Switching converter techniques for energy harvesting applications

Energy harvesting could provide a micro-sensor application with essentially a lifetime of power source, and there are many power management issues to be solved for efficient energy conversion. In this research, two design aspects of switch mode power converters targeted at employing an energy harvesting source were implemented. The first aspect is to start up a boost converter using a voltage close to the threshold voltages of MOS transistors, and converting a fluctuating input power to a regulated output voltage for sub-mA applications. The converter is called a threshold voltage startup (TVS) boost converter. The second aspect is store excess harvested power to a charge storage device such as a rechargeable battery or a super capacitor, to be retrieved when energy harvesting is periodically interrupted, such that the application could operate basically continuously. A single-inductor dual-input dual-output (SI DIDO) boost converter was developed to provide two regulated output voltages for the load and the energy storage device, and the energy harvesting source and the charge storage device are multiplexed to serve as the input. The TVS and SI DIDO boost converters were designed and fabricated using a 0.35μm CMOS process. Measurement confirmed that the TVS converter could start up with 0.65V that is midway between the threshold voltages of the NMOS and PMOS transistors and provided a regulated output voltage of 1.2V at 1mA with an input voltage that ranged from 0.2V to 0.9V. The SI DIDO converter could choose between two inputs and give two regulated output voltages, 1.2V and 2.4V. The 2.4V output was for the load, and the 1.2V was for the charge storage device