JPH0252920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for protecting against lightning surges and the like in a concentrator of a digital exchange.

In conventional line concentrators using mechanical contacts, subscriber lines and various control devices were electrically insulated, so they were not affected by lightning surges induced in subscriber lines. However, in the concentrators of digital exchanges that have appeared due to the recent advances in LSI technology, the above-mentioned electrical insulation cannot be ensured. Therefore, it has become essential for the line concentrator to introduce some kind of surge protection method. A perfect solution would be to connect the subscriber line and the subscriber circuit provided individually for each subscriber to the line concentrator using an optical coupling element, but each of these elements has its own drawbacks in terms of response speed, reliability, and economic efficiency. have.

An object of the present invention is to combine a subscriber circuit and a line concentrator into a unit in a line concentrator for a digital exchange, and to protect the line concentrator from surge currents with a simple configuration.

In order to achieve the above object, the present invention takes economic efficiency into consideration and divides the line concentrator into two types of units: N subscriber circuits provided for each subscriber and one circuit provided for each of the N circuits. A first unit is composed of an interface circuit, and a second unit is connected to m first units and performs line concentration and multiplexing for (N×m=)M subscribers. In order to prevent damage caused by surge intrusion from reaching the second unit, a power supply/earth system is provided separately for the first and second units, and both units are connected by a DC balanced transmission circuit and a common mode chain. This is what I did.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a line concentrator; 1 is the first unit; 2 is a subscriber circuit for the N subscribers; 3 is the interface circuit provided for the circuit;
Numerals 4, 5, 6, 7, and 8 are various power supplies and ground used in the first unit, and 4 is -48V (the first power supply supplied to the terminal via the subscriber line). 9
is from the first power supply to the second power supply (analog +
5V), a third power supply (-5V for analog), and a first power supply section that creates a fourth power supply (digital +5V);
5 to 7 are the second to fourth power supplies, and 8 is the first ground used by the first unit. 10 is the second unit; 11 is a second power supply unit that generates the fifth power supply (digital +5V) from the 4 to 5 power supply unit;
2 is the second ground used by the second unit. The main body 14 of the second unit 13 is a fifth power source. That is, the first and second types of units are connected to two different types of power supply/ground systems. Reference numeral 15 indicates a signal line transmitted and received between both units.

Next, regarding the configuration in Figure 1, M=2048, N=
128, m=16 will be explained as an example. The first unit consists of N=128 subscriber circuits and time-division multiplexes PCM data for each 16 subscribers to form eight highways. The interface circuit 3 further multiplexes these eight highways to form a high group highway, which is connected to the second unit. That is, the second unit is a line concentrator that further time division multiplexes the 16 high group highways. These interface circuits and the second unit handle PCM data, and are each equipped with a pair of up and down highways and a high group highway. In addition, in FIG. 1, for simplicity, only one first unit is shown, and the up and down highway is shown as one for convenience.

Further, 19 and 20 are a pair of subscriber lines, which connect the subscriber telephone and the subscriber circuit. In addition, the subscriber line is connected to the subscriber circuit via a surge absorption circuit installed in the main distribution frame (MDF) installed in the station building. Further, a power source 4 is also supplied from the station to the first unit and the second unit, and a first ground 8 for the power supply and a second ground 12 for the second unit are each provided independently.

Furthermore, a first power supply section 9 dedicated to the first unit is provided.
and a second power supply section 11 dedicated to the second unit. Both the first power supply section and the second power supply section generate voltages of +5V and -5V from DC -48V, and are constructed of transformers as is well known. Therefore, it is a dedicated power supply unit that is electrically isolated from the power supply from the station building. Therefore, as described above, the first and second units are each connected to two types of power supply and ground systems.

FIG. 2 is an inter-unit connection circuit showing details of the connection relationship between the interface circuit 3, second unit 10, and signal line 15 in FIG. In the figure, 15a and 15b are a pair of signal lines, and 16 is an unbalanced line.
Balanced conversion circuit, 17 is a common mode chain, 1
Reference numeral 8 indicates a balanced/unbalanced conversion circuit, and 21 and 22 indicate matching resistors.

