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Silicon monolithic circuits are best suited for applications with low power dissipation. Conventional approaches to audio power amplifiers have a rather limited efficiency, and are therefore not necessarily the best choice for integrated circuits. Pulse-width modulation, however, promises an efficiency of up to 100 percent and has several other advantages. Three approaches to amplitude to pulse-width conversion are discussed and compared: comparison of the audio signal with a triangle waveform, switching stages with hysteresis and RC feedback, and modified multivibrators. Possible configurations of output stages are listed. The use of complementary transistors results in higher efficiency and lower distortion.