Comparing three different energy harvesting circuits for a ZnO nanowire based nanogenerator

Three different output circuits for a zinc oxide (ZnO) nanogenerator are investigated. A full-bridge rectifier, synchronized switch harvesting on inductor (SSHI) and the LTC3588 IC are investigated through simulations and practical experimentation. A nanogenerator supplying a maximum of 5 V at 1.25 mu A is used for practical tests. The full-bridge rectifier functions well under small current situations, but does not charge the capacitor during an entire bending cycle. This is due to the diodes operating in the reverse-biased condition more, due to the charging of the output capacitor. The SSHI circuit is used to solve this problem by inversion of the piezoelectric voltage, thus charging the output capacitor during an entire cycle. This circuit, however, does not work under small current conditions, because it has additional circuit components, requiring more current than the nanogenerator can supply. Lastly the LTC3588 IC is used to drive an LED for 2 s at 1.8 V and a current of 0.17 mA. Although the LTC3588 cannot supply a constant voltage, but rather functions in a burst mode, it is the best candidate for the nanogenerator to date.