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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Small air diffuser. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Medicine The development of a new air ionizer was undertaken with the aim of creating a compact home appliance. But before the completed design appeared, the author conducted many experiments. At first, they were carried out with a simple trinistor high-voltage converter, which later had to be abandoned due to the electromagnetic interference it created and low efficiency. Subsequently, a single-transistor converter was made, which was the basis of the described air ionizer. Both types of converters made it possible to obtain a negative potential of up to 80 kV on the ionizing electrode. To change the voltage at the electrode, an adjustable autotransformer was used, from the output of which a supply voltage with a frequency of 50 Hz was applied to the converter. The voltage at the electrode was measured with a voltmeter with a magnetoelectric pointer indicator (total deflection current of the pointer, 50 μA) and an additional resistor with a resistance of 2 GΩ, composed of 20 series-connected resistors of 100 MΩ each). Thus, the limit of the measured voltage was 100 kV. In the experiments, an electrode was used in the form of a bundle of thin conductors pointed at the ends (in the form of a "dandelion"). The measurement results showed that already at a potential of 20 kV at a distance of 2 m from the ionizing electrode, the concentration of air ions is at the level of the maximum allowable sanitary standards. Therefore, for any large values of the potential on the electrode, the minimum distance at which a person can stay for a long time becomes even greater. Another important conclusion is that the concentration of light air ions decreases significantly with distance from the electrode - approximately 10 times for each meter of distance. This decline is due to the recombination (death) of ions, as well as their capture by various aerosol particles that pollute the air. Due to recombination, the average time of existence (duration of "life") of light air ions is very limited and practically does not exceed ten seconds. Therefore, it is fundamentally impossible to create a uniform distribution of air ions in the room, and even more so to try to saturate the air with them in several rooms if the ionizer is installed in only one of them. It is also useless to try to stock up on air ions for the future. After turning off the device, their concentration will quickly fall to the background level. But the benefits of a working device will still manifest itself for a long time in the form of clean air. If it is necessary to saturate several rooms with air ions, each of them must be equipped with an ionizer or use a portable device. Taking into account what has been said, a compact air ionizer was developed, named by the author "Korsan" (Fig. 1).
The high-voltage converter and the corona electrode in it are structurally integrated into one whole by means of a connector. Half of a plastic soap dish with external dimensions of 110x80x30 mm was used as the converter housing, in which there is a board of a single-transistor self-oscillator with transformerless power supply from a 220 V network, a diode voltage multiplier, a current-limiting protective resistor and a socket for attaching an electrode. There is no power switch on the body of the device, since it cannot be used due to the appearance of a static charge on the human body when approaching a working device. Therefore, the air ionizer is equipped with a long (at least 2 m) flexible power cord with a plug at the end, which turns the device on and off. The dimensions of the housing allow placing a diode multiplier of 40 kV or more in it. But based on the experience of a three-year operation of the ionizer in everyday life and in medical institutions, it should be recognized as appropriate for domestic use, the choice of potential on the electrode from 15 to 30 kV. The electrical circuit of the air ionizer is shown in fig. 2.
The alternating voltage of the network 220 V with the help of the diode bridge VD1 and the capacitor C1 is converted into a constant voltage of about 310 V, which feeds the high-voltage oscillator. It is made on a transistor VT1 and a transformer T1. Winding I and capacitor C2 form an oscillatory circuit connected to the collector circuit of the transistor in series with resistor R2 and indicator LED HL1 shunted by resistor R3. From the winding II through the decoupling capacitor C3, a positive feedback voltage is applied to the base of the transistor. Resistors R4-R6 determine the auto-bias mode on the base. On the step-up winding III, an alternating voltage develops with an amplitude of about 3 kV, which is supplied to the multiplier on diodes VD2-VD11 and capacitors C4-C13. With ten multiplication stages, a negative potential of 30 kV is achieved. When using an eight-stage multiplier, its output will be 24 kV, respectively. The output of the multiplier is connected to socket X2 through a protective resistor R7, which limits the current if the corona electrode is accidentally touched to a safe value. The most critical element of the device is a high-voltage transformer (Fig. 3). It is made on an eleven-section cylindrical frame 2 with a magnetic circuit 1 with a diameter of 8 mm made of M400NN ferrite.
