安森美50 瓦STB 电源解决方案

根据Natural Resources Defense Council 和Ecos Consulting，机顶盒现在消耗的电能比许多普通家用电器要多。因此机顶盒和电视机每年所消耗的电能比电冰箱要多。例如内置了DVR的高清晰机顶盒每年大约消耗350度电。因此如何降低机顶盒的耗电是一个重要的节能措施。安森美50 瓦GreenPoint™參考设计在工作模式时效率达到81%，能满足全球的能源标准。參考设计主要采用NCP1308，NCP1586，TL431A，MURA110，MC79L05，NTD4808N和NTB60N06L等器件。本文主要介绍了NCP1308的主要性能，内部电路架构图和典型应用电路以及50 瓦STB  AC/DC电源解决方案的电路图及主要元器件的简要性能。

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.