| Summary: | 碩士 === 國立中興大學 === 電機工程學系所 === 106 === There has been increasing attention to the issue of energy problem, more and more people pay concern on energy harvesters. Thus how to extract power from the environment become a discussed issue. There are two ways for using these energy, first way is to save it in the battery. Second way is to harvest stable energy from the environment and supply to chips. As an instance, this thesis takes vibration as the topic and focus on the piezoelectric energy harvesting systems. Besides, energy harvest from piezoelectric material is normally ac power, energy is also small. As a result, how to design a high-efficiency rectifier to reduce energy loss during the rectifying region is an important problem. In this thesis introduces two high-efficiency ac to dc rectifiers. Besides, the designed circuits can start up without other batteries, the energy used in circuits is all provided by piezoelectric material.
The first circuit proposed in this thesis is an active AC-DC rectifier with synchronous comparators controlled circuit. With four common-gate comparators to detect the relation between input and output voltage. Then synchronous controlled circuit will control the signal used on power MOS in order to reduce the power loss of piezoelectric source. The circuit is fabricated with TSMC 0.25μm 1P3M processes. The experimental results show that when input voltage is 5V and 240Hz, the maximum voltage conversion ratio can reach 93% at 200kΩ loading, and the maximum power efficiency is 86.6% at 10kΩ loading.
The second circuit proposed an active AC-DC rectifier with non-overlap circuit. This circuit detect positive and negative cycle by a voltage comparator, and output N power MOS signal. Then the circuit detect the input and output voltage by two common-gate comparators to control P power MOS. Besides, there is a non-overlap circuit used on N power MOS to prevent power loss when two N power MOS conduct at the same while. The circuit is also fabricated with TSMC 0.25μm 1P3M processes. Compared to the previous work, the measurement results show that the maximum voltage conversion ratio can reach 99% at 200kΩ loading, and the maximum power efficiency is 93.85% at 20kΩ loading.
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