Many IC manufacturers prefer primary-side feedback for LED lighting driver solutions

LED is called the fourth generation lighting 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 indications, displays , decorations, backlight sources, general lighting and urban night scenes. With the outstanding performance of LED applications in many markets such as lighting, backlighting, and display screens , many IC manufacturers have expanded into the LED field and engaged in the development of LED driver solutions. Different IC manufacturers choose their own target markets according to their own conditions. However, commonalities still exist. When faced with challenges such as volume, dimming control, cost, and conversion efficiency, their response strategies are worth discussing.

Primary-side feedback becomes a common choice

The main function of LED drivers is to provide stable and accurate operating current for LED lamps . Traditional LED driver solutions use secondary feedback to achieve accurate output current control, measure LED current through current sampling resistors on the secondary side, and provide feedback information with the help of optocouplers . Secondary feedback control will lead to an increase in driver cost and size and a decrease in conversion efficiency. In this case, primary feedback has become a common choice for many LED driver solution providers.

The primary-side feedback AC/DC control technology is a new type of AC/DC control technology developed in the last 10 years. Compared with the traditional secondary-side feedback optocoupler plus 431 structure, its biggest advantage is that it eliminates these two chips and a set of components that work with them, thus saving space on the system board, reducing costs and improving system reliability.

BCD Semiconductor 's LED driver chips AP3766 and AP1681 all use its unique patented primary side control (PSR) technology, which can achieve accurate secondary side LED drive current control without the need for secondary side feedback circuits. Its built-in temperature compensation, transformer compensation and line voltage compensation technologies ensure the output current accuracy of the driver under full temperature, wide voltage and mass production conditions.

Fairchild Semiconductor (Shanghai) Co., Ltd. also said that in terms of low- power LED lighting with AC input , LED driver circuits using primary-side control architecture have cost and performance advantages. For example, Fairchild Semiconductor's FSEZ1216, FSEZ1307 and FSEZ1317 use PSR to save optocouplers and other feedback circuits, thus achieving a good balance between cost and performance.

Nanjing Weimeng, a local company, has also launched similar products. Its LED driver chips ME8165/8108 all use primary feedback technology, without optocouplers, which greatly reduces the size of the product and reduces costs. Nanjing Weimeng is one of the backbone IC companies under China Huada Group. It is a high-tech enterprise engaged in the research, development and sales of dedicated analog integrated circuit chip products. Its products are used in information appliances , wireless communications , digital communications and network technologies. Nanjing Weimeng has a large share of the domestic display market. It is revealed that its total LED driver shipments last year exceeded 700 million.

Display driver achieves precise dimming control

Although there is no perfect unified standard for LED driver power supplies in the world , the rapid development of the industry has led to increasing requirements for LED driver power supplies.

In the LED display application market, precise control of LED light brightness is the main demand. Zhang Hongyu introduced that in order to meet the requirements of the display, it is necessary to ensure that the chip has good drive current consistency between bits, chips, and batches under different temperature conditions and harsh usage environments.

Nanjing Weimeng driver IC ME2604 in full-color LED display application performance.

Nanjing Weimeng has launched the display driver IC ME2604 to the market. This is a low voltage difference, 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 also controlled within 1% by the power supply voltage (VDD) and ambient temperature. ME2604 can use external resistors Rext of different resistance values ​​to adjust the current size of each output port of ME2604; at the same time, PWM modulation can also be used at the OE end, and the minimum pulse width can reach 50ns. Therefore, the brightness of the LED can be accurately controlled.

The backlight driver market is highly competitive, especially for LED TVs

The LED backlight driver market is mainly composed of LED TV, LED monitor, notebook, GPS , DPF, PDVD and other portable devices. The screen size ranges from large to small, and the proportion of LED backlight increases from small to large. The backlight of notebooks and portable products is basically 100% LED. In the past two years, the penetration rate of LED backlight of LCD monitors and LCD TV has been rising rapidly. As the LED TV and LED monitor backlight driver solutions that have emerged in the past two years, there are many schools of thought in the market.

Fairchild Semiconductor is one of the main solution providers for TV power solutions , and the LED backlight driver field is also our key market. The application of LED backlight for LCD TV is developing and changing rapidly, including the number of LED light strings, current and voltage parameters, topology, and coordination with AC-DC parts. He believes that although O2Micro and MPS have traditional advantages in CCFL backlight for LCD TVs, it will take some time for market verification to see the results in the LED backlight market.

BCD Semiconductor, with its customer advantages and product leadership in the mainland and Taiwan markets, has taken the lead in mass production of LED TV backlight driver solutions in the top TV manufacturers in the mainland. O2Micro, MPS, BCD, Supertex, Richtek and other companies are at the forefront.

The demand for color LCD displays in portable audio , printers, and other devices, including mobile phones and PCs, is increasing. ROHM has launched a variety of LED drivers for color LCD backlights. The number of LED lights can be installed from 1 to 96 depending on the size of the display. According to the function, there are LED drivers with dimming functions to achieve low power consumption, LDO built-in types that meet miniaturization requirements, RGB automatic dimming types that reduce software load, and space-saving Flash built-in types. In addition, there are LED drivers for single purposes such as decoration or Flash.

MCU manufacturer Shengyang Semiconductor has recently launched LED backlight driver IC integrated solutions for small and medium-sized displays. The company's current main target market is below 10 inches. Its new generation of WLED backlight driver series has high WLED driving capabilities, combined with high integration, small size, simple application circuit, high DC conversion path, energy saving and environmental protection, and has a very competitive price. It is widely used in NB, car GPS, PDVD, digital photo frame and other markets.