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

LED lighting has developed rapidly in recent years, and LED has been widely recognized as a green, environmentally friendly, clean light source. LED light sources have long service life, energy saving, simple and convenient application, and low cost, so they will be widely used in home lighting. According to a survey conducted by OSRAM Optical Semiconductors in 2008, the annual global shipment of home lighting lamp holders is about 50 billion.

LED light source technology is becoming more mature, and the luminous lumens per watt are increasing rapidly, which has led to a gradual price reduction. For example, the price of a 1W LED light source in the spring of 2008 was already one-third of the price in the spring of 2006, and will drop to one-quarter of the price in the spring of 2009.

The massive market of LED green lamps and the steady growth in demand for several years will be the super tsunami of the integrated circuit industry in the consumer electronics market after VCD, DVD, mobile phones and MP3!

The superior performance of LED lamps, such as high energy saving, long life and environmental protection, has been widely recognized.

LED is highly energy-efficient: DC drive, ultra-low power consumption (single tube 0.03W-1W), electro-optical power conversion is close to 100%, and the same lighting effect saves more than 80% energy compared to 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 life.

LED is good for the environment: LED is a green light source with better environmental benefits. There is no ultraviolet and infrared in the spectrum, low heat, no flicker, no radiation, and the waste is recyclable, no pollution, no mercury, cold light source, safe to touch, and is a typical green lighting source.

Working characteristics of LED light source:

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, grille lamps; high power LEDs are used for home lighting, spotlights, underwater lamps, wall washers, street lamps, tunnel lamps, car work lamps, etc. High power LED light sources are low voltage, high current driven devices, and their luminous intensity is determined by the current flowing through the LED. Too strong current will cause the LED light to attenuate, 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 LED use and achieve the ideal luminous intensity. In the field of LED lighting, in order to reflect the characteristics of energy saving and long life, it is crucial to choose a good LED driver IC. Without a good driver IC match, the advantages of LED lighting cannot be reflected.

LED lighting has developed rapidly in recent years. As a green and clean light source, LED has been widely recognized. LED light sources have long service life, energy saving, simple and convenient application, and low cost. Therefore, they will be widely used in home lighting. According to the survey statistics of OSRAM Optical Semiconductors in 2008, the annual global shipment of home lighting lamp holders is about 50 billion.

LED light source technology is becoming more mature, and the luminous lumens per watt are increasing rapidly, which has led to a gradual price reduction. For example, the price of a 1W LED light source in the spring of 2008 was already one-third of the price in the spring of 2006, and will drop to one-quarter of the price in the spring of 2009.

The massive market of LED green lamps and the steady growth in demand for several years will be the super tsunami of the integrated circuit industry in the consumer electronics market after VCD, DVD, mobile phones and MP3!

The superior performance of LED lamps, such as high energy saving, long life and environmental protection, has been widely recognized.

LED is highly energy-efficient: DC drive, ultra-low power consumption (single tube 0.03W-1W), electro-optical power conversion is close to 100%, and the same lighting effect saves more than 80% energy compared to 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 life.

LED is good for the environment: LED is a green light source with better environmental benefits. There is no ultraviolet and infrared in the spectrum, low heat, no flicker, no radiation, and the waste is recyclable, no pollution, no mercury, cold light source, safe to touch, and is a typical green lighting source.

Working characteristics of LED light source:

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, grille lamps; high power LEDs are used for home lighting, spotlights, underwater lamps, wall washers, street lamps, tunnel lamps, car work lamps, etc. High power LED light sources are low voltage, high current driven devices, and their luminous intensity is determined by the current flowing through the LED. Too strong current will cause the LED light to attenuate, 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 LED use and achieve the ideal luminous intensity. In the field of LED lighting, in order to reflect the characteristics of energy saving and long life, it is crucial to choose a good LED driver IC. Without a good driver IC match, the advantages of LED lighting cannot be reflected.

LED lamps' 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. 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 increases, and the LED light source will be burned out.

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. Larger currents are required for larger power sources. Therefore, the driver IC used in LED lighting fixtures must have sufficient current output. When designing products, the driver IC must work in the optimal working area of ​​70-90% of the full load output. Using a driver IC with full load output current will not dissipate heat well in the narrow space of the lamp, and it is easy to fatigue and fail early.

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. When the same batch of driver chips are used under the same conditions, their output current should be as consistent as possible, that is, the discreteness should be small, so that production on large-scale automated production lines can be effective and orderly. Driver chips with a certain discreteness of output current must be graded before leaving the factory or being put into the production line, and the resistance value of the current setting resistor (Rs) on the PCB board must be adjusted so that the constant current driver board of the LED lamps produced has consistent brightness for the same type of LED light source, maintaining 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 extending a pin directly outside the package, so that it can be directly soldered on the copper foil of the PCB board for rapid heat conduction (Figure 1). For example, if a 300-1000mA current is passed through a silicon chip tube core of similar size 4X4mm for a long time, there will inevitably be power consumption and heat, so the physical heat dissipation structure of the chip itself is also crucial.

5. The driver chip's ability to resist EMI, noise, and high voltage also affects whether the entire LED lighting product can successfully pass CE, UL and other certifications. Therefore, the driver chip itself must use excellent topological structure and high-voltage production process at the beginning of its 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 promotes the development of driver chips towards innovative designs. LED lighting is inseparable from driver chips, so LED light source driver ICs with multiple functions are needed. 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. Direct use of AC100-220V driver chips has higher technical requirements and greater difficulty due to the demanding application volume. Currently, 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.