Product category:
Capacitors
News Release from: Cap-XX | Subject: BriteFlash
Edited by the Electronicstalk Editorial
Team on 08 March 2006
Supercapacitors put power into
cameraphone flashes
A novel power architecture uses supercapacitors to provide LED flash camera phones with enough light to produce high-resolution images.
Cap-XX has developed its BriteFlash power architecture to provide LED flash camera phones with enough light to produce high-resolution images Some phone manufacturers have experimented with long flash exposure times to compensate for low-light problems, which then results in blurry photographs
This article was originally published on Electronicstalk on 13 Jun 2007 at 8.00am (UK)
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CAP-XX supercapacitors pack the highest energy and power densities into thin, lightweight, prismatic packages that will fit into slim portable devices.
Cap-XX's BriteFlash architecture provides enough flash power to eliminate both dark and blurry photos using high-capacitance (0.4 to 1F), low equivalent series resistance (less than 100mohm), thin (1 to 3mm) prismatic 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 optimises a supercapacitor to power flash LEDs.
"Greater than 2Mpixel camera phones require a high-intensity flash in medium to low light conditions to ensure good pictures", said Anthony Kongats, CEO of Cap-XX.
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"Some solutions are available but lack adequate power to produce quality photos in all light conditions".
"Our BriteFlash power architecture completes the equation with the power to drive today's LEDs".
Today's high-power white LEDs require a higher voltage than a Li-ion battery can supply, so power integrated circuit (IC) 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.
Cap-XX supercapacitors can deliver this pulse power.
Cap-XX has developed reference designs using standard flash drivers that offer multiple design options.
The Cap-XX BriteFlash power architecture is similar to a xenon flash solution used in digital cameras today, where a low-current charge pump (boost convertor) charges the supercapacitor to 5.5V then the supercapacitor drives the LED at very high current for the flash pulse.
Cap-XX's supercapacitor-based solution, however, delivers more light energy (flash power times flash duration) and has a much thinner form factor than the xenon one.
Designers are forced to choose thinner, hence reduced-capacitance 330V cylindrical electrolytic storage capacitors necessary in xenon designs to fit them in space-constrained camera phones.
These reduced-capacitance electrolytic capacitors, which are still bulky at 6 to 10mm, reduce the light energy the flash can provide.
Two versions of BriteFlash allow tradeoffs between the flash distances needed to take high-resolution photos, and the cost to implement them.
One version yields an effective flash up to 1.5m, compared with the 3m achieved with the maximum power alternative.
In the maximum power version, a dual-cell supercapacitor such as a 0.55F, 50mohm Cap-XX GS206 delivers over 25W to the LEDs, compared with 2 to 4W without a supercapacitor.
A supercapacitor also eliminates the need to shut down the rest of the phone because the battery isn't needed to supply any current during the flash, leaving it free to supply other power needs such as OLED display or RF transmission.
The battery only needs to provide a low-charging current of 250mA to the supercapacitor to support a recovery time between flashes of approximately 2s.
This is less time than the LED needs for thermal recovery between flashes.
The low-charging current allows designers to use lower-cost, smaller boost convertors or charge pumps because the supercapacitor supplies the peak current.
Without a supercapacitor, the boost convertor has to be sised for peak flash current.
The Cap-XX BriteFlash reference designs show how to optimise the power subsystem with a supercapacitor.
The alternative version supports a flash photo up to 1.5m using a single-cell lower-cost supercapacitor such as a Cap-XX GW101, which is half the volume of the GS206 device.
This version increases the LED current by approximately 40%, which allows the 50% increase in flash distance.
The supercapacitor is precharged prior to a flash pulse and the battery only needs to provide a relatively low-charging current of a few 100mA allowing an even smaller and lower-cost charge pump than the maximum power version.
To demonstrate the increased flash power and ease of design-in, Cap-XX engineers retrofitted several models of industry-leading camera phones with BriteFlash.
In one example, Cap-XX placed a dual-cell supercapacitor, replaced existing LEDs with four high-powered LEDs that can each handle a peak pulse current of 1A, then put the phone together again with no changes in external appearance.
The original phone delivered 1W of flash power for 160ms, whereas the Cap-XX-modified phone delivered 15W for the same amount of time.
The total cost of the Cap-XX BriteFlash solution is US $4 to $5 including the LEDs, supercapacitors and circuitry.
The supercapacitor alone costs $1.50 for the single-cell solution and $2.50 for the dual-cell one in quantities of 10,000 or more.
Cap-XX is working with flash/LED driver suppliers to develop supercapacitor-optimised charge pump LED drivers to further increase camera phone power subsystem integration and reduce costs.
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