Printed Circuit Board Transformer Research Articles

Noise and thermal performance of a sub-attofarad capacitance sensor for precision measurements, with applications in gravitational wave detectors.

We describe the design principles, fabrication, and characterization of a precision AC resonant capacitance bridge (RCB) sensor, based on a resonant differential planar printed circuit board transformer with a solid (ungapped) MnZn ferrite core, demonstrating a short-term sensitivity at 293K of 0.225 ± 0.005 aF/√Hz at around 120kHz resonance frequency and 1Hz Fourier measurement frequency. At 120K, the RCB short term noise sensitivity is 0.118 ± 0.005 aF/√Hz. We compare the ungapped configuration to five different RCBs: three with a core gap of 65 μm and two with a core gap of 130 μm. Their average room temperature short term noise sensitivities are 0.30 ± 0.01 and 0.45 ± 0.01 aF/√Hz, while the cryogenic operation of these transformers at 120K resulted in averaged sensitivities of 0.23 ± 0.01 and 0.36 ± 0.01 aF/√Hz, respectively. Multi-hour room temperature runs, with one core of each of the three gap types, proved the stability of their long-term sensitivities of 0.234 ± 0.005, 0.338 ± 0.009, and 0.435 ± 0.010 aF/√Hz for the ungapped (40-h duration) and the 65 and 130 μm (28-h duration) cores, respectively. At 0.1mHz, a critical frequency for space gravitational wave detectors, the respective sensitivities are 0.25 ± 0.02, 0.35 ± 0.02, and 0.53 ± 0.07 aF/√Hz. Measurements with the ungapped transformer configuration for temperatures from 325 to 349K further validate the dependence of the noise model on temperature and permeability. The performance of our RCB with an ungapped core matches the calculated performance value and shows an improvement in signal-to-noise ratio of two or more compared with capacitance bridges developed for similar applications. A further factor of about two noise reductions is achieved by cooling to 120K.

Termination Design Optimization of High-Current PCB-Winding Matrix Transformers

Due to their high power densities and efficiencies, high-frequency resonant converters using printed circuit board (PCB)-based transformers are gaining popularity in applications, such as datacenters and automotive. However, in such high-frequency, high-current applications, the PCB transformer's termination losses may become significant if not designed properly. This article aims to highlight multiple design considerations to minimize the termination losses while designing a PCB-based matrix transformer. Various termination techniques for full-bridge and center-tap secondary-rectifiers are studied, and it is shown that placing the devices and output filter capacitors directly on the secondary windings results in the lowest termination loss. However, this results in the output filter capacitors being split between the two secondary PCB layers, resulting in a long paralleling loop between them. It is demonstrated that the parasitic inductance of this loop undergoes parallel resonance with the filter capacitors, resulting in high circulating currents and, hence, high termination losses. Methods to mitigate this effect at the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converter's switching frequency are discussed. Improvements of the proposed terminations are demonstrated by modeling and measuring the transformer's ac resistance. Furthermore, the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> converters' efficiency improvements are also showcased with the improved terminations.

Wireless Low-Power Transfer for Galvanically Isolated High-Voltage Applications

For various applications, such as gate drivers for transistors, wireless chargers for mobile devices and cars, and isolated measurement equipment, an isolated DC power supply for electronic components is required. In this work, a new concept for an isolated power supply with insulation strength of 50 kV and power transmission of up to 60 W to supply measurement equipment with 12 or 24 V is presented. Furthermore, high overall efficiency of 82.5% at 55 W is achieved. Feasibility is demonstrated in a real application powering data acquisition electronics at high reference potential. Our new concept uses a coreless printed circuit board (PCB) transformer (15 cm × 10 cm × 4 cm and a weight of 480 g) designed for maximum efficiency via a coil layout and close proximity of adjacent coils on one PCB while reaching high isolation strength via the PCB material and potted coils. To increase efficiency, we investigated different coil geometries at different frequencies. A low-cost design consisting of two Qi charging coils mounted on one PCB is compared with our integrated PCB transformers manufactured from a four-layer PCB with ferrites applied on the outside. With this new design, high isolation voltages are possible while reaching high transformer efficiency of up to 90%.

