Power supply design in consumer electronics always poses serious challenges to the implementation of form factors, cost and efficiency metrics. The TV market is a good example. It is undergoing a dramatic shift from a bloated, CRT-based solution to a flat-panel TV using liquid crystal displays (LCDs) and plasma displays. LCD currently dominates the flat-panel TV market, and its expected sales in 2008 will exceed 100 million units. At the same time, content has shifted from analog to digital, and new features have increased dramatically, such as multi-tuners for picture-in-picture capabilities, full HD quality (1080p), enhanced audio, and even Internet access.
This article refers to the address: http://
In addition, the screen size limitations that exist in CRTs will no longer exist. Currently, 32-inch widescreen TVs are the most popular, followed by 40-42-inch TVs. While the adoption of new technologies has boosted sales and improved the viewing experience for TV users, it has also caused a significant increase in power consumption.
Energy-saving standards Historically, energy-saving standards for consumer electronics, such as the US Energy Star and the EU Ecolabel, focused on the impact of static power consumption. However, with the shift to flat-panel TVs, the issues that people need to care about extend to the work (active mode) power consumption.
The actual test shows that the power consumption of the 42-inch flat-panel TV is between 180 and 500W, and the specific values ​​are related to the technology (LCD or plasma display), feature set and design choice. In comparison, the power consumption of a 29-inch CRT TV is about 100W.
Obviously, some of the increased power consumption is directly related to the increase in screen size, but this is not the only reason. For example, LCD TV displays require a backlight subsystem; this portion of the power consumption cannot be ignored and is directly related to screen size. The increase in average power, combined with the increase in hours of use caused by games, music programs, web browsing, and home theater, has increased household electricity consumption.
Norms and government agencies are addressing this shift. The ENERGY STAR standard for television has just been revised and introduced version 3.0 (enabled since November 2008), which will include operating power limits. These limits are based on screen area and resolution (high definition or standard definition) and are independent of display technology (LCD, plasma or rear projection).
Calculating Power Limits There are several algorithms that can calculate power limits based on screen size and resolution. For example, for a high-definition TV with a screen area of ​​680 to 1068 square inches (4387 to 6890 cm2), the formula is as follows:
Pmax=(0.240×area+27)W
Note: The unit of area is square inches.
Therefore, the working power limit of a 32-inch HDTV is 120W, while the limit of a 42-inch HDTV is 208W. These limits are based on actual testing of multiple products from multiple vendors. In the test sample, 27.4% passed the target's working and static power requirements. Static power requirements remain the same: since July 2005 it has been the limit of 1W maximum.
A typical power supply for a 32-inch LCD TV (see Figure 1) produces several voltage rails to power various system modules, such as audio, backlight, and signal processing modules. The mains supply does not provide all of the required voltage values. Instead, the various low voltage rails are provided by local linear and DC/DC converters.
Figure 1 Common 32-inch LCD TV switching power supply
There may be five or more linear or low dropout regulators on the signal processing board, and several buck converters are used to generate low voltage supply rails for deep submicron digital signal processing modules. As shown in the figure, it is quite common for manufacturers to use a unified power supply that supports AC voltages of 90 to 265V. This approach makes it possible to use a single voltage design for a range of modules in different regions depending on the TV size, simplifying logistics and reducing development costs.
If the LCD TV is for the global market and the power exceeds 75W, then the TV must comply with the European standard IEC61000-3-2 for harmonic reduction. In this case, an operating power factor control stage is required.
Backlight power For TVs above 26 inches, backlighting is the most power-hungry part. The 24V rail provides power to the inverter stage while the latter drives the backlight cold cathode fluorescent lamp (CCFL). The inverter converts the 24V DC voltage into a high-voltage, low-current AC signal that is used to start and drive these fluorescent lamps.
The structure of the two main inverter units is common: one for powering the backlight inverter and the other for controlling audio/video and signal processing. Historically, the power level of the switching power stage was developed based on a single-switch quasi-resonant (QR) or fixed-frequency pulse-width modulation (PWM) flyback topology. Depending on the characteristics of the TV and the power requirements of the 12V and 5V rails, a dedicated switching power supply may be present in the circuit to provide static power and a static power limit of 1W.
Actual Power Topology As the screen area increases, the power required for the 24V DC rail will continue to increase until the flyback topology can no longer be used to implement the switching power supply. Therefore, many of the more powerful topologies, including the half-bridge dual inductor plus single capacitor (LLC) topology, are considered for high efficiency operation with low electromagnetic interference in a compact space.
The half-bridge LLC topology is considered a series resonant converter. As shown in Figure 2, LLC refers to the inductor-inductor-capacitor structure. The first inductor is connected in series in the circuit, the transformer represents the second inductor, and the capacitor is connected to the output of the transformer.
Figure 2 Simple LLC Half-Bridge Power Stage
The basic idea of ​​this method is that the half-bridge FET is driven by a 50% duty cycle waveform, and the power is adjusted by changing the frequency. Typically, this design is designed to allow the switching frequency to exceed the resonant frequency of the circuit.
In this region, the current is delayed by the voltage through the switch, so the switch is turned on in the zero voltage switching region, almost eliminating the capacitive switching loss. Because this is a resonant topology, it is very efficient over a wide voltage range.
Figure 3 shows an example of a complete power supply based on a half-bridge LLC structure. In this example, the HB-LLC stage produces multiple outputs. This design is part of a series of Greenpoint reference designs developed by ON Semiconductor that demonstrate a highly efficient power supply topology. In this example, for a 115 or 230V AC mains supply, the overall efficiency is greater than 88% in the range of 90-220W.
Figure 3 Block diagram of the complete 220W LCD TV power supply
In addition to achieving high overall efficiency, this power supply has a small form factor of only 25mm. For flat-panel TVs, the height of the power supply is important because it affects the total thickness of the TV. There is a growing interest in designing ultra-thin flat-panel televisions that can be easily hung on the wall. This trend poses a further challenge to the power supply because the volume needs to be reduced and the airflow through the power supply may be more limited.
The challenge of designing high-density, high-efficiency power supplies is driving power supply designers to adopt innovative power architectures to support these rapidly evolving consumer applications. The Half-Bridge Resonant LLC meets the efficiency and volume goals required for flat panel TVs while still providing the cost-effective solution required for consumer electronics.
With the introduction of new work power standards and consumer awareness of the energy consumption of switching to large-screen digital TV, the focus on energy-efficient solutions will increase. This not only requires switching to efficient power solutions, but also creating new systems to reduce signal processing and LCD panel power consumption.
Sexy Mouse Pad,Carpet Mouse Pad,3D Mouse Pad
Tianxiaxing Rubber Products Co., Ltd. , http://www.china-rubber-mat.com