JPH10136129A - Line speech current control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To install automatically a current control resistor in a line without manual operation by connecting a current control resistor with a normally closed relay switch connected in parallel therewith and a current sensing resistor in series in the line and opening the relay switch when the voltage produced across the current sensing resistor is a specified voltage or over. SOLUTION: A relay switch 12 is closed when no current flows to a line 2 and a private branch of exchange is not in operation. When the current flows to the line 2 for the first time, a voltage is produced across a voltage sensing resistor 11. When the voltage reaches a prescribed voltage, that is, the Vbe of a transistor(TR) 13 or over, the TR 13 starts the on-operation, drives and holds a relay coil 22 via other TRs, and the relay switch 12 is opened to insert a current control resistor 4. Thus, the current control resistor 4 is automatically installed without measurement of a current flowing in the line 2 and operation of a manual switch, thereby reducing the current flowing in the line 2 to have a specified value or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication current control circuit for a line, and more particularly to a circuit used for a line package of a private branch exchange.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional call current control circuit. In the figure, 1 is a line 2 such as a telephone line or a dedicated line.
A power supply circuit for supplying power to the power supply circuit and preventing the package from being burnt due to an excessive current in the line 2, a line detection unit 3 for detecting the line state of the other party based on whether or not a current is flowing through the line 2, A pair of current control resistors 5 provided between the line detection unit 3 and the pair of current control resistors 5 are manual switches connected in parallel to the respective current control resistors 5.

A conventional call current control circuit is constructed as described above. For example, when a private branch exchange is installed, a worker measures the current flowing through the line 2 with an ammeter, and the measured current is larger than a predetermined value. In this case, each manual switch 5 is turned off and the current control resistor 5 is inserted into the line 2 so that a current equal to or less than a predetermined value flows through the line 2 thereafter. The reason for this is that if the current flowing through the line 2 is large, a call failure occurs, so that the current flowing through the line 2 is set to a predetermined value or less to prevent the occurrence of a call failure. is there.

[0004]

In the conventional call current control circuit as described above, the current of the line 2 must be measured at the time of installation, which is troublesome. There is a problem that the incorrect setting of the current control resistor 4 may cause an erroneous setting due to the erroneous operation of 5 above.

[0005]

A call current control circuit according to the present invention is a normally closed circuit which is connected in parallel to a pair of current control resistors provided between a power supply circuit for supplying power to the line and the line. A relay switch, a voltage detection resistor provided between each current control resistor and the power supply circuit, and a switching element that is turned on based on a voltage of a predetermined value generated by a current flowing through each voltage detection resistor. A relay coil unit that is driven when the switching element is turned on to open the relay switch, and a relay holding voltage output circuit that keeps outputting an on-operation holding voltage to the switching element as the switching element is turned on And

In the present invention, when a current flows through a line, a normally-closed relay switch is connected between a power supply circuit and a line detecting section via a current controlling resistor connected in parallel to a voltage detecting resistor. When a current flows, a voltage is generated in the voltage detection resistor, and when the voltage reaches a predetermined value, the switching element is turned on. When the switching element is turned on, the relay coil unit is driven to drive the current control resistor. Since the relay switch connected in parallel to the switch is opened, the current that has been flowing through the relay switch flows through the current control resistor, and the current is controlled so that a current equal to or less than a predetermined value flows through the line. Keeps outputting the on-operation holding voltage to the switching element with the on-operation of the switching element. Will continue to down, the relay coil unit keeps its state when it is set to a time drive state, so that the current control to the line resistance is automatically installed.

[0007]

FIG. 1 is a configuration diagram of a call current control circuit according to an embodiment of the present invention. In the figure, the same components as those of the conventional example are denoted by the same reference numerals, and the description of the duplicated components will be omitted. Reference numeral 11 denotes a voltage detection resistor provided between the power supply circuit 1 and the current control resistor 4, and 12 denotes a current control resistor 4.
, A normally-closed relay switch connected in parallel to the first transistor 13, a first transistor serving as a switching element, a base of which is connected to a connection point between the current control resistor 4 and the voltage detection resistor 11, and an emitter connected to a power supply circuit 1 and voltage detection resistor 1
1 and its collector is grounded via a current limiting resistor 14. Reference numeral 15 denotes a filter resistor, one end of which is connected to the collector of the first transistor 13, and the other end of which is connected to the emitter of the first transistor 13 via the filter capacitor 16.
The filter resistor 15 and the filter capacitor 16 constitute a filter circuit for preventing malfunction due to excessive current from the line 2.

