The device and the circuit of inclusion of a fluorescent lamp

The fluorescent lamp (LL) is a light source created by an electric discharge in a medium of mercury vapor and an inert gas. This creates an invisible ultraviolet glow, acting on the phosphor layer, applied from the inside to a glass flask. A typical scheme for switching on a fluorescent lamp is a ballast with ballast (EMPA).

Device and description of LL

The bulb of most lamps always had a cylindrical shape, but now it can be in the form of a complex figure. At the ends there are electrodes in it, structurally similar to some spirals of incandescent lamps made of tungsten. They are soldered to outboard pins, which are energized.

The gas conducting medium inside the LL has a negative resistance. It manifests itself in the lowering of the voltage between the opposite electrodes when the current increases, which must be limited. The scheme of inclusion of the fluorescent lamp contains a ballast (throttle), the main purpose of which is the creation of a large voltage pulse for its ignition. In addition to it, the EmPra includes a starter - a glow discharge lamp with two electrodes placed inside it in an inert gas environment. One of them is made of a bimetallic plate. In the initial state, the electrodes are open.

Principle of operation LL

The starter circuit for switching on fluorescent lamps works as follows.

1. The circuit is energized, but first the current does not flow through the LL because of the large resistance of the medium. On the spirals of cathodes current passes and warms them. In addition, it also acts on the starter, for which the applied voltage is sufficient to cause a glow discharge inside.
2. When the starter contacts are heated from the passing current, the bimetallic plate closes. After that, the metal becomes the conductor, and the discharge stops.
3. The bimetallic electrode cools and opens the contact. In this case, the choke produces a high-voltage pulse due to self-induction, and the LL is ignited.
4. A current flows through the lamp, which then decreases by a factor of 2, as the voltage on the throttle drops. It is not enough to restart the starter, the contacts of which remain open when the LL is burning.

The scheme for the inclusion of two fluorescent lamps installed in the same luminaire provides for the use of one common throttle for them. They are connected in series, but each lamp is equipped with one parallel starter.

The disadvantage of the lamp is the disconnection of the second lamp, if one of them is out of order.

Important! With fluorescent lamps it is necessary to use special switches. For budget devices, the starting currents are large, and contacts can stick.

Chokeless switching of fluorescent lamps: circuits

Despite the cheapness, electromagnetic ballasts have drawbacks. They were the reason for the creation of electronic ignition circuits (electronic ballast).

How to start LL with electronic ballast

Chokeless switching of fluorescent lamps is performed through an electronic unit, in which a sequence of voltage changes is formed when they are ignited.

Advantages of the electronic startup scheme:

• Possibility of starting with any time delay;
• Do not need a massive electromagnetic throttle and a starter;
• Absence of buzzing and blinking of lamps;
• High luminous efficiency;
• Lightness and compactness of the device;
• Longer service life.

Modern electronic ballasts have compact dimensions and low energy consumption. They are called drivers, placing in the socle of a small bulb. Chokeless switching of fluorescent lamps allows the use of conventional standard cartridges.

The electronic ballast system converts the 220 V AC mains voltage into high-frequency. First, LL electrodes are heated, and then a high voltage is applied. At a high frequency, the efficiency is increased and flicker is completely eliminated. The scheme of switching on the fluorescent lamp can provide a cold start or with a smooth increase in brightness. In the first case, the life of electrodes is significantly reduced.

Increased voltage in the electronic circuit is created through the oscillatory circuit, which leads to resonance and ignition of the lamp. The launch is much easier than in the classical scheme with an electromagnetic throttle. Then the voltage also drops to the required discharge retention value.

The voltage is rectified by the diode bridge, after which it is smoothed in parallel with the connected capacitor C ₁ . After connecting to the network, the capacitor C ₄ is immediately charged and the dinistor is broken. The half-bridge generator on the transformer TR ₁ and the transistors T ₁ and T _{2 are started} . When the frequency reaches 45-50 kHz, a resonance is created with the help of a series circuit C ₂ , C ₃ , L ₁ connected to the electrodes, and the lamp is ignited. This circuit also has a choke, but with very small dimensions, allowing it to be placed in the lamp base.

Electronic ballast has an automatic adjustment for LL as the characteristics change. After a while, a worn-out lamp requires an increase in voltage for ignition. In the EmPra scheme, it simply does not start, and electronic ballast is adjusted to change the characteristics and thus allows the device to operate in favorable modes.

Advantages of modern electronic ballasts are as follows:

• Smooth switching;
• Economy of work;
• Preservation of electrodes;
• Exclusion of flicker;
• Working capacity at low temperature;
• Compactness;
• durability.

The disadvantages are a higher cost and a complicated ignition scheme.

Application of voltage multipliers

The method makes it possible to include LL without electromagnetic ballast, but it is used primarily to prolong the life of lamps. The scheme of inclusion of burnt down fluorescent lamps allows them to work for some time, if the power does not exceed 20-40 W. In this case, the filaments can be either whole or burned out. In both cases, the conclusions of each filament must be shorted.

After straightening, the voltage doubles, and the lamp lights up instantly. Capacitors C ₁ , C ₂ are selected for a working voltage of 600 V. Their disadvantage is a large size. Condensers С ₃ , С ₄ establish mica on 1000 V.

LL is not intended for DC power supply. Over time, mercury accumulates around one of the electrodes, and the glow weakens. To restore it, change the polarity by flipping the lamp. You can set the switch to not take it off.

The nonstarter scheme of switching on fluorescent lamps

The scheme with a starter requires a long heating of the lamp. In addition, it sometimes has to be changed. In this connection, there is another scheme with the heating of the electrodes through the secondary windings of the transformer, which also serves as a ballast.

When the fluorescent lamps are switched on without a starter, they must be marked RS (fast start). The luminaire with a starter start here will not work, as its electrodes are longer heated, and the spirals quickly burn out.

How do I turn on a burnt out lamp?

If the helix is out of order, the LL can be ignited without a voltage multiplier, using the conventional EMPRA circuitry. The scheme of inclusion of the burnt out fluorescent lamp slightly changes in comparison with usual. For this, a capacitor is connected in series to the starter, and the electrode pins are short-circuited. After such a small alteration the lamp will work for some time.

Conclusion

The design and the scheme of inclusion of a fluorescent lamp is constantly improved in the direction of economy, reduction of the sizes and increase of service life. It is important to properly operate it, to understand all the variety of produced types and to know effective ways of connection.