JPS62217793A - Trunk line interface circuit - Google Patents

Abstract

PURPOSE:To use a small-sized photocoupler and to scale down a circuit by installing a polarity inversion detection circuit on a circuit in parallel. CONSTITUTION:At the time of detecting an incoming, the contact point S1 of a switching relay S is in off position. Due to the arrival of a bell signal a current is conducted to the prescribed route, and a space across collectors and emitters in photocouplers PC1 and PC2 is switched. Signals are integrated (R5, C2), and incoming detection information can be obtained an OUT-2 terminal. At the time of inverting polarity a loop forming signal turns on the contact point S1 to form an outgoing loop.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a central office line trunk interface circuit of a switching device.

(Prior art and its problems) In recent years, the subscriber line interface of PBX and key telephone equipment has been computerized, and LS, generally called 5LIC, has been computerized.
I and H[C appear. As computerization progresses in this way, the parts of the system components that have been computerized and the parts that have not been computerized will be extremely unevenly mounted, and the mounting unit dimensions will inevitably become uneven. Compared to PBX and key telephone equipment, the extension side interface is becoming increasingly electronic.
The station line side interface still uses large transformers, relays, and large capacitors.

This is because the DC voltage 9 applied is excessive and the current capacity is also required to be more than 100 mA, and also for lightning protection.

In the current telephone switching network, when communicating between telephone terminals,
It is necessary to detect the reversal of the power supply polarity between the station lines L+ and Lz. For example, in private branch exchange equipment, it is necessary to detect the polarity reversal sent by the station when the other party answers the call.

Furthermore, when a call is received, a polarity reversal sent from the station is detected almost simultaneously with the ringing signal, and an automatic response or collision prevention function may be realized. In such an exchange device, it is necessary to detect changes in information on the other party. Further, an incoming call detection circuit is essential in a telephone switching network.

Next, a conventional circuit is shown in FIG. Here, L I +L
2 is subscriber line (office line) terminal, RA is incoming call detection circuit, PC
,, pcz is a photocoupler for incoming call detection, R6 is a resistor for adjusting the sensitivity of photocoupler P CI + P Cz, R5 and C2 are integrating circuits, RL is a dial pulse sending relay of the dial pulse sending circuit, and re is its contact point , C is a spark extinguishing capacitor, R is a spark absorption resistor, S is a switching relay, S is a contact point, SW is a communication path switch, T
E L, ,~place.

is a terminal telephone, T is an audio coupling transformer, PC4 is a photocoupler for detecting polarity reversal, and D is a diode for reverse voltage protection of the photocoupler PC3.

The operation when making a call to the z office line via the call path switch SW based on the call operation of the terminal telephone device (for example, station) will be explained. First, a collision prevention detection circuit (not shown),
The voltage between the L2 terminal and the ground is detected to determine whether a calling signal (polarity inversion information) is being applied. Here, in the case of signal heat, a loop formation signal is output to turn the S relay ON, and the S contact closes (the state shown in the figure), and at the same time, RL IJ I/- turns ON and the rE contact is closed. to form a DC loop. Also, if there is a signal, it is assumed that the station line is busy, and the same process is performed for the next station line.
This prevents collision with the calling signal for the operation of calling the central office line. After the loop is formed, a dial pulse will be sent out. First, the RL 'J relay is turned ON, and after the rβ contact is closed, the rβ contact is opened by the dial selection signal and a dial pulse (10/20PPS) is sent. It is sent to the central office line.

On the other hand, when an incoming call is received, when an incoming bell signal arrives, the switching relay S is in the OFF position, which is the opposite position from the illustrated state), (L + -P Cz = R2 = C +
"S + - L z ) or (L z = S r -
A current flows through the path C+ -Rz -P Cl-1-r), switches between the collectors and emitters of the photocouplers pc, pc2, and the signal is integrated by an integrating circuit made up of R, C, and 0UT- Outputs incoming call information to terminal 2. Both wave rectification is performed by photocouplers PC and PC2.
This is to ensure accurate incoming call detection even for Centrex incoming signals in which 16 Hz for 0.2 seconds is generated only twice in 3 seconds.

