The power consumption of smart camera in car black box varies significantly between light load and heavy load. The high efficiency voltage regulator is necessary in prolong the life of smart camera battery. Since the smart camera only recording the video when car is driving, the most time of the smart camera works in the sleep mode. Hence the light load efficiency is important in this application, however, conventional buck converter usually have high efficiency at heavy load but poor efficiency at light load. To increase the light load efficiency of buck converter, this research continues Yeago's two phase buck converter with optimum phase selection control and Zhao's two mode buck converter to further improve the light load efficiency for the target application. With 5V input voltage and 1.2V output voltage, the proposed two-mode synchronous buck converter can supply the load power from 12mW to 1.44W. To improve the light load efficiency of conventional buck converter, the proposed design applied Wei's baby buck concept to provide another light load power stage to reduce the switching loss and driving loss at light load. Then, the variable frequency ripple-based constant on-time control with discontinuous conduction mode (DCM) in light load is applied to the baby-buck mode to reduce the switching frequency to further reduce the switching loss. Also, the baby-buck mode uses the synchronous buck topology to remove the diode in asynchronous converter to increase the efficiency at light load. Finally, a sensorless mode selector remove the sensing resistor in power stage to increase the efficiency for entire load range, especially for the heavy load. The mode selector can select the optimum mode for different load condition, and the opposite mode would completely shut down to save the loss. The proposed design is implement in CMOS 0.25um technology. The proposed monolithic buck converter which include the power stage of heavy buck mode, baby-buck mode and the controller is fabricated. The measurement result shows the close loop efficiency varies from 70%-83% toward the entire load range. / Master of Science

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Internet of Things (IoT) är en kraftfull plattform för att koppla den fysiska världen till den digitala. IoT och modern sensorteknik möjliggör många nya applikationer inom till exempel industriell övervakning, hälsovård,miljöövervakning, smarta städer, smarta transport och smartlivsstil. I många av dessa applikationer är sensornoder utplacerade i utomhusmiljöer, där de bör fungera under långa tidsperioder. IoT-noder lider av kapacitetbergränsade batterier vilket innebär att deras funktion beror på batteriets livslängd. En lösning kan vara att implementera ett energikördsystem till IoT-noder utomhus. Solenergi är den mest lättillgängliga och användbara energikällan utomhus.Denna energi skördas med hjälp av en solcell (PV-cell). Energin som genereras av solcellspaneler varierar beroende på solstrålningsintensitet och andra faktorer. Syftet med denna undersökning har varit att utveckla en solcellsförsörjningsenhet för IoT-noder utomhus. Detta görs genom att hämta energi från omgivningen (solenergi) och använda den i samband med en Power ManagementIntegrated Circuit (PMIC) och en energilagringsenhet kan livslängden för IoT-noder förlängas samtidigt som underhållskostnader minskas.I undersökningen användes en uppskattningsmetod för att uppskatta solcellens totala energiproduktion, vilket hjälper för att konfigurera en solcellspanel som kan leverera lämplig energi till energiskördsystemet och minska energiförlusten i systemet. En lämplig energi krävs för att PMIC:n ska fungera väl samt systemet ska driva IoT-noder. Denna undersökning har visat att solenergiskördsystemet som består av en självgjord mindre panel, en BQ25570 och en energilagringsenhet (antingen en superkondensator eller ett batteri) kan översvämningsmätaren drivas under sommaren för det första fallet och under hela året för det andra fallet. Om två i parallell KXOB25-01X8F-TR används i systemet i stället för den mindre panelen kan luftkvalitetmätaren drivas under sommaren medan om tre iparallell KXOB25-01X8F-TR används i stället kan noden drivas under hela året. Energiskördsystemet ger mer än 80% effektivitet. / The Internet of Things (IoT) is a powerful platform for connecting the physical world to the digital. IoT and modern sensor technology enable many new applications in domains such as industrial monitoring, health care, environmentalmonitoring, smart cities and so on. In many of these applications, sensor nodes are deployed in outdoorenvironments, where they should operate for long periods oftime. But IoT nodes suffer from capacity-limited batteries,which means that their function depends on the battery life. One solution may be to implement an energy harvestingsystem for IoT nodes outdoors. Solar energy is the most readily available and useful source of energy outdoors. This energy is harvested using a solar cell (PV cell). The energy generated by solar cell panels varies depending on the solar radiation intensity and other factors. The purpose of this study has been to develop a solar cell supply unit for outdoor IoT nodes. This is done by extracting energy from the environment (solar energy) and using it in conjunction with a Power Management Integrating Circuit (PMIC) and energy storage device, the lifespan of IoT nodes can be extended while reducing maintenance costs. The study used an estimation method to estimate solar cell total energy production, which helps to configure a solar cellpanel that can supply suitable energy to the energyharvesting system and reduce the energy loss in the system. A suitable energy is required for the PMIC to work well and the system to power IoT nodes.This study has shown that the solar energy harvesting system consisting of a self-made smaller panel, a BQ25570 and an energy storage unit (either a supercapacitor or a battery), the flood meter can be operated during the summer for the first case and throughout the year for the second case. If two inparallel KXOB25-01X8F-TR are used in the system instead of the smaller panel, the air quality meter can be operated in the lower summer, while if three in parallel KXOB25-01X8F-TR areused instead, the node can be operated throughout the year. The energy harvesting system provides more than 80% efficiency.

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