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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Voltage converter for powering LDS with a power of 20-80 W. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Voltage converters, rectifiers, inverters Most voltage converter (PV) circuits are designed to power LDS with a power of not more than 30 watts. It is known that the battery capacity does not allow long-term operation of powerful energy consumers. That is why we strive to use low power LDS. And this is just unprofitable in terms of economy! As experimental studies have shown, small-sized LDSs are not highly efficient light emitters, if we take the ratio of the amount of light / the amount of energy consumed. In stationary conditions, it is more profitable to install a large-sized LDS than a small-sized one. In this way, increased light output is achieved with the same power consumption from the battery by these LDS. This, of course, is about the PN with the brightness control of the LDS glow. I do not mean any particular type or manufacturer of LDS and the PN scheme. Here is just one example. PN, operated with a 40 W LDS in the "night light" mode, consumed a current of 12 A from a 0,10,3 V battery. At the same time, it was so light in the room that a portable flashlight that consumed the same power (12 V; -0,1 A), was in the role of "firefly". Thus, if we are talking about saving battery power when the LDS is powered from the PN, then we should take appropriate care of both the design of the PN and the type of LDS. LDS produced in foreign countries is better than domestic ones. Suppose we have chosen a Philips LDS lamp with a power of 0,3 watts. They are not much more expensive than domestic ones, but they are noticeably superior to the latter in terms of characteristics. First, the brightness of Philips is greater than that of our LDS. The second, which is very, very important when powering the LDS from the PN and the battery, is almost half the gas ignition voltage inside the cylinder. We have approximately 40-600 V (for Philips) versus 700-1000 V and even more for LDU-1200. It is not necessary, apparently, to mention the reliability, durability when comparing these lamps. The circuitry of almost all published PNs "intersects somewhere". Let us dwell on the main points ("pitfalls") in the PN for LDS. In no way can one ignore the requirements for power pulse circuitry. For example, you can not install "random" transformers, low-frequency transistors, if we are talking about frequencies over 20 kHz. Mounting is tricky too. This is especially true for CMOS - chip series 176, 561, etc. I just happened to observe the work of beginners, when everything just listed took place in MON for LDS in several copies! The amazing thing was that LDS still worked! But it is almost unrealistic to "rock" an LDS with a power of 40 W, and even more so 80 W. In PN, the scheme of which is shown in Fig. 1, many of the necessary requirements for such equipment are taken into account. Actually, the rectangular pulse generator is assembled on a DD1 CMOS chip of the K561LE5 type. Brightness is regulated by changing the duty cycle of the pulses with resistor R2. The oscillator frequency (elements DD1.1 and DD1.2) depends on the capacitance of the capacitor C1 and, of course, on the capacitance of the installation and the microcircuit instance. From the output of the fourth element (pin 10) DD1, the control signal through the resistor R5 is fed to the gate of the MOSFET VT2 (KP901A). From the source of the latter, the signal is fed to the gate of a powerful field-effect transistor VT3 of the IR.Z34 type. But the diagram in Fig. 1 does not show one detail. This is a resistor R8 with a resistance of 33051 ohms, which is included in the gap of the gate of the transistor VT3.
