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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Tesla transformer power supply with microcontroller control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies Appearance of the proposed block together with the transformer powered by it. Tesla is shown in Fig. 1.
The unit is assembled in a case from a standard computer. BP. The primary winding of the transformer is connected to its output, consisting of five turns of an insulated mounting wire with a cross section of 2,5 ... 4 mm2, wound on a segment of a plastic plumbing pipe with an outer diameter of 110 mm. The frame of the secondary winding is a 0,8 liter plastic kefir bottle. An enameled wire with a diameter of 0,2 mm is wound on it in one row turn to turn until it is filled (about 1000 turns in total). The lower end of this winding is grounded - connected to the third contact (PE) of the network "euro socket". The upper end is provided with a copper pin, around which various high-voltage effects are observed. The secondary winding is protected from mechanical damage and interturn breakdowns by several layers of epoxy resin. Between the primary and secondary windings, an air gap is required with a width sufficient to prevent breakdowns between the windings and corona discharges. The inductance of the secondary winding and its own capacitance form an oscillatory circuit, due to resonance in which the voltage rises many times compared to the value calculated based only on the ratio of the number of turns of the windings, the analysis shows that the main factor determining the resonant frequency of the secondary winding is its dimensions. It is quite easy to measure this frequency. This is sufficient, as shown in Fig. 2, apply voltage to the primary winding of the manufactured transformer from a tunable signal generator G1.
Resistor R1 limits the current, its power must not be less than the power of the generator. Near the transformer, an oscilloscope is installed with an antenna WA1 connected to its input - a piece of any wire 100 ... 200 mm long. By rebuilding the generator, the dependence of the signal amplitude on the oscilloscope screen on the frequency is removed. For the transformer described above, it turned out to be the same as in Fig. 3.
The resonant frequency corresponds to the main maximum of the curve and in this case is equal to 600 kHz. Tesla transformer calculation programs available on the Internet gave similar results: 632 kHz. In the absence of an oscilloscope, it can be replaced by a simple indicator of the electromagnetic field, assembled according to the circuit shown in Fig. 4.
The WA1 antenna consists of two VD1 diodes soldered to the terminals and directed in different directions, a piece of wire about 100 mm long each. Resonance is determined by the maximum brightness of the LED HL1. Transformer power supply circuit. Tesla is shown in Fig. 5.
T3 is actually this transformer. On the elements DD1.1, DD1.2, a pulse generator is assembled, following with a frequency close to the resonant frequency of its secondary winding. Amplified by the DA3 chip (field-effect transistor driver) and a powerful field-effect transistor VT1 operating in key mode, these pulses are fed to the I winding of the transformer. The variable resistor R1 regulates the frequency of the pulses, achieving the brightest glow of a gas-discharge (for example, "energy-saving") lamp located near the transformer. The microcontroller generates pulses at its P85 output, which, when fed to the EN input of the DA3 driver, enable and disable the driver. These pulses modulate the pulse sequence supplied to the winding I of the transformer T3, and, consequently, the high voltage on its winding II. There are five operating modes of the microcontroller, switched around the ring by pressing the SB1 button. Each transition is confirmed by the blinking of the HL1 LED, the number of its flashes is equal to the number of the enabled mode. In the first mode, pulses with a duration of 1 ms are generated with pauses between them of 8 ms. In the second, the duration of pauses is increased to 10 ms, in the third - up to 12 ms, in the fourth - up to 14 ms, and in the fifth - up to 20 ms. Changing modes affects the nature of the sounds emitted by electric discharges, as well as their number and length. The longer the pause, the more the air in the discharge region has time to deionize by the beginning of the next burst of high voltage pulses. by changing the program, it is possible to modulate the pulse sequence with more complex signals. Transformer T1 with a rectifier according to the voltage doubling circuit on diodes VD1, VD2 supplies a voltage of 40 ... 60 V to the cascade on a field-effect transistor VT1, there is another power transformer - T2. From it, through the VD3 rectifier bridge and the DA1 integrated stabilizer with a voltage of 12 V, the DA3 driver is powered. The output voltage of the DA2 stabilizer (5 V) is intended for the DD2 microcontroller and the DD1 microcircuit. A drawing of the printed circuit board of the block is shown in fig. 6.
