Active Clamp Flyback Research Articles

A Flyback Converter With Novel Active Dissipative Snubber

The active clamp flyback converters (ACF) can provide features of high power density and high power efficiency. However, ACF is usually applied to in the applications of medium-to-high power range. For a low power application, the ACF may not be a cost-efficient choice. The flyback converter with a lossless snubber can provide high efficiency for low-power application, but it needs an additional inductor and generates more electromagnetic interference (EMI) emissions. The circuit designers also consider the balance between conversion efficiency, size, and cost. Based on the reasons above, the flyback converter with dissipative RCD snubber is still popular in the applications of low-to-medium power range. When the dissipative snubber is adopted to reduce EMI in the power converters, it increases the loss and hence reduces the efficiency. In this paper, a new concept, called active dissipative snubber, is proposed to suppress the resonance in the discontinuous conduction mode (DCM). In the proposed active dissipative snubber, the digital controller activates the dissipative snubber only when the EMI noise is occurring, then disabled after the noise is decayed or disappears. Digital logic makes the passive snubber smart, which can selectively absorb the EMI noise. Since the proposed snubber is not connected to the main circuit all the time, it can provide lower power loss, but still performs better EMI emissions and maintains conversion efficiency.

A Bulk-Capacitance Reduction Method Using Self-Driven Thyristor for AC–DC Converters

Universal serial bus power delivery fast chargers equipped with wide-bandgap devices are driven to higher power density and efficiency. The indispensable high-voltage bulk capacitors used to smooth the rectifier output could take 40% of the total system volume due to the large capacitance value required. This letter discussed a capacitor reduction method using a self-driven thyristor scheme comprised of only three components in total. No extra control circuit is needed. Circuit analysis and design equations are presented, and the design results are implemented in a 60-W GaN-based active-clamp flyback converter. The measurement results on the prototype show a 36.4% reduction of the bulk-capacitor size with similar efficiency compared to the conventional solution.

Design and Implementation of a Single-Stage PFC Active-Clamp Flyback Converter with Dual Transformers

This paper proposes an AC/DC single-stage structure by integrating a boost topology and an active clamp flyback (ACF) circuit with power-factor-correction (PFC) function. The PFC function can be achieved by controlling a boost PFC topology operated in the discontinuous conduction mode. With the coordination of active clamping components, a resonant technique is obtained and zero-voltage-switching (ZVS) can be achieved. The proposed converter is combined with the advantages of: (1) compared with two-stage circuit, a single stage circuit decreases the component of the main circuit and reduces the complexity of the control circuit; (2) a boost topology with PFC function operated in discontinuous conduction mode can be accomplished without adding any current detecting technique or detecting input signal; (3) by using the inductor from the PFC stage, ZVS function can be achieved without any additional inductor; (4) the increment of switching frequency facilitates the optimization of power density; (5) the conducting loss at the secondary side can be reduced by adding the synchronous rectification; (6) in this proposed scheme, the dual transformers with series-parallel connection are utilized, the current at the secondary side can be shared for lowering the conduction loss of the synchronous transistors. Finally, a prototype converter with AC 110 V input and DC 19 V/6.32 A (120 W) output under 300 kHz switching frequency is implemented. The efficiency of the proposed converter reaches 88.20% and 0.984 power factor in full load condition.

Performance of Active Clamp and Interleaved Active Clamp Fly back DC-DC Converters for PV Systems

The Flyback converter topology is a well-known and widely used for AC-DC and DC-DC power converters that cover a broad-spectrum including switching power supplies, photovoltaic (PV) system, electric cars, and fuel cell-based generation systems, and among other applications. In this work, Active Clamp Flyback (ACF) and Interleaved Active Clamp (IACF) converters are designed and simulated for the use of DC-DC converters of PV system applications. Two control systems are used to control the output voltage of the DC-DC converters for various PV conditions, which are PID (proportional integral derivatives) and FLC (fuzzy logic controller). MATLAB/SIMULINK is used to model and simulate the proposed system, where the proposed control systems are developed to regulate the output voltage for the load requirements. The simulation results of the proposed PV systems indicate that the output voltage stabilizes effectively to the required voltage (24 V) for various loads/applications while the input voltage (output from the solar panel) to the converters is varying regrading to different sun radiation levels and other parameters. The efficiency of ACF and IACF converters are found to be 88% and 90%, respectively.

