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POWER MANAGEMENT “You’ll see resonance charging as accessory products. Some OEMs will build it natively into, phones but it could also be an accessory back cover,” Hunsicker said. “The circuitry can be built into the phone.” “We’re not in the coils game. We’re in radio frequency,” Humavox CEO Omri Lachman told us. “Its characteristics give you a lot of freedom and releases setbacks like the need to align or couple the receiver and the transmitter. You have freedom to create, get rid of all inhibitions.” The Israeli company utilizes radio frequencies for wireless charging under its Eterna platform, where frequencies are transmitted and converted to DC voltage. The charge is converted by the company’s miniature antenna receiver, which is installed in a charging platform called Nest. With Humavox’s technology, a signal broadcast at 2.4 GHz sends energy to the receiver, which pushes voltage to a management IC. Frequency transmission occurs in the industrial, scientific, and medical band, though Lachman said the company has engineered compliance with a “very, very broad spectrum of frequencies to transmit in, from single MHz to high range of GHz.” The receiver operates at as low as 7 milliamps to support low-power devices such as hearing aids. Humavox has marketed its technology with a primary focus on healthcare and elders - a huge market with no rechargeable capability due to age segment. Lachman said the winning technology in the wireless charging market will be the most intuitive. “The user doesn’t want to learn new tricks when it comes to operating their device, especially when it comes to charging. For us, intuitive is not resonance. It’s not having my device charge from nowhere, because nine out of 10 people don’t want waves or infrared or laser beams in their living room, office, airport.” In addition, he said RF will champion coil-based systems in the wearable Internet of Things realm, because of scalability. RF is more easily integrated into small devices than magnetic or resonance charging. However, there are no massmarket devices that Fig. 4: Officials say Humavox’s miniaturized circuitry makes radio frequency wireless charging scalable. (Source: Humavox) feature radio frequency charging available today. “Approaches using RF have been aimed at this market before, and first-generation solutions were not widely accepted,” Sanderson said. “This doesn’t necessarily mean that we will not see them in the future.” Lachman said that he is skeptical about a single magnetic standard, and that the winning solution will integrate more than one power source. “We heard same promise of standards when WPC introduced Qi and Powermat was introduced, and now we’re hearing the same with resonance. Maybe it’s not going to be just radio frequency, but it has to be something - a receiving system that can be easily integrated in sense of form factor.” Low power design: how low is enough? By Tony Armstrong The portable power application space is both broad and diverse. Products range from wireless sensor nodes (WSNs) that consume average power measured in microwatts to cartbased medical or data acquisition systems with multi-hundred Watt-hour battery packs. However, despite this variety, a few trends emerge – designers continue to demand more power in their products to support increased functionality and look to charge the battery from any available power source. The first trend requires increased battery capacities. Unfortunately, users are often impatient and these increased capacities must be charged in a reasonable time, which leads to increased charge currents. The second trend requires tremendous flexibility from the battery charging solution. Each of these issues will be examined in greater detail. Consider modern handheld devices – both consumeroriented devices and industrial devices may include a cellular phone modem, a Wi-Fi module, a Bluetooth module, a large, back-lit display … the list continues. The power architecture of many handheld devices mirrors that of a cell phone. Typically, a 3.7V Li-Ion battery is used as the primary power source due to its high gravimetric (Wh/kg) and volumetric (Wh/m3) energy density. In the past, many high powered devices used a 7.4V Liion battery to reduce current requirements, but the availability of inexpensive 5V power management ICs has pushed more and more handhelds to the lower voltage architecture. The tablet computer illustrates this point well – a typical tablet computer incorporates significant functionality along with a very large (for a portable device) screen. When powered from a 3.7V battery, the capacity must be measured in thousands of milliamp-hours, for example 2200mAh. In order to charge such a battery in hours, thousands of milliamps of charge current are required. However, this high charge current does not prevent consumers from also wanting to charge their high powered devices from a USB port if a high current wall adapter is not available. To satisfy these requirements, a battery charger must be able to charge at a high current (>2A) when a wall adapter is available, but still efficiently make use of the 2.5W to 4.5W available from USB. Furthermore, the product needs to protect sensitive downstream low voltage components from potentially damagecausing overvoltage events and seamlessly direct high currents to the load from a USB input, a wall adapter or the battery while minimizing power loss. This represents an excellent opportunity for battery IC manufactures to develop an IC to safely manage the battery-charging algorithm and monitor critical system parameters. At the other end of the power spectrum are the nanopower conversion requirements of energy harvesting systems such Tony Armstrong is Director of Product Marketing at Linear Technology Corporation – www.linear.com 28 Electronic Engineering Times Europe March 2014 www.electronics-eetimes.com


EETE MAR 2014
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