With the advantages of large screen, low thickness and high definition , the penetration rate of LCD TVs in the market is rapidly increasing. According to market research, the overall market share of LCD TVs in 2009 will reach 50% . As the screen size continues to break, the power of LCD TVs is also rising. Higher power consumption will directly increase consumers' electricity bills and deviate from the trend of energy saving and environmental protection. Therefore, governments and regulatory agencies have issued or updated for energy efficiency norms television, such as the US Environmental Protection Agency (EPA) issued the "Energy Star" TV version 3.0 specification from November 1, 2008 came into force.
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In order to reduce the power consumption of larger-size LCD TVs, to meet various energy efficiency specifications, and to help reduce system cost and reduce solution size, LCD TVs are more popular with consumers. As far as LCD TV power supplies are concerned, we can take Through a variety of ways.
Figure 1 : Block diagram of a conventional LCD TV switching power supply using a standard DC 24 V inverter.
The main power supply comprises a conventional LCD TV AC - DC (AC-DC) converter, DC - DC (DC-DC) converter, and a high voltage inverter these parts. The AC-DC and DC-DC are on the same board, and the inverter is a separate board, usually supplied with the LCD panel. Among them, the AC-DC power supply section, the mains 110 Vac/220 Vac voltage is rectified, power factor corrected (PFC) and filtered, converted to a DC high voltage of 200 V / 400 V. Since the input voltage requirement of the conventional inverter is 24 V , the output voltage of the PFC 200 V/400 V must be step-down converted to generate multiple output voltages, one of which is supplied to the inverter at 24 V. after DC - AC (DC-AC) converter to exceed 1,000 V to 2,000 V and even up to high pressure, to drive the liquid crystal panel CCFL backlight. The functional block diagram of this standard 24 V inverter LCD TV switching power supply is shown in Figure 1 .
In the current LCD TV power supply on the market, this traditional power supply still accounts for the majority. It is worth mentioning that among various sizes of LCD TV models, LCD TVs larger than 26 inches, especially 32 inches and larger, dominate the market. For LCD TVs of 26 inches and above, a new inverter concept has emerged in recent years - LCD Integrated Power Supply ( LIPS) . Unlike traditional power supplies with inverters on separate boards, this LIPS solution combines AC-DC , DC-DC, and inverter on the same board.
After mains rectifying, and filtering and obtaining the PFC 200 V / 400 V DC voltage, directly using 200 V / 400 V inverter input voltage as required by a liquid crystal panel for the DC-AC step-up converter The high voltage is over 1,000 V and even 2,000 V. This eliminates the 24 V conversion section, reducing the amount of power loss that occurs during the high-voltage process of one or two kilovolts with a step-down to 24 V and then greatly boosting the backlight, thereby improving system energy efficiency, reducing chassis heat generation, and reducing total cost. .
In this regard, ON Semiconductor has partnered with Microsemi to combine high-performance LIPS solutions for a wide range of power levels . Currently, it has cooperated to develop a LIPS solution for 32 -inch LCD TVs ( as shown in Figure 2 ) . In terms of system board power, this solution uses ON Semiconductor's NCP1606 PFC controller and the NCP1351 PWM controller that acts as an auxiliary switching power supply . In the LIPS inverter section, Microsemi uses the soft-switching LX6503 phase shifting. Full-bridge driver that can perform zero-voltage switching (ZVS) at a fixed operating frequency . Compared to the half-bridge architecture, this full-bridge inverter solution offers significant advantages such as reduced 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. Specifications current transformer 4 and the full-bridge MOSFET structure is employed in the half of the half-bridge, which can directly drive the power MOSFET through the isolation transformer, the primary-side overcurrent protection is easier to implement (OCP) and the like.
In order to better respond to the market demand for larger size LIPS LCD TVs, ON Semiconductor is developing the next-generation LIPS LCD TV reference design and plans to introduce a 46/47 -inch reference design in mid - 2009 . In the LIPS inverter section, the same full-bridge inverter and backlight controller LX6503 as the 32 -inch solution is used , but the output power is greatly increased to drive more CCFL lamps. In terms of the power system board, can be flexibly selected Semiconductor solutions, such as other NCP1601, NCP1606 or NCP1631 PFC controllers, and the like, or NCP1351 NCP1379 PWM controller in accordance with specific design requirements. This new solution uses a dedicated standby switching power supply with relays to support ultra-low standby power consumption down to 150 mW . The component board on this solution has a component height of less than 16 mm ( system total less than 20 mm) and supports a slimmer LCD TV design.
It is worth mentioning that different regional markets such as the US / 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 the design. Reduce system size and reduce costs.
