Quasi-resonant Flyback Converter Research Articles

Analysis and Optimization of a Regenerative Snubber for a GaN-Based USB-PD Flyback Converters

This paper presents a high-efficiency GaN-based 65 W Quasi-Resonant (QR) Flyback converter. The converter is characterized by a wide input voltage range and a variable output voltage, and it is designed as a Switch Mode Power Supply (SMPS) for high power density USP-Power Delivery (USB-PD) applications. To increase the efficiency and power density, a regenerative snubber clamp solution has been used to limit the excursion of the drain voltage during the power switch turn-off. The activity involved the modeling of the converter, the sizing of the regenerative snubber, and the design of the flyback transformer. Furthermore, a dedicated test application board was used to verify the effectiveness of the solution. The results were compared with those obtained using a flyback converter with an RCD snubber.

Quasi-Resonant Flyback Converter in an 800 V Inductive Charging System: Abnormal Operation and Control Aspects

Quasi-Resonant Flyback Converter in an 800 V Inductive Charging System: Abnormal Operation and Control Aspects

Study on the C OSS Dynamic Loss of Superjunction MOSFETs in Quasi-Resonant Flyback Converters

Study on the <i>C</i> _OSS Dynamic Loss of Superjunction MOSFETs in Quasi-Resonant Flyback Converters

High power density battery chargers with fast-charging utilizing heat storage

While wide bandgap semiconductor technology, such as gallium nitride, has considerably enhanced power density in mobile battery charger applications, the development of smaller, cost- and resource-effective systems is hindered by thermal constraints arising from miniaturized components and compact housings. This work proposes a transient thermal management system that dynamically adjusts converter output power according to thermal boundaries, utilizing latent and sensible heat storage to enable an initial boosted performance. An analytical and numerical sensitivity analysis of power density limits was conducted to evaluate the impact of thermal and electrical boundary conditions. A 40W hardware prototype of a quasi-resonant flyback converter with transient thermal management was realized using epoxy resin and phase change material filling. The findings show a 40% higher effective power density when charging a conventional 50Wh laptop battery, all within the same thermal boundaries as common operation at constant output power, with a power density measurement accuracy of 5.2%. The system was implemented using PI controller for inner component and surface temperature control. This novel approach to fast-charging highlights the optimization potential of current systems through converter heat storage utilization and provides valuable insights, including analytical and numerical models, for developing chargers capable of overcoming thermal barriers.

On Silicon-Integrated Micro-Transformers and Their Applications in Quasi-Resonant Flyback Converters

This article has shown the design and characterization of silicon-integrated thin-film micro-transformers and their application in a quasi-resonant flyback converter. Two micro-transformers with different turn ratios of 4:4 and 3:3 were designed. The micro-transformers in this study have elongated spiral shape windings sandwiched between two layers of the thin-film magnetic core, and this structure can leverage the anisotropic core property. The micro-transformers were built on a silicon substrate using micro-electro-mechanical systems (MEMSs) fabrication process to ensure a high integration level and high power density. The inductance of 4:4 and 3:3 micro-transformers are 57.3 and 31.5 nH, respectively, their coupling coefficients are 90.5% and 82.7% at 30–40 MHz, and the measured quality factors are 7.82 at 21 MHz and 8.94 at 35 MHz, respectively. A resonant flyback converter topology deploying with a high electron mobility transistor [Gallium nitride (GaN)] was used to evaluate the electrical performance of two micro-transformers. Two resonant flyback converters operating at zero voltage switching (ZVS) reached the maximum conversion efficiency of 46.4% (3:3) and 45.7% (4:4), respectively, with 3.3 V input. The 3:3 micro-transformer developed in this work achieved the highest power density of 128 mW/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with a similar efficiency compared to other cored micro-transformers. The loss analysis of the flyback conversion circuit shows that the main losses in the circuit are the copper winding loss of the micro-transformer and the eddy current loss of the magnetic core. The conversion efficiency of the circuit will be improved by applying thicker copper and core lamination in the future.

