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Inductive devices are extensively employed in power electronic systems due to their magnetic energy storage and power transfer capabilities. The current trend is towards increasing the frequency of operation in order to reduce the size of the magnetic components, but the main drawback is that the parasitic capacitance effect can become significant, and degrade the performance of the system. This work analyses the influence of this stray capacitance, and considers how to improve the performance of the device. In general, the impact of the stray capacitance on a magnetic component can be reduced by two methods: reducing the parasitic capacitance between turns of the winding or, alternatively, modifying the arrangement of the connection between turns. To evaluate the last option, an approximated expression of the first self‐resonant frequency of the magnetic device is proposed. This gives a rapid assessment of the performance of different devices maintaining the overall equivalent inductance. The proposed expression accounts for the influence of the connection between turns in the bandwidth of the component. Finally, some numerical results are verified with planar coils manufactured on two‐layer printed circuit boards.

Purpose Litz wire manufacturing using mechanical procedures presents several limitations regarding reliability and repeatability, especially when a small strand diameter is used. This paper aims to propose a power supply design for Litz wire manufacturing using a high-frequency high-performance resonant converter. Design/methodology/approach This paper proposes the design of a resonant power supply for induction heating specially designed to tackle with the challenge of heating Litz wires quickly. Findings The proposed converter enables the removal of the isolating coating from the Litz wire through induction heating, improving significantly the manufacturing process. Originality/value The proposed converter improves significantly the manufacturing process of Litz wire through induction heating, with economic and reliability benefits.

The following paper describes the design and optimization method for a small inductor in printed circuit board, which is later used in the implementation of a flexible cooking surface prototype. The method combines analytical developments with finite element analysis (FEA) simulations, providing an important decrease of the computational costs. This is followed by the corresponding calculations in order to minimize conduction and proximity losses in the winding by optimizing the copper volume in the winding and the conductor cross-section dimensions. A parametric analysis is carried out to define the induction system that leads to the optimal efficiency, which, moreover, proves extra-thin PCBs as the most suitable solution. A laboratory prototype of a flexible cooking surface was implemented and tested under real working conditions. The empirical characterization produced good results, which are consistent with the simulations. Additionally, the correct thermal behavior of the arrangement and its adaptability to different pot sizes was verified.

Domestic induction cookers are evolving from fixed cooking areas to flexible surfaces in such a way that the pot can be placed at any position. This implies the use of a larger number of reduced-sized inductors, which present a lower efficiency. As a solution to increase the efficiency while maintaining the flexibility, we propose the use of partially overlapped inductors of a larger size. This concept is currently in use in wireless power transfer systems, where the transmitter arrangement consists of several overlapped coils. The aim of this paper is to evaluate this concept applied to domestic induction heating appliances, with special emphasis in analyzing the effects of introducing the multicoil system with dissipative media. Moreover, the losses in the winding will be studied in detail. The system will be prototyped and tested, delivering up to 3.7 kW.

Printed circuit board (PCB) implementations provide high repeatability and ease of manufacturing as well as potential cost savings for many applications. An optimization procedure is proposed for designing PCB inductors for use in domestic induction cooktops. Cables for classical inductors are built of multistranded round litz wire for efficiency reasons. A planar litz structure in a PCB has been applied to achieve a similar performance to that of traditional constructions (in terms of maximum output power, inductive efficiency, and thermal behavior). The inductor performance has been optimized by a finite-element-analysis-tool-based method taking into account the power losses in rectangular cross-sectional tracks of the cable as well as the geometrical constraints of PCB implementations and the requirements of the associated electronics. Finally, the proposed method has been validated by means of experimental measurements under large-signal conditions on a PCB inductor prototype.

PCB technology provides an alternative to conventional Wireless Power Transfer (WPT) coils made of wound copper wire. The most common wires for conventional coils are either a single wire or a multistranded cable conforming a litz wire structure. On the other hand, the implementation on printed board is suitable for medium-low power applications, presenting advantages as low cost, high repetibility and compact design. Moreover, for reduced losses, the litz wire structure can be adapted to a PCB implementation. In this paper, a mathematical description of the PCB litz structure is presented together with a method to automatically generate PCB layouts of custom coils. Following this method, several prototypes were built and tested. The experimental characterization of the samples shows that coils with PCB litz structure present reduced losses.

