| Summary: | 碩士 === 國立中央大學 === 電機工程研究所碩士在職專班 === 98 === The purpose of this paper is to explore the design and implementation of class-D audio amplifier. It is known that class-D amplifier is a nonlinear system. Somehow, in conventional method, class-D amplifier is usually designed through linear model. This indirect method in class-D amplifier design could not analyze the stability of the system directly. In this study, several significant class-D amplifiers in the literatures have been reviewed, and DSMs (Delta-Sigma Modulators) was chosen to be the A/D (Analog to Digital) converter for the class-D audio amplifier due to the low cost, simple circuit and accuracy in A/D converting. The sliding mode control design methodology is developed for designing the continuous time integrator DSMs. It effectively solves the problem for not analyzing the system on the stability in conventional way of designing DSMs. Meanwhile it also improves the drawbacks of DSMs which could only reach up to 50% modulation in stable operation and output data rates are more than 1MHz. In this paper, the design of second and third order DSMs are presented. The proposed DSMs enables the modulation rate up to 75% in stable operation and output data rate are decreased to 100kHz〜250kHz.
Furthermore, some parts of the D/A(Digital to Analog) in the system, which includes the shift of DSMs output levels, power MOSFET gate driver, switching output stage, and lossless low-pass filter for filtering high frequency switching noise, are analyzed and implemented as the practical needs.
A completed design method of class-D audio amplifier is presented in this study. The proposed amplifier exhibits the features in fast response, strong robustness, easy to implement, and can be produced directly by the commercial electronic elements. Experimental result confirms that the proposed design approach is surely feasible. In the 3.5 ohm load with the RMS output power of 100 watts, the measured maximum power efficiency is 80%, and THD+N that is less than 0.73%, and SNR of 75dB.The proposed class-D audio amplifier can be applied to general audio needs, and is more suitable for the application of the public broadcasting systems that require high efficiency, high power output, such as the air defense alarm system, disaster warning system, outdoor public address system, etc.
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