Integrated Off-Line Power Converter

Lin Fan

Research output: Book/ReportPh.D. thesisResearch

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The miniaturization trend of industrial and consumer electronics continuously drives the demand of reductions in size, weight, and cost of power supplies. The examples of such applications considered in this research are light-emitting diode (LED) drivers for intelligent lighting systems and internet of things (IoT). These power supplies convert the mains power of 220-240 Vrms AC in Europe to low DC voltages around 13 V with an output power of 5-20 W. This research focuses on the DC-DC power conversion, with rectified AC mains as input. The size reduction is the direct requirement, and it can only be obtained by simultaneously improving efficiency to maintain thermal limits at maximum losses. However, fundamental trade-off relationships exist between the power density and the efficiency. To achieve both high efficiency and high power density, systematic development is imperative for components, topologies, and architectures. The research started from integrating active components on a single chip, i.e. integrated high voltage (≥100 V) power MOSFETs in a Silicon-on-Insulator (SOI) process. The extreme performances (such as maximum switching speeds and minimum attainable on-resistances) of these devices are jointly determined by the device, layout, package, and PCB parasitic properties. The research highly contributes to the development towards Power Supply on Chip (PwrSoC) regardless of topologies and switching technologies. First, parasitic capacitances of power semiconductors are a part of the key design parameters of power supplies, for both hardswitched and soft-switched converters. A modelling method is proposed to systematically analyse the nonlinear parasitic capacitances of the power MOSFETs in different states, whereas datasheets typically specify capacitances only in transistor off-states. Second, the nonlinear figure-of-merits (FOMs), which might be used for device-to-device comparisons, are systematically analysed and optimized up to 18.3 times for a given device with quasi-zero voltage switching conditions. Third, four layout structures are proposed and their parasitic capacitive coupling effects are analytically compared, which shows that parasitic capacitances of on-chip interconnections could dominate over intrinsic capacitances of power devices. In addition, the parasitic effects of package and PCB are qualitatively analysed. For topologies and architectures, a two-stage power converter architecture is proposed, where the input stage is a high-voltage switched-capacitor converter and the output stage is a lowvoltage inductor-based converter. For the output stage, a buck converter using the integrated power MOSFETs is implemented with measured efficiencies around 93 %. For resonant converters, integrated power stages with parasitic bipolar effects, using piezo elements as resonant tanks, and discrete prototypes of class-DE series-parallel LCLC converters are investigated. The input stage is implemented as 380 V input switched-capacitor converters, using both Gallium Nitride (GaN) and Silicon Carbide (SiC) devices to properly address switching losses at high-voltage low-power levels. For power stages, a 10 W prototype reaches a peak efficiency of 98.6 % and a power density of 7.5 W/cm3. For converters including driver and its supply, a 21.3 W prototype achieves a full-load efficiency of 97.6 % and a power density of 2.7 W/cm3. For switching schemes, a concept of Asynchronous-Switched-Capacitor (ASC) is proposed for a 380 V, 4:1 switched-capacitor converter, and a peak efficiency of 95.4 % is achieved with reduced output voltage ripples. All these prototypes demonstrate the switchcapacitor feasibility at higher-voltage (> 200 V) lower-power (< 30 W) levels than previously published ones. 8 Integrated Off-Line Power Converter The main conclusions are that this research contributes to the analysis and design of the integrated high voltage power MOSFETs for on-chip integrated power converters, and contributes to the design and implementation of the switched-capacitor based two-stage architecture for discrete off-line power converters. It is concluded that efficient integrated off-line power conversion is currently in its infancy, and this research work fosters the framework and paves the way for future development in this area
Original languageEnglish
PublisherTechnical University of Denmark
Number of pages166
Publication statusPublished - 2018

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