High Efficiency Half Bridge Class-D Audio Amplifier System With Front-End Symmetric Bipolar Outputs LLC Converter

A high efficiency half bridge class-D audio amplifier (HB-CDAA) system with symmetric bipolar outputs LLC converter as front-end power supply is proposed and studied in this article. Symmetric bipolar outputs LLC converter provides symmetric bipolar outputs for the HB-CDAA system. The operation modes of class-D amplifier system with front-end bipolar outputs LLC converter in an audio frequency cycle are analyzed, and the effects of HB-CDAA on the operation of its front-end bipolar outputs LLC converter in a switching cycle are studied. It is found that class-D audio amplifier produces voltage pumping on bipolar output voltages in both positive and negative audio frequency cycle, which seriously affects the operation and the efficiency of its front-end bipolar outputs LLC converter and class-D amplifier. Soft switching of bipolar outputs LLC converter can be realized both in the positive and negative audio frequency cycle, which improves efficiency of the proposed HB-CDAA system. A 100 W prototype is built and experimental results show that front-end bipolar outputs LLC converter can provide symmetric bipolar outputs, and realize soft switching. The experimental results also show that voltage pumping on bipolar outputs seriously affects efficiency of the LLC converter. Efficiency of the LLC converter will increase with the decrease of voltage pumping.

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