JPH0355943A - Polarity inversion detection circuit for line - Google Patents

Abstract

PURPOSE:To provide high insulation between a line and a telephone set more than the conventional line and to attain the monitor of polarity of a line at all times by detecting a discharge current of a capacitor provided between lines with a photocoupler to detect the polarity inversion of the line. CONSTITUTION:A polarity inversion detection circuit 11 is constituted of a resistor 11 compensating a trunk line impedance connected in series between trunk lines 15 and 16, a rectifier diode 13, a capacitor 14 for charging a trunk line voltage and a photocoupler 12 connected in parallel with a diode 13. Suppose that the trunk line 15 is at an earth level and the trunk line 16 is energized by a-48V feeder line when a telephone set hooks on. When an incoming signal is going to reach a telephone set via the trunk lines 15, 16 and the potential of the trunk lines 15, 16 is inverted before the incoming signal is arrived, the trunk line 15 goes to-48V and the trunk line 16 goes to an earth level and the potential charged in the capacitor 14 is discharged through the photocoupler 12 and the resistor 11. In this case, the current flowing to the primary side of the photocoupler 12 is detected at a secondary side to detect the polarity inversion of the trunk lines 15, 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a line polarity reversal detection circuit that detects polarity reversal of a line connected to a telephone set.

[Conventional technology]

Conventionally, in a polarity reversal detection circuit for this type of line, as shown in the second @, the voltage of the office lines 25, 26 is high resistance 21, 22 .
23 to the voltage comparator circuit 24, and by determining the polarity of the station lines 25 and 26 based on this output, polarity reversal detection is performed.

Further, as shown in FIG. 3, by closing the relay contact 31, current flows through the current limiting resistor 32 to the diode 34 or photocoupler 33.

The polarity of the station wires 35 to 36 is determined by detecting the direction of the current based on whether the current flows through the photocoupler 33 or not, thereby performing polarity reversal detection.

[Problem to be solved by the invention]

In the case of the conventional line polarity reversal detection circuit described above, which uses the voltage comparator circuit 24 shown in FIG.
1.23, this polarity reversal detection circuit and the station wires 25, 2
6, but it cannot be done due to the resistance value. Furthermore, if there is a potential difference between the ground of the local lines 25 and 26 and the ground of this locality reversal detection circuit, there is a drawback that malfunction may occur.

In addition, in the case of the polarity reversal detection circuit shown in Fig. 3, which detects the polarity by passing a communication current, the polarity must be constantly monitored because the communication current is used to detect the polarity reversal of the central office line 35, 36. The disadvantage is that it cannot be done.

[Means to solve the problem]

The line polarity reversal detection line of the present invention includes a capacitor for charging the voltage of the line, a rectifying diode, and a resistor for compensating the inter-line impedance, connected in series to both ends of the line, and a resistor connected in parallel to the diode. and a photocoupler configured to discharge the potential charged in the capacitor when the polarity of the line is reversed.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, the polarity reversal detection circuit 1 of this embodiment includes a resistor 11 for compensating the station line impedance connected in series between the station line 15 and the station line 6, a rectifying diode 13, and a station line voltage charging circuit. The photocoupler 12 is connected in parallel to the diode 13, and the photocoupler 12 is connected in parallel to the diode 13.

Next, the operation of this embodiment will be explained.

It is assumed that when a telephone (not shown) incorporating this embodiment is on-hook, the central office line 15 is connected to the earth, and the central office line 16 is connected to -48V power. At this time, the capacitor 14 for charging the local line voltage is charged with a potential of 48V through the resistor 11 and the rectifying diode 13.

When an incoming signal is about to arrive at the telephone set 41 via the office lines 15 and 16, the potentials of the office lines 15 and 16 are reversed before the arrival of the incoming signal. That is, the central line 15 is 48V. Since the central line 16 is connected to the ground, the potential charged in the capacitor 14 is discharged through the photocoupler 12 and the resistor 11. At this time, the polarity reversal of the station wires 15 and 16 is detected by detecting the current flowing through the primary side of the photocoupler 12 on the secondary side.

Similarly, the photocoupler 12 detects the polarity reversal of the central office lines 15 and 16 when a call is made by the telephone and when the call destination responds and the call ends.

〔Effect of the invention〕

As explained above, the present invention detects the polarity reversal of the line by detecting the discharge current of the capacitor installed between the lines using a photocoupler, thereby providing greater insulation between the line and the telephone than the conventional circuit. This has the effect of constantly monitoring the line polarity.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, and FIGS. 2 and 3 are circuit diagrams showing conventional line polarity reversal detection circuits, respectively. l...Polarity reversal detection circuit, 11...Resistor, 12...
・Photocoupler, 13...Diode, 14...Capacitor, 15.16...Station line, 21, 22.23.
...Resistance, 24...Potential comparison circuit, 25.26...
Office line, 31... Relay contact, 3 2... Resistor, 3 3... Photo coupler, 34... Diode, 3 5, 3 6... Office line.

Claims (1)

[Claims] The line includes a capacitor for charging the voltage of the line, a rectifying diode, a resistor for compensating the impedance between the lines, and a photocoupler connected in parallel to the diode, which are connected in series to both ends of the line. A line polarity reversal detection circuit, characterized in that the line polarity reversal detection circuit detects the line polarity reversal by detecting the discharge of the potential charged in the capacitor with the photocoupler when the line polarity is reversed.