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  • 1.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Comparison of Two Layered and Three Layered Coreless Printed Circuit Board Step-Down Power Transformers2011In: 2011 INTERNATIONAL CONFERENCE ON INSTRUMENTATION, MEASUREMENT, CIRCUITS AND SYSTEMS (ICIMCS 2011), VOL 2: FUTURE COMMUNICATION AND NETWORKING, Shenzhen: IEEE conference proceedings, 2011, p. 59-62Conference paper (Refereed)
    Abstract [en]

    In this paper the comparative results of two layered and three layered coreless Printed Circuit Board (PCB) step down 2:1 power transformers operating in MHz frequency were addressed. The  two different step down transformers approximately having same self inductances, one in two layer and the other in three layer were designed and evaluated for the given power transfer application. The performance characteristics of these transformers under similar conditions were measured and the comparative parameters of these transformers in terms of their resistances, self, leakage, mutual inductances, and coupling coefficient are analyzed. For the given output power, the measured energy efficiency of the three layered transformer is improved by 3% and the area is reduced by 32% compared to two layered transformer. The efficiency of the three layered transformer is 94.5% approximately for an output power level of 25W at an operating frequency of 2.5MHz

  • 2.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Coreless Printed Circuit Board (PCB) StepdownTransformers for DC-DC ConverterApplications2010In: PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, ISSUE 70, OCTOBER 2010, ISSN:1307-6892, France: World Academy of Science Engineering and Technology , 2010, p. 380-389Conference paper (Refereed)
    Abstract [en]

    In this paper, multilayered coreless printed circuit board (PCB) step-down power transformers for DC-DC converter applications have been designed, manufactured and evaluated. A set of two different circular spiral step-down transformers were fabricated in the four layered PCB. These transformers have been modelled with the assistance of high frequency equivalent circuit and characterized with both sinusoidal and square wave excitation. This paper provides the comparative results of these two different transformers in te rms of their resistances, self, leakage, mutual inductances, coupling coefficient and also their energy efficiencies. The operating regions for optimal performance of these transformers for power transfer applications are determined. These transformers were tested for the output power levels of about 30 Watts within the input voltage range of 12-50 Vrms. The energy efficiency for these step down transformers is observed to be in the range of 90%-97% in MHz frequency region.

  • 3.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Effect of Air Gap on the Performance of Hybrid Planar Power Transformer in High Frequency (MHz) Switch Mode Power Supplies (SMPS)2012In: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Conference paper (Refereed)
    Abstract [en]

    A half bridge transformer with novel winding strategy was designed and tested up to the output power level of 50W with a maximum energy efficiency of 98% in 1-6 MHz frequency region. In this paper, the effect of air gap on the performance of the designed transformer for high frequency (MHz) Switch Mode Power Supplies (SMPS) was studied and analyzed. The air gap of the transformer was varied from 0 – 2mm and the effect on self, leakage, mutual inductances, coupling coefficient and power transfer capability was recorded in 1 - 6MHz. The parameters of the transformer with different air gaps were extracted using network analyzer. The transformer was excited with sinusoidal voltages using power amplifier and the performance characteristics such as input impedance, power transfer capability and hence the energy efficiency was measured. At a particular operating frequency of 3MHz, the maximum power transferred for the given excitation voltage with 0mm air gap was found to be 22W whereas it is only 8W with the 2mm air gap . The measured energy efficiency of the transformer at 3MHz with 0mm and 2mm air gap was found to be 93% and 79% respectively. With this study, for the given power transfer application, at a particular high frequency operation of converter, an optimum air gap without sacrificing the energy efficiency and core saturation was proposed

  • 4.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Effect of Dielectric Material on the Performance of Planar Power Transformers in MHz Frequency Region2012In: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012, 2012Conference paper (Refereed)
    Abstract [en]

    In this paper, the effect of two different dielectric materials in planar printed circuit board (PCB) transformers applicable for power transfer applications in MHz frequency region is discussed. The 2-D model of the planar transformer was developed and the effect of the dielectric material on the magnetic field and the current distribution in the transformer was analyzed. Based on the FEA analysis, the power transformers of two different dielectric materials were designed, manufactured and characterized by using ‘S’ parameters obtained from network analyzer in order to determine the performance of dielectrics at high frequencies. The electrical parameters such as inductances, capacitances and resistances of the transformers were obtained and the changes in these parameters with the variation of the dielectric material were analyzed in the MHz frequency. This paper discusses the effect of dielectric material on the magnetic field distribution and the current density which results in the variation of the coupling coefficient and the eddy current losses of the transformer. By changing the dielectric material from a traditional FR-4 to a Rogers, the coupling coefficient was improved by a maximum of 5% and the copper losses of transformer were also decreased in the MHz frequency region. The power gain/energy efficiency obtained from the network analyzer with a resonant capacitor is verified with those obtained using a power amplifier and the simulations. An overall energy efficiency improvement of about 2-5% was achieved with a Rogers’s material in MHz frequency region compared to traditional FR-4 laminate.

     

  • 5.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    High Performance Planar Power Transformer with High Power Density in MHz Frequency Region for Next Generation Switch Mode Power Supplies2013In: 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference And Exposition (APEC 2013), IEEE conference proceedings, 2013, p. 2139-2143Conference paper (Refereed)
    Abstract [en]

    The authors report the utilization of the core based transformer for power transfer applications with high power density and high energy efficiency in the MHz frequency region. A custom made POT core center tapped transformer of 4:1:1 turn’s ratio using novel winding strategy with the core diameter of 16mm is designed and evaluated. The designed transformer has been characterized using sinusoidal excitation for a given output power in the frequency range of 1 – 10MHz and determined the operating frequency region of the transformer. The power tests of the transformer has been carried out up to the power level of 62W at an operating frequency of 6.78MHz with a peak energy efficiency of 98.5% resulting in the record power density of ~1100W/in3. The designed transformer has been characterized using class E isolated DC-DC converter topology at an output power of approximately 18W. The simulated energy efficiency of the converter is 88.5% under the full load condition. This work provides the significant step for the development of next generation high power density isolated converters (both AC/DC and DC/DC) in MHz frequency region

