Research On High Power Density Half Bridge Class-D Audio Amplifier System Without Power Supply Pumping

Audio amplifiers have been widely used in various applications today,such as car audio system,public address system and commercial audio system.Audio amplifier is to amplify the audio signal from 20 Hz to 20 k Hz in frequency range efficiently and reliably,so as to drive the speaker.Traditional audio amplifier usually uses linear audio amplifier,which has good distortion characteristics of output voltage,but the efficiency of amplifier system is low,and the volume of amplifier system is large.In recent years,with the development of portable consumer electronic devices,high efficiency,high power density and low distortion have become the key indicators of audio power amplifier.Compared with linear power amplifier,the efficiency of Class-D audio amplifier can reach 100% theoretically.Therefore,Class-D audio power amplifier has more advantages.Class-D audio amplifier mainly includes half bridge Class-D audio amplifier and full bridge Class-D audio amplifier.Compared with full bridge Class-D,half bridge Class-D audio amplifier features few components and simple circuits.Especially,in the Class-D audio amplifier system with 2.1 channel,5.1 channel and 7.1 channel output,half bridge structure can greatly reduce the number of components and the cost.Half bridge Class-D audio amplifier can be classified by single power supply and dual power supply.The dual power supply does not need a large output DC isolation capacitor,which is conducive to improving the power density of amplifier system,but needs symmetric positive and negative power supply.Thus,the front-end DC-DC converter of half bridge Class-D audio amplifier needs to meet the characteristics of bipolar output.The performance of the power supply will significantly affect the performance of the audio power amplifier system.Therefore,the front-end DC-DC converter has become the research focus,which has simple and reliable circuit structure and control strategy.And high efficiency and high power density of amplifier system are the key index.Aiming at the disadvantages of the current half bridge Class-D audio amplifier power supply circuit,such as the large number of components,complex control strategy and the difficulty of soft switching.In order to improve the performance of audio amplifier system,based on isolated front-end DC-DC converter and DC-Transformer,a unidirectional voltage doubler rectified half bridge DC-Transformer(VDR HB-DCX)is proposed in this dissertation.The unidirectional VDR HB-DCX provides biopolar outputs for the half bridge Class-D audio amplifier without complex structure and controller.In addition,the zero-voltage-switched(ZVS)turn-on of the unidirectional VDR HB-DCX switches can be realized both in the positive and the negative audio frequency cycles.Therefore,the efficiency of the proposed Class-D audio amplifier system is improved.The positive and negative supply voltage of half bridge Class-D audio amplifier fluctuates with the positive and negative output current.Especially,the lower the audio frequency,the more serious the power supply pumping.The causes and influencing factors of the power supply pumping,the influence of the supply pumping on the audio amplifier system are analyzed in this paper.The results show that the power supply pumping is mainly related to the frequency of audio amplifier and the output capacitance of unidirectional VDR HB-DCX.Increasing the output capacitance can reduce the power supply pumping,but it will reduce the power density of audio amplifier system,increase the cost of audio amplifier and reduce the service life of output capacitance.At the same time,the voltage stress and the loss of the half bridge Class-D audio amplifier would be significantly increased.Thus,the efficiency of the proposed audio amplifier system is reduced.Aiming at the problem of voltage pumping on the outputs of the front-end DC-DC converter,a bidirectional voltage doubler rectified half bridge DC-Transformer(VDR HB-DCX)audio amplifiers system is proposed.Compared with the traditional half bridge Class-D audio amplifier system,the bidirectional VDR HB-DCX provides symmetric biopolar outputs for the half bridge Class-D audio amplifier without voltage pumping on the outputs of the VDR HB-DCX.Thus,the voltage stress of the switch is reduced,and the output capacitance of the former DC-DC converter is greatly reduced.At the same time,under any load conditions,the switches in the bidirectional VDR HB-DCX can achieve ZVS conduction,which realizes the high efficiency and high power density of the audio power amplifier system.The output capacitances of the bidirectional VDR HB-DCX and voltage stress of the half bridge Class-D audio amplifier are significantly reduced.Thus,the efficiency and power density of the proposed Class-D audio amplifier system can be improved.In addition,the zero-voltage-switched(ZVS)turn-on of the bidirectional VDR HB-DCX switches can be realized both in the positive and the negative audio frequency cycles.Therefore,the efficiency of the proposed Class-D audio amplifier system is improved.The key circuit parameters are calculated and the reasonable components are selected.The simulation circuit and experimental prototype of unidirectional / bidirectional VDR HB-DCX half bridge Class-D audio power amplifier system are built respectively.The corresponding simulation and experimental results are given and compared.The correctness of the theoretical analysis is verified.