JPH02215235A - Protection circuit for communication equipment - Google Patents

Abstract

PURPOSE:To protect an internal circuit against a high voltage such as lightning by connecting a protective element having a discharge start voltage slightly higher than a signal voltage generated between terminals of windings of a transformer connecting to a communication line side. CONSTITUTION:When in-phase high voltage invades between connecting terminals 15, 16 with a communication line via a communication line, ground voltage protective elements 4, 5 start discharging. When there is any 'dispersion' in the discharge start voltage of the elements 4, 5, a high voltage is generated between the terminals 15 and 16. The line voltage protective element 3 starts discharge by the high voltage, but the line voltage does not decrease below various voltages in existence on the communication line. In this case, a high voltage exist among terminals 8-1 to 8-4 of a transformer 8. However, since the elements 1, 2 exist, a high voltage is generated in a DC interruption high breakdown capacitor 9, only a low voltage is generated among the terminals 8-1 to 8-2 and terminals 8-3 to 8-4. Thus, only a low voltage is generated between terminals 8-5 to 8-6.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a protection circuit against surge voltages such as those caused by lightning intruding into communication equipment from communication lines, and particularly relates to a circuit for protecting against surge voltages such as those caused by lightning that intrude into communication equipment from communication lines. This invention relates to a protection circuit for communication equipment against surge voltages from balanced communication lines.

[Conventional technology]

An example of a conventional protection circuit for communication equipment is shown in FIG. 2 and will be described.

In conventional communication equipment, protection is provided against surge voltages that enter through communication lines using a circuit configuration as shown in FIG.

In Figure 2, 4.5 is a vertical voltage protection element inserted between each communication line and the ground, 3 is a horizontal voltage protection element connected between the communication lines, and 6 and 7 are electronic circuits in communication equipment. It is a protective element.

8 is a transformer, 8-1, 8-2...8-6 is a terminal of transformer 8, 9 is a high-voltage capacitor for DC cutoff,
10 is a transmission circuit of the electronic circuit, 11 is a reception circuit of the electronic circuit, 12 is a power supply voltage terminal of the electronic circuit, 13 is a power supply ground of the electronic circuit, 14 is a ground for lightning protection, and 15.16 is a connection point terminal with a communication line. , 17 is an input point for a transmitted signal, and 18 is an output point for a received signal.

In the case of the circuit configuration shown in FIG. 2, if the signal voltage passing through the communication line is several volts or less, it is possible to lower the discharge starting voltage of the protective elements 4.5 and 3 for vertical voltage and horizontal voltage. can. Therefore, even if a high voltage is applied to the communication line, the voltage transmitted to the electronic circuit side via the transformer 8 is low, and the possibility of breaking the electronic circuit components is extremely low, which is a dangerous problem.

However, in actual communication lines, not only information signals but also direct current or low-frequency voltages are passed between signal lines or between the signal line and the ground for power supply, ceiling current, etc., and for testing cables and communication equipment. Therefore, it is necessary to insert vertical voltage protection elements 4, 5, and 3 into the communication line, which do not react to these direct current or low frequency voltages.

[Problem to be solved by the invention]

In the conventional protection circuit for communication equipment described above, when a high voltage is applied to the communication line, a voltage several times higher than the power supply voltage of several tens of volts is applied to the electronic circuit via the transformer, and the protective element is applied to the electronic circuit. However, there was a problem in that large currents always flowed through the power source, increasing the possibility of damaging electronic circuit components.

[Means to solve the problem]

The protection circuit for communication equipment of the present invention has a voltage slightly lower than the signal voltage generated between the terminals of each winding of a transformer connected to the communication line side of a communication equipment that performs balanced transmission using a transformer. By connecting a protective element with a high firing voltage, the electronic circuit inside the communication device is protected from the high voltage that enters from the communication line.

[Effect]

In the present invention, electronic circuits inside communication equipment are protected from high voltages that enter from communication lines.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

FIG. 1 is a circuit diagram showing an embodiment of a protection circuit for communication equipment according to the present invention.

