| 摘要 |
PURPOSE:To improve efficiency while maintaining acoustic characteristics by connecting the output of a PWM circuit as a high-efficiency amplifying circuit to the output element of an audio power amplifier in series and by supplying electric power. CONSTITUTION:An audio signal is inputted to a terminal 15 and voltage-amplified 14 and the amplified signal is inputted to a power amplifying circuit 18 and also supplied as a modulated signal to the comparator 22 of a PWM circuit 21. The comparator 22 receives the output of a triangular-wave generating circuit 23 at the other input terminal to output a PWM signal. This output is amplified by pulse amplifying circuits 24 and 25 respectively and their outputs are passed through switching transistors (TR)28 and 29 to apply outputs of filter circuits 36 and 37 to TRs 16 and 17 of a circuit 18 in series. With this constitution, the voltage gain of the circuit 21 is increased above that of a circuit 14 and while the acoustic characteristics of the amplifying circuit are maintained, power amplification is performed efficiently. |
