JPS63316994A - Trunk circuit - Google Patents

Abstract

PURPOSE:To obtain inexpensive small sized circuit suitable for circuit integration by detecting the switching operation of a relay circuit and connecting a polarity inversion circuit at outgoing and a loop current detection circuit at incoming to a communication line depending on the result of detection. CONSTITUTION:Each relay contact is switched respectively to the position shown in figure in the standby and incoming state. A loop current is supplied to the communication line 1 called by the opposite party from feeding circuits 3a, 3b and the loop current is detected surely by a photocoupler (PC)2 for loop current detection. On the other hand, in case of the outgoing in the standby state, a transistor Qr is turned in according to the instruction of a control circuit, a relay circuit 6 is activated, relay contacts k3a, k3b are switched to disconnect the feeding circuits 3a, 3b from the communication line 1 respectively and a photocoupler PC3 for detecting polarity inversion is connected to the communication line 1 to be the state enabling to detect polarity inversion.

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION Field of Industrial Application The present invention relates to improvements in trunk circuits used in private branch exchanges.

(Prior art) Conventionally, a private branch exchange has a two-wire communication line.
Some devices are equipped with a 2-wire TIE trunk for connecting P[3X]. FIG. 3 shows an example of this two-line TIE)-rank cycle. In the same figure, 21
An audio signal path 2 is connected to a communication line 1 made of i1 metallic through relay contacts kIa and 1b for sending out polarity inversion signals, and relay contacts 2a and 2b for sending out dial pulses. Power supply circuits 3a and 3b are connected to the signal path 2 via relay contacts 3a and 3b. These power supply circuits 3a and 3b each have a power supply resistance circuit using transistors Qa and Qb and a diode bridge circuit Qa and Qb, and supply the IIL voltage (-48V) to the communication line 1 through these circuits. supply The reason why the power supply resistance circuit was configured using transistors is that it has a low resistance of 100 to 200Ω for direct current (11), and an impedance of Z)6 for audio signals.
This is to obtain a high resistance of 00Ω. In addition, a loop current detection circuit 4 is connected to the audio signal path 2 via a relay contact 4.
and the polarity reversal detection circuit 5 are selectively connected. These detection circuits 4.5 both use photocouplers as detection elements.

In such a configuration, first, during standby, each relay contact is set as shown in the figure, so that the number of communication times is reduced. ! 21 is applied with a power supply voltage of 148 cm from the power supply circuits 3a and 3b, and a loop current detection circuit 4 is connected to the communication line 1. Therefore, if the opposing PBX or central office switching trunk is also in the standby state, the equivalent circuit between each trunk at this time becomes as shown in FIG. If V2 is equal, no loop current will flow through the communication line 1.

If one party makes a call in this state, the trunk of the calling party disconnects relay contact 3a and switches relay contact 3b, thereby causing power supply circuits 3a and 3b.
is disconnected from the communication line 1, and the communication line 1 is shunted by a loop resistor.

At the same time, the relay contact 4 is switched to connect the polarity reversal detection circuit 5 to the communication line 1. Therefore, the equivalent circuit between each trunk at this time is shown in FIG.
), a loop current is supplied to the communication line 1 from the trunk on the receiving side. Then, this loop current is detected by the loop current detection circuit 4 of the trunk on the receiving side,
By detecting this loop current, the trunk on the receiving side knows that the other party is calling. Then, the trunk on the receiving side generates an instantaneous polarity reversal signal (generally called a wink pulse) as shown in FIG. 6 by switching the relay contacts kla and klb. On the other hand, the trunk on the calling side detects the above polarity reversal signal using the polarity reversal detection circuit 5 as shown in FIG. A dial pulse is sent by touching and separating. When the trunk on the called side responds to this, the trunk on the calling side detects this response and thereafter shifts to a talking state.

At the same time, the trunk on the called side also enters the talking state.

In this way, the 2-wire TIE trunk disconnects the power supply circuits 3a and 3b from the communication line B1 when making a call and connects the polarity reversal detection circuit 5, while when receiving a call, the power supply circuits 3a and 3b
is connected to the communication line 1, and a loop current detection circuit 4 is connected to the communication line 1 instead of the polarity reversal detection circuit 5.

