Active Clamp Flyback Converter Research Articles

A Chua’s Chaotic Chirp Spread-Spectrum Power Spectral Homogenization Strategy Based on Distribution Transformation

When utilizing high-dimensional chaotic signals for frequency modulation, achieving a uniformly distributed power spectrum is a challenging task. This paper addresses this challenge by proposing a power spectrum homogenization strategy based on distribution transformation. The strategy transforms the task of achieving a uniformly distributed power spectrum in frequency modulation of high-dimensional chaotic signals to solve and equalize the probability density function of the chaotic signals, thereby further enhancing the ability of high-dimensional chaotic signals to suppress electromagnetic interference. Firstly, the difficulty of obtaining a smooth probability density function of chaotic modulation signals is solved using the kernel density estimation algorithm. Then, a distribution transformation algorithm is proposed to convert non-uniformly distributed chaotic modulation signals into uniformly distributed chaotic modulation signals. By using uniformly distributed chaotic modulation signals for frequency modulation, the objective of power spectrum equalization is achieved. Finally, taking the Chua’s chaotic signal as an example, the effectiveness of the proposed strategy is verified using an experimental platform based on a digital signal processor-controlled active clamping flyback converter.

Development of Active-Clamp Flyback Converter for Improving Light-Load Efficiency

Development of Active-Clamp Flyback Converter for Improving Light-Load Efficiency

A Hierarchical Driving Control Strategy Applied to Parallel SiC MOSFETs

SiC (silicon carbide) MOSFETs have been extensively used in the power electronics industry due to their exceptional characteristics. First, it was found in this study that their driving loss is larger than their conduction loss in high-frequency applications. Based on this finding, this study proposes a hierarchical driving control strategy for improving the parallel-converter efficiency of SiC MOSFETs under light loads. Efficiency under light loads is of great importance for battery-based energy storage systems. To minimize the sum of the conduction loss and driving loss in parallel devices, this study proposes a current-monitoring hierarchical driving strategy based on an active-clamped flyback converter. By monitoring the output current of the converter, the strategy minimizes the sum of the driving and conduction losses by switching the driving state under different loads. The results of simulations indicate the effectiveness of the load-current-monitoring strategy. To verify the effectiveness of this method, a principle prototype of two SiC MOSFETs connected in parallel at 12 V/5 A was fabricated and tested, and the test results showed that there was a maximum improvement of 1.4% in the converter’s efficiency when the load current was in the range of 0.5–1.5 A.

Modeling, Analysis and Mitigation of Radiated EMI Due to PCB Ground Impedance in a 65 W High-Density Active-Clamp Flyback Converter

This paper first reviewed the modeling and prediction techniques for the radiated electromagnetic interference (EMI) in active-clamp Flyback (ACF) power converters. An improved radiated EMI model was then developed including the PCB ground impedance based on the ACF converter under investigation. Next, the improved radiated EMI model was quantified and experimentally verified. Two mitigation techniques were developed for the radiated EMI based on the improved model. Experiments were conducted to verify the developed analysis and mitigation techniques for the radiated EMI. The proposed modeling and mitigation techniques were finally extended to other isolated power converter topologies.

Design and Implementation of Active Clamp Flyback Converter for High-Power Applications

This paper proposes a solar-powered isolated DC–DC converter for high-power applications. The main aim of this paper is to achieve voltage regulation in the output side of the converter and to integrate a lossless active clamp flyback circuit (LACF) to compensate for the high-voltage issues that arise from one-stage DC–DC converters. Hardware is developed with a power rating of 2 kW to test the performance of the proposed circuit. The circuit is designed using low-voltage devices and features such as soft switching and regeneration due to the LACF, which enhances efficiency. A novel luminous control algorithm is presented to improve the converter performance. The proposed circuit’s performance and feasibility are compared with existing converter parameters, such as the number of components in the circuit, voltage rating, and regeneration.

Adaptive Dead-Time and Partial-ZVS Regulation for GaN-Based Active Clamp Flyback Converter With Predictive Hysteresis Current Mode Control

Active clamp flyback (ACF) converter is regarded as a good candidate in high-frequency small-size adapters. With adaptive dead-time optimization method, there is no reverse conduction loss and switching-on loss in power switches, then ACF can realize optimum full-ZVS control at every operating conditions. However, the other losses such as the conduction loss of clamp switch, the primary winding loss of transformer may be increased to counteract this efficiency advantage, but which has not been outlined. Therefore, this paper proposes a higher-efficiency predicted hysteresis current mode (PHCM) control strategy with adaptive dead-time and partial-ZVS regulation for GaN-based ACF converter for the first time. Firstly, the accurate analytical model by considering above losses is derived. Secondly, the optimal valley current is calculated by the minimum loss, to determine the conduction time of clamp switch and the dead time of main switch. Finally, a digital controlled GaN-based ACF converter is designed to verify the method. The computation speed of needed analytical equations and the magnetizing inductance offset are considered in implementation process. The experimental results show the proposed method can improve efficiency by 0.4% than existing method, which also show a fast dynamic response since the cycle-by-cycle variable-frequency control concept.