When detecting polarity reversal, the switching relay S is in the ON position (the state shown in the figure), and when L+ is positive + LZ is negative, the light emitting diode side of the photocoupler PCi does not emit light, and the polarity reversal information output terminal 0UT- The polarity reversal information of 1 is HIGH (
+5V). However, when Ll is negative and L2 is positive, the light emitting diode of photocoupler PC3 emits light and outputs LOW (OV) as polarity information, so it is possible to detect that the polarity has changed. This photo coupler P
C3 is required to flow a current of about 120 mA.

Therefore, a general-purpose small photocoupler does not have enough current capacity, is expensive, and must be large in size. Further, a current of about 120 mA must be passed through the transformer T, which similarly requires a high price and a large size. In addition, the inductance cannot be made large, and it is difficult to obtain crosstalk characteristics where the coupling characteristics due to leakage magnetic flux between the transformers are below a certain value.

Recently, in order to realize a circuit that does not use this large transformer,
Computerization is progressing. An example of this electronic circuit is shown in FIG. Here, T1 is an audio coupling transformer, C1 is a capacitor that blocks direct current, PC is a photocoupler for detecting polarity reversal, D2 is a reverse voltage protection diode for photocoupler PC4, 1 is a diode bridge, and 2 is a central line. When viewed from the side, the electronic sink circuit exhibits a resistance value of approximately 50 to 300 ohms in terms of direct current, and a resistance value close to infinity in terms of alternating current. 3 is a dial pulse sending circuit.

To explain the operation of this conventional example when making a call to the central office line, first, a collision prevention detection circuit (not shown) detects the voltage between the L2 terminal and the earth (earth) and determines whether a ringing signal is being applied. do. Here, in the case of signal heat, a loop formation signal is output to turn on the S relay,
The contacts close (state a as shown) and at the same time the dial pulse output path operates to form a DC loop. If there is a signal, it is assumed that the station line is busy, and the same procedure is applied to the next station line to prevent collision with the calling signal in the operation of calling the station line.

On the other hand, the electronic sink circuit 2 is required to pass a direct current but not an alternating current. For this reason, A in the figure,
This synchro path is driven by human power that smooths the voltage across B. The dots in the figure are the above-mentioned smoothing voltages.

The operation when sending out dial pulses is as follows. When making a dial, use the TT that supports dial operation.
L level or C-MOS level dial signal manual power is L
It becomes OW, and the current loop of (L, → D2 → diode bridge 1 - electronic synchronization log 2 digital pulse sending circuit 3 - diode bridge 1 → S, → Lz) or (L z = S l - diode bridge 1 - A current loop of electronic sink circuit 2 - dial pulse sending circuit 3 → diode bridge 1 - P Cm -L+ is created, so capacitor C4 is charged with charge, then transistor Q is turned on, and electronic sink circuit 2 works. At dial break, the above dial signal is HIGH
The charge stored in capacitor C2 is mainly
It is discharged through the base of transistor Q and resistor R8. Furthermore, a portion of the current is discharged through the resistor R1, but this current is small compared to the former.

In addition, when making a dial, the electronic sink circuit 2 must be driven immediately after the meter, and a DC loop must be formed for L2. However, since the charge on capacitor C4 has decreased, charging is performed first. Thereafter, the transistor Q is turned on and the electronic sink circuit 2 performs normal operation.

As explained above, from the perspective of L+ and Lx, when transmitting dial pulses, when moving from break to meter, it takes time to charge capacitor C4, which has the disadvantage that the transmitted dial pulse waveform is deformed. be.

