JPS593914B2 - Overcurrent automatic cut-off method for telephone exchange subscriber circuits - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent outflow prevention circuit for a subscriber circuit of a telephone exchange.

In the subscriber circuit of an electronic telephone exchange, a protection circuit such as an overcurrent cutoff circuit is provided in case an overcurrent flows out due to a subscriber line failure or the like.

FIG. 1 is a telephone current supply system diagram of a subscriber circuit of a telephone exchange.

In FIG. 1, 1 is a telephone exchange subscriber circuit, 2 is a telephone current supply circuit, 3 is a voice transmission transformer, 4 is a DC interrupting capacitor, 5 is a subscriber line, and 6 is a subscriber telephone.

38 and 39 are connection terminals for subscriber lines.

If the subscriber removes the handset (not shown) from the telephone 6,
A hook switch (not shown) in the telephone 6 is closed, and telephone current is supplied from the telephone current supply circuit 2. However, if a fault occurs in the subscriber line 5, for example a ground fault indicated by a dotted line in the figure, an overcurrent may flow out and the current supply circuit 2 may burn out. For this reason, protection measures are taken for the current supply circuit 2. Figure 2 is an example of this.

In FIG. 2, reference numerals 10, 11, 12, and 13 are transistors for switching the power supply, and reference numerals 8 and 9 are transistors forming a circuit for driving the current supply transistors 10 to 13.

14 is a transistor for detecting excessive current outflow, 15, 1
6 is a diode, 17 is a light emitting diode that displays excessive current outflow, T, 18 is a NAND gate, 19 is a flip-flop for accumulating excessive current outflow information, 20 is a capacitor, and the impedance seen from terminals 38 and 39 is expressed as an audio signal. This is for feedback to increase the frequency band.

21 to 35, 41, and 42 are resistors, 38 and 39 are current supply terminals, and 40 is an alarm sending terminal, which sends an excessive current outflow alarm to the exchange control system.

Further, 36 is an input terminal for instructing current supply from the exchange control system, and 3T is an input terminal for similarly resetting the flip-flop 19. When an instruction to supply current is given to the terminal 36 from the exchange control system, the current supply transistors 10, 11, 12, and 13 operate via the NAND gate 7, transistor 8, and J9, and the potential of the station battery VBB (→ However, the ground potential is also sent to the terminal 38. At this time, if an excessive current flows to the terminals 38 and 39, the transistor 14 detects this and the flip-flop 19
is set, and its output Q is sent to the NAND gate T, which turns off the current supply transistors 10, 11, 12, and 13, and stops the current supply. Also flipflop 19
The other output Q passes through the NAND gate 18 and sends an alarm to the terminal 40, while the light emitting diode 17 indicates a visible alarm. With this output from terminal 40, the exchange control system releases the current supply instruction given to terminal 36. After repairing the fault, in order to restore the current supply state, the switch control system issues an instruction to the terminal 37 to restore the flip-flop 19, opens the NAND gate 7, turns on the transistors 8 and 9, and connects the terminal 36 again. Give a current supply instruction and restart the current supply.

In the current supply circuit described above, when the current supply is stopped, excessive current no longer flows out and a fault alarm is sent out. However, once a fault is detected and the current supply is stopped, a separate fault recovery is performed. There is a disadvantage in that it requires a procedure to detect this, input fault recovery to the exchange control system, and cancel the current supply stoppage.

In addition, in order to protect the communication current supply transistors in the subscriber circuit of the telephone exchange, the abnormal current that flows out in the event of a subscriber line fault, etc. should be removed when there is a ground fault on the terminal side (line A) to which the station power supply is connected. Since this current value is the maximum value, the capacity of the transistor for supplying the communication current is approximately determined by this current value, and special heat dissipation measures are required to prevent heat generation due to this abnormal current.
As described above, in the conventional current supply circuit, in order to prevent the outflow of overcurrent in the event of a ground fault, a separate procedure is required to cancel the stoppage of the current supply.

Furthermore, since this method monitors the current flowing in one line (line A), the level at which ground faults are detected differs depending on the line length of the subscriber line. For this reason, if the detection threshold is set to a level that can detect a ground fault in a short-distance subscriber line that carries a relatively large current even in normal conditions, that threshold may not be able to detect a ground fault in a long-distance subscriber line. This may lead to potential ground faults and unnecessary power consumption. The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, protect the circuit from destruction in the event of a ground fault, prevent wasteful power consumption, and provide an automatic overcurrent system that can automatically resume normal operation upon recovery from a ground fault fault. The purpose is to provide a blocking method.

