Supplemental power for battery operated modems

A battery operated modem comprising:

• a modem circuitry;
• a pulse-width modulator;
• a pulse-width modulated switching power supply controllable by an output of said pulse-width modulator, said pulse-width modulated switching power supply adapted to receive input power from a telephone line and adapted to output a dc power voltage to said modem circuitry;
• and
• a shunt impedance between an input to said pulse-width modulated switching power supply and said telephone line, said shunt impedance being adapted to switch in and out in correspondence with said output of said pulse-width modulator to shunt said switching power supply.

A modem device comprising:

• a modem circuitry;
• a pulse-width modulator;
• a pulse-width modulated switching power supply controllable by an output of said pulse-width modulator, said pulse-width modulated switching power supply adapted to receive input power from a telephone line and adapted to output a dc power voltage to said modem circuitry;
• and
• a constant current regulator between said pulse-width modulated power supply and said input power from said telephone line, said constant current regulator being adapted to limit a maximum current drawn from said telephone line by said pulse-width modulated switching power supply.

A method of providing supplemental power to a battery operated modem, comprising:

• providing a modem to interface with a telephone line;
• powering said modem from a battery source;
• supplementally powering said modem with dc power extracted from said telephone line by a switching power supply;
• and
• switching a shunt impedance in and out of a circuit between an input to said switching power supply and said telephone line;
• wherein input impedance fluctuations of said switching power supply are minimized.

A method of providing supplemental power to a battery operated modem, comprising:

• providing a modem to interface with a telephone line;
• powering said modem from a battery source;
• supplementally powering said modem with dc power extracted from said telephone line by a switching power supply;
• switching a shunt impedance in and out of a circuit between an input to said switching power supply and said telephone line;
• wherein input impedance fluctuations of said switching power supply are minimized;
• and
• matching an impedance value of said shunt impedance to an average input impedance of said switching power supply measured during charging of a capacitor of said switching power supply from said telephone line.

A method of providing supplemental power to a battery operated modem, comprising:

• providing a modem to interface with a telephone line;
• powering said modem from a battery source;
• supplementally powering said modem with dc power extracted from said telephone line by a pulse-width modulated switching power supply;
• and
• limiting a maximum amount of dc current drawn from said telephone line with a current regulator;
• wherein input impedance fluctuations of said switching power supply are minimized.

A modem device comprising:

• modem means for generating an information signal for transmission over a telephone line;
• switching power supply means for dc-to-dc converting input power drawn from a telephone line into a lower voltage, higher current dc power to power said modem means;
• and
• shunt impedance means between an input to said switching power supply means and telephone line, said shunt impedance means being switched in and out in correspondence with an output of a switching control signal of said switching power supply means to shunt said switching power supply.