Large size LED backlight development of the first year of major chip manufacturers to accelerate penetration

2010 is an important year for the development of large size LED backlight, LED backlight ultra-thin, energy saving and environmental protection, high quality color display has become the motive power to promote the development of the back light. According to the forecast data, research institutions in 2010, the global LED LCD TV sales will reach 32 million units, accounted for approximately 19% of the proportion of LCD TV with LED backlight; 2011 large-size panel shipments ratio will reach 56%, the traditional backlight panel shipments will decline to 44%; by 2015, the LED panel shipment in Chinese tablet penetration will reach 78%. on the market in the past two years, LED will surpass CCFL ordinary LCD tv.

A Morimi (OnSemi) and portable power semiconductor products of global sales and marketing senior director Zheng Zhaoxiong said that the traditional LCD TV uses cold cathode fluorescent lamp (CCFL) backlight is generally PFC voltage through 24V conversion (traditional power) or without 24V (LIPS power conversion) rising to more than 1000V or 2000V AC high voltage to drive a CCFL lamp type or U type; LED backlight LCD TV adopts a plurality of LED light, mainly in the side light or backlit to backlight, so an important requirement for power management is to provide high efficiency; in addition, the case of TV set, due to the ultra-thin LED backlight LCD TV appearance an important selling point, so the power management scheme should have low height to fit the slim design, at the same time, but also take into account the heat dissipation, reduce electromagnetic interference, different channel brightness matching, and dimming Fault diagnosis and protection.

"As mentioned above, these requirements of semiconductor devices and solutions for high efficiency, the more compact (especially low height) components to fit more slim design, at the same time improve heat dissipation, reduce electromagnetic interference, provide high brightness matching degree (in order to provide a consistent brightness backlight), dimming, diagnosis and protection etc.. Zheng Zhaoxiong added.

At present, Anson beauty at the same time provide side light type and direct type LED backlight solution. The side light type scheme as an example, A Morimi Semiconductor provides multi channel linear LED side light scheme cost-effective, this scheme in the half bridge transition section with NCP1397 primary side controller and 500V high voltage MOSFETNDF05N50, while using the target efficiency linear LED driver CAT4026.CAT4026 6 channel is higher than 90%, the typical energy efficiency reached 94%, with "excellent current + 2% matching precision and" 1% 400HzPWM dimming range, and the use of an external power bipolar transistor to provide heat, better heat treatment.

In addition to NCP1397, NDF05N50 and CAT4026 linear side light based program, A Morimi semiconductor also provides NCP1397 based, NDF05N50 and NCP1034 under direct buck drive program. NCP1034 uses a programmable switching frequency of up to 500kHz to drive a pair of external N channel MOSFET, which can flexibly adjust the integrated circuit (IC) to meet the system requirements. In addition, the use of the internal 1.25V reference voltage on the output voltage precision regulator for low voltage applications. This device provides protection against electrical faults, such as under voltage lockout and intermittent (hiccup) current limits, to provide system level security at the event of a failure. Advantages include driving a high efficiency field effect transistor (FET) and providing a fixed frequency for 1 or more devices.

It is worth mentioning that A Morimi Semiconductor provides a complete solution for the LED backlight LCD TV, in addition to the side light type or direct backlight scheme, including power factor correction (PFC), and the standby switching power supply rectifier, operational amplifier, MOSFET and discrete devices, providing a one-stop solution for the customer to choose.

Linear technology (Linear) products marketing director TonyArmstrong believes that the traditional LCDHDTV adopts CCFL as backlight lamp, but can provide the contrast ratio is only 450cd/m2~650cd/m2, the main problem lies in the "can't completely shut off the CCFL backlight or local dimming" on it. That is to say, the current generation of LCDHDTV is unable to obtain the real "black", and all the color of the dynamic range are low.

In contrast, when using the HBLED backlight, a back lighting to "LED group" to carry out local dimming or shut off operation of the LED array (for the 46 inch display, LED number up to 1600) than the CCFL design provides almost an order of magnitude higher than the contrast ("4000cd/m2). In addition, by adjusting the brightness of the backlight LED group, but also to reproduce more middle tones, making the image more vivid.

"Another benefit is the ability to locally LED completely shut off, thereby reducing motion blur. The image blurring caused by the fast moving object will be eliminated by closing the LED between frames. Therefore, the fast response rate of LED is very important. "Tony says.

He once again stressed the importance of the IC drive for reliability and life performance of LED. That in addition to make the scheme more delicate, compact and flat, IC is still in operation driven high switching frequency conditions, based on the topology structure of DC/DC switch inductor, number, size and cost of these high switching frequency can reduce the output inductor and capacitor. In addition, in some cases, the drive IC is also able to achieve on-chip integration of Schottky diodes and boost diodes, thereby reducing the number of external components. This in turn reduces design complexity and reduces the size and cost of solutions.