Coreless printed circuit board (PCB) transformers for powerMOSFET/IGBT gate drive circuits

Gate drive circuits for modern power electronic switches, such as MOSFET and insulated gate bipolar transistor (IGBT), often require electrical isolation. This paper describes the modeling and experimental results of some coreless printed circuit board (PCB)-based transformers that can be used for MOSFET and IGBT devices at high-frequency (500 kHz to 2 MHz) operation. PCB-based transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits. With no core loss, coreless transformers are found to have favorable characteristics at high-frequency operations. This project demonstrates an important point that the size of the magnetic core can approach zero and become zero when the frequency is sufficiently high     

Some electromagnetic aspects of coreless PCB transformers

In this paper, some EMI aspects of using coreless PCB transformers are addressed. Based on the antennas theory, the radiated power of a coreless PCB transformer is estimated and found to be negligible. The electromagnetic field plot of a power electronic circuit using a gate drive circuit isolated by a coreless PCB transformer has been recorded. The major radiated EMI source in the frequency range of 30 MHz to 300 MHz is found to be the copper tracks of the power circuit, where switching transients occur, rather than the coreless PCB transformer. Coreless PCB transformers essentially operate at relatively low frequency (8 MHz in this case) by near-field magnetic coupling. Experimental results have confirmed that the application of coreless PCB transformer in gate drive circuit will not impose any serious EMI problem on the power electronic circuit     

Coreless printed circuit board (PCB) transformers with multiplesecondary windings for complementary gate drive circuits

This paper describes the modeling and implementation of a coreless printed circuit board (PCB)-based transformer with “multiple” secondary outputs. This new PCB transformer has been successfully applied in complementary gate drive circuits in a novel low-profile power converter with high-power density and a converter bridge. The PCB-based transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits. The use of the multiple secondary outputs can in principle simplify the complementary gate drive circuits that are often required in many power electronics applications     

A low-profile low-power converter with coreless PCB isolationtransformer

Very small manually wound transformers for sub-watt DC-DC converters are notorious for their relatively high cost and low reliability. In this paper, an isolated low-profile low-power 8 MHz soft-switching power converter using a coreless printed circuit board (PCB) transformer is described. Coreless PCB transformers eliminate several problems of their core-based counterparts in low-power applications. The diameter of the coreless PCB transformer is merely 0.46 cm. The converter's power output is about 0.5 W with a typical transformer efficiency of 63%. The high-frequency capability, high reliability and the low-profile structure make coreless PCB transformers a viable and attractive option for reliable mega-hertz switching converters and micro-circuits     

Coreless planar printed-circuit-board (PCB) transformers-afundamental concept for signal and energy transfer

Magnetic cores have been used in transformers for over a century. In this paper, the authors present a fundamental concept of using “coreless” printed-circuit-board (PCB) transformers. With the aid of a high-frequency equivalent circuit, the use and basic characteristics of coreless PCB transformers are described. Optimal operating conditions for minimum input power requirement and maximum efficiency operations are identified. Coreless PCB transformers have the advantages of low costs, very high power density, no limitation due to magnetic cores, no magnetic loss and ease of manufacturing. They have the potential to be developed in microcircuits. A printed planar PCB transformer with a diameter of about 1.0 cm and power capability of 19 W has been successfully tested. The power density of the PCB transformer demonstrated in this paper is 24 W/cm². The maximum efficiency can be greater than 90%. The analysis has been confirmed with experiments. Coreless printed transformers have great potential in applications in which stringent height and space requirements have to be met     

Coreless printed circuit board (PCB) transformers with high power density and high efficiency

The authors report the use of a coreless printed circuit board transformer for power conversion with very high power density and efficiency. A coreless PCB transformer with an outermost radius of /spl sim/1 cm and 19 turns for both the primary and secondary windings can transfer 19 W at an efficiency of 90%, resulting in a record power density of 24 W/cm/sup 2/. The power density and energy efficiency of a coreless PCB transformer are higher than those of core-based microtransformers. Coreless transformers are simpler in structure, easier to implement in silicon wafer and cheaper than core-based planar transformers.     