Quasi-Resonant Flyback Converter as Auxiliary Power-Supply of an 800 V Inductive-Charging System for Electric Vehicles

This paper presents evaluation of quasi-resonant flyback (QRF) dc-dc converter 57 W with valley-switching in an emerging application. The QRF was supplied from an 800 V variable dc-link and was used as the auxiliary power-supply of a wireless inductive-charging system (ICS). Comparison of state-of-the-art QRF control ICs is presented and suggestions for their improvements are given. Notes on the power-supply architecture, design items specific for the ICS application, over-power protection, and key-component choice are provided. During experiments several original and novel results are generated. The efficiency graphs in ICS power transfer, ICS stand-by, and constant-load operation are analyzed. The maximum efficiency of 87.1 % was reached at 620 V and rated load. Moreover, the unique analysis of QRF losses at no-load, showed their quadratic dependency vs. input-voltage. The measured “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">switching frequency vs. load</i> ” graph is presented. It was changeable with load and input-voltage as expected. From Bode plots the bandwidth, phase-margin, and gain-margin are extracted and plotted versus input-power—for the first time. They were changeable with input-voltage and load as expected. Comparison of simulated and measured Bode plots showed that, even when they were not matched, one can design a Type-2 compensator that ensures stable operation. Evaluation of cross-regulation, when output with 24.1 % of total power was regulated, showed that such approach—contrary to the more common of regulating the biggest one—is feasible too. It is discovered that, for a QRF with variable switching frequency, choice of compensator or the regulated output has influence on its efficiency. The power-thresholds to ensure valley-switching operation represented as “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">input power vs. input voltage</i> ” are shown for the first time. Comparison of bandwidth, phase margin, and gain margin vs. input power, between an ACF and the QRF, were discussed. Conclusion is that QRF, for the same specification, cannot have the same compensator as an ACF. The difference must be at least in a placement of a zero.

Implementation of Time Division Multiplexing With Commercial Flyback Controller for Multi-Outputs USB Power Delivery Charger

Universal serial bus power delivery (USB-PD) chargers are more attractive to consumers with multiple output ports where more devices can be charged simultaneously. Existing multiple-port charger designs take multi-stage approaches, which increases power loss, charger size, and cost. This paper addresses this issue by presenting a time-division multiplexing (TDM) quasi-resonant (QR) flyback converter that eliminates the buck converter stages with simple and commercial analog implementations without the need of microprocessors. The circuit operation and practical design considerations are discussed in detail. An universal AC input, dual-USB-C GaN prototype validates the concept, while demonstrating USB-PD compliant operation, passed conducted EMI, and superior efficiency which passes the most stringent efficiency standards with margin where the benchmark GaN charger fails. Thanks to the elimination of buck stages, the proposed dual-USB-C charger achieves 1.9 W/cm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{3}$</tex-math></inline-formula> uncased power density, close to that of single-USB-C charger.

Active-Clamp Flyback Converter as Auxiliary Power-Supply of an 800 V Inductive-Charging System for Electric Vehicles

Investigation of active-clamped flyback (ACF) dc-dc converter 57W used as the auxiliary power-supply (APS) of an inductive-charging system (ICS) is presented. The ACF was supplied from variable-dc-link 800V which was challenge for its design. Anyway, some findings are applicable to any ACF. An overview of ACF control ICs is presented revealing that only two vendors have appropriate devices for ICS. The key-parts’ choice and suggestion of new features targeting ACF in this emerging-application are given. Striving for high switching-frequency in ICS is not needed due to large safety-distances of transformer. Measured “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">maximum-efficiency vs. magnetizing-inductance</i> ” graph showed that extremes are reached for 400 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{H}$ </tex-math></inline-formula> . It was based on four transformers with manually-optimized resonant-tanks. Measurements of “ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">circulating-power losses vs. input-voltage</i> ” are compared for several transformers. Those losses are in the range of few watts and increase with input-voltage. Measurements of “bandwidth, phase-margin and gain-margin vs. input-power”, for different input-voltages, are discussed. Those quantities were changeable with load and input-voltage as expected. The short-circuit behavior is analyzed showing that usage of the hybrid-clamp with multi-mode control-ICs is mandatory. Finally, comparison with conventional flyback and quasi-resonant flyback converters showed that both are ≈23% cheaper, occupy ≈11% less board-space, and have similar or higher efficiencies. The reason for such efficiency is that ACF circulating-power losses were high as well as dc-voltage-conversion-ratio. Although this is a drawback, for an APS the efficiency is not the key-parameter as long as there are no thermal problems. Moreover, as ACF converter is known for having less EMI-problems that could be the key-advantage for this application. But problem is not-enough electronic components on the market that are suitable for ICS.

