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1.发明公开Telephone set comprising a dial pulsing circuit having a switching transistor with a base current related to the telephone line current 失效电话机与该Wählimpulsschaltung包括开关晶体管，其基极电流是正比于线路电流。
公开(公告)号：EP0252556A1
公开(公告)日：1988-01-13
申请号：EP87201222.4
申请日：1987-06-26
IPC分类号： H04M1/31
CPC分类号： H04M1/312
摘要： For a dial pulsing telephone set it is desirable to have a low voltage drop across the pulsing switch 4, and a control voltage of the pulsing switch situated between the voltages of the leads 2-1 and 2-2. These demands can be met by selecting for a switching element a bipolar transistor of such a conductive type that the emitter is connected to the subscriber line. To keep this switching transistor constantly in the saturated state irrespective of the magnitude of the line current, this transistor is driven via a current source 14 supplying a current linearly related to the line current. In order to prevent the control circuit from causing too large a voltage drop for this current source, consequently leaving too little voltage for the remaining circuits of the telephone set, this current source is designed as a voltagecurrent source. Driving this current source can be realised by means of a voltage linearly related to the line current. Such a voltage can easily be obtained without too large a voltage drop arising across this element.
摘要翻译： 对于拨号脉冲电话机希望具有跨越脉冲开关4的低电压降，和位于导线2-1和2-2的电压之间的脉冲开关的控制电压。 这些要求可通过选择用于开关元件的搜索导电类型的双极晶体管做的发射极被连接到用户线路来满足。 到在不考虑线路电流的大小的饱和状态不断保持这个开关晶体管，该晶体管通过电流源14驱动供给线性相关的线电流的电流。 为了防止控制电路从曹景伟太大该电流源的电压降，因此留下太少电压为电话机的其余电路，该电流源被设计为电压的电流源。 驱动该电流源可通过线性相关的线电流的电压来实现。 这样的电压可以容易地获得，而不太大跨越所产生此元件的电压降。
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