| 摘要 |
PURPOSE:To prevent an output stage element from thermally destroying by reducing heat radiation by removing a fruitless electric power loss by varying a voltage supplied to an electric power amplifying circuit according to the properties of an input signal waveform. CONSTITUTION:Acoustic signal S outputted from voltage amplifying circuit 1 of the audio unit is applied to bases of power transistors TR1 and TR2 of electric power amplifying circuit 2, where electric power is amplified before being applied to speaker 3 and both-wave rectifying circuit 4. Then circuit 4 rectifies acoustic signal S and applies rectified signal SR to peak value detecting circuit 5 and mean value detecting circuit 6 and while peak value signal Sp is outputted from circuit 5, mean value signal Sm is outputted from circuit 6 to comparator 7. Comparator 7 compares signal Sp to signal Sm to find the difference in signal level, from which whether acoustic signal S is in a sine waveform or pulsive is discriminated to control switching circuit 10 of electric fpower source circuit 9 by the output of phase control circuit 8, so that a voltage supplied to circuit 2 will be varied. |
