1 Introduction: At present, on the global scale, LCD TV is rapidly entering the family with its advantages of advanced technical performance, beautiful and fashionable appearance, stable work and high reliability. It is expected that in the next few years, LCD TV will be the mainstream product in the digital TV era. With the increasing use of LCD TVs, the consumption of electrical energy is also increasing, and the pressure on energy saving and environmental protection has increased dramatically. Therefore, the demand for improving the energy efficiency of LCD TV switching power supplies is becoming more and more urgent. To this end, many government agencies and industry organizations in the world have formulated new power consumption specifications for TVs of different sizes, such as the "Energy Star 3.0" standard in the United States and the "Blue Angel" standard in Germany. Improve the efficiency of the use of electrical energy and reduce electrical energy consumption. The author will discuss how to optimize the design scheme of PFC level, main DC / DC level and standby converter, in order to better improve the energy efficiency of LCD TV switching power supply and meet the new power consumption standard. 2 LCD TV power management system structure: To improve the energy efficiency of LCD TV switching power supplies, an important aspect is to analyze the structure of the LCD TV power management system, analyze the source of power loss, and take targeted measures to reduce energy consumption. Usually the LCD TV power management system is composed of three parts: power supply unit, DC / AC inverter and signal processing system. Its typical structure is shown in Figure 1. The power supply unit is composed of PFC pre-regulator, main DC / DC stage and standby converter, which is used to convert AC input voltage (85 ~ 265 V) into lower DC output voltage (24 V, 12 V, 5 V and 3.3 V), where the 24 V or 12 V DC voltage output from the main DC / DC stage is used to power the backlight inverter and signal processing system, and the 5 V or 3.3 V DC voltage output from the standby converter is the standby component and the microcontroller powered by. The DC / AC inverter is responsible for converting 24 V or 12 V DC voltage into a high AC voltage (for example, 1 200 V AC voltage) to power the backlight. The signal processing system is used to control and process sound and image signals. 3 PFC pre-regulator solution: In order to reduce the power consumption of the PFC level and achieve the goal of improving the energy efficiency of the PFC level, the topology and the working mode of the PFC controller need to be considered. Considering the complexity of the design and the total cost of the power solution, the best solution is: the topology is Boost boost structure, and the working mode of the PFC controller is continuous conduction (CCM) mode. For the CCM working mode, the PFC controller can choose the solution provided by ON Semiconductor or Infineon Technology Co., Ltd. (referred to as "Infineon"), which can make the power factor higher than 93% and meet the ICE61000-3-2 standard requirements . However, if you consider the various factors such as cost performance, reliability, and high power factor, choosing the PFC controller NCP165 4 from ON Semiconductor is a more reasonable solution. Using this controller requires very few external components, which makes the design of the PFC class more concise. This controller has very low power consumption and can meet the requirements of improving PFC energy efficiency. At the same time, it also has the characteristics of fast transient response, extremely low startup current and shutdown current, and has many safety protection features, such as inrush current detection, Overvoltage protection, undervoltage detection for open loop detection, soft start, accurate overcurrent limit, true overload limit, etc. In short, it integrates all the features required to build a compact and robust PFC. In addition to the controller part, choosing the new CP series Cool-MOS switch with low on-resistance and low parasitic capacitance and soft recovery boost diode is also the best choice to improve efficiency. In summary, the PFC converter circuit in the LCD TV switching power supply is shown in Figure 2.
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According to the calculation of ON Semiconductor ("On Semiconductor"), the PFC level loss and the main DC / DC level loss of the LCD TV switching power supply are the main losses of the LCD TV switching power supply, of which the PFC level loss accounts for about 40% of the total power loss %, The main DC / DC level loss accounts for about 60% of the total power loss. To this end, the author will optimize the design of the PFC level and the main DC / DC level to reduce the power consumption of the two, and at the same time design the standby converter to meet the new power consumption specification of the standby power consumption of the switching power supply should be less than 1 W standard requirement. 