Powerful "field workers" are good for many, except for large internal capacitances between the electrodes. In this case, we are talking about a gate-source capacitance that exceeds 1000 pF. To improve the efficiency of the PN, i.e., to reduce the power dissipated by the transistor VT3, it is necessary to quickly turn this transistor on and off. This cannot be done without a quick charge and discharge of the VT3 input capacitance. Much has been said about this in professional literature and very little in amateur radio. A person believes that the installation of a powerful field-effect transistor with a low drain-source resistance (on state) already solves the problem of switching power losses. But it's not! This design provides for special measures for the accelerated discharge of the input capacitance of the transistor VT3. For this, additional elements are installed in the PN circuit: transistor VT1, resistor R6 and boost capacitor C6. The essence of this system is quite simple. Since antiphase pulses are always present at the outputs of the elements DD1.3 and DD1.4, it is easy to understand the algorithm of the circuit. Transistor VT1 forcibly discharges the input capacitance VT3 when a log is present at the output of element DD1.3. "1". When setting the log. "0" at the output of DD1.3, the transistor VT1 closes rapidly, for this, "afterburner" is installed in the form of capacitor C6. We can say that it would be easier to reduce the resistance of the resistor R7, for example, 10-30 times. Easier, but not economical or efficient, because this resistor will dissipate (almost uselessly) part of the battery power. About efficiency. The fact is that thanks to the elements of the circuit VT1, R6 and C6, a very peculiar auto-regulation circuit is formed for almost the most advantageous operating mode of the PN. And this, in turn, affects the stability of the PN operation when the brightness of the LDS changes over a very wide range. Without these elements, the circuit works much worse. The charge of the input capacitance VT3 is provided by a powerful field-effect transistor of the KP901A type, which has a relatively small input capacitance C3I (about 100 pF according to specifications). Resistor R5 is antiparasitic, it prevents VT3 from working on HF and VHF bands, which is quite realistic for such "fast" transistors as KP901A (fgr ~ 400 MHz). The microcircuit is powered through an RC filter, since RF power ripples can disrupt the normal operation of the generator. About the details. Instead of K561LE5, you can install K561LA7, instead of the KT645A transistor - KT3142A. It is not excluded the use of other transistors as VT1, experiments will show which is better and which is worse. If the lamp power is not more than 30 W, then instead of KP901A, you can also use KP902A. The terminal transistor type IR.Z34 can be replaced by any similar one. You can even install domestic type KP922A, but their cases will heat up more. Therefore, several instances are installed in parallel. The problem is in the selection of specimens with close values of the threshold voltages Uthr. Of the ones I have, I once had 12 pcs. KP922A Upor. had from 3,5 to 6,5 V! So the choice is clear, and the price of our KP922A is even higher than that of such transistors as IR.640 (and this despite the fact that the parameters of the latter are two times better than ours). IR.640 is also not very suitable here, and only because of the increased drain-source resistance when on. The reader will be interested to know that initially ... a bipolar type KT3A was installed as a transistor VT8101! True, in this case, a germanium GT1E was installed as a transistor VT311. Otherwise, the high saturation voltage Uke.us will not be able to discharge the input capacitance of the KT8101A transistor. It is likely that KT827A will also be used. But the problem of dissipation of non-primary carriers in the base requires a negative voltage during the turn-off of the bipolar transistor. This can be done, but the PN circuitry is completely modified. The resistor R2-SP-1 (A-1 VT-II) is installed (soldered) directly into the printed circuit board PN (Fig. 2). This is the only way to solve the problem with a sharp decrease in mounting capacity.
Pay attention to the capacitance of the capacitor C1, it is approximately 15 pF. About the pulse transformer T1. A lot depends on this transformer. Ferrite rings cannot be used here. Therefore, in order not to waste time on trifles, a ferrite core from TPI was used (the TPI brand was not established, since the core was bought separately, i.e. without coils and windings). Ferrite Ш16Х Х20 М2000 НМ1-14. It is quite enough (in terms of maximum efficiency of this design) the following execution of the pulse transformer T1. First, we wind 300 turns of PEV-2 D0,6 wire. On top we wind 12 turns of wire PEV-2 D2,4 mm. Between the windings is a layer of electrical tape. About making a frame. We wind 17-21 layers of electric cardboard onto a wooden mandrel with a section of 1x2 mm (if it is not there, then any cardboard of sufficient strength will do). We leave a margin on the cheeks of the frame. We make cuts and "fitting" on a ferrite rod. The newly-minted frame should be completely free to enter the halves of the ferrite