| 摘要 |
PURPOSE:To prevent switch-on-shock noise and to prevent excess current flowing to a speaker at the same time by controlling both a current source transistor (TR) and a feedback TR of a differential amplifier in response to application of power. CONSTITUTION:Since TRs Q1, Q8 are PNP TRs, TRs Q4, Q2 are turned on at the moment of power-on to increase a common emitter potential of the differential PNP TRs Q1, Q8, the capacitor C2 is charged and the base potential of a TR Q5 is increased at the same time. Since a terminal voltage of the input coupling capacitor C1 is 0V in this case, the Q1 is turned on and the Q8 is turned off, TRs Q7, Q8 of a pre-driver circuit and TRs Q11, Q14 of output lower side TRs are turned on so as to keep the output potential V0 to a ground potential at the moment of power-on and for some time after that. Then the input coupling capacitor C1 is charged, a negative feedback capacitor C8 is charged, the base potential of the differential PNP TRs, Q1, Q8 rises gradually, operated linearly and the output potential V0 reaches a setting value of 1/2Vcc.
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