Analysis and design of electronic transformers for electric powerdistribution system

A transformer performs many functions such as voltage transformation, isolation and noise decoupling, and it is an indispensable component in electric power distribution systems. However, at low frequencies (60/50 Hz), it is a bulky and expensive component. In this paper, the concept of electronic transformers is further extended and explored for its suitability in power distribution systems. It should be noted that from the input/output behavior, the electronic transformer and the conventional transformer are identical. Possible topologies employing static converters connected on the primary and secondary sides are explored to realize high-frequency operation of the magnetic core. To assist the commutation process, a four-step switching has been developed which does not require the use of snubbers. Reduced size, losses, higher efficiency, and better voltage regulation are some of the advantages of this approach. A 10 kVA design example along with experiment results are discussed. It is shown that a transformer designed with a conventional grain-oriented silicon-steel core can process three times the power at 1 kHz operating frequency as compared to 60 Hz. The proposed method is scalable in voltage/current with the currently available insulated gate bipolar transistor (IGBT) devices connected in series without special snubbers     

片上变压器隔离门极驱动器的优点

在许多应用中,电气隔离是一项重要的要求,特别是在涉及高功率电路和低功率电路的地方,以及高边和低边接地需要分开的地方。尽管隔离技术已经存在多年了,但已演变以满足新应用的需求,如可再生能源的逆变器、工业自动化、储能以及电动和混合动力汽车的逆变器和正温系数(PTC)加热器,通常使用基于IGBT技术的功率开关来实现这些应用的电...     

Coreless printed-circuit board transformers for signal and energytransfer

The authors describe the optimal use of a printed-circuit board transformer with minimum power consumption. The proposed transformer is much smaller than a standard pulse transformer and is suitable for both signal and energy transfer. It can be operated in the megaHertz frequency range. With the use of modulation/demodulation circuits it can be used for digital signal transmission over a wide frequency range from DC to ~300 kHz. The proposal can replace core-based transformers in many low power applications     

A near-zero current-switching series resonant inverter using GTOs

A novel implementation of fast gate-turn-off thyristors (GTOs) for a series resonant power converter operating above 10 kHz and an output power rating of 10 kW or greater is presented. A zero current switching gating strategy that eliminates the need for large negative gate drive circuits is presented. This permits the operation of the converter at a near-unity load power factor independent of the operating frequency. Consequently, for a given output power, the installed kVA capacity of the converter is minimized, and the system simplicity is maintained. A simplified analysis and component ratings for the GTO-based converter are presented. All the results are verified experimentally     

Integrated current regulation for a brushless ECM drive

An enhanced means of regulating phase currents in a brushless electronically commutated motor (ECM), without the use of any discrete current sensors, such as shunts or current transformers, is described. Current feedback information is provided by current sensors integrated into MOS-gated power switches (MOSFETs and IGBTs), and the current regulation is performed by gate drive power integrated circuits. A high degree of drive circuit integration is achieved with this scheme, in addition to providing protection against dangerous fault currents not sensed by conventional bus-shunt configurations. Available power semiconductor switches and power integrated circuits make this technique applicable to permanent magnet ECM drives operating at bus supply voltages up to 500 VDC with power ratings from fractional to >10 hp     

一种80 MHz隔离式DC-DC变换器

介绍了一种80 MHz隔离式DC-DC变换器,无芯PCB变压器实现了VHF隔离,利用交叉耦合电路和无芯PCB变压器形成持续振荡,采用肖特基二极管作为整流器件,电压反馈环路保证整个系统能够稳定输出。采用FEM和EDA软件实现了无芯PCB变压器的设计和整体电路的仿真。测试结果表明,该变换器能够提供3.3 V隔离电压输出和0.3 W功率输出,效率约为43%。     

A new driving scheme for synchronous rectifiers: single windingself-driven synchronous rectification

Single winding self-driven synchronous rectification (SWSDSR) approach is a new driving circuit that overcomes the limitations of the traditional driving schemes, becoming an interesting alternative to supply new electronic loads such as microprocessors. Traditional self-driven synchronous rectification (SDSR) technique has shown very good performance to improve efficiency and thermal management in low-voltage low-power DC/DC converters, however it can not be extended to the new fast dynamic, very low voltage applications. SWSDSR scheme is based on an additional winding in the power transformer (auxiliary winding). It allows for maintaining the synchronous rectifiers (SRs,) on even when the voltage in the transformer is zero, which is impossible to do in traditional self-driven approaches. It also makes it possible to drive properly the SRs even in very low voltage applications, 1.5 V or less. Coupling of the windings strongly affects the performance of the SWSDSR technique. The influence of the coupling between the different windings is analyzed through simulations of different transformers designed for the same application. Models of transformers are generated with a finite element analysis (FEA) tool. Goodness of the SWSDSR scheme is validated through experimental results     

A low-profile power converter using printed-circuit board (PCB)power transformer with ferrite polymer composite

A new design of low-cost and low-profile power transformer is presented in this paper. The manufacturing cost of a power transformer can be reduced using the proposed printed-circuit board (PCB) transformer. The transformer windings are etched on the opposite sides of a double-sided PCB. Self-adhesive ferrite polymer composite (FPC) sheets are stuck on the two PCB surfaces to shield the magnetic flux induced from the transformer windings. The PCB transformer does not require manual winding and bobbin. A power converter prototype employing the PCB transformer has been implemented. The technique of choosing the optimum switching frequency of the power converter using the PCB transformer is addressed in this paper. The maximum power delivered from the prototype is 94 W. The maximum efficiency of the power converter is 83.5%     