  • 6.
    Ambatipudi, Radhika
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Radiated Emissions of Multilayered Coreless Printed Circuit Board Step-Down Power Transformers in Switch Mode Power Supplies2011In: 8th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2011-ECCE Asia 2011, IEEE conference proceedings, 2011, p. 960-965Conference paper (Refereed)
    Abstract [en]

    This paper addressesradiatedEMI issues in Coreless PCB step-down transformers used for power transfer applications. In case of SMPS circuits, since the waveforms are not sinusoidal in nature, most of theradiatedemissionsare not only from fundamental frequency component but also from harmonic contents. According to antenna theory,radiatedEMI for three different power transformers of different radii were estimated for fundamental frequency of 2MHz to 300MHz. The computations were made for both sinusoidal and square wave excitations and at a load power of 20W. The calculatedradiatedpower obtained for simulated waveforms and for practical measured current waveforms are in good agreement with each other up to certain bandwidth. These computational results confirm thatradiatedpower can be reduced in three layered 2:1 transformer compared to two layered 2:1 transformer. Also theradiatedemissionsare negligible in case of sinusoidal excitations compared to square wave excitations. © 2011 IEEE.

  • 7.
    Andersson, Henrik
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Processing and Characterization of a MOS Type Tetra Lateral Position Sensitive Detector with Indium Tin Oxide Gate Contact2008In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 8, no 9-10, p. 1704-1709Article in journal (Refereed)
    Abstract [en]

    A 2-D tetra lateral position sensitive detector (PSD) based on the metal-oxide-semiconductor (MOS) principle has been manufactured and characterized. The active area of the device is 5 nun x 5 mm and the intention is to use the central 4 nun x 4 nun for low nonlinearity measurements. The gate contact is made of indium tin oxide (ITO) that is a degenerate electrically conducting semiconductor, which, in addition, is also transparent in the visible part of the spectrum. The use of a MOS structure results in a processing with no necessity to use implantation or diffusion in order to make the resistive p-layer as in a conventional p-n junction lateral effect PSD. Position measurements show good linearity in the middle 4 nun x 4 mm area. Within the middle 2.1 mm x 2.1 mm, the nonlinearity is within 1.7% of the active area with a position detection error of maximum 60 mu m. Measured MOS IV characteristics are compared to a level 3 spice model fit and show good agreement. The threshold voltage is determined to be -0.03 V. Responsivity measurements show a high sensitivity in the visible spectral region.

  • 8.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan Muhammad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A phase shifted full bridge converter with novel control over the leakage inductance2016In: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE), Institute of Electrical and Electronics Engineers (IEEE), 2016, article id 7695545Conference paper (Refereed)
    Abstract [en]

    The electronics industry is progressing towards the high density board solutions due to the requirement of compact and intelligent electronic systems. In order to meet the industry demands, the power system is required to be of high power density. This article proposes one of the solution to improve the power density for the medium power applications. In phase shifted full bridge converter, the intrinsic leakage inductance of the main transformer is not high enough to obtain the zero voltage switching of the power switches for the entire operating conditions. An additional shim inductor is usually connected in series with the primary winding of the main transformer to increase the collective leakage inductance. This additional shim inductor degrades the power density of the converter. This paper proposes a method to embed and control the resonance inductance inside the main transformer. In addition to the increased inter-winding spacing, this paper proposes a practical approach to integrate the ferrite rods inside the main transformer for further increase in the leakage inductance. A power transformer is constructed and investigated by using the modelled equations to estimate the leakage inductance. A prototype phase shifted full bridge converter is also developed to investigate the performance of the proposed transformer. The converter is designed for the switching frequency of 400kHz, and tested up to 600watts output power at the input voltage of 200Vdc. The performance of the proposed converter is also compared with the converter of using an external inductor. The investigations show that, in addition to the improved power density, the converter with the proposed transformer is more efficient than the converter with the traditional transformer.

  • 9.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    An improved modelling and construction of power transformer for controlled leakage inductance2016In: Environment and Electrical Engineering (EEEIC), 2016 IEEE 16th International Conference on, IEEE, 2016Conference paper (Refereed)
    Abstract [en]

    In this work, a transformer with increased leakage inductance for the soft switched power applications is presented as a practical solution by constructing a transformer with good control over the leakage inductance. An analytical reluctance based model is presented, which accurately predicts the leakage inductance. With the presented approach, a transformer is designed with a leakage inductance varying between 3-7μH. Increasing the efficiency and improving the power density has been the main focus of power electronics researchers in the recent years. In this regards, transformers with increased leakage inductance are becoming more popular in order to accomplish different soft switching concepts and for improving the power density.

  • 10.
    Bakar, Muhammad Abu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    High frequency (MHz) soft switched flyback dc-dc converter using GaN switches and six-layered PCB transformer2016In: IET Conference Publications, UK: Institution of Engineering and Technology, 2016, Vol. 2016, p. 1-6, article id CP684Conference paper (Refereed)
    Abstract [en]

    The increased switching losses with increasing switching frequency are the biggest concerns in designing high power density converters. This paper presents the investigation of an energy efficient DC-DC flyback converter in combination with six layered printed circuit board transformer. The recorded efficiency of the low profile transformer for the frequency range of 1-5MHz is 98% at power density of 770W/in3. The proposed converter is characterized for frequencies up to 4MHz by using possible soft switching techniques such as Boundary Mode and Quasi Resonant Mode. The emerging Gallium Nitride (GaN FET) devices are used as power switch. The control is incorporated with Digital Signal Processor (dsPIC) for both the Boundary and Quasi Resonant Modes of operations. The proposed flyback DC-DC converter is tested on a prototype Printed Circuit Board (PCB). The performance of the proposed converter is investigated for the telecom input voltage range of 36-72Vdc. The maximum obtained energy efficiency of the converter is about 94%. According to the authors' knowledge, this is the maximum efficiency ever achieved in flyback converters switching in MHz frequency range. The results are very encouraging for the development of high frequency, high power density and low cost isolated power converters.

