| 摘要 |
In a protection circuit for an audio amplifier, a power relay is provided on a primary side of a power source of the audio amplifier. When a power switch has instructed power-on, a drive power is supplied from an auxiliary power source to the power relay by an instruction given by a control section which is supplied with an operating power thereby to turn on the power relay. A primary voltage is thereby supplied to the power source to set the audio amplifier to a power-on state. When the audio amplifier is in the power-on state, an excess current flowing in an output stage of a power amplifier and dc voltage occurring in an output signal line of the power amplifier and, if necessary, an abnormal voltage occurring in the power source are detected and the power relay is cut off by an instruction from the control section when either one of the abnormalities takes place whereby a primary side of the power source is accurately cut off when an abnormality has occurred. According to the invention, since the primary side of the power source is accurately cut off when abnormality has occurred, damage to circuit elements and loudspeakers can be prevented even when abnormality has occurred in the power source.
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