However, in this type of conventional circuit, switching between the loop N flow detection circuit 4 and the polarity reversal detection circuit 5 is performed using relay contact 4. For this reason, the trunk circuit becomes expensive due to the necessity of providing a relay circuit, and since the relay circuit cannot be integrated, it is not possible to reduce the size of the circuit1;

(Problems to be Solved by the Invention) As described above, the conventional circuit uses a relay circuit to switch between the loop current detection circuit and the polarity reversal detection circuit, making the circuit expensive and compact. However, the present invention focuses on this point and makes it possible to switch between the loop current detection circuit and the polarity reversal detection circuit without using a relay circuit. The present invention aims to provide a trunk circuit that is suitable for integration and allows for miniaturization of the circuit.

A trunk circuit comprising a loop current detection circuit A that detects loop current, a polarity reversal detection circuit B that detects polarity reversal, and a relay circuit C that connects and disconnects a power supply circuit to a communication line in response to outgoing and incoming calls. , comprising a switching operation detection means for detecting the switching operation of the relay circuit C, and a semiconductor switch circuit E, and drives the semiconductor switch circuit E in accordance with the detection result of the switching operation detection circuit to generate a signal. When a call is made, the polarity reversal detection circuit B is connected to the communication line, and when a call is received, the loop current detection circuit A is connected to the communication line.

(Function) As a result, it is possible to eliminate the need for a relay circuit for switching between the loop current detection circuit and the polarity reversal detection circuit, thereby making it possible to reduce the cost of the circuit. Furthermore, by using a semiconductor switch circuit in place of a relay circuit, the circuit can be easily integrated, thereby making it possible to downsize the circuit.

(Embodiment) FIG. 2 shows the configuration of a trunk circuit in an embodiment of the present invention. In this figure, the same parts as those in FIG. 3 are given the same reference numerals and detailed explanations will be omitted.

A power supply circuit 3b is connected between each signal line (corresponding to the tip line and ring line of the communication line 1) of the audio signal path 2 via a relay contact 3b, and this power supply circuit 3b
A photocoupler PC2 for loop current detection and a photocoupler PC3 for polarity reversal detection are connected to both ends of the photocoupler PC3 via a semiconductor switch circuit 7, respectively. The semiconductor switch circuit 7 has transistors Q71 to Q73 and bias resistors R71 to R77 connected as shown in the figure, and connects relay contacts 3a and 3b to a detection signal of a photocoupler PC1 that detects the operation of the relay circuit 6 for driving. Accordingly, a switching operation is performed to selectively connect the photocouplers PC1 and PC2 for loop current detection and polarity reversal detection to the communication port l111.

Note that Qr is a switching transistor that drives and controls the relay circuit 6 according to instructions from a υ1 immediate circuit (not shown).

In such a configuration, first, each relay contact is switched to the state shown in the figure during a standby state and when a call is received. In this state, the switching transistor Qr is in the off state and the relay circuit 6 is in the non-operating state.
The phototransistor of the photocoupler PCI for relay operation detection is in an off state. Therefore, a voltage divided by resistors R71 to R73 and resistor R74 is applied between the base and emitter of transistor Q71 of semiconductor switch circuit 7. At this time, the resistance values of each of the resistors R71 to R74 are set so that the voltage between the base and emitter of the transistor Q71 is approximately 0.7 V, so that the transistor Q71 is turned on and the loop current is detected. The photocoupler PC2 is ready for detection operation. In reality, it is necessary to detect 15 mA as a loop current, and the total voltage applied to each resistor R71 to R74 in this case is approximately 3 V, so each resistor R71
~The resistance value of R74 is Ω and R72 for R71-22, respectively.
-10 is Ω, R73-4, 7 is Ω, R74-4, 7 is Ω
It is sufficient to set it to a certain degree. In addition, in this state, the transistor Q72 is turned on, so that the transistor Q72 is connected between the base and emitter of the transistor Q73.
A voltage obtained by dividing the saturation voltage of 1 by resistors R76 and R77 is applied. At this time, since the saturation voltage of transistor Q72 is about 0.4 V, transistor Q73 is turned off. Therefore, the photocoupler PC3 for detecting polarity reversal is set to be disconnected from the communication line 1.

In this case, in order to turn on the transistor Q72 and turn off the transistor Q73, resistors R75 to R
77 to R75-10 and Ω to R76-8,2, respectively.
, R77-4, 7 may be set to about Ω.

Therefore, in such a state during standby and when receiving a call, when the other party makes a call, the power supply circuit 3a is connected to the communication port ii.
, 3b, and this loop current is reliably detected by a photocoupler PC2 for loop current detection. Thus, the calling party is detected.

