CR2450 battery.Commonly used filament preheating circuits for fluorescent lamps

Commonly used filament preheating circuits for fluorescent lamps - Abstract: Electronic ballasts have been widely used due to a series of advantages such as energy saving, flicker-free lighting and easy implementation of networked control (such as the relevant requirements of IEC929 Appendix E). If fluorescent lamps use appropriate filament preheating methods,

Abstract: Electronic ballasts have been widely used due to a series of advantages such as energy saving, flicker-free lighting and easy implementation of network control (such as the relevant requirements of IEC929 Appendix E). If fluorescent lamps use appropriate filament preheating methods, it will play a very important role in improving the life of fluorescent lamps. Several commonly used fluorescent lamp filament preheating methods and characteristics are introduced.

1Commonly used lighting methods and characteristics

Commonly used electric light sources mainly include thermoluminescent light sources, gas discharge luminescent light sources, and solid luminescent light sources.

Thermoluminescent light sources, such as incandescent lamps, use Snephant-Boltzmann's law, that is, the higher the temperature of an object, the greater the energy it radiates. This can be expressed by equation (1).

E=μ×ξ×T4 (1)

In the formula: E is the total infrared radiation energy per unit area and unit time of the object at temperature T; Figure 1μ is the Snephan-Boltzmann constant (μ=5.6697×10-12W/cm2·K4), ξ is the specific emissivity, which is the ratio of the radiation power of the object surface to the radiation power of the black body;

T is the absolute temperature of the object.

Electric light sources based on the principle of thermoluminescence are simple to make and low in cost, but their luminous efficiency is low, only about 11%, and the rest of the energy is consumed in the form of heat (infrared and thermal energy consumption account for 69% and 20% respectively) . Figure 2: Solid light-emitting light sources, such as light-emitting diodes, plasma light-emitting devices, etc., although they have high luminous efficiency, they are not yet capable of high power (such as hundreds of watts). Therefore, there is still time for solid-state light-emitting devices to enter the stage of large-scale practical use. some distance.

Gas discharge light-emitting devices, such as fluorescent lamps (Florescent), metal halide lamps (Hilide), high-intensity discharge lamps (HID), etc., have luminous efficiency several times that of ordinary incandescent lamps. Because the power of gas discharge lamps can be larger (up to kilowatts) and the luminous efficiency is high, they are a green lighting source. Among them, fluorescent lamps are low-pressure mercury gas discharge lamps filled with argon gas. Their luminous efficiency and lifespan are higher than those of incandescent lamps. The luminous efficiency of fluorescent lamps is about 23%, and infrared and thermal energy account for 36% and 41% of the total energy consumption. Fluorescent lamps emit uniform light, moderate brightness, and soft light color. They are ideal indoor lighting lamps and have been widely used in lighting. Fluorescent lamps ignite thin mercury vapor in the lamp tube to perform arc discharge. The mercury ions are stimulated to produce ultraviolet rays, which excite the phosphor coating on the inner wall of the lamp tube to emit visible light. However, due to the negative resistance characteristics of fluorescent lamps, ballast devices must be used when using them. 2 About the filament preheating of fluorescent lamps

The International Electrotechnical Commission standard IEC929 and my country's professional standard ZBK74012-90 both state that when electronic ballasts are used under normal circumstances, the lamp should be started without causing damage to the lamp performance; the minimum time for applying the cathode preheating voltage The time should not be less than 0.4s" and "the crest factor of the open circuit voltage shall not exceed 1.8; during the minimum preheating period, even an extremely narrow voltage peak that does not affect the effective value shall not be generated" and other regulations.

Preheated start means that the lamp is triggered after the lamp cathode is heated to thermionic emission temperature. Usually, the cathode current is controlled for preheating or the cathode voltage is controlled for preheating. No matter which method is used to start, the following requirements should be met:

1) Before the lamp cathode reaches the electron-emitting state, the open-circuit voltage between the lamp terminals or between the lamp and the starting aid should be kept below the level of glow discharge that would cause damage to the cathode; 2) After the cathode reaches the emitting state , the open circuit voltage should be high enough to enable the lamp to start quickly without having to repeat it many times;

3) When the cathode is already in the emitting state, if the open circuit voltage must rise before the lamp can be started, the transition of the open circuit voltage from low to high must be completed while the cathode is still at the thermionic emission temperature;

4) During the cathode preheating stage, the preheating current or preheating voltage must not be too large or too high to cause damage to the emitting material on the cathode due to overheating.

Lamp cathode preheating start can be divided into the following two situations.

2.1 Filament preheating by controlling lamp cathode current

2.1.1 Effective preheating current and emission time (te)

The heat required to reach the minimum emission temperature of a certain type of cathode can be expressed by time, current and a constant determined by the physical characteristics of the cathode. This relationship can be expressed by equation (2).

In the formula: te is the time to reach the emission state, ≥0.4s (1);

a is a constant for a specific type of cathode;

ik is the minimum effective filament preheating current (A) required to obtain te;

im is the absolute value of the minimum filament current required to reach the emission state (A) (2);

Note: (1) The preheating time to reach the emission state is usually less than 0.4s. Practice has proved that the cathode filament cannot always be fully preheated within this time.

(2) This value assumes that the filament preheating current is applied for a long enough time from the cold state (such as ≥30s).

