LED is called the fourth generation of illumination source or green light source. It has the characteristics of energy saving, environmental protection, long life and small size. It can be widely used in various fields such as indication, display, decoration, backlight, general illumination and urban night scene. With the outstanding performance of LED applications in lighting, backlighting, display and many other markets, many IC manufacturers have expanded into the LED field and are engaged in the development of LED driver solutions. Eight Immortals cross the sea, each show its magic, and different IC manufacturers choose their target markets according to their own situation. However, the commonality still exists. In the face of challenges such as volume, dimming control, cost, and conversion efficiency, the coping strategy is worth discussing.
Primary feedback method becomes a common choice
The main function of the LED driver is to provide a stable and accurate operating current for the LED Lamp. The traditional LED driver scheme uses secondary feedback for precise output current control, current-sampling resistors on the secondary side to measure LED current, and optocouplers to provide feedback. Secondary feedback control can result in increased drive cost, size, and reduced conversion efficiency. In this case, the primary feedback method has become the common choice of many LED driver solutions suppliers.
The AC/DC control technology of the primary feedback mode is a new AC/DC control technology developed in the last 10 years. Compared with the traditional secondary feedback optocoupler plus 431 structure, the biggest advantage is that these two are omitted. A chip and a set of components that work with it saves space on the system board, reduces cost, and increases system reliability.
Newly advanced (BCD) semiconductor LED driver chips AP3766, AP1681, etc. are all using their unique primary side control (PSR) patent technology, which can achieve accurate secondary side LED drive current control without secondary side feedback circuit. Its built-in temperature compensation, transformer compensation and line voltage compensation technology ensure the output current accuracy of the driver under full temperature, wide voltage and mass production conditions.
Fairchild Semiconductor (Shanghai) Co., Ltd. also stated that LED driver circuits with primary side control architecture have cost and performance advantages in low-power LED lighting for AC input. For example, Fairchild's FSEZ1216, FSEZ1307 and FSEZ1317 use PSR to save optocouplers and other feedback circuits, which combines cost and performance.
Nanjing Weimeng from the locality also launched similar products. The LED driver chip ME8165/8108 of Nanjing Weimeng adopts the primary side feedback technology, which does not require optocoupler, which greatly reduces the product volume and reduces the cost. Nanjing Weimeng is one of the backbone companies of China Huada Group. It is a high-tech enterprise engaged in the research, development and sales of special analog integrated circuit chip products. Products are used in information appliances, wireless communications, digital communications and network technology. Nanjing Weimeng has a large share of the domestic display market. According to reports, its total number of LED driver shipments exceeded 700 million last year.
Display driver for precise dimming control
Although there is no comprehensive standard for LED driver power supply in the world at present, the rapid development of the industry has made the requirements for LED driver power supply continuously improved.
In the LED display application market, precise control of LED illumination brightness is the main appeal. Zhang Hongyu introduced that in order to meet the requirements of the display screen, it is necessary to ensure that the chip has good consistency of the drive current between the chip bit and the bit, between the chip and the chip, and between the batch and the batch under different temperature conditions and harsh use environments.
The application performance of Nanjing Weimeng driver IC ME2604 in full-color LED display.
Nanjing Micro-Mall has launched the display driver IC ME2604, which is a low-dropout, high-precision 16-bit constant current driver chip. It uses a high-precision constant-current drive circuit and a temperature compensation circuit. The current is regulated by the power supply voltage (VDD). The change in ambient temperature is also controlled at 1%. The ME2604 can use external resistors Rext with different resistance values ​​to adjust the current of each output port of the ME2604. At the same time, PWM modulation can be used at the OE end, and the minimum pulse width can reach 50ns. Therefore, the luminance of the LED can be accurately controlled.
The backlight driver market is highly competitive, especially LED TV
LED backlight driver market is mainly composed of LED TV, LED monitor, notebook and portable market such as GPS, DPF, PDVD, etc. The screen size is from large to small, the proportion of LED backlight is from small to large, and the backlight of notebook and portable products is basically 100. % LEDs have been used, and the LED backlight penetration of LCD monitors and LCD TVs has risen rapidly in the past two years. As the LED TV and LED monitor backlight driver solutions that have emerged in the past two years, there are hundreds of schools in the market.
Fairchild Semiconductor is one of the major solution providers for TV power solutions, and our LED backlight driver segment is also our key market. LCD TV LED backlight applications are rapidly evolving, including the number of LED strings, current and voltage parameters, topologies, and coordination with the AC-DC section. He believes that although the two semiconductor companies O2Micro and MPS have traditional advantages in the CCFL backlight of LCD TVs, it will take some time for market verification to see the LED backlight market.
With its customer advantage and product leadership in the mainland and Taiwan markets, Newcomer (BCD) Semiconductor has taken the lead in mass production of LED TV backlight driver solutions in the top TV manufacturers in mainland China. O2Micro, MPS, BCD, Supertex, Richtek, etc. are among the top companies.
The demand for color liquid crystal displays in portable audio, printers and other devices led by mobile phones and PCs is increasing. ROHM has introduced a variety of LED drivers for LCD backlights for color LCD displays. According to the size of the display, 1 to 96 lamps can be installed according to the size of the display. According to the function, the dimming function type that realizes low power consumption, the LDO built-in type that meets the miniaturization requirements, and the RGB automatic dimming type that reduces the software load, Space-saving Flash built-in LED drivers, and LED drivers for single use only for decoration or flash.
MCU manufacturer Shengyang Semiconductor also recently introduced an LED backlight driver IC integration solution for small and medium size displays. Below 10 inches is the company's current main target market, its new generation of WLED backlight driver series, with high drive WLED capability, combined with high integration, small size, simple application circuit, high DC conversion path, energy saving and environmental protection, and Very competitive price, widely used in NB, car GPS, PDVD, digital photo frame and other markets.
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