| Audio amplifier is widely used in many applications in modern time.20Hz~20kHz audio signal is mainly amplified by audio amplifier.In the process of audio signal amplified,low output voltage distortion is important.Traditional linear audio amplifier has low output voltage distortion,but the efficiency of the linear audio amplifier is so low that increases the volume of the amplifier system.In some portable speaker applications,small volume,high efficiency,low distortion and high power-density are the key index.Switching audio amplifier benefits from these advantages,which is studied and utilized widely in recently years.Compared with linear audio amplifier,the efficiency of switching audio amplifier is 100% in theory,and thus switching audio amplifier starts to flourish in applications where linear amplifiers once dominated.class-D audio amplifier is a kind of switching audio amplifier,which can be classified by half bridge and full bridge topology.Half bridge class-D audio amplifier features simple circuits and low cost,which is suitable for low power audio amplifier application.However,half bridge class-D audio amplifier needs symmetric positive and negative power supply.Thus,front-end single input symmetric bipolar outputs DC-DC converter is necessary for half bridge class-D audio amplifier.Thus,high performance classD audio amplifier with embedded front-end DC-DC converter becomes an imperative requirement.In half bridge class-D audio amplifier,when output current is positive,the charge is stored in negative power supply and bus voltage pumping across negative power supply is caused.When output current is negative,the charge is stored in positive power supply and bus voltage pumping across positive power supply is caused.Especially,when the output voltage frequency is lower than 200 Hz,power supply pumping of half bridge class-D audio amplifier is severe and ripple voltage is even several times of power supply voltage,which maybe destroy the devices and deteriorate THD+N of the audio amplifier system.Large electrolytic capacitor is always paralleled with the bipolar outputs of front-end DCDC converter to reduce power supply voltage ripple of half bridge class-D audio amplifier,but the power density of the audio amplifier system would be reduced.In order to eliminate the power supply pumping of half bridge class-D audio amplifier system without large electrolytic capacitor,a front-end single input symmetric bipolar outputs bidirectional DC-DC converter is proposed in this dissertation.The proposed DC-DC converter consists of Buckboost cell and Zeta cell,which provides symmetric bipolar outputs for half bridge class-D audio amplifier and achieves ZVS turn-on of all the switches.Recently,high-frequency-link DC-AC is more and more popular due to high efficiency and high power-density.In this dissertation,a quasi single stage high-frequency-link audio amplifier consists of DC-transformer(DCX)and half bridge class-D is proposed.The frontend bidirectional soft switching DCX composed of quasi single stage high-frequency-link DC-AC converter is proposed,and power supply pumping of half bridge class-D audio amplifier is eliminated by the proposed DCX.In the proposed DCX,ZVS turn-on of all the switches can be achieved with bidirectional power conversion,and only small output capacitors are needed.Due to omitted controller,single stage power conversion and reduced output capacitors,the proposed audio amplifier system achieves high efficiency and low output voltage distortion.Based on high-frequency-link DC-AC converter,a single-stage soft switching audio amplifier is proposed in this dissertation.Compared with traditional class-D audio amplifier,the proposed single-stage soft switching audio amplifier is new switching audio amplifier,which achieves single-stage bidirectional power conversion and has no power supply pumping.Because single-stage power conversion and soft switching of all the switches,the proposed single-stage soft switching audio amplifier has higher system efficiency.Besides,the proposed audio amplifier adopts bipolar PWM modulation,which has no duty cycle loss and improves THD+N of the audio amplifier.In order to verify the theoretical analysis,corresponding simulation and prototypes are built.Simulation and experimental results show that the proposed audio amplifier systems achieve high efficiency,low output voltage distortion and no power supply pumping. |
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