| 摘要 |
PURPOSE:To accelerate a muting action in an application mode of power supply by connecting an electrolytic capacitor and an npn Tr to the emitter of a pnp Tr which performs the muting action and then connecting the collector and the base of the npn Tr to the 1st and 2nd power supply terminals respectively. CONSTITUTION:A curve A shows the rise of a positive voltage power supply terminal 9 in an application mode of power supply. In this case, the voltage rise of an output terminal 14 of a stabilized power supply circuit 30 has a delay by a time constant as shown by a curve B. In the power supply application mode a Tr19 conducts at a point tONA where the voltage of the terminal 9 reaches the base-emitter voltage VBE 0.6V. Thus a base current route of a Tr20 formed. The Tr20 conducts when the voltage Vsat+VBE (Vsat: collector-emitter voltage obtained in a Tr conduction mode) of the terminal reaches 0.8V, i.e., a point tONB. Under such conditions, the positive voltage is delivered to a terminal 22 to perform a muting action. When the power supply is cut off, the emitter voltage of the Tr19 is held by an electrolytic capacitor 21. Therefore the voltage relation between the base and the emitter of the Tr19 is reversed compared with that obtained before the power supply is cut off. Then a muting action is carried out. Thus the muting action is started at the voltage VBE+Vsat of a low level in the power supply application mode. As a result, this muting action is accelerated.
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