Patent ID: 7480378

Claim:
An indoor, unearthed cable telephony device, comprising: an input power source; a control signal source; means for converting power from the input power source into a high voltage battery ring signal in response to the control signal source being in a ring state, wherein the converting means includes a fly back transformer; and a feedback regulator for controlling the fly back transformer primary current through a primary current transistor interposed between an output pin of the feedback regulator and a current-exiting end of the transformer primary, the regulator being configured for providing a reference voltage from a reference voltage pin and further being configured for receiving a feedback signal at a feedback pin, the regulator determining the voltage at the output pin based on the feedback signal voltage; an op amp circuit wherein the inverting input thereof receives input from the high voltage battery ring signal; a feedback transistor, the base of which is connected to the control signal source and the collector of which is connected to the non-inverting input of the op amp through a draw-down resistor, the feedback transistor being biased such that it is off when the control signal is at a low voltage state and on when the control signal voltage is at a high voltage state, whereupon the current flows from the non-inverting input through the draw-down resistor and through the collector to emitter of the feedback transistor and from the emitter to ground; and a voltage divider including a first resistor that is interposed between the non-inverting input and ground and wherein a second resistor is interposed between the non-inverting input and the reference voltage pin, the first resistor being in parallel with the draw-down resistor when the control signal voltage is in a high state.