We evaluate copper tubes as alternative of litz wire for planar coils of inductive power transfer (IPT) systems. For this purpose, a design methodology focused on maximizing the product of the magnetic coupling and the quality factor is proposed. The methodology is based on a combination of FEA simulations and analytical calculations of the skin and proximity losses in the tube. Analytical calculations are based on solutions of Maxwell''s equations for a tubular geometry. These solutions are oriented to extract both skin and proximity losses in the tube. Performance of a prototype of 1.5 kW is evaluated and compared with a conventional litz-wire implementation.

In this work, a model for induction heating cooktops with non-linear loads is presented. The model includes both the electronic converter and the inductor-pot system, which is usually modeled by its frequency-dependent equivalent impedance. Due to the non-linear relation between the magnetic field and the magnetic flux density in ferromagnetic media, the equivalent impedance of the inductor-pot system is significantly dependent on the excitation level. In this direction, two common materials have been experimentally characterized by their permeability curve for a wide range of excitation levels. Once the magnetic properties of the materials are known, a simulation model was developed including the non-linear behavior. By means of the simulation model, the equivalent impedance is obtained as a function of the excitation frequency and level. The modeled non-linear load is finally introduced in the power converter model from which the main waveforms can be extracted. Finally, the model was experimentally verified. The system was tested under real working conditions showing good concordance with the simulations.

Printed circuit board (PCB) windings are convenient for many applications given their ease of manufacture, high repeatability, and low profile. In many cases, the use of multistranded litz wires is appropriate due to the rated power, frequency range, and efficiency constraints. This paper proposes a manufacturing technique and a semianalytical loss model for PCB windings using planar litz structure to obtain a similar ac loss reduction to that of conventional windings of round wires with litz structure. Different coil prototypes have been tested in several configurations to validate the proposal.

In this letter, a method to calculate the ac losses, including skin effect and proximity losses, in planar windings with rectangular cross-sectional conductors is proposed. The aim is proposing proper ac losses expressions similar to the formulas available for round cross-sectional wires, to be used for the calculation of the ac losses and the optimization of planar magnetic windings implemented in the printed circuit board. The proposed model is based on the decomposition into conduction and proximity losses. Conduction losses only depend on the properties of the conductor, whereas proximity losses are calculated by using the orthogonal decomposition of the magnetic fields in which the conductors are immersed. Functions including the frequency and geometrical dependences of the both types of losses are extracted by means of finite element method simulation. Finally, several prototypes are used to verify the proposed expressions and some design considerations are also outlined.

Mutual inductance is a key parameter of the inductively coupled circuits such as transformers and contactless energy transfer systems. This parameter is particularly required to design the power electronics associated with each application. However, its value is usually extracted from measurements performed in a previously built prototype, which is an expensive and time-consuming task. In this paper, an analysis of the mutual inductance between two planar circular windings is developed. The analysis takes into account the effect of the media that can be part of the complete system. As a result, an analytical calculation of the mutual inductance with respect to the main parameters of the system such as the number of turns of the coils, geometry, frequency of the currents, and the properties of the media can be carried out. The analysis can also be used to explore the tendencies of the mutual inductance for design purposes and, thus, it allows speeding up the design process. The analysis has been verified by means of experimental results.

The operation of a domestic induction cooktop is based on the wireless energy transfer from the inductor to the pot. In such systems, the induction efficiency is defined as the ratio between the power delivered to the pot and the consumed power from the supplying converter. The non-transferred power is dissipated in the inductor, raising its temperature. Most efficiency-measuring methods are based on measuring the effective power (pot) and the total power (converter output). While the converter output power is directly measurable, the measurement of the power dissipation in the pot is usually a cause of inaccuracy. In this work, an alternative method to measure the system’s efficiency is proposed and implemented. The method is based on a pot with a reversible base to which the inductor is attached. In the standard configuration, the inductor is placed below the pot in such a way that the delivered power is used to boil water, and the power losses are dissipated to the air. When the pot base is flipped, the inductor is immersed into the water. In this case the losses in the inductor also contribute to heating up and boiling the water. The induction efficiency is calculated from the boiling rates in both configurations. A commercial inductor was tested under real working conditions with consistent results.