High-Voltage Insulation Design of Coreless, Planar PCB Transformers for Multi-MHz Power Supplies

This article investigates the insulation design for printed, planar, coreless, and high-frequency transformers with high isolation-voltage. By using finite element analysis on 2-D axial-symmetry, the transformer circuit parameters and electric field distribution are modeled and estimated. Several transformers are designed for an operating frequency of 6.78 MHz. The high frequency, coreless design allows for using thicker insulation material while ensuring a high transformer efficiency. The inclusion of the coupling capacitance in the design optimization results in several design solutions with the same figure of merit, but with different footprint and isolation voltages. Moreover, high electric fields are identified around the sharp edges of the printed circuit board (PCB) windings. Finally, the electrical and isolation performance is verified experimentally. The measured electrical properties are close to the simulated values, validating the chosen model. Breakdown tests demonstrate the feasibility of isolation voltage levels up to several tens of kilovolts. The majority of breakdowns occurs at the outer edge of the PCB winding that was identified as a high-field area. Additionally, a concept for grading the electric field of PCB windings is also proposed. Based on the results, the design aspects are discussed in detail for planar, high-frequency isolation transformers with medium-voltage isolation level.

Highly Efficient HBT Power Amplifier Using High-Q Single- and Two-Winding Transformer With IMD3 Cancellation

This paper presents a highly efficient InGaP/GaAs HBT power amplifier (PA) implemented using a proposed high- Q single- and two-winding transformer. A single- and two-winding transformer is designed with a printed circuit board (PCB) to combine the output power with a reduced passive loss. Compared to a typical 1:2 two-winding transformer, an additional unit amplifier is connected at the mid-point of the secondary winding to construct a single-winding transformer without additional windings. An IMD3 cancellation technique using a single- and two-winding transformer is also proposed to obtain a high linear output power with high power-added efficiency (PAE) without additional design circuitry. The IMD3 components of the two input currents in the single- and two-winding transformer are 180° out-of-phase cancelling each other at output. The proposed PA is integrated with an InGaP/GaAs HBT process using a PCB transformer. The experimental results demonstrate that the PA achieves a saturated output power of 33.3 dBm, with a PAE of 61.3% at 0.91 GHz. The proposed PA is also tested with an orthogonal frequency-division multiplexing (OFDM) 64-quadrature amplitude modulation (QAM) signal having a bandwidth of 10 MHz and peak-to-average power ratio (PAPR) of 7.8 dB at 0.91 GHz to evaluate the improvement in linearity. The PA achieves an adjacent channel leakage ratio (ACLR) of -42 dBc up to an output power of 26.0 dBm with a PAE of 26.8% and current consumption of 297 mA.

Analysis and Suppression of Common-Mode EMI Noise in 1 MHz 380 V-12 V DCX Converter With Low NFoM Devices

For the thriving information technology industrial applications, the series resonant converter (SRC) dc transformer (DCX) using integrated printed circuit board (PCB) windings is a preferred candidate because of its high efficiency and high power density characteristics by pushing the frequency to megahertz. However, the planar PCB transformer possesses large interwinding capacitance, which leads to severe common-mode (CM) noise and a large electromagnetic interference filter. Hence, the total volume of the conversion system is still high. In this article, a series inputs and parallel outputs (ISOP) structure for DCX is analyzed and discussed to demonstrate the CM noise reduction with the static point construction method, in which several dv/dt static points are constructed. Unlike most of the present suppressing methods, it can maintain high efficiency as well. Additionally, the ISOP structure provides more opportunities for optimizing control strategies to achieve the cancelation effect and further reducing the CM noise by the interleaving within a cell and the interleaving among cells. The excellence of the aforementioned methods is verified by experiments on 1-MHz 380 V–12 V 1.8-kW SRC DCX prototypes with a peak efficiency of 98.3%. The proposed methods ultimately reduce the CM noise by 50 dB.