Surge currents that enter the subscriber line are absorbed by the surge absorption circuit provided in the MDF described above. However, the surge absorption circuit provided in MDF is generally intended to absorb a large amount of surge energy, and is large in size and has a slow response speed. Therefore, the steep portion of the dielectric lightning enters the subscriber circuit as residual energy through the subscriber line.

Of course, the subscriber circuit is also provided with a surge absorption circuit, and the surge current absorbed by this surge absorption circuit flows to the first ground.

In this way, the first ground can absorb surge currents, but excessive surge energy can further infiltrate the concentrator through circuit elements inside the subscriber circuit, so this is prevented. There is a need to.

The connection circuit of the interface circuit 3, the second unit 10, and the pair of signal lines 15a and 15b shown in FIG. 2 corresponds to the above-mentioned high group highway, and this high group highway will be described in detail below. As explained, it is composed of a DC balanced transmission circuit.

As shown in Figure 2, the interface circuit 3
An unbalanced/balanced conversion circuit 16 is provided on the transmitting side of the line concentrator 10 (second unit), and a balanced/unbalanced conversion circuit 18 is provided on the receiving side of the line concentrator 10 (second unit). Connect with 15a and 15b. Unbalanced/balanced conversion circuit 16, pair of signal lines 15a, 15b, and balanced/unbalanced conversion circuit 1
8 constitute a DC balanced transmission circuit, and DC balanced transmission is performed between the interface circuit 3 and the line concentrator 10.

Due to electromagnetic coupling or capacitive coupling between the pair of signal lines 15a, 15b and other cables (power cables, etc.), the pair of signal lines 15a, 15b
External noise (AC induction) is induced. However, DC balanced transmission is performed in the pair of signal lines 15a, 15b, and this external noise is superimposed on each of the pair of signal lines 15a, 15b in phase. Since the balanced/unbalanced conversion circuit 18 performs balanced/unbalanced conversion by outputting a differential signal between the signal lines 15a and 15b, this in-phase component that becomes external noise is canceled out.

Here, if a steep part of the induced lightning surge enters the subscriber circuit via the subscriber line, the ground potential 8 will fluctuate due to this lightning surge. This effect is
Unbalanced/balanced conversion circuit 16, pair of signal lines 15
a, 15b to the concentrator 10, which is the second unit, and the ground potential 1 of the concentrator 10 is
2 will fluctuate.

The manner in which the ground potential changes will be explained in more detail. Here, the potential of ground 8 is Vg, and the potential of ground 12 is
The potential of the signal line 15a is V1, and the potential of the signal line 15b is V2.

The unbalanced/balanced conversion circuit 16 connects a signal Va having the same phase as the input signal V and a signal Vb having the opposite phase to the ground 8.
signal lines 15a and 15b with reference to the potential Vg of
Send to. Therefore, a voltage of Va=V1-Vg is sent to the signal line 15a, and the signal line 15a is
For b, a voltage of Vb=V2-Vg is sent out.

Signal line 15a on the balanced/unbalanced conversion circuit 18 side
The potentials of and 15b are V1 and V2, respectively, the same as the potential on the unbalanced/balanced conversion circuit 16 side. The balanced/unbalanced conversion circuit 18 is a differential amplifier that operates with the ground potential Ve as a reference, and its non-inverting input receives a voltage of V′a=V1−Ve, and its inverting input receives a voltage of V′b= A voltage of V2−Ve is input. and,
A differential signal V′a−V′b is output.

Here, as mentioned above, Va=V1−Vg and Vb
= V2−Vg, so V′a and V′b are expressed as follows.

