| 摘要 |
An amplifier includes an amplifying block (26) for receiving an input signal to drive a speaker (23), and a power supply block (25) for supplying an output voltage to the amplifying block. The amplifying block (26) includes a PWM-signal generation circuit (4) which converts the input signal into a PWM signal, a speaker driving circuit (20) which drives the speaker based on the PWM signal, and a duty detection circuit (8) which outputs a time difference signal proportional to a difference between the pulse width and the pulse interval of the PWM signal. The power supply block (25) controls the output voltage thereof based on the time difference signal. If the volume of a speaker (23) is loud, the amplifier increases the drive voltage of the speaker (23) to suppress distortion of the volume.
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