Design Methodology of Quasi-Resonant Flyback Converter With a Divided Resonant Capacitor

The leakage inductance in flyback converters can induce high-voltage spikes in power switches as well as power losses. Although conventional resistor-capacitor-diode (RCD) snubbers and active clamp circuits can be used to suppress these voltage spikes, the clamping operation of RCD snubbers increases power consumption, while the active clamps require additional power switches. To address these issues, a quasi-resonant flyback converter featuring a divided resonant capacitor is proposed in this article, in order to suppress voltage spikes in power switches and improve the power conversion efficiency. The operational principle of a divided resonant capacitor is analyzed to obtain the design methodology of the divided resonant capacitor. Furthermore, the validity of the proposed design method is verified via experiments, using 15-W prototype quasi-resonant flyback converter. The results indicate that the proposed design effectively reduces voltage spikes and improves power conversion efficiency.

Capacitor Charging by Quasi-Resonant Approach for a Pulsed Plasma Thruster in Nano-Satellite

In this article, a quasi-resonant (QR) flyback converter has been proposed for capacitor charging in a pulsed plasma thruster (PPT) of a nano-satellite. The energy in the transformer leakage inductance can be recycled to the resonant capacitor, suppressing the switch-off voltage spikes on the semiconductor power switch. The power switch is turned on with a hybrid switching mode. In this mode, valley-voltage-switching (VVS) is applied until the zero-voltage stress on the power switch is obtained, and zero-voltage-switching (ZVS) is used in the remaining charging process. Consequently, the switching-on loss is reduced, and charging efficiency is improved. When a capacitor bank of $2\mu \text{F}$ is charged to 1.5 kV (i.e., 2.25 J), the switching loss contribution of QR flyback converter using hybrid switching approach is reduced significantly to 0.61% while a flyback converter using hard-switching technique has a switching loss contribution of 15.24%. As a result, the proposed QR flyback converter improves the charging efficiency by 2.43%, from 72.69% to 75.12%. Moreover, the diode in the secondary side can be turned-on with zero-voltage and off with zero-current. Hence, the turn-on overshoot voltage and recovery loss are reduced.

A Single-Switched High-Switching-Frequency Quasi-Resonant Flyback Converter

The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. A single-switched quasi-resonant flyback converter that features low switching loss and low switching noise at high switching frequency is investigated in this paper. In order to realize near fully soft switching, a resonant inductor of primary side and a resonant capacitor of secondary side are utilized to recycle the transformer leakage energy and realize zero-current switching (ZCS) at turn off and valley switching (VS) at turn on of the primary switch, and ZCS at turn off of diode. The VS is utilized based on the resonance between the resonant inductor and the equivalent switch drain capacitor. In the closed-loop control, a pulse frequency modulation mode with time fluctuation of switching period is implemented to realize VS at turn on of switch and an on – off control mode is utilized to improve the overall efficiency. Low cost, low losses, and low switching noise are all realized in the proposed prototype. The proposed concept has been validated on a 1 MHz 12 V/3 A prototype with 80 V dc input. The peak efficiency is 90.3% in the on – off mode by using GaN device without synchronous rectification.

