The technology of LED light source is becoming more and more mature, and the luminous luminous per watt is growing rapidly, prompting it to decrease its price year by year. Taking the 1W led light source as an example, the price in the spring of 2008 was already one-third of the price in the spring of 2006, and the spring of 2009 will be reduced to a quarter of the price in 2006. The massive market of LED green lamps and the continued steady growth in demand for several years will be the super tsunami in the consumer electronics market after VCD, DVD, mobile phones, MP3 in the integrated circuit industry!
The superior performance of LED lamps with high energy saving, long life, and environmental protection is widely recognized.
LED high energy saving: DC drive, ultra low power consumption (single tube 0.03 watt-1 watt) electro-optic power conversion is close to 100%, the same lighting effect is more than 80% energy saving than traditional light sources. Led long life: LED light source is called long life lamp. The solid cold light source is encapsulated with epoxy resin, and there is no loose part in the lamp body. There are no shortcomings such as easy burning of the filament, thermal deposition, and fast light decay.
LED lifespan : The service life can reach 50,000 to 100,000 hours, which is more than 10 times longer than the traditional light source.
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, no strobe, no radiation, and waste can be recycled, no pollution does not contain mercury, cold light source, can be safely touched, it is a typical green lighting source.
Working characteristics of led light source The VF voltage of the led light source for lighting is very low, generally VF = 2.75-3.8V, IF is 15-1400mA; so the output voltage of the LED driver IC is VF XN or VF X 1, IF constant current is 15- 1400mA. There are two types of LED light sources: low-power (IF = 15-20mA) and high-power (IF》 200mA). Low-power LEDs are mostly used for led fluorescent lamps, decorative lights, and grille lamps; high-power LEDs are used for Home lighting, spotlights, underwater lights, wall washer lights, street lights, tunnel lights, car work lights, etc. Power LED light source is a device driven by low voltage and large current. The intensity of its light emission is determined by the current flowing through the LED. Too much current will cause the attenuation of the led light. Too weak current will affect the luminous intensity of the led. The drive needs to provide a constant current power supply to ensure the safety of high-power LEDs while achieving the ideal luminous intensity. In the field of led lighting, to reflect the characteristics of energy saving and long life, it is very important to choose a good LED driver IC. Without good driver IC matching, the advantages of led lighting cannot be reflected. The technical details of LED lighting design need to pay attention to the requirements of LED lamps for low-voltage driver chips:
1. The nominal input voltage range of the driver chip should meet DC8-40V to cover the needs of the application. It is better if the withstand voltage can be greater than 45V; the output voltage of a simple bridge rectifier with AC 12V or 24 V input will vary with the grid voltage Fluctuation, especially when the voltage is too high, the output DC voltage will be too high. If the driver IC cannot adapt to a wide voltage range, it will often be broken down when the grid voltage rises, and the LED light source will be burned.
2. The nominal output current of the driver chip is required to be greater than 1.2-1.5A. As the LED light source for lighting, the nominal operating current of 1W power led light source is 350mA, and the nominal operating current of 3W power led light source is 700mA, power Larger ones require more current, so the driver IC selected for LED lighting must have sufficient current output. When designing the product, the driver IC must work in the optimal working area of ​​70-90% of the full negative output. Driver ICs that use full and negative output currents do not dissipate heat easily in the narrow spaces of lamps, and are prone to fatigue and early failure.
3. The output current of the driver chip must be constant for a long time, the LED light source can emit light stably, and the brightness will not flicker; the same batch of driver chips used under the same conditions, the output current size should be as consistent as possible, that is, the dispersion should be small, so Only large-volume automated production lines can be effective and orderly; for driver chips with a certain output current discreteness, they must be selected at the factory or before the production line, and the resistance value of the current setting resistance (Rs) on the PCB board is adjusted to make The constant current driving board of the led lamps produced has the same luminous brightness to the similar led light sources, and maintains the consistency of the final product.
4. The package of the driver chip should be conducive to the rapid heat dissipation of the die of the driver chip. For example, the die is directly bound to the copper board, and a pin extends directly outside the package, which is convenient for soldering directly on the copper foil of the PCB board. Conduct heat quickly (Figure 1). For example, on a silicon wafer die similar to 4X4mm, if a current of 300-1000mA is required for a long time, there will be power consumption and heat will inevitably occur. The physical heat dissipation structure of the chip itself is also crucial.
5. The ability of the driver chip itself to resist EMI, noise, and high voltage is also related to whether the entire led lamp product can successfully pass CE, UL and other certifications. Therefore, the driver chip itself must select an excellent topology and high voltage at the beginning of the design. Production Process.
6. The power consumption of the driver chip itself is required to be less than 0.5W, and the switching operating frequency is required to be greater than 120Hz, so as to avoid visible flicker due to power frequency interference. Led green lighting promotes the development of driver chips to innovative design. LED lamp lighting is inseparable from the driver chip, so LED light source driver ICs with multiple functions are required. Non-isolated power supply can be considered for the AC power supply of 36V or less for led lamps. If 220V and 100V AC power supply are selected, isolated power supply should be considered. Directly using the AC100-220V driver chip, due to the demanding application volume, there are higher technical requirements and greater difficulty in technology. At present, all countries are working hard to develop. The massive demand market for led lamps gives all IC design companies a chance to succeed again, with rapid transformation and early product release, and many opportunities to win.
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