Energy harvesting is an emerging application field that shows great promise for helping designers cut the power cord for remote applications. However, designing circuits for this field presents some vexing technical challenges on the power management side. Rethinking some circuit design parameters and building modules specifically suited for this purpose can unlock the potential for energy harvesting as a viable power source for many different electronic applications.
Everywhere around the world, wireless technology is removing the shackles from adoption like never before in history. By eliminating the need to put in wires for sending data back and forth, companies can save millions on the installation costs for new applications and researchers can gather data from more remote locations for longer periods of time.
Energy harvesting presents yet another way of taking wireless technology further by removing the limitations of AC power lines or batteries. Applications like wireless sensor networks and remote controls can be further unshackled from these power sources and energy harvesting is now making that feasible for real-world applications.
Energy harvesting is still in its infancy, however, and there are technical challenges that need to be addressed to make it a mainstream replacement for batteries and AC power. Among those challenges is the electronic circuitry needed to capture, accumulate and store energy from energy harvesting energy sources. The circuitry must then switch the power from an energy storage device and then supply it to the application.
Energy harvesting sources that generate power from ambient sources present problems in generating a predictable flow of electricity for the operation of electronic circuits. At times these sources generate zero power. At other times they generate trace amounts of power that are unusable. Then there are times when the power generated is so great that a charge from an energy harvesting source could burn out the circuitry.
The typical characteristics of an energy harvesting energy source capture and produce electricity only when input energy is available. For example, a mechanical energy converter produces electricity only when an excess of kinetic energy is added to the source. The energy source produces electrical energy in an intermittent, uncontrolled and irregular manner with varying source impedances. When the electrical energy arrives, it is also unpredictable. The electricity produced can be regarded as energy packets in the form of charge impulses, each arriving in different voltage amplitude, current magnitude and timing waveforms.