Modeling a Dual-Mode Controller Design for a Quasi-Resonant Flyback Converter

The proposed system can overcome the disadvantage of a high peak current in quasi-resonant fly-back (QRF) converters when operated under heavy load conditions. The operating mode and control scheme of a QRF converter with dual-mode control were established and analyzed. The dual-mode control scheme not only enabled a valley-switching detection technique that satisfied the zero-voltage switching condition but also provided a constant frequency mechanism to reduce the conduction loss in QRF converters when operated in a continuous conduction mode and under heavy load conditions. The small-signal equivalent circuit model of QRF converter circuits was constructed using an average approximation method. The technological advancement of a QRF converter with a dual-mode controller was presented in this study. The circuit simulation result of the proposed QRF converter with a mix control scheme proved that the derived circuit component parameters meet the requirements of the converter.

The Novel Quasi-Resonant Flyback Converter With Autoregulated Structure for Parallel/Serial Input

In this paper, a novel quasi-resonant flyback converter that mainly comprises two modules of flyback converters is proposed. A relay is connected in series to the input terminals of two transformers, and the transformer input structure is adjusted according to the input voltage to improve the conversion efficiency. In addition, a novel frequency-limiting quasi-resonant control strategy for solving the limitations of the conventional quasi-resonant control strategies is proposed, wherein the switching frequency is increased under light load conditions. Here, the current-mode pulsewidth modulation IC is used as the core controller. The operating principle and design parameters of the converter are analyzed and discussed in detail. The experimental results prove the feasibility of the proposed circuit.

Multitransformer Primary-Side Regulated Flyback Converter for Supplying Isolated IGBT and MOSFET Drivers

This paper presents primary-side voltage regulated multitransformer quasi-resonant flyback converter (MTFC) for supplying isolated power switch drivers. The proposed topology offers distinct advantages over frequently used flyback converter possessing one high frequency transformer with isolated multiple outputs. Particularly, when a large number of separate dc supply units is required, then MTFC enables improved regular distribution of magnetic coupling between the common primary and the multiple secondary transformers' windings providing a high degree of galvanic and electromagnetic isolation between multiple outputs. Primary side voltage regulation is based on the average output voltage estimation using auxiliary RDC circuit mounted across the primary windings. Operation principles of MTFC are enhanced with analytical study of cross regulation of multiple output voltages at unbalanced load conditions, indicating reduced voltage deviation of multiple outputs by applying the primary-side average voltage regulation. Experimental results of prototype 2-, 3-, and 6-transformer quasi-resonant flyback converters confirmed their cross regulation quality and application potential for independent multiple output supplies.

Analysis, design and performance evaluation of an LED driver with unity power factor and constant-current primary sensing regulation

This work focuses on an isolated offline driver to power LED lamps, realized with a high-power-factor quasi-resonant (Hi-PF QR) flyback converter with peak current mode control and employing constant-current primary-sensing regulation (CC-PSR). The converter is controlled with a recently introduced control technique that enables this kind of converter to ideally draw a sinusoidal current from the input source and, at the same time, to accurately regulate the dc output current using only quantities available on the primary side. The resulting absence of an optocoupler or other means crossing the isolation barrier to close a feedback loop not only reduces size and cost of the driver but also brings greater safety and reliability. The analysis addresses those factors inherent in the control method that affect the shape of the input current that have not been covered in the existing literature. The aim is to set up some design guidelines to minimize the Total Harmonic Distortion (THD) of the input current. The experimental work shows that using this technique enables the design of an LED driver for wide range mains (90 to 264 Vac) that achieves output current regulation better than ±2%, power factor close to unity and THD of the input current <10% over the input voltage range and over a 2:1 range of the output voltage.

