Gas-discharge lighting - from the accumulator. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Lighting

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During road trips, life in tents, converters for gas-discharge lamps have proven themselves well. Battery lighting is a very expensive thing. It is much cheaper to use a car battery as a source of energy. Incandescent bulbs of 10 or 15 watts are practically enough to light the inside of the tent. At the same time, at the same energy, the luminous flux from a gas discharge lamp is significantly greater, since its efficiency is much higher than that of a traditional incandescent lamp. In addition, an additional advantage of the discharge lamp is that the light source is not a point, so the illumination will be more uniform.

I give a description of two converters for gas-discharge lamps; both require a 12V supply voltage. The first one is used for 6W lamps and the second one for 18W lamps.

Rice. 1. Schematic diagram of the converter for gas discharge lamps 6 W

Converter for gas discharge lamps 6 W. Its schematic diagram is shown in Fig.1. Capacitor C1 is charged through resistors P1 and R1. When the voltage across the capacitor reaches about 0,6 V, transistor T1 opens. The collector current that appears creates a magnetic field using the winding n1. Under the influence of changes in the magnetic flux in the winding n2, a voltage is induced, which is added to the voltage available on the capacitor C1. The flow of the process is ensured by proper connection of the beginning and end of the winding n2. With an increase in the base current, the transistor T1 is in a state of saturation; the increase in collector current stops. At the same time, the growth of the magnetic flux in the core of the transformer stops. Once the magnetic flux stops changing, no induced voltage occurs.

The base current of transistor T1 drops sharply. As a result, the collector current also decreases. As soon as the magnetic flux begins to decrease, the voltage induced at the ends of the feedback winding changes polarity, so it is subtracted from the voltage across the capacitor C1. Transistor T1 turns off. Due to the presence of positive feedback, the opening and closing processes are very fast. The described process is repeated periodically. The oscillation frequency depends on the resistance of the potentiometer P1. The lower the resistance, the greater the charging current and, therefore, the higher the oscillation frequency. The resistance value R2 determines the base current of the transistor T1. With this resistance, the efficiency of the blocking generator can be adjusted to the optimum value. The waveform at the collector of the transistor is shown schematically in Fig.2.

Rice. 2. Waveform at the collector of transistor T1

The transformer Tr is wound on a ferrite core. In the prototype of the device, a pot (segment) core with a diameter of 26 mm, A was used._L=630, Siemens. In this case, the oscillation frequency for the gas discharge lamps used was 40 kHz. The winding sequence of the transformer windings is shown in Fig.3. The n2 winding provides the "ignition" voltage for the discharge lamp. The capacitance of capacitor CXNUMX determines the amount of current flowing in the lamp. The larger this capacitance, the lower the capacitance X_C and, consequently, the greater the current flowing in the lamp. As the current increases, the amount of luminous flux emitted by the lamp also increases.

Rice. 3. The winding sequence of the transformer windings

A discharge lamp is essentially a gas-filled discharge tube. A low-pressure gas discharge occurs in it. UV radiation is converted into visible light using a luminescent powder deposited on the walls of the lamp. The advantages of gas discharge lamps are that their service life is much longer than that of incandescent lamps, and for the same power consumption, the amount of light emitted (luminous flux) of fluorescent lamps is also much greater.

With regard to the operation of these lamps, attention should be paid to the following. To initiate a discharge, a so-called ignition voltage is needed. After ignition of the discharge, as the current increases, it is necessary to reduce the amount of voltage applied to the lamp terminals. When the lamp is operating in a conventional network, this task is performed by a choke connected in series with it.

In our case, this is provided by a blocking generator. There are many possibilities for starting a lamp. The essence of the "cold start" method is that at the time of connection, 5 ... 10 times more voltage is applied to the lamp. After the lamp is ignited, the normal “burning” voltage is applied to it.

The second, much more reliable, is the "hot ignition" method. In this case, the filaments located at the ends of the gas-discharge lamp are heated; then, at the moment they are turned off, a voltage pulse is applied to the lamp, which ignites it. The delay time is provided by a special glow discharge lamp (starter), which is used when using lamps in the mains. The disadvantage of this method is that the lamp life is reduced. Another significant point is that the long incandescence of the lamp filaments significantly reduces the efficiency of the converter.

