JPH0350479B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a polarity reversal detection circuit used in a central branch trunk interface of a private branch exchange.

(Prior art and its problems) In recent years, the subscriber line interface of PBX and key telephone equipment has been computerized, and SLIC is generally used.
LSIs and HICs called 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. In PBX and key telephone equipment, the extension side interface is becoming increasingly computerized, but the central office line side interface is dependent on large transformers,
Relays and large capacitors are used. This is because the applied DC voltage and incoming signal are excessive, and the current capacity also requires a hundred and several tens of mA, and is also a measure against lightning.

In current telephone switching networks, when communicating between telephone terminals, it is necessary to detect reversal of power supply polarity between central office lines L ₁ and L ₂ . 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 a switching device, it is necessary to detect a change in polarity.

Next, a conventional circuit is shown in FIG. Here, L ₁ ,
L ₂ is a subscriber line (office line) terminal, RA is an incoming call detection circuit, T is an audio coupling transformer, PC ₁ and PC ₂ are photocouplers for polarity reversal detection, and RL is a dial pulse sending circuit of the dial pulse sending circuit. relay,
rl is the contact point, C is the spark absorption capacitor, R ₀ is the spark absorption resistor, S is the switching relay, S ₁ is the contact point, SW is the communication path switch, and TEL ₁ to TELn are terminal telephones.

The operation when making a call to the central office line via the call path switch SW based on the call operation of the terminal telephone TEL (for example, TEL ₁ ) will be explained. First, a collision prevention detection circuit (not shown) detects the voltage between the _L2 terminal and the ground, and determines whether a calling signal is being applied. If there is no signal, a loop formation signal is output to turn on the S relay, the _S1 contact closes (state shown), and at the same time the RL relay turns on.
Then, the rl contact is closed and forms a DC loop. Also, if there is a signal, it is assumed that the station line is busy,
The same procedure is applied to the next central office line to prevent collision with the calling signal during the central office line origination operation. After forming the loop, a dial pulse will be sent,
First, the RL relay is turned ON and the RL contact is closed, then the RL contact is opened by the dial selection signal and a dial pulse (10/20PPS) is sent to the central office line.

When the DC loop is closed, two types of conditions occur: When L ₁ and L ₂ are, [L ₁ → Transformer T → Photocoupler PC ₁ → Transformer T → Contact
rl → contact S ₁ → L ₂ ], the light emitting diode side of photocoupler PC ₁ emits light, and conduction occurs between the collector and emitter on the light receiving side, and the polarity information, that is, the loop detection output, is LOW at the output terminal OUT ₁ . (0V)
Output. Next, when L ₁ and L ₂ are, [L ₂
→Contact S ₁ →Contact RL→Transformer T→Photocoupler
A current flows through the path of PC ₂ → transformer T → L ₁ ], the light emitting diode side of the photocoupler PC ₂ emits light, and conduction occurs between the collector and emitter on the light receiving side, and the polarity information, that is, the loop detection output, is output from the output terminal OUT ₂ .
It becomes LOW (0V). When the DC loop is open,
No current flows through photocouplers PC ₁ and PC ₂ , and loop detection outputs OUT ₁ and OUT ₂ become HIGH (+5V). Through such operations, loop detection and polarity reversal detection are performed.

However, since a maximum current of about 120mA is required to flow through the light emitting diode side of this photocoupler PC ₁ or PC ₂ , a general-purpose small photocoupler does not have enough current capacity, and a large and expensive one is required. . At the same time, transformer T
It must be able to flow a current of around 120mA, which means it is expensive and requires a large size. Furthermore, the inductance cannot be set large, and it is difficult to obtain crosstalk characteristics below a predetermined value due to the coupling characteristics due to leakage magnetic flux between the transformers.

Recently, digitization has been progressing with the aim of eliminating large transformers. An example of this conventional electronic polarity reversal detection circuit is shown in FIG. Here, T ₁ is an audio coupling transformer, C ₁ is a DC current blocking capacitor of the transformer, PC ₁ and PC ₂ are photocouplers for loop detection, 1 is a diode bridge,
2 is an electronic sink circuit that exhibits a resistance of about 50 to 300 Ω in direct current and a value close to infinity in alternating current;
3 is a dial pulse sending circuit.