This work presents a method for calculating losses in PCB windings used in multi-coil contactless charging systems. This includes an electromagnetic model which combines analytical developments with FEM simulations in order to calculate the frequency-dependent resistance in a rectangular cross-sectional conductor. The obtained resistance per unit length is then applied to a PCB winding composed of multi-stranded turns in which strands rotate their positions building a Litz structure. The proposed model considers a generic case of a multi-coil assembly in which one of the inductors is supplying power to the load. As other coils may be positioned in the immediate vicinity of an alternating magnetic field source, these coils will produce a loss contribution due to proximity effect. The model has been experimentally validated and the results present consistence when compared with the calculations.

Optimization of the efficiency of an induction heating application is essential in order to improve both reliability and performance. For this purpose, multi-stranded cables with litz structure are often used in induction heating applications. This paper presents an analysis and optimization of the efficiency of induction heating systems focusing on the optimal copper volume of the winding with respect to different constraints. The analysis is based on the concept of a one-strand one-turn coil, which captures the dissipative effects of an induction heating system and reduces the number of variables of the analysis. An expression for the efficiency of the induction heating system is derived. It is found that, with the geometry and the other parameters of the system fixed, efficiency depends on the copper volume of the windings. In order to use this result to optimize the efficiency of an application, volume restrictions, the packing factor and the window utilization factor are also considered. The optimum frequency for an induction heating system is also studied in this work. An experimental verification for both planar and solenoidal cases is also presented.

This article proposes the two first blocks of an analogue front-end suitable for plastic optical fibre systems suitable for the standard IEEE 1394. These blocks consist of a preamplifier followed by an equaliser which employs low-cost commercial components and are designed with two different bipolar technologies. With a supply voltage of 3.3 V, the front-end consumes 396 mW. The total gain is 70 dBΩ and it operates at up to 800 Mb/s. At this bit rate, with fibre lengths of up to 30 m, the circuit has a BER ≤ 10−12 and a maximum jitter of 170 psrms.

A compact robust CMOS limiting amplifier (LA) for high data traffic optical links is presented in this work. The core considers two different blocks. First, four common-source inverter amplifiers are included, which optimize the gain-bandwidth product of the structure. And second, two additional compensation stages are placed strategically between the gain stages alleviating the pernicious load effect. These stages develop two different compensation techniques simultaneously thus increasing the bandwidth. The proposed design consumes 113 mW with a single 1.8 V supply. It achieves a cut-off frequency up to 3 GHz and provides a gain of 21 dB. The circuit is packaged in a QFN24 and mounted on a commercial FR4 PCB.

PCB implementation of planar windings replicates the structure of conventional litz wires in order to reduce the ac losses. This structure consists of a set of fine trace electrically connected in parallel which are transposed by means of changes of both trajectory and layer. An appropriate transposition strategy is essential to reduce the winding ac losses, however PCBs with high number of vias could result expensive and not reliable. Taking advantage of the field profile of planar windings, in this work is studied the minimization of the number of vias without significant reduction of performance. The work is carried out by means of a combination of finite-element analysis (FEA) simulations and experimental verification on ultra-thin (0.3 mm) PCB prototypes of planar inductors oriented to a domestic induction heating application.

This paper extends a previous formula for the mutual inductance between single-turn coils to include all coils in air with rectangular cross sections, without any restrictions on the dimensions (including overlapping coils). The formula is compared with a wide spectrum of examples from the literature and agreement is excellent in every case. Experimental results are presented to validate the formula for both solenoid and disk coils. The formula is relevant to coreless transformers, inductive coupling, wireless power transfer, and leakage inductance in resonant converters.

The effect of the twisting on the losses of multistranded wires is investigated by means of the combination of a general purpose CAD tool and 3D-FEA simulation. The 3D simulation shows that at bundle level appears both skin and proximity effects which are not usually considered in 2D analyses. These effects generate extra losses in the cable which depend on the helix pitch and the isolation between strands. A loss model including these effects is not concluded from this study however, some manufacturing guidelines are pointed out. The results suggest that it is convenient to avoid small helix pitches and to increase the isolation between strands. Results of the 2D and 3D analysis and the loss model of isolated strands are compared.

In this work, a design calculation method for common-mode chokes (CMC) is presented. With this purpose, a similar method to that employed in a typical inductor design where the input current characteristics define both the maximum magnetic flux and the winding losses has been adapted. In order to get a suitable design that provides a CMC optimization, considerations with regard to both current components, the common-mode (CM) and the differential-mode (DM) current, have been taken into account. Therefore, the CM current contributes to the magnetic flux in the core, which is associated to the core saturation and core losses, whereas the DM current generates the copper losses. Finally, a CMC for domestic induction heating appliances is designed.

