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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Network LED lamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting Until recently, the most popular light sources were incandescent lamps despite their low efficiency and limited resource - only 1000 hours. They were replaced by energy-saving compact fluorescent lamps (CFLs) with a declared resource of up to 10 hours. the service life of such a lamp should be at least five years, but in practice it often turns out to be much shorter - the electronic ballast (electronic ballast, also called electronic ballast) fails, the filaments burn out. Currently, lamps based on super-bright white LEDs are increasingly being used, the resource of which reaches 000 hours (the estimated service life with the same daily operation is over 100 years). In other words, such a lamp is practically eternal. However, to realize the potential resource of LEDs, a network power supply is required that does not reduce the reliability of LEDs, because, as is known, the reliability and durability of the system are determined by the parameters of its least reliable and durable element. In recent years, the magazine "Radio" published descriptions of several lamps based on LEDs. Some of them [1, 2] are powered by mains sources with a ballast capacitor. The disadvantage of such lamps is low reliability. When connected to the network, dangerous current pulses can flow through the LEDs, they are not protected from the effects of impulse noise, which can damage them. Lamps with switching power supplies are not without drawbacks [3, 4]. They contain a relatively large number of elements and do not have sufficient reliability. As practice shows, more than half of all electronic equipment failures occur due to the failure of switching power supplies, and with service life of more than five years, their failures become predominant. A common drawback of these lamps is a small number of LEDs, which makes it impossible to organize uniform illumination of a sufficiently large area.
When I needed an economical lamp for additional illumination of seedlings, I made it according to the scheme shown in fig. 1. The device contains a bridge rectifier VD2, a smoothing capacitor C2, a current stabilizer based on an integral parallel stabilizer DA1 and a transistor VT1, and 90 super-bright LEDs EL1-EL90. Resistor R1 performs several functions: it limits the breakdown current of the suppressor diode (suppressor) VD1 when it is triggered by impulse noise and the charging current of capacitors C1 and C2, forms, together with the first of them, a filter that reduces the level of high-frequency and impulse noise, and, finally, serves as a kind a fuse (fusible link) that burns out in case of possible short circuits and breakdown of capacitors and a diode bridge. Capacitor C2 reduces the ripple of the rectified voltage and increases the brightness of the LEDs. The suppressor VD1 limits impulse noise, significantly increasing the reliability of the device. The current stabilizer circuit is borrowed from [5] and recalculated to stabilize the collector current at the level of 20 mA. This value, according to [6], is optimal for most white superbright LEDs with a diameter of 3 and 5 mm. The direct voltage drop across them is 3 ... 4 V, so the number of LEDs in the lamp must be selected experimentally, by controlling the voltage at the collector of the transistor VT1. The larger it is, the wider the range of the mains voltage, the luminaire is operational, but the lower the efficiency, and vice versa. Resistors R1, R2 (MLT-0,5) and R3 (MLT-0,25) it is desirable to use aged, 70-80s production (their resistance during the operation of the lamp will change much less than recently manufactured ones). Capacitor C1 - imported film noise suppression with a capacity of 0,15 ... 0,47 μF with a rated alternating voltage of at least 250 V, C2 - oxide imported, capable of operating at elevated temperatures (there is usually an inscription "105 ° C" on the case of such a capacitor) . To increase durability, it is desirable to seal the end of its body and conclusions with an epoxy compound. This is a very effective measure: K50-6 capacitors modified in this way, for example, have been working for me since the 70s of the last century without losing capacity. The symmetrical suppressor 1.5KE400CA can be replaced by two back-to-back 1,5KE400 or 1,5KE400A from SGS-Thomson or less powerful P4KE400, P6KE400 from other companies. The reverse voltage of the VD2 diode bridge must be at least 800 V, the rectified current must be at least 1 A (except for the one indicated on the RS107 diagram, for example, DB107, 2W10, DF10 are suitable). You can also use a bridge from individual diodes with the same parameters (1 N4007, FR107, KD257G, KD247D). We will replace the TL431CLP parallel stabilizer with the domestic KR142EN19A - in the applied mode, it works quite reliably. The transistor is chosen from the following considerations: when given nom resistor R2 base current, its static current transfer coefficient h21e must be at least 30 and, in addition, it must withstand without damage a short circuit of the load (i.e. collector voltage 300 V) and dissipate power of at least 300 V x 0,02, 6 A = 940 W. These requirements are met, for example, by domestic transistors KT8108A, KT8127B, KT1A2 and imported 1446SC2, 2241SCXNUMX. Ultra-bright white LEDs can be of any type and diameter, capable of reliably operating at a current of 20 mA. By combining LEDs with different radiation angles, the necessary uniformity of illumination is achieved. To give the light the desired shade, some of them are replaced by LEDs of the corresponding glow color.
Based on the specifics of the application, two lamps were made (Fig. 2). In one of them (upper according to the figure), designed to illuminate a small area, all the LEDs and the mains power supply are mounted in one housing made from a piece of an electrical box (cable channel) with a cross section of 25x16 mm and a length of 400 mm. The power supply of the second lamp is mounted in the mains plug, and the LEDs in groups of 10 pcs. placed in nine cases (one of them is shown in Fig. 2 below), made of sections of the cable channel with a section of 16x16 mm. This design allows you to quickly change the level and area of illumination. When installing the lamp, the housings are connected to each other and to the power supply with insulated wires. The installation of both devices is hinged, the parts in the cases are fixed with hot glue. It should be noted that ultra-bright LEDs are very sensitive to overheating, so care must be taken when soldering. A technological technique will help prevent overheating: before soldering, cotton swabs soaked in distilled water are placed between the leads of the LEDs, which are removed after soldering. Literature
Author: K. Moroz
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