ON of semiconductor companies BernieWeir consumer power design of electronic applications have been there the appearance, cost and energy efficiency targets difficult challenge. The TV terminal market has been from the cathode ray tube (CRT) technology steering plasma, liquid crystal display (LCD) and rear wide range of digital TV display technology. , LCD has established a clear lead, It is predicted that in 2008, global shipments of LCD TV (LCDTV) for the first time more than the CRT TV shipments expected to reach 100 million. At the same time, the content has been shift from analog to digital format, display resolution has increased, and has been widely adopted by the widescreen format, also added a multi-tuner picture-in-picture function, Full HD (1080p), enhanced audio and even Internet access and other enhanced features.
In addition, the CRT screen size limitations disappear, the average screen size has increased, resulting in a 32-inch widescreen TV has now become the most popular models, the range of 40 to 42 inches, followed by screen size greater than 50-inch TV is also very common. Although the use of new technologies to promote market growth and to improve the user's viewing experience, but also attracted more and more attention to the impact of this shift on global energy consumption.
From a historical point of view, the U.S. Energy Star (ENERGYSTAR) "and the EU eco-labeling (Eco-lable)" for the field of consumer electronics voluntary energy efficiency standards will focus on the impact of the standby power consumption, but With the popularity of digital flat-panel TVs, the attention has been extended to the energy consumption of the working mode. 42-inch flat-panel TV energy consumption in the real world, according to the different technology (LCD or plasma), the feature set and design choices range between 180 ~ 500W. This power range compared with the 29-inch CRT TV about 100W of power consumption, it can be seen, in part because of the increased energy is to be attributed to an increased area of the screen. But not all, of the reason, because the display technology is not the same.
For example, an LCD TV is behind the panel with a backlight subsystem, which increases the average power. Meanwhile, watch for games, music, web browsing and other activities caused by use of TV time, and home theater system also contributed to the the family increased use energy. As a result, norms and government agencies have to consider how to respond to this shift. TV's "Energy Star" standards are modified to version 3.0 process for the first time into working power (activepower) specification.
The standard is now in the final draft review stage, the goal is to take effect from November 2008. Regardless of the maximum power limit and display technology (LCD, plasma or rear projection), only the screen size and resolution (HD or SD). High-definition (HD) is defined as a higher resolution than the 480 vertical lines. Different according to the size and resolution of the screen, there are several algorithms that can be used to calculate the maximum operating power limits. For example, the area between 680 to 1068 square inches (4387 ~ 6890cm2) between the range of high-definition television with the formula:
Therefore, a 32-inch high-definition television may have a 120W power limit, while a 42-inch LCD TV power limit you will be 208W. These limits are set based on the combined with a variety of different display types, representative samples from a number of manufacturers, test. For under test samples, 27.4% by the proposed work and standby requirements. The 3.0 version of the standby power consumption requirements did not change the maximum 1W limit has been implemented since July 2005.
Different voltage input terminal for the audio, backlight, control and signal processing, such as different system modules supply. The main power on the TV within all of these voltages do not produce the desired, on the contrary, using local linear and DC / DC converter to power for the interface module, the analog circuit and the signal processing circuit. Control the audio and video signal board may have five or more linear or low-dropout (LDO) voltage regulator, and a few buck converter to produce low-voltage power supply input for deep submicron digital signal processing module. TV manufacturers support 90 ~ 265Vac voltage universal power supply is quite common.
This allows a single power supply design for a series of TV models in different regions of the same TV size range, and simplify logistics and reduce development costs. If the LCD TV is designed for the global market and power higher than 75W, it is necessary to comply with European harmonic reduction standard IEC61000-3-2, so they would have to use the the work power factor control segment. For size larger than 26-inch LCD TV, the backlight module consumes the largest part of the electrical energy and 24V power input of the power supply for the inverter segment, inverter drive for the screen backlight cold cathode fluorescent lamp (CCFL) .
The inverter functionality for conversion 24Vdc voltage to the high voltage, low current AC signal, for lighting and driving the lamp. Usually there are two main power section, one for the backlight and another for controlling the audio / video and the signal processing. At this power level, SMPS segment based on a single switch quasi-resonant (QR) or a fixed-frequency, pulse-width modulation (PWM) flyback topology. According to the feature set of the TV and 12V and 5V input of the power, may also have a dedicated switching power supply
is used as a standby power supply to meet the 1W limit standby requirements. For the larger size of the television, includes features for audio, the power of the signal processing and control functions is also increased, so that the use of a dedicated standby power supply become more common.
With increasing area of the screen, the power required by the 24Vdc input continues to increase, until no longer applied to the switching power supply of the flyback topology. As a result, a variety of higher power topology, including half bridge dual single sense a plus single capacitor (HBLLC) of topological structure has been considered for a compact space, to achieve high energy efficiency and very low electromagnetic interference ( EMI). This topology is regarded as a serial resonant converter. Which the LLC is the inductance - inductance - capacitance configuration. A first inductor in series with the transformer representing the second inductor, and the capacitor in the output of the transformer. The basic concept behind this method is the half-bridge field effect transistor (FET) by the 50% duty cycle waveform of drive, and the power adjusted by changing the frequency. Under normal circumstances, so designed that the switching frequency is higher than the resonant frequency of the circuit. In that region, the current in order to switch to the voltage delay and conduction switching in the zero-voltage switching (ZVS) area, which practically eliminates the capacitive switching losses; And because this is the topology of the resonant mode, it is in a very wide power the range has a high energy efficiency.
Based on the example of the complete power half-bridge LLC half-bridge LLC segments produce multiple outputs. This design part of the the Semiconductor Development Greenpoint reference design series, showcasing the application of energy-efficient power topology. In this example, in the 115 and 230Vac main power, cover the power range of 90 ~ 220W power supply has a higher than 88% of the overall energy efficiency.
In addition to achieve a higher overall energy efficiency in a wide power range, the power supply is also designed to low height, the most height of only 25mm. For flat-panel TVs, the power height is very important, because it is one of the major influencing factors of the total thickness of the TV. The industry is growing interest in the design can be easily mounted on the wall very thin flat-panel TVs. Decreasing TV casing, and the flow of air through the power supply
may be more restrictive, slim light Ying trend of flat-panel TVs for a further challenge to the power supply design.
With the growth of the large flat-screen TV, the challenge of more energy-efficient high-density power design needs to promote the adoption of innovative power architecture power supply designers. The half-bridge resonant LLC flat-panel TV energy efficiency needs and space objectives can be achieved, and also to provide cost-effective solutions for the price-sensitive consumer electronics products. In addition, with the new power standards are emerging, but the energy costs for consumers aware of the need to pay turned to the big screen, more and more attention on energy-efficient solutions. This involves not only turned to more energy-efficient power solutions, and also relates to the LCD panel.