Talking about the selection skills of LED lighting driver chip

LED lighting has developed rapidly in the near future, and LED has been widely recognized as a green and clean light source. LED light source has long service life, energy saving, simple and convenient application, and low cost. Therefore, it will be widely used in home lighting. As early as 2008, there were about 50 billion home lighting lamp holders shipped worldwide each year.

The technology of LED light source is becoming more and more mature, and the lumens per watt are growing rapidly, prompting it to reduce prices year by year. 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 the VCD, DVD, mobile phones and MP3 in the integrated circuit industry! The superior performance of LED lamps with high energy saving, long life, and environmental protection is widely recognized.

1. High energy-saving LED: DC drive, ultra-low power consumption (0.03 ~ 1W per tube) electro-optical power conversion is close to 100%, the same lighting effect is more than 80% energy saving than traditional light sources.

2. Long-life LED: LED light source is called long-life lamp. Solid cold light source, epoxy resin encapsulation, no loose parts in the lamp body, there are no shortcomings such as filament burning easily, thermal deposition, fast light decay, etc. The service life can reach 50,000 to 100,000 hours, which is 10 years longer than the traditional light source More than times.

3. LED is environmentally friendly: LED is a green light source with better environmental protection benefits. 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 2.75 ~ 3.8V, 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 ~ 1,400mA. There are two types of LED light sources used in LED lamps: low power (IF is 15 ~ 20mA) and high power (IF is greater than 200mA). Low-power LEDs are mostly used to make LED fluorescent lamps, decorative lamps 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. The power LED light source is a device driven by low voltage and large current, and its luminous intensity is determined by the current flowing through the LED. Excessive current will cause LED light attenuation, too small current will affect the LED's luminous intensity. Therefore, the LED driver needs to provide a constant current power supply to ensure the safety of high-power LEDs, while achieving the desired luminous intensity. In the field of LED lighting, in order to reflect the characteristics of energy saving and long life of LED lamps, the correct choice of LED driver IC is essential. Without good driver IC matching, the advantages of LED lighting cannot be reflected.

The requirements of LED lamps for low-voltage driver chips

1. The nominal input voltage range of the driver chip should meet the DC 8 ~ 40V to cover a wider range of application needs. The pressure resistance is better than 45V. When the input is AC 12V or 24V, 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 does not have a wide input voltage range, it will often be broken down when the grid voltage rises, thereby burning the LED light source.

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 power LED light source is 350mA, and the nominal operating current of a 3W power LED light source is 700mA. High-power LED light sources require more current. Therefore, the driver IC selected for LED lighting must have sufficient current output. When designing the product, the driver IC must also work in the optimal working area of ​​70 ~ 90% of the full load output. Driver ICs that use full-load output current do not dissipate heat in the narrow spaces of the lamps, which can easily cause fatigue and early failure of the lamps.

3. The output current of the driver chip must be kept constant, so that the LED can emit light stably without flickering. The same batch of driver chips are used under the same conditions, and the output current size should be as consistent as possible, that is, the dispersion should be small, so that it can ensure effective and orderly when it is produced on a large-volume automated production line. For the driver chips with a certain discrete output current, it is necessary to select in stages before leaving the factory or put into the production line, adjust the resistance value of the current setting resistor on the PCB board, so that the constant current driver board of the LED lamps produced by the same The brightness of the light source is consistent 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 die. For example, the die is directly bonded to the copper board, and a pin extends directly outside the package, so that it is directly soldered to the copper foil of the PCB Quickly conduct heat (picture). If you need to pass 300 ~ 1,000mA current on a chip like 4X4mm for a long time, it will inevitably produce power consumption and heat. Therefore, the physical heat dissipation structure of the chip itself is also very important.

Driver IC cross-sectional view (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 lamp product can successfully pass CE, UL and other certifications. Therefore, when designing the driver chip, an advanced topology structure and high-voltage production process must be used.

6. The power consumption of the driver chip is required to be less than 0.5W, and the operating frequency of the switch is required to be greater than 120Hz, so as to avoid visible flicker caused by power frequency interference.

In short, LED green lighting promotes the development of driving chips to innovative designs. LED lighting can not be separated from the driver chip, so a multi-function LED light source driver IC is required. If the LED lamps use AC power below 36V, you can consider non-isolated power supply; if you choose 220V and 100V AC power, you should consider isolated power supply. Directly using AC 100 ~ 220V driver chips, because of the demanding requirements of the application, there are still higher technical requirements and greater difficulties. At present, all countries are working hard to develop.

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