Driver technology is the key to LED reliability and long life

Under the global trend of energy saving and carbon reduction, LED lighting is highly anticipated, and with the increasing luminous efficiency of high-brightness LEDs in recent years, the unit cost has also declined, prompting high-brightness LED applications to be no longer limited to small and medium-sized electronic products, or It is a large-size backlight application and LED display board for notebook computers, monitors, TVs, etc. At present, it has begun to replace traditional incandescent lamps and other lighting products. LED has undoubtedly become an important source of illumination for the next generation of general illumination.

In view of the market prospects of LED lighting, industry insiders pointed out that in 2012, the global LED lighting output value is expected to grow to 11 billion US dollars, increased to 19.2 billion US dollars in 2015, and the compound growth rate of nearly 4% in four years. Industry insiders analyzed that consumer electronics products are suffering from poor economic performance, and the replacement effect of new display technologies such as AMOLED is gradually expanding, which makes the LED backlight market relying on consumer electronics products to face bottlenecks. In contrast, even if LED lighting grows slowly, the market prospects are established, and it is expected to bring new hope to the LED industry within five years.

In particular, the government's policy to ban incandescent lamps will begin to ferment in 2012, and more than two-thirds of the world's regions have begun to ban incandescent or high-watt incandescent lighting. After the incandescent lamp period has come, the importance of LED in lighting applications has been highlighted, and the next four years will be the final critical period for the LED layout lighting market. In the application market segment, outdoor lighting will be prioritized, commercial lighting, industrial lighting, and automotive lighting will be seconded, and finally penetrated into the home market.

High efficiency, reliability and long life, the driver is the key

In the LED lighting application market, the replacement of the lamp market is the most popular at this stage. The success factors of this market include high efficiency, sufficient working reliability and longevity of the driving power supply. For these conditions, the LED driver plays an extreme role. Important role. In response to this, Pan Dawei, vice president of sales for IR Asia Pacific, pointed out that the solid-state lighting industry is developing rapidly, so the demand for low-cost driver electronic components is increasing day by day, so that high-brightness and high-power LEDs supply constant current output.

To meet these needs, IR has introduced a new high-voltage buck regulator control IC, the IRS2980, for LED bulb replacement, LED tube lighting and other non-isolated LED driver applications. The IRS2980 is the company's first product in the high-voltage LED driver IC family, rated at 600V, and uses hysteresis average current mode control for precise current regulation. The new LED step-down driver includes a low-side MOSFET driver with a high-voltage internal regulator and high-side current sensing. The converter is compatible with electronic pulse width modulation dimming, and the current control covers 0 to 100%.

Pan Dawei further pointed out that the new IRS2980 can improve performance at a lower system cost than other solutions for non-isolated LED driver applications. The IRS2980 in an SO-8 package provides top-level electrical overstress protection and higher field efficiency with an IR advanced high voltage IC process that incorporates the latest high voltage level shifting and termination technology.

Digital power control method solves many problems

Basically, the driver for LED replacement lamp is mostly realized by step-down switching regulator. ROHM pointed out that in order for LEDs to illuminate at a fixed brightness, an LED driver IC that performs constant current control must be installed. In general, a step-down switching regulator is usually used. This is because the traditional method will cause the input voltage/output voltage to change too much, and depending on the application conditions, it is possible to redesign the power module.

When the input voltage changes too much, the frequency of the AC voltage (after full-wave rectification: 100Hz-120Hz) will cause the input voltage to chop, and the brightness of the LED will become unstable. If you want to stabilize the input voltage, it is necessary to add some ingenuity to the power module design. When the input voltage changes more, it is necessary to change the constant of the external parts according to the output voltage (number of LEDs) of the light source. As a result, the style of the power module is increased, and the design man-hour is consumed.

In response to the above problems, the BD555AKFV developed by ROHM uses the digital power control method to eliminate the need for external components. As long as the coil current is detected, the above problems can be solved. With the digital power control method, the target of controlling the average value of the LED current can be achieved regardless of the input/output voltage value. In this method, the coil current is sampled (A/D converted) and digitized, and then the peak current value is calculated according to the sampling data, so that the average current of the LED current reaches a stable target. Then, the calculation result is D/A converted and fed back to the comparator for detecting the peak current.

Suppress in a more cost effective manner

In addition to the business, Taiwanese industry group Holtek has also launched the universal isolated step-down LED lighting driver control IC-HT7L2102 and HT7L2103 for the LED lighting market. Both drivers support complete LED protection, and the group is specifically targeted at EMI. The suppression adds the FrequencyJitter function, which reduces EMI by 5-8dB and saves EMI costs.

In addition, in the face of diversified LED load conditions and serial number, the HT7L2102 and HT7L2103 have built-in GreenMode power-saving mode, allowing users to drive different LED load strings in a single circuit design without Reduce conversion efficiency. In the dimming support, both of them have built-in support for PWM dimming interface. The HT7L2102 is designed for T8/T9 lamp applications and the HT7L2103 is designed for E26/E27 bulb applications. Holtek Semiconductor emphasizes that the HT7L2103 integrates more functions due to the small space of the E26/E27 bulbs, enabling isolated AC-DC power supply in a limited space.

High-quality LED drivers drive the LED lighting market

According to forecasts, LED driver IC market revenue will be nearly 2 billion US dollars in 2010, reaching nearly 3.5 billion US dollars in 2015. The market growth rate of LED driver ICs for lighting is expected to reach 40% between 2010 and 2015.

Since the LED driver IC is responsible for controlling the LED illumination quality of electronic products, the quality and stability of the chip are very important. In contrast, the design capabilities of international manufacturers are better, and the brand awareness and quality assurance are also of a higher standard. The market still has a large share. However, it is worth noting that in recent years, LED driver ICs in Taiwan have actively invested in the field of LED replacement lamps, and have also provided foreign markets with alternatives.

Overall, the LED light source is a low voltage, high current driven device whose luminous intensity is determined by the amount of current flowing through the LED. If the current is too large, the LED light will be attenuated. If the current is too small, the LED's luminous intensity will be affected. Therefore, the LED driver needs to provide a constant current power supply to ensure the safety of the use of high-power LEDs while achieving the desired luminous intensity. In the field of LED lighting, in order to reflect the characteristics of LED lamp energy saving and long life, it is very important to choose LED driver IC correctly. Only by selecting a good matching of driver IC can the LED lighting advantage be highlighted, and then the LED lighting can be accelerated. .