JPH0654037A - Line current detector - Google Patents

Abstract

PURPOSE:To reduce a mount space by detecting a line current through a DC current consumption circuit or a resistor of a speech network and outputting a line current presence signal when a terminal voltage of the resistor exceeds a reference voltage. CONSTITUTION:A line current fed to lines 2a,2b is rectified by a rectifier 7, its AC component is smoothed in a DC current consumption circuit 8, and when a transistor(TR) 11 is operated in the operating region, a current flows to a resistor 12 and a voltage is obtained at a connection neutral point B. On the other hand, a rectified output is impressed to voltage division resistors 22,23 at an output circuit of the rectifier 7 via a constant current source 21, and a reference voltage is obtained at a connection neutral point A. A comparator 24 compares the voltage of the connection neutral points A,B, and when the voltage at the connection neutral point B exceeds the voltage at the connection neutral point A, the comparator 24 outputs a line current detection signal. Thus, the need for the use of a reed relay is eliminated, the mount area and space is made narrow and the cost is reduced and adverse effect of a magnetic field onto each circuit section is avoided with a low loss.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line current detecting device for detecting the presence / absence of a line current at the time of capturing a line in a telephone terminal such as a facsimile.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a conventional line current detecting device. In FIG. 3, 1 is a lead coil connected in the middle of line 2a among lines 2a and 2b, and 3 is a lead coil 1. AC bypass capacitors 4 connected in parallel are reed switches that form a reed relay R together with the lead coil 1, and are connected in series between a DC power supply P and an earth E via a resistor 5. Reference numeral 6 is an output terminal for outputting a signal indicating the presence / absence of a line current.

Reference numeral 7 is a bridge-type rectifier connected between the lines 2a and 2b, and 8 is a direct current consumption circuit connected to the output side of the rectifier 7, which includes a transistor, a bias resistor 9 and a capacitor 10. A resistor 11 for detecting a DC potential at the midpoint of connection between the resistor 9 and the capacitor 10 and a resistor 12 for current consumption connected to the emitter of the transistor 11. Reference numeral 13 is a transformer whose primary side is connected to the output side of the direct current consumption circuit 8 via a capacitor 14, and a modem 16 is connected to the secondary side of this transformer 13 via a hybrid circuit 15.

In the line current detecting device having such a configuration,
When the line current is supplied to the lines 2a and 2b, first, the reed coil 1 of the reed relay R is energized, so that the reed switch 4 is turned on. Therefore, the DC voltage P is grounded via the resistor 5, so that the potential of the output terminal 6 which has been at the high level until now is lowered, whereby the capture of the line current can be detected.

On the other hand, the line current is rectified by the rectifier 7 and input to the DC current consuming circuit 8, the AC component is smoothed by the resistor 9 and the capacitor 10, and the transistor 11 is controlled according to the applied line current. Then, the DC current input to the DC current consumption circuit 8 is consumed through the resistor 12.

The DC-consumed output voltage is input to the hybrid circuit 15 via the transformer 13, and further input to the modem 16 for demodulation.

[0007]

However, since such a conventional line current detecting device is constructed as described above, since the reed relay R is used, the mounting area and space are increased and the voltage loss is increased. However, there is a problem that each part of the circuit may be affected by the magnetic field generated by the lead coil 1.

The present invention has been made to solve the above-mentioned conventional problems. By avoiding the use of a reed relay, the mounting area, space can be narrowed and the cost can be reduced, and the cost can be reduced. It is an object of the present invention to obtain a line current detecting device which can eliminate the influence of a magnetic field on a circuit due to loss.

[0009]

A line current detecting device according to the present invention is a rectifier for rectifying a line current in a telephone terminal device, and a DC current consumption circuit for receiving the output of the rectifier and detecting the presence or absence of the line current. A speech network and a resistor connected to the direct current consumption circuit or the speech network for detecting the magnitude of the line current,
And a comparator for comparing the terminal voltage of the resistor and a reference voltage and outputting a line current presence / absence signal according to the comparison result.

[0010]

The resistance of the DC current consumption circuit or the speech network according to the present invention detects the magnitude of the line current, and if the terminal voltage of this resistor exceeds a preset reference voltage for detecting the line current, a comparison is made. It operates so that the presence / absence signal of the line current is output from the device.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 2a and 2b are lines, 7 is a rectifier,
Reference numeral 8 is a DC current consumption circuit, which has the same configuration and connection as that shown in FIG.

On the output circuit side of the rectifier 7, a constant current source 21 and a voltage dividing resistor 2 are provided for the DC current consumption circuit 8.
A series circuit composed of 2 and 23 is connected in parallel, and the connection midpoint A of the voltage dividing resistors 22 and 23 and the connection midpoint B of the emitter of the transistor 11 and the resistor 12 are the negative terminals of the comparator 24. And positive terminals respectively.

