MIT has pulled out all the stops in an energy scavenging circuit for piezoelectric power sources

The traditional way to extract power from these is simply to connect a bridge rectifier to the piezo generator, followed by a reservoir capacitor.

However, a piezo generator is effectively an AC current source in parallel with a capacitor, so on every half cycle the current source wastes energy discharging the internal capacitance, then charging it to the opposite polarity.

Described at ISSCC (International Solid-State Circuits Conference) in San Francisco this week, MIT retains the rectifier and reservoir, but switches an inductor across the piezoelectric generator output.

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