It was only a few short years ago that I heard the first serious rustlings about energy harvesting and energy scavenging. The venue was a conference (no surprise) and presenters were showing their early attempts to commercialize harvesting and scavenging technologies for practical applications.

By the way, the best differentiation of the two terms—harvesting and scavenging—that I’ve heard hinges on whether the energy source was a part of the application benefitting from the activity. Attempting to capture waste energy from within an application (harvesting) or from an independent source (scavenging) present somewhat different engineering challenges due to the difference in energy-source predictability implied by the two cases. This distinction does not enjoy universal respect (or even universal acceptance) but many in the industry have found it useful because it helps categorize expected source behavior.

Not surprisingly absent at the time were the major semiconductor manufacturers. Their contributions at the time were the then current wave of low-power (some might say ultra-low power) signal processing ICs—mostly op amps, ADCs, and an interesting array of low-power radios supporting protocols such as ZigBee. These all assumed that you had an energy source—hardwired, harvested, or scavenged.

Since then, the industry’s interest in harvesting and scavenging energy has grown but with little help from semiconductor companies in the form of ICs to facilitate energy capture. That has changed recently with two announcements from Linear Technology. The first, the LTC3108 is an ultralow-voltage step-up converter and power-management IC. Linear Technology designed the ‘3108 to operate from energy transducers that produce modest outputs such as TEGs (thermo-electric generators), thermopiles, and solar cells.

The transducer connects to the converter through a compact off-the-shelf step-up transformer, which forms part of a resonant converter. The device can operate with an input potential as small as 20 mV. The boost converter charges an off-chip capacitor to a pin-programmable output voltage of 2.35 V, 3.3 V, 4.1 V, or 5 V. The converter provides a second gated output controlled by a logic input signal. A separate 2.2 V rail is available from an on-chip LDO for a low-power microcontroller core. The device also produces a “power good” logic signal. The device’s quiescent current is about 6 μA.

The LTC3108 can also operate in concert with a battery or supercap to allow operation when a scavenged energy source is unavailable to meet an application’s immediate energy needs. The device’s ultralow voltage operation allows it to function, for example, on the output of a Peltier cell with only a few degrees temperature differential.

Given the small amounts of energy that energy-capture systems usually have available, minimizing losses is of great concern when developing an application. The LTC3108’s data sheet does an excellent job, in my opinion, identifying appropriate transformers, capacitors, and even TEGs.

Linear Technology’s second announcement marks a second harvester IC—this one a step-down converter for use with piezo-electric transducers. I’ll report on that device in part two.