JPS61288548A - Current supply circuit having grounding, inter-line contact and protecting function - Google Patents

Abstract

PURPOSE:To detect grounding and inter-line contact with simple constitution by comparing an output voltage of a current voltage conversion means with two present threshold voltages. CONSTITUTION:A window type voltage comparator CMP having two different reference voltage sources Vref1, Vref2 is provided. If a terminal 4 is grounded, no current flows to a resistor R1b and a transistor (TR)Q3b is cut off. A grounding current Isa decided by a current supply circuit flows to a resistor R1a and a current expressed as (R1a.Isa-Vbca)/R7a flows to the collector of a TRQ3a, where Vbea is a base-emitter voltage of the TRQ3a. Thus, a voltage Vd at the detection point is compared with one Vref2 of the reference voltages of the window comparator CMP to form Vd2<Vref2, then a potential difference is generated between outputs of the voltage comparator CMP, photocouplers PC1A,PC1B are conducted to limit a grounding current.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to detection of ground faults and cross-contact in balanced current supply circuits used in subscriber circuits of telephone exchanges, and protection circuits in the event of ground faults and cross-contact. In particular, the present invention relates to a current supply protection circuit suitable for semiconductor devices.

[Prior art]

Conventionally, many semiconductor current supply circuits of this type have been devised, an example of which is shown in FIG. The details can be found in the published patent publication 1985-14061 r Current Supply Circuit (
Tokunaga et al.). However, in this circuit, if the line terminal 4 is grounded or the line terminal 3 is in contact, the power consumption of the output transistor Qla or Qlb increases and abnormal heat generation occurs. This has caused problems such as parts being damaged and reliability being reduced.

As a countermeasure to this problem, a ground fault detection method has been considered, and a circuit such as the one described in the published patent publication 1977-37762 "Ground fault detection circuit" (Kitano et al.) has been devised. The circuit is constructed using a large number of transistors, and some additional circuits are required to detect cross-contact.

In addition, in order to detect and protect against ground faults, we have developed a technology described in Japanese Patent Application Publication No. 57-37967, "Telephone Current Supply Protection Circuit".
(Nakanishi et al.) has been proposed. This is a method in which a detection circuit with a fixed threshold is inserted in series with the communication line on the battery line side and the ground line side, and the output of this is input into a logic circuit to check whether the communication current values match or do not match. There is a problem in that a logic circuit with a low breakdown voltage is mixed in the current supply circuit, which is a relatively high voltage, large current section, which is not desirable in terms of the breakdown voltage of the device.

[Purpose of the invention]

The present invention relates to an improvement of a protection means for a current supply circuit that reduces communication current and prevents semiconductors from generating excessive heat when a ground fault or cross contact occurs in the current supply circuit, and has a simple configuration. The purpose of the present invention is to provide a protection circuit for a current supply circuit.

[Summary of the invention]

The present invention provides means for generating a current proportional to the current on the battery wire side of the track and means for generating a current proportional to the current on the grounding wire side, and the current proportional to the current on the battery wire side and the grounding wire. By adding a current proportional to the current on the side to a current-voltage conversion means that generates a voltage proportional to the difference between the two currents, and comparing the output voltage of the current-voltage conversion means with two preset threshold voltages. , which detects ground faults and contacts, and detects the absolute value of the difference between the current on the battery wire side and the current on the ground wire side due to a ground fault or contact on the terminal device or line.
When the current exceeds a preset value, the output of the voltage comparison means is reversed to detect a ground fault or cross contact, and at this time the current in the current supply circuit is reduced to protect the circuit. .

[Embodiments of the invention]

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

FIG. 1 shows an embodiment of a current supply circuit equipped with a protection circuit according to the present invention, and is constructed of a current supply circuit with an emitter grounded configuration. In the figure, terminals 1 and 2 are respectively power supply terminals, normally terminal 1 is connected to earth, terminal 2
is connected to the battery. Terminal 3.4 is a current supply terminal connected to a pair of communication lines. Further, Qla and Qlb are output transistors of the current supply circuit, and Rla and Rl
b is a resistance that determines the communication current, and the resistance values of Rla and Rlb are the same. Q3a, R7a is R1a
Q3b and R7b are circuits for generating a current proportional to the current flowing through Rlb. R8a and R8b are resistors that determine the detection point voltage Vd during normal operation. Furthermore, CMP is a window type voltage comparator that has two different reference voltage sources Vrefl and Vref2.
is a photocoupler that operates based on the output result of the voltage comparator, and RO3 and RO4 are current limiting resistors for the light emitting diodes PCIA-1 and PCIB-1 of the photocoupler. It is a resistor that determines the reduced current flowing in the line upon detection.

First, when one line is normal and the subscriber is on-hook and no communication current flows, Rla.

Since no current flows through Rlb, transistors Q3a and Q
3b is in a cut-off state. Therefore, since the input voltage Vd of the voltage comparator is, set Vrefl and Vref2 so that Vref2<Vdl<Vrefl,
At this time, the voltages v1 and v of the two outputs of the voltage comparator
Make sure that 2 are equal. Therefore, under normal conditions, the photocouplers PCIA and PCIB do not operate in the on-hook state.