  • 11.
    Bertilson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo Simulation of 4H and 6H-SiC short channel MOSFETs2001In: High Temperature Electronics Network. HITEN ; 4 (Oslo) : 2001.06.05-08: Proceedings of the International Conference on High Temperature Electronics : held in Oslo, Norway, 5th - 8th June 2001, Oxford: Oxford Applied Technology Ltd, , 2001, p. 199-Conference paper (Refereed)
  • 12.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nästa generations kompakta spänningsomvandlare2012In: Thule, Kungl. Skytteanska Samfundets Årsbok 2012, ISSN 0280-8692, Vol. 1, no 1, p. 153-157Article in journal (Other (popular science, discussion, etc.))
  • 13.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation and Optimization of SiC Field Effect Transistors2004Doctoral thesis, monograph (Other scientific)
  • 14.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Transformer2010Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A printed circuit board transformer comprises at least one primary winding and one secondary winding, each in the form of at least one layer of turns inside or at the surface of a printed circuit board. The transformer is designed for a step-up/down-operation. Each of the two layers (10, 11) has an elongated winding element (12, 13, 13′) substantially following an elongated winding element of the other layer while being in an overlapping relationship therewith as seen perpendicularly to said printed circuit board over substantially the entire extension of said winding elements. A second (11) of the layers belonging to the secondary winding has a fewer number of turns than the first (10) of said layers belonging to said primary winding.

  • 15.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Monte Carlo simulation of vertical MESFETs in 2H, 4H and 6H-SiC2001In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 10, no 3-7, p. 1283-1286Article in journal (Refereed)
    Abstract [en]

    The 4H-SiC static induction transistor (SIT) is a very competitive device for high frequency and high power applications (3-6 GHz range). The large breakdown voltage and the high thermal conductivity of 4H-SiC allow transistors with extremely high current density at high voltages. The SIT transistor shows better output power capabilities but the unity current-gain frequency is lower compared to a MESFET device. In this work we show, using a very accurate numerical model, that a compromise between the features given by the SIT structure and the ordinary MESFET structure can be obtained using the vertical MESFET structure. The device dimension has been selected very aggressively to demonstrate the performance of an optimized technology. We also present results from drift-diffusion simulations of devices, using transport parameters obtained from the Monte Carlo simulation. The simulations indicate that 2H-SiC is superior to both 4H and 6H-SiC for vertical devices. For lateral devices, 2H-SiC is slightly faster compared to an identical 4H-SiC device

  • 16.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Dubaric, Ervin
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of a low atmospheric-noise modified four-quadrant position sensitive detector2001In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 466, no 1, p. 183-187Article in journal (Refereed)
    Abstract [en]

    A modified four-quadrant position sensitive detector (PSD) is developed. This structure is less sensitive to atmospheric turbulence that is a major drawback with the traditional four-quadrant detector. The inter-electrode resistance is as high as for the four-quadrant detector, which is an advantage compared to the lateral effect PSD. The linearity for the modified four-quadrant detector is good in the whole active range of sensing. The structures are limited to small sensing areas with well focused beams and are suitable for use in detectors up to 1 mm in size.

  • 17.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Harris, C
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Calculation of lattice heating in SiC RF power devices2004In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, no 12, p. 1721-1725Article in journal (Refereed)
    Abstract [en]

    Silicon carbide MESFET devices are suitable for high-speed and high-power applications. In this paper we are studying thermal effects in 4H-SiC RF power devices. The simulations are based on a combination of 2D device simulations for the electrical transport, and 3D thermal simulations for the lattice heating. We show that the method gives good accuracy, efficiency, flexibility and capacity dealing with tasks, where a 2D coupled electrical-thermal simulation is not sufficient. We also present an improvement of Roschke and Schwierz mobility model, based on Monte Carlo simulations for the temperature dependencies of the mobility parameters beta and v(sat).

  • 18.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Harris, C.I.
    Comparison of bipolar and unipolar SiC switching devices for very high power applications2007In: Silicon Carbide and Related Materials 2006, Trans Tech Publications Inc., 2007, Vol. 556-557, p. 975-978Conference paper (Refereed)
    Abstract [en]

    Both unipolar and injection SiC devices can be used for high voltage switching applications; it is not determined, however, for which applications one approach is preferred over the other. In this paper, simulation studies are used to compare the suitability of unipolar devices, in this case a JFET (Junction Field Effect Transistor) against an equivalent FCD (Field Controlled Diode) configuration up to very high voltages. The calculations are performed in a finite element approach, with commercial drift-diffusion software. Numerous drift layers have been simulated in a Monte-Carlo approach to ensure that the optimal design of the drift layers for different breakdown is used. In a static case, purely conductive losses in the drift layer in both unipolar and injection configuration are compared. Additionally the total losses are studied and compared in switched applications for different switching frequencies and current levels.

  • 19.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Optimization of 2H, 4H and 6H-SiC high-speed vertical MESFETs2002In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 11, no 3-6, p. 1254-1257Article in journal (Refereed)
    Abstract [en]

    Silicon carbide vertical MESFET devices are well suited for high speed and high power electronic devices. In this work we have optimized the geometry of vertical MESFETs for microwave applications, using iterative two-dimensional simulations. Relevant parasitics are included in the simulations to investigate the performance of realistic devices. The state of the art device has f(T)=7 GHz and we show that vertical MESFETs fabricated with traditional technology are totally limited by parasitics. Two different approaches to reduce the parasitics in the vertical MESFET are proposed where f(T) increases significantly.

  • 20.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Optimization of 2H, 4H and 6H-SiC MESFETs for High Frequency Applications2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, p. 75-77Article in journal (Refereed)
    Abstract [en]

    Silicon carbide MESFET devices are well suited for high speed, high power and high temperature electronics due to high saturation velocity, high critical electrical field, good thermal conductivity and large band-gap. Optimization of a high performance device demands a substantial number of numerical simulations, where several different design parameters have to be investigated thoroughly. In this work, we optimize the geometry of lateral MESFETs for maximal unity current-gain frequency (fT) using iterative 2-dimensional simulations. We also present a comparison of performance for individually optimized devices, realized with lithographic resolutions ranging from 0.2 to 2 μm in different SiC polytypes.

  • 21.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    The power of using automatic device optimization, based on iterative device simulation, in design of high-performance devices2004In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 48, no 10-11, p. 1721-1725Article in journal (Refereed)
    Abstract [en]

    An automatic optimization tool for semiconductor devices based on iterative device simulations is developed. The tool is used for optimization of different kinds of semiconductor devices using various performance measures. High performance optimization algorithms, both local and global, are used to achieve an efficient design in shortest possible time. In this paper the effects of different optimization algorithms, performance measures, and number of variables in the optimization are studied. Both the computational efficiency and the devices achieved with different performance measures are studied. We give a demonstration of the usefulness of this method in a comparison between different device topologies, which have been optimized for best performance.