On the other hand, when a call is made in the standby state, the transistor Qr is turned on according to the instruction from the control circuit, and the relay circuit 6 is operated, thereby causing the relay contacts 3a and 3 to
b are switched, and the power supply circuits 3a and 3b are disconnected from the communication line 1.

Furthermore, when the transistor Qr is turned on, the photocoupler PC1 for relay operation detection is turned on. Therefore, the transistor Q71 is turned off, the photocoupler PC2 for detecting the loop current is disconnected from the communication port Fi1, and since the transistor Q71 is turned off, the transistor Q72 is turned off, and the transistor Q7
3 is turned on, and as a result, the photocoupler PC3 for detecting polarity reversal is connected to the communication line 1 and becomes capable of detecting polarity reversal. Therefore, if a polarity inversion signal arrives from the trunk of the called party in this state, this signal will be reliably detected by the photocoupler PC3, thereby allowing the called party to recognize that the signal can be received.

In this example, the power supply circuit 3a.

The operation of the relay circuit for disconnecting 3b from communication circuit 1i11 is supervised by the photocoupler PCI, and this photocoupler P
Each transistor Q71 to Q73 according to the monitoring output of CI.
This turns on and off the photocoupler PC2 for loop current detection and the photocoupler PC3 for polarity reversal detection.
is selectively connected to the communication line 1, it is possible to switch between the photocoupler PC2 for loop current detection and the photocoupler PC3 for polarity reversal detection using a semiconductor switch without using a relay. The circuit can be made inexpensive, integrated, and miniaturized. In addition, since the operation of the relay circuit 6 is detected by the photocoupler PCI, it is possible to electrically connect the relay circuit 6 and the loop current and polarity reversal detection circuit. It is possible to eliminate the problem that the loop current and polarity reversal detection circuit malfunctions due to the generated switching noise.

Note that the present invention is not limited to the above embodiments. For example, in the above embodiment, a bipolar transistor was used as the semiconductor switch circuit, but other semiconductor switch elements such as an FET may also be used. In addition, the configuration of the semiconductor switch circuit, the configuration of the relay operation detection circuit, the configuration of each loop current and polarity reversal detection circuit, etc. can be modified in various ways without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the switching operation of the relay circuit for connecting/disconnecting the power supply circuit to the communication line is detected by the switching operation detection means, and the switching operation detection circuit detects A semiconductor switch circuit is driven according to the result, and the polarity reversal detection circuit is connected to the communication line when a call is made, and the loop current detection circuit is connected to the communication line when a call is received. Switching between the loop current detection circuit and the polarity reversal detection circuit can be performed without any delay, thereby making it possible to provide a trunk circuit that is inexpensive, suitable for integration, and capable of reducing the size of the circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the functional configuration of a trunk circuit of the present invention, FIG. 2 is a circuit configuration diagram of a trunk circuit according to an embodiment of the present invention, and FIG. 3 is a circuit configuration of a conventional trunk circuit. Figures 4 to 6 are for explaining the operation of the trunk circuit shown in Figure 3. Figure 4 is its equivalent circuit diagram, and Figures 5 and 6 are for signal waveforms and relay contacts, respectively. It is a figure which shows a switching state. 1... Communication line, 2... Audio signal path, 3a, 3b.
...Power supply circuit, 6...Relay circuit, 7...Semiconductor switch circuit, PCl...Photocoupler for relay operation detection, PO2...Photocoupler for loop current detection, PO
2... Photocoupler for detecting polarity reversal, kla, klb
... Relay contact for generating a polarity reversal signal, k2a. k2b...Relay contact for dial pulse generation, k3
a, 3b...Relay contact for connecting and disconnecting the power supply circuit. Applicant's agent Patent attorney Takehiko Suzue Figure 1

Claims (1)

[Claims] A loop current detection circuit that detects loop current in a communication line, a polarity reversal detection circuit that detects polarity reversal, a relay circuit that connects and disconnects a power supply circuit to the communication line in response to outgoing and incoming calls, and this relay circuit. switching operation detection means for detecting the switching operation of the switching operation; and a switching operation detection means that operates according to the detection result of the switching operation detection circuit to connect the polarity reversal detection circuit to the communication line when a call is made, and the loop current detection circuit when a call is received. and a semiconductor switch circuit for connecting the communication line to the communication line.