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Electronic Ballast is a kind of ballast, which uses electronic technology to drive the electric light source to produce the required lighting. Corresponding to it is the inductive ballast. More and more modern fluorescent lamps use electronic ballasts, which are light and compact, and people can even integrate electronic ballasts with lamps.
Electronic Ballast is a kind of ballast, which uses electronic technology to drive the electric light source to produce the required lighting. Corresponding to it is the inductive ballast. More and more modern fluorescent lamps use electronic ballasts, which are light and compact, and people can even integrate electronic ballasts with lamps. At the same time, electronic ballasts usually have the function of a starter, so they can save money for a separate starter. Electronic ballasts can also have more functions, such as improving or eliminating the flickering phenomenon of fluorescent lamps by increasing the current frequency or current waveform (such as a square wave). It can also make fluorescent lamps use DC power through the power inversion process.
The electronic ballast is a converter that converts power frequency AC power into high-frequency AC power. Its basic working principle is:
After the industrial frequency power supply passes through a radio frequency interference (RFI) filter, full-wave rectification, and a passive (or active) power factor corrector (PPFC or APFC), it becomes a DC power supply. Through the DC/AC converter, the output of high-frequency AC power of 20K-100KHZ is added to the LC series resonance circuit connected to the lamp to heat the filament, and at the same time, a resonance high voltage is generated on the capacitor, which is applied to both ends of the lamp tube, making the lamp tube from the discharge state to the on state, and then enters the light-emitting state.
At this time, the high-frequency inductance plays a role in limiting the increase of current, ensuring that the lamp tube obtains the voltage and current required for normal operation. Various protection circuits are often added, such as abnormal protection, surge voltage, and current protection, temperature protection, and so on.
It reflects how the combination of ballast and lamp effectively uses the input power of the power supply, which is expressed as Watt/VA or COSΦ in some places. Generally speaking, the PF of inductance ballast is 0.5, and can only reach about 0.8 after capacitance correction. Electronic ballasts can usually achieve 0.95 to 0.99. You can use up every watt of power supplied by the power plant, and it is environmentally friendly.
It refers to the sum of the odd harmonic components in the input power supply current after the lamp reaches a stable working state when the ballast and the lampwork under the rated power supply voltage.
According to Fourier's definition, a rectangular wave is composed of a series of sine waves with a common period but different frequencies. The greater the harmonic content, the greater the damage to the input sine wave.
On the occasions where there are more electronic ballasts, if the THD value is large, it will affect the neutral current of the three-phase AC input, and the neutral current will be too large. Therefore, we generally choose the THD with a cost-performance ratio between 15%-25% when using electronic ballasts on a large scale.
Under the rated power supply voltage, when the ballast works with the lamp, after the lamp reaches a stable working state, the ratio of the peak value of the output current through the lamp to the root mean square value CF=PK/rms. Generally speaking, the smaller the CF value, the more stable the current flowing through the lamp tube, and the longer the lamp tube life. The IEC/GB standard is CF≤1.7.
It's the ability that the equipment or system can work normally in an electromagnetic environment and does not form an unbearable electromagnetic disturbance for anything in the environment.
There are different implementation standards in Europe and America.
● lFCC (USA Standard ClassA; ClassB)
● lCISPR (International Electrotechnical Commission CISPR15)
● lEN55015 (European Standard).
When the user is using a standard ballast, its peripheral electronic equipment will not be interfered with, such as electronic computers, wireless phones, and some professional electronic equipment.
1. Energy-saving. The fluorescent ballast is of the frequency of 20-60khz to supply the lamp tube so that the luminous efficiency of the lamp tube is about 10% higher than that of the power frequency(assume the tube length is 4 feet). Its own power consumption is low so that the total input power of the lamp is reduced by about 20%, which has a better energy-saving effect.
2. Eliminate strobe flash and make light emission more stable. The electronic ballast can improve visual resolution and efficiency. It can also reduce visual fatigue after continuous operation, which can protect our eyesight.
3. The starting point is more reliable. After the starter successfully started after preheated once, avoiding starting several times.
4. High power factor. Fluorescent lamps above 25W that meet the national standards have a power factor higher than 0.95. However, it should be noted that the national standards set a high harmonic limit for lamps below 25W, so that its power factor drops to 0.7-0.8.
5. Stable input power and output luminous flux. High-quality electronic ballasts have good voltage stabilization performance. When the power and voltage deviations are large, the light source can still maintain constant power and stabilize the illuminance, which is conducive to energy saving.
