| Class-D audio amplifiers have been widely used both in low and high-power applications today,such as public address system,professional audio amplification,home theatre,car audio system and portable speaker.When the class-D audio amplifier supplied by line voltage,a switching mode power supplies(SMPS)with high frequency transformer is always added as a preceding stage to provide DC voltage and electrical isolation.The DC-DC conversion stage of SMPS and DC to AC conversion stage of class-D amplifier are integrated into a single power conversion stage with utilization of high frequency link single-stage inverter circuit,called as single-stage switching amplifier(SSA).The rectifier and bulky DC filter circuits of SMPS is reduced in SSA.Furthermore,the output pulse width modulation(PWM)waveform frequency of SSA is twice the switching frequency,which means that to achieve the same PWM waveform,the switching frequency of of SSA can operate at half the frequency of traditional class-D amplifier.With single stage power conversion and reduced switching frequency,SSA can achieve higher system efficiency.The aforementioned advantages make SSA attractive in next generation switching amplifier with high efficiency and high power density.However,the flowing paths of the filter inductor and leakage inductor current of SSA is blocked during the dead time of cycloconverter,which results in large voltage spikes.Various methods have been developed to solve this problem.Auxiliary absorbing circuits can provides freewheeling path for filter inductor current.However,the efficiency decreases significantly due to dissipative consumption.To recycle the energy of filter inductor during cycloconverter dead time as well as keep low voltage stress across power switches,full bridge clamp(FBAC)circuit is developed for SSA with unipolar phase shift modulation(UPSM).However,UPSM FBAC-SSA has the disadvantages of narrow pulse drops,high power loss at low output power and only full bridge circuit with four switches can be used at primary-side.In this paper,bipolar phase shift modulation(BPSM)is applied to FBAC-SSA and the wide range soft switching methods are developed.Three types of active clamp circuits including back-end half bridge clamp,fore-end half bridge clamp and for SSA have been proposed.Furthermore,low power loss of the proposed BPSM FBAC-SSA at low output power and idle state is realized due to wide range ZVS.The results present that with active clamp,the energy of filter inductor,leakage inductance is recycled,and the voltage across cycloconverter switches is clamped.The efficiency of SSA with active clamp is much higher than the one with dissipative consumption.Though excellent performance can be achieved with FBAC used in BPSM SSA,it is complex as four clamp switches are used.To simplify the clamp circuit,voltage clamp principle of BPSM SSA has been studied and the two conditions for voltage clamp across cycloconverter switches are given.Half bridge active clamp(HBAC)circuit for BPSM SSA has been proposed in this dissertation.High efficiency and low distortion of output voltage has been achieved in the proposed BPSM HBAC-SSA with simplified clamp circuit.Since more than one channel is required when stereo speaker is connected to the amplifier,two-channel(TC)SSAs are widely studied.In this dissertation,BPSM TC-SSA with transformer multiplexing and HBAC are proposed.The modulation principle of the proposed TC-SSA is analyzed and the soft switching range of primary-side is studied.The number of switches,soft range and interaction of the two channels is compared with other circuit architecture.A.The results present that the proposed TC-SSA achieves single stage power conversion,soft switching of power devices low distortion of output voltage by simplified circuit structure.2.1-channel audio switching amplifier has two amplifier channels for high frequency audio amplification and one audio amplifier channel for low frequency audio amplification.For 2.1-channel class-D amplifier,it has simple circuit architecture but the efficiency is power and there is serious bus voltage pumping problem,which results in very high voltage stress across switches and filter capacitors.For multi-channel SSA,high efficiency can be obtained and there is no problem of bus voltage pumping.However,it is too complex to build 2.1-channel SSA audio amplifier.In this dissertation,a 2.1-channel audio amplifier with SSA/class-D mixed architecture has been proposed to improve efficiency as well as eliminate bus voltage pumping.In the proposed 2.1-channel amplifier,SSA operates as low frequency audio amplifier and two class-D amplifiers operate as high frequency audio amplifiers.As SSA handles a large part of output power with low audio frequency,the efficiency is improved evidently and bus voltage pumping is avoided.In order to verify the correctness of the theoretical analysis,a mass of simulation results are provided and corresponding prototypes in lab is set up to present experimental results.Simulation and experimental results have a good agreement with the theoretical analysis presented in this dissertation. |
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