That is, in the present invention, when a ground fault occurs in the subscriber line, a difference occurs between the current flowing through line A and the current flowing through line B. This difference is detected by a comparator, and the output is This reduces the communication current and prevents its destruction, and when the ground fault is recovered, the comparator detects that the difference between the A line current and the B line current disappears and cancels the reduction in the communication current. It is characterized by this.

The present invention will be explained in detail below with reference to the drawings.

FIG. 3 is an embodiment of an electronic communication current supply circuit using an automatic overcurrent cutoff system according to the present invention. In FIG. 3, the same parts as in FIGS. 1 and 2 are designated by the same reference numerals.

In FIG. 3, 50 and 51 are diode portions of the photocoupler, and 50' and 51' are transistor portions thereof.

43 and 44 are resistors for taking out the output of the photocoupler, 47 is a level comparator, and 45 and 46 are resistors, which are used to send out a predetermined current when the transistors 11 and 13 are cut off.

Also, 48 and 49 are diodes and photocouplers 50 and 51
It protects the In FIG. 1, if the subscriber line connected to the terminal 39 on the side to which the local power source is connected experiences a ground fault as indicated by the dotted line in FIG. 1, an excessive current flows through the transistor 13 in FIG. If there is a large ground fault current, there is a risk of destruction.

At this time, the current passing through the photocoupler 51 is larger than that passing through the photocoupler 50, so a difference occurs between the outputs of the photocoupler transistor sections 5' and 512, which is detected by the level comparator 47. Outputs to terminal 40 to give an alarm, and also outputs to NAND gate 7
turns off transistors 8, 9 and thus current supply transistors 10, 11 and 12, 13.
is turned off to stop the current supply. Note that the resistance is 45,4
6, a small amount of current is supplied regardless of this cut-off operation, so the output of the level comparator 47 does not disappear until the ground fault is recovered. Thus, the cut-off operation is maintained. When the fault recovery work is performed and the line returns to normal, the difference in the outputs of the photocoupler transistors 5', 51/ of both lines disappears, and the level comparator 4
Since the output of transistor 7 disappears, transistors 8 and 9 are turned on, and current supply is automatically restarted. In the above embodiments, the subscriber circuit has been described, but it is clear that the circuit for supplying reciprocating direct current to other pairs of lines can be similarly applied to a trunk.

As described above, according to the present invention, since a ground fault is detected based on the difference between the A line current and the B line current, a threshold value can be set regardless of the line length, and detection accuracy can be improved.

This prevents potential ground faults and reduces wasteful power consumption. Furthermore, since the communication current is reduced in the event of a ground fault and the differential current is subsequently monitored, it is possible to prevent overcurrent from flowing out and to perform automatic recovery when a fault is recovered, which is convenient for maintenance.

[Brief explanation of drawings]

Figure 1 is a telephone current supply system diagram of the telephone exchange subscriber circuit.
FIG. 2 shows an example of a conventional communication current supply circuit, and FIG. 3 shows an embodiment of an electronic communication current supply circuit using an automatic overcurrent cutoff system according to the present invention. 1... Telephone exchange subscriber circuit, 2...
Call current supply circuit, 3... Voice transmission transformer, 4... DC cutoff capacitor, 5...
・Subscriber line, 6...Subscriber telephone, 8-13・
...Transistor, 7...NAND gate, 20...Capacitor, 21-31, 41-4
6... Resistance, 36... Current supply instruction terminal, 38, 39... Current supply terminal, 40...
... Fault display terminal, 47 ... Lebel comparator, 4
8, 49... Diode, 50, 51...
...Photocoupler diode section, 50', 5"...
...Photocoupler transistor section.

Claims (1)

[Claims] 1. In an electronic call current supply circuit of a telephone exchange, there is a means for monitoring the current flowing through each of the subscriber lines making up the pair, a comparison means that receives the output of the monitoring means as input, and a means for monitoring the current flowing through each subscriber line. means for reducing the communication current by outputting a predetermined value or more from the comparison means according to the difference between the two;
and means for canceling the reduction in the communication current when the output of the comparison means falls below a certain value in accordance with the difference between the respective currents. Blocking method.