JPS58151165A - Ground fault detection circuit - Google Patents

Abstract

PURPOSE:To detect grounding and to attain one line actuation, by detecting the grounding of a subscriber line with the output of a comparator means in a subscriber circuit feeding power to the subscriber line from the power supply at a station in floating state. CONSTITUTION:As a comparator means, a comparator COMP, a series resistor RC, and a preset reference potential VDET are used. The comparator COMP usea a voltage generated across the resistor RC as one (+) input, and compares a feedback current I1 with the VDET set the other input (-), and when the I1 exceeds a prescribed value and the voltage drop across the RC exceeds the reference voltage, the comparator COMP outputs a signal from an output terminal OUT. Thus, grounding of a subscriber line as a failure, grounding at one line start by grounding one of the subscriber lines with key operation at a telephone set, are detected through the presence of the signal at the OUT.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a ground fault detection circuit, and more particularly to a DC-D
The present invention relates to a circuit for detecting a ground fault in a subscriber line in a subscriber circuit that is equipped with a C converter power supply and supplies power to the subscriber line from a local power supply in a floating state.

Technical background A subscriber circuit system that uses a DC-DC converter in the subscriber line power supply circuit and supplies power to the subscriber line with a floating convergent line that completely separates the station power supply and the subscriber line in terms of direct current is known, for example, as proposed by the Institute of Electronics and Communication Engineers. Technical research report 5E79-107. Hita,
Hamasato: “Various forms of electronic subscriber circuits and their evaluation J 19
As shown on January 22, 1980, the subscriber line has a good ground balance and has the advantage of being easy to protect against line faults such as ground faults.

Prior Art and Problems However, the above-mentioned conventional 70-ting type subscriber line power supply system can maintain a state where calls can be made even if there is a ground fault on the line, so it is possible to avoid wrinkles due to ground faults on the line. It is easy to become latent,
Furthermore, there are drawbacks such as the inability to transmit earth signals and the inability to activate one line from a subscriber terminal device (telephone).

Next, the drawbacks of this conventional method will be explained with reference to FIG. FIG. 1 is a connection diagram of an example of a conventional floating type power supply circuit. In FIG.
C: shows the switch section, transformer, diode, and capacitor that constitute the ff7 inverter C0NV, and also shows the P'mn
A station power supply, FIL is a filter circuit, R1° side terminal, LA
, LB is the subscriber line, RL is the telephone load circuit, RL
A, RLE/d - equivalent load circuits for subscriber lines LA and LB, respectively; RG is an equivalent load circuit that is assumed to be inserted when a ground fault occurs on the line.

DC-DC* y /< -II C0NV turns on and off the power input from the station power supply 1'BB with the switch part SF.
By turning off, the voltage is transferred from the primary winding of the transformer T to the secondary winding, further rectified by the diode D (and capacitor C, and sent to the filter circuit FIL.The ripple is removed by the power expansion filter circuit FIL of Jin). , terminal Jl, B
Power is supplied to the load RL via the. R1 and R are high resistances for applying a negative voltage to the subscriber line in order to prevent electrolytic corrosion of the line.
Connect to El.

The load circuit RO shown by the dotted line connected between the LA line and the earth is connected to the LA I ground fault or the company subscriber terminal equipment (telephone).
It shows the equivalent impedance connected when starting a single line from a wire, and exhibits a resistance in the range of, for example, 0Ω to several kilohms.

According to this power supply method, the subscriber lines LA, LB and the telephone set are placed in a 70-ring (direct current cutoff) stratification with respect to the local power supply, so that the load circuit RG is connected to the subscriber line, for example, the LA line. Even if it is connected to the negative power source - through the high resistance λ1 @ To, only a small current flows through the negative power supply, and the power supply continues and the communication status is maintained. Even if it continues for a long time, it will not cause damage to the power supply circuit, but if one line of the subscriber line (IJ or L
Only one side of the A line is connected to the ground via the load circuit xx, tWk, which causes the balance with the ground to collapse and deteriorates the call quality.On the other hand, since this stratification cannot be detected, it continues for a long time. There was a drawback that the above-mentioned disability employment became latent. Furthermore, in subscriber terminal equipment (telephones), there was a drawback in that it was impossible to start up the exchange by grounding one line of the subscriber line with a key or the like, that is, it was impossible to start up one line.

OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned drawbacks and provides a ground fault detection circuit capable of detecting ground faults in subscriber lines in the above-mentioned 70-ting type power supply system. The purpose is to enable quick detection and one-line activation.

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

In FIG. 2, which is a connection diagram of the first embodiment of the present invention, the same symbols as in FIG. 1 indicate the same things as in FIG.
Note that RA, RB, and RC are resistors, cl is a conductor, and Q
sld register, coxp comparator, OU
T is an output terminal. In this embodiment, the resistor R
Connect A and RE to subscriber lines LA and LE, respectively,
Connect the intermediate connection point between resistors FA and RE to the base of current feedback transistor Q1 and capacitor C! The collector of the transistor 9 is connected to the subscriber line LB, and its emitter is connected in series with the resistor EC to the negative power supply -El. A series resistor AC and a comparator COM? are used as comparator means to send out an output when the feedback current exceeds a preset threshold. and a reference voltage rDM are provided. One end of the series resistor AC is connected to one input terminal (+) of the comparator caMp, and the other terminal of the resistor 11C is connected to the reference voltage rD.
The other input terminal (-
), and the output of the comparator COMP is connected to the output terminal ovr of the comparator means.

Next, the operation will be explained. Subscriber line, i.e. LA line, LM
If there is no ground fault at @, the load circuit RG shown by the dotted line would not exist, and the potential r at the intermediate connection point of resistors RA and RJ would be equal to both @LA.
, LB, and its value is similar to the negative power supply -El connected through a high resistance N1tN1 to provide a negative voltage to the subscriber line.

For example, if a ground fault occurs in the LA line, the line becomes a converging line to which the load resistor JG is connected as shown.

In this case, the pace-eightener circuit of the transistor Q1 is configured by the path. In this case, the potential r at the intermediate connection point between the resistors λA and RE is given - from the DC-DC converter C0Nr to the terminal A side and from the terminal B side, so the potential r from the load circuit RG to the O ground. The air potential becomes higher. That is, the base of transistor Q10 is given a potential higher than the ground potential. The emitter side of the transistor Q1 is connected to the negative power supply -, and since the base potential of the transistor (h is higher than its emitter potential), the transistor Qs is in the active state. A feedback current I flows through the series resistor RC to the side of the building.

However, if no ground fault occurs in the subscriber line, the negative power supply -Em
In the range of conditions >-El, the above-mentioned pace-emitter circuit of the transistor Ql does not occur, the transistor Q1 is inactive, and therefore the means for feeding back the current comprising the transistor Ql are ineffective.

This feedback current 11 increases until the intermediate connection negative potential r between the resistors RA and RB and the voltage drop (-xcxl*) produced in the series resistor EC by the feedback current 11 are in equilibrium, and the load circuit RG The smaller the value of , the more the feedback current 11 in the above-mentioned unbalanced state increases. Furthermore, :1/den?
The resistor RA and RB are used to prevent malfunctions caused by alternating current signals, and constitute a low-pass filter together with the resistors RA and RB.

Furthermore, a comparator means is provided which outputs an output signal when the feedback current If flowing through the feedback means exceeds a preset threshold value, and the presence or absence of a ground fault in the subscriber lines LA and LBO is detected from this output.

In this embodiment, a comparator means, a comparator COMF, a series resistor RC, and a preset reference potential VDIA are used. comparator c
aMp Id,, the voltage generated across the series resistor RC is input to one (+), and the reference voltage -FDm? set to the other input terminal (-)? By comparing the feedback current Il
The feedback current 1'1 exceeds a certain value, so the resistance RC caused by the feedback current 11
If the voltage drop of co exceeds the reference voltage, the comparator co
The ip ld signal 1fS is output from the output terminal OUT of the comparator means.

Therefore, whether a ground fault in the subscriber line as a fault or a ground fault when one line is activated by grounding one side of the subscriber line by pressing a key on the telephone, depends on the presence or absence of a signal at the output terminal ovr. Can be detected.

