Circuit for supplying power to a network termination unit of a message ...

(54) CIRCUIT FOR SUPPLYING POWER TO A NETWORK TERMINATION UNIT OF A MESSAGE TRANSMISSION SYSTEM

(75) Inventor: Peter Kovarik, Vienna (AT)

(73) Assignee: Flextronics International GmbH & Co. Nfg. KG, Kindberg (AT)

( * ) Notice: Subject to any disclaimer, the term ol this patent is extended or adjusted under 35 U.S.C. 154(b) by 0 days.

(21) Appl. No.: 10/239,347

(22) PCT Filed: Mar. 22, 2001

(86) PCT No.: PCT/AT01/00084

§ 371 (c)(1),

(2), (4) Date: Dec. 24, 2002

(87) PCT Pub. No.: WO01/72026 PCT Pub. Date: Sep. 27, 2001

(65) Prior Publication Data

US 2003/0102852 Al Jun. 5, 2003 (30) Foreign Application Priority Data

Mar. 22, 2000 (AT) 483/2000

(51) Int. CI. 1102.1 7/00

(52) U.S. CI 307/64; 379/221.03; 379/221.04;

379/323; 379/413

(58) Field of Search 307/23, 44, 45,

307/64, 65; 379/221.03, 221.04, 322, 323,

413, 413.02

(56) References Cited

U.S. PATENT DOCUMENTS

5,289,359 A * 2/1994 Ziermann 363/21.11

5,610,451 A * 3/1997 Symonds 307/66

6,314,270 Bl * 11/2001 Uchida 455/67.7

6,504,874 Bl * 1/2003 Timmermann et al 375/257

6,560,333 Bl * 5/2003 Consiglio et al 379/413

6,584,197 Bl * 6/2003 Boudreaux et al 379/413.02

6,603,220 B2 * 8/2003 Vergnaud 307/64

6,665,404 B2 * 12/2003 Cohen 379/413

FOREIGN PATENT DOCUMENTS

DE 197 09 888 C * 9/1998

EP 0 514 171 Al * 11/1992

EP 0863 654 A * 9/1998

JP 11-89113 A * 3/1999

JP 11-318076 A * 11/1999

* cited by examiner

Primary Examiner—Adolf Berhane

Assistant Examiner—Gary L. Laxton

(74) Attorney, Agent, or Firm—Henry M. Feiereisen

(57) ABSTRACT

The invention relates to a circuit for supplying power to a network termination unit (55) of a message transmission system, which is connected to a central station via a subscriber line (30). A local power supply voltage source (41), which is arranged in the network termination unit (55) and which supplies power during a normal operating state, is provided as well as a remote power supply source, which is arranged in the central station and which supplies power during an emergency operating state in the case of a failure or malfunctioning of the local power supply voltage source (41). The network termination unit (55) comprises a direct current converter with a transformer and a clocked switch (20). The primary winding (1) of the transformer is connected via the clocked switch (20) to the local power supply voltage source (41), and a connection of the primary winding (1) is connected via a first controllable switch (5) to a wire of the subscriber line (30).

14 Claims, 2 Drawing Sheets

1

CIRCUIT FOR SUPPLYING POWER TO A
NETWORK TERMINATION UNIT OF A
MESSAGE TRANSMISSION SYSTEM

BACKGROUND OF THE INVENTION

The invention relates to a circuit for supplying power to a network termination unit of a message transmission system, which is connected to a central station via a subscriber line. A local power supply voltage source, which is arranged in the network termination unit and which supplies power during a normal operating state, is provided as well as a remote power supply source, which is arranged in the central station and which supplies power during an emergency operating state in the case of a failure or malfunctioning of the local power supply voltage source. The network termination unit includes a direct current converter with a transformer and a clocked switch. The primary winding of the transformer is connected via the clocked switch to the local power supply voltage source.

In a service-integrating digital message transmission system (ISDN), the subscriber neighborhood is formed essentially by a network termination unit, an S-interface and subscriber terminals. Power to these terminals is supplied in a normal operating state from the network termination via a local supply voltage and the S-interface. The available power enables operation of the terminals connected to the network termination.

