The article is about D-class power amplifier and matching circuit designed for 20~30 k spectrum underwater sound transducer.PWM circuit is more efficient and smaller than linear circuit,so we choose PWM modulation in D-class power amplifier.D-class power amplifier is composed of triangle wave generator,comparator,power tube and protection module,realizes high efficiency and low distortion power amplification.The output of D-class power amplifier typically fil-ters out high-frequency signals through a low-pass filter,restores low-frequency signals. Underwater sound transducer is capacitive load,and it will produce large reactive power.You should design the matching circuit,including tuning and im-pedance matching.The matching circuit greatly reduces reactive power of underwater sound transducer,and enhances effi-ciency of power amplifier,ensuring underwater sound transducer in good working condition.%是针对20 k~30 k频段的水声换能器设计D类功率放大器和匹配电路，PWM电路相对线性电路具有效率高、尺寸小等优点，所以D类功放一般选用PWM调制，D类功放由三角波发生器、比较器、功率管以及保护模块组成，实现高效率、低失真的功率放大。 D类功放的输出一般都要通过一个低通滤波器来滤除高频信号，来还原低频信号。由于水声换能器是容性负载，会产生很大的无功功率，因此需要设计匹配电路，匹配包括调谐和阻抗匹配。匹配电路的加入能大大减少水声换能器的无功功率，进而提高功放的效率，使水声换能器在工作频段内能稳定工作。
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