۱- Introduction

۲- Circuit configuration

۳- Theoretical analysis

۴- SPICE simulation

۵- Experiments

۶- Conclusion

References

Abstract

For vibration energy harvesting, we propose an inductor-less step-up ac/dc converter in this paper. To realize the inductor-less design, the proposed ac/dc converter consists of two converter blocks: Cockcroft–Walton circuit and charge pump. Unlike existing ac/dc converters for vibration energy harvesting, the proposed ac/dc converter can achieve less electro-magnetic interference (EMI), because no magnetic component is necessary. Furthermore, owing to the Cockcroft–Walton circuit, a fullbridge circuit is not necessary to convert vibration energy. Therefore, small vibration energy, namely, as 0.3 V@1 MHz, can be converted directly to dc voltage. Through theoretical analysis and simulation program with integrated circuit emphasis (SPICE) simulation, the performance of the proposed converter with 6× voltage gain is investigated, where the proposed converter is designed by assuming 0.18 µm CMOS process. The proposed converter demonstrates that about 62% power efficiency can be provided, where the output power is 30 µW, the output voltage is about 1.6 V, and the ripple factor is 0.8%. Furthermore, the feasibility of the proposed ac/dc converter is confirmed by breadboard experiments. The inductor-less design provides us to integrate the proposed ac/dc converter into a hybrid IC chip.

Introduction

Over the past few decades, wireless sensor network (WSN) systems [1] are receiving much attention for monitoring various environment parameters. The bottleneck of the WSN systems is the limited lifetime of WSN nodes, because the WSN nodes are usually driven by a battery source. For this reason, in order to extend lifetime of WSN nodes, some of wasted energy are captured by energy harvesting collectors and are used as a power supply source in recent years. There are several types of ambient energy sources, such as solar, wind, vibration, thermoelectric. Among others, we focused on vibration energy, which is a kind of kinetic energy, because it widely exists in the ambient, including the vibration of industrial machinery, transportation vibration, body movement, and so on. In the energy harvesting collectors, the ambient energy is converted into electrical energy by power converters. To utilize vibration energy, an ac/dc converter is necessary as a vital component of energy harvesting collectors. For this reason, several types of ac/dc converters have been proposed in recent years. For example, Shi et al. [2] suggested the ac/dc converter by combining a full-bridge circuit with two buck-boost converters. Wang et al. [3] designed the ac/dc converter by combining a full-bridge circuit with a synchronized switching harvesting on inductor. Shareef et al. [4] realized the ac/dc converter without full-bridge circuits. However, due to the magnetic component, such as inductors, these existing converters becomes bulky. Furthermore, these converters are applied only for low frequency ac input. To solve these problems, we undertake the development of an inductor-less ac/dc converter for vibration energy harvesting.