JPH05219199A - Subscriber circuit - Google Patents

Abstract

PURPOSE:To increase the stability of a telephone exchange system by detecting the power source disconnection of a subscriber circuit which is made into a semiconductor integrated circuit, forcibly controlling the monitoring signal of the subscriber circuit by means of the detection output and executing alarm display. CONSTITUTION:When a -48V power source 6 is disconnected, a transistor Q2 is turned off and the transistor Q1 is turned on since a base current is supplied from the +5V power source 5 by way of a register R1 in a loop detection output stopping circuit 3. A loop detection output is fixed to ground potential and stopped. When the -48V power source 6 is disconnected, the transistor Q3 is turned on since the base current is supplied from the +5V power source 5 by way of the register R1 in an alarm display circuit 4. The current is made to flow in a light-emitting diode D1 so as to make light emitted and it is displayed as alarm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a subscriber circuit integrated into a semiconductor integrated circuit connected to a two-line subscriber line in a telephone exchange.

[0002]

2. Description of the Related Art Conventionally, this type of subscriber circuit supplies a call current to a terminal connected to a two-wire type subscriber line.
+ 5V (-5V power supply may be added) for transmitting AC (voice) signal or digital signal to V power supply
Power was being used.

This subscriber circuit supplies a call current (DC current) for making a call to a terminal (for example, a telephone) and a subscriber circuit when the handset of the telephone is lifted to start a call. And a loop detection circuit for detecting a flowing call current and outputting it as a subscriber (terminal) monitoring signal.

When this subscriber circuit is realized by a semiconductor integrated circuit, the aforementioned power source is supplied to the semiconductor integrated circuit, and the lowest potential of the power source, -48V, becomes the substrate potential of the semiconductor integrated circuit.

[0005]

In the conventional subscriber circuit described above, when the -48V power supply is cut off due to a failure or the like, the output of the loop detection circuit malfunctions depending on the method of constructing the loop detection circuit of the subscriber circuit. However, even if the call current does not flow, an output indicating that it is flowing is output. For example, the loop detection circuit is composed of an operational amplifier, and when the negative power supply of the operational amplifier is cut off, the output of the operational amplifier does not become a normal output. In this case, since a signal indicating that a call current has flowed is output from all subscriber circuits in which the -48V power supply of the telephone exchange has been cut off, there is a problem that the exchange processing amount exceeds the processing capacity.

Further, even if the power supply of -48V is cut off, the display is not made, and there is a problem that it is left in an abnormal state for a long time. Further, even if the subscriber circuit is regularly tested, there is a problem that it is left in an abnormal state for the duration of the test cycle.

[0007]

SUMMARY OF THE INVENTION The subscriber circuit of the present invention comprises:
In a subscriber circuit having a call current supply circuit for supplying a direct current to a terminal via a two-wire subscriber line, and a loop detection circuit for detecting that a call current has flowed to the terminal, the call current supply A circuit and the loop detection circuit are constituted by a semiconductor integrated circuit requiring at least two power supplies,
A loop detection output stop circuit that detects a power failure and stops loop detection output when the power supply of the lowest potential among the power supplies is disconnected, and an alarm display circuit that detects the power failure and displays an alarm ing.

The loop detection output stop circuit includes a first resistor connected in series between the first power source and the second power source, first and second transistors, a Zener diode, and a second resistor. A loop detection output is input to the collector of the first transistor, and the first resistor is connected to the base of the first transistor and the collector of the second transistor via the first resistor. Connect the power supply,
Ground is connected to the emitter of the first transistor and the base of the second transistor, and a second power source is connected to the emitter of the second transistor via the Zener diode and the second resistor. The alarm display circuit is the first when the second power source is cut off.
A third transistor that is turned on when a base current is supplied via a first resistor between the power source and the ground, and a light emitting diode that emits light when the third transistor is turned on.

[0009]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a subscriber circuit of the present invention.

When the handset of the telephone 7 is lifted, -48V
A call current is supplied from the power supply 6 and the earth to the telephone 7 via the call current supply circuit 1 and the subscriber line 8. The loop detection circuit 2 is supplied with + 5V power supply 5 and earth,
The call current is detected and used as the loop detection output. The loop detection output stop circuit 3 detects the disconnection of the -48V power supply 6 to stop the output of the loop detection circuit 2 and the alarm display circuit 4
Display the alarm with.

FIG. 2 is a circuit diagram showing an example of a concrete circuit configuration of the loop detection output stop circuit and the alarm display circuit in FIG.

The loop detection output stop circuit 3 includes resistors R1 and R
2 and Zener diodes ZD1 and ZD2, and transistors Q1 and Q2. When the −48V power supply 6 is cut off, the transistor Q2 is turned off and the transistor Q2 is turned off.
1, a base current is supplied from the + 5V power source 5 via the resistor R1, and the transistor Q1 is turned on. For this reason,
The loop detection output is fixed to the ground potential and the loop detection output is stopped. The alarm display circuit 4 is composed of a light emitting diode D1, a resistor R3 and a transistor Q3. When the −48V power source 6 is cut off, a base current is supplied to the transistor Q3 from the + 5V power source 5 via the resistor R1. Transistor Q3 is turned on. Therefore, a current flows through the light emitting diode D1 to emit light, which is displayed as an alarm.

[0013]

As described above, according to the present invention, a power failure of a subscriber circuit integrated into a semiconductor integrated circuit is detected, the detection signal is used to forcibly control the supervisory signal of the subscriber circuit, and an alarm is displayed. This has the effect of increasing the stability of the telephone exchange system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a subscriber circuit of the present invention.

2 is a circuit diagram showing an example of a specific circuit configuration of a loop detection output stop circuit and an alarm display circuit in FIG.

[Explanation of symbols]

 1 Call current supply circuit 2 Loop detection circuit 3 Loop detection output stop circuit 4 Alarm display circuit 5 + 5V power supply 6-48V power supply 7 Telephone (terminal) D1 Light emitting diode Q1, ~ Q3 Transistor R1, ~ R3 Resistance ZD1, ZD2 Zener diode

Claims (3)

[Claims] 1. A subscriber circuit having a call current supply circuit for supplying a direct current to a terminal via a two-wire subscriber line, and a loop detection circuit for detecting that a call current has flowed to the terminal. The speech current supply circuit and the loop detection circuit are configured by a semiconductor integrated circuit that requires at least two power supplies, and when the power supply of the lowest potential among the power supplies is cut off, the power supply cutoff is detected and a loop detection output is output. A subscriber circuit, comprising: a loop detection output stop circuit for stopping the power supply; and an alarm display circuit for detecting the power failure and displaying an alarm. 2. The loop detection output stop circuit includes a first resistor connected in series between a first power supply and a second power supply,
A first and a second transistor, a Zener diode,
A second resistor, a loop detection output is input to the collector of the first transistor, and the base of the first transistor and the collector of the second transistor are connected to the first resistor via the first resistor. 1 power source is connected, ground is connected to the emitter of the first transistor and the base of the second transistor, and the emitter of the second transistor is connected to the emitter of the second transistor via the Zener diode and the second resistor. The subscriber circuit according to claim 1, wherein a second power supply is connected. 3. The alarm display circuit includes a third transistor which is turned on when a base current is supplied between the first power supply and the ground through a first resistor when the second power supply is cut off. The subscriber circuit according to claim 1, further comprising: a light emitting diode that emits light when the third transistor is turned on.