Flyback Converter with Current Ripple Reduction

• Main Authors: Li-Wei Shih, 施立緯
• Other Authors: Ching-Shan Leu
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/47er9a

碩士 === 國立臺灣科技大學 === 電機工程系 === 103 === Employing Power over Ethernet (PoE) technology, power devices (PDs), such as VoIP, security cameras and wireless LAN system node are thus powered over the cable without connecting to an AC source. Therefore, system reliability is increased and a DC-DC converter is built in the power device. Currently, flyback converter with RCD clamped topology is the most commonly used in power device due to it’s simple and low cost for PoE applications. To investigate the pros and cons, a thorough discussion will be provided in the chapter 2. However, it suffers from the power dissipations in the RCD network. It occupies precious space and degrades the power efficiency. To improve the efficiency, a lossless passive snubber circuit is used instead and a flyback converter with current ripple reduction (FYRR) topology for the PoE applications is proposed in this thesis. In addition to saving the RCD loss, it also has an input current ripple reduction function by utilizing the clamp capacitor and the leakage inductance of the transformer as an embedded notch filter. Consequently, the EMI noise level can be attenuated with smaller EMI filter components to meet the EMI regulation. In addition to the descriptions of the operation principle, theoretical analysis, and design considerations, two hardware circuits, the flyback with RCD snubber and the FYRR, with 250 kHz, 44-57V input and 12V/24W output specifications are built and tested.