Design of an On-Grid Microinverter Control Technique for Managing Active and Reactive Power in a Microgrid

This paper presents the design and implementation of an on-grid microinverter control technique for managing active and reactive power based on a dq transformation. The system was implemented in a solar microinverter development kit (Texas Instruments—TMDSSOLARUINVKIT). This microinverter has two stages: DC-DC and DC-AC. The DC-DC stage contains an active clamp flyback converter, where the maximum power point tracking (MPPT) of the solar panel is obtained with a current-based incremental conductance algorithm. The DC-AC stage comprises a dual-buck inverter in which voltage-, current-, and phase-tracking control loops are implemented to control the active and reactive power. These techniques were simulated in MATLAB using the proposed mathematical model and experimentally validated in the solar development kit. The results show that the simulated model behaved similarly to the real system, and the control techniques presented good performance. The maximum power point (MPP) of the solar panel was monitored in the DC-DC stage using a current reference provided by the incremental conductance MPPT algorithm and was regulated by a 2P2Z control. The algorithm is robust against continuous changes in irradiance, as it quickly follows the ideal power and continually operates at a point close to the MPP. In addition, the active and reactive power control in the DC-AC stage enables the microinverter to supply the maximum active power. Moreover, the microinverter supplies reactive power according to a defined reference and within the established limits. The proposed mathematical model of the microinverter can be used to design new control techniques and other microinverter topologies. In addition, this active and reactive power-control technique can be implemented in low-power and low-cost microinverters to successfully maintain power quality in small microgrids.

Design of a Wide-Input-Voltage PCB-Embedded Transformer Based Active-Clamp Flyback Converter Considering Permeability Degradation

Today, high power density, high efficiency, and wide-input-voltage operation are becoming increasingly important in power electronics for automotive applications. Active-clamp flyback (ACF) converters, showing a good tradeoff between simplicity and efficiency, are widely used in this industry. With benefits of small profile, low cost, and high reliability in mass production, the printed-circuit-board (PCB) embedding technique of magnetic components has attracted strong interest; however, magnetic cores can lose significant permeability due to the mechanical stress during this fabrication process; as a result, transformer properties, such as leakage inductance, coupling coefficient, and effective turns ratio change, affecting the input-voltage operating range as well as the working temperature. In this article, a detailed analysis of the design constraints of automotive ACF converters with a wide-input-voltage requirement is presented, focusing on the impact that the embedding process has on the transformer properties and the converter operation. Specifically, experiments are performed to investigate the permeability degradation effect, based on which correction factors are derived and added to the proposed design optimization process. A 10-W dual-output high power density (53.2 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) integrated ACF converter prototype based on GaN devices operating at 1 MHz is built and demonstrated for this purpose.

Resonant Push–Pull Converter With Flyback Regulator for MHz High Step-Up Power Conversion

With the trend toward achieving high efficiency, high power density and high operating frequency in power converters, a galvanic isolated circuit architecture is proposed in this article for high step-up applications with wide input-voltage range. This converter consists of a current-fed resonant push-pull (PP) converter as a dc transformer (dcX) dealing with most of the power with high efficiency and an active clamp flyback converter (ACF) as a regulator within a large conversion range. As a single-stage converter, the ACF regulator is paralleled with PP converter to share the total power and regulates the high output voltage. An experimental prototype with an input-voltage range of 24-32 V and output 400 V/400 W is built under 1 MHz switching frequency. A peak efficiency of 97.1% and a power density of 210 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (or 13 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) are achieved. Experimental result validates the correctness of the analysis and proves the feasibility of the proposed converter for MHz high step-up dc-dc conversion.

