Method and system for increasing subscriber line interface circuit voltage during ringing
View Patent ↗A voltage controller increases a DC input voltage in response to a ring instruction received from a processor in a control signal. The increased voltage is converted to an AC ring signal that causes a telephone to ring. The ring signal voltage is generated at a battery high node (“V BH ”) and may be routed to a SLIC before being sent to an on-hook telephone. The voltage at V BH is kept low during off-hook and other periods when a ring instruction is not present. Thus, voltages internal to an indoor device that houses the controller are kept below a predetermined safe threshold, thereby allowing the periods of high voltage to be deemed as transient. Accordingly, if the device is unearthed, or not grounded to the earth, the device may nevertheless obtain listing by a certifying and testing organization without being subjected to abnormal testing and possible failure thereof.
1. 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.