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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Desktop air ionizer. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Medicine A lot has already been said about the benefits of negative air ions for human health. Let us briefly recall what artificial air ionization gives us. First, and most importantly, computer monitors and televisions neutralize the negative ions in the indoor air. Therefore, at a minimum, devices are needed that can effectively suppress the positive charges generated by monitors and televisions. In addition, air ionizers must create the necessary additional amount of negative ions in the air space of the room, i.e., aeroionizer devices must not only compensate for the shortage, but also produce an additional amount of negative ions. We list the main negative effects from a lack of negative air ions in the air: fatigue, irritability, insomnia, acute respiratory diseases (ARI), disorders of the central nervous system (CNS) and the cardiovascular system. The advantages of using air ionizers are described very well in [1]. With the use of an ionizer, the aging process slows down, the process of treating multiple sclerosis, senile marasmus takes place, the processes of bone fusion in old age improve. Immunity improves. The authors rightly warn that only the systematic inhalation of ionized air gives the desired results. I cannot but agree with this opinion. Everything would be fine, but the Chizhevsky chandelier has significant dimensions, which causes corresponding problems in our cramped apartments, especially with low ceilings. But that's not all that is fraught with the use of such "suckers" on the ceilings. In [2], it was rightly noted that the ceiling is covered with fine dust. It is necessary either to make additional insulation of the ceiling surface where the Chizhevsky chandelier is located, or to reduce the height of the suspension of the latter, or to do both at the same time. The large dimensions of the chandelier are caused solely by the expediency of obtaining the necessary efficiency of negative ion generation. The way out of this situation seemed to be provided by the so-called wire emitters of negative ions [2]. Long-term operation of these radiators has confirmed their superiority in the efficiency of radiation of negative air ions. But at least they have two significant drawbacks that hinder their operation. First, the walls are covered with fine dust along the stretched wire. Secondly, the room becomes unpleasantly "littered" with such emitters: no, no, and someone will break these wires. And why not make a desktop version of the air ionizer? After all, only in this case we can breathe ionized air in any room, without "cling" to the ceilings in every room. This design of the air ionizer device will allow you to install it directly at our workplace. Whether it is a desk, or a workplace of a radio mechanic engineer, a specialist programmer, near a sports simulator, etc. The traditional use of network voltage converters at low frequencies of ∼220 V to the required high voltage of negative polarity is highly undesirable. This has already been mentioned in the literature. Significant ripple amplitudes appear, superimposed on the high-voltage voltage. You can get rid of this in the simplest way by increasing the frequency at which the converter circuit operates. You can get away from the problems associated with binding to a low-voltage power supply if you modify the circuitry of the converter. After all, you must admit that voltage converters for air ionizers, published, for example, in [2] or [3], are quite efficient. The construction from [2] worked for a long time without problems with the stability and reliability of the system as a whole. But binding to a 12 V voltage stabilizer only interferes in terms of system mobility, especially when it comes to ion emitters ("chandeliers"). Similar statements are quite fair with respect to the construction [3]. This converter requires two voltage sources: 30V (280mA) and 5V (40mA). The design (Fig. 1) allows to get rid of the installation of a network stabilizer when supplying the converter circuit to the air ionizer.
The current consumed by this circuit does not exceed several tens of mA. Almost all parts, except for the design multiplier, are housed in a small plastic case. Only the transistor VT2 is equipped with a small heatsink. The mains voltage to the diode bridge VD1-VD4 is supplied through current-limiting resistors R1 and R2. Thus, under the most unfavorable set of circumstances (for example, a breakdown of the electrolytic capacitor C1), the current through the diode bridge cannot exceed 0,5 A. The 1N4007 diodes can withstand a direct current of at least 1 A (Uobr ≤ 1000 V). And for critical cases, there is a fusible insert in the circuit for a current of 0,25 A (.U1). The positive voltage from the capacitor C1 is supplied simultaneously to two sections of the circuit. The first is through the resistor R7 to the pulse transformer T1 and to the collector of the high-voltage transistor VT2. The second - through the ballast resistors R3-R6 to pin 14 of the DD1 microcircuit and through the limiting resistor R12 to the collector of the "buildup" transistor VT1. The power supply of this section of the circuit is stable due to the presence of the VD5 zener diode. The master oscillator of the design is assembled on a well-proven "diode" circuit for a long time. These are elements DD1.1, DD1.2, C5, VD6, VD7, R9 and R10. The power-up of the circuit is carried out by parallel inclusion of two additional elements of the microcircuit DD1.3, DD1.4. From the output of the current-limiting resistor R11, rectangular control pulses are fed to the transistor VT1. The small capacitance of the boost capacitor C6 contributes to the rapid blocking of the transistor VT1. From the emitter of this transistor, the signal is fed to the base of the final stage (transistor VT2). A distinctive feature of this