| 1. |
- Kotte, Hari Babu, 1979-, et al.
(författare)
-
A ZVS Half Bridge DC-DC Converter in MHz Frequency Region using Novel Hybrid Power Transformer
- 2012
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Ingår i: 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.. - 9783800734313 ; , s. 399-406
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 2. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
Comparison of Two Layered and Three Layered Coreless Printed Circuit Board Step-Down Power Transformers
- 2011
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Ingår i: 2011 INTERNATIONAL CONFERENCE ON INSTRUMENTATION, MEASUREMENT, CIRCUITS AND SYSTEMS (ICIMCS 2011), VOL 2: FUTURE COMMUNICATION AND NETWORKING. - Shenzhen : IEEE conference proceedings. - 9780791859902 ; , s. 59-62
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Konferensbidrag (refereegranskat)abstract
- 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
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| 3. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
Coreless Printed Circuit Board (PCB) StepdownTransformers for DC-DC ConverterApplications
- 2010
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Ingår i: PROCEEDINGS OF WORLD ACADEMY OF SCIENCE, ENGINEERING AND TECHNOLOGY, ISSUE 70, OCTOBER 2010, ISSN:1307-6892. - France : World Academy of Science Engineering and Technology. ; , s. 380-389
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 4. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
Effect of Air Gap on the Performance of Hybrid Planar Power Transformer in High Frequency (MHz) Switch Mode Power Supplies (SMPS)
- 2012
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Ingår i: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012.
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Konferensbidrag (refereegranskat)abstract
- 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
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| 5. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
Effect of Dielectric Material on the Performance of Planar Power Transformers in MHz Frequency Region
- 2012
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Ingår i: Proceedings of INDUCTICA 2012, Coil Winding, Insulation and Electrical Manufacturing International Conference and Exhibition (CWIEME), Berlin, Germany 26-28 June 2012.
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 6. |
- Ambatipudi, Radhika, 1982-
(författare)
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High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend inrelation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the convertercircuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses whichare functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers.The first part of the thesis concentrates on the investigation of high power density and highly energy efficient coreless printed circuit board (PCB) step-down transformers useful for stringent height DC-DC converter applications, where the core losses are being completely eliminated. These transformers also maintain the advantages offered by existing core based transformers such as, high coupling coefficient, sufficient input impedance, high energy efficiency and wide frequencyband width with the assistance of a resonant technique. In this regard, several coreless PCB step down transformers of different turn’s ratio for power transfer applications have been designed and evaluated. The designed multilayered coreless PCB transformers for telecom and PoE applications of 8,15 and 30W show that the volume reduction of approximately 40 - 90% is possible when compared to its existing core based counterparts while maintaining the energy efficiency of the transformers in the range of 90 - 97%. The estimation of EMI emissions from the designed transformers for the given power transfer application proves that the amount of radiated EMI from a multilayered transformer is lessthan that of the two layered transformer because of the decreased radius for thesame amount of inductance.The design guidelines for the multilayered coreless PCB step-down transformer for the given power transfer application has been proposed. The designed transformer of 10mm radius has been characterized up to the power level of 50Wand possesses a record power density of 107W/cm3 with a peak energy efficiency of 96%. In addition to this, the design guidelines of the signal transformer fordriving the high side MOSFET in double ended converter topologies have been proposed. The measured power consumption of the high side gate drive circuitvitogether with the designed signal transformer is 0.37W. Both these signal andpower transformers have been successfully implemented in a resonant converter topology in the switching frequency range of 2.4 – 2.75MHz for the maximum load power of 34.5W resulting in the peak energy efficiency of converter as 86.5%.This thesis also investigates the indirect effect of the dielectric laminate on the magnetic field intensity and current density distribution in the planar power transformers with the assistance of finite element analysis (FEA). The significanceof the high frequency dielectric laminate compared to FR-4 laminate in terms of energy efficiency of planar power transformers in MHz frequency region is also explored.The investigations were also conducted on different winding strategies such as conventional solid winding and the parallel winding strategies, which play an important role in the design and development of a high frequency transformer and suggested a better choice in the case of transformers operating in the MHz frequency region.In the second part of the thesis, a novel planar power transformer with hybrid core structure has been designed and evaluated in the MHz frequency region. The design guidelines of the energy efficient high frequency planar power transformerfor the given power transfer application have been proposed. The designed corebased planar transformer has been characterized up to the power level of 50W and possess a power density of 47W/cm3 with maximum energy efficiency of 97%. This transformer has been evaluated successfully in the resonant converter topology within the switching frequency range of 3 – 4.5MHz. The peak energy efficiency ofthe converter is reported to be 92% and the converter has been tested for the maximum power level of 45W, which is suitable for consumer applications such as laptop adapters. In addition to this, a record power density transformer has been designed with a custom made pot core and has been characterized in thefrequency range of 1 - 10MHz. The power density of this custom core transformer operating at 6.78MHz frequency is 67W/cm3 and with the peak energy efficiency of 98%.In conclusion, the research in this dissertation proposed a solution for obtaining high power density converters by designing the highly integrated, high frequency(1 - 10MHz) coreless and core based planar magnetics with energy efficiencies inthe range of 92 - 97%. This solution together with the latest semiconductor GaN/SiC switching devices provides an excellent choice to meet the requirements of the next generation ultra flat low profile switch mode power supplies (SMPS).
