Technical details that need to be paid attention to in LED lighting design

LED lighting has made great progress recently. As a green and clean light source, LED has been widely recognized. LED light sources have long service life, energy saving and power saving, simple and convenient application, and low cost of use. Therefore, they will be widely used in home lighting. According to the survey statistics of OSRAM Optical Semiconductors in 2008, the annual shipment of home lighting lamp holders in the world is about 50 billion.
The technology of LED light sources is becoming more and more mature, and the luminous lumens per watt are increasing rapidly, which has led to a decrease in price year by year. Taking a 1W LED light source as an example, the price in the spring of 2008 was one-third of the price in the spring of 2006, and it will drop to one-quarter of the price in the spring of 2009.
The massive market of LED green lamps and the continuous and stable growth demand for several years will be the super tsunami of the consumer electronics market after VCD, DVD, mobile phone and MP3 in the integrated circuit industry!
The superior performance of LED lamps in high energy saving, long life and environmental protection has been widely recognized.
LED high energy saving: DC drive, ultra-low power consumption (single tube 0.03 watt-1 watt), electro-optical power conversion is close to 100%, and the same lighting effect saves more than 80% energy than traditional light sources.
LED long life: LED light source is called long-life lamp. Solid cold light source, epoxy resin encapsulation, no loose parts in the lamp body, no filament burning, heat deposition, fast light decay and other shortcomings, the service life can reach 50,000 to 100,000 hours, more than 10 times longer than the traditional light source.
LED is environmentally friendly: LED is a green light source with better environmental benefits. There is no ultraviolet and infrared in the spectrum, low heat and no flicker, no radiation, and waste can be recycled, no pollution, no mercury, cold light source, safe to touch, a typical green lighting source.
LED light source working characteristics
The VF voltage of LED light sources for lighting is very low, generally VF = 2.75-3.8V, IF is 15-1400mA; therefore, the output voltage of LED driver IC is VF XN or VF X 1, IF constant current is 15-1400mA. There are two types of LED light sources used in LED lamps: low power (IF=15-20mA) and high power (IF>200mA). Low power LEDs are mostly used for LED fluorescent lamps, decorative lamps, and grille lamps; high power LEDs are used for household lighting, spotlights, underwater lamps, wall washers, street lamps, tunnel lamps, and car work lamps. High power LED light sources are low voltage, high current driven devices. The intensity of their light is determined by the current flowing through the LED. Too strong current will cause the LED light to decay, and too weak current will affect the luminous intensity of the LED. Therefore, the LED driver needs to provide a constant current power supply to ensure the safety of high power LEDs and achieve the ideal luminous intensity. In the field of LED lighting, it is very important to choose a good LED driver IC to reflect the characteristics of energy saving and long life. Without a good driver IC match, the advantages of LED lighting cannot be reflected.

LED lamps have the following requirements 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 surface. It is better if the withstand voltage can be greater than 45V. When AC 12V or 24V is input, the output voltage of a 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 cannot adapt to the 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 an LED light source for lighting, the nominal operating current of a 1W LED light source is 350mA, and the nominal operating current of a 3W LED light source is 700mA. Large power requires a larger current. Therefore, the driver IC selected for LED lighting fixtures 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 load output. The driver IC with full load output current has poor heat dissipation in the narrow space of the lamp, which is prone to fatigue and early failure. 3. The output current of the driver chip must be constant for a long time, so that the LED light source can emit light stably and the brightness will not flicker; the output current of the same batch of driver chips should be as consistent as possible when used under the same conditions, that is, the discreteness should be small, so that production on a large-scale automated production line can be effective and orderly; for driver chips with a certain discreteness of output current, they must be graded before leaving the factory or putting into the production line, and the resistance value of the current setting resistor (Rs) on the PCB board must be adjusted to make the constant current driver board of the LED lamps produced have the same brightness for the same LED light source, so as to maintain the consistency of the final product. 4. The package of the driver chip should be conducive to the rapid heat dissipation of the driver chip tube core, such as directly binding the tube core (Die) on the copper plate, and a pin directly extending outside the package, so as to facilitate direct welding on the copper foil of the PCB board for rapid heat conduction (Figure 1). For example, on a silicon chip tube core similar to 4X4mm, if a current of 300-1000mA is passed for a long time, there will inevitably be power consumption and heat, and 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 also affects whether the entire LED lamp product can successfully pass CE, UL and other certifications. Therefore, the driver chip itself must use excellent topological structures and high-voltage production processes at the beginning of the design. 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 to avoid visible flickering caused by power frequency interference.
LED green lighting has prompted the driver chip to develop innovative designs. LED lamp lighting is inseparable from the driver chip, so a variety of LED light source driver ICs are required. LED lamps can consider non-isolated power supply when using AC power below 36V. If 220V and 100V AC power are used, isolated power supply should be considered. Directly using AC100-220V driver chips has higher technical requirements and greater difficulties due to the demanding application volume. At present, all countries are working hard to develop them. The massive demand market for LED lamps gives all integrated circuit design companies the opportunity to succeed again. Rapid transformation and early product launch will give them many opportunities to win.