JPH02164228A - Overvoltage protector for - Google Patents

Abstract

PURPOSE: To filter the noise arising at the place lower than the standard clamp voltage by providing a means which is connected between the first means and the second means so as to filter the voltage signal of a first lead wire and a second lead wire, corresponding to the turn on of the current by the first means and the second means connected between the first lead wire and the second lead wire. CONSTITUTION: An overvoltage protective circuit 10 is connected between a TIP lead wire and a RING lead wire, and also is connected to earth potential. A gas discharge pipe 12 clamps transient voltage, and when there is no transient voltage, it gives impedance. Transient voltage suppressors (V)18 and 20 are turned on when they get over the specified breakdown potential. The gas discharge pipe 12, a resistor (r) 14 and 16, and V18 and 20 protect a communication device from danger voltage. V24 and 30 are selected to have higher breakdown voltage than the specified voltage. R14 and a capacitor 22 and V24 suppress noise and transient voltage signals. R16, a capacitor 28, and V30 clamp noise and transient voltage signals.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to overvoltage protection circuits for a pair of telephone lines and similar data communication channels, and more particularly to overvoltage protection circuits for a pair of telephone lines and similar data communication channels. This invention relates to circuits for filtering noise and transient voltage signals that are larger than the signal.

BACKGROUND OF THE INVENTION Various configurations are utilized to protect telephone and communication equipment from dangerous voltages caused by lightning strikes and power surges. However, conventional configurations only serve to clamp voltage transients to a selected rated potential above the ringing signal of a typical communication system. A typical ringing signal has an AC peak of about 170 volts, with a frequency in the range of 15 to 30 Hz, and for conventional configurations, the rated clamp voltage is typically about 200 volts. Therefore, such a configuration cannot filter out noise or transient voltage signals that occur below this standard lamp voltage.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an overvoltage protection arrangement that overcomes many of the drawbacks of known systems.

Another object of the invention is to provide an improved overvoltage protection device for connecting subscriber stations to telephone systems or other similar communication sources.

Yet another object of the present invention is to provide an overvoltage protection device that operates to protect communication equipment from dangerous voltages due to lightning strikes or power surges.

Yet another object of the present invention is to provide an overvoltage protection device that suppresses or minimizes noise and transient voltage signals that occur below the specified potential of ringing signals sent by telephone or other communication systems.

SUMMARY OF THE INVENTION In accordance with a preferred embodiment of the present invention, a first
and an overvoltage protection arrangement for connecting the subscriber station to the second conductor. The overvoltage protection arrangement is connected between the first conductor and the second conductor to conduct current at a first breakdown voltage and to block current when below the first breakdown voltage. a first means for conducting current at a second breakdown voltage and blocking current when below the second breakdown voltage;
said first means for filtering voltage signals on said first and second conductors in response to said second means conducting current;
and means connected in series between the means and the second means.

According to an important feature of the present invention, the overvoltage protection arrangement serves to suppress noise and transient voltage signals occurring above the data signal, and the transient voltage signal does not need to exceed the ringing signal for operation.

BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.

In FIG. 1, an overvoltage protection circuit constructed in accordance with the present invention is indicated generally by the reference numeral 10.

This overvoltage protection circuit 10 has, at its input.

It is connected to a telephone system or other similar communications source via TIP and RING conductors. A subscriber station, such as a keyset, modem or dedicated branch switch, is connected to circuit 1.
Connected to the output of 0. The overvoltage protection circuit 10 comprises a gas discharge tube 12 or similar device, which
It is connected between the conducting wire and the RING conducting wire, and is also connected to the ground potential at the ground line G. TIP
A resistor 14 is connected in series with the line and RI
A resistor 16 is connected in series with the NG line.

A transient voltage suppressor 18 is connected between the resistor 14 and ground potential.
A similar transient voltage suppressor 20 is also connected between the resistor 16 and the ground potential. Gas discharge tube 12 clamps voltage transients appearing on both the TIP and RING conductors to ground line G and provides a high impedance to ground line G when high transient voltages are not present. As the gas discharge tube 12,
A three-electrode gas discharge tube device 1 is used, for example, a Milli-Triac part number MLTO090 manufactured by Reynolds Industries with a rated breakdown voltage of 600V. The transient voltage suppressors 18 and 20 are arranged such that the potential applied to the TIP or RING line is set to a predetermined breakdown potential, e.g., 200V.
Conduction occurs when the voltage exceeds . Gas discharge tube 12, resistor 14
and 16. Transient voltage suppressors 18 and 20 are shown enclosed within a dotted line in the accompanying drawings and serve to protect communications equipment from dangerous voltages caused by lightning strikes and power surges. , a type of transient voltage suppressor manufactured and sold by Square D Company of General Semiconductor Industries, Inc. under the registered trademark rTransZorbJ (part number SCM170C; reverse standoff voltage that does not conduct at 170V and break in the range 189-231V). It is convenient to use a down voltage rated).

Between the junction 26 of the series-connected resistor 14 and the transient voltage suppressor 18 and the ground line G.