A Novel Digital Control Method of Primary-Side Regulated Flyback With Active Clamping Technique

Because of the different working principles between conventional flyback and active-clamped flyback (ACF), the existing primary-side regulation (PSR) technology cannot be applied to ACF. And in order to achieve PSR of ACF, a low-cost digital sampling method based on the auxiliary winding of the transformer is proposed. In the conventional peak current mode (PCM) controlled ACF, the sampling resistor of primary current may introduce additional power loss, and high-frequency oscillations during sampling may reduce system's stability. Therefore, a digital feedback-feedforward control (FFC) method is proposed to eliminate the sampling resistor. The stability of the proposed control method and its influence on the dynamic response are studied. In addition, since GaN device has higher power loss during reverse conduction than its Si counterpart, design considerations of reverse conduction time of power switches are also discussed in this paper. All control methods and design considerations are verified on a GaN-based 12V-3A ACF, and the proposed control strategy is implemented by FPGA.

A Constant Current Digital Control Method for Primary-Side Regulation Active-Clamp Flyback Converter

Constant current controlled flyback converter is widely used in low power applications for its simple structure and low cost. In order to further improve the output power and the efficiency, active-clamp flyback converter with soft-switching technique is always used. To avoid the nonlinearity and temperature drift of opto-coupler in the feedback circuit, a constant current digital control method is proposed for a primary-side regulation active-clamp (PSRAC) flyback converter in this article. Soft-switching technique is realized in discontinuous conduction modulation mode with a modified active-clamp technique. To compensate the nonlinearity of the secondary diode current with primary-side regulation, a new output current estimation algorithm is put forward based on the charge balance principle. The output current is predicted from primary current and the auxiliary winding voltage, and constant output current control is realized with primary peak current control method. The cost is low as only one low speed digital-to-analog converter, three comparators and a digital controller are required. The proposed control scheme was verified by a field-programmable gate array controlled 5.4-10.8 V/1.80 A PSRAC flyback converter. The output current accuracy is within in 1.2% in different input and output condition and the peak efficiency is improved by 3.6% after active-clamp technique is used.

How to Design and Implement an Adapter Power Supply With Active Clamp Flyback: An All Silicon Design Methodology

Designing power supplies, especially for power adapters, requires that the designer possess a particular level of expertise and insight into implementing the best architecture. This level of expertise is especially relevant when using a power architecture known as Active Clamp Flyback (ACF). This article will demonstrate, to designers, a practical design method to obtain a reliable, robust, efficient, and high power density, ACF architecture with the bonus of fast time-to-market. Designers can eliminate that conventional Resistor Capacitor Diode (RCD) snubber circuit in their flyback converter design and learn the more efficient ways of active clamp operation. The ultimate solution is an all-Silicon design in a single package which also includes continuous advanced adaptive cycle-by-cycle digital control circuit for im proved performance over varying line/load/temperature as well as component tolerances. The outcome of the proposed design is high efficiency and power density, low EMI, and stringent line/load regulation.

Small Signal Modeling and Control Loop Design of Critical Conduction Mode Active Clamp Flyback Converter

Critical conduction mode (CrCM) active clamp flyback (ACF) converter is regarded as a good candidate to be applied in high-frequency small power supplies. This article focuses on the modeling, analysis, and controller design of CrCM-ACF converter. The small signal model of the converter is derived based on a zero-input resonant equivalent circuit and extended describing function (EDF) method for the first time, then the obtained full-order model is simplified to a low-order model. This procedure establishes an insightful understanding about the effects of the converter parameters and working conditions. Based on the simplified model, a control loop compensator is designed in a single-loop voltage-feedback control scheme for high dynamic performance. An experimental prototype of digital controlled CrCM-ACF converter is built, the accuracy of the derived model is verified by comparing with experimental and simulation results. The performance of the compensator is experimentally evaluated by applying abrupt load current and reference voltage changes in the operating conditions of the converter. From the experimental results, it is demonstrated that the derived analytical model and designed compensator are effective in regulating the output voltage in CrCM-ACF converter.

Modeling and Reduction of Radiated EMI in a GaN IC-Based Active Clamp Flyback Adapter

This article first develops a radiated electromagnetic interference (EMI) model for a gallium nitride (GaN) integrated circuit (IC)-based active clamp flyback converter. Important capacitive couplings, which play a big role in the radiated EMI, are identified, extracted, and validated in the converter. The radiated EMI model is improved to characterize the impact of capacitive couplings. Based on the improved model, techniques to reduce capacitive couplings and the radiated EMI are proposed and experimentally validated.

