Showing papers by "Khai D. T. Ngo published in 2005"

Synthetic-ripple modulator for synchronous buck converter

Abstract: Comprising a hysteretic comparator and a ripple synthesizer, the synthetic-ripple modulator (SRM) allows voltage-hysteretic modulation to be realized in low-voltage buck converters where the natural voltage ripple is too small for reliable hysteretic operation. Circuit implementation, steady-state operation, and design equations are described for an SRM controlling a buck dc-dc converter. The basics are verified experimentally by a buck converter switched at 420 kHz and delivering 10 A at 1.8 V.

Converter and controller for micro-power energy harvesting

Abstract: A pulsed-resonant ac-dc converter and an integrated-circuit (IC) controller have been designed, fabricated, and tested for harvesting energy from low-voltage (12 V), low-power (1-100 muW) energy transducers with output frequency in the 10 Hz-1 kHz range Simulations using foundry models suggest that the silicon loss could be as low as 06 muW, and the efficiency could reach 70% With the IC experimentally packaged, the measured efficiency is between 50% and 70%, depending on the size and the loss in the resonant inductor

Analysis of an AC/DC Resonant Pulse Power Converter for Energy Harvesting Using a Micro Piezoelectric Device

Abstract: In order to harvest power in an efficient manner from a micro piezoelectric (PZT) device for charging the battery of a remote system, a new AC/DC resonant pulse power converter is proposed. The proposed power converter has two stages in the power conversion process. The first stage includes N-type MOSFET full bridge rectifier. The second stage includes a boost converter having an N-type MOSFET and a P-type MOSFET. MOSFETs work in the 1st or 3rd quadrant region. A small inductor for the boost converter is assigned in order to make the size of the power converter as small as possible, which makes the on-interval of the MOSFET switch of the boost converter ultimately short. Due to this short on-interval, the parasitic junction capacitances of MOSFETs affect the performance of the power converter system. In this paper, the performance of the new converter is analytically and experimentally evaluated with consideration of the parasitic capacitance of switching devices.

Pulsewidth modulator with carriers derived from converter waveforms

Abstract: Carrier signals for pulsewidth modulation are generated using simple filters operating on the waveforms readily available in a power converter. Also containing the averaged dynamics, such carrier signals can be bonded to a signal to be controlled to realise fast, linear transient responses. The operating principle and circuitry are described and validated for the buck and boost DC–DC converters.

Hybrid Power Filter with Output Impedance Control

Abstract: Next-generation microprocessors requires 150 A/0.8 V with slow rates of >70 A/ns. At 10 GHz switching frequencies, the ESL of the packaging capacitors presents more problems than the ESR. This paper highlights a unique hybrid power filter using output impedance matching to allow seamless compatibility of the VRM, packaging capacitors, microprocessor die, and active filter. This topology reduces required capacitors by roughly 90%, with simulations showing <100 mV ripple at projected slew rates. An experimental prototype is demonstrated to suppress undershoot caused by 25 A load transients at 160 A/mus with off-the-shelf components

Thermal behavior of a dynamic domain-wall motion model for hysteresis in power ferrites

Abstract: In this letter, we characterize the temperature dependence of the parameters of a frequency-dependent hysteresis model from room temperature to the Curie temperature, at different field amplitude and frequency. Empirical formulas based on power, rational, and gamma functions are suggested for the thermal variations to facilitate the use of the hysteresis model in computer-aided design. We demonstrate a parameter extraction procedure and provide experimental data for a commercial MnZn power ferrite magnetized up to 0.4 T, between 10 kHz and 1 MHz, and between 25/spl deg/C and 225/spl deg/C.

Effective parameters for toroidal cores based on nonlinear magnetization

Abstract: We propose a method to determine the effective parameters for toroidal cores. We have found the method effective in generating the initial flux-magnetomotive-force curve, as well as minor and major flux-MMF loops for a wide range of commercial toroids, using three commercial power manganese-zinc (MnZn) ferrites. In the method, a material-dependent function is used to approximate the initial magnetization curve. Material-independent, geometry-dependent expressions are then derived for the effective parameters. We compare initial-magnetization-based l/sub e/ and A/sub e/ with those published by core producers.