| 摘要 |
PURPOSE:To miniaturize components and to stabilize the characteristic by charging a capacitor being a component of a ripple filter with a constant current at application of power so as to expand the muting time even with the same capacitance. CONSTITUTION:In applying a voltage to a power terminal 6, a capacitor 7 is charged by a constant current through a transistor (TR) 10 being a component of a current mirror, and when the voltage of the capacitor 7 gets higher, the TR10 is saturated and the capacitor 7 is charged by a current decided by the resistor 13. Since a TR11 is turned off while its base voltage is low, the collector voltage gets higher, the TR2 is turned on, the signal from an input terminal 3 is attenuated and does not appear at an output terminal 4. When the capacitor 7 is charged further and the TR11 is turned on, the TR2 is turned off. In this case, muting is applied for a prescribed period. Thus, the charging time of the ripple filter is prolonged more than that by the resistor only and the circuit is immune to the fluctuation of power supply.
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