Step-up winding III contains 3300 turns of PELSHO 0,06 wire and is evenly laid in frame sections of 300 turns each. Winding I contains 300 turns of PELSHO 0,1 and is wound in three rows on sleeve 4, located on the edge of the frame from the left side according to the winding output scheme III. Four turns of feedback winding II are wound with PELSHO 0,1 wire over winding I and separated from it by a layer of insulating tape (adhesive tape) 3. The length of the frame with the magnetic core can be in the range of 70...100 mm and is determined by the dimensions of the case. The frame 2 and sleeve 4 of the transformer can be glued together from 3-4 layers of paper used for printers or copiers. Cheeks for separating sections can be made of thick paper 0,3 ... 0,5 mm thick. But it is best, of course, to carve a sectional frame from a dielectric (fluoroplast, polystyrene, plexiglass, ebonite or dense wood). The beginning and end of winding III are soldered to terminals 5, glued to the edges of the frame. The conclusions are easy to make from a single-core copper wire with a diameter of 0,4 ... 0,5 mm, but it is impossible to create short-circuited turns. With the same conclusions, the transformer is attached to the board. The conclusions of the windings I and II are soldered to the board in compliance with the phasing indicated on the diagram. The described design allows the operation of the transformer without any special impregnation. The best results will be obtained if, instead of the bipolar transistor KT872A indicated on the circuit, any BSIT transistor from the KP810, KP953 or KP948A series is used (the gate terminal is used as a base, drain - collector, source - emitter). Diode bridge VD1 - any, designed for a rectified current of at least 100 mA and a reverse voltage of at least 400 V; rectifier poles VD2-VD11 - KTs106B-KTs106G or any of the KTs117, KTs121-KTs123 series. Capacitor C1 - with a capacity of 1 to 10 microfarads for a voltage of at least 315 V; C2, C3 - any type, but C2 for an operating voltage of at least 315 V; C4-C13 - K15-5 with a capacity of 100-470 pF for a voltage of 6,3 kV. LED - any with visible radiation. Resistors R1-R6 - C2-23, C2-33, MLT, OMLT; R7 - C3-14-0,5 or C3-14-1. When using serviceable parts and error-free installation, the air ionizer starts working immediately. It is convenient to control the operation of the oscillator and measure its main parameters using an AC milliammeter with a measurement limit of 25-50 mA and an oscilloscope that allows you to observe an electrical signal with a swing of at least 600 V on the screen. The current meter allows you to determine and minimize the power consumed from the network, and oscilloscope - visually monitor and optimize the operation of the device, as well as indirectly determine the value of the constant voltage at the output of the multiplier. An AC meter is included in the break of any network wire. But before inserting the X1 plug into the mains socket, remember that the air ionizer is powered without an isolation transformer and, therefore, any of its elements is under voltage dangerous to humans relative to the neutral wire. So remember the safety measures and follow them! The first inclusion is advisable to do without a diode multiplier. In the absence of generation (controlled by an oscilloscope connected to the collector of the transistor), attention should be paid to the current consumed (quiescent current). If it does not exceed 1 mA, the transistor may have a reduced base current transfer ratio, and it is better to replace it. But you can try to increase the quiescent current by selecting a resistor R5 with less resistance. If the quiescent current is within 2 ... 5 mA, and there is no generation, the reason for its absence may be the incorrect phasing of the transformer winding leads. In this case, it is enough to swap the ends of any of the windings - I or II. If after this generation does not occur or there are oscillations, but of a very small amplitude (the transistor operates without cutoff), it will be necessary to increase the number of turns (by 1 ... 2) of the feedback winding II. In a normally operating generator (its frequency is 40 ... 60 kHz), the peak voltage on the collector relative to the common wire is in the range of 500 ... exceeds 600 mA. In this mode, no more than 90 W of power is released in the transistor, and it can be used without a heatsink. It should be borne in mind that the efficiency of the generator is related to the cutoff angle of the transistor. The value of this parameter is easy to optimize using an oscilloscope by selecting the resistor R4 and the voltage on the winding II. The higher the voltage (more turns) and the lower the resistance of the resistor, the larger the cutoff angle. The dependence of the efficiency on the cutoff angle is extreme, and the optimal mode is achieved at an angle of 80-100°. After the generator tuning is completed, it is possible to measure the voltage amplitude on the step-up winding III using an oscilloscope. To do this, the easiest way is to use a capacitive voltage divider (Fig. 4).
Capacitor C1 must be with an operating voltage of at least 3000 V, for example KVI, and capacitor C2 - of any type. The division factor of such a chain with the indicated values of capacitors and the input capacitance of the oscilloscope 100 pF is 100. With sufficient accuracy, the voltage on the ionizing electrode (on socket X2) is determined by multiplying the amplitude value of the voltage on the step-up winding III by the number of stages of the diode multiplier. At the end of the setup, you can test the operation of the device with a connected multiplier. To do this, it must be connected to the step-up winding III with wires at least 10 cm long and placed on a sheet of good dielectric (plexiglass, getinax, etc.). The best way to check is to measure the negative potential at the output of the multiplier with respect to the ground wire using a high voltage voltmeter. But you can limit yourself to a simple inclusion. In a normally operating converter, as a rule, a corona discharge occurs between the terminals of the capacitors of the diode multiplier, accompanied by a characteristic hiss and smell of ozone, but spark discharges are also possible. Of course, it is impossible to operate an air ionizer in this form. At least sealing of the multiplier with a dielectric compound is required. If a decision is made to seal only one multiplier, then the design of the entire ionizer should be such that the distance between the corona electrode and the high-voltage unit is at least 1 m. Otherwise, the reliability of the air ionizer drops sharply and it may fail in a few months. Microcurrents begin to flow through the housing of the high-voltage unit through the existing joints and gaps, eventually turning into spark discharges, which is due not only to the inevitable settling of aerosol particles on its surface, but also to their penetration into the housing. In the described design, all parts of the device are sealed with EDP epoxy adhesive. Before pouring, the units and elements are mounted in a dielectric housing with a wall thickness of at least 1,5 mm. Measures must be taken to eliminate possible leakage of resin through the holes used to attach the connector, LED and power cord entry. To do this, the diameter of the holes must be exactly matched to the corresponding elements. You can use the preliminary sealing of these places with PVA glue, "Moment", BF, etc. EDP glue is used in accordance with the instructions attached to it. Before mixing with the hardener, the base is heated to a temperature of 70...90°C to increase fluidity and accelerate the curing process. But it must be taken into account that after mixing the components, the curing reaction occurs with the release of a large amount of heat. Resin volumes greater than 50 ml may self-heat with boiling and curing within minutes. Therefore, it is necessary to use a filler (quartz or river sand) introduced into the mass already prepared for pouring in a volume ratio of 1:1. Operation of the device is possible not earlier than 24 hours after filling the case. Author: V.N.Korovin
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