This issue has already been highlighted in various literature. However, it all came down to one thing - how to make old lamps work, whose filament had burned out. I would like to remind the reader that old lamps are lamps in which the phosphor is already losing its activity, there are huge black spots near the ends to the left and right. In general, it is not a sin to throw out such a lamp, especially since the power consumption of the lamp is very large - the so-called 20-watt lamps consume about 80 W from the network (doubters can check, for this it is necessary to measure the current and determine the power according to the well-known formula: P = UI, where P is the power in W; U is the mains voltage of 220 V; I is the current consumption in A. (as a rule, the current is within about 0.4 A.) The so-called 40-watt lamps consume about 150 watts, respectively.
Now we will try to approach the problem of saving from the other side, namely, we should purchase a new imported fluorescent lamp. At present, this is not a problem, its cost on the market is about 10 UAH, and the luminous intensity is almost 2 times higher (measurements were carried out with a Yu-116 type luxmeter), although this can be noticed visually. This lamp should be connected to the generator circuit, the pulse repetition rate of which is selected in such a way that the eye does not notice the flicker, and the power consumed by the lamp is 5-6 times lower on the power supply network, it is during normal (standard) switching on. Moreover, the generator should be not only economical in terms of the parts used, but also relatively small. All these requirements are met by a generator assembled on two high-voltage transistors (Fig. 1). It should be noted that fans of old lamps (with burnt out heating filaments) can also use them in this circuit.
The circuit can use resistors of the MLT-0.25 type, with the exception of R8 and R9 (they must be wound with a manganin wire with a diameter of 0.25 mm, the length of the wires is 20 mm). The ELI lamp is a 20-watt lamp, although it should be noted that an 18-watt lamp (the difference between these lamps is a smaller diameter, about 25 mm) gives an illumination of 10-15% more, which once again indicates that the wattage is a conditional value. It is advisable to use ceramic or mica capacitors of the KT-2, KSO or K73-17 type. C1-C4 for a voltage not lower than 500 V; C5 and C6 are also desirable type K73-17, they can be replaced with electrolytic type K50-53 for a voltage of at least 50 V (although the reliability of the circuit will decrease). C7 - electrolytic capacitor, to increase efficiency, it is desirable to increase the capacitance to 20 μF. C8 and C9 - capacitors of the K73-17 type for a voltage of at least 630 V. Standard LI choke type DM (inductance 0.1-0.5 μH). Diodes VD1-VD6 of type KD209 with any letter index, in principle, VD3-VD6 can be replaced with KTs402, KTs405, KD105, D226. Transistors are plastic KT8164, KT858, metal transistors KT840, KT838. The KT809 works well, although the luminous intensity of the lamp is 10-15% less. Pay attention to pulse transformer manufacturing.
The core of the transformer armored type B-18 or B-22 made of ferrite grade 2000 NM. When assembling, a gap of 0.2 mm should be left, this can be ensured by paper inserted between the cups. The primary winding is wound with a PEV-2 wire with a diameter of 0.23 mm, the length of the wire is 7.5 m. The secondary and third windings each have 6 turns of a similar wire. The armor core can be replaced with an W-shaped one made of the same ferrite, or even bettermake on the base toroidal magnetic circuit, fortunately now there is a huge assortment of toroidal cores. The ohmic resistance of the primary winding is 5 ohms. Setting up the scheme is as follows. If the circuit does not work, it is necessary to swap the ends of the third winding. The current consumed by the operating circuit is 50-60 mA. For fans of powering lamps with constant voltage, we can recommend the circuit shown in Fig. 2. In the circuit, dinistors with any letter index starting from A. are confidently working. An industrial type D-29-1.2-0.28 is used as a TV1 transformer. D-20-1.2-0.2 works somewhat worse, due to the fact that the consumed lamp current is more than 200 mA, the heating temperature of the choke reaches 50 ° C. Diodes VD1-VD5 type KD105 or D226. Resistor R1 type MLT-2.
Disadvantages of the scheme: - if the lamp is old and does not start well, the resistor R1 begins to heat up strongly, since the start generator, assembled on the dinistor, works continuously; -the appearance with time of a black spot on one side of the lamp.