LED strip in a table lamp. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Lighting
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When the 8 W U-shaped fluorescent lamp in the table lamp once again burned out, the question arose of replacing it with a more durable light source - LED. However, to manufacture a lamp containing a large number of LEDs is a very laborious task. At the same time, in stores selling lighting products, it is relatively inexpensive to purchase trimmings (remnants) of LED strips of various glow colors, including white, which is most suitable for a table lamp.
Most often, such a tape is a set of cells connected in parallel, each of which consists of three frameless LEDs connected in series and a current-limiting resistor (Fig. 1). The supply voltage of the tape I purchased is 12 V, the current consumed by one cell is 20 mA, and its length is 50 mm (the cells are clearly visible on the tape).
Fig. 1
As it turned out, in the body of my lamp, you can place six pieces of LED strip, three cells each. When the cells are connected in parallel, the supply voltage of such a lamp is 12 V, the current consumption is 0,36 A. It can be powered either from a low-voltage rectifier based on a step-down transformer, or from a transformerless pulse unit. In the first case, I would have to make a power supply in the form of a separate structure (it is impossible to place its parts in my lamp) and, in addition, transfer the switch located in the lamp to it, which would reduce the convenience of using a table lamp. Switching power supply can be mounted in the lamp housing, however, such devices are quite difficult to implement.
Fig. 2
I found a way out by connecting 18 LED strip cells in series and using a transformerless power supply with a ballast capacitor (Fig. 2). To do this, I cut the LED strip into separate cells (it is convenient to connect them in series, turning each subsequent cell by 180o with respect to the previous one).
Using an adhesive layer on the tape, I glued the cells to a 1 mm thick electric cardboard base, cut to the size of the compartment, and connected them together with a bare tinned wire with a diameter of 0,4 mm. Since the light source is covered with a light-diffusing ceiling, such a design is completely electrically safe.
Fig. 3
I placed the parts of the power supply in the electronic ballast compartment (Fig. 3) and fixed it with drops of hot glue. We can replace the 1W10 (VD1) diode bridge with RS107 or DB107, but you can also assemble it from 1N4007 diodes. Resistor R1 - MLT-0,5, capacitor C1 - film K73-17, C2 - imported oxide.
With sufficient brightness of the glow of the upgraded lamp, the power consumption has halved and its reliability has significantly increased.
Author: K. Moroz
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