A Bridge-Less Hybrid SSHI Rectifier With High Efficiency Over Wide Load Range for Piezoelectric Energy Harvesting

As the load deviates away from the maximum power point (MPP), the output power of the current piezoelectric energy harvester with synchronous switch harvesting on inductor (SSHI) drops quickly. To achieve high energy harvesting efficiency under a wide load range, this article presents a hybrid SSHI (H-SSHI) interface circuit for piezoelectric energy harvesting (PEH), combining the advantages of series SSHI (S-SSHI) and parallel SSHI (P-SSHI) techniques. An additional bias-flip estimation strategy has been implemented to mitigate charge loss during light load conditions, thereby enhancing energy harvesting efficiency. Only two on-chip switches are employed for bias-flip operations in addition to an external inductor and storage capacitor. The bridge-less topology can also decrease the flipping loss. The proposed H-SSHI circuit is fabricated in a 0.18- $\mu $ m BCD process. A maximum of 974% harvesting improvement is measured compared to the ideal full-bridge rectifier (FBR). Moreover, when both the efficiency enhancement and the load range are considered, this design achieves a figure of merit (FOM) of 76, which proves the significant harvesting efficiency improvement for bias-flip circuits over a wide load range.