Research And Design Of Low Input Voltage High Efficiency Flyback Converter For Energy Harvesting Systems

The progress of integrated circuit technology keeps pushing forward the development of portable electronic devices and at the same time introduces new demands for the power management modules such as smaller size, higher efficiency and higher level of integration. Meanwhile, more and more portable devices are using energy harvesting systems as power supplies in which the DC-DC converters should be able to work under very low supply voltage and load current while maintain high power transfer efficiency.After comprehensive survey on the development and application of energy harvesting system, this thesis analyzes and compares the working principle and some critical characteristics of different energy generators. Based on it, taking the thermoelectric converter as an example, the demands of energy harvesting systems on power supply modules are summarized, which are applying to portable devices. And an ultra-low start-up voltage flyback converter is proposed to meet the demands. Furthermore, the burst-mode constant-on-time control method is adopted in this system. It improves the power efficiency by reducing the operation period and working in the discontinuous conduction mode (DCM). The converter regulate the constant conduction time according to supply voltage of the energy generator which ensures that the converter can provide energy to load at the highest efficiency point under various conditions, thus achieves maximum power point tracking (MPPT).The chip is designed in UMC0.18μm CMOS process. The simulation results show that the whole system can start up at a ultra-low input voltage of20mV-300mV, and it can provide a stable1.8V output voltage. The MPPT accuracy is98%which improves energy utilization. By using dynamic power management, when MPPT control block and zero current switching control block are shut down, the current consumption of controller is only0.6uA. The peak efficiency is91%when input voltage is larger than100mV. And the efficiency is75%when input voltage is20mV. Thus a low power high efficiency converter is achieved, which meets the design expectations.