A Bridgeless Boost Rectifier for Low-Voltage Energy Harvesting Applications

Conventional ac–dc converters for energy harvesting and conditioning usually consists of two stages A diode bridge rectifier typically forms the first stage, while the second stage is a dc–dc converter to regulate the rectified ac voltage to a dc voltage. However, the diode bridge would incur considerable voltage drop, making the low-voltage rectification infeasible. To overcome these drawbacks, CMOS diodes with low voltage drops are investigated in the bridge rectifiers, to substitute conventional p-n junction diodes. Such reported diodes include diode-connected passive MOSFET, which adopts threshold voltage cancellation techniques, and MOSFET, which is actively controlled by a comparator. In either case, the low-voltage-drop diode techniques require either additional bias networks or external comparators. Thus, both the complexity and the power loss of the circuitry would increase. Some converters reported in the literature use transformers as the first stage boosters to overcome the voltage drop in semiconductor devices. However, the size of the transformer could be unacceptably large in low-frequency energy harvesting applications. In this project, a single-stage ac–dc power electronic converter is proposed to efficiently manage the energy harvested from electromagnetic microscale and mesoscale generators with low-voltage outputs. The proposed topology combines a boost converter and a buck-boost converter to condition the positive and negative half portions of the input ac voltage, respectively. Only one inductor and capacitor are used in both circuitries to reduce the size of the converter. A 2 cm × 2 cm, 3.34-g prototype has been designed and tested at 50-kHz switching frequency, which demonstrate 71% efficiency at 54.5 mW. The input ac voltage with 0.4-V amplitude is rectified and stepped up to 3.3-V dc. Detailed design guidelines are provided with the purpose of minimizing the size, weight, and power losses. The theoretical analyses are validated by the experiment results by using DPCM techniques.