D類音訊放大器與AC/DC返馳式供電轉換器電路實現

Abstract

本論文目的是研製一具有高轉換效率之集成式音訊放大系統，結合了AC-DC電源供應級與音訊功率放大級。音訊功率放大級為採用脈波寬度調變技術之D類放大器，利用將輸出端電晶體操作在飽和區與截止區改善傳統線性放大器轉換效率不佳的問題，輸出端採用全橋式架構消除偶次諧波增進THD表現。AC-DC電源供應級為返馳式架構，並應用準諧振切換技術降低切換損失，提升電源轉換器的整體效 率。文中詳細介紹各部分電路工作原理與設計方法，並實際製作一調變頻率為300 KHz音訊放大器，實驗用揚聲器阻抗為8 Ω，供應36 V下最大輸出功率約50 W；電源供應器輸入為90 V rms ~130 V rms，規格為 36 V /100 W，滿載切換頻率為50 KHz。從實驗數據可知D類放大器最 高效率可達92 %；電源供應級滿載下平均效率則高達達91.8 %。

This thesis investigates an integrated audio amplifier system with high power efficiency. It consists of an AC to DC power converter and an audio power amplifier. The structure of audio amplifier stage is Class D which features pulse width modulation switching technique and the output configuration is Bridge-Tied-Load. To raise the conversion efficiency of AC to DC power supply, Quasi-Resonant Flyback was adopted as its topology. Theorems and circuit working principles are revealed in this thesis. A 300 KHz modulation frequency audio amplifier prototype was built and the maximum output power is about 50 Watt when the supply voltage is 36 Volt. Impedance of the speaker is 8 Ohm in experiments. Power supply accepts wide input range from 90 Vrms to 130 Vrms and can deliver 36 V/100 W to the output. The minimum switching frequency is 50 KHz under full load condition. The overall efficiency performance of the prototype is higher than 90 %.