Satish Prabhakaran

Design and Fabrication of Low-Loss Toroidal Air-Core Inductors

The design and fabrication of high-Q air-core toroidal inductors are described. Designs are optimized for maximum Q for a given size and inductance, independent any particular fabrication process. A fabrication process using a combination of thin-film processes and conventional machining has been used to make prototypes. Measurements performed on the first prototypes confirm the predicted Q of 115 at 50 MHz.

Microfabricated V-Groove Power Inductors for High-Current Low-Voltage Fast-Transient DC-DC Converters

Microfabricated thin-film inductors for high-frequency DC-DC power conversion at high currents and low voltages with fast transient response have been fabricated and tested. Inductors with a Co-Zr-O thin-film core and a copper conductor have been fabricated in a silicon substrate. Prototype inductors have been characterized and applied in a 3.3-V-to-1.1-V, 8-A, 5-MHz DC-DC converter and have been shown to exhibit efficiency of up to 89% and power density up to 96 W/cm2 of substrate area. The inductors discussed in this paper emerge as strong candidates for high-efficiency, high-power-density DC-DC converters for advanced digital systems such as microprocessors wherein the fast transient response of the microfabricated inductors can result in significant reduction in the converters output capacitance

Microfabricated coupled inductors for DC-DC converters for microprocessor power delivery

High-current, low-voltage power converters with fast transient response are needed for powering digital systems such as microprocessors. Microfabricated coupled inductors for such power converters are discussed. A four-phase microfabricated magnetic structure with 14 nH of inductance per phase has been fabricated for a 5 MHz, 5 V-to-1 V, 10 A dc-dc converter. The first prototype devices have been built with nickel-iron (NiFe) cores and copper conductors on a silicon substrate. Small-signal measurements on the inductors have been performed and predictions have been confirmed. A model for analyzing the performance of coupled inductors is presented. The devices have been implemented in a prototype converter and the measured performance is compared with the predicted results.

Impedance-analyzer measurements of high-frequency power passives: techniques for high power and low impedance

Challenges for measurements of high-frequency passive components for power electronics applications include the difficulty in measuring the small real impedance of an efficient component, the need for high-level excitation to match operating conditions for a nonlinear component, and in some applications, the need to measure very low impedances. Commercial impedance analyzers are tested and shown to be able to meet some of these requirements. To extend their capabilities, a new test fixture with less than 100 pH stray inductance has been developed for measurements of low impedances. The use of a power booster to extend drive capability to higher powers is also presented.

Comparison of magnetic materials for V-groove inductors in optimized high-frequency DC-DC converters

The tradeoff between saturation flux density and resistivity in soft magnetic materials for thin film inductors is examined quantitatively. We use an optimization routine to evaluate the achievable efficiency and power density using designs individually optimized to make best use of particular materials. The optimization selects switching frequency, ripple ratio, inductor dimensions and MOSFET sizes. For the example application of a 3.3- to 1.1-V, 7-A output dc-to-dc converter, Co-Zr-O, Fe-Al-O and Co-Fe-B-Si-O materials are considered. Predicted efficiencies are in the range of 80% to 90% at power densities of 20 W/cm/sup 2/ to 1000 W/cm/sup 2/. Different materials show advantages in different power-density or efficiency ranges.

Fabrication of thin-film V-groove inductors using composite magnetic materials

A new fabrication process is described for high performance embedded or integrated inductors for power converters. The process includes etching V-grooves in a silicon substrate, depositing granular composite magnetic materials, and electroplating the copper conductors.

Development of a High-Lumen Solid State Down Light Application

Light-emitting diode (LED)-based solid-state lighting (SSL) products have been exceeding the predicted performances especially at the chip and package levels. This has led to new SSL-based products for energy savings and long lifetimes. Large amounts of government funding and private investments have been made during the last decade to accelerate and guide the technology. This paper focuses on the development of an LED-based high-lumen luminaire technology. The critical subcomponents of the luminaire are the LED light engine (LED chips and optical system), thermal management, and driver electronics. Each of these subcomponents will be discussed in detail for a 100 W incandescent replacement technology. The paper addresses system integration of each of the subcomponents. While the design of new products evolve, the lack of reliability data poses a risk of premature failure of LED-based products. Premature failures would trigger customer rejection and may delay market penetration. Therefore, luminaire reliability is an important aspect of luminaire design. In cohort with this notion, finally, the luminaire reliability has been discussed.

A high-field high-frequency permeance meter for thin-film materials

Inductors using thin-film magnetic cores are attractive for high-frequency power converters. For developing accurate loss models for these inductors complex permeability measurements of the thin-film core materials have to be made at high magnetic fields and high frequencies. We describe a high-field high-frequency permeance meter capable of measuring complex permeability of thin-film materials in the 50 MHz frequency range with applied fields up to about 100 Oe.

Rogowski current sensor design and analysis based on printed circuit boards (PCB)

This work presents a new Rogowski current sensor design implemented in printed circuit boards. The proposed structure utilizes a modular design for a variety of applications. Feasibility was first demonstrated using standard printed circuit boards. Test results detail performance with high repeatability with less than 0.8% difference in sensed voltages and less than 0.3% difference in sensed voltages with respect to position of installation. In order to have a less complex, more manufacturable and modular Rogowski current sensor, a flexible printed circuit (FPC) solution was also designed and demonstrated. By using the FPC solution, high sensitivity and much higher power density was achieved. Coupling analysis of a 3-phase system was also conducted both from simulation and experiments.

High-frequency, high-current transformer designs for Silicon Carbide based LLC converters

The introduction of 1200 V Silicon Carbide (SiC) based technologies has enabled the use of high performance LLC converters for high input voltage (>500 VDC) applications such as datacenter power conversion. In this paper, we describe performance of the magnetics for a 2 kW-level LLC converter, operating at 100 kHz with SiC devices. We present magnetics designed for high converter efficiencies (> 96%) at high-current outputs (65 A). We focus on the design considerations to minimize the leakage inductance of a center-tapped transformer with a high voltage transformation ratio. We present a variety of winding strategies and show the efficacy of a hybrid solution that combines foil windings with litz winding for the application described. We demonstrate the performance improvements through finite element simulations and measurements from several prototypes.