To explain the operation when making a call from a central office line, first,
A collision prevention detection circuit (not shown) detects the voltage between the _L2 terminal and the ground, determines whether a ringing signal is applied, and outputs a loop formation signal if no signal is applied. Turn on the S relay, close the _S1 contact (state shown), and at the same time the dial pulse sending circuit operates to form a DC loop, but if there is a signal, the station line is considered busy,
The same procedure is applied to the next central office line to prevent collision with the calling signal during the central office line origination operation.

On the other hand, the electronic sink circuit 2 is required to pass a direct current but not an alternating current. For this reason,
This sink circuit is driven by an input obtained by smoothing the voltage between A and B in the figure. Point D in the figure is the above-mentioned smoothing voltage.

The operation when sending out dial pulses is as follows. When making a dial, the TTL level or C/MOS level dial signal input corresponding to the dial operation becomes LOW, and [L ₁ → PC ₁ → Diode bridge 1 → Electronic sink circuit 2 → Dial pulse sending circuit 3 → Diode Bridge 1 → S ₁
→L ₂ ] current loop or [L ₂ →S ₁ → diode bridge 1 → electronic sink circuit 2 → dial pulse sending circuit 3 → diode bridge 1 →
Since a current loop of PC ₂ →L ₁ ] is formed, the capacitor C ₂ is charged, and then the transistor Q is turned on and the electronic sink circuit 2 is operated. At dial break, the dial signal is HIGH, and the charge stored in the capacitor _C2 is mainly discharged through the base of the transistor Q and the resistor _R3 . Furthermore, a portion is discharged through resistor R ₂ , but this current is small compared to the former.

Note that when making dials, it is necessary to drive the electronic sink circuit 2 immediately after making the dials to form a DC loop for L ₁ and L ₂ . but,
Since the charge on capacitor C ₂ is decreasing, charging takes place first. Thereafter, the transistor Q is turned on and the electronic sink circuit 2 performs normal operation. As explained above, when looking at L ₁ and L ₂ , when sending dial pulses, when moving from break to make, it takes time to charge capacitor C ₂ , so the waveform of the dial pulses sent is distorted. There are also disadvantages.

The transformer T ₁ in the figure cuts off the direct current with a capacitor C ₁ , and causes the aforementioned current of about 120 mA to flow not to the transformer T ₁ but to the electronic sink circuit 2 . Therefore, it is not necessary to use the large transformer shown in FIG. 1, and the transformer _T1 is miniaturized. However, there is still a photocoupler PC ₁ for polarity reversal detection,
Approximately 120mA must flow through PC ₂ , and it is large and expensive. Furthermore, when the dial pulse sending circuit is in the on state, the DC resistance seen from L ₁ and L ₂ must be 50 to 300Ω. The voltage drop in the forward voltage on the light emitting diode side of the photocouplers PC ₁ and PC ₂ makes it difficult to satisfy the above-mentioned direct current resistance restriction. As described above, conventional DC loop detection circuits cannot be made smaller or lower in price.

(Objective and Features of the Invention) The present invention provides a polarity reversal detection circuit that has a circuit configuration that allows the use of a general-purpose small photo coupler without using these large photo couplers, and can be realized in a small size and at low cost. purpose.

The present invention is characterized in that it does not include a photocoupler in series with the sink circuit as in the prior art, and has a circuit configuration that is not affected by the forward voltage of the photocoupler.

(Example) The present invention will be explained 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 ₃ and PC ₄ are photocouplers for detecting polarity reversal information,
Q ₁ and Q ₂ are transistors that operate as switch elements, D ₁ and D ₂ are diodes for reverse voltage protection of photocouplers PC ₅ and PC ₆ , R ₄ and R ₅ are resistors for reverse voltage protection,
R ₆ and R ₇ are sensitivity adjustment resistors, and R ₈ , R ₉ , R ₁₀ , and R ₁₁ are resistors. OUT ₁ and OUT ₂ are output terminals to which a polarity inverted signal is output depending on the polarity of L ₁ and L ₂ . Monitoring both OUT ₁ and OUT ₂ outputs provides a loop detection output. The operations of the switching relay S and the dial pulse sending circuit 3 described above are the same as those of the prior art, so a description thereof will be omitted.

