Some features of one of the industrial designs of LDS. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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Recently, the domestic market has been flooded with small-sized fluorescent lamps (LDS) with built-in ballasts based on transistor inverters. In general, the use of such LDS is economically justified, but the consumer will be able to feel it at least after a year of operation of these lamps. Manufacturers on the packaging of their products declare the operating time of LDS to failure of more than 6 ... 8 thousand hours.

Many purchases are now being made in spontaneous markets... At one of the sales, LDS CIXING 40W SL * PRIS-MATIC was sold out quite well. This was facilitated by the low price of the goods. The seller conscientiously checked the goods, briefly including the LDS in the network. They lit up, but, as it turned out at home, this could not be called "work". Some stopped igniting altogether, others stopped their work after 1 ... 2 minutes of burning, one regularly flashed during operation. Of the five lamps purchased, all refused and very quickly. The protracted wait of the director of a trading company prompted me to look at the circuit of a defective 40 W LDS (Fig. 1). It was compiled according to the drawing of a real printed circuit board of the product (Fig. 2).

Fig. 1

Fig. 2

Externally, the circuit was typical: a half-bridge inverter based on transistors VT1, VT2. It is very similar, in particular, to the diagram in Fig. 1 [1]. The main difference is that one of the LDS terminals is connected not to the positive terminal of the rectifier, but to the common point of the capacitors Cl, C2. This made it possible to use two lower-voltage, and therefore less expensive, filter capacitors instead of a high-voltage filter capacitor. This, of course, was not the main task of the designers. It was more important for the manufacturer to deviate from the prototype at least a little, so that it could be argued that the applied scheme is the intellectual property of this particular company. The second difference between the circuit in Fig. 1 and the prototype was ... the place where the capacitor C4 was turned on. In theory, this is a snubber capacitor designed to start an oscillator. It was this capacitor that turned out to be the culprit of most device failures performed by the company according to the scheme of Fig. 1. It was worth soldering this capacitor to its standard place, in parallel with the resistor R4 (Fig. 2), and the circuit worked. The printed circuit board does not need to be changed. It is enough to remove the capacitor C4 from it and solder it from the side of the pattern of printed conductors in parallel with the resistor R4. To isolate the capacitor, it is enough to put a piece of vinyl chloride tubing on it. Diode VD6 type 1 N4007 was not installed in the board by the manufacturer in order to save money! It is desirable to do this when upgrading the board.

As the measurement of the capacitance value of capacitors C4 showed, they have a large spread. A significant decrease in the capacitance of C4 led to blinking in one of the LDS specimens. It was possible to eliminate the defect by increasing the capacitance of this capacitor: on the side of the printed conductors, another one was soldered parallel to this capacitor, of the same size, which was at hand. By the way, in most LDS circuits, the value of the snubber capacitor is chosen around 1500 pF.

Fig. 3

Fig. 4

The assumption about the causes of failures of LDS CIXING 40W and the way to eliminate them was fully confirmed by the manufacturer. She released the CIXING 36W LDS, where the location on the C4 circuit (Fig. 3) and the printed circuit board pattern (Fig. 4) were changed, the VD6 diode was installed on the board. It is a pity that before the more conditioned 36 W LDS appeared on sale, the trade needed to sell defective 40 W LDS. In appearance and packaging, both types of LDS are absolutely identical. So guess what you're buying!

Literature

1. Yakovlev E.L. Electronic daylight ballast/radio circuit. - 2007. - No. 1. - From 18

Author: E.L. Yakovlev, Uzhgorod; Publication: radioradar.net

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