An Electrolytic Capacitor-Free Half Bridge Class-D Audio Amplifier System without Bus-Voltage Pumping

Conventional half bridge class-D audio amplifier (HB-CDAA) systems typically suffer from serious bus-voltage pumping. Such a bus-voltage pumping increases the device stress and deteriorates the total harmonic distortion and noise (THD+N) of HB-CDAA. To reduce the bus-voltage pumping of HB-CDAA system, large electrolytic capacitors are usually required at the input of downstream HB-CDAA, which seriously affects the power density of HB-CDAA system. In this article, an electrolytic capacitor-free HB-CDAA system without bus-voltage pumping is proposed, which consists of a front-end bipolar-symmetric-outputs (BSO) bidirectional dc-dc converter and a downstream HB-CDAA. By providing a bidirectional current flowing path in the front-end dc-dc converter, the bus-voltage pumping of the HB-CDAA system is eliminated without using large electrolytic capacitors. Zero voltage switching (ZVS) of all switches in the front-end BSO dc-dc converter can be achieved over the full audio load range. Compared with the HB-CDAA system with a unidirectional front-end dc-dc converter, the proposed audio amplifier system benefits from high power density, low-output voltage THD+N, and voltage stress of switches. The bus-voltage pumping problem is identified, the operation of the proposed HB-CDAA system is analyzed, and the design parameters of the converter are derived to ensure ZVS of all switches. Experimental results with a 40-W prototype of the proposed audio amplifier system are presented to verify the design.