If the local supply voltage, which for safety reasons is typically 24 VDC or 20 VAC, fails or decreases below an acceptable level, then the network termination automatically switches into an emergency operating state, wherein the essential functions of the network termination are maintained by remotely supplied power via a remote supply voltage source arranged at a central location, for example in an exchange. The remote supply voltage is thereby supplied via the subscriber line that exists between the central location and the network termination, wherein only a relatively small amount of power is available in the emergency operating state. The remote supply voltage is typically ±60 VDC.

Such power supplies are mainly used with ISDN systems, but can also be employed with other transmission systems, such as for example ADSL, HDSL, pair-gain systems (PGS) and the like.

The voltage supplied by the local supply power source as well as from the remote supply voltage source is converted by direct current converters to the values required for the various operating states.

To eliminate supply interruptions during switching from the normal to the emergency operating state, conventional current supply circuits have at least two separate direct current converters or a converter with two separate primary circuits which are arranged in such a way that when the local supply fails, the remote supply is available without interruption. For this purpose, two direct current converters or at least two separate primary circuits have to continuously and in parallel supply the output voltage. Each direct current converter or primary circuit, however, requires a separate control and a corresponding separate transformer winding which take up a relatively large space compared to the other components, making miniaturization of the circuit difficult. In addition, using two direct current converters increases the manufacturing costs.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a compact circuit of the aforedescribed type which uses relatively little space and has low manufacturing costs.

2

This is achieved according to the invention in that a terminal of the primary winding is connected via a first controllable switch with a wire of the subscriber line.

If the local power supply voltage source fails or has 5 insufficient voltage, then the remote supply voltage can be connected via the controllable switch directly with the primary winding of the direct current converter-transformer, so that the remote supply voltage can be converted using one and the same primary circuit, making a second direct current 1° converter unnecessary.

According to another embodiment of the invention, the terminal of the primary winding connected with the first controllable switch can be connected via a second controllable switch with a buffer capacitor.

In this way, the network termination unit can be switched from the normal operating state, in which all terminals are supplied by the network termination, unit into the emergency operating state, in which only the most important 2Q operating functions of the network termination unit are maintained, using only a single direct current converter and/or only a single primary circuit and only a single transformer, without encountering a supply bottleneck. The charge stored in the buffer capacitor is thereby capable of 25 supplying to the primary winding of the transformer of the direct current converter the energy necessary to switch into the emergency operating state.

According to another embodiment of the invention, the first and second controllable switch can be formed by field 30 effect transistors, which require only a small control energy.

According to another embodiment of the invention, the buffer capacitor can be connected via a charging branch with a charging voltage source. The buffer capacitor is then continuously charged to compensate for losses in the capaci35 tor.

According to another embodiment of the invention, the charging branch can be formed by a charging resistor which is connected with the subscriber line preferably via a blocking diode.

40 The charging resistor limits the charging current to the maximum allowable value of the current of the remote supply voltage.

According to another embodiment of the invention, a

45 voltage monitoring unit can be provided whose inputs are connected with the local power supply voltage source, and an output of the voltage monitoring unit can be connected with a unit for controlling the first and second controllable switch.

50 The voltage monitoring unit monitors the voltage supplied by the local power supply voltage source. If this voltage source fails or the voltage drops below a minimum voltage, a control signal is supplied that controls the second controllable switch, whereby the buffer capacitor is dis

55 charged into the primary winding of the transformer. In this way, energy required for switching from the normal operation to the emergency operation is provided during the switch-over time.

According to another feature of the invention, an addi

60 tional voltage monitoring unit can be provided, whose inputs are connected with the subscriber line, whereby an output of the additional voltage monitoring unit is connected with the unit that controls the first and the second controllable switch. The additional voltage monitoring unit can continuously

65 monitor the remote supply voltage which is required for transforming the network termination into the emergency operating state.