In Fig. 1, the same numbers as in Fig. 2 indicate corresponding parts, and 1 and 2 are protective elements (transverse voltage protective These are for each winding of the transformer 8 connected to the communication line side of a communication device that performs balanced transmission using the transformer 8, that is, the terminals 8-1, 8-2 of the transformer 8.
and terminals 8-3 and 8-4 of the transformer 8, respectively.

Next, the operation of the embodiment shown in FIG. 1 will be explained. First, in the circuit configuration shown in FIG. The element 3 has a discharge starting voltage and a discharge sustaining voltage that exceed various currents or low frequency voltages existing on the communication line. The DC interrupting high voltage capacitor 9 has a voltage resistance higher than the discharge starting voltage of the lateral voltage protection element 3.

Next, the connection point terminal 15.1 with the communication line is connected to the communication line via the communication line.
Let us consider the case where a high voltage of the same phase enters into 6. In this case, the vertical voltage protection elements 4 and 5 start discharging.

If there is a "discrepancy" in the discharge starting voltage of the vertical voltage protective elements 4 and 5, the connection point terminal 15 with the communication line.
A high voltage is generated between 16 and 16. This high voltage causes the lateral voltage protection element 3 to start discharging, but the voltage cannot be lowered below the various voltages present on the communication line. At this time, a high voltage is generated between terminals 8-1 to B-4 of the transformer 8, but due to the presence of the lateral voltage protection elements 1 and 2, a high voltage is generated in the high voltage withstand voltage capacitor 9 for DC interruption. , terminal 8- of transformer 8
Only a low voltage is generated between questions 1 to 8-2 and terminals 8-3 and 8-4. Therefore, terminals 8-5 of transformer 8
The voltage generated between 8-6 and 8-6 is determined by the turns ratio of the transformer, the voltage between terminals 8-1 and B-2 and between 8-3 and 8-4, and the frequency characteristics of the transformer. A slightly higher voltage will only occur for a very short time. Therefore, only a small current flows through the electronic circuit protection element 6.7, and the possibility of damaging the electronic circuit components is extremely low.Similarly, the connection point terminal 15.16 with the 1 communication line Similarly, when a high voltage enters the lateral voltage protection element 3-. −
A high voltage is generated across the high-voltage capacitor 9 for DC interruption, but because of the lateral voltage protection elements 1 and 2, the voltage between the terminals 8-1 and 8-2 of the transformer 8 is high.

High voltages tend to occur between 8-3 and 8-4 and between 8-5 and 8-6. Therefore, the possibility of damaging electronic circuit components is reduced.

〔Effect of the invention〕

As explained above, the present invention has the advantage that the signal voltage generated between each winding of a transformer connected to the communication line side of a communication device that performs balanced transmission using a transformer is slightly higher than the signal voltage generated between the terminals of these windings. By connecting a wild goose protection element having a discharge starting voltage, there is an effect that the internal circuit of the communication device can be protected against high voltages such as those caused by lightning that enter the communication device from the communication line.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a protection circuit for a communication device according to the present invention, and FIG. 2 is a circuit diagram showing an example of a conventional protection circuit for a communication device. 1-3・φ・・Protective element for horizontal voltage, 4, 5・・・Protective element for vertical voltage, 6, 7・・・・・Protective element for electronic circuit, 8
...Transformer, 9...High voltage withstand capacitor for DC cutoff, 10...Electronic circuit transmission circuit, 11...
Receiving circuit of electronic circuit, 12 life... φ Power supply voltage terminal of electronic circuit, 13... Lightning of electronic circuit, source ground, 14...
... Ground for lightning protection, 15, 16... Connection point terminal with communication line, 17... - Input point of transmission signal, 18...
・Output point of received signal.

Claims (1)

[Claims] For communication equipment that performs balanced transmission using a transformer, a protective element with a discharge starting voltage slightly higher than the signal voltage generated between the terminals of these windings is installed for each winding of the transformer connected to the communication line side. 1. A protection circuit for communication equipment, characterized in that when connected, electronic circuits inside the communication equipment can be protected from high voltage intruding from communication lines.