A capacitor 22 and a transient voltage suppressor 24 are connected in series. Similarly, a capacitor 28 and a transient voltage suppressor 30 are connected between the ground line G and the junction point 32 of the resistor 16 and transient voltage suppressor 20 connected in series. It is convenient to use as suppressors 24 and 30 devices similar to those used as transient voltage suppressors 18 and 20, but with lower breakdown voltage ratings, e.g., devices with breakdown voltage ratings of 6.4-7V. For example, part number SCM5.0C has a breakdown voltage rating in the range of 11.1-13.6V. Transient voltage suppressors 24 and 30 are TIP and R
a specified potential of the data signal carried by the ING conductor;
For example, it is selected to have a breakdown voltage rating higher than 5V or 10V.

In operation, a resistor 14 and a capacitor 2 are connected in series.
2 and transient voltage suppressor 24 suppress noise and transient voltage signals that are greater than the breakdown voltage of suppressor 24 and have a specified threshold rate of change. This prescribed threshold rate of change or frequency response is determined by the component values of resistor 14 and capacitor 22.

For example, capacitors 22 and 28 may be between 0.1 and 1μ.
resistors 14 and 16 are in the range of 10 to 30
Selected within the range of Ω. During normal operation, the data signal is otherwise unaffected by the frequency response of the filter consisting of resistor 14 and capacitor 22 or by the current blocking action of suppressor 24. Similarly, resistor 16, capacitor 28, and transient voltage suppressor 30 clamp noise and transient voltage signals occurring on the RING line.

In FIG. 2, another embodiment of an overvoltage protection circuit according to the present invention is indicated generally by the reference numeral 10'. Components similar to those in FIG. 1 are given the same reference numerals. The protection circuit 10' comprises a star configuration of unipolar transient voltage suppressors 34, 36 and 38. These transient voltage suppressors 34.
36 and 38 are the bidirectional suppressors 24 and 3o described above.
performs the same function as This single-pole transient voltage suppressor is manufactured by General Semiconductor Industries, Inc. under the registered trademark TransZorb J and has the device model SCM5. It is sold as OA or SCM170A.

In both protection circuits 10 and 10', the gas discharge tube 12 can be eliminated. Furthermore, both protection circuits can be provided without bidirectional transient voltage suppressors 18 and 20. Gas discharge tube 12 and suppressors 18 and 2
It should be appreciated that even with the removal of zeros, protection circuits 10 and 10' act to suppress noise and transient voltage signals that are larger than the data signal.

Although the invention has been described in detail with reference to preferred embodiments thereof, many changes and modifications may be made without departing from the invention. It is therefore intended that all such changes and modifications be included within the scope of the claims of the present invention.

[Brief explanation of the drawing]

FIG. 1 is an electrical circuit diagram showing an overvoltage protection device constructed based on the principles of the present invention, and FIG. 2 is an electrical circuit diagram showing another overvoltage protection device constructed based on the principles of the present invention. It is. 10.10'...Overvoltage protection circuit 12...Gas discharge tube 14.16...Resistor 18.20.24.30...Transient voltage suppressor 22.2
8... Capacitor Date of Heisei 1 1 Indication of the case 1986 Patent Application No. 99303 2 Name of the invention Overvoltage protection device for telephone and data 3 Name of the person making the amendment Relationship to the case 4 Representation Man

Claims (11)

[Claims] (1) An overvoltage protection circuit for a pair of telephone lines and similar data communication channels, comprising first voltage clamping means for clamping a voltage signal on said line to a first predetermined potential; second voltage clamping means for clamping the voltage signal to a second predetermined potential; and a filter responsive to the second voltage clamping means for filtering the voltage signal greater than the second predetermined potential. An overvoltage protection circuit comprising means. (2) The overvoltage protection circuit according to claim 1, wherein the first voltage clamping means includes a gas discharge tube. (3) The overvoltage protection circuit according to claim 2, further comprising a pair of bidirectional semiconductor transient voltage suppressors connected across the gas discharge tube. (4) The first predetermined potential is higher than the specified potential of the ringing signal carried by the line.
Overvoltage protection circuit described in . 5. The overvoltage protection circuit of claim 1, wherein said second predetermined potential is higher than voice and data signals carried by said line. (6) The voltage protection circuit according to claim 1, wherein the second voltage clamping means includes a pair of bidirectional semiconductor transient voltage suppression devices. 7. The overvoltage protection circuit of claim 1, wherein said second voltage clamping means comprises a star configuration of three unipolar semiconductor transient voltage suppressors. (8) The transient voltage protection circuit of claim 1, wherein said filter means operates to filter said voltage signal above a predetermined frequency. (9) The overvoltage protection circuit according to claim 1, wherein the predetermined frequency is higher than a frequency range of a prescribed ringing signal. (10) The overvoltage protection circuit according to claim 1, wherein the filter means includes a resistor and a capacitor connected in series between the first voltage clamp means and the second voltage clamp means. (11) An overvoltage protection device for connecting a subscriber station to first and second conductors connected to a telephone system or other similar communications source, which conducts current when at a first breakdown voltage; a first means connected between the first conductor and the second conductor to block current flow when the voltage is below the first breakdown voltage; and to conduct current flow when the second breakdown voltage is lower than the first breakdown voltage; a second means for blocking the current when less than the second breakdown voltage; and a second means for filtering the voltage signal on the first and second conductors in response to the second means conducting the current. and means connected in series between the first means and the second means.