Different regulator configurations for audio and video signal processing power supply for output current demand
For audio and video signal processing, the input voltage is typically + 5 V or +12 V , which can be configured according to the output current requirements in terms of regulator or controller configuration. In general, low-dropout regulators (LDOs) are used for lower output currents, typically ranging from 0.1 to 1.5 A ; high-current LDOs , bias input LDO controllers, and integrated buck converters are used to provide 1.5 A to 5 A output current. For higher currents, a synchronous buck controller with an external switch and a synchronous rectifier can be used to provide a current output greater than 5 A. ON Semiconductor offers a range of high performance LDO regulators such as NCP699/633 , NCP5500/5501 , NCP3334/3335A , NCP5661/5662/5663 , NCP605/606 and NCP3520/3521 .
From a development trend, as more chipsets are integrated more in audio and video processing, a single IC may require multiple output voltages ( as required for 3.3 VI/O and 1.25 V cores ) , making linear The choice of program (LDO) is increasing. In addition, due to the smaller board size, the board space that can be allocated for LDO power dissipation is reduced. Accordingly, LDOs in DFN packages can be used to increase power density, while integrated MOSFETs and LDO controllers can help reduce PCB footprint.
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 LDO to switching regulator. Switching regulators and controllers are moving toward higher switching frequencies, from 50 kHz to 150 kHz , 350 kHz , 500 kHz, or 700 k Hz , allowing for reduced external inductors and capacitors for easier manufacturing Slim LCD TV. And to help reduce system size and reduce cost, switching regulators tend to integrate multiple outputs, such as dual regulators. In addition, the current requirements on some voltage inputs are getting higher and higher, even greater than 5 A , which leads to integrated switching regulators with higher current capability, as well as discrete controllers with higher switching frequencies + FETs. (FET) combination and promotes the application of synchronous rectification technology.
ON Semiconductor's NCP312x family of dual 2 A/2 A and 3 A switching regulators are ideal for +5 V or +12 V input applications on LCD TV signal processing boards , with frequencies from 200 kHz to 750 kHz Adjusted between ranges, provides a voltage reference of 0.8 V ± 1% , and supports 180 ° out-of-phase operation, and the user can control the automatic tracking and sorting functions.
Supports ultra-thin LCD TV design with novel PFC architecture
Figure 3 : Functional block diagram of an interleaved PFC architecture implemented with two NCP1601 PFC controllers .
On the PFC side, the PFC controllers such as ON Semiconductor's NCP1606 and NCP1654 have been used to reduce the thickness of LCD TVs. To support ultra-thin designs as low as 10 mm , two relatively small ones can be used. The NCP1601 chip is implemented using an interleaved architecture, as shown in Figure 3 . The so-called interleaved PFC , the main idea is to place two smaller PFCs in parallel at the place where a single larger PFC was originally placed . The two smaller PFCs operate alternately with a phase shift of 180° , and when they are accumulated at the input or output, the main portion of the current ripple per phase will cancel.
In order to provide customers with more choices, ON Semiconductor also plans to introduce a new interleaved PFC controller NCP1631 in 2009 . This is a single-chip solution, alternatively 2 The NCP1601, but can achieve the same low design height, 10 mm thickness for a very slim design LCD TV, but also extend the power range to minimize current ripple.
Standby energy consumption tends to be less than 100 mW ?
The standby power consumption of LCD TVs is another point of concern. The ENERGY STAR version 3.0 TV specification, which came into effect in November 2008 , is less than 1 W for standby power consumption . Although this standard is not mandatory, it still has a high guiding significance in the market.
The standby energy consumption of LCD TVs will be further reduced in the future. For example, when the output power of 50 W at a small dedicated microprocessor increasing energy condition lower than 600 mW, using dedicated standby power consumption in the switching power supply condition of less than 400 mW, and using a dedicated standby power switch and relay increases (thus when the switching power supply and disconnect all PFC) when the standby power consumption is less than 200 mW. If manufacturers want to use more "green" technology to differentiate products, establish a higher brand image and increase profit margins, it is necessary to further improve the design, so that standby energy consumption below 100 mW may become the next important trend.
to sum up:
While the LCD TV market continues to grow and develop, its power consumption problems are also attracting 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 replacing traditional inverters with LIPS solutions, and innovating The PFC architecture supports ultra-thin LCD TV designs. This article focuses on the impact of these trends on LCD TV power supply design, and combines ON Semiconductor's products and reference designs to illustrate how these latest trends can be supported to help electronics manufacturers reduce the development of products that meet the requirements of different global application markets. Cycle to speed up the listing process.
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