28.4cc ultra-density 65W type-C adaptor with current mirror integration method

With the increasing requirements for charging speed of portable electronic products and the demand for portable performance, the fast-charging adapter industry is facing challenges. Adapters mainly have the problems of being too large in volume, low power density and low charging efficiency. This paper introduces an ultra-density adaptor for type-c power delivery (PD) applications. The principle of active clamp flyback converter (ACF) is explained briefly. Advanced technology with Gallium nitride (GaN) devices and novel ACF controller are applied. Power density is increased by current mirror integration method. It can achieve high efficiency, especially at low line input. Finally, a 28.4cc 65W prototype based on GaN Power IC and ACF controller was made with EMI CE passing. The efficiency at full load reaches about 93% with current mirror integration method.

High Precision Primary Side Regulation Constant Voltage Control Method for Primary and Secondary Resonant Active Clamp Flyback Converter

Active clamp flyback (ACF) converter has been demonstrated that which is better than traditional flyback in high-frequency power-adaptor applications. According to the circuit structure, ACF has two modes, primary resonant ACF (PR-ACF) and secondary resonant ACF (SR-ACF). In order to improve the power density, a high-precision primary side regulation (PSR) constant voltage control method for ACF converter is proposed in this article. The proposed method not only can be effectively adopted in PR-ACF but SR-ACF converter. The high-precision output voltage is predicted by highly accurate sampling points on primary auxiliary voltage. The applied microcontroller environment improves the practicability and increases the power density of the ACF system. To verify the proposed PSR method, a prototype that can be changed into PR-ACF and SR-ACF is designed. The output voltage offset, operation efficiency, and dynamic performance are analyzed. The tested results show that high-precision output is obtained in ACF converter by using the proposed method and the maximum output voltage deviation which are 4% and 3.5% in PR-ACF and SR-ACF converter, respectively. Moreover, SR-ACF has a higher efficiency compared with PR-ACF converter, and a smaller voltage shoot during dynamic process, which needs a larger regulation time since the additional output inductor.

A Secondary-Resonance MHz Active-Clamp Flyback Converter With Partial Power Processing

A 1 MHz active-clamp flyback converter for solar street-lighting applications, featuring a partial power processing, is proposed in this article. The secondary-side resonance between the output capacitor and transformer leakage inductor is utilized to reduce rms current and conduction losses. In comparison with the traditional light-emitting diode drivers based on full power converters (FPCs), the proposed approach that uses partial power converters (PPCs) can significantly improve the overall system efficiency by eliminating the redundant power handling process. The universal schemes are discussed and the optimal solution is eventually determined by the partial power ratio. The advantages of PPC compared with FPC in device stress, losses, and regulation capability are demonstrated by simulation. With GaN devices, a 100 W/1 MHz prototype was built to verify the analysis. The experimental results show that the proposed topology can reduce the power rating of the converter by up to about 80% while increasing the system efficiency by up to 95.8%.

A Digital Adaptive Control Method for Optimizing Valley Current of Active Clamp Flyback Converter

In an active clamp flyback (ACF) converter working in critical mode (CRM), the zero-voltage switching (ZVS) of the main power switch can be realized by the negative valley current, which is related to conduction loss and switching loss. Therefore, how to control the negative valley current will affect the overall efficiency of the system. This article investigates and compares the three existing technologies and summarizes their limitations in practical applications. Therefore, a digital adaptive control method is proposed to regulate the valley current according to different working conditions. Meanwhile, small-signal analysis is performed to ensure the stability of the proposed control method. The proposed control method is verified by a field-programmable gate array (FPGA)-based 12-V, 3-A ACF, and experimental results show that the proposed theoretical model should be accurate and practical and there is an average efficiency improvement of 1.34% compared to conventional control.

An Active Clamp Flyback Converter With High Precision Primary-Side Regulation Strategy

The active clamp flyback (ACF) converter has been widely adopted because of the feature of isolation, soft-switching, and high conversion efficiency. On the other hand, due to the characteristic of the circuit cost reduction and the fast control response, the primary-side regulation (PSR) has become a popular control method for isolated power converters. However, high precision PSR strategies for ACF converters are not exposed. Therefore, the aim of this article is to propose a high precision PSR strategy for the ACF converter. Relations between the primary-side current and the secondary-side current are analyzed and derived. Both of the continuous conduction mode operation and the discontinuous conduction mode operation will be considered. The output voltage control mode or the output current control mode can be selected via the proposed strategy. In addition, a secondary-side losses compensation (SSLC) strategy is developed to deal with the non-ideal circuit characteristics as well as to enhance the control accuracy. Operational principles and thorough mathematical derivations will also be revealed. Finally, both simulation and experimental results obtained from a 100 W prototype circuit demonstrate the performance and feasibility of the proposed PSR and SSLC strategy. Validations show that the control accuracy of the output voltage and the output current are 98.54% and 98.42%, respectively.