2.1.2 Maximum effective preheating current

A large effective filament preheating current can be applied in a short period of time (t≤0.4s) without damaging the cathode, but after exceeding 0.4s, as time goes by, this current value should gradually decrease until it reaches 2s or For longer periods of time, this value must not significantly exceed the value for starting with a glow starter at 50Hz.

Illustrations of the above requirements are shown in Figures 1 and 2.

2.1.3 Open circuit voltage and switching time ts During the starting process of the lamp, when the open circuit voltage is increased at te and the cathode preheating process ends at te (the preheating current is interrupted), the switching time of the open circuit voltage ts Should be ≤100ms (as shown in Figure 2).

In the case where the cathode always maintains the emitting state during the switching time of the open circuit voltage, the switching time ts can be >100ms.

Since the lamp cathode is heated to the emitting state when the preheating time reaches te, the effective preheating current must not decrease below the absolute minimum value (im) during the lamp startup transition period to ensure that the lamp cathode is in the emitting state.

Some types of lamps stipulate that the maximum value of the open-circuit voltage before reaching te is higher than or equal to the minimum value of the open-circuit voltage after reaching te. Therefore, the ballast designed for this type of lamp does not need to increase the open circuit voltage in order to make the lamp start reliably. Voltage.

2.2 Use ballasts that control lamp cathode voltage for preheating

2.2.1 Root mean square voltage and voltage application time

When the cathode voltage exceeds 3.0V (low-resistance cathode) or 6.0V (high-resistance cathode), and the voltage is applied for ≥0.4s, the cathode emission temperature can be reached.

In order to prevent the cathode temperature from being too high, the maximum value of the applied voltage should be specified. When the applied voltage is greater than 10V, transverse arc discharge will occur at both ends of all cathodes.

2.2.2 Open circuit voltage

Before reaching the cathode thermionic electron emission, if the open circuit voltage of the lamp is lower than the value for cold start, it is allowed to apply the cathode preheating voltage and the lamp voltage simultaneously. Although electronic ballasts can provide a variety of voltage control methods, all should adhere to the principle of maintaining the lamp voltage below the lamp cold start level before reaching hot start.

The maximum effective preheating current of the filament shall not exceed the specified maximum value at any time during the preheating process, and the preheating time shall be ≥0.4s.

2.2.3 Requirements for ballasts

The ballast should provide the required cathode preheating voltage, cathode operating voltage and lamp starting voltage to the lamp.

The ballast should provide the starting voltage to the lamp at the specified value. The starting voltage can be applied simultaneously with the cathode preheating voltage, or it can rise to this value after an interval of 0.4s. But any voltage applied before 0.4s must be below the voltage level that causes the lamp to activate.

The change rules between the preheating, ignition and fluorescent lamp operation of a good-performing electronic ballast and the change of the electronic ballast operating frequency are shown in Figure 3. The relationship curve between the electronic ballast's preheating, ignition and fluorescent lamp work and the operating frequency is shown in Figure 4.

3 Filament preheating methods and characteristics of several commonly used fluorescent lamps

3.1 Single lamp filament current preheating type

The single-lamp filament current preheating circuit structure is shown in Figure 5. In this filament preheating circuit, the filament is preheated by utilizing the current passing between the filament and the starting capacitor during circuit preheating. It has the characteristics of simple circuit and easy implementation, and is widely used in practice.

3.2 Single lamp filament voltage preheating type

The single-lamp filament voltage preheating circuit structure is shown in Figure 6. In this filament preheating circuit, the voltage on the two filament windings wound together with the ballast inductor (L) is used to achieve filament preheating. The characteristic is that during the entire working process of the lamp, voltage is applied to both ends of the filament.

3.3 Double lamp series filament voltage preheating type

The structure of the dual-lamp series filament voltage preheating circuit is shown in Figure 7. In this filament preheating circuit, the voltage on the three filament windings (L) wound together with the ballast inductor is used to achieve filament preheating. The characteristic is that during the entire working process of the lamp, voltage is applied to both ends of the filament, and the current through the middle filament winding (L) should be twice the filament current of the upper and lower filament windings (L).

3.4 Double lamp series filament current preheating type

The structure of the double-lamp series-connected filament current preheating circuit is shown in Figure 8. In this filament preheating circuit, the secondary voltage on a filament transformer (T2) in series with the ballast capacitor is used to achieve filament preheating.

3.5 Double lamp parallel filament current preheating type

The dual-lamp parallel filament current preheating circuit is shown in Figure 9. The working principle of the circuit is the same as that of the single lamp filament current preheating circuit. 3.6 Double lamp parallel balancing transformer filament preheating type

The structure of the dual-lamp parallel balanced transformer filament preheating circuit is shown in Figure 10. A balancing transformer (T) is used in the circuit to preheat the filament. The working principle of the circuit is the same as that of the single-lamp filament voltage preheating circuit. The characteristic of the circuit is that the balancing transformer in the circuit can make the operating current of the two lamps consistent. 3.7 Double lamp parallel filament voltage preheating type

The dual-lamp parallel filament voltage preheating circuit is shown in Figure 11. The working principle of the circuit is the same as that of the single lamp filament voltage preheating circuit. 4 Conclusion

This article mainly discusses the preheating of fluorescent lamps, the main technical requirements for preheating and several main filament preheating circuits and characteristics. Since the filament preheating of fluorescent lamps plays an important role in improving the life of the fluorescent lamp, this article has certain practicality. significance.
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