A Low Startup Voltage High Step Up Ratio Energy Harvesting Power Conversion System

The conventional PV module is composed of the series chains of PV cells. When the shading effect happens, the whole output efficiency of the PV array will reduce severely, it will even damage the PV array. In this thesis, a new power conversion system using the 0.5V voltage generated from PV cell or other energy harvesting transducer as input is proposed. This power conversion system is implement with TSMC 0.25μm CMOS HV process. Firstly, we use the charge pumps to convert the voltage to higher than 2.6V respectively. Then, a switching inductor boost converter raise the voltage to 11V for charging the battery. Because the voltage generated by single solar cell is lower than the threshold voltage of transistors, it cannot turn on the switch of charge pump, especially for the transistors at latter stage, which suffer from body effect. Some literatures propose the backward control bias and two-branch structure with body bias to solve the threshold voltage problem. However, most of the CMOS processes which are used in power electronics integrated circuit does not provide the deep n-well technique. In our first chip, we modify these architectures and propose the all P-type output switch technique to reduce the body effect. To enhance the whole efficiency, a switching frequency optimization (SFO) control is adopted. The measurement result shows that this chip can provide 2.6V output voltage with 0.42V input voltage, and the conversion efficiency of power stage (Vout,measured/Vout,ideal) is higher than 80%. In the second chip, we adopt a current mode boost converter to rise the voltage generated by first chip to over 11V. the post-layout simulation result shows that this chip can provide 11V output voltage stably under 2.6~4.2V supply voltage. And the output current can be in the range of 10mA to 200mA with efficiency over 82%.