circuit is the presence of a low-resistance resistor R13 (51 ohms), namely 51 ohms. As is known, the UKEmax value of high-voltage transistors is guaranteed only with strict regulation of the resistance of the resistor connected between the base and emitter terminals. Radio amateurs simply forget about it, marveling at the "lethal" outcomes of high-voltage transistors in their designs. That is why, until recently, the output stages of voltage converters of high-voltage circuits with "buildup" by a pulse transformer were so common. The latter was connected between the base and emitter of the output transistor. This "killed two birds with one stone." The first is a short circuit (almost short-circuited) by direct current of the outputs of the base and emitter of the transistor. That is, the problem of UKEmax is solved automatically (UKEmax, limited by the resistance between the base and the emitter). The second is receiving, the possibility of supplying pulses during the locking of this transistor. But, as you know, this is the best method of "suction" of minority carriers from the base of a bipolar transistor. But since there are no large switching powers in the circuit of Fig. 1, it turned out to be possible to get by with a simple control system for the key transistor VT2. Since our system is resonant, we had to carefully select the pulse parameters. This is done using two trimming resistors R9 and R10 installed on the board. Separately, the duration of the pause (tp) and the pulse (ti) are selected. This is the only way to achieve good performance in terms of power consumption at the required high output voltage (≥25 kV). The frequency is selected by changing the capacitance of the capacitor C5 (20-50 kHz). It must be emphasized that not only the clock generator chip, but also the transistor VT3 is powered from the simplest parametric stabilizer (R6-R5, VD1). That is why it is so important to optimize the control circuit for the powerful output transistor VT2. By the way, my design option remains operational until the resistance of the resistor R13 is reduced to 33 ohms inclusive. That is, a low-power voltage source is actually used, and one for "two fronts". The resistor installed in the collector circuit (R12) serves as just such a kind of pulse shape optimizer. Thanks to its presence, it was possible to "squeeze out" everything necessary from the circuit, i.e. complete the tasks. The load of the transistor VT2 is the primary (I) winding of the pulse transformer T1. Together with the capacitor C13 I, the winding forms an oscillatory circuit. This design provides a high and stable efficiency of the ionizer as a whole. Diode VD8 serves to protect the transistor VT2 from reverse voltage. About capacitor C4. Without this element, the circuit will not function normally. To be honest, several variants of the output stage circuits and the nodes that feed these circuits were tested. If a resistor is installed with an amplifier load, then a blocking capacitor is not only needed, it is necessary. Otherwise, the normal operation of the amplifying element itself is not ensured. Moreover, the installation of a "ringing" instance as a blocking capacitor leads to sad results. If the load "oscillates" with a frequency of 20-30 kHz or more, then the blocking capacitor must be able to extinguish these "oscillations", i.e. "take over" and close to a common wire. Consider sound engineering. How much is said about the distortions fixed by the measuring equipment. And only occasionally there are comments about the quality of the capacitors used. The lowest frequency capacitors are electrolytic. That is why, in critical cases, they are shunted with higher frequency - non-electrolytic ones. From the secondary (II) winding of the pulse transformer T1, the alternating voltage is supplied to the high-voltage voltage multiplier, which is assembled on the elements C7-C12, C14-C17 and D9-D18. The increased number of multiplier links (10 versus 6 traditional ones) made it possible to reduce the output voltage from the winding II of the pulse transformer T3 to 2,5 kV (1 kV is already enough). And this pushes the operating mode of the transformer away from the area of its operation near a possible electrical breakdown. The latter circumstance is very dangerous for this hank knot. As experiments and operation have confirmed, up to 4 kV the transformer operates stably, without "corona" and other effects dangerous for it. Increasing the voltage on the II winding up to 5 kV can cause a breakdown of the insulation between the turns, which disables the transformer. That is, when the pulse transformer is made without filling with a compound, its reliable operation is permissible only at an output voltage of not more than 4 kV. And I didn’t want to fill this product with a compound. Therefore, it was decided to increase the number of multiplier links. This, among other things, unloads the elements of the voltage multiplier according to the voltage established on them. The latter circumstance will thank us by the absence of failures of the elements of the voltage multiplier. At the same time, I have already repaired six-stage high-voltage multipliers, and both diodes and capacitors were to be replaced ("output" was -30 kV, there were no output short circuits). Details. Rectifier bridge diodes VD1-VD4 type 1N4007 are replaceable by any similar ones with a permissible forward current of at least 0,3 A and a reverse voltage of at least 400 V, for example, type KD105 (B, V, G), KD226 (V-E), KD243 ( Ms.), KD247 (Ms.), KD209 (A-G), etc. It is quite possible to use diode bridges such as KTs405, KTs402, KTs407, etc. But in this case, the PCB layout needs to be modified. Capacitor C1 of any type for the required voltage with a capacity of 10-30 microfarads. In my design, K50-12 is installed ("lying"). Capacitor C2 type K50-35, its capacitance is also not critical and can be in the range of 50-200 microfarads. The operating voltage must be greater than the stabilization