 µF capacitor. At this moment, a discharge is formed on the coil, and the signal goes through the OS to the driver. The driver changes the direction of the current in the GDT and the transistors change (the one that was open closes, and the second one opens). And this process is repeated as long as there is a signal from the breaker.

GDT is best wound on an imported ring - Epcos N80. The windings are wound in a ratio of 1:1:1 or 1:2:2. On average, about 7-8 turns, you can calculate it if you wish. Let's consider an RD chain in the gates of power transistors. This chain provides Dead Time. This is the time when both transistors are closed. That is, one transistor has already closed, and the second has not yet had time to open. The principle is this: the transistor opens smoothly through a resistor and quickly discharges through a diode. The oscillogram looks something like this:

If you do not provide dead time, it may turn out that both transistors will be open and then a power explosion will occur.

Go ahead. OS (feedback) is made in this case in the form of a CT (current transformer). The CT is wound on an Epcos N80 ferrite ring with at least 50 turns. The lower end of the secondary winding is pulled through the ring and grounded. Thus, the high current from the secondary winding is converted into sufficient potential at the CT. Next, the current from the CT goes to the capacitor (smoothes out interference), Schottky diodes (pass only one half-cycle) and the LED (acts as a zener diode and visualizes generation). For generation to occur, the phrasing of the transformer must also be observed. If there is no generation or very weak, you just need to turn the CT over.

Let's look at the breaker separately. Of course I sweated with the breaker. I collected about 5 different ones... Some swell from HF current, others do not work as they should. Next I’ll tell you about all the breakers I made. I'll probably start from the very first - on TL494. The scheme is standard. Independent adjustment of frequency and duty cycle is possible. The circuit below can generate from 0 to 800-900 Hz if you replace the 1 uF capacitor with a 4.7 uF capacitor. Duty ratio from 0 to 50. Just what you need! However, there is one BUT. This PWM controller is very sensitive to RF current and various fields from the coil. In general, when connected to the coil, the breaker simply did not work, either everything was at 0 or CW mode. Shielding partially helped, but did not completely solve the problem.

The following breaker was assembled using UC3843 very often found in IIP, especially ATX, that’s where I actually took it from. The scheme is also not bad and is not inferior TL494 by parameters. Here it is possible to adjust the frequency from 0 to 1 kHz and the duty cycle from 0 to 100%. This suited me too. But again these pickups from the coil ruined everything. Even shielding didn't help here. I had to refuse, although I assembled it well on the board...

I decided to return to oak and reliable, but low-functional 555 . I decided to start with burst interrupter. The essence of an interrupter is that it interrupts itself. One microcircuit (U1) sets the frequency, another (2) the duration, and the third (U3) sets the operating time of the first two. Everything would be fine if it were not for the short pulse duration with U2. This breaker is designed for DRSSTC and can work with SSTC, but I didn’t like it - the discharges are thin, but fluffy. Then there were several attempts to increase the duration, but they were unsuccessful.

Generator circuits for 555

Then I decided to fundamentally change the circuit and make independent duration on the capacitor, diode and resistor. Many may consider this scheme absurd and stupid, but it works. The principle is this: the signal goes to the driver until the capacitor is charged (I think no one will argue with this). NE555 generates a signal, it goes through a resistor and a capacitor, and if the resistance of the resistor is 0 Ohm, then it goes only through the capacitor and the duration is maximum (as long as the capacitance is enough) regardless of the duty cycle of the generator. The resistor limits the charging time, i.e. The greater the resistance, the shorter the pulse will take. The driver receives a signal of shorter duration, but of the same frequency. The capacitor discharges quickly through a resistor (which goes to ground 1k) and a diode.

Advantages and disadvantages

pros: frequency independent duty cycle adjustment, SSTC will never go into CW mode if the breaker burns out.

Minuses: the duty cycle cannot be increased “infinitely”, as for example on UC3843, it is limited by the capacitance of the capacitor and the duty cycle of the generator itself (it cannot be greater than the duty cycle of the generator). The current flows smoothly through the capacitor.

I don’t know how the driver reacts to the latter (smooth charging). On the one hand, the driver can also smoothly open the transistors and they will heat up more. On the other side UCC27425- digital microcircuit. For it there is only a log. 0 and log. 1. This means that as long as the voltage is above the threshold, the UCC works; as soon as it drops below the minimum, it does not work. In this case, everything works as normal, and the transistors open completely.

Let's move from theory to practice

I assembled a Tesla generator into an ATX housing. Power supply capacitor 1000 uF 400V. Diode bridge from the same ATX at 8A 600V. I placed a 10 W 4.7 Ohm resistor in front of the bridge. This ensures smooth charging of the capacitor. To power the driver, I installed a 220-12V transformer and a stabilizer with a 1800 uF capacitor.

I screwed the diode bridges onto the radiator for convenience and for heat removal, although they barely heat up.

The breaker was assembled almost like a canopy, took a piece of PCB and cut out the tracks with a utility knife.

The power unit was assembled on a small radiator with a fan; it later turned out that this radiator was quite sufficient for cooling. The driver was mounted above the power one through a thick piece of cardboard. Below is a photo of the almost assembled design of the Tesla generator, but it is being tested; I measured the power temperature in various modes (you can see an ordinary room thermometer attached to the power one on thermoplastic).

The coil toroid is assembled from a corrugated plastic pipe with a diameter of 50 mm and covered with aluminum tape. The secondary winding itself is wound on a 110 mm pipe 20 cm high with 0.22 mm wire about 1000 turns. The primary winding contains as many as 12 turns, made with a margin in order to reduce the current through the power section. I did it with 6 turns at the beginning, the result is almost the same, but I think it’s not worth risking transistors for the sake of a couple of extra centimeters of discharge. The frame of the primary is an ordinary flower pot. From the beginning I thought that it would not pierce if I wrapped the secondary with tape and the primary on top of the tape. But alas, it broke through... Of course, it also broke through in the pot, but here the tape helped solve the problem. In general, the finished design looks like this:

Well, a few photos with the discharge

Now everything seems to be done.

A few more tips: don’t try to plug a coil into the network right away, it’s not a fact that it will work right away. Constantly monitor the power temperature; if it overheats, it may boom. Do not wind too high-frequency secondary transistors 50b60 can operate at a maximum of 150 kHz according to the datasheet, in fact a little more. Check the breakers, the life of the coil depends on them. Find the maximum frequency and duty cycle at which the power temperature is stable for a long time. A toroid that is too large can also damage the power supply.

Video of SSTC operation

P.S. Power transistors used IRGP50B60PD1PBF. Project files. Good luck, I was with you [)eNiS!

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