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

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.

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

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/pel2.12133

A robust passivity based control strategy for quasi-resonant converters

In the conventional peak current controlled active-clamped flyback converter, the primary side current sampling resistor R s brings many problems, among which the additional power consumption and instability are the most obvious ones. A new peak current control method without sampling resistor is proposed, which is suitable for both analog control (based on Analog IC or discrete components) and digital control (based on FPGA, ASIC, MCU, DSP, etc.). To exemplify, the FPGA-based digital control method is taken as case study, and the proposed control method is verified by experimental results. In a GaN-based 12V-3A ACF, the average efficiency is improved by upto 2.92% compared to the conventional peak current control methods. In addition, the dynamic response is greatly improved, and analysis is given to explain this improvement.1

An Improved Peak Current Control Method for GaN-based Active-clamped Flyback Converter

DC-DC converters have wide applications in the field of battery charger, distributed generation, power supplies and so on. There are various isolated and non-isolated topologies available which has to be chosen based on the size, cost , weight, application, power range and duty of the converter. Due to increasing applicability of DC-DC converters, it is essential to enhance the efficiency, controllability and output regulation to a step ahead. Resonant converters at high frequency has gained attention in the market to a large scale due to its low size and weight. With the developing enthusiasm for this subject, it is essential to have a detailed review to sum up and update a unique reference about the soft switching configurations for better performance of the converter. The paper provides a brief overview in two and three element soft switching configurations. Moreover, The current technologies evolved in the field of resonant converters are also briefed for wide input voltage applications.

https://iopscience.iop.org/article/10.1088/1757-899X/1091/1/012074/pdf

Overview on second & third order resonant switch mode power converter for variable input voltage applications

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.

Kai-Yu Huang

Papers

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