A Modulation Method for Capacitance Reduction in Active-Clamp Flyback-Based AC–DC Adapters

Recent developments of fast-charging power delivery protocols are driving ac–dc adapters to 100-W power ranges. Conventional solutions in this power range employing a two-stage topology and a big twice-line frequency buffer capacitor are generally costly and bulky. This article presents a patent-pending modulation method for an active-clamp flyback converter, allowing for a single-stage adapter design with reduced capacitance requirements and higher efficiency. This is achieved by exploiting the inherent energy storage capability of the clamping capacitor while turning it into an active power buffer. No hardware modifications are needed, while all salient features of active-clamp flyback converter, i.e., soft switching and leakage recycling, are retained. Operating principles and detailed controller design are discussed, and a 100-W laboratory prototype is built. The prototype achieves 94% peak efficiency and up to 92% size reduction of the buffer capacitor. The experimental evaluation shows that the new single-stage solution enabled by the proposed modulation method is superior to the conventional two-stage and single-stage solutions in terms of cost, conversion efficiency, and power density.

Active-clamped flyback DC-DC converter in an 800V application: Design notes and control aspects

Abstract This paper presents findings for active-clamped flyback (ACF) DC-DC converter 57 W used as an auxiliary power-supply of a wireless inductive-charging system 800 V. Measurements of magnetizing and leakage inductances for three transformers demonstrated how big differences between them could be depending on chosen vendor. Comparison of simulated and measured Bode plots showed that, even when those plots were not matched, one could design a compensator that ensures stable operation. Evaluation of cross-regulation when output with low power (9.62 % of total) was regulated showed that such approach was feasible too. The switching frequency vs output-power and drain-source voltage of switch vs output-power graphs are presented for the first time. Comparison of bandwidth, phase-margin and gain-margin vsinput-power, between the ACF and conventional flyback converter were discussed too. Those quantities were changeable with load and input-voltage as expected. The conventional flyback converter in DCM has higher bandwidth than the ACF which resulted in lower phase- and gain-margins. That showed that it cannot have the same compensator as an ACF.

Resonant Asymmetrical Half-Bridge Flyback Converter

The active clamp flyback (ACF) converter is gradually becoming popular in the application field of low or medium output power range due to its advantage of soft switching and high conversion efficiency. An asymmetric half-bridge (AHB) flyback converter has been proposed in previous studies. The main advantages of the AHB flyback are the same number of components as the ACF converter and the soft switching technique. In this paper, an AHB flyback converter with constant off-time (COT) plus pulse frequency modulation (PFM) is proposed, so that the resonant time is not affected by the input voltage and load, and can achieve a wide range of zero voltage switching (ZVS) operating range. Compared to pulse width modulation (PWM), the PFM control with COT can make the system more stable. Finally, a prototype circuit with a specification input of 48 V to an output of 2.5 V/8 A is made for verification.

Parasitic Capacitance Effects on Active Clamp Flyback Output Characteristics: Application to IPOP Connection

Different mechanisms for balancing power between parallel connected modules have been presented in recent years. They have been broadly classified into active and passive methods. The high output impedance of topologies, including active clamp networks, suggests that they can achieve output current sharing passively when they are connected in parallel. However, some parasitic elements, such as stray capacitances and leakage inductances, have not been considered in the theoretical analyses. Moreover, these need to be taken into account when a high step-up ratio is required because they modify the behavior and output impedance of a module, which changes the current balance. This paper presents a detailed analysis of the influence of parasitic capacitances on active clamp flyback converters that were parallel connected, using the output impedance as a current self-balance method. The proposed solution to alleviate the negative effects on current balance was also studied and validated as a successful method that did not increase the complexity of the controller. Finally, the results that were obtained using an experimental prototype with two 100W modules helped to verify the theoretical results.

A Dual-Mode Control Scheme to Improve Light Load Efficiency for Active-Clamp Flyback Converter

A novel dual-mode control scheme is proposed in this paper that permits the active-clamp flyback (ACF) converter to operate in both the quasi-resonant (QR) mode under light load and the active-clamp mode under medium or heavy load. The mode transition is performed based on the external dual-mode control circuit. In addition, the proposed converter incorporates a new QR mode valley switching (VS) control circuit that reduces switching loss in the main switch by achieving VS. Under medium to full load, the proposed converter becomes an ACF converter designed to achieve zero-voltage switching (ZVS), which reduces switching losses in both power switches. The proposed dual-mode control ACF converter has the following advantages: (1) compared with conventional ACF converters, the proposed ACF converters minimize switching losses by combining VS and ZVS; (2) under light load conditions, the frequency-limiting QR control mechanism is used to avoid disadvantageous switching losses caused by high switching frequencies. The 65 W ACF converter prototype with a DC 155 V input and a DC 19 V/3.42 A output under 65 kHz switching frequency was implemented. The experimental results demonstrate the feasibility of the proposed control scheme. The efficiency of the proposed converter reached 79% at a load of 3.5 W, which is 11% higher than the conventional ACF converter.

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.

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.

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.