| 摘要 |
PURPOSE:To change continuously an output voltage of an amplifier by providing a feeding circuit changing operating feeding amount to an amplifier by a control electric quantity and a control electric quantity generating circuit connected to its control electric quantity input. CONSTITUTION:The titled system consists of a voltage variable circuit 10, the feeding circuit 11 comprising transistors (TRs) Q0, Q1 of a connection such as Darlington connection, and a control voltage generating circuit 12 applying a control voltage (control electric quantity) changing the feeding current to an amplifying TR2 and connected to a base of the TRQ0. Then the circuit 12 consists of a resistor 15 and a variable resistor 16 connected between a power supply terminal 13 and a reference potential such as a common potential, and a noise bypass capacitor 17 connected to an output terminal 16A of the variable resistor 16, and a DC voltage appearing at the output terminal 16 is fed to the base of the TRQ0 as the control voltage. A circuit changing the operating feeding amount to the amplification TR2 as above is inserted between a power supply supplying a prescribed voltage and the TR2. Thus, the operator wearing a breast receiver at a telephone attendant board or the like is relived from feeling of displeasure due to noise to improve the job efficiency.
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