Green energy power converter eases apps

Freescale Semiconductor has developed an integrated mixed signal chip that can convert the output from a single solar cell into a usable power source.

Freescale's dc-to-dc power conversion technology, was announced today at the Applied Power Electronics Conference and Exposition (APEC, Feb. 16-19, Washington D.C.)

Besides photovoltaic (PV) cells, thermoelectric-generators, electromagnetic-generators and even bioelectric energy can be harvested with Freescale's technology.

"Our power converter starts working at just 0.32 volts, allowing it to convert power from a variety of low-voltage sources," said Kevin Parmenter, applications engineering manager for the analog, mixed-signal and power division of Freescale Semiconductor Inc. (Tempe, Ariz.) "All sorts of green energy harvesting devices that had to be ganged together before to get their voltage up can now be used individually--from single solar cells to thermopiles to bioelectrics."

Most electronic power supplies work in the four-volt range, necessitating the use of multiple units in series. For instance, solar cells outputting 0.4 volts, would have to be put into a series of 10 cells to achieve an output voltage of four volts. Unfortunately, if something goes wrong with any cell, the output from the whole array is adversely affected. But by converting the power from individual cells, smaller more reliable devices can be built.

Last month, Advanced Linear Devices Inc. (ALD, Sunnyvale, Calif.) said it was planning to use its floating-gate Mosfet process to start building discrete transistor arrays that could be used to build low-voltage power converters that turned on at 0.4 volts. Freescale, however, claims to have one-upped ALD with its 0.32 start-up voltage power conversion technology that is completely integrated on a single chip and already available today.

"All you need to add to our power converter is a small inductor in series with the input, and a couple of bypass capacitors in parallel with the input and output," said Parmenter. "Using a discrete implementation will raise the cost because of all the extra components you need, plus the interconnects between components will degrade efficiency due to parasitic ac and dc losses."

Freescale claims that its power converter has from 82-to-90 percent efficiency, thanks to its use of the company's Smartmos-10 mixed-signal process that allows digital, analog and power devices to be housed on the same die. The key to using the 130 nm Smartmos-10 process for power converters was the ability to fabricate transistors that begin turning-on at just 0.32 volts. For low-impedance connections to the circuit board, Freescale's power converters use a flip-chip on leadframe (FCOL) package.

To reduce size, Freescale's power converter operates at 1 MHz, permitting the use of a small inductor on the input despite the one watt power handling capability.