Reference numeral 17 denotes a second transistor which is a switching element. The base of the second transistor is connected to a connection point between the filter resistor 15 and the filter capacitor 16 via a bias resistor 18, and the emitter thereof is connected to the first transistor 13.
And its collector is grounded via a current limiting resistor 19. Reference numeral 20 denotes a Darlington-type third transistor which is a switching element for driving the relay, and its base is connected to a second transistor via a bias resistor 21.
, And the emitter thereof is connected to the emitter of the first transistor 13. Reference numeral 22 denotes a relay coil unit, one end of which is connected to the collector of the third transistor 20, and the other end of which is grounded via a current limiting resistor 23. Reference numeral 24 denotes a fourth transistor, which is a switching element, whose base is connected to the collector of the third transistor 20, whose collector is connected to the base of the third transistor 20, and whose emitter is connected via a current limiting resistor 25. Grounded. The fourth transistor 24 and the current limiting resistor 25 constitute a relay holding voltage output circuit that keeps outputting an on-operation holding voltage to the third transistor 20 as the third transistor 20 turns on.

Next, the operation of the above embodiment will be described. When the private branch exchange is installed and no current is flowing through the line 2 yet, the relay switch 12 is closed. In this state, when a current flows through the line 2 for the first time, a voltage is generated in the voltage detecting resistor 11. When the voltage becomes equal to or higher than a predetermined value, that is, equal to or higher than Vbe of the first transistor 11, the first transistor 11 is turned on. At this time, the charge accumulated in the filter capacitor 16 starts discharging with a time constant τ = C · R with the filter resistor 15, and the second transistor 1
7 indicates that the base potential drops and the base-emitter voltage becomes V
If it is less than be, it will be off until now. The filter circuit composed of the filter capacitor 16 and the filter resistor 15 prevents a malfunction of the second transistor 17 due to an excessive current such as an inrush current from the line 2 and a malfunction of the relay coil unit 22.

Next, when the second transistor 17 is turned off, the base voltage of the third transistor 20 connected to the collector via the bias resistor 21 increases,
The third transistor 20 turns on. Then, a current flows through the relay coil section 22, the relay coil section 22 is driven, and the relay switch 12 is opened. Therefore, the current that has been flowing through the relay switch 22 until now flows through the current control resistor 4 and the current that is equal to or less than the predetermined value flows through the line 2. Thereafter, when the current stops flowing through the line 2, the first transistor 11 is turned off and the second transistor 17 is turned on. However, the fourth transistor 24 has already been turned on, a current flows from the ground to the resistor 21 via the resistor 25, and the third transistor 24
Since the base voltage of the transistor 20 is equal to or higher than Vbe, the third transistor 20 does not return to the off state. Therefore, once the relay coil unit 22 is driven and the relay switch 12 is set to open, the state is maintained even if the current stops flowing through the line 2, and the line
The current control resistor 4 is automatically installed on the line 2 without measuring the current of the line or operating the manual switch. In this embodiment, an example is shown in which a communication current control circuit for inserting the current control resistor 4 into the line 2 on the −48 V side is provided. Is also provided with a similar call current control circuit, and has the same configuration, operation, and effect, so that illustration and description thereof are omitted.

Further, the present invention can be implemented even if the relay switches 12 connected in parallel to the current control resistors 4 for the -48 V side and the ground side line 2 are driven by one relay coil section 22. Needless to say. Further, in the above embodiment, a relay is used,
A photomoss relay can be used. In this case, the drive current can be suppressed, and the third transistor 2
0 may be of the small signal type.

[0012]

As described above, according to the present invention, when a current flows through a line, a normally closed relay switch is provided between the power supply circuit and the line detection unit via a current control resistor connected in parallel. A current flows through the voltage detection resistor, and a voltage is generated in the voltage detection resistor.When the voltage reaches a predetermined value, the switching element is turned on, and when the switching element is turned on, the relay coil unit is turned on. When driven, the relay switch connected in parallel with the current control resistor is opened, so that the current that has been flowing through the relay switch flows through the current control resistor and is set so that a current equal to or less than a predetermined value flows through the line. At the same time, the relay holding voltage output circuit keeps outputting the on-operation holding voltage to the switching element with the on-operation of the switching element. Ring element will be continuously turned on, relay coil unit when set to a time driving state maintaining that state, or by measuring the line current as in the prior art,
This has the effect that the current control resistor is automatically installed on the line without operating the manual switch.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a call current control circuit according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional call current control circuit.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 power supply circuit 2 line 3 line detection unit 4 current control resistor 11 voltage detection resistor 12 relay switch 20 third transistor (switching element) 22 relay coil unit 24 fourth transistor (relay holding voltage output circuit) 25 current limit Resistor (relay holding voltage output circuit)

Claims (1)

[Claims] 1. A normally closed relay switch connected in parallel to a pair of current control resistors provided between a power supply circuit for supplying power to a line and the line, each current control resistor and a power supply circuit. A switching element that is turned on based on a voltage of a predetermined value generated by a current flowing through each of the voltage detecting resistors; and a driving element that is driven when the switching element is turned on. A relay coil unit for opening a relay switch; and a relay holding voltage output circuit that keeps outputting an on-operation holding voltage to the switching element in accordance with the on-operation of the switching element. circuit.