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Now showing items 1 - 6 of 6

  • Self-assembled liquid bridge confined boiling on nanoengineered surfaces

    Foulkes, Thomas   Oh, Junho   Pilawa-Podgurski, Robert   Miljkovic, Nenad  

    Increasing electrification of mechanically controlled or driven systems has created a demand for the development of compact, lightweight electronics. Removing waste heat from these high volumetric and gravimetric power dense assemblies, especially in mobile applications, requires non-traditional thermal management strategies with high heat flux potential and low integration penalty. Here, we develop and study confined subcooled pool boiling on nanoengineered surfaces which enables self-assembly of liquid bridges capable of high heat flux dissipation without external pumping. Using high-speed optical imaging coupled with high-fidelity heat transfer experiments in pure vapor environments, we study the physics of liquid bridge formation, bridge lifetime, and heat transfer. We demonstrate heat flux dissipations >100 W/cm(2) from a gallium nitride (GaN) power transistor residing above a horizontally parallel superhydrophobic nanostructured aluminum cold plate. To understand the confined bridge dynamics, we develop a hydrodynamic droplet bridging model and design rules capable of predicting the effects of gravity, intrinsic contact angle, contact angle hysteresis, and device heat flux. Our work not only demonstrates an ultra-efficient mechanism of heat dissipation and spreading using nanoengineered surfaces coupled to fluid confinement, but also enables the development of fully three-dimensional integrated electronics. (C) 2018 Elsevier Ltd. All rights reserved.
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  • Self-assembled liquid bridge confined boiling on nanoengineered surfaces

    Foulkes, Thomas   Oh, Junho   Pilawa-Podgurski, Robert   Miljkovic, Nenad  

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    High power output may be obtained from a photovoltaic (PV) system by controlling each photovoltaic cell of a solar array individually to operate at its maximum power point. Each cell may have associated power electronics and control circuitry that may be integrated together on a chip which may be advantageously implemented in CMOS, enabling reductions in cost and size. A perturb and observe algorithm may be used to find the maximum power point by measuring the power produced at different operating points, and modifying the operating point in the direction of increased power production. In one aspect, performance of a perturb and observe algorithm may be improved in the presence of noise.
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  • A Three-Level Boost Converter With Full-Range Auto-Capacitor-Compensation Pulse Frequency Modulation

    Liu, Wen Chuen   Ng, Pei Han   Pilawa-Podgurski, Robert  

    A three-level boost converter enables efficient voltage step-up power conversion with high power density by reducing the inductance and blocking voltage requirements in a conventional boost converter. An auto-capacitor-compensation pulse frequency modulation (ACC-PFM) controller, combining peak and valley current-mode controls, is proposed to resolve the issue of unbalanced flying capacitor voltage, as well as to regulate the output voltage. The capacitor balance is further strengthened through a delay-equalized level shifter that generates duty ratios with only sub-nanosecond deviations. The step-up power conversion from the input voltage of 0.3-3.0 V to the output voltage of 2.4-5.0 V is demonstrated through a prototype converter implemented in a 65-nm CMOS process with 0.28 mm(2) active area. This converter achieves 96.8% peak efficiency and an 83-mA peak output current, with an 83-mA peak step-up conversion ratio.
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  • Split-Phase Control:Achieving Complete Soft-Charging Operation of a Dickson Switched-Capacitor Converter

    Lei, Yutian   May, Ryan   Pilawa-Podgurski, Robert  

    Switched-capacitor (SC) converters are gaining popularity due to their high power density and suitability for on-chip integration. Soft-charging and resonant techniques can be used to eliminate the current transient during the switching instances, and improve the power density and efficiency of SC converters. In this paper, we propose a split-phase control scheme that enables the Dickson converter to achieve complete soft-charging (or resonant) operation, which is not possible using the conventional two-phase control. An analytical method is extended to help in the analysis and design of split-phase controlled Dickson converters. The proposed technique and analysis are verified by both simulation and experimental results. An 8-to-1 step-down Dickson converter with an input voltage of 150 V and rated power of 36 W is built using GaN FETs. The converter prototype demonstrated a five fold reduction in the output impedance (which corresponds to conduction power loss) compared to a conventional Dickson converter, as a result of the split-phase controlled soft-charging operation.
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  • Integrated CMOS Energy Harvesting Converter with Digital Maximum Power Point Tracking for a Portable Thermophotovoltaic Power Generator

    Pilawa-Podgurski, Robert   Li, Wei   Celanovic, Ivan   Perreault, David  

    This paper presents an integrated maximum power point tracking system for use with a thermophotovoltaic portable power generator. The design, implemented in 0.35-μm CMOS technology, consists of a low-power control stage and a dc-dc boost power stage with soft-switching capability. With a nominal input voltage of 1 V, and an output voltage of 4 V, we demonstrate a peak conversion efficiency under nominal conditions of over 94% (overall peak efficiency over 95%), at a power level of 300 mW. The control stage uses lossless current sensing together with a custom low-power time-based analog-to-digital converter to minimize control losses. The converter employs a fully integrated digital implementation of a peak power-tracking algorithm, and achieves a measured tracking efficiency above 98%. A detailed study of achievable efficiency versus inductor size is also presented, with the calculated and measured results.
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