Note that the threshold voltage VDM'! of the comparator COMF for comparing and detecting the value of the feedback current 1 ri is VDM'! In addition to being set to a constant value, it is possible to configure the threshold voltage to be changed to different threshold voltages depending on whether the subscriber terminal device has activated one line or a line fault has occurred.

FIG. 3 is a connection diagram of a second embodiment of the present invention.

The symbols in FIG. 6 indicate the same as those in FIG.

In addition to the configuration of the first embodiment shown in FIG. 2, the second embodiment shown in FIG. 1
0K comparator COMP is connected to the output terminal OUT of the comparator means. The switch section SIF of the DC-DC converter CONV is its control terminal 1.
When there is a control input at 0, the power supply is limited (including stopping). - Next, the operation of the second embodiment will be explained. The second embodiment is exactly the same as the first embodiment in that when the feedback current 11 due to a ground fault in subscriber lines LA and LB exceeds a certain value, a detection output is generated at the output terminal OUT from the comparator COMP. It is. In this case, the detection output of the comparator cohrp is the control terminal 10 of the switch section sr.
input to limit the output of the DC-DC converter C0NI', that is, the supplied power. According to this second embodiment:
The feedback current 11 necessary for a series of detection operations for detecting a ground fault is secured, and the feedback current 1. It is possible to prevent the power from increasing more than necessary, and since the supplied power is limited when a ground fault is detected, unnecessary heat generation in the circuit can be prevented.

Although the present invention has been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made within the technical scope thereof.

Effects of the Invention Since the present invention is configured as described above, the first invention is that in a floating power supply system, the advantages of 70-Ting power supply are not impaired, υ, single-line actuated layer, and addition. This has the effect of making it possible to detect ground faults on provincial lines.

In addition, the second invention not only has the same effect as the first invention, but also has a ground fault detection output compared to the first invention.
DC-1) Since a means for controlling the switch unit 'sr of the C converter C0NV to limit the fI8 electric power is added, the feedback current 11 necessary for a series of detection operations for detecting a ground fault is secured, and Feedback current! ! This is a construction that has the effect of preventing the power from increasing more than necessary, and preventing unnecessary heat generation in the circuit because the supplied power is limited when a ground fault is detected.

[Brief explanation of drawings]

Fig. 1 is a connection diagram of an example of a conventional 70-ring type power supply circuit, Fig. 2 is a connection diagram of a first embodiment of the present invention, and Fig. 3 is a connection diagram of a second embodiment of the present invention. It is. F'BI "' Station power supply, C0NTf-1) C-DC near y park, SF... switch section, T... transformer, D (... diode, c, cl... capacitor, FIL...・Filter circuit, (h...transistor, COMP...comparator, LA, LB...
Subscriber line, R wing, R power, RA, RB, AC...Resistor, RL...Telephone load circuit, IILA, RL
B...Subscriber line LA. LB equivalent load circuit, RG...Equivalent load circuit in case of ground fault, -E, , -zm...Negative power supply, VDM Te...Reference voltage patent applicant Fujitsu Limited (one other person) side Patent attorney Gobe Tamamushi (3 others)

Claims (2)

[Claims] (1) In a subscriber circuit that is equipped with a DC-1) C converter power supply circuit and supplies power from the local power source to the subscriber line in a 70-proboscis-like manner, there is no effect if there is no ground fault in the subscriber line. However, if there is a ground fault in the subscriber line, there is a means to return current from the subscriber line to the negative power supply.
Comparator means for sending out an output when the feedback current flowing through the feedback means exceeds a preset threshold, and a ground fault in the subscriber line is detected by the output of the controller means. Ground fault detection circuit. (2) In a subscriber circuit that is equipped with a DC-DC converter power supply circuit and supplies power to the subscriber line from the station power supply in a 70-degree condition, there is no effect when there is no ground fault in the subscriber line. means for returning current from the subscriber line to the negative power supply when a ground fault exists in the subscriber line;
Comparator means for sending out an output when the feedback current flowing through the cough feedback means exceeds a preset threshold; the comparator means detects a ground fault in the subscriber line based on the output of the controller means; The output of is given as a control input to the switch section of the DC-DC converter, and when the comparator means has a ground fault detection output, the output of the DC-DC converter is limited to reduce the supplied power. Ground fault detection circuit.