| 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. |
