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Latest regulations, challenges and applications of ultra-low standby power chargers and adapters
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Thursday 5 July 2012

Vendors have been devoted to providing high-performance power chips and corresponding solutions in a bid to help the industry create small-sized power supplies for ultra mobile devices (UMDs), enhance conversion efficiency and reduce standby power consumption. This will save considerable amount of energy for over 100 million consumer electronics devices, mobile devices and home appliances around the world.

During the recent DTF 2012 Ultra Mobile & Ecosystem Forum, Vincent Chang, NXP senior regional product marketing manager power solutions ICs - BL power & lighting/BU HPMS, introduced latest international regulations on ultra-low standby power chargers and adapters as well as NXP's latest power IC solutions, hoping to help the industry conquer the challenges of design in the era of UMDs.

NXP, the spin-off of Philips Semiconductors in 2008, offers high-performance mixed signal and standard products such as transistors and solutions for logic devices.

Brief introduction on NXP power IC solutions

The standby power consumption of NXP's power IC is ultra-low at milli-W levels and in compliance with strict requirements of Energy Star or EUP Lot 6. Chang continued by sharing information about power consumption of home appliances, PC peripherals, mobile devices and the emerging-saving market, before lecturing on ultra-low standby power solutions' indispensability and regulatory challenges. In the last part of the speech he introduced charger and adapter power solutions NXP launched for reducing standby power consumption and boosting power, and shared some case studies on product designs.

Trends of low standby power consumption design for power controllers

Most power supplies now are based on the second generation low power platform (with low standby power consumption and high efficiency), with a size as small as possible for better portability. USB chargers are noiseless and easy to use. Currently, USB 3.0 chargers provide for up to 0.9A (about 4-5W), while next generation USB chargers can deliver up to 9-10W. Statistics from Energy Star show that 29% of global energy consumption goes to heating, with 17% for cooling, 13% for home appliances, 12% for lightening and the remaining 11% for usage in external power supply, telecom equipment, STB, home video/audio recreation, etc. Home appliances and 3C/PC/NB products, amounting to 25% of all energy consumption, can help reduce power consumption by using power chips designed for lower power consumption and higher efficiency.

Gartner forecasts that annual desktop PC shipment around the world will stay above 150 million units by 2017, but annual notebook shipment (ultrabooks included) will reach 400-450 million units. Tablet PC shipments are expected to surpass the 300 million units mark by 2015. Smartphones will enjoy significant growth, with annual shipment hitting around 500 million units in 2012 before increasing three-fold to 1.5 billion in 2015. These all represent great opportunities for charger and power supply makers.

Chang demonstrated a 90W ultra-thin power adapter developed by his client, a device in an LC framework as small as a business card case. He emphasized that NXP chips can help adapter vendors break through barriers on standby power consumption and create LC-framework products with a low 0.2W power consumption. Meanwhile, NXP also offers 40-50W adapter solutions for ultrabooks, and even smaller versions of 5-10W.

As for regulations on lower standby power consumption, LG, Motorola, Nokia, Samsung and Sony Ericsson in 2007 agreed on a five-star rating scheme regulating standby power consumption: zero star for consumption greater than 0.5W, one star for 0.35-0.5W, two stars for 0.25-0.35W, three stars for 0.15-0.25W, four starts for 0.03-0.15W and five stars for consumption lower than 0.03W. Energy Star requires that power supplies below 50W must consume less than 0.5W for AC-AC and 0.3W for AC-DC. Adapters in 50-250W, AC-AC or AC-DC, have to consume less than 0.5W.

Starting January 7, 2009, EUP Lot 6 demands that all home alliances, PCs, consumer electronics products and even toys have to consume energy of less than 1W under standby, sleep or off modes, or 2W if including status display. Products sold after January 7, 2013 cannot consume more than 0.5W under off and standby modes, or 1W if including status display.

In compliance with EUP Lot 6, NB adapters and LCD TV power supplies have to respectively meet the 0.5W and 0.25W maximum energy consumption under standby and off modes. As NBs from some major brands would need 0.5W just for chipsets alone, many solutions still fail to meet the requirements. China requires an even lower maximum of 0.5W/0.2W, and Japan is also stricter with a 0.5W/0.15W limit.