In the conventional example shown in FIG. 2, the incoming bell signal detection circuit RA is exactly the same as the circuit shown in FIG. In the figure, the DC component of the transformer T is cut off by the capacitor C1, and the current of about L2QmA described above is not passed to the transformer T1, but to the electronic sink circuit 2. Since there is no need to use the large transformer shown in FIG. 1, the transformer is miniaturized. However, the photocoupler P for polarity reversal detection is still
Approximately 120mA must be passed through C4, and the size and price are large and expensive. Furthermore, when the DC loop is closed, L r
, L z must be 50 to 300 Ω, but due to the voltage drop of the forward voltage on the light emitting diode side of photocoupler PCa or the forward voltage of diode D2, the above-mentioned DC resistance restriction It is difficult to configure the electronic sink circuit 2 so as to satisfy the following.

(Objective of the Invention) The present invention provides a polarity reversal detection circuit in parallel with the line, thereby using a general-purpose small photocoupler instead of a large photocoupler, and sharing the incoming call detection circuit and the polarity reversal circuit. The present invention provides a station line interface circuit that reduces the amount of noise.

(Structure of the Invention) To achieve this object, the station line interface circuit of the present invention connects the current detection means between the station lines during standby and in parallel with the DC loop via a parallel connection path when forming a DC loop. configured to be connected to the office line, and detects an incoming call on the office line during the standby period by the current detection means;
When the DC loop is formed, a response from the other party is detected by reversing the polarity of the cough line.

(Example) Examples of the present invention will be described in detail below.

FIG. 3 shows an embodiment of the present invention. Here, the same reference numerals as in FIGS. 1 and 2 indicate the same items.

PC, is a photo coupler for incoming call detection, PC2 is a photo coupler used for incoming call detection and polarity reversal detection, R,,D
, is the reverse voltage protection resistor and diode, and D4 is the current Ll.
A diode for blocking the current flowing through the resistor R, which is connected in parallel with the light emitting part of the photocoupler PC2 when flowing from to Lz, D3 is a diode provided so that the current flowing in both directions is equal when detecting an incoming call, Q, , Q2 are transistors. The operation of the dial pulse output path 3 of the switching relay 81 described above is the same as the conventional one, so the explanation thereof will be omitted.

The operation when an incoming call is detected will be explained. S is located off. When the bell signal comes, (L, → PC2-DJ-R2-
CI-3. (OF F)→L or (t, z-3, (O
Current flows through the paths FF)→C,→R, -D3-PC, -Ll). Photocabra pc,, pc.

A switch operates between the collector and emitter of R5IC2.
The signal is integrated by an integrating circuit, and incoming call detection information is output to the 0UT=2 terminal. The reason why photocoupler PC and PC2 perform double-wave rectification is to obtain accurate incoming information even for Centrex incoming signals, as mentioned above.
The principle operation of the present invention can be performed even without PChD3.

The operation when polarity is reversed will be explained. At this time, the loop forming signal causes the contact S of the switching relay S to be turned on so as to form a transmission loop (the state shown in the figure).

■ During standby, is e), and when Lx is θ, during normal times, L is ■ (L + −P Cz = RI.

→Ql-05-3L(ON)-Lz), a DC loop is formed. At this time, the resistance R1° causes alternating current loss, so the resistance RIG cannot be reduced much. However, in order to operate the photocoupler PCt in the emotional region, it is necessary to supply as much current as possible to the photocoupler PC2. Therefore, the diode D4 is (L, →R
1→RIG-'Ql→Ds→Sl(ON)-Lm).

Also, in this state, when dial breaks, Ll.

The DC resistance seen from Lz must appear to be 10 OKΩ or more. Therefore, at the time of dial break, the dial sending signal is set to HIGH, turning on the transistor Q2, causing the photocoupler PC to emit light, and turning off the transistor Q. Therefore, (Ll-PC2-R,.-Q l-D s
→S, (ON)→L2) loop is broken, Ll, Lx
Increase the DC resistance seen from At this time (Ll→R11→
PCs → D5-81 → L2] and (L, → R7 → D, →
S1→L2) current loop also occurs, but R9+R13
can be made large enough. For example, R11 is 20O
It can be made more than KΩ. Moreover, R7 is Ql,
P.C.