  • 22.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    The power of using automatic device optimization, based on iterative device simulations, in design of high-performance devices2003In: 2003 International Semiconductor Device Research Symposium, ISDRS 2003 - Proceedings, 2003, p. 152-153, article id 1272038Conference paper (Refereed)
    Abstract [en]

    Device design is a time consuming work, where the influence of many design parameters has to be investigated carefully. In advanced devices optimal performance is often achieved taking multiple trade-off into consideration, and manual device optimization is often insufficient. In this paper we present the feasibility of using device optimization for design on electronic devices. An optimization tool is developed, which runs device simulations and automatically changes the design parameters, searching for optimal performance according to a specified performance measure. This has been shown to be a very time and cost efficient way for device design, as the search for optimal performance is fuily automatic working in a systematic way 24 hours 7 days a week. From an industrial point of view this is very important as it can reduce the evaluation and optimization cost for new devices considerably. It is impossible to give a fair comparison between different devices unless these are designed to give optimal performance. We give a demonstration of the usefulness of this method in a comparison between different device topologies which individually have been optimized for best performance.

  • 23.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Hjelm, Mats
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Käckell, P.
    Persson, C.
    The Effect of Different Transport Models in Simulation of High Frequency 4H-SiC and 6H-SiC Vertical MESFETs2001In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 45, no 5, p. 645-653Article in journal (Refereed)
    Abstract [en]

    A full band Monte Carlo (MC) study of the high frequency performance of a 4H-SiC Short channel vertical MESFET is presented. The MC model used is based on data from a full potential band structure calculation using the local density approximation to the density functional theory. The MC results have been compared with simulations using state of the art drift-diffusion and hydrodynamic transport models. Transport parameters such as mobility, saturation velocity and energy relaxation time are extracted from MC simulations

  • 24.
    Bertilsson, Kent
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Petersson, Sture
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulation of anisotropic Breakdown in 4H-SiC Diodes2000In: IEEE Workshop on Computers in Power Electronics: COMPEL 2000, IEEE , 2000, p. 118-120Conference paper (Refereed)
    Abstract [en]

    The breakdown characteristics of two-dimensional 4H-SiC diode structures have been studied using an anisotropic drift-diffusion model. The degree of anisotropy was estimated from recent full band Monte Carlo simulations. Identical diode structures have previously been used in the literature to measure the hole impact ionization coefficients of 4H-SiC. The reported measurements from different research groups show large differences in the impact ionization coefficients. Our numerical simulations show that the differences in these measurements can be explained by the difference in device geometry used by the research teams if one considers an anisotropic impact ionization process. This indicates that it is very important to consider anisotropic impact ionization in design and characterization of 4H-SiC power devices.

  • 25.
    Dubaric, Ervin
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Simulations of Submicron MOSFETs in 2H, 4H and 6H-SiC2002In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. 101, p. 14-17Article in journal (Refereed)
    Abstract [en]

    In this paper, we present numerical studies of the high frequency performance of a submicron MOSFET in 2H-, 4H- and 6H-SiC. The studies are based on simulations where commercial two-dimensional drift-diffusion and hydrodynamic carrier transport models have been used. The results have been compared with those obtained from full band Monte Carlo simulations. The Monte Carlo carrier transport model is based on data from a full potential band structure calculation using the Local Density Approximation to the Density Functional Theory. In 6H-SiC the bulk transport properties in the direction perpendicular to the c-axis, are slightly lower than in 2H- and 4H-SiC. However, in the direction parallel to the c-axis the transport properties are considerably less favourable than in the other two polytypes. The effects of these differences, on surface mobility device performance and carrier energy, have been studied.

  • 26. Harris, Christopher
    et al.
    Basceri, Cem
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Schottky diode with incorporated pn- junctions2007Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A semiconductor device of unpopular type has Schottky-contacts (6) laterally separated by regions in the form of additional layers (7, 7') of semiconductor material on top of a drift layer (3). Said additional layers being doped according to a conductivity type being opposite to the one of the drift layer. At least one (7') of the additional layers has a substantially larger lateral extension and thereby larger area of the interface to the drift layer than adjacent such layers (7) for facilitating the building-up of a sufficient voltage between that layer and the drift layer for injecting minority charge carriers into the drift layer upon surge for surge protection.

  • 27. Harris, Christopher
    et al.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Konstantinov, Andrei
    Method of manufacturing silicon carbide self-aligned epitaxial MOSFET for high powered device applications2010Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A self-aligned, silicon carbide power metal oxide semiconductor field effect transistor includes a trench formed in a first layer, with a base region and then a source region epitaxially regrown within the trench. A window is formed through the source region and into the base region within a middle area of the trench. A source contact is formed within the window in contact with a base and source regions. The gate oxide layer is formed on the source and base regions at a peripheral area of the trench and on a surface of the first layer. A gate electrode is formed on the gate oxide layer above the base region at the peripheral area of the trench, and a drain electrode is formed over a second surface of the first layer.

  • 28. Harris, Christopher
    et al.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Konstantinov, Andrei
    Silicon carbide self-aligned epitaxial MOSFET for high powered device applications2008Patent (Other (popular science, discussion, etc.))
    Abstract [en]

    A self-aligned, silicon carbide power metal oxide semiconductor field effect transistor includes a trench formed in a first layer, with a base region and then a source region epitaxially regrown within the trench. A window is formed through the source region and into the base region within a middle area of the trench. A source contact is formed within the window in contact with a base and source regions. The gate oxide layer is formed on the source and base regions at a peripheral area of the trench and on a surface of the first layer. A gate electrode is formed on the gate oxide layer above the base region at the peripheral area of the trench, and a drain electrode is formed over a second surface of the first layer.