Desktop PCs are under standby mode for an average of 36% of time, while NBs are on stand by 34% of time and the figure is even higher at 43% for computer monitors or TV. With 200 million notebooks and 2 billion smartphones around the world, a 50% cut in standby power consumption might save NT$20-30 billion on electricity bills each year.

Case studies on design of lower standby power consumption applications

Using a conversion efficiency chart of switching power supply, Chang pointed out that energy losses consist of switching losses, magnetic losses and conduction losses. Conduction losses would be constant when the system is in full load,while switching losses are constant in no-load status. Synchronous rectification is adopted to reduce conduction losses at heavy load, using TEA1791/1761 as a flyback switching power supply or replacing Shottky-barrier diodes with TEA1791A/1795 linear rectification. The MOS process can also be adopted to reduce on-resistance. Higher conversion efficiency at a lower load can be achieved with the burst mode, soft switching, quasi-resonant (QR) or switching frequency.

For Flyback QR to deliver high performance at a heavy load, multi-mode operation can be adopted to reduce power chip frequency at a heavy load, while QR can minimize switching losses and reduce electromagnetic interference (EMI). For flyback QR to deliver high performance at lower load, the PFC converter should be shut down under the low-load mode to reduce energy losses. TEA175X power chips will allow feedback circuits to adopt the more sensitive sense resistor IC.

Next Chang showed the audience a switching power line chart with load demand as one variable, adding the power chip's power consumption into the calculation. With power chips developed by avoiding the frequency range between 22KHz and 28KHz, the burst mode, which often requires high power in dozens of milliseconds, can reduce switching losses and raise efficiency under difference load status. For example, TEA1733/1738 can reduce switching losses by lowering switching frequency, while current output is cut by 25% as compared to peak current.

For low-load application environment with output power lower than 65W, active x-cap discharge circuit and high-ohm sensor patterns can be added to replace low-power TL431 IC and achieve better precision. Moreover, TEA1733 IC only consumes 0.01W at no-load mode due to extremely low operating current for IC at 0.03W. For chargers and adapters with power output lower than 20W, the TEA172X series is recommended for burst mode with switching frequency between 400Hz and 1850Hz. Standby power consumption will be reduced and the operating current is only one fourth of peak volume. The frequency should be fixed between 22.5Khz and 51.5Khz under normal operation mode.

TEA1731, which is in TSOP6 package with an average 90.55-90.9% conversion efficiency, can be applied 19.5V, 40W adapters. Components made with SOI process are recommended if further reduction of ICs power consumption is desired, as leakage will be significantly lowered with each transistor being wrapped in dielectric. For example, TEA1738 is made with the SO8 process in the same 90.55-90.9% conversion efficiency needs a merely 10μA for start-up current and 5μA operating current, which is about one third or one fourth of those required by rival products.

GreenChip SR TEA1792 chips can be used as power supply for notebook adapters, chargers and LCD TV. Adoption of SO8 process, 8.5-38V ultra high working voltage and 10V high voltage output will also further raise the conversion efficiency. For EUP Lot 6-compliant power supply with over 100W output power, TEA1713 plus TEA1716 are recommended to meet the 0.25W standby power consumption requirement.

The TEA172x family of power chips- from 5W TEA1721(TEA1721AT/BT/DT/FT), 8W TEA1722 to 11W TEA1723 (TEA1723AT/BT/DT/FT)- is recommend for low standby power consumption solutions on USB chargers, smartphones, tablets or even home appliances. Such solutions offer support to high c/p value design and require less than 30 components on the bill of material (BoM). Standby power consumption is below 5mW under 115V power supply, and the conversion efficiency will also be higher than EPA 2.0 requirements (an average 75-78% .in 5W). For example, a 5W (5V/1A) small-sized UBS cell phone charger based on 5W TEA1721 is only 40mm in length, 28mm in width and 14mm in height.

NXP Sr. regional product marketing manager power solutions ICs - BL power & lighting/BU HPMS, Vincent Chang

NXP Sr. regional product marketing manager power solutions ICs - BL power & lighting/BU HPMS, Vincent Chang

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