A low-profile wide-band three-port isolation amplifier withcoreless printed-circuit-board (PCB) transformers

Galvanic isolations are essential in many electrical patient-monitoring devices and industrial applications. In this paper, a low-profile wideband three-port isolation amplifier using coreless printed-circuit-board (PCB) transformers for isolation is studied. The PCB thickness used in the isolation amplifier is 0.4 mm. The diameters of the two coreless PCB transformers are 9.75 and 5.856 mm, respectively. Operating conditions of the transformers and a design guideline of the isolation amplifier are detailed in this paper. Experimental results show that the isolation amplifier under investigation can transmit an analog signal from 20 mHz to 1.1 MHz with good linearity. Comparison of the prototype with an industrial isolation amplifier is also included     

Recommended Practice for Voice-Frequency Electrical Noise Tests of Distribution Transformers

The practice described herein provides instruction on the testing of distribution transformers as voice-frequency noise generators, to measure the degree to which they may contribute to electrical noise in communication circuits that are in parallel with the power supply circuits serving the transformers. Transformers have a characteristic common to other iron-core devices of causing harmonic currents at voice-frequencies to flow in supply circuits to the transformers. The magnitudes of these currents, and of interference that may result, vary according to design of the transformer as well as excitation voltage. The tests described in this practice provide a standard method for use by the transformer manufacturer, user and others in industry for the purpose of better evaluating the design choices available and moving toward industry objectives as to levels of harmonic exciting current expressed asI . T[current × telephone influence factor (TIF)].     

无芯PCB 变压器的基本结构及其特性

本文主要介绍无芯印刷电路板变压器的基本概念、结构、特性。并介绍了无芯印刷电路板变压器的等效电路、电压增益、输入阻抗函数,同时说明了应用无芯PCB变压器的可靠性及其优点。无芯变压器消除了磁芯对频率、磁饱和度和磁芯损耗。运用现代化的印刷电路板技术,能够精确地控制印刷线圈的函数,易于大规模生产。它主要应用于高频的信号和能量转换,具有很大的应用潜能。     

Optimum design of a high-power, high-frequency transformer

A procedure for optimum design of a high-power, high-frequency transformer is presented. The procedure is based on both electrical and thermal processes in the power transformer and identifies: (a) the VA-rating of ferrite cores in relation to the operating frequency; (b) the optimum flux density in the core; and (c) the optimum current densities of the windings providing maximum transformer efficiency. Since the transformer is the major contributor to the volume and weight of the power supply, the results of transformer analysis can be used for entire power supply optimization as well. Two high-power, high-frequency transformers are optimally designed, built, and tested. Practical results show good agreement with the theory     

Ultra-low-Voltage high-performance CMOS VCOs using transformer feedback

A transformer-feedback voltage-controlled oscillator (TF-VCO) is proposed to achieve low-phase-noise and low-power designs even at a supply below the threshold voltage. The advantages of the proposed TF-VCO are described together with its detailed analysis and its cyclo-stationary characteristic. Two prototypes using the proposed TF-VCO techniques are demonstrated in a standard 0.18-/spl mu/m CMOS process. The first design using two single-ended transformers is operated at 1.4 GHz at a 0.35-V supply using PMOS transistors whose threshold voltage is around 0.52 V. The power consumption is 1.46 mW while the measured phase noise is -128.6 dBc/Hz at 1-MHz frequency offset. Using an optimum differential transformer to maximize quality factor and to minimize the chip area, the second design is operated at 3.8 GHz at a 0.5-V supply with power consumption of 570 /spl mu/W and a measured phase noise of -119 dBc/Hz at 1-MHz frequency offset. The figures of merits are comparable or better to that of other state-of-the-art VCO designs operating at much higher supply voltage.     

PCB integrated inductors for low power DC/DC converter

This paper discusses the use of printed circuit board (PCB) integrated inductors for low power DC/DC buck converters. Coreless, magnetic plates and closed core structures are compared in terms of achievable inductance, power handling and efficiency in a footprint of 10 /spl times/ 10 mm/sup 2/. The magnetic layers consist of electroplated NiFe, so that the process is fully compatible with standard PCB process. Analytic and finite element method (FEM) methods are applied to predict inductor performance for typical current waveforms encountered in a buck converter. Conventional magnetic design procedures are applied to define optimum winding and core structures for typical inductor specifications. A 4.7 /spl mu/H PCB integrated inductor with dc current handling of up to 500 mA is presented. This inductor is employed in a 1.5 W buck converter using a commercial control integrated circuit (IC). The footprint of the entire converter measures 10 /spl times/ 10 mm/sup 2/ and is built on top of the integrated inductor to demonstrate the concept of integrated passives in power electronic circuits to achieve ultra flat and compact converter solutions.