  • 29.
    Hjelm, Mats
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Full Band Monte Carlo Study of Bulk and Surface Transport Properties in 4H and 6H-SiC2001In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 184, no 1-4, p. 194-198Article in journal (Refereed)
    Abstract [en]

    The bulk and surface electron transport properties of the 4H and 6H polytypes of silicon carbide (SiC) are studied using a full band Monte Carlo (MC) program. The model for the electrons is based on data from a full potential band structure calculation using the density functional theory (DFT) in the local density approximation (LDA). Both SiC polytypes have anisotropic transport properties, but the degree and characteristics of the anisotropy is different. In this study, we show how the anisotropy affects the bulk mobility for intermediate angles between the crystal axis and the plane perpendicular to it. Simulations of surface transport properties have also been performed for semiconductor-interface angles up to 15 degrees from the plane perpendicular to the c-axis. We present results for surface mobility and velocity as a function of the electric field component parallel to the interface plane. In the surface mobility simulations, a semi-empirical model for the semiconductor-insulator interface has been used, where it is assumed that the electrons are reflected in two perpendicular planes.

  • 30. Intarasiri, S.
    et al.
    Hallén, A.
    Lu, J.
    Jensen, J.
    Yu, L.D.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Wolborski, M.
    Singkarat, S.
    Possnert, G.
    Crystalline quality of 3C-SiC formed by high-fluence C+-implanted Si2007In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 253, no 11, p. 4836-4842Article in journal (Refereed)
    Abstract [en]

    Carbon ions at 40 keV were implanted into (100) high-purity p-type silicon wafers at 400 oC to a fluence of 6.5×1017 ions/cm2. Subsequent thermal annealing of the implanted samples was performed in a diffusion furnace at atmospheric pressure with inert nitrogen ambient at 1100 oC. Time-of-flight energy elastic recoil detection analysis (ToF-E ERDA) was used to investigate depth distributions of the implanted ions. Infrared transmittance (IR) and Raman scattering measurements were used to characterize the formation of SiC in the implanted Si substrate. X-ray diffraction analysis (XRD) was used to characterize the crystalline quality in the surface layer of the sample. The formation of 3C-SiC and its crystalline structure obtained from the above mentioned techniques was finally confirmed by transmission electron microscopy (TEM). The 1 results show that 3C-SiC is directly formed during implantation, and that the subsequent high-temperature annealing enhances the quality of the poly-crystalline SiC.

  • 31.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    A 45W LLC resonant Converter in MHz Frequency Region for Laptop Adapter Application using GaN HEMTs2013In: PCIM Europe Conference Proceedings, Berlin: Mesago PCIM GmbH , 2013, p. 1029-1035Conference paper (Refereed)
    Abstract [en]

    The authors report the feasibility of low profile, high power density and energy efficient isolated DC/DC converter in 3 – 4 MHz frequency region corresponding to low line input voltage of 90 – 110 Vac suitable for 45W laptop adapter application. Using novel hybrid power transformer, GaN HEMTs, the simulation and experimental results of LLC resonant converter for DC input voltage range of 127 – 155Vdc with a regulated output voltage of 22Vdc was presented. The maximum energy efficiency of converter at the full load condition is reported to be approximately 91% whereas light load efficiency was improved using pulse skip modulation technique.

  • 32.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A ZVS Flyback DC-DC Converter using Multilayered Coreless Printed Circuit Board (PCB) Step Down Power Transformer2010In: World Academy of Science, Engineering and technology, Paris: World Academy of Science,Engineering and Technology , 2010, p. 148-155Conference paper (Refereed)
    Abstract [en]

    The experimental and theoretical results of a ZVS (Zero Voltage Switching) isolated flyback DC-DC converter using multilayered coreless PCB step down 2:1 transformer are presented.The performance characteristics of the transformer are shown which are useful for the parameters extraction. The measured energy efficiency of the transformer is found to be more than 94% with the sinusoidal input voltage xcitation. The designed flyback converter has been tested successfully upto the output power level of 10W,with a switching frequency in the range of 2.7MHz-4.3MHz. The input voltage of the converter is varied from 25V-40V DC.Frequency modulation technique is employed by maintaining constant off time to regulate the output voltage of the converter. The energy efficiency of the isolated flyback Converter circuit under ZVS condition in the MHz frequency region is found to be approximately in the range of 72-84%. This paper gives the comparative results in terms of the energy efficiency of the hard switched and soft switched flyback Converter in the MHz frequency region.

  • 33.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Comparative Results of GaN and Si MOSFET in a ZVS Flyback Converter using Multilayered Coreless Printed Circuit Board Step-Down Transformer2010In: Proceedings of 2010 3rd International Conference on Power Electronics and Intelligent Transportation System, Shenzhen: IEEE conference proceedings, 2010, p. 318-321Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to compare two different material MOSFETs performance namely GaN (Gallium Nitride) and conventional Si (Silicon) in Zero Voltage Switching (ZVS) flyback converter circuit with Coreless PCB step down transformers. The switching frequency of the regulated converter is in the range of 3.2-5MHz. In high frequency circuits, proper selection of MOSFETs is required in order to have low gate drive power consumption so that high energy efficiency of the converter can be achieved. Even though Si MOSFET has already known for its popularity in low to medium power converters and high frequency applications, GaN MOSFET device could produce better results.  This can be done by reducing the total switching loss, conduction loss because of its low Rds-on and gate drive power consumption of the converter as a result of low gate charge, Qg. From the experimental results, it can be observed that GaN MOSFET can produce higher energy savings including gate drive power by gaining approximately 8%-10% efficiency compared to its counterpart, Si MOSFET in a regulated 45-15V isolated DC-DC converter.

  • 34.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Design and Analysis of 45W Multi Resonant Half Bridge Converter in MHz Frequency Region using GaN HEMTsManuscript (preprint) (Other academic)
  • 35.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    High Speed Cascode Flyback Converter Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2011In: Proceedings of 8th International Conference on Power Electronics-ECCE Asia, IEEE conference proceedings, 2011, p. 1856-1862Conference paper (Refereed)
    Abstract [en]

    In this paper, design and analysis of the high speed isolated cascode flyback converter using multilayered coreless PCB step down power transformer is presented. The converter is tested for the input voltage variation of 60-120V with a nominal DC input voltage of 90V. The designed converter was simulated and tested successfully up to the output power level of 30W within the switching frequency range of 2.6-3.7MHz. The cascode flyback converter is compared with the single switch flyback converter in terms of operating frequency, gate drive power consumption, conduction losses and stresses on MOSFETs. The maximum energy efficiency of the cascode converter is approximately 81% with a significant improvement of about 3-4% compared to single switch flyback converter. The gate drive power consumption which is more dominant compared to conduction losses of the cascode converter using GaN MOSFET is found to be negligible compared to single switch flyback converter.

