Cold cathode fluorescent tubes relevant principles
2015/12/15 view:
And "cold" and "hot", as usual electron-emitting material, namely the
cathode, cold and heat are two points we usually understand.
Hot cathode current mode refers to the cathode when heated to temperatures above 800C for electronic cathode within the due obtained after converting thermal energy into kinetic energy and emitted outside;
Cold cathode means without heating the cathode, but the use of an electric field to control the potential change in the interface, so that the cathode within the electronic potential energy is converted to kinetic energy of the emitted outwards.
Two kinds of cathode biggest feature is that you can use a hot cathode low voltage electron emission can be generated, and the cold cathode often need to produce a high voltage electron emission.
Hot cathode life is relatively short, relatively long lifetime of the cold cathode. Therefore, in the CCFL, and often use a cold cathode.
CCFL principle should be applied when the high pressure in the tube ends, resulting in secondary electron emission electron minority after high-speed crash inside the tube electrodes to start discharge, due to the lower cathode temperature, so named.
Secondary electron emission cathode is an important process CCFL.
Glow discharge, the Townsend ionization coefficient is ion bombardment third secondary electron emission coefficient at the cathode surface, the process is generally the cathode surface ions in the Auger neutralization process (Auger neutralization of an ion), also known as Hagstrum theory (see: Homer D. Hagstrum, "Theory of Auger Ejection of Electrons from Metals by Ions," Phys Rev. 96, (1954) 336-365.).
When the positive ions move to the cathode surface of the cathode material free electron recombination, while the release of ionizing energy; in other post-cathode electron obtain the ionization energy to overcome the surface barrier but outward from the cathode emission, which is called the Second secondary electron emission, field emission is an indirect process. At the same time, positive ions will form a positive ion cloud near the cathode surface area, the positive ion cloud relative to the cathode as a positive electric field is applied, it is also a direct field emission. So, CCFL which can use DC drives, AC drives can also be used.
Cold cathode discharge surface process is extremely complex.
1 . About the cold cathode tubes, whether hot or cold cathode tube cathode tube, it is the principle on terms of a fluorescent tube fluorescent tube emitting the same general principle. It ran from the electrode to the electron impact of mercury (xenon may also be used), to release the mercury UV excitation, the ultraviolet radiation to the fluorescent coating on the inside of the glass tube body become visible.
A big difference between the cold cathode tubes and hot cathode tubes is the electrode portion. Simply because of the cold cathode tube structure, it can be very thin fluorescent tubes. Since the electron emission electrode is not hot electron emission, it is referred to as a cold cathode tube (ColdCathodeFluorescentLamp, cold cathode fluorescent lamp).
2 . Applications of the cold cathode tubes and hot cathode tube
Hot-cathode tube can not be due to the construction of its electrode miniaturization, it is not suitable for thin fluorescent tubes. Therefore, the heat pipes are mainly used in high-power cathode fluorescent tube. General lighting with fluorescent tubes almost all this. On the other hand, the cold cathode tube due to the fine pattern having the characteristics, mainly used for liquid crystal back light (backlight). Moreover, lately you can see the color of the cold cathode tubes used in automotive and other decorations, by everyone's attention. If you see through the car from the side in blue or purple decorations, it is a cold cathode tube. In addition, compared with the hot cathode tube, a cold cathode tube has a long life, small size and low power features that are living for ordinary light and so on, the increasingly widespread use.
3. Heat the cold cathode tube is misunderstood: usually think of the cold cathode tube cathode cooler, so the heat generated at the cathode may be relatively small. This is a great mistake, heat the cold cathode tube cathode occurred much more than a hot cathode tube of the same power. A cold cathode tube and hot cathode tube internal voltage gradient as shown in Fig. Here, note that the voltage drop is intended cathode arc column is reduced. Regardless of the cold cathode tube or a hot cathode tube, actually consume into light energy portions are part of the arc column. Since the cathode voltage drop is not used for the light emitting portion, so that all energy is converted into heat are wasted. The cathode voltage drop on a hot cathode tube is small, and in the cold-cathode tube large. Namely: the efficiency of the cold cathode tube lower than the hot-cathode tube. Cold-cathode tube useless energy consumption in the vicinity of the cathode, as a result, "cold" cathode tube is hot electrode. Thus, using a cold cathode tube design of the machine, pay attention to make good heat near the cathode.
4. Electrical characteristics of the cold cathode tubes
Because of the cold cathode tube cathode voltage drop is large, in order to improve efficiency, so increasing the arc column (Japanese: the sun column) impedance values, can make the most of the actual energy consumption in the visual light. As a result, the tube current becomes smaller, the resistance value (impedance) increases. Chart 2 backlight lamp current -? Tube impedance characteristic impedance of the cold cathode tube if you want to use the notebook computer, typically 5 0KΩ 2 00KΩ. When compared with this, a hot cathode tube used in general lighting as 2 00KΩ? About 1KΩ. If the tube current increases, the resistance value is drastically reduced, and there is a negative impedance characteristic. Cold cathode tube discharge voltage laptops with generally about 700V. When the hot-cathode tube of about 70V to 140V. Tube high voltage cold cathode tube lamp impedance (resistance) is high, it will be strongly affected by stray capacitance.
Impedance Generally, the cold cathode tube (impedance) (tube voltage / tube current) to the tube current --5 / proportional to the fourth power, which is well known. In addition, the minute current field of tube voltage is known to be the starting voltage, or voltage lighting. Lighting voltage in the sense that once the cold cathode tube if not placed such a high voltage condition is not discharged, but there are still great cold cathode tubes questions. This is because the cold cathode tube assembly after the backlight, this feature will be a big change.