This is a resistor for reverse breakdown voltage protection, and its resistance value is sufficiently high. This resistor R9 may be several hundred ohms and is not relevant to the essence of the invention.

When the polarity is reversed, the diode D5 has the opposite polarity (
Lz is ■), no current flows to the photocoupler PCI, and L
These polarity reversal detection circuits can be ignored since they do not affect the direct current resistance seen from l and Lz.

■ During standby, when Ll is θ+L2 is O, since L1 is θ+L and z is O, the diode Ds has the opposite polarity, so no current flows through the photocoupler Pct, and at this time the DC seen from L I and L t The resistance also increases at the time of dial break, and the DC resistance seen from Lz is sufficiently high and has no effect, so the polarity reversal detection circuit can be ignored.

When the polarity is reversed, L becomes ■+L2 becomes e, so (Ll
-PCg-R+o-Q+=Ds-3+(ON)-Lz)
Current flows through the path. Again, diode D4 is (
L I-RI-R+ o -Q I-D s = S
1(ON)-Lz) functions to prevent current from flowing into the path. The present invention easily configures a sink circuit that satisfies the DC resistance limit (50 to 300Ω) seen from L, Lz without inserting a photocoupler for polarity detection in series in the loop, and also allows an incoming call detection circuit to be configured. It is shared and the circuit scale is reduced. The resistor R9 is added for the purpose of protecting the transistor Ql and the photocoupler PC3, and has no relation to the essential part of the present invention.

Furthermore, when connecting to a central office line, in a switching device where the polarity is set in advance as θ + L2 = ■, when making a call, always Ll
is e and L2 is ■, and the polarity is the same at dial break, so D becomes the cutoff. Therefore, as in the embodiment of FIG. 4, the photocoupler pc5. Transistor Ql
l Resistor R9+ RIO+ R13 is omitted and the resistor R
14 can be replaced by a diode Db.

(Effects of the Invention) As explained above, according to the present invention, by providing the polarity reversal detection circuit in parallel with the DC loop forming circuit for the line, a general-purpose small-sized It has the advantage that a photocoupler can be used, and the incoming call detection circuit and polarity inversion circuit can be shared, reducing the circuit scale.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional polarity reversal detection circuit and an incoming call detection circuit, FIG. 2 is a circuit diagram showing another example of a conventional polarity reversal detection circuit and an incoming call detection circuit, and FIGS. FIG. 4 is a circuit diagram showing an embodiment of the present invention. L + , L 2... Office line terminal, 1... Diode bridge, 2... Electronic sink circuit, T
, T,...Transformer, D,~D6...Diode, C,C,~C4...Capacitor, RA...Incoming call detection circuit, Q,Q,,Q2 river transistor, PC,
~PC,... Photocoupler, R, R, ~RI4... Resistor, S W Middle channel switch, T E L + ~ Ll... Terminal telephone.

Claims (3)

[Claims] (1) The current detection means is configured to be connected between the office lines during standby and to the office line in parallel with the DC loop via a parallel connection path when forming a DC loop, and the current detection means The office line interface circuit is configured to detect an incoming call on the office line when on standby, and to detect a response from the other party by reversing the polarity of the office line when forming the DC loop. (2) The current detection means includes a series circuit in which a photocoupler and a diode are connected with the same polarity, and the parallel connection path is a current path formed in parallel to the DC loop from the connection point of the photocoupler and diode. A central office line interface circuit according to claim 1, characterized in that the central office line interface circuit comprises: (3) The interface circuit according to claim 2, wherein the current path includes a switch element that is controlled to be turned on or off by a dial pulse.