  • 36.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    High Speed (MHz) Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2013In: IEEE transactions on power electronics, ISSN 0885-8993, E-ISSN 1941-0107, Vol. 28, no 3, p. 1253-1264Article in journal (Refereed)
    Abstract [en]

    In this paper, design and analysis of an isolated low profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) power transformer was presented. For obtaining the stringent height switch mode power supplies (SMPS), a multilayered coreless PCB power transformer of approximately 4:1 turn’s ratio was designed in a four layered PCB laminate which can be operated in MHz switching frequency. The outermost radius of the transformer is 10mm with achieved power density of 16W/cm2. The energy efficiency of the power transformer is found to be in the range of 87-96% with the output power level of 0.1-50W operated at a frequency of 2.6MHz. This designed step-down transformer was utilized in SRC and evaluated. The supply voltage of converter is varied from 60-120V DC with a nominal input voltage of 90V and has been tested up to the power level of 34.5W. The energy efficiency of converter under Zero Voltage Switching (ZVS) condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75MHz. By using constant off-time frequency modulation technique, the converter was regulated to 20V DC for different load conditions. Thermal profile with converter loss at nominal voltage is presented.

  • 37.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    High Speed Series Resonant Converter (SRC) Using Multilayered Coreless Printed Circuit Board (PCB) Step-Down Power Transformer2011In: Proceedings of 33rd International Telecommunications Energy Conference (INTELEC 2011), Amsterdam: IEEE conference proceedings, 2011, p. Art. no. 6099785-Conference paper (Refereed)
    Abstract [en]

    In this paper, simulation and experimental results of an isolated low profile, series resonant converter (SRC) using multilayered coreless printed circuit board (PCB) step-down power transformer are described. The designed converter prototype was operated in MHz switching frequency region. For obtaining the stringent height switch mode power supplies (SMPS), a new multilayered coreless PCB power transformer of approximately 4:1 turn’s ratio was designed in a four layered PCB laminate. The outermost radius of the step-down power transformer is 10mm with achieved power density of 16W/cm2. The energy efficiency of the power transformer is found to be in the range of approximately 87-96% with the output power level of 0.1-50W in the frequency range of 1.5-4MHz. This designed step-down power transformer was utilized in SRC and evaluated.The supply voltage of converter is varied from 60-120V DC with a nominal input voltage of 90V. The SRC has been tested successfully upto the output power level of 34.5W. The energy efficiency from the converter prototype under Zero Voltage Switching (ZVS) condition is found to be in the range of 80-86.5% with the switching frequency range of 2.4-2.75MHz. By using constant off-time frequency modulation technique the output voltage of converter is regulated to 20V DC for different load conditions. Thermal profile and the loss estimation of SRC at nominal voltage are also presented.

  • 38.
    Kotte, Hari Babu
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Haller, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    A ZVS Half Bridge DC-DC Converter in MHz Frequency Region using Novel Hybrid Power Transformer2012In: Proceedings of International Exhibition and Conference for Power Electronics, Intelligent Motion, Power Quality (PCIM) 2012, 8-10 May 2012, Nuremberg, Germany., Berlin: Curran Associates, Inc., 2012, p. 399-406Conference paper (Refereed)
    Abstract [en]

    The significant problems in increasing the switching frequency of isolated converters to achieve low cost and high power density are increased magnetic and switching losses. This paper presents solution with the investigation of newly designed high frequency, low profile, hybrid power transformer together with commercially available GaN MOSFETs. For achieving stringent power converters, a center tapped 4:1:1 half bridge transformer was designed in a multilayered PCB laminate with a total height of transformer as 4.2mm. The maximum obtained energy efficiency of transformer is 98% in the frequency region of 1 – 5MHz. The designed transformer possesses better high frequency characteristics in the frequency range of 3 - 5MHz with tested power density of 47W/cm3 at an operating frequency of 3MHz. This transformer has been utilized in the multi resonant zero voltage switching (ZVS) half bridge converter with synchronous rectification using GaN MOSFETs and then evaluated. The maximum achieved efficiency of multi resonant ZVS half bridge converter with this transformer is 92% in 3 – 4.5 MHz switching frequency range with characterized output power of 40W. This is to the author’s knowledge, the best energy efficiency ever reported for an isolated DC-DC converter in this frequency range and power levels. At a specified input voltage, the converter has been regulated to 15V within 1% for both line and wide load variations. This work provides considerable step for the development of next generation ultra flat low profile isolated DC-DC/AC-DC converters operating in MHz frequency region.

  • 39.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Haller, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    High Frequency Half-Bridge Converter using Multilayered Coreless PrintedCircuit Board Step-Down Power Transformer2011In: 8th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2011-ECCE Asia, IEEE conference proceedings, 2011, p. 1177-1181Conference paper (Refereed)
    Abstract [en]

    This paper introduces high frequencyhalf bridgeDC-DC converter, using multilayered coreless Printed Circuit Board (PCB) step down power transformer. The converter is simulated and then implemented on a PCB. Complementary Pulse Width Modulated (PWM) signals are generated to turn on high and low side Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) alternately by a micro-controller. The isolated gate drive signals are provided to the high side MOSFET by using high frequency coreless PCB isolation transformer. We tested the converter for switching frequency range of 2 to 3 MHz, and for maximum input voltage up-to 170 V. The maximum output power achieved is 40 W and the maximum energy efficiency is approximately 82 %. © 2011 IEEE.

  • 40.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Analysis of radiated EMI for power converters switching in MHz frequency range2013In: Proceedings - 2013 9th IEEE International Symposium on Diagnostics for Electric Machines, Power Electronics and Drives, SDEMPED 2013, IEEE conference proceedings, 2013, p. 428-432Conference paper (Refereed)
    Abstract [en]

    The higher switching frequency in combination with di/dt loops and dv/dt nodes in the power stages of high frequency power converters generates higher order harmonics which cause Electro Magnetic Interference (EMI). It is commonly perceived that high frequency converters are more vulnerable to radiated EMI, thus, it is very important to analyze the radiated emission of these converters. According to the author’s knowledge, the analysis of the radiated emission of power converters switching in the MHz frequency region has not been presented until now. Therefore, in this paper, the measurements, and analysis of the near field radiated emissions of these emerging power converters is presented. These measurements are beneficial in the early design stage of power converters. Both E-field and H-field and captured and analyzed for a half bridge converter switching at 3 MHz and at the output power level of 25 W. The effects of the magnetic and electric field emissions with the addition of a Y-capacitor and secondary side common mode choke are analyzed.

