| 摘要 |
<p>PURPOSE:To realize a gentle supply/cut-off of the call current, by connecting a circuit consisting of operational amplifiers between a telephone circuit and a power source and securing a connection between the input terminals of the operation amplifiers with capacitors and a switch. CONSTITUTION:When the DC current is cut off in an off-hook mode, a photocoupler 26 is turned on to set the negative input voltage of operational amplifiers 17 and 18 at the intermediate value between the positive power supply voltage and the negative power supply voltage. The outputs of the amplifiers 17 and 18 are changed instantaneously to the positive/negative power supply voltage. These changes are eased by an integrated circuit comprising resistances 13 and 14 plus capacitors 11 and 12 to be supplied to transistors (TR) 33 and 34. Thus the supply current to a terminal is cut off gradually. In case the DC current is supplied in an off-hook mode, the photocoupler 26 is turned on. Thus each of the amplifiers 17 and 18 starts charging to the integrated circuit. Owing to this charging time, the Trs 33 and 34 work slowly and accordingly the DC current to be supplied to the terminal increases slowly.</p> |
