The penetration rate of liquid crystal televisions (LCD TVs) in the market has increased rapidly. Some market research predicts that with the advantages of large screens, low thickness and high definition, the overall market share of LCD TVs will reach 50% in 2009. With the continuous breakthrough of screen size, the power of LCD TVs is also rising. Higher power consumption will directly increase consumers' electricity bills, and departs from the trend of energy saving and environmental protection. Therefore, governments and regulatory agencies in various countries have issued or updated energy efficiency specifications for televisions, such as the "Energy Star" version 3.0 television specifications issued by the US Environmental Protection Agency (EPA), which took effect on November 1, 2008.
LIPS solution replaces traditional LCD TV power supply
In order to reduce the power consumption of larger-size LCD TVs, make them comply with various energy efficiency specifications, and help reduce system cost and solution size, so that LCD TVs are more popular with consumers, as far as LCD TV power is concerned, we can take Through multiple channels.
Figure 1: Block diagram of a traditional LCD TV switching power supply using a standard DC 24 V inverter
The traditional LCD TV power supply mainly includes AC-DC (AC-DC) conversion, DC-DC (DC-DC) conversion and high-voltage inverter. AC-DC and DC-DC are located on the same circuit board, while the inverter is an independent circuit board, usually provided with a liquid crystal panel. Among them, the AC-DC power supply part, the 110 Vac / 220 Vac voltage of the commercial power is converted to 200 V / 400 V DC high voltage through rectification, power factor correction (PFC) and filtering. Since the input voltage of the traditional inverter is 24 V, the output voltage of the PFC 200 V / 400 V must undergo a step-down conversion to generate multiple output voltages. One of the 24 V voltages is provided to the inverter. After DC-AC conversion to a high voltage exceeding 1,000 V or even 2,000 V, the CCFL backlight of the LCD panel is driven. The functional block diagram of this standard 24 V inverter LCD TV switching power supply is shown in Figure 1.
In the LCD TV power supply currently on the market, this traditional power supply is still the majority. It is worth mentioning that, among LCD TV models of various sizes, LCD TVs larger than 26 inches, especially 32 inches and larger, dominate the market. For LCD TVs with a size of 26 inches and above, a new inverter concept has emerged in recent years-high-voltage liquid crystal display integrated power supply (LCD Integrated Power Supply, abbreviated as LIPS). Unlike the traditional power supply where the inverter is located on a separate circuit board, this LIPS solution combines AC-DC, DC-DC and the inverter on the same circuit board, after rectifying, PFC and filtering the mains After the 200 V / 400 V DC voltage is obtained, the 200 V / 400 V voltage is directly used as the input of the inverter, which is converted into a high voltage exceeding 1,000 V or even 2,000 V required by the LCD panel through DC-AC boosting. This eliminates the 24 V conversion stage, reducing the large amount of power loss in the process of first stepping down to 24 V and then substantially boosting the backlight with a high voltage of one or two kilovolts, thereby improving system energy efficiency, reducing chassis heat generation, and reducing total cost .
Figure 2: ON Semiconductor ’s full-bridge high-voltage LIPS solution functional block diagram for 32-inch LCD TVs
(LDO) is used for lower output current, generally in the range of 0.1 to 1.5 A; while high current LDO, bias input LDO controller and integrated buck converter are used to provide output current of 1.5 A to 5 A. In terms of higher current, a synchronous buck controller with external switch and synchronous rectifier can be used to provide a current output greater than 5 A. ON Semiconductor provides a series of high-performance LDO regulators, such as NCP699 / 633, NCP5500 / 5501, NCP3334 / 3335A, NCP5661 / 5662/5663, NCP605 / 606 and NCP3520 / 3521.
From the perspective of development trends, as the integration of more audio and video processing chipsets becomes higher and higher, a single IC may require multiple output voltages (such as 3.3 VI / O and 1.25 V core), making linear The choice of programs (LDO) is increasing. In addition, because the size of the circuit board tends to be smaller, so that the board space that can be allocated to the power dissipation of the LDO is reduced, accordingly, the DFN packaged LDO can be used to increase the power density, and the integrated MOSFET and LDO controller can help reduce PCB area.
On the other hand, in order to improve power conversion efficiency and support high-current operation and out-of-phase operation, some outputs need to be converted from LDOs to switching regulators. Switching regulators and controllers are tending to use higher switching frequencies, such as from 50 kHz to 150 kHz, 350 kHz, 500 kHz, and even 700 k Hz, thereby allowing the size of external inductances and capacitors to be reduced, which is more convenient for manufacturing. Slim LCD TV. And to help reduce system size and cost, switching regulators tend to integrate multiple outputs, such as dual regulators. In addition, the current requirements on some voltage input terminals are getting higher and higher, even greater than 5 A, which has led to integrated switching regulators with greater current capability, as well as discrete controllers + FETs with higher switching frequencies (FET) combination and promote the application of synchronous rectification technology.
ON Semiconductor ’s NCP312x series of dual 2 A / 2 A and 3 A switching regulators are ideal for +5 V or +12 V input applications on the signal processing board of LCD TVs. Their frequencies can range from 200 kHz to 750 kHz Adjustable between ranges, providing a voltage reference of 0.8 V ± 1%, and supporting 180 ° out-of-phase operation, and users can control the automatic tracking and sequencing functions.
