Line circuit for driving a ringer and a service indicating lamp in a telephone set

摘要

A line circuit for driving a ringer and a service indicating lamp in a telephone set, including a high frequency transformer (T2), a switching circuit (22) for intermittently disconnecting a D.C. voltage applied to the primary winding of the transformer (T2), and a control signal generating circuit (23). The control signal generating circuit generates a first control signal having high frequency and having a first duty ratio when the ringer is to be rung; and generates a second control signal having the same frequency but having a second duty ratio smaller than the first duty ratio when the service indicating lamp is to be lit. The first or the second control signal is applied to the switching circuit so that the high frequency transformer generates a ringing signal or a D.C. voltage to light the lamp. Since the high-frequency transformer is commonly used for generating the ringing signal and the D.C. voltage for the lamp, the line circuit can be made small and light.