voltage of the Zener diode VD5. Capacitor C3 type K73-17, its capacitance can be in the range of 0,022-0,1 uF. Capacitor C4 must be of high quality (small tgδ, i.e., the dielectric loss tangent must be smaller). I applied type K78-2. These are good capacitors. They are even suitable for separating elements between tube stages of a high-quality sound amplifier. Capacitor C5 is mica type KSO, and C6 is KD. The loop capacitor C13 is composed of two series-connected capacitors of the K15-5 type with a capacity of 2200 pF and an operating voltage of 6,3 kV each. The total capacitance is 1000 pF, and the equivalent voltage is 12 kV. Trimmer resistors R9 and R10 type SP3-38b. Resistor R14 high-voltage type KEV-2. The remaining resistors are of the MLT type (MT can be used). High-voltage multiplier diodes D9-D18 type KTs106G, you can install KTs106V and even KTs106B. Now on the market you can buy a wide variety of radio components. But, as practice shows, radio elements often fail due to overvoltages than from current overloads. And it often happens that the details simply do not correspond to the parameters that are guaranteed in the specifications. Multiplier capacitors C7-C12 and C14-C17 should also have a lower load factor (not 0,7, as is usually allowed by voltage). I installed K15-4 (470 pFx20 kV), so the safety margin is sufficient. The fact is that it is easiest to burn the elements of the multiplier precisely in the process of adjustment (or experiments, as it happened). So the electric strength margin in this case is not a luxury, but a necessity. During experiments, voltage pulses (surges) may well occur on the II winding, which significantly exceed the rated or operating voltage of the II winding of the transformer T1. And this leads to defects in the diodes and capacitors of the multiplier. And only in a well-established scheme can elements with a load factor of 0,7 or 0,5 be installed without the risk of damaging them. Now about the most "terrible" - a pulse transformer. The reliability of the device as a whole largely depends on the accuracy of the manufacture of this product. The core is a ferrite magnetic circuit of the brand 600NN ∅ 8 mm and a length of 160 mm. Both windings are placed on a sectioned frame. To avoid unnecessary hassle with turning the sectional frame, a more affordable version of the sectioned version of the T1 transformer windings was tested. This method does not require the use of turning work and is the best suited for home production of sectioned coils and transformers in pulse circuitry. First, 3-4 layers of transformer (paraffinized) paper are wound on a ferrite rod. Any other thick paper will do. After that, the diameter of the resulting product is measured with a caliper. Blanks are cut from non-foiled fiberglass of a square shape with a size of 30x30 mm. There should be 11 of them. Any other electrical insulating material with a thickness of more than 0,5 mm is also suitable. In the center of the workpieces, we drill a hole according to the diameter of the workpiece, measured with a caliper. These blanks should subsequently be at hand, since the manufacturing technology will require the speed of its installation on the rod. All windings are wound with PELSHO 0,25 wire. This wire is double insulated, and it's not overkill here. It is not worth winding with a thicker wire, since the wire will not fit in the provided sections, and the windings will take up unreasonably bulky space in the device case. Smaller diameter please. So, the first insulating gasket is fixed on the ferrite rod with glue or tape near one of the ends of the ferrite. There should be ten sections in total on the ferrite rod. Therefore, we make markings with any writing object to accommodate future spacers-partitions of the necessary sections-windings. After that, install the second insulating gasket. We fix it with threads from the side where we will wind it. In the resulting coil, we wind 300 turns. We do this 10 times in a row. We consider that the second winding is already wound and contains 3000 turns of PELSHO 0,10,25 wire. Now it remains to wind the I winding. It is located on top, i.e. over the second winding. It is also "broken", but only into four sections, counting from the "cold" end (the top output of the I winding according to the diagram). In no case should winding be carried out near the output of the II winding, where a voltage of several kilovolts will be present! Each of the four sections contains 75 turns of the same wire as before (i.e. 300 turns in total). Thus, it is possible to avoid technological problems with the manufacture of a sectioned frame and deficiencies in the process of manufacturing a high-frequency transformer. Indeed, measure the capacitance of this coil (winding II) with a capacitance measuring device. Pleasantly surprised by the fact that the capacity is actually negligible! The same is true for the I winding of this transformer (pF units!). I note that the length of the ferrite rod can be either reduced by 1,5 times or increased by 1,5 times. You can change within a wide range and the ratio of turns. But electrical breakdown (see above) cannot be avoided in any way without a dielectric filler (sealer), if you want to "pull" a higher voltage from the II T1 winding. Due to the fact that the shape of the cheeks of the sectioned frame is square, the transformer can be easily mounted on the printed circuit board. Transistor VT1 is selected with the parameter ∆h21e>>300 (Ib=const=1 μA). Transistor VT2 is selected using a Ukemax meter (>> 1200 V). Instead of the KT828A transistor, we also install KT838A. I did not check the operation of the air ionizer with other types of transistors. Although it can be assumed that both KT872A and BU508 production from far abroad, etc. are quite suitable. Structural execution. All elements of the circuit in Fig. 1, except for the voltage multiplier, are placed on a printed circuit board (Fig. 2), which is placed in a plastic case 150x180x45 mm in size.
