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As an important part of LED fluorescent tubes, switching power supplies are divided into two types: isolated power supplies and non-isolated power supplies.
Isolated power supply means that the input and output have transformer isolation, which can isolate the input and output and have high security. Due to the addition of the isolation transformer, the efficiency of the power supply will be reduced, usually around 85%, and the size of the transformer is relatively large, and it will be quite tight when placed inside the lamp.
A non-isolated power supply means that there is a direct electrical connection between the input and the output, so there is a risk of electric shock in the touch output. At present, more non-isolated step-down power supplies are used, that is, AC current is rectified to obtain DC high voltage, and then Buck circuit is used for buck and constant current control.
The characteristics of the non-isolated power supply are: simple circuit and small volume; usually the efficiency is between 88-90%; the high voltage can be output to support hundreds of LEDs through different series and parallel strings. However, such non-isolated power supplies are also limited because non-isolated power supplies can direct the high voltage of the AC power source to the output section, posing a risk of electric shock. Usually, the AC input is insulated from the printed circuit board by the printed circuit board. Although this withstand voltage can be 2000V, it is still difficult to pass CE and other safety certifications.
Comprehensive comparison, these two power sources have their own advantages, non-isolated power supply focuses on efficiency, reducing energy consumption, while isolated power supply pays attention to safety, and is slightly inferior to non-isolated power supply in terms of efficiency, so different choices are also different. Although the scheme of isolated power supply can simplify the design of heat dissipation and lampshade, because of the small size, high efficiency, low cost and high cost performance of non-isolated power supply, people still use non-isolated power supply more, preferring the structure and lamp housing of the lamp. Work hard.
With the T8 LED fluorescent tube, the power supply can be built-in and external. The biggest advantage of the built-in type is that it can directly replace the existing fluorescent tube without any modification. The built-in power supply can be divided into two cases:
The first is to make a growing strip power board, placed in the aluminum casing of the lamp, because the temperature of the lamp beside the power supply and the power supply will be very high, seriously affecting the life of the power supply and the lamp bead, so it is not considered here; The two-stage power supply is divided into two circuit boards which are respectively placed in the lamp caps at both ends of the lamp tube. The two-stage power supply is relatively complicated due to the narrow space of the lamp cap.
Based on the above considerations, the two-stage power supply scheme with built-in non-isolation method is an ideal choice for T8 LED fluorescent tubes. The goal is to achieve the following parameters and performance: input voltage range 85V-265Vac, power factor >0.9, power efficiency >90%, insulation voltage between the AC input and the aluminum casing is 3000Vac, can meet the relevant EMC standards, can pass CE and UL certification requirements.
For more information, please refer to the May issue of "High- tech LED- Technology and Applications" magazine. 
LED fluorescent tube drive power solution
[Source: "Engineering LED- Technology and Application" May issue of Sun Dong Wu Yaqiong At present, LED lighting used in daily becoming increasingly popular, from outdoor lighting to indoor lighting, can see the footprints of LED lighting products, LED energy saving It is also an important member of indoor lighting applications because of its long life and power saving.