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Novel Non-isolated LLC Resonant Converters

To shrink the size of passive components in the point-of-load buck converter, a high switching frequency is needed. However, the typical buck converter has large turn-on, driving, and turn-off losses at high switching frequencies. The typical benefits of LLC resonant converters are a lack of turn-on loss and little turn-off loss for the primary side switches and nearly ZCS (zero current switching) for the output rectifier, which are suitable for high-frequency DC/DC applications. However, the large turns ratio of the transformer is an issue due to the high ratio of input and output voltage.

The proposed non-isolated LLC converter can achieve ZVS, low turnoff loss and a self-driven synchronous rectifier. Due to the non-isolated technique, the turns ratio of the transformer is also reduced. The typical waveforms are shown in Fig. 1(c) below.

(c) Waveforms of non-isolated LLC converter
Fig.1 Novel non-isolated LLC resonant converter.