The high-voltage voltage multiplier is placed in a separate housing measuring 140x70x60 mm. Capacitors K15-4 have threaded contacts on one side of the case. Therefore, they are attached to the insulating plate with nuts. Diodes KTs106G are soldered directly to the terminals of these capacitors. An insulating tube D16 mm and a length of about 20 cm is installed in the upper cover of the plastic case. 14 nichrome wires ∅ 12 mm and a length of about 0,15 cm are soldered to the terminal of the resistor R30. These conductors go out through the insulating tube. This is the emitter of negative air ions. It is a kind of panicle of 12 wires more than 10 cm long, counting from the edge of the insulating tube. And one more very important point. Details of the high voltage multiplier must be filled with compound. Paraffin works well. Do not believe the descriptions of ionizer designs, where the high voltage is ≥25 kV and no compounding is required. Allegedly, it is enough to round off the edges of sharp solder joints and that's it. But it's not. The higher the voltage, the stronger the processes are, accompanied only by progression. And this too quickly leads to a defect in the parts of the multiplier. A completely different matter is the sealing of the parts of the multiplier. And only by blocking the access of air (oxygen!) to the elements of high-voltage circuits, we protect them from quick defects. That's why all voltage multipliers for TVs are sealed, although their high voltages are in the range of 16-27 kV (and even less). The converter block and the multiplier block are interconnected by a high-voltage cable about 120 cm long. If such a cable is not available, then it is replaced with a home-made one. Such a cable is made from a radio frequency television type RK-75. To do this, just remove the braid-screen. According to the scheme, the tap II of the winding of the transformer T1 is connected with a separate stranded insulated conductor. We give preference to the RK-75 cable with a stranded central conductor. This is especially important if the ionizer is planned to be used for private job changes. The wire will bend many times, which means that its reliability and strength must correspond to this. If the design is made in a single housing, then all the internal space will have to be filled with a compound. Otherwise, the generator chip and other elements of the voltage converter fail. But on the other hand, we can easily get rid of the connecting high-voltage cable. About forging. The circuit, assembled on serviceable radio components, starts working immediately. The first switching on is carried out using a laboratory autotransformer (LATR) with an ammeter having a current measurement limit of 0-100 mA. Having set the voltage of the LATR to a minimum, we gradually increase it. A good circuit should not draw much current. But a detuned design can draw 50-70 mA or more. Therefore, the output transistor, equipped with a small CAL radiator (70x70x1,5 mm), will get very hot. And at the same time, a well-established instance consumes a current from the network of about 33 mA (no more than 40 mA). Now the transistor will be barely warm to the touch. When the voltage at the zener diode becomes close to the stabilization voltage, you can start adjusting the generator parameters. We leave the engines of trimmer resistors in such a mode of operation of the generator, which provides the highest output voltage at the output of the multiplier. During the adjustment, I disconnected the multiplier from the second winding of the transformer T1. We use a unipolar rectifier on the KTs106G diode and one capacitor 470 pFx20 kV. In addition, we use a current-limiting resistor with a resistance of 100 MΩ of the KEV-2 type and a 50 μA head. We get a voltmeter with an upper limit of 5 kV. However, the voltage can also be controlled at the point of connection of capacitors C8 and C10 with diodes VD10 and VD11 through the same resistor. But this is possible as long as the multiplier is not sealed. In my design, the resistance of the resistor R9 is 125 kOhm, and R10 = 287 kOhm (measured with a universal voltmeter type B7-38). After that, the resistances of resistors R12 and R13 are selected. Resistor R13 may not be selected if its resistance in the range of 47-100 ohms does not impair the operation of the circuit as a whole. The resistance of the resistor R12 is selected from the point of view of obtaining the maximum voltage on the winding II of the transformer T1. It is necessary not only to "get into resonance" with the circuit formed by the 1st winding of the transformer T13 and the capacitor C12, but also to find (in the literal sense of the word!) the most advantageous mode of operation of the converter. And the resistor R2 just affects this mode of operation of the transistor VT1. To be honest, all adjustments affect both the magnitude of the pulse voltage at the output of the II winding TXNUMX, and the current consumed by the device from the network. And further. We must not forget about safety, since the elements of the converter circuit are galvanically connected to the electrical network! References:
Author: A.G. Zyzyuk
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