Analysis of the power supply development trend of full HD TV

In recent years, based on the concept of high definition (HD), the concept of full high definition (Full HD) has begun to be accepted and welcomed by the market. LCD monitors, LCD TVs and plasma (PDP) TVs above a certain size can support full HD resolution. Among them, LCD monitors above 24 or 26 inches can support full HD, and for LCD TVs, 32-inch models can support full HD, but to get a better display effect, it is more realistic to have an LCD TV of 37 inches and above.

While these large-size full HD displays or TVs provide consumers with a better viewing experience, they also come with the problem of rising power consumption. Higher power consumption will directly increase consumers' electricity bills and is contrary to the trend of energy conservation and environmental protection . In view of this, governments and regulatory agencies have issued or updated energy efficiency regulations for TVs, such as the " Energy Star" version 3.0 TV regulations issued by the US Environmental Protection Agency (EPA) , which came into effect on November 1, 2008. This specification covers the specifications for TVs that support full HD, as shown in Figure 1. This specification is neutral for different display technologies (such as LCD, plasma, rear projection, etc.), that is, no matter what technology is, it only needs to follow the common energy efficiency specifications. In addition to the US " Energy Star", the European Union, Japan and China are also revising relevant standards and formulating working energy consumption requirements for TVs.

LIPS solution replaces traditional power solution

Among various types of full HD TVs, larger-sized LCD TVs have the largest share. Therefore, this article mainly discusses LCD TVs. In order to reduce the power consumption of larger-sized LCD TVs, make them meet various energy efficiency regulations, and help reduce system costs and reduce solution size, making LCD TVs more popular with consumers, we can take a variety of approaches in terms of LCD TV power supply.

The traditional LCD TV power supply mainly includes AC/DC conversion, 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 together with the LCD panel. Among them, in the AC/DC power supply part, the mains 110Vac/220Vac voltage is converted into 200V/400V DC high voltage after rectification, power factor correction (PFC) and filtering. Since the input voltage requirement of the traditional inverter is 24V, the output voltage of PFC 200V/400V must be buck-converted to generate multiple output voltages, one of which is 24V voltage provided to the inverter, that is, it is converted to a high voltage of more than 1,000V or even 2,000V through DC-AC (DC/AC) to drive the CCFL backlight of the LCD panel. The functional block diagram of this standard 24V inverter LCD TV switching power supply is shown in Figure 2.

Figure 1: Energy Star TV Product Specification Version 3.0 for some characteristic size TV operating energy consumption requirements.

This traditional power supply still accounts for the majority of LCD TV power supplies on the market. For LCD TVs of 26 inches and above, a new inverter concept has emerged in recent years - high-voltage LCD integrated power supply (LCD Integrated Power Supply, abbreviated as LIPS). Unlike traditional power supplies where the inverter is located on a separate circuit board, this LIPS solution combines AC/DC, DC/DC and inverter on the same circuit board. After rectifying, PFC and filtering the mains power and obtaining a 200V/400V DC voltage, the 200V/400V voltage will be directly used as the input of the inverter, and converted to a high voltage of more than 1,000V or even 2,000V required by the LCD panel through DC/AC boost. This eliminates the 24V conversion stage and reduces the large amount of power loss in the process of first stepping down to 24V and then significantly boosting the backlight source to use a high voltage of one or two kilovolts, thereby improving system energy efficiency, reducing chassis heat, and reducing total costs.

Figure 2: Block diagram of a traditional LCD TV switching power supply using a standard DC 24V inverter.

In this regard, ON Semiconductor and Microsemi have collaborated to combine their expertise to provide a complete set of high-voltage LIPS solutions suitable for multiple power levels. Currently, they have jointly developed a LIPS solution for 32-inch LCD TVs (as shown in Figure 3). In terms of system motherboard power supply, this solution uses ON Semiconductor 's NCP1606 PFC controller and NCP1351 PWM controller as an auxiliary switching power supply ; and in the LIPS inverter part, Microsemi's LX6503 phase-shifted full-bridge driver using soft switching technology is used, 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 backlight drive current waveform, and no additional power diodes are required on the bridge. The current specifications of the four MOSFETs and transformers used in this full-bridge structure are half of those 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), etc.