6. Extend lamp life. The constant power of high-quality products, the decrease of lamp current, and the reliable starting point can extend the lamp life.
7. Low noise. The noise of high-quality electronic ballast can reach below 35db, which people can't feel at all.
8. It can be dimmed. For places that need dimming, such as those that originally used incandescent lamps or tungsten halogen lamps for dimming, replace them with high-efficiency fluorescent lamps with dimmable electronic ballasts, which can achieve wide-range dimming from 2% to 100%.
Figure 1. Dimmable Electronic Ballast
It should be noted that only well-designed electronic ballasts can play the above advantages. Although they are all electronic ballasts, the electronic ballasts used for metal halide lamps are much more complicated than those used for fluorescent lamps, or almost completely different. If the design or manufacturing process is not appropriate, a very small omission will cause failure.
1. Special tows one and tows two electronic ballasts for lightboxes are specially designed for outdoor lightboxes and billboards. Their advantages are as follows:
1) Safe operation process, high insulation performance, and good waterproof and moisture-proof performance. The low-temperature rise of the ballast will not affect the lightbox cloth or lightbox sheet to turn yellow due to the heat.
2) Convenience:
● It can be directly plugged into the bare pin without connecting and installing the terminal;
● There is a sponge sticker attached to the bottom of the ballast, which can fix the ballast;
● It's equipped with a metal buckle, and the lamp can be fixed without the lamp holder;
● It can save the trouble of frequently replacing the starter.
figure 2. Lightbox Electronic Ballast
2. Tows one and Tows two ordinary electronic ballasts are suitable for the installation and replacement of lamps in various general lighting occasions;
3. Ring light electronic ballast is specially designed for ring lights. It is suitable for installation in ceiling lamps, such as home balcony lighting, walkway lighting, staircase channel lighting, and other public place lighting.
4. Quartz germicidal lamp ballast is specially designed for 35W-60W low-pressure quartz germicidal lamps. The downlights with it have a long life (4 times that of incandescent lamps), high brightness, constant color temperature, and small size. It can be used for general lighting in shops, display windows, exhibition halls, jewelry stores, bars, museums, specialty stores, etc., or accent lighting in special areas.
Electronic ballasts have obvious advantages in improving the energy efficiency and quality of lighting systems, which are the trend of future development. So how do we use it correctly? Here are some matters that should be noted during the operation.
1. In continuous and intense visual workplaces and places with high requirements for visual conditions (such as design, drawing, typing, etc.), and in places that require particularly quiet (patient rooms, consulting rooms, etc.) and places where the youth often stay(classrooms, reading rooms, etc.), the electronic ballasts should be used first.
2. In places where dimming is required, tri-color fluorescent lamps can be equipped with dimmable digital ballasts to replace incandescent lamps or halogen lamps, which can greatly improve energy efficiency.
Figure 3. Dimmable Digital Ballast
3. High-quality, low-harmonic products should be selected. We should not focus too much on the prices, the technical requirements for use should be met, and we should also consider the operation and maintenance effects and make a comprehensive comparison.
4. When using fluorescent lamps less than 25W, as mentioned above, the harmonic limit specified by the GB19625.1-2003 standard is very wide. If a large number of applications are used in a building, it will cause a variety of undesirable consequences. Effective measures should be taken to limit the design.
5. The selected product should not only examine its total input power but also understand its output luminous flux. According to regulations, the lumen coefficient (μ) of the ballast should not be lower than 0.95. The European Union stipulates the energy efficiency grade of the ballast and accordingly stipulates the lumen coefficient μ≥0.96.
Matters needing attention when choosing
(1) Pay attention to the harmonic content. Users should pay attention to that the harmonic limits of lamps below 25W are very loose. If a large number of such low-power fluorescent lamps (including T8, T5 lamps, and compact fluorescent lamps with a length of 2 feet) are used in a building, there will be undesirable consequences such as serious waveform distortion, excessive neutral wire current, and reduced power factor.
(2) Pay attention to product quality and level. There are many electronic ballasts on the market, and the quality and level are quite different. Some of them have large harmonic content, low lumen coefficient, low reliability, and short service life. Although these products are low in price, they're easy to cause undesirable consequences while used, which are not recommended.
This dimming control method uses the pulse duty cycle of the power switch in the high-frequency inverter to adjust the output power. The maximum duty cycle of the half-bridge inverter is 0.5 to ensure the two switch tube has a dead time to avoid the two switch tubes conduct at the same time and get damaged.
