Here is an energy harvesting product that Sparkfun sells, based on the LTC3588. They have some lower cost piezo transducers. But I am sure a lot lower ratings. http://www.sparkfun.com/commerce/pro...oducts_id=9946

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Features:
  • 950nA Input Quiescent Current (Output in Regulation – No Load)
  • 450nA Input Quiescent Current in UVLO\
  • 2.7V to 20V Input Operating Range
  • Integrated Low-Loss Full-Wave Bridge Rectifier Up to 100mA of Output Current
  • Selectable Output Voltages of 1.8V, 2.5V, 3.3V, 3.6V
  • High Efficiency Integrated Hysteretic Buck DC/DC
  • Input Protective Shunt – Up to 25mA Pull-Down at VIN ≥ 20V
  • Wide Input Undervoltage Lockout (UVLO) Range
Just as interesting to me was their mini 8 pin soic 4 volt solar cell. Pretty cute.
http://www.sparkfun.com/commerce/pro...oducts_id=9962

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