  • 41.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Alam, Farhan
    SEPS Technologies AB, Holmgatan 10, 851 70 Sundsvall, Sweden.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    EMI Suppression in High Frequency Half Bridge Converter2013In: Elektronika ir Elektrotechnika, ISSN 1392-1215, Vol. 19, no 9, p. 75-80Article in journal (Refereed)
    Abstract [en]

    Electromagnetic effects influence the design of power converters switching in MHz frequency region. In these converters, the high switching frequency in combination with sudden changes in current and voltage levels generate higher order harmonics which causes Electro Magnetic Interference (EMI). To study the effects of increased switching frequency on conducted EMI, the harmonics amplitudes are analyzed by increasing the switching frequency of a two wire input half bridge power converter from 1.32 MHz to 3 MHz. In order to suppress the Common Mode (CM) conducted EMI, different possibilities of connecting the Y- capacitor in a two wire universal input half bridge converter are discussed and the conducted EMI is measured and analyzed by connecting the Y- capacitor at different points. The line filters are designed, characterized and implemented in order to suppress conducted EMI. The effects of increased switching frequency on the line filter design are studied by analysing the EMI spectrum of both the converters. The analysis of results indicates that the filter size is reduced by increasing the switching frequency of the power converter. 

  • 42.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    EMI filter design for high frequency power converters2012In: 2012 11th International Conference on Environment and Electrical Engineering, EEEIC 2012: Conference Proceedings, IEEE conference proceedings, 2012, p. 586-589Conference paper (Refereed)
    Abstract [en]

    With the emerging power semiconductor devices in GaN and SiC technology and the development of high frequency multilayered PCB power transformers, power efficient DC-DC converters are designed in megahertz switching frequency range. The increased switching frequency in combination with sudden changes in current “di/dt” or voltage “dv/dt” levels generate higher order harmonics, which cause Electro Magnetic Interference (EMI). One of the major challenges, to design the power stage of these converters, is to minimize the EMI because it affects their Electro Magnetic Compatibility (EMC). There is a spread belief that the EMI becomes much worse in a MHz switching converter compared to the current ones operating below 150 kHz. This paper investigates the consequences on implementation of a line filter for suppressing conducted EMI in high frequency power converters. The results are based on electronic simulations, comparing EMI and filter design, for a 200 kHz and 2 MHz buck converter under similar conditions. By analyzing the noise frequency spectrum of both the converters it is observed that the size of filter components, such as capacitors and common mode chokes is greatly reduced in case of 2MHz Buck converter. The results show that the size reduction that can be accomplished by increasing the switching frequency to MHz range can be improved further by a smaller implementation of the line filter as well.

  • 43.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Design and implementation of EMI filter for high frequency (MHz) power converters2012In: IEEE International Symposium on Electromagnetic Compatibility, IEEE conference proceedings, 2012, p. Art. no. 6396738-Conference paper (Refereed)
    Abstract [en]

    The fabrication of emerging power semiconductor devices and high frequency PCB power transformers has made it possible to design the power converters in MHz switching frequency range. However, the higher switching frequency, di/dt loops and dv/dt nodes in power stages of these converters generate higher order harmonics which causes Electro Magnetic Interference (EMI). It is commonly believed that the EMI has worst affect in the converters switching in MHz frequency range than the converters operating below 150 kHz. Thus, it is important research direction to investigate the consequences of implementing a line filter to suppress the conducted EMI in high frequency power converters. In this paper, the measurements, and analysis of the conducted EMI in emerging power converters, switching in MHz frequency range, and the design of the filter for its suppression is presented. The design of LISN and its PCB implementation for EMI measurements is presented. The measurement of conducted EMI of a half bridge DC-DC converter switching at          3.45 MHz and the analysis of the frequency spectrum is discussed. The design, PCB implementation and characterization of the EMI filter and the measurement of the suppressed conducted noise by applying the filter are also discussed.

  • 44.
    Majid, Abdul
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Saleem, Jawad
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Kotte, Hari Babu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Ambatipudi, Radhika
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Haller, Stefan
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Analysis of feedback in converter using coreless printed circuit board transformer2013In: Electrical Machines and Power Electronics and 2011 Electromotion Joint Conference (ACEMP), 2011 International Aegean Conference on, IEEE conference proceedings, 2013, p. 601-604Conference paper (Refereed)
    Abstract [en]

    Power supply is an inevitable component for all electronic instruments as a constant DC source. Almost all power supplies use feedback loop to achieve constant DC output voltage. In a feedback loop, the galvanic isolation is required between input and output. It can be achieved either by implementation of opto-coupler feedback on the secondary side or magnetic feedback. In this paper both opto-coupler and auxiliary feed-back techniques are implemented and analyzed in a high frequency half bridge converter using coreless Printed Circuit Board (PCB) power transformer. The implementation of opto-coupler feedback is temperature sensitive and has relatively high cost. The auxiliary winding of transformer can also be used to provide feedback signals as alternate to opto-coupler. Auxiliary feedback implementation is cheaper, temperature stable and insensitive to temperature variations. In this paper, the feasibility of feedback using auxiliary winding of coreless PCB power transformer is investigated. It is observed that this technique can be used as an alternative to opto-coupler feedback.

  • 45.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Manufacturing and characterization of a modified four-quadrant position sensitive detector for out-door applications2004In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 531, no 1-2, p. 134-139Article in journal (Refereed)
    Abstract [en]

    Position sensing detectors (PSDs) are useful in many applications such as vibration, displacement and triangulation measurements. In this paper we have constructed a novel structure, which has higher inter-electrode resistance than a lateral effect PSD and is more robust to atmospheric turbulence than a conventional four-quadrant PSD (Nuclear Instruments and Methods in Physics Research A 466 (2001) 183). The detector structure is useful for applications with detector windows less than 0.5 x 0.5 mm(2), but the nonlinearity is the main concern for a detector of that size. Without any corrections for non-linearity the standard deviation of the error is 9 mum (2.2%). Using a simple analytical expression and a 2-d correction-function stored in a look-up table the positioning error is reduced to 6 (1.5%) and 2 (0.5%) mum, respectively.