Adopt novel PFC architecture to support ultra-thin LCD TV design
As we all know, the thickness of LCD TVs can now be made thinner. The latest trend is that the thickness of electronic modules tends to be less than 10 mm. Such a thin thickness brings more stringent challenges to power supply design, such as the need to use low-height transformers (which is particularly critical for high-voltage LIPS that requires isolation and leakage) or multiple components (PFC coils) connected in series and using low The height of the heat sink, install the components horizontally, and limit the height of all vertically inserted capacitors to less than 10 mm.
Figure 3: Functional block diagram of an interleaved PFC architecture implemented with two NCP1601 PFC controllers
In this regard, ON Semiconductor cooperates with Microsemi to combine the expertise of both parties to provide a complete set of high-voltage LIPS solutions suitable for multiple power levels. At present, we have cooperated to develop LIPS solutions for 32-inch LCD TVs (as shown in Figure 2). In terms of system motherboard power supply, this solution uses ON Semiconductor's NCP1606 PFC controller and NCP1351 PWM controller acting as an auxiliary switching power supply; and in the LIPS inverter part, Microsemi's LX6503 phase shift using soft switching technology is used Full-bridge driver, which can perform zero-voltage switching (ZVS) at a fixed operating frequency. Compared with the half-bridge architecture, this full-bridge inverter solution has significant advantages, such as reducing electromagnetic interference (EMI) and power loss, while improving the drive current waveform of the backlight, without the need for additional power diodes on the bridge, which The current specifications of the four MOSFETs and transformers used in the full-bridge structure are half that of the half-bridge structure. It can directly drive the power MOSFET through the isolation transformer, making it easier to implement primary-side overcurrent protection (OCP).
In order to better respond to the market's demand for larger-size LIPS LCD TVs, ON Semiconductor is developing a next-generation LIPS LCD TV reference design, and plans to launch a 46 / 47-inch reference design in mid-2009. In the LIPS inverter part, the same full-bridge inverter and backlight controller LX6503 as the 32-inch solution are used, but the output power is greatly improved, which can drive more CCFL lamps. In terms of system motherboard power supply, you can flexibly choose ON Semiconductor solutions based on specific design requirements, such as NCP1601, NCP1606 or NCP1631 and other PFC controllers, and NCP1351 or NCP1379 and other PWM controllers. This new solution uses a dedicated standby switching power supply with relays to support ultra-low standby energy consumption as low as 150 mW. The height of the components on the circuit board of this solution is less than 16 mm (the total degree of the system is less than 20 mm), which supports a slimmer LCD TV design.
It is worth mentioning that different regional markets such as the United States / North America and China / EU have different power requirements. ON Semiconductor provides corresponding power solutions for different power requirements in different regions of the world, aiming to optimize design, Reduce system size and cost.
Adopt different voltage regulator configurations for audio and video signal processing power supply according to output current demand
For audio and video signal processing, the input voltage is usually +5 V or +12 V. In terms of voltage regulator or controller configuration, it can be configured according to the output current requirements. Generally speaking, for low-dropout regulators, PFC controllers such as ON Semiconductor ’s NCP1606 and NCP1654 can be used to reduce the thickness of LCD TVs to a lower level, and in order to support extremely slim designs down to 10 mm , You can use two relatively small NCP1601 chips, using an interleaved architecture to achieve, as shown in Figure 3. The main idea of ​​the so-called interleaved PFC is to place two smaller PFCs of half power in parallel where the single larger PFC was originally placed. These two smaller PFCs work alternately with a 180 ° phase shift. When they are accumulated at the input or output, the main part of the current ripple in each phase will cancel out.
In order to provide customers with more choices, ON Semiconductor also plans to launch the new interleaved PFC controller NCP1631 in 2009. This is a single-chip solution that replaces two NCP1601s, but it can achieve the same extremely low design height, suitable for a very thin LCD TV design with a thickness of 10 mm, and also expands the power range and reduces current ripple.
Standby energy consumption tends to be below 100 mW?
LCD TV standby energy consumption is another point of concern. The "Energy Star" version 3.0 TV specification, which came into effect in November 2008, has a standby power consumption standard of less than 1 W. Although this standard is not mandatory, it still has high guiding significance in the market.
The standby energy consumption of LCD TVs will be further reduced in the future. For example, under the condition of adding a small dedicated microprocessor, the power consumption is less than 600 mW when the output power is 50 W, and the power consumption is less than 400 mW when using a dedicated standby switching power supply, and using a dedicated standby switching power supply and adding a relay (thus Disconnect all PFC and switching power supply during standby) when the energy consumption is less than 200 mW. If manufacturers want to use more "green" technology to differentiate products and establish a higher brand image to increase profitability, they need to further improve the design, so that standby energy consumption less than 100 mW may become the next important trend.
While the LCD TV market continues to grow and develop, its power consumption issues have also attracted more attention. An important way for electronics manufacturers to stand out in the market competition is to continuously optimize their LCD TV power supply design and design to meet the latest energy efficiency specifications and other important development trends, such as the use of LIPS solutions to replace traditional inverters, through innovation The PFC architecture supports ultra-thin LCD TV design, etc. This article focuses on the analysis of the impact of these trends on LCD TV power supply design, and combined with ON Semiconductor products and reference designs, explains in detail how to support these latest trends, thereby helping electronic manufacturers to shorten the development of products that meet the requirements of different global application markets Cycle to speed up the listing process.
To use these connectors, the ribbon cable is inserted into the Ribbon Connector and the connector is then plugged into the Ribbon Connector on the circuit board. The connectors are designed to provide a secure and reliable connection that can withstand repeated insertions and removals.
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