Hot cathode current mode refers to the cathode when heated to temperatures above 800C for electronic cathode within the due obtained after converting thermal energy into kinetic energy and emitted outside;
Cold cathode means without heating the cathode, but the use of an electric field to control the potential change in the interface, so that the cathode within the electronic potential energy is converted to kinetic energy of the emitted outwards.
Two kinds of cathode biggest feature is that you can use a hot cathode low voltage electron emission can be generated, and the cold cathode often need to produce a high voltage electron emission.
Hot cathode life is relatively short, relatively long lifetime of the cold cathode. Therefore, in the CCFL, and often use a cold cathode.
CCFL principle should be applied when the high pressure in the tube ends, resulting in secondary electron emission electron minority after high-speed crash inside the tube electrodes to start discharge, due to the lower cathode temperature, so named.
Secondary electron emission cathode is an important process CCFL.
Glow discharge, the Townsend ionization coefficient is ion bombardment third secondary electron emission coefficient at the cathode surface, the process is generally the cathode surface ions in the Auger neutralization process (Auger neutralization of an ion), also known as Hagstrum theory (see: Homer D. Hagstrum, "Theory of Auger Ejection of Electrons from Metals by Ions," Phys Rev. 96, (1954) 336-365.).
When the positive ions move to the cathode surface of the cathode material free electron recombination, while the release of ionizing energy; in other post-cathode electron obtain the ionization energy to overcome the surface barrier but outward from the cathode emission, which is called the Second secondary electron emission, field emission is an indirect process. At the same time, positive ions will form a positive ion cloud near the cathode surface area, the positive ion cloud relative to the cathode as a positive electric field is applied, it is also a direct field emission. So, CCFL which can use DC drives, AC drives can also be used.
Cold cathode discharge surface process is extremely complex.
1 . About the cold cathode tubes, whether hot or cold cathode tube cathode tube, it is the principle on terms of a fluorescent tube fluorescent tube emitting the same general principle. It ran from the electrode to the electron impact of mercury (xenon may also be used), to release the mercury UV excitation, the ultraviolet radiation to the fluorescent coating on the inside of the glass tube body become visible.
A big difference between the cold cathode tubes and hot cathode tubes is the electrode portion. Simply because of the cold cathode tube structure, it can be very thin fluorescent tubes. Since the electron emission electrode is not hot electron emission, it is referred to as a cold cathode tube (ColdCathodeFluorescentLamp, cold cathode fluorescent lamp).
2 . Applications of the cold cathode tubes and hot cathode tube
Hot-cathode tube can not be due to the construction of its electrode miniaturization, it is not suitable for thin fluorescent tubes. Therefore, the heat pipes are mainly used in high-power cathode fluorescent tube. General lighting with fluorescent tubes almost all this. On the other hand, the cold cathode tube due to the fine pattern having the characteristics, mainly used for liquid crystal back light (backlight). Moreover, lately you can see the color of the cold cathode tubes used in automotive and other decorations, by everyone's attention. If you see through the car from the side in blue or purple decorations, it is a cold cathode tube. In addition, compared with the hot cathode tube, a cold cathode tube has a long life, small size and low power features that are living for ordinary light and so on, the increasingly widespread use.
3. Heat the cold cathode tube is misunderstood: usually think of the cold cathode tube cathode cooler, so the heat generated at the cathode may be relatively small. This is a great mistake, heat the cold cathode tube cathode occurred much more than a hot cathode tube of the same power. A cold cathode tube and hot cathode tube internal voltage gradient as shown in Fig. Here, note that the voltage drop is intended cathode arc column is reduced. Regardless of the cold cathode tube or a hot cathode tube, actually consume into light energy portions are part of the arc column. Since the cathode voltage drop is not used for the light emitting portion, so that all energy is converted into heat are wasted. The cathode voltage drop on a hot cathode tube is small, and in the cold-cathode tube large. Namely: the efficiency of the cold cathode tube lower than the hot-cathode tube. Cold-cathode tube useless energy consumption in the vicinity of the cathode, as a result, "cold" cathode tube is hot electrode. Thus, using a cold cathode tube design of the machine, pay attention to make good heat near the cathode.
4. Electrical characteristics of the cold cathode tubes
Because of the cold cathode tube cathode voltage drop is large, in order to improve efficiency, so increasing the arc column (Japanese: the sun column) impedance values, can make the most of the actual energy consumption in the visual light. As a result, the tube current becomes smaller, the resistance value (impedance) increases. Chart 2 backlight lamp current -? Tube impedance characteristic impedance of the cold cathode tube if you want to use the notebook computer, typically 5 0KΩ 2 00KΩ. When compared with this, a hot cathode tube used in general lighting as 2 00KΩ? About 1KΩ. If the tube current increases, the resistance value is drastically reduced, and there is a negative impedance characteristic. Cold cathode tube discharge voltage laptops with generally about 700V. When the hot-cathode tube of about 70V to 140V. Tube high voltage cold cathode tube lamp impedance (resistance) is high, it will be strongly affected by stray capacitance.
Impedance Generally, the cold cathode tube (impedance) (tube voltage / tube current) to the tube current --5 / proportional to the fourth power, which is well known. In addition, the minute current field of tube voltage is known to be the starting voltage, or voltage lighting. Lighting voltage in the sense that once the cold cathode tube if not placed such a high voltage condition is not discharged, but there are still great cold cathode tubes questions. This is because the cold cathode tube assembly after the backlight, this feature will be a big change.
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