Figure 3: Functional block diagram of ON Semiconductor's full-bridge high-voltage LIPS solution for 32-inch LCD TVs.

In order to better meet the market demand for larger-sized LIPS LCD TVs, ON Semiconductor is developing the next generation of LIPS LCD TV reference designs 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 to drive more CCFL lamps. In terms of system motherboard power supply, ON Semiconductor's solutions can be flexibly selected according to specific design requirements, such as PFC controllers such as NCP1601, NCP1606 or NCP1631, and PWM controllers such as NCP1351 or NCP1379. This new solution uses a dedicated standby switching power supply with relays to support ultra-low standby power consumption as low as 150mW. The component height on the circuit board of this solution is less than 16mm (the total system height is less than 20mm), supporting a slimmer LCD TV design. ON Semiconductor's LCD TV reference designs fully meet the Energy Star specification for Full HDTV power consumption requirements with a large margin.

It is worth mentioning that different regional markets such as the United States/North America and China/EU have different requirements for power supply. ON Semiconductor provides corresponding power supply solutions for different power supply requirements in different regions of the world, aiming to optimize design, reduce system size and reduce costs.

Novel PFC architecture supports ultra-thin Full HD TV designs

As we all know, LCD TVs are now thinner, with the latest trend being that the thickness of the electronic modules tends to be less than 10mm. Such a thin thickness brings more stringent challenges to power supply design, such as the need to use a low-profile transformer (which is particularly critical for high-voltage LIPS where isolation and leakage are considered) or multiple components (PFC coils) in series, and use a low-profile heat sink to install the components horizontally, and limit the height of all vertically inserted capacitors to less than 10mm.

In terms of PFC, the use of PFC controllers such as ON Semiconductor's NCP1606 and NCP1654 has reduced the thickness of LCD TVs to a minimum. In order to support an extremely slim design as low as 10mm, two relatively small NCP1601 chips can be used to implement an interleaved architecture, as shown in Figure 4. The main idea of ​​the so-called interleaved PFC is to place two smaller PFCs with half the power in parallel where a single larger PFC was originally placed. The two smaller PFCs work alternately with a phase shift of 180°, and when they are accumulated at the input or output, the main part of the current ripple in each phase will be offset.

Figure 4: Functional block diagram of an interleaved PFC architecture implemented using two NCP1601 PFC controllers.

In order to provide customers with more choices, ON Semiconductor also plans to launch a new interleaved PFC controller NCP1631 in 2009. This is a single-chip solution that replaces two NCP1601s, but can achieve the same extremely low design height, suitable for the design of extremely thin LCD TVs with a thickness of 10mm, and also extends the power range and reduces current ripple.

Standby power consumption tends to be less than 100mW?

The standby power consumption of LCD TVs is another point worth paying attention to. The Energy Star 3.0 TV specification, which came into effect in November 2008, sets a standard for standby power consumption of less than 1W. Although this standard is not a mandatory requirement, it still has a high guiding significance in the market.

The standby power consumption of LCD TVs will be further reduced in the future. For example, the power consumption will be less than 600mW when the output power is 50W with the addition of a small dedicated microprocessor, less than 400mW with a dedicated standby switching power supply, and less than 200mW with a dedicated standby switching power supply and an additional relay (thus disconnecting all PFC and switching power supplies in standby). If manufacturers want to use more "green" technology to differentiate their products, establish a higher brand image and increase profit margins, they will need to further improve the design, so that the standby power consumption of less than 100mW may become the next important trend.

Conclusion

Full HD technology that provides 1,080 lines of progressive scan (1,080p) vertical resolution is gaining popularity among consumers. This article uses a larger LCD TV that supports Full HD as an example to analyze the development trend of Full HD TV power supplies and explores architectures and technology innovations designed to reduce energy consumption and size, such as eliminating the traditional 24V inverter power supply through Liquid Crystal Integrated Power Supply (LIPS) and using a novel interleaved architecture to reduce the thickness of the PFC module to support the design of extremely thin Full HD TVs. As a leading global supplier of energy-efficient power management solutions, ON Semiconductor provides high-performance power solutions and reference designs to help electronics manufacturers shorten the development cycle of Full HD TV products that meet the requirements of different global application markets and accelerate the time to market.