In this paper, an elliptic inductor intended to implement low-cost flexible active surfaces for induction cooktops is presented. A 3-D Finite Element Analysis (FEA) platform including the parameterization of the geometry has been developed for simulation purposes. By means of this platform, the main parameters of the induction system, such as the equivalent impedance including the dependence of the position of the pot, the ferrite sizing and the wiring requirements, are analyzed. Finally, experimental results of the developed inductor prototype at both small and large signal levels are shown.

In this paper, the design and implementation of small inductors in printed circuit board (PCB) for domestic induction heating applications is presented. With this purpose, we have developed both a manufacturing technique and an electromagnetic model of the system based on finite-element method (FEM) simulations. The inductor arrangement consists of a stack of printed circuit boards in which a planar litz wire structure is implemented. The developed PCB litz wire structure minimizes the losses in a similar way to the conventional multi-stranded litz wires; whereas the stack of PCBs allows increasing the power transferred to the pot. Different prototypes of the proposed PCB inductor have been measured at low signal levels. Finally, a PCB inductor has been integrated in an electronic stage to test at high signal levels, i.e. in the similar working conditions to the commercial application.

In this paper, an analysis of the resistance of multi-track coils in printed circuit board (PCB) implementations, where the conductors have rectangular cross-section, for spiral planar coils is carried out. For this purpose, different analytical losses models for the mentioned conductors have been reviewed. From this review, we conclude that for the range of frequencies, the coil dimensions and the planar configuration typically used in domestic induction heating, the application in which we focus, these analysis are unsatisfactory. Therefore, in this work the resistance of multi-track winding has been calculated by means of finite element analysis (FEA) tool. These simulations provide us some design guidelines that allow us to optimize the design of multi-track coils for domestic induction heating. Furthermore, several prototypes are used to verify the simulated results, both single-turn coils and multi-turn coils.

In this paper, a power control strategy focused on improving the efficiency of induction heating appliances is presented. This strategy uses the distance between the inductor and the load as a control parameter, which is combined with the switching frequency of the resonant inverter. Therefore, a study of the efficiency of the involved subsystems is carried out. From these analyses, the theoretical efficiency of the combined converter-inductor system is analyzed. In order to verify experimentally the proposed power control strategy, an experimental setup has been built in which both distance inductor-vessel and switching frequency can be varied. By using this setup, a mixed electric-calorimetric energy balance is performed with the objective of measuring the impact of the proposed strategy in the appliance efficiency. The calorimetric method shows that the efficiency tendency of the appliance follows the predictions of the theoretical analysis.

In this paper, a method to calculate the ac losses (including skin effect and proximity losses) in planar magnetic devices having rectangular cross-section conductors is presented. A similar model to that employed in the losses calculation with round wires is developed for the mentioned conductors. The aim is to obtain a proper design procedure, especially for magnetic devices in printed circuit board (PCB) implementations. Basically, the losses model is based on the superposition of different losses in the wire (conduction and proximity losses) and also in an orthogonal decomposition of the field where the conductors are immersed. As a consequence, to provide us a computation time reduction, the number of functions, needed to calculate the proximity losses is reduced to one, as it occurs in round wires. This function and also the function that describes the conduction losses, both include the size and frequency dependencies, are calculated and tabulated by means of Finite Element (FEM) calculations. Thus, the ac losses are obtained with a computation time reduction employing the losses model developed with FEM field calculations. Finally, several prototypes are used to verify the proposed method and some optimization results are also extracted.

This paper presents a transimpedance amplifier (TIA)-equalizer combination optical receiver for 2.5 Gbit/s communications realized in a standard 180 nm CMOS process. The first stage, a transimpedance amplifier (TIA), is based on a conventional structure with an inverting voltage amplifier and a feedback resistor, but incorporates a technique to prevent the TIA saturation at high input currents. Simulation results show an optical sensitivity of 4 µA for a BER = 10−12 and a maximum input current of 1.5 mA pp , what leads to an input dynamic range above 52 dB. The TIA is followed by an equalizer which compensate the typical frequency response of an integrated photodiode. The power consumption is 6.5 mW for the TIA and 4.1 mW for the equalizer with 1.8 V supply.