English

This paper presents the electromagnetic interface (EMI) impact on the current transformer with amorphous HB1-M core, printed circuit board (PCB) power transformer and the filter of inductor for Internet of Things (IoTs) device. According to the antenna principle, the radiation emission power responses of PCB transformer and current transformer are estimated and found to be negligible due to the EMI experimental report. Based on this reason, consideration of the amorphous core in design manufacturing and EMI filter development is indispensable. Thus, the current transformer of amorphous HB1-M core is annealed at 350°C and soaked for 1.5 h. The simulation results of electromagnetic field show an EMI impact on filter performance. EMI frequency between 50 to 400 MHz for filter is found to be suitable for PCB. Experimental results have confirmed that the application of PCB transformer with HB1-M would be performed as well in high permeability and sensitivity. Key words: Internet of things (IoTs), electromagnetic interface (EMI), soft magnetic sensor.

Tunable 500–1200-MHz Dual-Band and Wide Bandwidth Notch Filters Using RF Transformers

This paper presents a novel tunable dual-band bandstop filter based on doubly tuned RF transformers. This design results in two distinct notch frequencies in a single resonator using silicon varactor diodes. The 2-pole tunable dual-band bandstop filters are implemented using printed circuit board (PCB) transformers and air-coil transformers. With PCB transformers, the lower frequency can be tuned at 513-845 MHz while the higher frequency can be tuned at 715-1151 MHz with a notch level > 16 dB. With air-coil transformers, a single-band 2-pole notch filter with wide rejection bandwidth is achieved. The design results in 604-982 MHz tuning with a 20-dB rejection bandwidth of 27-45 MHz. Also, by implementing a series varactor in a transformer, the separation between two coupled frequencies can be changed. The topology can be easily extended to higher order filters and design equations are presented.

Design Control of Performance in Nested and Interleaved Winding Printed Circuit Board Transformers for Ethernet Applications

Miniature toroidal, ferrite-core, wire-wound transformers are currently used to isolate and interface all Ethernet devices to the twisted pair cable media. Alternative lithographically fabricated transformers with less process variation must be carefully studied to achieve the isolation, insertion loss, and bandwidth requirements of Ethernet networks. In this paper, dielectric-core toroidal transformers fabricated by printed circuit board methods are studied. The transformer inductances and parasitic capacitances were found to trade-off as the dimensions of the wedge-shaped turns were varied; the winding mode and turn number were also changed. Core layer thickness was found to significantly change the magnitude of intra-winding capacitance. Loading behavior is also examined.

A New Contactless Assembly Method for Paper Substrate Antennas and UHF RFID Chips

This paper deals with a low-cost method for the assembly of flexible substrate antennas and UHF RF identification silicon (Si) chips. Such a method exploits a magnetic coupling mechanism, thus not requiring for galvanic contacts between the Si chip and antenna itself. The magnetic coupling is established by a planar transformer, the primary and secondary windings of which are implemented on flexible substrate and Si chip, respectively. As a result, the Si chip can be assembled on the antenna with a mere placing and gluing process. First, the idea has been validated by theory. Electromagnetic simulations of a square heterogeneous transformer (1.0-mm side) show a maximum available power gain (MAG) of -0.4 dB at 868 MHz. In addition, the heterogeneous transformer is also quite tolerant with respect to misalignment between primary and secondary. An offset error of 150 μm reduces the MAG to - 0.5 dB. A sub-optimal matching strategy, exploiting a simple on-chip capacitor, is then developed for antennas with 50- Ω input impedances. Finally, the idea has been experimentally validated exploiting printed circuit board (PCB) prototypes. A PCB transformer (1.5-mm side) and a transformer rectifier (two-diode Dickson multiplier) have been fabricated and tested. Measurements indicates a MAG of -0.3 dB at 868 MHz for the transformer and the capability of the developed rectifier to supply a 220-kΩ load at 1.5 V with a - 2-dBm input power.

Evaluation of a quasi‐coaxial printed circuit board transformer

PurposeThe purpose of this paper is to investigate the possibility of utilizing printed circuit board (pcb) technology to manufacture coaxial transformers and to increase the predictability, accuracy and repeatability of the transformers leakage inductance.Design/methodology/approachThe geometry of a coaxial transformer is approximated using pcb techniques. Several different geometries are presented with the outer coaxial conductor being approximated by discrete conductors varying from four to 36 in number. Finite element methods as well as experimental results are used to support the proposed ideas. A planar transformer is also analyzed in the same way to emphasize the design advantages offered by the proposed quasi‐coaxial transformer.FindingsThe proposed multi‐conductor structures can be applied as co‐axial transformers. The experimental values obtained for the leakage inductance of the coaxial structures correspond well to the predicted values. This is not the case for conventional planar structure where adjustments need to be made in the finite element analysis simulations to accommodate the shortcomings of the analytical calculations.Originality/valueIn applications where the prediction of the leakage inductance of a transformer is important, this method may be applied and has the advantage of conventional pcb manufacture techniques.

