公开(公告)号：US4761812A

公开(公告)日：1988-08-02

申请号：US807085

申请日：1985-12-10

申请人： David L. Hollis ,  John L. Reynolds, III

发明人： David L. Hollis ,  John L. Reynolds, III

IPC分类号： H04M19/00

CPC分类号： H04M19/008

摘要： A line circuit is described which provides isolated power to a subscriber telephone line in a manner that produces a constant power characteristic over the normal range of telephone line loop resistance. The isolated feed characteristic of the present invention simplifies protection against lightning and other transients. The constant power characteristic limits power dissipation under short loop, i.e. low resistance, or short circuit conditions yet allows enough current flow under short loop conditions to activate the voice level reducing varistor in the telephone sufficiently to prevent excessive loudness. This eliminates the need for additional circuits at the telephone central office for detecting short loops and for providing voice frequency (VF) level attenuation under such conditions.

摘要翻译： 描述了以在电话线路回路电阻的正常范围内产生恒定功率特性的方式向用户电话线路提供隔离电力的线路电路。 本发明的隔离进料特性简化了防雷击和其它瞬变的保护。 恒定功率特性限制了在短路环路（即低电阻或短路条件）下的功率耗散，但是在短路环境下允许足够的电流流动来激活电话中的语音电平，从而足以防止过大的响度。 这消除了在电话中心局需要额外的电路来检测短路环路，并且在这种条件下提供话音频率（VF）电平衰减。