| 摘要 |
PROBLEM TO BE SOLVED: To surely detect a DC component in an audio amplifier output when a signal is inputted. SOLUTION: An attenuation coefficient A of an attenuator 2 for volume control is made into value corresponding to a volume desired by a user. An audio signal is inputted via the attenuator 2 for volume control, and an output voltage of a power amplifier circuit 3 for amplifying and outputting a power is fully rectified by a full rectification means 11. When the attenuation coefficient of the attenuator 2 is defined as A and an allowable maximum amplitude of the output voltage of the power amplifier circuit 3 is defined as C, the output of the full rectification means 11 is multiplied by 1/A and defined as E, and a maximum value ofΔE=E-C when E exceeds C is found by an arithmetic means 12 to estimate a maximum level of a DC voltage component. The maximum value ofΔE is then compared with a predetermined threshold by a comparison means 13 and when it is larger than the threshold, abnormality detection is outputted to open a relay switch 5 interposed between the power amplifier circuit 3 and a loudspeaker 4. COPYRIGHT: (C)2004,JPO
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