Transistor VT1 is equipped with a ribbed heat sink. A significant part of the board surface is free from parts and printed conductors. Transformers T1 and T2 are strengthened here. As SA1, a switch is used, which is already in the computer power supply, in the case of which the board is placed. Its length (145 mm) shown in the figure can be changed depending on the dimensions of the housing used. If it has a fan, it can be turned on by applying a voltage of 12 V from the output of the DA1 stabilizer. This will help to reduce the temperature of the transistor VT1, however, in this case, the stabilizer must also be equipped with a heat sink. The 74NS14 microcircuit can be replaced by the domestic KR1564TL2 or another logic microcircuit containing Schmitt triggers, inverters, AND-NOT, OR-NOT elements. If necessary, on the remaining free elements, you can assemble a pulse generator that replaces the microcontroller. However, the ability to quickly change operating modes and create new visual and sound effects by changing the microcontroller program will be lost. A replacement for the IRFP460 transistor should be selected with a permissible drain-source voltage of at least 200 V and a maximum drain current of at least 10 A. Transformer T1 must have a secondary winding with a voltage of 20 ... 30 V at a load current of 3 A. If there is a transformer with twice as much voltage of the secondary winding, doubling the voltage in the rectifier connected to it (diodes VD1, VD2, capacitors C1, C2) can be abandoned and a conventional bridge rectifier can be used.
After the unit is manufactured and a programmed microcontroller is installed in it, the configuration of which must correspond to that shown in the table (this is exactly how it is installed at the factory), it is recommended not to connect a transformer to the unit. T3, apply voltage 220 V, 50 Hz only to winding I of transformer T2. The HL1 LED should blink twice, confirming that the microcontroller is working. Now you need to check the voltage at the outputs of the integrated stabilizers DA1, DA2 and the presence of pulses at the inputs and outputs of the DA3 driver. On the screen of the oscilloscope connected to its input IN (pin 2), rectangular pulses with an amplitude of about 5 V should be observed, the repetition rate of which is regulated by a variable resistor R1 within the range of at least 300 ... 900 kHz. If this is not the case, you need to check the generator on the elements DD1.1, DD1.2. The parameters of the pulses arriving at the EN input (pin 3) of the driver from the microcontroller must correspond to those specified in the description of the unit's operating modes. At the output of the driver (pins 6 and 7) and at the gate of the field-effect transistor VT1, bursts of high-frequency pulses with pauses corresponding to the selected mode should be observed. After making sure that everything is in order, you can connect the T3 transformer to the unit and apply mains voltage to the primary winding of the T1 transformer. By placing an energy-saving lamp next to the winding II of the transformer T3 and rotating the variable resistor R1, you need to achieve the brightest possible glow of the lamp. Around the pin connected to the upper terminal of the winding, discharges (streamers) similar to those shown in fig. 7.
The glow of gas-discharge lamps that are not connected anywhere, but simply held in the hand, is the simplest effect that occurs when working with a Tesla transformer. This is the result of exposing the gas inside the lamp to a high frequency electromagnetic field surrounding the transformer. With the design in question, the effect is observed at a distance of up to 20 cm from the transformer and makes a great impression on viewers who are not familiar with its essence. Discharges can also be observed inside lamps filled with gas at a relatively high pressure (Fig. 8), including ordinary incandescent lamps (Fig. 9). but for this they need to be connected with one output to the output of the transformer. The length of the filamentous high-frequency discharges in the air, called streamers, arising during the operation of the considered transformer reaches 20 ... 30 mm. It is believed that it is numerically equal to the amplitude of the high-frequency voltage developed on the secondary winding of the transformer, expressed in kilovolts. It is interesting to observe the change in the color of the streamers when various chemicals, such as common salt, are applied to the tip of the pin, which ends the winding. Discharges during the operation of the device under consideration arise and go out with the modulation frequency of the pulse sequence supplied to the transformer. As a result, a characteristic sound is heard, the fundamental frequency of which is equal to the modulation frequency. Since the streamers die out in each pause, and those that appear after it often follow different paths, the apparent number of streamers increases. If you install a light wire pinwheel with ends bent in a horizontal plane in different directions on the tip of a high-voltage pin, discharges will occur at these ends. The resulting ions, repelled from the ends of the spinner, will set it in motion. Of course, for this model of ion drive to work, the spinner must be very light and well balanced. A positive property of the described source, which ensures the safety of working with it, is the absence of a high direct voltage inside. Arising during the operation of the transformer. High-frequency Teslas are practically safe for experimenters, because when a discharge reaches the human body, its current, since it is high-frequency, flows only through the skin, without reaching the vital organs. This well-known phenomenon in radio engineering is called the skin effect and manifests itself when a high-frequency current flows through any conductors. Of course, even such a current can cause burns, but this happens only with discharges many times greater than the power. The presence of a microcontroller in the described device gives considerable scope for experimentation. By changing its program, you can, for example, without making any changes to the circuit, play simple rhythms and melodies, and by replacing the microcontroller with a more productive one, connect a MIDI keyboard to it or control the device using a computer. Because the transformer. Tesla is a source of a powerful electromagnetic field, it is not recommended to turn it on near expensive electronic equipment or important information carriers. Author: Elyuseev D.
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