Digitally controlled GaN‐based MHz active clamp flyback converter with dynamic dead time optimisation for AC–DC adapter

The active clamp flyback (ACF) converter utilising gallium nitride (GaN) devices with high-switching frequency and high efficiency is impressive in system miniaturisation for AC–DC adapters. Owing to poor reverse conduction of GaN devices, the improper dead time between two switches can cause large power consumption in high frequency. This study proposes a dynamic dead time optimisation technique for GaNs ideal zero-voltage switching (ZVS) to address the issue. It adjusts the clamp switch on time to avoid large reverse conduction voltage stress on the main switch in different loads conditions. In addition, a new control scheme for clamp switch is introduced for enhancing efficiency in light to medium load. These techniques are experimentally verified on a 45 W (20 V/2.25 A) prototype of an ACF converter with a field-programmable gate array. The controller enables the system to operate at 1 MHz and dynamically modulates the dead-time under universal input and full load. With the light load ZVS control scheme, the system can achieve a maximum efficiency of 94.12 and 80.23% in the worst case. The prototyped converter can achieve power density (exclude case and controller) of 18 W/in3.

Sampled-Data Modeling for PCM and ZVS Controlled Critical Conduction Mode (CrCM) Active Clamp Flyback (ACF) Converter at Variable Switching Frequency

Critical conduction mode (CrCM) active clamp flyback (ACF) converter is regarded as a good candidate for low power adaptor applications. However, the most adopted control strategy of variable-frequency peak current mode (VF-PCM) and discrete zero voltage switch (ZVS) control makes it difficult to get the accurate small signal model. Therefore, by using sampled-data modeling method, this paper proposes an exact small signal model of CrCM ACF converter for the first time. In the modeling process, the influence of discrete-ZVS control is firstly considered. The conduction time of power switch is regarded as the control signal, which is different from constant-frequency converter. The total current close-loop transfer function is simplified by the linear combination of single VF-PCM and discrete-ZVS control model. After considering the sampling effect and the modulator gain from the derived sampled-data model respectively, the control-to-output transfer function of CrCM ACF converter is developed. The analytical results are analyzed by comparing with single VF-PCM and the widely used average model. Finally, to validate the accuracy of the proposed model, a 65W 20V output CrCM ACF converter is simulated and measured. The verification shown that the proposed sampled-data model is basically agreement with the simulation and experimental results.

Analysis and Optimal Design of High-Frequency and High-Efficiency Asymmetrical Half-Bridge Flyback Converters

The asymmetrical half-bridge (AHB) flyback converter is capable to achieve zero voltage switching and has lower voltage stress compared to the active clamp flyback converter. This topology gives much margin for components selection and transformer turns ratio design. It is well adapted to voltage step-down applications. However, the optimal design for AHB flyback converter taking current dip effect causing by components parasitic capacitances, and each component effect to power loss into consideration has never been explored. This article gives detailed operation and mathematical analyses of this effect. The optimal design procedure with the consideration of each circuit parameter is presented in this article. The transformer benefits low power loss from interleaving winding layout. A 56 W/inch3 1 MHz 65 W prototype with 100–250 V input is built to verify the feasibility of the converter. Experimental results show the peak efficiency 96.5% is achieved with 127 V input and the whole system efficiency under the entire input voltage range is above 93%.

Experimental validation of solar panel integrated modified three-port active clamp flyback converter fed micro-inverter

In this paper, a photovoltaic (PV) tied modified three-port active flyback converter (MTPACFC) operated three-phase micro-inverter is presented to provide enhanced voltage gain with fewer components. The proposed micro-inverter transfers the power generated on the 12 V PV power generation system to 400 V, AC grid. Generally, the DC-DC converter designed with an active clamp circuit provides improved power transfer capability to transfer the power from the PV array. The conventional active clamp flyback converters are designed to offer a limited boost factor for the input voltage. The recommended three-port altered flyback converter is intended to offer double boosting for the input voltage with extended performance. Besides, a synchronous reference frame theory with an artificial neural network based grid side controller is adapted to provide low total harmonic distortion at the point of common coupling. The outcomes of the simulated and test models are introduced to approve the boosting capacity and performance of the proposed MTPACFC.

