The detailed circuit behaviour of the asymmetrical half bridge flyback converter is analysed. The specific relationships between the duty cycle and the different types of energy in the energy storage elements are thoroughly investigated. From the analytical results, the maximum duty cycle is not bounded by 50%, which means that the converter can now be optimally used for the different applications. The zero voltage switching (ZVS) conditions of the power switches are derived. Mathematical equations and design considerations are also given. According to the presented design guidelines, the ZVS operations of the power switches can be maintained from no-load to full-load conditions. A 5V/20A prototype has been built to verify the analytical results under real life conditions.

Analysis and design of asymmetrical half bridge flyback converter

A feed-forward frequency compensator for an asymmetrical pulsewidth modulated (APWM) half-bridge (HB) flyback converter is proposed to increase its power conversion efficiency Under a variable input voltage, the APWM HB flyback converter cannot be satisfied with the zero-current switching (ZCS) condition of output rectifiers because the variation of the turn-ON duration of main switches, which regulate the output voltage, induces their improper turn-OFF duration This means that the resonance of a primary current during the turn-OFF of the switches is out of the ZCS operation of the output rectifiers To avoid this improper operation, the resonant network should be designed with a marginal turn-OFF duration that guarantees the ZCS However, this makes the converter operate with poor efficiency because of increasing conduction losses The proposed feed-forward frequency compensator can properly change the converter's operating frequency to reduce the conduction losses according to the variation of the input voltage satisfying the ZCS condition of the output rectifiers Operation principles, steady-state analysis, and soft-switching conditions are analyzed to derive the frequency compensation algorithm of the APWM HB flyback converter Experimental results using a 240-W prototype converter show that the proposed compensation algorithm can improve the power conversion efficiency of the APWM HB flyback converter under the input-voltage variation

Feed-Forward Compensator of Operating Frequency for APWM HB Flyback Converter

This paper presents a novel asymmetrical half bridge flyback converter with synchronous rectifier. To achieve a higher efficiency and a lower switching stresses than a conventional topology, the proposed APWM flyback converter can achieve ZVS operation of the power switches, and ZCS operation on output rectifier using MOSFET switch. In addition, its simple configuration enables the cost to be reduced with the smallest number of components. In this paper, analytical approach and proposed design guide are also described. A 12V/20A prototype has been implemented to verify the proposed topology and theoretical operation under full load condition.

Asymmetrical ZVS PWM Flyback Converter with Synchronous Rectification for Ink-Jet Printer

Flyback derived converters are attractive because of their simple capacitive output filter when compared with other converters used in multiple-output or cost-sensitive applications. This paper analyzes the detailed circuit behavior of the asymmetrical half bridge flyback converter. Several practical issues, including the specific relationships between the duty cycle and the different types of energy in the energy-storage elements, and the zero voltage switching (ZVS) conditions of the power switches have been thoroughly examined. Mathematical equations have also been given. A 5 V/20 A prototype has been built to verify the analytical results.

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Characterization of asymmetrical half bridge flyback converter

An asymmetrical half bridge flyback converter without output inductor is presented in this paper, in which the power switches can be turned on with ZVS and the output diode can be turned on and off with ZCS. While the ZVS is obtained from the magnetizing current, the ZCS is achieved from the resonant current. The ZVS and ZCS conditions can be maintained for full load range. The characteristics of the proposed converter rely on the utilization of resonant inductor and blocking capacitor as resonant energy delivery devices rather than linearly charging and discharging components. The operational principle and circuit analysis of the proposed converter is described in this paper. The experimental test of a 90 W prototype converter is performed and the results are presented.

A half bridge flyback converter with ZVS and ZCS operations

The asymmetrical PWM converter with the flyback output rectifier (asymmetrical PWM flyback converter) is proposed in this paper. The asymmetrical PWM flyback converter has the feature of zero-voltage switching (ZVS) in the active switches using resonance of the parasitic components. Moreover, the diode in the rectifier stage can commutate softly which minimizes the loss and noise during the commutation interval. The design procedure is presented, which includes the ZVS range of the active switches, and the component value satisfying the zero-current switching (ZCS) of the diode. Experimental results confirm the validity of this topology.

O.J. Lee

Papers

Asymmetrical PWM flyback converter