Supercaps “Power Boost” Mobile Phones
According to Australia’s CAP-XX Pty Ltd, 2007 will see the first mobile phones that are power-boosted by the company’s supercapacitors hit the market. These “supercaps” are the result of research conducted in collaboration with the CSIRO, Australia’s largest scientific research body.
CAP-XX’s devices have already been sold into niche industrial power and transport applications. The technology is based on the company’s research in carbon and experience in capacitor manufacturing. The materials used are readily available, environmentally benign, and easily fabricated.
Supercap Devices
Supercaps are energy and power storage devices that have technical and economic advantages in a diverse range of applications. In some markets they compete with batteries (UPS), in others they form hybrids with batteries (phones). They also provide power that can’t be delivered economically by batteries (actuators).
“For the mobile phone market, our supercapacitors not only extend the run time of phones, they can facilitate features which aren’t currently available in the marketplace,” said CAP-XX CEO Anthony Kongats. “For instance, our mobile platform now includes our recently announced BriteFlash supercap technology. For phones with built-in cameras of 2Mpixels or more, BriteFlash provides the extra light needed to take good quality photos in low light or no ambient light situations.”
BriteFlash Architecture
While some phone manufacturers have experimented with long flash exposure times to compensate for low-light problems, this usually results in blurry photographs. Only a few mm thick, BriteFlash architecture units provide enough flash power to illuminate dark photos using high-capacitance (0.4 to 1 farad), low equivalent-series-resistance (less than 100 milliohms) supercapacitors to support a battery and deliver the pulse power to drive an LED to full light intensity. CAP-XX also developed the power architecture that optimizes a supercapacitor to power flash LEDs.
According to Kongats, today’s high-power white LEDs require a higher voltage than a Li-ion battery can supply, so power integrated circuit suppliers have developed special-purpose DC/DC and charge pump ICs to drive these LEDs. “However, these new LEDs need up to 400% more power than a battery can provide to achieve full light intensity and our CAP-XX supercapacitors can deliver this pulse power,” Kongats said.
The BriteFlash power architecture is similar to a Xenon flash solution used in digital cameras today, where a low-current charge pump (boost converter) charges the supercapacitor to 5.5V and the supercapacitor drives the LED at very high current for the flash pulse. However CAP-XX’s supercapacitor-based solution delivers more light energy and has a much thinner form factor than the Xenon option.
Flash Power, Bass Notes
To demonstrate the technology’s ease of design and increased flash power, CAP-XX engineers retrofitted several models of industry-leading camera phones with the BriteFlash solution (see Fig). In one example, CAP-XX placed a dual-cell supercapacitor, replaced existing LEDs with 4 high-powered LEDs that can each handle a peak pulse current of 1A, then put the phone together again with no change in external appearance. The original phone delivered 1W of flash power for 160 milliseconds while the CAP-XX-modified phone delivered 15W for the same amount of time.
CAP-XX is currently working with flash/LED driver suppliers to develop supercapacitor-optimized charge pump LED drivers to further increase camera phone power subsystem integration and reduce costs.
According to Kongats, the extension of running time for mobile phones represents another use for the company’s supercaps. “Battery has a certain impedance. As you try to draw current from that battery, the impedance will cause the voltage on the battery to drop. And if the voltage drops far enough, it may drop below the minimum voltage required to operate the phone or a particular feature. For instance, the power amp used in a phone might be at 3.1 to 3.3V and so the nominal running voltage
of Li-ion battery might be 3.7V; but as the battery ages or discharges, and you try to draw high currency from the battery, the impedance of the battery may cause that 3.7V to drop below the 3.1 or 3.3V required to run the PA and the call will drop out. So that is one instance where our supercaps can solve a problem.”
Kongats said that another application is to use the supercapacitor to provide the power necessary to provide good quality audio in the bass regions for when external speakers are attached to a mobile phone.