Diversified solutions for backlight applications

Driven by more and more emerging demands and green energy saving trend, the application of power supply and power management technology that can improve the energy efficiency of power supply will grow rapidly. Backlight is a typical application demand.

Although the backlight of liquid crystal television is still dominated by the traditional cold cathode fluorescent lamp (CCFL), with the increasing awareness of global energy conservation and environmental protection, the new led backlight has been widely concerned and become a strong competitor of CCFL.

In terms of portable applications, the LCD backlight LED drive scheme needs to meet the requirements of high energy efficiency, extended battery life, and reduced area of printed circuit board.

This paper will discuss the characteristics and requirements of the backlight market and application with the solution of ansemer semiconductor.

The needs and challenges of backlighting applications

LED with high color saturation, environmental durability and other advantages, has been widely used in a variety of small and medium-sized LCD panels, is now gradually to notebook computers, LCD TVS and other large and medium-sized LCD backlight market penetration.

In 2009, the proportion of LCD TVS using LED backlight was only 3%. In the next three or four years, it will rapidly climb to 40% to 50%, bringing huge business opportunities for manufacturers developing LED driver solutions.

Compared with CCFL, LED backlight color performance has more advantages.

LED USES 5 V ~ 24 V low voltage drive, very safe, drive circuit design is relatively simple, but also very power saving.

LED does not use mercury harmful to the environment, there is no mercury leakage and other problems.

LED technology also faces some challenges, such as low luminous efficiency, high cost, expensive.

As LCD backlighting shifts to a variety of LED technologies, design engineers are also dealing with new challenges in power management, thermal management, and color management.

Currently, automotive electronics, mobile devices, LCD backlight, addressable signs and general lighting are all potential application fields of LED technology, among which LCD backlight will become the next main battlefield of LED technology.

In addition, the growing number of battery-powered portable applications and their smaller sizes make these devices increasingly power-hungry.

The use of low-power LED drivers will help save power consumption, extend battery life, and bring consumers a better experience.

Asme semiconductor's diverse backlight solutions

1. Medium and large size LCD TV LED backlight solution

LED backlight LCD TV mainly has two schemes of side light type and backlight type.

In addition, because the LED backlight LCD TV is an important selling point for its ultra-thin appearance, its power management scheme to low height to match the composite thin design, but also to take into account heat dissipation, reduce electromagnetic interference, different channel brightness matching, dimming and fault diagnosis and protection and other issues.

(1) side light scheme: the cost-effective multi-channel linear LED side light scheme of ansemer semiconductor adopts NCP1397 primary side controller and 500v high-voltage MOSFET NDF05N50, as well as 6-channel linear LED driver CAT4026 in the half-bridge conversion section.

CAT4026 is a multi-channel linear LED driver with high cost performance for large-size side-light LED backlight LCD TVS. It can support 6 channels with a single IC. It can be easily classified into up to 12 or 18 channels (2 or 3 controllers are used accordingly).

Provide < 2% excellent current matching accuracy and <1% of 400 Hz PWM dimming range, and external power bipolar junction transistor to achieve better heat dissipation.

The scheme is composed of LED backlight converter (NCP1397, etc.) and LED controller (CAT4026, etc.) (see figure 1). It supports the design of low-height LED backlight LCD TV.

(2) straight-down scheme: in addition to the side-light scheme, asme also provides the straight-down step-down drive scheme based on NCP1397, NDF05N50 and NCP1034.

NCP1034 USES a programmable switching frequency of up to 500 kHz to drive a pair of external N channel MOSFET, which can flexibly adjust the work of the integrated circuit to meet the system-level requirements.

In addition, the internal 1.25v reference voltage can be used to precisely stabilize the output voltage for low-voltage applications.

The device has protective features against electrical failures, such as under-voltage locking and hiccup current limits, to provide system-level security in the event of a failure.

Its advantages include driving high energy efficiency field effect tubes (FET) and providing a fixed frequency for one or more devices.

Asme also provides more one-stop solutions for LED backlit LCD TVS, including power factor correction (PFC), standby switching power, and related rectifiers, operational amplifiers, MOSFET and discrete devices.

2. Portable LED backlight solution

For designers of portable electronic devices, efficiency and small size are often top priorities.

Various semiconductor introduced all kinds of LED backlight and optimization scheme for carrying type equipment, such as used for button cell power supply equipment of low power LED back disc motor, and used in mobile phones and digital cameras and other LED back disc motor, to cooperate with customers in small size design of prolong the life time of the battery at the same time, introduced in accordance with user needs innovation product.

(1) button battery-powered LED cd-rom power unit: more and more innovative portable devices have adopted button battery, such as glucose meter, digital thermometer, blood oxygen meter, respiratory analyzer and physiological monitor.

Because of the unique nature of the battery and its long working life, these compact applications require custom LED drives that not only manage backlighting, but also monitor battery power.

A new CAT3661 single LED driver can be used in this type of application. The application circuit diagram is shown in figure 3.

The device USES the patented Quad Mode charge pump architecture from amsemi semiconductor, with an energy efficiency of up to 92% and A static current as low as 150 A, providing adjustable low battery detection, robust LED fault detection, soft start and short circuit limits, and A low height 3 x 3 mm tqfn-16 package for this type of application.