The working characteristics of LED light source The VF voltage of LED light source for illumination is very low, generally VF=2.75-3.8V, IF is 15-1400mA; therefore the output voltage of LED driver IC is VFXN or VFX1, IF constant current is 15-1400mA. The LED light source used in LED lamps has two types: low power (IF=15-20mA) and high power (IF>200mA). The low power LEDs are mostly used for LED fluorescent lamps, decorative lights, and grille lights; high-power LEDs are used to make Home lighting, spotlights, underwater lights, wall washers, street lights, tunnel lights, car work lights, etc. The power LED light source is a device driven by a low voltage and a large current. The intensity of the light emission is determined by the size of the current flowing through the LED. If the current is too strong, the LED light will be attenuated. If the current is too weak, the light emitting intensity of the LED will be affected. Therefore, the LED The driver needs to provide a constant current power supply to ensure the safety of high power LED use while achieving the desired luminous intensity. In the field of LED lighting, to reflect the characteristics of energy saving and long life, choosing a good LED driver IC is essential, there is no good driver IC matching, the advantages of LED lighting can not be reflected. LED lighting requirements for low voltage driver chips:
1. The package of the driver chip should be conducive to rapid heat dissipation of the driver chip die, such as directly binding the die (Die) to the copper plate, and there is a Pin directly extending to the outside of the package, which is convenient to be directly welded on the copper foil of the PCB board. Rapid heat conduction. For example, on a 4X4mm wafer die, if a current of 300-1000mA is passed for a long time, there must be power consumption, and it will inevitably generate heat. The physical heat dissipation structure of the chip itself is also crucial.
2. The ability of the driver chip itself to resist EMI, noise, and high voltage is also related to the ability of the entire LED lamp product to successfully pass CE, UL, and other certifications. Therefore, the driver chip itself must use excellent topological structure and high voltage at the beginning of design. Production Process.
3. The power consumption requirement of the driver chip itself is less than 0.5W, and the switching frequency requirement is greater than 120Hz to avoid the visible flicker caused by the power frequency interference. LED green lighting promotes the development of the driver chip to innovative designs. LED lighting is inseparable from the driver chip, and therefore requires a variety of functions of the LED light source driver IC. LED lamps use less than 36V AC power supply can consider non-isolated power supply, such as the choice of 220V and 100V AC power supply should consider isolated power supply. Directly using the AC100-220V driver chip, due to the application of the volume of demanding, technically there are still higher requirements, greater difficulty, at present all countries are working hard to develop. The massive market demand for LED lamps has given all IC design companies a chance to succeed again. They will quickly transform and produce products early and win many opportunities.
4. The nominal input voltage range of the driver chip should meet DC8-40V to cover the needs of the application surface. If the withstand voltage is more than 45V, the output voltage of a simple bridge rectifier will fluctuate with the grid voltage when AC12V or 24V is input. In particular, when the voltage is high, the output DC voltage will be too high. If the driving IC cannot accommodate a wide voltage range, it will often be broken when the power grid voltage increases, and the LED light source is also burned.
5. The nominal output current requirement of the driver chip is greater than 1.2-1.5A. As the LED light source for illumination, the nominal operating current of the LED light source of 1W power is 350mA, and the nominal operating current of the LED light source of 3W power is 700mA. Larger currents require more current. Therefore, the driver ICs used in LED lighting fixtures must have sufficient current output. When designing a product, the driver IC must work in a 70-90% optimal working area with a full negative output. Driver ICs with full and negative output currents dissipate heat in tight spaces in lamps, fatigue, and premature failure.
6, the output current of the driver chip must be permanently constant, LED light source can be stable light, the brightness will not flicker; the same batch of driver chips used under the same conditions, the output current size to be as consistent as possible, that is, small discrete, so that High-volume automated production line production can be effective and orderly; for the output current of a certain discrete drive chip must be selected before delivery or put into production line, adjust the resistance value of the current setting resistor (Rs) on the PCB board, so that The production of LED lamps and constant current driver board for the same LED light source brightness uniformity, to maintain the consistency of the final product.
Low-voltage LED chips do not adapt to LED general lighting market will be eliminated
The reason why the LED general-purpose lighting market is full of people's appetites today attracts the attention of so many people. The reasons are nothing more than the following three aspects. First, its market is large enough; Second, LED common after the end of this year or early next year The first year of the lighting market will come, that is, the ratio of LED lighting fixtures to total lighting fixtures will exceed 10%. Third, the market for incandescent, fluorescent and energy-saving lamps is basically supplied by a few companies such as GE, Philips and OSRAM. Different from the business monopoly, the LED lighting fixtures produced by these big lighting suppliers today account for only about 10% of the total lighting market. That is, the LED general lighting market is not yet a monopoly market, and everyone has the opportunity to play inside.
However, most LED chip suppliers today are in danger of going out of business because the low-voltage LED chips they produce today will be increasingly difficult to sell into the LED general lighting market. Why? Because high-voltage LEDs appear, high-voltage LEDs have two distinct competitive advantages over low-voltage LEDs:
First, at the same output power, high-voltage LEDs require much lower drive current than low-voltage LEDs. For example, Epistar's high-voltage, blue light 1W LED has a forward voltage drop of up to 50V, which means that it can output 1W with only 20mA of drive current, while a 1W LED with a normal forward voltage drop of 3V requires 350mA of drive current. Can output 1W power, so the output power of the high-voltage LED in the work of power dissipation is much lower than the low-voltage LED, which means that the cost of aluminum heat sink can be greatly reduced.
Second, high-voltage LEDs can significantly reduce the loss of AC-DC conversion efficiency. Taking 10W output power as an example, if a 1W high voltage LED with a forward voltage drop of 50V is used, the output can be configured with 2 and 4 strings, and the forward voltage drop of 4 series LEDs is 200V, which means that only from the city Electricity 220V AC (AC) using bridge rectifier and drop 20V on it. However, if we use a 1W low voltage LED with a forward voltage drop of 3V, even if the forward voltage drop of 10 strings is not more than 30V, it means that we need to step down from 220VAC to 30VDC. We know that the lower the differential pressure between input and output, the higher the conversion efficiency from AC to DC. It can be seen that if a high voltage LED is used, the efficiency of the transformer can be greatly improved, which can greatly reduce the power loss during AC-DC conversion. A reduction in heat consumption can further reduce the cost of the heat sink.
It can be seen that high-voltage LEDs can bring about an effective reduction in the cost and weight of LED lighting fixtures, but its more important significance is to significantly reduce the design requirements of the cooling system, which effectively clears the largest LED lighting fixtures into the indoor lighting market. Technical obstacles. Therefore, high-voltage LEDs will dominate the future of the LED general lighting market.
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