A Dynamic Resonant Period Control Technique for Fast and Zero Voltage Switching in GaN-Based Active Clamp Flyback Converters

Compared to Si FETs, when the main GaN FET is in full zero voltage switching condition, maximum switching loss reduction can be achieved. Therefore, in this article, an active clamp flyback converter with GaN devices that implements fast ZVS by using the proposed dynamic resonant period control (DRPC) technique can reduce large transformer leakage inductance energy loss on the active resonant circuit. As the loading changes, the DRPC technique can dynamically adjust the on -time in auxiliary switch to prevent large voltage stress on the components in the primary side. In full load condition, the leakage energy loss can be reduced, thereby transferring more energy to the secondary side with maximum efficiency up to 94%.

Ultralow Input–Output Capacitance PCB-Embedded Dual-Output Gate-Drive Power Supply for 650 V GaN-Based Half-Bridges

Wide-bandgap devices have been widely used to reduce the size and increase the efficiency of power converters by operating at a high switching frequency, at the expense of heightened radiated and conducted electromagnetic inference (EMI) emissions, of which the latter circulates through the power loop and ancillary circuitry. In effect, the parasitic isolation capacitance $C_{i}$ of the gate-driver power supply represents a key EMI propagation path to be controlled in order to ensure the operational integrity of power converters. To this end, this paper proposes an integrated, dual-output gate-drive power supply for gallium-nitride (GaN) 650 V, 60 A, half-bridge phase legs, rated at 2 W (2 × 1 W), 15 to 2 × 7 V, featuring an ultralow $C_{i}$ of 1.6 pF, an output-to-output parasitic capacitance of 1.6 pF, a power density of 72 W/in3, and an efficiency of 85%. All this is attained using an active-clamp flyback converter switching at 1 MHz using 65 V GaN high-electron-mobility transistor devices and Schottky output rectifiers, and a Pareto-optimized transformer design minimizing its interwinding capacitances, volume, and losses. Finally, the transformer is fully embedded in a printed circuit board (PCB) material, doubling as a substrate for the topside active layer of the power supply. The paper presents the complete design procedure, processing, and experimental demonstration of the proposed integrated power supply, evaluating as well the reliability impact of the magnetic-PCB material interface in high ambient temperature applications (>200 °C).

Resonant Hybrid Flyback, a New Topology for High Density Power Adaptors

In this article, an innovative power adaptor based on the asymmetrical pulse width modulation (PWM) flyback topology will be presented. Its benefits compared to other state-of-the-art topologies, such as the active clamp flyback, are analyzed in detail. It will also describe the control methods to achieve high efficiency and power density using zero-voltage switching (ZVS) and zero-current switching (ZCS) techniques over the full range of the input voltage and the output load, providing comprehensive guidelines for the practical design. Finally, we demonstrate the convenience of the proposed design methods with a 65 W adaptor prototype achieving a peak efficiency of close to 95% and a minimum efficiency of 93.4% at full load over the range of the input voltage, as well as a world-class power density of 22 W/inch3 cased.

Highly Efficient Secondary-Resonant Active Clamp Flyback Converter

Both high switching frequency and high efficiency are critical in reducing power adapter size. The active clamp flyback (ACF) topology allows zero voltage soft switching (ZVS) under all line and load conditions, eliminates leakage inductance and snubber losses, and enables high frequency and high power density power conversion. Traditional ACF ZVS operation relies on the resonance between leakage inductance and a small primary-side clamping capacitor, which leads to increased rms current and high conduction loss. This also causes oscillatory output rectifier current and impedes the implementation of synchronous rectification. This paper proposes a secondary-side resonance scheme to shape the primary current waveform in a way that significantly improves synchronous rectifier operation and reduces primary rms current. The concept is verified with a ${\mathbf{25}}\hbox{--}{\text{W/in}}^{3}$ high-density 45-W adapter prototype using a monolithic gallium nitride power IC. Over 93% full-load efficiency was demonstrated at the worst case 90-V ac input and maximum full-load efficiency was 94.5%.