Telephone line power supply
View Patent ↗A telephone line driven power supply and power supply method capable of creating high yield, low voltage power using power drawn from a telephone line and supplementing the low voltage power with power from a battery-powered host device, such as a laptop PC, when the voltage level falls below a predetermined voltage level. The telephone line power supply includes a polarity guard, a gyrator, an oscillator, a pulse circuit, an inductor, a startup circuit, a converter, a shunt regulator, and a combiner circuit. The method includes supplying line power from power drawn from a telephone line, receiving host power from a host device, supplying the line power to an electrical device, and supplementing the line power with the host power when the voltage level of the line power falls below a predetermined level.
1. A power supply circuit for powering an electrical device using power from a telephone line, said circuit comprising:
a gyrator having an input coupled to the telephone line and an output;
an inductor having and input and an output;
an oscillator having an output;
a pulse circuit coupled to said oscillator and coupled between the output of said gyrator and the input of said inductor;
a converter coupled between the output of said inductor and the electrical device, said converter producing line power at an output; and
a combiner having a input coupled to a host power supply and an output coupled to the output of said converter, said combiner supplementing said line power with host power from said host power supply when the voltage level of said line power falls below a predetermined level.
2. The circuit of claim 1 , wherein said combiner comprises a diode, said diode having an anode coupled to said host power supply and a cathode coupled to the output of said converter.
3. The circuit of claim 2 , wherein said diode is Schottky diode.
4. The circuit of claim 1 , further comprising:
a polarity guard coupled between the telephone line and said gyrator.
5. The circuit of claim 1 , further comprising:
a startup circuit coupled to said pulse circuit, said startup circuit controlling said pulse circuit at startup.
6. The circuit of claim 1 , further comprising:
a shunt regulator coupled to the output of said converter.
7. The circuit of claim 1 , wherein said pulse circuit comprises a switch coupled between said gyrator and said inductor.
8. The circuit of claim 1 , wherein said converter comprises:
a divider circuit having an input coupled to said oscillator and outputs;
a transformer having a primary coil and a secondary coil with a center tap coupled to the output of the inductor;
a dual switch coupled between the outputs of said divider circuit and said transformer;
a clamping circuit coupled to said dual switch; and
a rectifier having inputs coupled to said primary coil of said transformer and an output producing said line power.
9. The circuit of claim 1 , wherein said converter comprises:
a rectifier having inputs coupled said inductor and an output producing said line power.
10. The circuit of claim 1 , wherein the electrical device is a telephone modem.
11. The circuit of claim 1 , wherein the electrical device is a rechargeable battery.
12. The circuit of claim 1 , wherein said oscillator is configured to oscillate at about 500kHz and produce about 250 ns pulses and said pulse circuit pulses said inductor with current for about 250 ns every 2 μs.