Circuit and method for operating a radio telephone upon loss of AC power

A method of operating a radio telephone branched with a wire telephone by a telephone line even when power failure of said radio telephone occurs, said radio telephone having a fixed unit and a portable unit, said fixed unit being connected to said telephone line and connected to a power supply source, said method comprising the steps of:

• checking for a loss of power from said power source while engaged in a call using said radio telephone;
• placing said telephone line in a holding state and generating a signal indicating said holding state if said power is lost;
• checking whether said power from said power source is on again while in said holding state;
• transmitting power-off cancel data to said portable unit if power is on again while in said holding state, cancelling said holding state of said telephone line and stopping said signal indicating said holding state if a response signal in response to said power-off cancel data is received from said portable device, and then going to said step of checking for a loss of power;
• checking whether said wire telephone is hooked off during a given time, if power is not on again or if said response signal is not received;
• and
• cancelling said holding state of said telephone line and stopping said signal indicating said holding state, if said wire telephone is hooked off or if said given time has elapsed.

A method of operating a radio telephone having a fixed means powered by an external source and a portable means, and branched with a wire telephone by a telephone line, even when a power failure occurs, said method comprising:

• determining whether said fixed means fails to receive ac power from said external power source while a user is engaged in a call
• placing said telephone line in a holding state when said ac power is not received;
• terminating said holding state if the wire telephone is placed in a hook-off state;
• terminating said holding state if a given time has elapsed after said telephone line is placed in said holding state;
• determining whether said fixed means is again receiving said ac power after said step of placing said telephone line in said holding state;
• transmitting a power-off cancel signal to said portable means if said fixed means is again receiving said ac power;
• determining whether said portable means transmits a response signal to said fixed means in response to said power-off signal.

A a radio telephone having a fixed means and a portable means, said fixed means for operating the radio telephone branched with a wire telephone by a telephone line, said fixed means having a circuit for operating the radio telephone even when power failure from an ac power source occurs, said circuit comprising:

• line control means connected to the telephone line for interfacing an input/output signal through the telephone line, for holding said telephone line in a holding state during said power failure, and for controlling connection of a telephone call to the circuit;
• supply voltage generating means for generating a first supply voltage having one of a first and second state in dependence upon receipt of an alternating current voltage from said ac power source, said supply voltage generating means attenuating said alternating current voltage to an attenuated voltage and rectifying said attenuated voltage to generate said first supply voltage;
• rectifying means for rectifying said line voltage on the telephone line to generate a second supply voltage, said rectifying means comprising:
• a choke coil and a zener diode connected at a node, said choke coil and said zener diode being connected in series between said line control means and a ground terminal, said choke coil receiving said line voltage means, and
• rectifier means connected in series between said node and said ground terminal, said rectifying means providing said second supply voltage;
• control means for controlling said line control means;
• first supply voltage control means for alternatively supplying one of said first and second supply voltages to said line control means and said control means in dependence upon the state of said first supply voltage;
• and
• second supply voltage control means for supplying said first supply voltage to said radio communication means.

A circuit in a fixed means of a radio telephone also having a portable means, for operating the radio telephone branched with a wire telephone by a telephone line, even when power failure from an ac power source occurs, said circuit comprising:

• line control means connected to the telephone line for interfacing an input/output signal through the telephone line, for holding said telephone line in a holding state during said power failure, and for controlling connection of a telephone call to the circuit;
• communication means for processing said input/output signal of the telephone line through said line control means;
• radio communication means connected to said communication means for communicating between the fixed means and the portable means by a radio signal;
• hook off sensing means for sensing a hook off condition of the wire telephone in response to a variation of a line voltage on the telephone line to generate a hook off signal;
• supply voltage generating means for generating a first supply voltage having a first or second state in dependence upon receipt of an alternating current voltage from said ac power source, said supply voltage generating means dropping said alternating current voltage to a dropped voltage and rectifying said dropped voltage to generate said first supply voltage;
• rectifying means for rectifying said line voltage on the telephone line to generate a second supply voltage;
• control means for controlling said line control means and said radio communication means;
• first supply voltage control means for alternatively supplying one of said first and second supply voltages to said line control means, communication means, hook off sensing means and said control means in dependence upon the state of said first supply voltage;
• second supply voltage control means for supplying said first supply voltage to said radio communication means.