Inner Supply Data Transmission in Quasi-Resonant Flyback Converters for Li-Ion Battery Applications Using Multiplexing Mode

This paper proposes data transmission method between primary and secondary of the flyback converter without additional communication circuit while simultaneously transferring power. In some application such as a battery charger, the data exchanges between the primary and secondary sides are necessary. In the conventional system, an additional line or wireless communication modules is used for data exchanges, thereby increasing the system and connector size. The proposed system, in comparison, does not use additional signal transceiver but instead exchanges data by simply alternating operation mode of the flyback converter, thus adding communication function while not increasing the volume of the terminal and overall system. The waveform of transformer voltage is used to count the number of resonant pulses, which is used for decoding and encoding the data packet. Bidirectional communication between primary and secondary sides is possible while power is transferred to the output using an appropriate communication protocol. This paper proposes data transmission method for both single output and the multioutput cases. Also, both half-duplex and full-duplex communication using the proposed method is explained. The experimental results are presented to verify the performance of the proposed communication method.

A High-Switching-Frequency Flyback Converter in Resonant Mode

The demand of miniaturization of power systems has accelerated the research on high-switching-frequency power converters. A flyback converter in resonant mode that features low switching losses, less transformer losses, and low switching noise at high switching frequency is investigated in this paper as an alternative to a conventional quasi-resonant (QR) flyback topology to increase power density. In order to find a compromise between magnet size, electromagnetic interference (EMI), and efficiency, the concept utilizes the resonant behavior between transformer leakage inductance and snubber capacitor to achieve near-zero-voltage switching at both turn-on and turn-off of the primary switch, low core loss due to a continuous transformer magnetizing current, and reduced EMI due to low di / dt and dv / dt values. Meanwhile, the concept uses the regenerative snubber to recycle the transformer leakage energy with two snubber diodes and one snubber capacitor. The proposed concept has been validated on a 340-kHz 65-W prototype. Compared to the conventional QR flyback converter operating at the same switching frequency, the proposed concept has 2% efficiency improvement and better EMI performance.

A Study on the New Active Clamp Snubber Applied Quasi Resonant Flyback Converter

In this paper, active clamp snubber method was proposed to reduce effectively the switching surge voltage of the conventional quasi resonant(QR) flyback converter. The usefulness and practicality of the proposed method in QR flyback converter were verified through steady state analysis and its experimental results. The performance of the proposed circuit was compared with the RCD snubber method. It was verified from the experimental results that the switch peak voltage of the proposed method was limited below 5% while the switch peak voltage of the RCD snubber was continuously increasing accordingly with the load current. Furthermore, this new active clamp snubber method could be applied to QR flyback and its power conversion efficiency was superior to the RCD snubber one.

Novel Frequency Swapping Technique for Conducted Electromagnetic Interference Suppression in Power Converter Applications

Quasi-resonant flyback (QRF) converters have been widely applied as the main circuit topology in power converters because of their low cost and high efficiency. Conventional QRF converters tend to generate higher average conducted electromagnetic interference (EMI) in the low-frequency domain due to the switching noise generated by power switches, resulting in the fact they can exceed the EMI standards of the European Standard 55022 Class-B emission requirements. The presented paper develops a novel frequency swapping control method that spreads spectral energy to reduce the amplitude of sub-harmonics, thereby lowering average conducted EMI in the low-frequency domain. The proposed method is implemented in a control chip, which requires no extra circuit components and adds zero cost. The proposed control method is verified using a 24 W QRF converter. Experimental results reveals that conducted EMI has been reduced by approximately 13.24 dBμV at 498 kHz compared with a control method without the novel frequency swapping technique. Thus, the proposed method can effectively improve the flyback system to easily meet the CISPR 22/EN55022 standards.

Single Power-Conversion LED Backlight Driving System With High Power Factor Control

A single power-conversion LED backlight driving system with high power factor control is proposed. The proposed converter is composed of a full-bridge diode rectifier and a quasi-resonant flyback converter. The proposed converter provides a simple structure, a low cost, and high power factor of 0.988 by using the novel control algorithm without the PFC circuit. To achieve good controllability, the novel control algorithm is transformed by adding a nominal value predetermined to relax its control burden. Detailed analysis and experimental results for a 90-W prototype are discussed.