Publications (152) View all
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Conference Proceeding: GaN-FET based dual active bridge DC-DC converter
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ABSTRACT: This paper describes a high step-down unregulated, fixed-ratio DC-DC converter (DCX) based on the dual active bridge (DAB) power stage operating at high switching frequency using enhancement-mode Gallium-Nitride-on-Silicon (GaN) transistors. The DAB power stage design as well as a comparison of losses using GaN and silicon MOS devices is based on a detailed state-plane analysis of resonant transitions. Experimental results are presented for a 150 W, 150-to-12 V prototype DCX operating at 1 MHz switching frequency.Applied Power Electronics Conference and Exposition (APEC), 2011 Twenty-Sixth Annual IEEE; 04/2011 -
Article: Power Management of Wideband Code Division Multiple Access RF Power Amplifiers With Antenna Mismatch
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ABSTRACT: This paper focuses on a combination of adaptive power supply and adaptive impedance tuning for WCDMA RF power amplifiers (RFPA) in wireless handsets in order to improve the system efficiency under different transmit power levels and antenna mismatch. The adaptive power supply is a noninverting buck-boost power converter. It is shown that precise output voltage positioning and low output voltage ripple over a wide output voltage range, including buck, boost, and buck/boost transition modes, can be accomplished using ??-?? modulation in combination with a small, low-resolution DPWM core. A two-mode digital controller is presented, in which the compensator parameters are changed upon buck/boost mode transitions in order to improve closed-loop dynamic performance. Furthermore, improvements in system efficiency are demonstrated using this adaptive power supply combined with an adaptive RF impedance tuner between the RFPA and the antenna. The results are verified on an experimental test bed that consists of a discrete RFPA, impedance tuner, a prototype 0.5 ??m CMOS power stage IC that integrates power MOSFETs, drivers and deadtime control logic, and a digital power management controller implemented on an FPGA.IEEE Transactions on Power Electronics 05/2010; · 4.65 Impact Factor -
Conference Proceeding: Load-interactive steered-inductor dc-dc converter with minimized output filter capacitance
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ABSTRACT: The paper introduces a concept of load-interactive digitally controlled point-of-load (POL) dc-dc converters where the size of the output filter capacitor can be minimized based on the enhanced load-related communication between the digital load and the converter controller. Based on the information about upcoming load changes, the inductor current of the dc-dc converter is adjusted such that the converter output current matches the new load, thus minimizing the energy storage requirements for the output filter capacitor. The effectiveness of this approach is verified on a digitally controlled 3.3 V/ 30 W experimental prototype, where the dc-dc converter is a steered-inductor non-inverting buck-boost. Transient response results show that, compared to standard converters with near-time optimal control, the new system has about three times smaller voltage deviation, allowing for a proportionally significant reduction in the output capacitor size.Applied Power Electronics Conference and Exposition (APEC), 2010 Twenty-Fifth Annual IEEE; 03/2010 -
Article: Hybrid Digital Adaptive Control for Fast Transient Response in Synchronous Buck DC–DC Converters
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ABSTRACT: This paper presents a hybrid digital adaptive (HDA) control for fast step-load transient responses in synchronous buck DC-DC converters. The proposed HDA controller results in near-time-optimal step-load transient responses even when the output voltage is sampled using a relatively low-resolution, narrow-range window A/D converter. The controller is a combination of a standard constant-frequency pulsewidth-modulated (PWM) control in the vicinity of steady-state operating point and a bank of switching surface controllers (SSCs) away from the reference. The switching surface slope is adaptively selected by a supervisor based on an inductor current estimate. Furthermore, the controller is capable of taking into account a maximum inductor current limitation. A large-signal stability analysis is presented for all possible cases during transients when one of the SSCs is active. Experimental results demonstrate fast transient responses for a 1.3 V, 10 A synchronous buck converter over a wide range of step-load transients.IEEE Transactions on Power Electronics 12/2009; · 4.65 Impact Factor -
Article: An Online Stability Margin Monitor for Digitally Controlled Switched-Mode Power Supplies
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ABSTRACT: This paper presents a practical injection-based method for continuous monitoring of the crossover frequency and phase margin in digitally controlled switched-mode power supplies (SMPS). The proposed approach is derived from Middlebrook's loop-gain measurement technique, adapted to a digital controller implementation. A digital square-wave signal is injected into the feedback loop and the injection signal frequency is adjusted while monitoring loop signals to obtain the system crossover frequency and phase margin online, i.e., during normal closed loop SMPS operation. The approach does not require open loop or steady-state SMPS operation and is capable of convergence in the presence of load transients or other disturbances. A method for designing the stability margin monitor, based on small-signal models derived using an envelope modeling approach, is also presented. Experimental results are given for multiple power stage configurations demonstrating close matches between monitored and expected crossover frequencies and phase margins.IEEE Transactions on Power Electronics 12/2009; · 4.65 Impact Factor