core. Otherwise, you can expect a "surprise" after winding the windings - it will not go into place. I do not advise in any way to use ferrites that were in use. And there are at least two good reasons for this. Ferrite may be "shrunken", i.e., not have what is meant in the TS. Second - do not overheat ferrite products! Their parameters literally disappear when heated to more than 100-200 ° C (depending on what brand of ferrite). Radio amateurs are stubbornly silent about this. Only in the relevant literature it is said that the parameters of ferrites are preserved up to certain temperatures. But it is in this way (heating!) that amateurs disconnect the halves of "cups" and other ferrite products. Personally, I have "stumbled" on such ferrite "things". The gap between the two halves of the magnetic circuit should not be large. Its optimal value is about 0,1 mm. Now about the installation of the structure as a whole. The PN board is located near the VT3 transistor, the latter is on a heat sink with a cooling surface of 300 cm2. A 33 ohm resistor (R8) is soldered directly to the gate pin of this transistor. This is very important: both the presence of this resistor and its location. Even more important is the length of the connecting wires PN. The shortest length should be the wire connecting the drain of the transistor VT3 and transformer T1 ("hot" tap of the latter). Similar requirements are also valid for connecting the "cold" terminal I of the winding of the transformer T1 with the capacitor C5 and the PN board. Power from the battery is first supplied to the terminals of the capacitor C5, and only then it is supplied to the PN board. Subsequently, a non-electrolytic capacitor 4,7 uF x 63 V (K73-17) was located directly on the terminals of the capacitor. Structurally, the PN is located in the case of a network ferroresonant stabilizer of the CH-315 type that has served its time. The mains power supply (PSU) is also located here. Agree that a network power supply is a very convenient and necessary thing when the battery is low or not at all. It's no secret that creating a PN from the network, and even with brightness control, is much more difficult than this low-voltage PN. And our system can now work both from the battery and from the mains power supply. About network power supply. Do not get carried away by increasing the supply voltage. Continuous stabilizers reduce the efficiency of the entire system. Key stabilizers are a completely different matter. But personally, I don't like "bells and whistles". I was satisfied with the diode bridge KD213A, placed on fiberglass (diodes need to have cooling with a 40 W LDS lamp!). AC voltage from winding II ~ 14 V. The rectifier filter capacitor is K50-32A with a capacity of 22,000 μFx40 V. For a 80 W LDS lamp, U1 is used for 10 A. A 1 A ammeter is connected in series with .U10. And this is not a luxury, but very operational control over the work of the PN. About the network transformer. A toroidal magnetic circuit from the same unusable CH-315 was used. The primary winding contains 946 turns of PELSHO 0,64 wire; secondary - 60 turns of wire PEV-2 D1,8 mm. Dimensions of the toroidal magnetic core: external D92,5 mm, internal D55 mm, height 32 mm. No-load current about 10 mA (~220 V). The brand is unknown. But, judging by the results, the steel is of high quality. Establishment. Correctly assembled, without errors, the circuit works immediately. But the first inclusion is carried out from the mains power supply unit with the obligatory limitation of the current consumption. It is better to use an electronic current limiter. Instead of capacitor C1, a trimmer is temporarily installed - a tuning capacitor (8 ... 30 pF). Resistor R1 selects the range of brightness changes within the desired range. Resistor R2 is set to the position corresponding to the maximum brightness of the LDS glow. By selecting the capacitance of the capacitor, the greatest brightness is achieved. Capacitor C6 is selected from the condition of the greatest stability of the operation of the PN when the brightness changes from maximum to minimum. At the same time, it is necessary to monitor the heating of the heat sink of the transistor VT3. The more it heats up, the more battery power is wasted. Here, you may have to tinker with the selection of capacity C1, C6. If you decide to install a VT3 bipolar transistor, then the frequency will still have to be reduced, and the radiator area should be increased, since the heating will increase significantly. The quality of the MOSFETs used plays an important role. There shouldn't be any valve leaks at all. Transistor VT1 should also not be low-frequency. By the way, instead of W-ferrites, ferrites from horizontal transformers are also suitable. But I warn you right away about what was said above. The circuit works with almost all (without ballasts) LDS. It is only necessary to provide a power limit, otherwise, after all, LDS also fail at large overloads (more often at start-up). To start the lamp at low power, a push-button switch is provided, the contacts of which at the time of starting close the corresponding taps of the resistor R2 (not shown in the diagram). Author: A.G. Zyzyuk
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