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Design optimization of magnetic components, which considers both electrical and thermal performance, can help in designing power converters with a high power density. This paper proposes an approximate analytical model for thermal resistance of inductor and transformer windings, including litz wire, which only requires knowledge of thermal properties of constituent materials and geometric dimensions. The model is based on regular square and hexagonal packing of insulated wires and is derived by integration of infinitesimal thermal resistances along a specified heat flow path. The model closely agrees with finite-element analysis (FEA) and can be used in place of time-consuming FEA as part of larger thermal network models for magnetic components. The model is also experimentally validated using a toroidal inductor with a litz-wire winding; the model has less than 12% error compared to the experimental measurement. Application of the model for practical windings, including litz-wire windings, is also discussed. The model can be used during the design process of magnetic components of a switching power converter to evaluate the temperature and potential hot spots. The model provides closed-form results, hence fast computation times, and so can be used in design optimization procedures. [ABSTRACT FROM AUTHOR]

This paper presents the derivation and verification of a sinusoidal steady-state equivalent-circuit model for microfabricated inductors developed for use in integrated power electronics. These inductors have a low profile, a toroidal air core, and a single-layer winding fabricated via high-aspect-ratio molding and electroplating. Such inductors inevitably have a significant gap between winding turns. This makes the equivalent resistance more difficult to model. The low profile increases the significance of the energy that is stored in the winding, which together with the winding gap makes the equivalent inductance more difficult to model. The models presented here account for these effects. Finally, the models are verified against results from 2-D and 3-D finite-element analysis (2-D FEA and 3-D FEA) direct measurement, and from in-circuit experimentation. In all cases, the equivalent-circuit model is observed to be accurate to within several percentage. [ABSTRACT FROM PUBLISHER]

The PowerChip research program is developing technologies to radically improve the size, integration, and performance of power electronics operating at up to grid-scale voltages (e.g., up to 200 V) and low-to-moderate power levels (e.g., up to 50 W) and demonstrating the technologies in a high-efficiency light-emitting diode driver, as an example application. This paper presents an overview of the program and of the progress toward meeting the program goals. Key program aspects and progress in advanced nitride power devices and device reliability, integrated high-frequency magnetics and magnetic materials, and high-frequency converter architectures are summarized. [ABSTRACT FROM AUTHOR]

Integration of efficient power converters requires technology for efficient, high-power on-chip inductors and transformers. Increases in switching frequency, facilitated by advances in circuit designs and silicon or wide-bandgap semiconductors, can enable miniaturization, but only if the magnetics technology works well at the higher frequencies. Technologies, geometries, and scaling of air-core and magnetic-core inductors and transformers are examined, and their potential for integration is discussed. Air-core inductors can use simpler fabrication, and increasing frequency can always be used to decrease their size, but magnetic cores can decrease the required thickness without requiring as high a frequency. [ABSTRACT FROM AUTHOR]

We present a noncontact method to measure the resistivity of multilayer magnetic thin films under high-frequency excitation. A multilayer thin-film magnetic material separated by dielectric has been used in microfabricated magnetic components in power applications. High-frequency resistivity is necessary for predicting core loss in magnetic materials. Traditional measurement methods using contacting probes cannot provide a reliable measurement of the resistivity of multilayer thin-film materials. Noncontact methods eliminate the use of electrical probes. Eddy-current loss induced by an applied external magnetic field is measured and the high-frequency resistivity of multilayer material is extracted from eddy-current loss measurements. The application of this method to measure the resistivity of multilayer thin-film materials and magnetic materials is investigated. The high-frequency resistivity of a 6-\mum-thick multilayer Co-Zr-O thin-film magnetic granular material is measured. Comparisons between theoretical and experimental results are presented. [ABSTRACT FROM PUBLISHER]

The design and fabrication of coupled inductors with low profile, low cost, and high power density for tapped-inductor high-step-down dc–dc power converters in the very-high-frequency (30–300 MHz) range are presented. The inductor consists of a multilayer thin-polyimide printed circuit board with nanogranular thin-film magnetic material deposited on both sides and on beveled cuts to form a fully linked closed core. The magnetic material Co–Zr–O has good soft magnetic properties, high resistivity, and high flux density capability. Multilayer Co–Zr–O/ZrO_2 thin films are used to improve the performance of the magnetic core. A winding loss model of this coupled inductor is presented. Coupled inductors with turns ratios 2 and 10 for several different converter applications have been designed, fabricated, and measured. Loss in the magnetic material is investigated. Small-signal and large-signal measurements show good performance of the fabricated components with high-frequency, high-field excitation. [ABSTRACT FROM PUBLISHER]