Reference numeral 25 is a photocoupler connected to the output side of the comparator 24, 26 is a voltage detecting resistor for extracting the line current detection signal output from the photocoupler 25, and 27 is a signal for increasing the line current detection signal. It is a high-cut filter that cuts out the area and takes it out. In addition, the same components as those shown in FIG. 3 are denoted by the same reference numerals, and duplicate description thereof will be omitted.

In the line current detecting device having such a configuration,
When the line current is supplied to the lines 2a and 2b, the line current is rectified by the rectifier 7 and input to the DC current consumption circuit 8.

In the DC current consumption circuit 8, the AC component of the line current is smoothed by the resistor 9 and the capacitor 10,
When the transistor 11 enters the operating region, a current flows through the resistor 12, and a voltage is obtained at both ends of the resistor 12, that is, at the connection midpoint B.

On the other hand, on the output circuit side of the rectifier 7, the rectified output is applied to the voltage dividing resistors 23 and 24 via the constant current source 21, so that the connection reference point A has a predetermined reference voltage. can get. Therefore, the comparator 24 inputs the voltage at each of the connection midpoints A and B, and the voltage at the connection midpoint B becomes equal to the connection midpoint A.
It is determined whether the voltage exceeds the reference voltage of.

As a result of this judgment, when the voltage at the connection midpoint B exceeds the voltage at the connection midpoint A, the comparator 24 outputs a signal to activate the photocoupler 25, and through the high cut filter 27. The line current detection signal will be output to the external circuit. Note that the operation of supplying the output signal, which has been DC-consumed, to the modem 16 is the same as that of the conventional one, and therefore the duplicated description thereof is omitted here.

FIG. 2 shows another embodiment of the present invention. This is a system in which a speech network 31 is connected to the lines 2a and 2b via a rectifier 7, and a speech output receiver 32 and a speech input microphone 33 are connected to the speech network 31. Reference numeral 34 is a resistor connected to the load terminal of the speech network 31 to detect the magnitude of the line current.

Further, 35 and 36 are voltage dividing resistors connected to the bias terminals of the speech network 31, and the reference voltage is obtained from the connection midpoint C between them. 37
Is a comparator that receives the terminal voltage of the resistor 34 and the reference voltage.

The output of the comparator 37 has a resistor 3
The base of a transistor 40 for turning on / off a current flowing through the photocoupler 39 via 8 is connected. 41
Is a resistance for voltage detection connected between the photocoupler 39 and the ground, and 42 is a high cut filter for cutting a high frequency portion of the voltage output obtained by the resistance 41 and outputting it as a line current detection signal. .

In the line current detecting device having such a configuration,
The magnitude of the line current is detected from the terminal voltage of the resistor connected to the load terminal of the speech network 31, and when this terminal voltage exceeds the reference voltage divided by the voltage dividing resistors 35 and 36, the photo coupler 39 is connected. The operation is turned on to obtain a voltage in the resistor 41.

Then, this voltage cuts the high frequency band of the high cut filter 42 as a line current detection signal and outputs it to the outside.

Since the present invention is constructed as described above, the voltage dividing resistors 22, 23 and 3 are used in any of the embodiments.
By arbitrarily selecting the divided voltage values of 5 and 36, the detection level of the line current can be freely set.

[0024]

As described above, according to the present invention, the rectifier for rectifying the line current in the telephone terminal equipment, the DC current consumption circuit or the speech network for receiving the output of the rectifier and detecting the presence or absence of the line current, A comparator connected to the DC current consuming circuit or the speech network to detect the magnitude of the line current, the terminal voltage of the resistor and a reference voltage, and output a line current presence / absence signal according to the comparison result. As a result, it is possible to reduce the mounting area and space by reducing the size of the structure and to reduce the cost, and to obtain the one that can avoid the adverse effects of the conventional magnetic field on each circuit part. There is.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a line current according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a line current detecting device according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional line current detection device.

[Explanation of symbols]

 2a, 2b Line 7 Rectifier 8 DC current consumption circuit 12,34 Resistor 24,37 Comparator 31 Speech network

Claims (1)

[Claims] 1. A rectifier for rectifying a line current in a telephone terminal device, a DC current consuming circuit or a speech network for receiving the output of the rectifier and detecting the presence or absence of the line current, and connected to the DC current consuming circuit or the speech network. And a resistor that detects the magnitude of the line current,
A line current detecting device, comprising: a comparator that compares a terminal voltage of the resistor with a reference voltage and outputs a line current presence / absence signal according to the comparison result.