| Summary: | 博士 === 國立臺灣科技大學 === 電子工程系 === 102 === This dissertation proposes a hybrid-switching technique for active-clamp circuit or half bridge circuit that can be applied to the flyback converter in order to increase the range of zero-voltage-switching (ZVS), and enables the output diode to operate in zero-current-switching (ZCS) and minimizing the switching loss. Given the high efficiency and high power density requirements of the switch-mode power supply, the proposed technique is an attractive design for future off-line applications. Design considerations are very simple because the converter still operates at a fixed frequency and no extra components are need. The hybrid-switching technique incorporates resonant operation into a conventional pulse-width modulation (PWM) circuit in a single switching cycle, while preserving the merits of both PWM and resonant operations.
First, the hybrid-switching technique is introduced and analyzed, then the proposed technique is integrated into three different topologies in order to improve the converters’ performance. One of the converters is the hybrid-switching active-clamp flyback converter. The detailed analysis and design are described, then the ZVS condition of the MOSFETs, the ZCS condition of output diode, and duty cycle are studied. Next, there is the hybrid-switching active-clamp integrated single-ended primary-inductor converter (SEPIC). The input current of SEPIC is continuous, therefore there are good electromagnetic interference (EMI) features. However, the range of ZVS operation is highly dependent on the input inductor, therefore, a detail analysis will be given regarding the relationship between input inductance and range of the ZVS operation. This converter still preserves the ZCS turn-off operation of the output diode and the minimized duty loss. Lastly, a hybrid-switching asymmetric half-bridge flyback is studied for low-voltage output applications. The ZVS condition of the MOSFETs and ZCS condition of the output diode are studied. The introduction of this technique does not require the addition of components into the original topology. Furthermore, the control scheme is fixed frequency PWM, therefore, the control is simple and straight forward, while still being highly reliable.
The experimental results of the three topologies after integrating the proposed technique are presented. Finally, the performance between the proposed converter and the conventional converter are compared to verify the practicality of each approach and highlight the improved performance.
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