Low loss telephone circuit

Details Low loss telephone circuit Low loss telephone circuit

1994-12-20

1997-05-27

Zele, Krista M.

Telephonic communications

Subscriber line or transmission line interface

Network interface device

379398, 379399, 379412, H04M 1908

Patent

active

056339259

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a circuit for a telephone line power strip off which is capable of recovering of the order of 80% of the power presented to the terminals of the phone. Switch mode power supply regulators are used to achieve this efficiency along with a re-design of much of the "front end" of the phone.
The amount of power extracted from the line determines the level of features and performance of the phone. Previous products have had to exceed the D.C. voltage requirements (with permission from the Telephone Regulating Authorities). It is unlikely that such permission will be granted in the future and thus it is necessary to produce circuits which extract power from the line efficiently. It is an object of the present invention to produce such a circuit which takes power from the line efficiently and therefore allows the features and performance characteristics of the phone which are currently available, but still meeting the voltage requirements.


SUMMARY OF THE INVENTION

According to the present invention there is provided a telephone circuit including a low loss polarity guard sub-circuit, a low loss line seize sub-circuit, a low loss speech sub-circuit and a switch mode power supply, having an output voltage of less than that of the input voltage.
The polarity guard circuit comprises P and N type MOSFETS connected in an "inverted" mode.
The idea behind the circuit of the invention is to use a method of power extraction to present the maximum amount of power possible from the line to a switch mode power supply (SMPS) in order to achieve efficient delivery of power at the required voltage.
The various sub-circuits in the line current path have been designed to drop only small voltages, allowing the line current to be extracted at a high voltage, without upsetting transmit and receive characteristics. Step down switch-mode regulators may then be used to convert this increased power efficiently to the desired voltage at a current which is greater than that supplied by the line.


BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be readily understood one embodiment thereof will now be described by way of example only, with reference to the accompanying drawings.
In the drawings
FIG. 1 shows a block diagram of one circuit with an indication of the voltage drops occurring in the various sub-circuits;
FIG. 2 shows a circuit for a MOSFET bridge;
FIGS. 3a, 3b and 3c show alternative approaches for modulating the line current for a speech sub-circuit and
FIG. 4 shows a circuit diagram for a typical speech sub-circuit coupled to the transformer stage of FIG. 3c.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1 where the idea is to present the maximum amount of power possible from the line to a switched mode power supply (SMPS) and to achieve as low a voltage drop over the various sub-circuits as possible. This allows the line current to be extracted at a higher voltage than previously without upsetting transmit and receive characteristics. Step down switch mode regulators can then be used efficiently to convert this increased power to the desired voltage. In FIG. 1 power is supplied to Lines 1 and 2 at a voltage of 8.63 volts at 20 milliamps. The current passes to a line protection sub-circuit 3 and from there to a MOSFET bridge 4 which is a low loss polarity guard circuit and the voltage drop across these sub-circuits is very small. In sub-circuit 3 the drop of 0.272 volts is achieved, across the bridge 4, 0.14 volts, and across the line seize circuit 5, 0.02 volts. Incoming signals pass from the line seize circuit to the receive line 6. The line current passes through an active transformer stage 7, and through a filter 8. Signals to be transmitted from the transmit line 9, are injected through the transformer stage 7. The voltage drop in the transformer stage is only 0.3 volts. From the filter 8, the line current and the voltage available across the capacitor 14, is transferred through an SMPS 13, with an efficiency greater t

REFERENCES:
patent: 3819951 (1974-06-01), Moore
patent: 4306119 (1981-12-01), Kutzavitch
patent: 5038375 (1991-08-01), Sinberg

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