None of the scientists involved in pioneering the world’s first visible spectrum LED in 1962 could have dreamt of the innumerable applications that would utilise their invention 48 years later. While the development of the LED heralded a breakthrough in scientific terms, there were a number of problems with their practical applications. Early LEDs were costly and their low brightness made them insufficient to illuminate sufficient areas, so their only real practical use was as indicator lights. Since then, LED costs have come down and performance improved, spawning a host of new applications in the automotive industry, lighting and consumer products, ranging from miniaturised mobile phones to large panel LCD TVs.
By EB Bureau
Friday, August 12, 2011: LED is good source
One of these new applications is LED backlighting technology. Once the little brother of cold cathode fluorescent lamp (CCFL) technology, the increasing use of LED backlighting as a viable and even preferable alternative to CCFL has been made possible by advances in technology which get around the traditional problems of LED backlighting. With those obstacles removed, many manufacturers have opted to use LED backlighting in a number of different types of devices because of the advantages it enjoys over alternative backlighting technologies—in terms of power consumption, LEDs are far more energy efficient, and integrating an ambient light sensor can reduce energy consumption even further. Their lifecycle is potentially far longer, often measured in hundreds of thousands of hours, depending on physical operating factors such as temperature. They eliminate the use of mercury that is still a feature of some CCFL solutions, and also avoid the ‘flicker’ effect of CCFL, a known cause of eye strain. The physical space required by an LED device is usually far less than the non-LED equivalent, facilitating the demand for smaller consumer electronic devices such as smartphones.
So it is not surprising that LEDs are replacing rival backlighting technologies in a host of products featuring display panels like smartphones, tablets, notebooks, photo frames, TVs, etc. To meet the growing LED lighting needs of various backlighting applications, some semiconductor companies like ON Semiconductor offer LED solutions to make customers’ applications more efficient.
There are two alternative ways to achieve LED backlighting of medium to large panel screens—either by using dynamic RGB LEDs, which are positioned behind the panel, or by using white edge lit LEDs positioned around the rim of the screen which use a special diffusion panel to spread the light evenly behind the screen. This latter approach allows for extremely thin LCD TVs, and is the approach that a device from ON Semiconductor, the CAT4026, is designed for. The CAT4026 is an LED controller that works by driving six long strings of LEDs with an equivalent anode output voltage centred around 105 V (90 V min and 121 V max). The complete power supply system includes an off line PFC unit (or high voltage power supply), the HB-LLC board and the LED load. Featuring robust fault detection and prevention in every possible fault scenario, the CAT4026 is suitable for use in large LCD panels, such as large LCD TVs.
ON Semiconductor also offers the NCP1294 fixed frequency flyback pulse width modulation (PWM) LED controller. Properly driven and controlled, LEDs offer a dimming range that is more than 10 times better than CCFL dimming.
Since the 1960s, the efficacy (measured in cost per lumen) and light output of LEDs has made great strides, in much the same way predicted by LED pioneer Dr Roland Haitz (a trend sometimes referred to as ‘Haitz’s law’). This rapid development mirrors the progress made in other areas of semiconductor and materials technology. The combined effect of these advances is that LED technology has expanded into entirely new markets, including backlighting.
Electronics Bazaar, South Asia’s No.1 Electronics B2B magazine