Periodic Analysis of MR-Safe Transmission Lines

In this paper, a theoretical analysis is presented of transmission lines that are periodically interrupted by isolation transformers. Such lines have application as safe interconnects in MRI with internal coils, where the transformers act to block common-mode signals excited by the transmitter while passing differential-mode signals from a detector. The dispersion characteristics are derived, and it is shown that the line is a form of metamaterial supporting magneto-inductive (MI) waves. Propagation can take place in a series of bands, each close to one of the standing wave resonances of an isolated segment. However, it is shown that additional series capacitors are required to implement the protection strategy correctly and the line then operates on a low-frequency lumped-element MI band. Lines operating at 63.8 MHz frequency are constructed using coaxial cables and printed circuit board transformers, and the existence of multiple propagating bands is confirmed.

Toward the Next Level of PCB Usage in Power Electronic Converters

A means for power electronics to exploit the level of 3-D packaging already being implemented in compact consumer products, such as digital cameras, is investigated in order to increase its power density. The increase in functionality and usage of printed circuit board (PCB) in power electronic converters is highlighted and improvements proposed to boost PCB usage to the next level. The material and manufacturing cost of an embedded planar transformer in a PCB-assembled power converter has been substantially reduced by introducing flexible-foil PCB to create the many windings without increasing the remaining number of (expensive) rigid PCB layers. Aspects such as the required folding pattern and its PCB material usage receive qualitative and quantitative attention. Furthermore, increasing of PCB functionality as regards integration of passives, geometrical packaging, and 3-D thermal management enhancement has been addressed. Not only is it shown that the integration of passives into a single, multifunctional PCB transformer structure is feasible but also that the same integral PCB can be used to geometrically package the remaining bulky, low-frequency, discrete components to create a power-dense converter and enhance the 3-D thermal management. A power density improvement of 66% (from 150 to 250 W/L) is achieved by the technology demonstrator.

Filters With Inductance Cancellation Using Printed Circuit Board Transformers

Capacitor parasitic inductance often limits the high-frequency performance of filters for power applications. However, these limitations can be overcome through the use of specially-coupled magnetic windings that effectively nullify the capacitor parasitic inductance. This paper explores the use of printed circuit board (PCB) transformers to realize parasitic inductance cancellation of filter capacitors. Design of such inductance cancellation transformers is explored, and applicable design rules are established and experimentally validated. The high performance of the proposed inductance cancellation technology is demonstrated in an electromagnetic interference (EMI) filter design.

Evaluation of the shielding effects on printed-circuit-board transformers using ferrite plates and copper sheets

This paper presents an effective shielding technique and a simple structure for printed-circuit-board (PCB) transformers. The performance of PCB transformers using the proposed shielding technique is evaluated using thin ferrite plates and copper sheets. Without affecting the transformer energy efficiency, the shielding method under investigation can achieve 28 dB shielding effectiveness (SE), which is much higher than the SE (about 4 dB) obtained by shielding the transformer windings with only two ferrite plates. The proposed PCB transformer structure is very simple and has high energy efficiency (>90%) for Megahertz operation.

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 low-power converter with coreless PCB isolation transformer

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.

A low-profile wide-band three-port isolation amplifier with coreless 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.

Characterization of coreless printed circuit board (PCB) transformers

In this paper, coreless printed-circuit-board transformers are characterized. A range of coreless printed circuit board (PCB) transformers with different geometric parameters have been fabricated and tested. Based on a recently reported analytic method, the self inductance of these transformers is calculated. This analytical method is also extended to cover the prediction of the transformers' mutual inductance. All calculated parameters have been confirmed with measurements for the frequency range from 100 kHz to 30 MHz. These results provide useful information for the optimal design of coreless PCB transformers.

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 ~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/cm2. 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.