Harvest time near for energy ICs

Here is an up-close look at a demonstration harvesting system that includes Powercast’s P2100 Powerharvester chip. Also visible on the circuit substrate is a small form-factor capacitor and a low-power wireless board (TI eZ430-RF2500T).
Select figure to enlarge.

“No batteries required,” is still a far-off dream for most everyday applications that run on electrical power. But some kinds of systems are closing in on that ideal by harvesting energy from their environments.

Energy harvesting is more of a buzzword than a reality for most mainstream IC makers, and the playing field is still relatively small. Yet there is a growing collection of “energy scavenger” systems, ultra-low-power circuits and peripherals that store and make use of ambient energy collected by piezoelectric, solar, thermal, and various other “free energy” elements. All the component parts are coming into place — source/transducer, regulator/charger, thin-film battery and supercapacitor — supported by IC nanowatt technologies already in place.

IC makers in the traditional analog space are starting to provide products designed to work with what might be called harvesting-type sensors, usually photovoltaic and piezoelectric devices. The necessary building blocks to put together such a system typically include a detector, power supply and power management stage, energy storage, and an output switch. These blocks can be discrete chips or stand-alone, plug-and-play modules.

Such modules typically include the input and output stages (energy capturing element through wireless RF transmitter/transceiver for communications). They're available from well-known IC makers as well as from producers of thin-film batteries, and from numerous lesser-known energy harvesting names as well, many of them startup companies partnering with IC firms.

Towards perpetual motion

“While there are interesting transducer technologies (piezo, thermal, photovoltaic, motion, electromagnetic), the real difficulty or missing link is in the harvesting of power from them. You have to do it in such a way that the power management system can generate useful output power without consuming more power than the transducer can deliver,” says Don Paulus, vice president and general manager of power products for Linear Technology Corp. (Milpitas, Calif.).

The current-drain qualities of a typical system powered by scavenged energy often look something like this plot for the MSP430 processor from Texas Instruments. The unit spends most of its time in an ultra-low power standby mode and awakes only to service interrupts. Use of multiple oscillators makes possible both the ultra-low power standby mode and on-demand highperformance processing. A low frequency auxiliary clock is what enables the ultra-low-power standby mode.
Select figure to enlarge.

It's still early in the game. That leaves IC makers to focus on building general energy delivery systems, with specific applications left to the imagination of system designers. Today, the action focuses on getting the most from low-voltage, low-impedance sources such as solar cells; and from piezoelectric transducers, high-impedance, high-voltage sources. Each sensor provides its own system design challenge.

“The most-used sources commonly are solar panels, and the cost per unit output is highest,” explains Adrian Valenzuela, Texas Instruments Inc. product marketing engineer for the MSP430 (microcontroller) business. “Complexity is low, and they're readily available. Beyond that, it tends to be an applications-specific scenario. We do have thermal-based elements, magnetic resonators that are in vibration-based systems, and lots of piezoelectric. There's a lot of potential in piezoelectric. We can get some extremely high output from these. But typically customers want the cost-per-unit comparable to that of a battery. In today's market, piezoelectric elements in some cases are hundreds of dollars per unit. Hopefully, as production volume ramps up, the cost of piezoelectric will come down. In a few years, piezo will be on the same level as solar panels.”

Continue to next page.