All these points are taken into account in the transistor ignition unit. At the moment of switching on, the uncharged electrolytic capacitor C3 forms a kind of short circuit. This capacitor begins to charge through resistor R4 and the base-emitter junction of transistor T2. The collector current arising under the influence of the base current leads to the operation of relay J. The relay contacts close the electrodes of the discharge lamp, and they heat up. As soon as the capacitor C3 is charged, the base current of the transistor T2 disappears. The relay opens; the voltage surge that occurs on the PZ winding lights the lamp. Resistor R3 contributes to the complete closing of the transistor T2. Diode D1 protects transistor T2 from inductive voltage surges that occur when the relay is turned off.

Rice. 4. Converter circuit board for 6 W discharge lamps

This converter is protected against battery connection with reverse polarity. When the polarity is reversed, diode D3 opens and fuse Bi blows.

Rice. 5. The layout of the parts of the converter for gas discharge lamps 6 W

The printed circuit board of the converter for gas discharge lamps 6 W is shown in Fig. 4; the layout of parts on it is shown in Fig.5. Those tracks through which a large current passes should have an increased width and be well tinned. To improve heat dissipation, a thin layer of silicone grease is applied between the radiator (Fig. 6) and the switching transistor T1. In the prototype, a reed relay with a winding resistance of 1 kOhm for an operating voltage of 12 V (type MGR04-A3) was used. Naturally, other relays with similar parameters can be used here. True, due to a different pin arrangement, it will be necessary to slightly modify the printed circuit board. To avoid possible breakdowns, the leads of the transformer windings are insulated with thin plastic tubes.

Rice. 6. Radiator design

Transformer parameters are given in Table 1. The pot-shaped core is screwed to the board with a copper or aluminum screw. A rubber gasket is placed between the core and the printed circuit board - the fastening of the core will be elastic and it will not crack.

Table 1

The converter for gas-discharge lamps can be placed in a plastic case. In order to avoid connecting the converter in the wrong polarity, it is advisable to install a cigarette lighter connector at the end of the power cable.

Rice. 7. Schematic diagram of the converter for gas discharge lamps 18 W

Setting up the device is very simple. The assembled converter is supplied with a supply voltage of 12 V from a power supply unit or a car battery. The consumed current is measured, and using the potentiometer P1 its value is set equal to 200 ... 220 mA. In this case, the luminous intensity of the gas-discharge lamp will be quite significant. The operation of the converter has been tested with different types of lamps; in all cases it worked fine. It is necessary to ensure that the battery voltage is in the range of 10 ... 14 V; the lamp ignites reliably, and its luminous flux does not change.

Rice. 8. Winding sequence of transformer windings

Converter for gas discharge lamps 18 W. Its circuit is shown in Fig. 7, and it is completely the same as the circuit in Fig. 1; only the types and ratings of parts differ. Naturally, the principle of operation is the same for them. Since an 18W lamp is used, the switching transistor must be more powerful; the pot-shaped core of the transformer is also large. The sequence of transformer windings is shown schematically in Fig. 8; the number of turns of the windings and the diameter of the wire are given in Table 2. The increase in the ferrite core led to the need to modify the printed circuit board. The printed circuit board of the converter for gas-discharge lamps 18 W is shown in Fig. 9, and the layout of parts on it is shown in Fig. 10. The filaments of the 18 W gas discharge lamp have a large area, and therefore more time is needed for reliable ignition, as a result of which the resistor R4 has a greater resistance.

Rice. 9. Converter circuit board for 18 W discharge lamps

The converter for 18W lamps is configured in the same way as for 6W lamps. Potentiometer P1 sets the current to 1,1 ... 1,3 A. In this case, the frequency of the converter oscillations is approximately equal to 10 kHz, and the lamp has a significant light output. With this setting and a supply voltage in the range of 10 ... 14 V, the lamp is reliably ignited, and the luminous flux is almost uniform. This converter has been tested with various types of lamps and worked well with all.

Rice. 10. The layout of the parts of the converter for gas discharge lamps 18 W

Table 2

Rediotechnika Evkonyve 2000, translated by A. Belsky; Publication: radioradar.net

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