LED lighting has been rapidly developed in the near future, and LED has been widely recognized as a clean and clean light source. LED light source has long service life, energy saving, simple and convenient application, and low cost of use. Therefore, it will be used in a large number of home lighting applications. As early as 2008, the annual global sales of home lighting fixtures was about 50 billion.
The technology of LED light source is becoming more and more mature, and the luminous lumen per watt is growing rapidly, which makes it reduce the price every year. The massive market of LED green lamps and the continuous growth and demand for several years will be the super tsunami in the IC industry after the VCD, DVD, mobile phones and MP3s! The high performance, long life and environmentally friendly performance of LED lamps are widely recognized.
1, LED high energy-saving: DC drive, ultra-low power consumption (single tube 0.03~1W) electro-optical power conversion is close to 100%, the same lighting effect is more than 80% energy saving than traditional light source.
2, LED long life: LED light source is called long life light. Solid cold light source, epoxy resin package, there is no loose part in the lamp body, there are no shortcomings such as filament light-emitting, heat deposition, fast light decay, etc. The service life can reach 50,000 to 100,000 hours, which is longer than the traditional light source. More than double.
3, LED environmental protection: LED is a green light source, environmental protection benefits are better. There is no ultraviolet and infrared rays in the spectrum, low heat and no stroboscopic, no radiation, and waste can be recycled, no pollution, no mercury, cold light source, safe touch, is a typical green lighting source.
LED light source working characteristics
The VF voltage of the LED light source for illumination is very low, generally 2.75~3.8V, and IF is generally 15~1,400mA. Therefore, the output voltage of the LED driver IC is VFxN or VFx1, and the IF maintains a constant current of 15 to 1,400 mA. The LED light source used in LED lamps has two types of low power (IF is 15~20mA) and high power (IF is more than 200mA). Small power LEDs are often used to make LED fluorescent lamps, decorative lamps and grille lamps. High-power LEDs are used for home lighting, spotlights, underwater lights, wall washers, street lights, tunnel lights, car work lights, etc. The power LED light source is a low voltage, high current driven device whose luminous intensity is determined by the amount of current flowing through the LED. Excessive current causes the LED light to attenuate. If the current is too small, it will affect the LED's luminous intensity. Therefore, the LED driver needs to provide a constant current power supply to ensure the safety of the use of high-power LEDs while achieving the desired luminous intensity. In the field of LED lighting, in order to reflect the characteristics of LED lamp energy saving and long life, it is very important to correctly select the LED driver IC. Without the matching of good driver ICs, the advantages of LED lighting cannot be realized.
LED luminaires for low voltage driver chips
1. The nominal input voltage range of the driver chip should meet the DC 8~40V to cover a wide range of application needs. The pressure resistance is preferably greater than 45V. When the input is AC 12V or 24V, the output voltage of the simple bridge rectifier will fluctuate with the grid voltage, especially when the voltage is high, the output DC voltage will also be high. If the driver IC does not have a wide input voltage range, it will often be broken down when the grid voltage rises, thus burning the LED light source.
2. The nominal output current requirement of the driver chip is greater than 1.2~1.5A. As an LED light source for illumination, the nominal operating current of a 1W power LED light source is 350 mA, and the nominal operating current of a 3 W power LED light source is 700 mA. A high-power LED light source requires more current. Therefore, the driver IC used in the LED lighting fixture must have sufficient current output. When designing the product, the driver IC must be operated at 70-90% of the optimal working area of ​​the full-load output. Driver ICs that use full-load output currents are not well cooled in the narrow space of the luminaire, which can easily lead to fatigue and early failure of the luminaire.
3. The output current of the driver chip must be kept constant, so that the LED can be stably illuminated without flickering. The same batch of driver chips are used under the same conditions, and the output current should be as uniform as possible, that is, the dispersion is small, so that the production and the order can be ensured in the production of large-volume automated production lines. For the driver chip with a certain discrete output current, it is necessary to select the bin before the factory or put into the production line, adjust the resistance value of the current setting resistor on the PCB, and make the LED lamp constant current drive board to the same kind of LED. The brightness of the light source is uniform to maintain consistency in the final product.
4. The package of the driver chip should facilitate the rapid heat dissipation of the driver chip. For example, the die is directly bonded to the copper board, and a pin extends directly outside the package to facilitate soldering directly on the copper foil of the PCB. Rapid thermal conductivity (figure). If a 300~1,000 mA current is passed for a long time on a 4X4mm chip, power consumption and heat generation will inevitably occur. Therefore, the physical heat dissipation structure of the chip itself is also very important.
Drive IC profile (left) and top view (right)
5, the ability of the driver chip to resist EMI, noise and high voltage is also related to whether the entire LED lighting products can successfully pass CE, UL and other certifications, so the design of the driver chip must use advanced topology and high-pressure production process.
6. The power consumption requirement of the driver chip is less than 0.5W, and the switching operating frequency requirement is greater than 120Hz, so as to avoid visible flicker caused by power frequency interference.
In short, LED green lighting has driven the development of drive chips to innovative designs. LED lighting is inseparable from the driver chip, so a multi-function LED light source driver IC is required. If the LED lamp uses AC power below 36V, non-isolated power supply can be considered; if 220V and 100V AC power supply is selected, isolated power supply should be considered. Direct use of AC 100~220V driver chip, due to the demand for volume requirements, there are higher technical requirements and greater difficulty. At present, countries are working hard to develop.
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