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| 安森美50 瓦STB 电源解决方案 | |||||
作者：安森美 文章来源：安森美 点击数： 更新时间：2008-3-17  |
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ON Semiconductor Introduces a 50 Watt AC-DC Power Supply GreenPoint™ Reference Design for Set-Top Boxes According to the Natural Resources Defense Council and Ecos Consulting, set-top boxes now consume more energy than many common home appliances. Together, the box and its attached TV could easily consume more energy per year than a refrigerator. For example, a new high-definition set-top box with built-in DVR consumes about 350 kilowatts per hour (kWh) per year. With one to two set-top boxes in most U.S. households, it is estimated that these appliances consume over 23 billion kWh of electricity nationwide, resulting in power plant emissions of over 15 million tons of carbon dioxide (CO2), a heat-trapping greenhouse gas contributing to global warming. “The way they are designed today, most set top boxes cannot be significantly powered-down without being physically unplugged from the wall,” said Andy Williams, senior vice president and general manager of ON Semiconductor’s Automotive and Power Regulation Group. “This has made efficiency in active mode a paramount concern for power supply design engineers. Our new 50 watt GreenPoint™ reference design achieves active-mode efficiency of 81 percent. Additionally, this design expands our offering of reference design solutions for home entertainment consumer electronics. It is yet another example of ON Semiconductor’s commitment to helping customers streamline their design cycles, meet a wide variety of global efficiency standards, and deliver greener power technology solutions to consumers worldwide.” The NCP1308 combines a true current mode modulator and a demagnetization detector to ensure full borderline/Critical Conduction Mode in any load/line conditions and minimum drain voltage switching (Quasi-Resonant operation). Due to its inherent skip cycle capability, the controller enters burst mode as soon as the power demand falls below a predetermined level. As this happens at low peak current, no audible noise can be heard. An internal 10 _s timer prevents the free-run frequency to exceed a high frequency (therefore below the 150 kHz CISPR-22 EMI starting limit), while the skip adjustment capability lets the user select the frequency at which the burst foldback takes place. The Dynamic Self-Supply (DSS) drastically simplifies the transformer design in avoiding the use of an auxiliary winding to supply the NCP1308. This feature is particularly useful in applications where the output voltage varies during operation (e.g. battery chargers). Thanks to its high-voltage technology, the IC is directly connected to the high-voltage DC rail. As a result, the short-circuit trip point is not dependent upon any VCC auxiliary level. The transformer core reset detection is done through an auxiliary winding which, brought via a dedicated pin. If an OVP is detected on the VCC pin, the IC permanently latches off. Finally, the continuous feedback signal monitoring implemented with an Overcurrent fault Protection circuitry (OCP) makes the final design rugged and reliable. NCP1308主要特性： _Free-Running Borderline/Critical Mode Quasi-Resonant Operation _Current-Mode with Adjustable Skip Cycle Capability _Dynamic Self-Supply Type of VCC _Auto-Recovery Overcurrent Protection _Improved UVLO for VCC below 10 V _Latching Overvoltage Protection on VCC _500 mA Peak Current Source/Sink Capability _Internal 1.0 ms Soft-Start _Internal 10 _s Minimum TOFF _Adjustable Skip Level _Internal Temperature Shutdown _Internal Leading Edge Blanking _Direct Optocoupler Connection _SPICE Models Available for TRANsient Analysis _This is a Pb-Free Device NCP1308典型应用： _AC-DC Adapters for Notebooks, etc. _Offline Battery Chargers _Consumer Electronics (DVD Players, Set-Top Boxes, TVs, etc.) _Auxiliary Power Supplies (USB, Appliances, TVs, etc.)  图1. NCP1308内部电路架构图  图2. NCP1308典型应用电路图 The 50 W ac-dc internal power supply reference design addresses all functional blocks of the adapter, utilizing several of ON Semiconductor’s power management devices and drawing from its leading discrete component portfolio to achieve superior efficiency performance.  图3. 50 瓦STB AC/DC电源电路图 參考设计所用的关键元件包括： Key Products in the Reference Design Include: NCP1308: This controller combines a true current mode modulator and a demagnetization detector to minimize the EMI signature and maximize efficiency, by operating in quasi-resonant mode. The NCP1308DR2G is offered in a SOIC-8 package, and priced at $0.47 per unit in 2,500-unit quantities. NCP1586: This controller provides an optimal level of integration to reduce size and cost of the power supply. Features include a 1 ampere (A) gate driver and an internally set 275 kHz oscillator. The NCP1586DR2G is offered in a SOIC-8 package, and is priced at $0.45 per unit in 2,500-unit quantities. TL431A: This three-terminal programmable shunt regulator diode is offered in a SOIC-8 package and priced at $0.21 per unit in 2,500-unit quantities. MC79L05: This 100 milliamp (mA), 5 volts (V), negative voltage regulator is offered in a TO-92 package and is priced at $0.22 per unit in 2,500-unit quantities. MURA110: This 1 A, 100 V ultrafast rectifier is offered in a SMA package and is priced at $0.13 per unit in 5,000-unit quantities. NTD4808N: This 30 V, 63 A power N-Channel MOSFET is offered in a DPAK package and is priced at $0.25 in 2,500-unit quantities. NTB60N06L: This 60 A, 60 V power N-Channel logic level MOSFET is offered in a D2PAK 3-lead package and is priced at $0.86 in 800-unit quantities. |
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