Next, when the line is normal and the subscriber is off-hook, a communication current flows, and a current proportional to the communication current flows through transistors Q3a and Q3b, but since their magnitudes are equal, the potential of Vd is Vdl. It remains the same and does not change. Therefore, as in the on-hook case described above, PCIA-2, P
CIB-2 is not conductive.

Now, when a ground fault occurs in such a current supply circuit (when the terminal 4 falls to the ground), no current flows through Rlb, and the transistor Q3b is cut off. R
A ground fault current Isa determined by the current supply circuit flows through la, and therefore, (R1a ・I
A current of sa-Vba a)/R7a flows.

Here, Vbea is the base-emitter voltage of Q3a. Therefore, the voltage Vd at the detection point is (-RIA・Ias+Vbea))=Vd2...(2
) becomes. Therefore, this voltage can be connected to the window comparator C
When compared with V r e f 2, one of the reference voltages of MP, and set so that Vd 2 < V r e f 2, a potential difference occurs between the outputs of the voltage comparator CMP, and the photocouplers PCIA and PCIB conducts and limits ground fault current.

Furthermore, when a line cross-contact fault occurs in the current supply circuit (when the terminal 3 comes into contact with the battery wire), the current flowing through Rla decreases and the current flowing through Rlb increases. This R
The difference between the currents flowing through la and Rlb appears as a fluctuation in the voltage at the detection point, similar to the case where the line is grounded. However, the detection point voltage Vd in the case of contact is expressed by the following equation (3).

R8a+R8b R7b (Rlb-Ibs-Vbeb))=Vd3...(3) Here, Ibs is the current flowing to the B wire at the time of contact, and V
b e b is the base-emitter voltage of Q3b. That is, in the case of cross contact, the detection point voltage Vd will rise above R8a+R8b. Therefore, Vd in the above formula (3) is
By comparing it with another reference voltage Vrefl of the window comparator and making sure that Vd3>Vrefl, a potential difference will occur between the outputs of the voltage comparator CMP, as in the case of the ground fault, and therefore the photocouplers PCIA and PCIB will Provides continuity and limits current in the event of contact.

In the above explanation, the ground fault resistance at the time of ground fault and cross contact is used.

Although the cross-contact resistance is set to zero, even if these resistances have a certain finite value, there is a difference in the current value flowing through the resistors R1a and Rlb, so it is possible to detect and protect against ground faults and cross-contact. That is,
A ground fault or cross contact occurs through a finite resistance and terminal 3
If a current Ia flows to the terminal 4 side depending on the side,
The above detection point voltage Vd is 2 R7 (However, R8a=R8b, R1a=R1b=R1,
R7a=R7,b=R7%Vbea=Vbeb), and the current difference Ib-Ia is the above two reference voltages V
When the current difference becomes larger than the current difference determined by refl and V r e f 2, ground fault and contact detection is performed.

It can be configured to perform a protective operation.

〔Effect of the invention〕

The embodiments of the present invention have been described above, and by implementing the present invention, it is possible to reduce power consumption in the event of a ground fault or cross-contact failure, and therefore prevent a decline in component reliability due to abnormal heat generation. In other words, it has the effect of realizing an inexpensive current supply circuit that does not require any special parts. Furthermore, it is clear that the present invention can be used not only for subscriber circuits as in this embodiment, but also for trunk circuits and power supply circuits that require current supply.

[Brief explanation of the drawing]

FIG. 1 shows an example of a current supply circuit according to the present invention, and FIG. 2 shows an example of a known current supply protection circuit. Explanation of symbols Vd...Detection point voltage V r e f 1, V r e f 2 - Reference voltage Q
la, Qlb, Q2a, Q2b, Q3a, Q3b...
Transistor CMP...Window type voltage comparator PCIA, PCIB...Photocoupler COI, CO2
...Capacitors Rla, Rlb, R2a, R2b, R3a, R3b, R
4a, R4b, R5a. R5b, ROI, RO2...Resistors R6a, R6b, R7a, R7b, R8a, R8b,
R9a, R9b, RO3, RO4...Resistance

Claims (1)

[Scope of Claims] 1. A first means for generating a current proportional to the current on the battery line side of the current supply circuit and a second means for generating a current proportional to the current on the grounding line side, and the output of these is provided. , is applied to the connection point between the first resistor and the second resistor connected in series between the earth and the battery, and the potential at the connection point is compared with two preset reference voltages and a voltage comparator. A current supply circuit having earth fault, cross contact, and protection functions, which detects a ground fault or cross contact by comparison, and limits current. 2. A patent characterized in that the output of the voltage comparator is connected to the input terminal of a means for increasing the direct current resistance of the current supply circuit, thereby reducing the current flowing through the battery wire and the ground wire in the event of a ground fault or cross contact. A current supply protection circuit according to claim 1.