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Solar-powered cell phones are on the horizon

TI step-up chip can drive electronics on as little as 0.3v

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TI has developed an ultra-low-voltage DC/DC booster chip that could lead to mobile phones and other electronic devices that never need recharging.

The TPS61200 step-up chip can work with input voltages as low as 0.3v at over 90 percent efficiency, TI claimed. That means it can run directly off low power energy sources such as fuel cells and solar panels, while still putting out a usable 3v to 5v.

It can also work the other way around if the input voltage goes too high - for example, during a start-up surge – by dropping it to the desired output level.

Current step-up converters need an input of at least 0.7v, said TI's product line director Uwe Mengelkamp. That means they are OK for running 3v electronics off a single 1.2v NiCad battery, but not a single solar cell - solar cells are at their most efficient between 0.4v and 0.5v cell voltage.

The new chip will allow designers to incorporate solar cells and fuel/air cells – which work best at 0.4v to 0.6v - without having to put several in series to boost the voltage, Mengelkamp said. He added that cells in series need over-voltage protection circuitry, and can be damaged if one is blocked from the light or air but the others are not.

"Designers, including those in the portable medical, wireless and audio fields, are continuing to look at how to apply solar and fuel cell technology to extend battery life and differentiate their products," he said. "It’s not certain what we will see first, but the ideas are endless."

He said that a 25cm² solar cell (2in. square) could generate around 11mA in indoor daylight, and more in bright sunlight. That means a built-in solar charger in a device could fully charge a 600mA battery in 60 hours – that's 10 daylight hours a day for six days.

Of course, there are potential drawbacks to the solar-powered phone or MP3 player. It will be harder to keep it hidden from thieves for a start, and we will kick ourselves if we leave it in a bag or pocket too long. Still, it could be a nice boost for the makers of transparent carry-cases. ®

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