Problems of Duty Cycle Dimming Method
If the inductor current is continuous and lags behind the half-bridge voltage Uxy, the switch may work in a zero voltage state when it is turned on. Therefore, an absorption capacitor needs to be used to reach the zero current switchings (ZCS) working condition at the moment of turning off, so that it can enter zero voltage switching(ZVS) working mode, and the EMI and switch tube stress can be significantly reduced.
However, if the duty cycle is too small, and the inductor current is discontinuous, the ZVS operating characteristics will be lost, and the stress on the switch tube will increase due to the high DC voltage of the power supply. This discontinuous current conduction state will reduce reliability and increase EMI radiation.
In addition, when the lamp fails, there will also be a discontinuous current working state. When there is an open-circuit fault on the lamp, the inductive current will flow through the resonant capacitor. Because the capacitance of this capacitor is small, the impedance is relatively large. Unless the two switching tubes are protected by an absorption circuit, they will withstand great voltage stress.
Frequency modulation dimming is also a commonly used dimming method. If the switching frequency of the high-frequency AC electronic ballast increases, the impedance of the inductor increases, so that the inductor current will decrease.
Limitations of FM dimming method
(1) The dimming range is determined by the frequency modulation range. If the frequency modulation range is not large, the power adjustment range is not large.
(2) In order to realize dimming under low power working conditions, the frequency modulation range should be very wide (that is, from 25KHZ--50KHZ). The frequency range of the magnetic core, drive circuit, and control circuit may limit the dimming range.
(3) It is not easy to achieve soft switching in the entire frequency modulation range. When the load is light, the soft switch cannot be realized, and the voltage stress on the switch tube is increased. The transient transition of hard switching is the main source of EMI radiation.
Figure 4. Soft Switching
(4) If the half-bridge inverter does not work in the soft-switching state, the loss of the inverter will increase and the efficiency will decrease.
(5) When the switching frequency is within the frequency range of the infrared remote control, the fluorescent lamp will emit low-level infrared. If the frequency modulation range is large, other infrared remote control devices such as televisions will be affected.
(6) The lamp current is approximately inversely proportional to the inverter switching frequency, and the relationship between dimming and switching frequency is not linear.
(7) When the lamp has an open circuit fault, the discontinuous conduction mode(DCM) working state will appear, especially when the switching frequency is very low.
This method has the following advantages:
(1) Adjust the power supply voltage of the half-bridge inverter to achieve dimming.
(2) Use a fixed duty cycle (about 0.5) method, making the half-bridge inverter work in a wide dimming range with continuous soft-switching inductor current (this can also simplify the switching control circuit).
(3) Since the switching frequency is fixed, the control circuit design can be simplified for a given lamp model.
(4) Since the switching frequency is just greater than the resonant frequency, reactive power can be reduced and the work efficiency improved.
(5) Because the switching frequency is fixed, the parameters of passive components can be determined more conveniently.
(6) Can maintain ZVS working conditions in a wide range of lamp powers (5%-100%).
(7) At a very low half-bridge inverter supply voltage, the soft switching characteristics will be lost, and a discontinuous working state of inductor current will occur. However, when the DC power supply voltage is very low, this working state is no longer a problem. At this time, the stress and loss of the switch tube will be very small, even if the hard switching is under low DC power supply voltage (such as 20V), there will be not too much EMI radiation.
(8) Can achieve smooth and almost linear lamp power control characteristics.
(9) A low-power solution can be obtained. The power supply voltage of the half-bridge inverter can be very low (such as 5%-100% dimming range corresponding to 30-120V), so that low-voltage capacitors and MOSFETs can be used.
(10) The dimming control is only realized by controlling the output voltage of the SEPIC converter. Since the half-bridge inverter works in a constant frequency state, simple AC/DC control can be used to achieve dimming.
(11) The lamp current is approximately proportional to the voltage of the DC converter, and the dimming is almost proportional to the output DC voltage of the SEPICDC converter.
The output power is adjusted by adjusting the conduction phase of the two switching tubes in the half-bridge inverter, so as to achieve the purpose of output dimming.
The phase-controlled dimming method mainly has the following characteristics:
(1) Dimmable to 1% of the original;
(2) It can be started at any dimming setting;
(3) It can be used in multi-lamp applications;
(4) The dimming phase lamp has a good power relationship.
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