V′a=V1−Ve=Va+(Vg−Ve)…(1) V′b=V2−Ve=Vb+(Vg−Ve)…(2) Here, as mentioned above, interface circuit 3 and concentrator The device 10 is provided with a power supply system and a ground system separate from each other. That is, the interface circuit 3 has a power supply 9 and a ground 8, and a concentrator 10.
has a power source 11 and a ground 12, which are separated from each other. Therefore, as can be seen from equations (1) and (2), under normal conditions where lightning surges do not flow into the ground 8, Vg = Ve = 0, and the voltage applied to the transmitting side (unbalanced/balanced conversion circuit 16) The voltages Va and Vb are equal to the voltages V'a and V'b applied to the receiving side (balanced/unbalanced conversion circuit 18), and the circuit operates normally.

However, when a lightning surge flows to the ground 8, the potential Vg of the ground 8 changes greatly, but the potential Ve of the ground 12 does not change and remains at 0V.
This includes the interface circuit 3 and the line concentrator 10.
This is because the ground and ground are separated. In this case, the voltages Va and Vb applied to the transmitting side (unbalanced/unbalanced conversion circuit 16) are the same as in the normal state, but the voltage applied to the receiving side (balanced/unbalanced conversion circuit 18)
A voltage containing the potential Vg of the ground 8 is applied to V'a and V'b. Due to the surge current, Vg becomes approximately several hundred volts, so a high voltage is applied to the balanced/unbalanced conversion circuit 18, making it impossible to compensate for the subsequent balanced/unbalanced conversion operation. That is, the balance of the balanced/unbalanced conversion circuit 18 will be disrupted, and the ability to cancel out the common mode component will be degraded.

In order to eliminate the influence of this variation in ground potential Vg, a common mode yoke 17 is connected to the output of the unbalanced/balanced conversion circuit 16. Due to the electromagnetic energy conservation effect of the common mote yoke 17, the steep part of the induced lightning surge that has entered the subscriber circuit is completely absorbed, and the balanced/unbalanced conversion circuit 18 on the concentrator circuit 10 side has a ground potential. Vg
fluctuations are not transmitted.

That is, when a surge appears in the output of unit 16, it is absorbed by the chain coil of unit 17 and the surge energy is reduced, thereby making it possible to improve the surge resistance between both units. Of course, the value of the inductance of the chiyoke must be selected so as not to affect the original signal transmission. Also, as the inductance value increases, the surge resistance between the aforementioned units improves.

Figure 2 explains the connection format for the signal line when the signal is sent from the first unit and received by the second unit. This can also be handled in the same way as in FIG.

According to the present invention, it is economically possible to protect against surge currents and voltages that have entered the subscriber circuit unit, and also to protect against surge currents and voltages generated in the subscriber circuit that have entered the concentrator multiplexing unit. Become.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a power supply/grounding system in a line concentrator, and FIG. 2 is a diagram illustrating a signal line connection format between units. 1...First unit, 2...Subscriber circuit for N subscribers, 3...Interface circuit, 4-8...
...Various power supplies and ground, 9...First power supply section, 1
0...Second unit that performs line multiplexing, 1
1...Second power supply section, 12...Second ground, 1
3...Second unit main body, 16...Unbalanced balance conversion circuit, 17...Common mode chain, 1
8...Balanced unbalanced conversion circuit, 19, 20... Matching resistor.

Claims (1)

[Scope of Claims] 1. In a surge protection system that protects against intrusion of surge voltage and surge current induced in a subscriber line, N subscriber circuits (N: an integer of 2 or more) installed corresponding to the subscriber line are provided. Then, one interface circuit provided for the N subscriber circuits is considered to be one unit, and a subscriber circuit unit group is formed from the m units (m is an integer of 2 or more), and the m subscribers' circuits are A line concentration/multiplexing unit that interfaces with the subscriber circuit unit is provided, and the same first power supply and
The line concentrator and multiplex unit is configured with a second power source and ground system different from the power source and ground, and the subscriber circuit unit has an unbalanced/balanced conversion circuit and the line concentrator and multiplex unit has an unbalanced and balanced converter circuit. - Has an unbalanced conversion circuit, or has an unbalanced/balanced conversion circuit in the line concentrator/multiplexing unit and a balanced/unbalanced conversion circuit in the subscriber circuit unit, and connects a pair of signal lines between the conversion circuits of both units. A surge protection method characterized by connection with a common mode choke.