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| 7. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
High Performance Planar Power Transformer with High Power Density in MHz Frequency Region for Next Generation Switch Mode Power Supplies
- 2013
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Ingår i: 2013 Twenty-Eighth Annual IEEE Applied Power Electronics Conference And Exposition (APEC 2013). - : IEEE conference proceedings. - 9781467343558 ; , s. 2139-2143
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Konferensbidrag (refereegranskat)abstract
- 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
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| 8. |
- Ambatipudi, Radhika, 1982-
(författare)
-
Multilayered Coreless Printed Circuit Board (PCB) Step-down Transformers for High Frequency Switch Mode Power Supplies (SMPS)
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Power Supply Unit (PSU) plays a vital role in almost all electronic equipment. The continuous efforts applied to the improvement of semiconductor devices such as MOSFETS, diodes, controllers and MOSFET drivers have led to the increased switching speeds of power supplies. By increasing the switching frequency of the converter, the size of passive elements such as inductors, transformers and capacitors can be reduced. Hence, the high frequency transformer has become the backbone in isolated AC/DC and DC/DC converters. The main features of transformers are to provide isolation for safety purpose, multiple outputs such as in telecom applications, to build step down/step up converters and so on. The core based transformers, when operated at higher frequencies, do have limitations such as core losses which are proportional to the operating frequency. Even though the core materials are available in a few MHz frequency regions, because of the copper losses in the windings of the transformers those which are commercially available were limited from a few hundred kHz to 1MHz. The skin and proximity effects because of induced eddy currents act as major drawbacks while operating these transformers at higher frequencies. Therefore, it is necessary to mitigate these core losses, skin and proximity effects while operating the transformers at very high frequencies. This can be achieved by eliminating the magnetic cores of transformers and by introducing a proper winding structure.A new multi-layered coreless printed circuit board (PCB) step down transformer for power transfer applications has been designed and this maintains the advantages offered by existing core based transformers such as, high voltage gain, high coupling coefficient, sufficient input impedance and high energy efficiency with the assistance of a resonant technique. In addition, different winding structures have been studied and analysed for higher step down ratios in order to reduce copper losses in the windings and to achieve a higher coupling coefficient. The advantage of increasing the layer for the given power transfer application in terms of the coupling coefficient, resistance and energy efficiency has been reported. The maximum energy efficiency of the designed three layered transformers was found to be within the range of 90%-97% for power transfer applications operated in a few MHz frequency regions. The designed multi-layered coreless PCB transformers for given power applications of 8, 15 and 30W show that the volume reduction of approximately 40-90% is possible when compared to its existing core based counterparts. The estimation of EMI emissions from the designed transformers proves that the amount of radiated EMI from a three layered transformer is less than that of the two layered transformer because of the decreased radius for the same amount of inductance.Multi-layered coreless PCB gate drive transformers were designed for signal transfer applications and have successfully driven the double ended topologies such as the half bridge, the two switch flyback converter and resonant converters with low gate drive power consumption of about half a watt. The performance characteristics of these transformers have also been evaluated using the high frequency magnetic material made up of NiZn and operated in the 2-4MHz frequency region.These multi-layered coreless PCB power and signal transformers together with the latest semiconductor switching devices such as SiC and GaN MOSFETs and the SiC schottky diode are an excellent choice for the next generation compact SMPS.
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| 9. |
- Ambatipudi, Radhika, 1982-, et al.
(författare)
-
Radiated Emissions of Multilayered Coreless Printed Circuit Board Step-Down Power Transformers in Switch Mode Power Supplies
- 2011
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Ingår i: 8th International Conference on Power Electronics - ECCE Asia: "Green World with Power Electronics", ICPE 2011-ECCE Asia 2011. - : IEEE conference proceedings. - 9781612849560 - 9781612849584 ; , s. 960-965
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Kotte, Hari Babu, 1979-, et al.
(författare)
-
A 45W LLC resonant Converter in MHz Frequency Region for Laptop Adapter Application using GaN HEMTs
- 2013
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Ingår i: PCIM Europe Conference Proceedings. - Berlin : Mesago PCIM GmbH. - 9783800735051 ; , s. 1029-1035
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Konferensbidrag (refereegranskat)abstract
- 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.
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