JPS6051410A - Abnormal current protecting circuit - Google Patents

Abstract

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

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to an abnormal current protection circuit for a signal transmission line that also serves as a power supply line.

Prior Art and Problems In a PCM signal transmission line into which a repeater is inserted, a direct current serving as a power supply for the repeater flows in a superimposed manner along with the PCM signal.

Figure 1 schematically shows such signal transmission lines, including Il+,
j! 2 is a pair of core wires of the bare cable, R1, 1, RI2
．． ...... are multiple repeaters inserted in the outbound signal line, R21, R22, ...... are multiple repeaters inserted in the return signal line, and ZD is each relay This is a zener diode connected in parallel to the device. Core wire e+, j! 2 has a bipolar signal Sl, 3 as shown in FIG.
2 is placed on it, and a direct current ■ is applied as shown by the arrow +al in the figure. The direct current I causes a constant voltage drop in each zener diode, which causes each relay R11, R1
2°...The power supply voltage is R21, R22,...

The power supply side is equipped with a switch regulator 10 that outputs an adjustable AC voltage, a transformer 12, a rectifier and a filter 14, as shown in Figure 2+a), and a transformer J2 to stabilize the potential of the line (1+, l!2). The middle point of the secondary winding has high resistance 1
(The potentials of the lines 7!1β2 are, for example, +100V and -100V, and if there is no center point grounding, when one line is grounded, the other lines may become ±200V). Also, line β1. Current control is performed by a circuit including a current detection resistor 20, a current deviation detection circuit 16, and a sui-nochi regulator 10 so that the current {circle around (2)} flowing through β2 becomes a constant value. For current control, as shown in FIG. 2 fte1, there is also a method in which a transistor 22 is inserted into the line 121 and the base of the transistor is controlled by the current detection resistor 20 and the current deviation detection circuit 16. In any case, a pair of core wires Nl.

12, current is detected and controlled so that the current is constant.

However, such control has problems when grounding accidents occur due to lightning strikes, errors during construction, and the like.

Figure 2 (mark 24 on BL) indicates two groundings, and since the power supply has positive and negative power supply, when grounding occurs, current 11.I2 flows as shown in the figure.This is on the power supply side. This is because the center point is grounded.The current 11 flows between the control surfaces 1i20 and 16.
．． Since the current is controlled to be constant by 22, there will be no excessive current. However, there is nothing to control this, and if the resistance value of the grounding resistor 18 is low or the voltage is high, the current will become large. There is a fear. Also, in Figure 2 (h) 26
．． 28 is the line β1. It shows a load resistance of β2, but if the ground 24 occurs at the - end of the resistor 26, a large current flows through the line e1.
1 tends to flow, and in the current control as shown in FIG. 2 +al, the DC power supply voltage is lowered, and since the resistor 26 is also included in addition to the resistor 28, there is a problem that the current I2 on the line β2 is excessively reduced.

OBJECT OF THE INVENTION The present invention aims to improve the above-mentioned problems and to prevent overcurrent and undercurrent from flowing in the signal transmission line even in the case of mid-point grounding due to low resistance. be.

Structure of the Invention The present invention provides a protection circuit for abnormal current caused by a ground fault or the like in a signal transmission line consisting of a pair of wires that are supplied with power by a power source whose center point is grounded and are controlled to have a constant current. In addition to one line of the signal transmission line in which the detection resistor is inserted, a current detection resistor is also inserted in the other line, and a switch is inserted in the other line, so that the other line detected by the current detection resistor When the current is abnormal, connect the other wire to the switch.
It is characterized by being cut off by a notch, which will be explained next with reference to Examples.

Embodiments of the Invention FIGS. 3 to 5 show embodiments of the present invention, in which the same parts as in FIGS. 1 and 2 are given the same reference numerals.

30 is a resistor inserted into the line 7!2, which detects the current I2 flowing through the line, like the resistor 20 inserted into the line 7!1.

32 is a current deviation detection circuit that detects whether the current in line 722 detected by resistor 30 is too large or too small. 34 is line 7
! The switch circuit inserted in the switch circuit 2 is turned on and off by the output of the detection circuit 32. A comparator 36 produces an output when the current T+ flowing through the line j21 and the current 2 flowing through the line β2 do not match. Also, 38 is a switch circuit inserted into line 11,
The second switch circuit 34 performs the same type of function as the second switch circuit 34.

To explain the operation, in FIG. 3, when a ground fault 24 occurs and the current I2 in the line I12 becomes larger or smaller than the specified value (=1+), the detector 32 detects this and causes the detection circuit 16 to operate. Then, the switch 34 is opened so that no current flows through the wire 7!2. When an excessive current flows in the line ρ2, the switch 34 of the primitive wire e2 is opened to prevent excessive current from flowing in the primitive wire, but the constant current control circuit of the wire β1 is left as is, that is, the constant current is controlled. Although it is possible to keep the constant current control circuit of the line 7!1 inactive, since normal communication cannot be performed if the line 12 is off. Also, in FIG. 4, a ground fault occurs and the current 11 in line 11 and line 7!
When a difference occurs between the currents 2 and 2, the comparator 36 detects this, stops the function of the detection circuit 16, and opens the switch 34.

Furthermore, in FIG. 4, when a ground fault occurs and a difference occurs between the current 11 in the line 11 and the current I2 in the line 12, the comparator 36 detects this, stops the function of the circuit 16, and switches the switch 34 inserted into the line β2. open. Figure 5 shows the current I2 flowing in line 7!2.
When becomes greater or less than a specified value, the detection circuit 32 opens the switch 34.38 to prevent current from flowing through the line II+, /It. These switches 34°38 are wire 11+
, I12, on the power supply side, in FIGS. 1 and 2, it is inserted at the left end.

It is also possible to insert a transistor 22 or the like in the line p2 in the same way as the line ρ1 and use this to control the current, but it is an abnormality that a ground fault occurs in the transmission line, and it is better to leave the abnormality as it is. It's not good, and when it comes to the royal palace, transistor 22
It is preferable to leave the line in a fully on state because it reduces power loss, but in this state, even if you can limit the current, you cannot increase it, so if the current in your own line decreases, take measures. For reasons such as, the power supply to the repeater of the line becomes insufficient, and the switches 34 and 38 are simpler than the analog current adjustment element 22.
The use of switches 34,38 is suitable.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, it is possible to easily prevent abnormal current from flowing through a pair of signal lines fed by a center-grounded power source due to a ground fault, etc., by a simple means, and the system can significantly improve safety and reliability.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a PCM signal transmission line with a repeater inserted, Fig. 2 is an explanatory diagram of a constant current control section of the transmission line of Fig. 1, and Figs. 3 to 5 are examples of the present invention. FIG. In the drawing, βl and p2 are a pair of wires, 1.0 and 12°14 are their power supplies, 24 is a ground fault, 20 and 30 are current detection resistors, and 34 is a switch. Applicant Fujitsu Limited Representative Patent Attorney Minoru Aoyagi

Claims (1)

[Claims] The current detection resistor for constant current control is inserted in a protection circuit for abnormal current caused by a ground fault, etc. of a signal transmission line consisting of a pair of wires that are supplied with power by a power source whose midpoint is grounded and are subject to constant current control. In addition to one line of the signal transmission line, a current detection resistor is inserted in the other line, and a switch is inserted in the other line, and the current in the other line detected by the current detection resistor is abnormal. An abnormal current protection circuit characterized in that the other line is cut off by the switch when the other line is cut off.