JPS6135118A - Malfunction voltage protecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement of an abnormal voltage protection circuit in a device for connecting a two-wire line such as a subscriber line or an interoffice trunk line to an exchange.

Subscriber lines that connect telephones, etc. installed in subscriber premises to exchanges, or inter-office trunk lines that connect exchanges,
Two-track lines are no longer widely used.

A DC voltage (for example, -48 volts) from the main power source of an exchange, the positive terminal of which is grounded, is applied to such two-wire line in order to supply communication current to the telephone.

Furthermore, an abnormal voltage that far exceeds the DC voltage may be applied to this type of two-wire line from the outside due to a lightning strike, induction from a power line, or the like. In such a case, it is necessary to provide an abnormal voltage protection means using a voltage limiting element such as a varistor so that the exchanger will not be damaged by the abnormal voltage.

[Conventional technology]

FIG. 3 is a diagram showing an example of a conventional abnormal voltage protection circuit in a digital exchange, and FIG. 4 is a diagram showing an example of the voltage relationship in FIG. 3.

In FIG. 3, the A and B terminals of subscriber circuit 1 are
A telephone set 3 is connected via a two-wire subscriber line 2. In the subscriber circuit 1, a DC potential of -48 volts is applied to one wire (hereinafter referred to as the A line) of the subscriber line 2 from the negative pole of the main power supply 5 whose positive terminal is grounded via the power supply circuit 4a. , and the other line of subscriber line 2 (hereinafter referred to as B
A ground potential is applied to the line (referred to as a line) from the positive electrode of the main power supply 5 via the power supply circuit 4b. In addition, between the A and B# terminals of the subscriber circuit 1 and the earth potential, in order to protect the power supply circuit 4, etc. from abnormal voltages applied to the subscriber line 2 due to lightning strikes, induction from power lines, etc. Harris black a and 6
b is connected. Each varistor 6a and 6b controls the abnormal voltage applied to the subscriber line 2 to a predetermined limiting voltage.
Note that the limiting voltage (1) is set sufficiently higher than 48 volts so as not to limit the DC potential (-48 volts) applied to the A line and the B line during normal operation.

[Problem that the invention seeks to solve]

As is clear from the above explanation, in the conventional abnormal voltage protection circuit, one end of the varistors 6a and 6b are both connected to the ground potential, so the limit voltage v1 is set to the main power supply voltage (48 volts). It needed to be done. Furthermore, when the DC potential applied to the A and B terminals of the subscriber circuit 1 is limited to ±V1, the voltage Vb applied to the power supply circuit 4b is 1 volt, but the voltage Vb applied to the power supply circuit 4a is The voltage ■a is (VI+48) volts, and there is a problem that the voltages Va and vb applied to the power supply circuit 4a and the power supply circuit 4b do not match.

[Means for solving problems]

The problem is that in a device that supplies DC voltage to a two-wire line from a DC power source whose positive terminal is grounded, voltages are generated between each wire of the two-wire line and a potential intermediate between the two poles of the DC power source. This is solved by the invention, which is characterized in that the limiting element is connected.

[Effect]

According to the present invention, if the DC power supply voltage is 48 volts, for example, by connecting a voltage limiting element with a limiting voltage v2 between the DC potential -24 volts and each filament, it is possible to connect each filament and the DC power supply. The voltages applied to all connected circuits will be limited to V2-24 (volts), and there will be no difference in the voltages applied to each circuit.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an abnormal voltage protection circuit according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of the voltage relationship in FIG. 1. Note that the same reference numerals refer to the same objects throughout the plan.

Also in FIG. 1, the subscriber circuit 1 is connected to the feeder circuit 4 from the negative terminal of the main power supply 5 whose positive terminal is grounded to the A line of the subscriber line 2.
A DC potential of -48 volts is applied to the line B through the power supply circuit 4b, and a ground potential is applied to the B line from the positive electrode of the main power supply 5 through the power supply circuit 4b. On the other hand, between the A and B terminals and the DC potential of both poles of the main power supply 5, that is, the DC potential of -24 volts, which is the intermediate value between O port and -48 volts, a control voltage ■2
Varistors 5 a + and 6 b′ having the following values are connected. As shown in Figure 2, the limiting voltage V2 is the DC potential (-48
and O volts) are set sufficiently higher than 24 volts so as not to limit them. As shown in FIG. 2, the varistors 6a' and 6b' convert the abnormal potential applied to the A line and B line of the subscriber line 2 into +(V2-24) volts or -(V2-24) volts.
V2+24) volts. A line is + (V2-24
) volt, the applied voltage ■a' of the power supply circuit 4a becomes (V2+24>volts, and the A line is -
When limited to (V2+24) volts, the applied voltage y a l of the power supply circuit 4a becomes (2-24) volts. On the other hand, when the B line is limited to +(V2-24) volts, the applied voltage vb' of the power supply circuit 4b is (V2-24)
) volts, and when the B line is limited to -(V2+24) volts, the applied voltage vb' of the power supply circuit 4b becomes (V2+24) volts.

As is clear from the above description, according to this embodiment, by connecting one end of the varistors 6a1 and 5b1 to a DC potential of -24 volts, C17.2. Ta 5 a
The limiting voltage (2) of l and 6b' can be set to 24 volts. Further, the abnormal potentials applied to the A line and the B line are both limited to +(V 2 = 24) volts or -(v2+24) volts, and the applied voltages Va' and ■b' of the power supply circuits 4a and 4b are (V2 ±24)
bolts, and the limit is much lower than before.

Note that FIGS. 1 and 2 are merely examples of the present invention, and for example, the DC potential to which the varistors 6 al and 65° are connected is not limited to 124 volts,
Even if it is set to any DC potential between the two poles of the main power supply 5 (0 port and -48 volts), the effects of the present invention will not change.

Further, the voltage of the main power source 5 is not limited to 48 volts, and many other modifications may be considered, but the effects of the present invention will not change in any case. Also, the subscriber circuit 1 is the power supply circuit 4
The present invention is not limited to connecting a and 4b to the A and B lines, and many other modifications may be considered, but the effects of the present invention will not change in any case. Further, the voltage limiting element is not limited to a varistor, and many other modifications may be considered, but the effects of the present invention will not change in any case.

Furthermore, it goes without saying that the object of the present invention is not limited to subscriber circuits and subscriber lines of digital switchboards.

〔Effect of the invention〕

As described above, according to the present invention, the abnormal voltage applied to the two-wire line is limited to a low level, and it becomes possible to more reliably protect the devices connected to the two-wire line.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an abnormal voltage protection circuit according to an embodiment of the present invention, Fig. 2 is a diagram showing an example of the voltage relationship in Fig. 1, and Fig. 3 is an example of a conventional abnormal voltage protection circuit in a digital exchange. FIG. 4 is a diagram showing an example of the voltage relationship in FIG. 3. In the figure, 1 is a subscriber circuit, 2 is a subscriber line, 3 is a telephone, 4a and 4b are power supply circuits, 5 is a main power supply, 6a,
6b, 6a° and 6b' are varistors, Vl and V2
does not indicate the limiting voltage, and Va, Vb, Va" and vb' indicate the applied voltage.

Claims (1)

[Claims] In a device for supplying DC voltage to a two-wire line from a DC power source whose positive pole is grounded, a voltage limiting element is connected between each wire of the two-wire line and a potential intermediate between the two poles of the DC power source. An abnormal voltage protection circuit characterized by: