1. Field of the Invention
This application is directed to telephones generally and, more particularly, to illumination means for illuminating a portion of a telephone over a wide range of line conditions without degrading or attenuating voice signals on the telephone line.
2. Description of Prior Art
Illumination means have been provided in the past for illuminating portions of a telephone, such as a rotary dial or the pushbuttons of a digital keypad. It is highly desirable that such lighting arrangements be powered from the telephone line itself, which carries both a DC operating voltage and AC voltage signals representing voice inputs and outputs. It is important that the illumination circuit not degrade the quality and strength of the AC voice signals on the telephone line and that there not be excessive current drain from the telephone line at low DC operating voltages.
Light-emitting diode (LED) circuits are well known and have been employed for many purposes including illumination. These known arrangements are not, however, generally applicable to telephone illumination since they will not provide adequate protection against attenuation of the AC voice signals over a wide range of line conditions and excessive current drain under low voltage conditions.