  • 46.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martin, Hans
    SenseAir.
    Thermal simulation and design optimization of a thermopile infrared detector with SU-8 membrane2009In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 5, p. 055016-Article in journal (Refereed)
    Abstract [en]

    Simulation and optimization tools are commonly used in the design phase of advanced electronics devices. In this work, we present a thermal simulation and design optimization tool for infrared thermopile detectors based on a closed membrane structure. The tool can be used to simulate and optimize thermopile detectors with an arbitrary number of design parameters. The optimization utilizes the Nelder–Mead and the adaptive simulated annealing optimization algorithms to maximize the system performance. A thermopile detector with an SU-8-based closed membrane and metal–metal thermocouples has been simulated and optimized. Based on the results generated by the tool, an optimized detector has been fabricated and characterized. The results from the measurements presented are in good agreement with the simulation results.

  • 47.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martin, Hans
    SenseAir AB.
    Design of a Micromachined Thermopile Infrared Sensor with a Self-Supported SiO2/SU-8 Membrane2008In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 8, no 12, p. 2044-2052Article in journal (Refereed)
    Abstract [en]

    In the infrared region of the spectrum thermoelectric detectors such as the thermopile, are extensively used. These detectors rely on the well-known Seebeck effect, in which there is a direct conversion of thermoelectric differentials into electrical voltage. The temperature difference over thermocouple junctions is in general, created by forming a thin membrane connected to the silicon bulk. In many existing thermopiles, materials such as Si and Si3N4 have been used as membrane. These materials suffer from relatively high thermal conductivity, which lowers the membrane temperature and reduces the sensitivity of the detector. A material such as SU-8 2002 has a much lower thermal conductivity and is applied using standard photolithographic processing steps. This work presents thermal simulations regarding the use of SU-8 2002 as a thermal insulating membrane as compared to Si and Si3N4. The simulation results presented show that the temperature increase in a 5 µm SiO2/SU-8 membrane is about 9% higher than in a 1 µm Si3N4 membrane, despite the membrane thickness being increased by a factor of 5. A thermopile consisting of 196 serially interconnected Ti/Ni thermocouples positioned on a 5 µm SiO2/SU-8 2002 membrane has been fabricated. The sensitivity of the fabricated device has been evaluated in the infrared region, using a 1.56 µm IR laser and a xenon arc lamp together with a monochromator. The measurement results show a sensitivity of approximately 5 V/W over the wavelength range between 900 - 2200 nm. Measurements performed in a vacuum chamber show that the sensitivity of the detector could be increased by more than a factor of 3 by mounting the detector in a vacuum sealed capsule.

  • 48.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martin, Hans
    Development of an infrared thermopile detector with a thin self-supporting SU-8 membrane2007In: Proceedings of IEEE Sensors, New York: IEEE conference proceedings, 2007, p. 836-839Conference paper (Refereed)
    Abstract [en]

    In this paper we present the development and characterization of thermopile detector on a 4 mum thin self-supporting membrane made of the epoxy based photoresist SU-8. The membrane is realized using silicon bulk micromachining techniques. In many existing thermopile detectors, a temperature difference over the thermocouple junctions is achieved by connecting a thin membrane of either Si or Si3N4 to a silicon bulk. These materials suffer from relatively high thermal conductivity, which lowers the sensitivity of the detector. A material such as SU-8 has much lower thermal conductivity and is applied using standard photolithographic processing steps. Simulation results are presented which verifies SU-8 as a better choice than Si and Si3N4 when used as thermal insulating membrane in a thermopile detector. A thermopile consisting of 196 series coupled Ti/Ni thermocouples has been fabricated. Results from measurements are presented, showing a sensitivity of 5.6 V/W and a noise equivalent power (NEP) of 9.9 nW/radicHz.

  • 49.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martin, Hans
    SenseAir.
    Fabrication and characterization of a design optimized SU-8 thermopile with enhanced sensitivity2009In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, no 11, p. 115202-Article in journal (Refereed)
    Abstract [en]

    In the infrared wavelength region, thermopiles are an important type of detectors. A major advantage of thermopiles is their non-cooling requirement. Depending on the applied absorption layer, their responsivity is often rather flat within a large wavelength region. This work presents the fabrication and characterization of a sensitivity and design optimized thermopile detector with a 4 µm self-supported SiO2/SU-8 membrane. The structure consists of 240 series interconnected thermocouple junctions obtained by a metal evaporation and lift-off. Two metal combinations have been evaluated, namely, nickel/titanium and aluminium/bismuth. Series resistances of 76 k and 283 k were measured for the Ni/Ti thermopile and the Al/Bi thermopile respectively. For the Al/Bi thermopile a responsivity of 60 V/W was achieved using a 1.56 µm fibre coupled diode laser with a power of 3.5 mW. Using a white light source with a radiation flux of 0.45 W/mm2 a voltage response of 68 V mm2/W was measured for the Al/Bi thermopile. The time constant of the characterized detectors was calculated as being 70 ms, using the pulsed IR laser.

  • 50.
    Mattsson, Claes
    et al.
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Thungström, Göran
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Bertilsson, Kent
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Nilsson, Hans-Erik
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Technology and Media.
    Martin, Hans
    Fabrication and evaluation of a thermal sensor formed on a thin photosensitive epoxy membrane with low thermal conductivity2008In: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, Institute of Physics (IOP), 2008, p. 082048-Conference paper (Refereed)
    Abstract [en]

    This article present the fabrication and development of a thin metal film bolometer IR detector connected in a Wheatstone bridge configuration. The bolometer is constructed on a 4 μm thin self-supported SU-8 2002 membrane. A polymer material such as SU-8 has low thermal conductivity and is applied using standard photolithographic processing step, and this could increase detector sensitivity and lower the production cost. Thermal simulation results are presented, which verifies SU-8 as a better choice of materials compared to common membrane materials such as Si and Silicon nitride. Measurements on the fabricated nickel resistance bolometer on SU-8 2002 membrane show a sensitivity of 9.3 V/W when radiated by an IR laser with a wavelength of 1.56 μm.

12 1 - 50 of 63
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