Since the polarity connected to L ₁ and L ₂ is usually unknown in button telephone devices, it is necessary to consider two cases.

In this embodiment, when detecting a current loop, photocouplers PC ₅ and PC ₆ are off and either transistor Q ₁ or Q ₂ is conducting.

Normally, when _{L1 and L2} are in this state, the loop forming signal causes the contact _S1 of the switching relay S to be turned on (the state shown in the figure) so as to form a transmission loop.

The current is [L ₁ → PC ₄ → R ₇ → Q ₂ → D ₂ → S ₁ → L ₂ ]
, and the photocoupler PC ₄ collector/
There is continuity between the emitters, and the loop detection output is OUT ₂
Outputs LOW to.

Normally, when L ₁ and L ₂ are in this state, the loop forming signal causes the contact S ₁ of the switching relay S to be turned on (the state shown in the figure) so as to form a transmission loop.

The current is [L ₂ →S ₁ →PC ₃ →R ₆ →Q ₁ →D ₁ →L ₁ ]
, and the photocoupler PC ₃ collector/
There is continuity between the emitters and the loop detection output OUT ₁ .
Outputs LOW. When the loop is open,
Since both of the above-mentioned paths are not formed and no current flows, the loop detection outputs OUT ₁ and OUT ₂ become HIGH.

Here, since no photocoupler is inserted in series between the station lines L ₁ and L ₂ , the condition that the resistance seen from the station lines L ₁ and L ₂ must be 50 to 300 Ω is satisfied.

However, at the time of dial break, the central office lines L ₁ and L ₂
There is a condition that the impedance seen from is 100KΩ or more.

In order to satisfy this requirement, at the time of dial break, the photocouplers PC ₅ and PC ₆ are made conductive, and the transistors Q ₁ and Q ₂ are each turned off. That is,
At dial break, [L ₁ →PC ₄ →R ₇ →Q ₂ →D ₂ →
S ₁ →L ₂ ] or [L ₂ →S ₁ →PC ₃ →R ₆ →Q ₁ →D ₁ →
The loop of [L ₁ ] is broken, and [L ₁ →R ₉ →PC ₆ →D ₂ →
S ₁ →L ₂ ] or [L ₂ →S ₁ →R ₈ →PC ₅ →D ₁ →L ₁ ]
route enters between the station wires L ₁ and L ₂ , but the resistances R ₈ and R ₉
can be set to a value of 100KΩ or more, so this is not a problem.
In this way, loop detection is performed and the configuration satisfies the above-mentioned conditions.

FIG. 4 shows an example in which the polarity of the office line is fixed, that is, when dialing, for example, _L1 is set to _L2 . Since the polarity is fixed, photocoupler PC ₅ in Figure 3 can be removed. That is, at the time of dial break, diode D ₃ ,
Since the photocoupler PC ₇ has the opposite polarity, the loop that is connected in parallel between L ₁ and L ₂ [L ₁ → D ₃ → R ₁₂ → PC ₇ → S ₁ → L ₂ ] is broken.

As is clear from the above description, the polarity reversal detection circuit of the present invention shown in _{FIG .}
In the central office trunk of the switching equipment connected to
A first series detection circuit constituted by a series connection of a first switching element Q 1 and _{a resistor R 6 controlled} by a light-emitting side element of a photocoupler PC ₃ and a light-receiving side element of a second photocoupler PC ₅ ; A second switching element controlled by the light-emitting side element of the photocoupler PC ₄ of No. 3 and the light-receiving side element of the fourth photocoupler PC ₆ .
A second circuit formed by a series connection of Q ₂ and resistor R ₇
The series detection circuits are connected to each other with opposite polarity to the direct current loop forming circuit (L ₁ -1-2-3-1-) of the central office line trunk.
L ₂ ) is connected to the office line in parallel with
The first photocoupler PC ₃ and the third photocoupler PC ₄ are used to detect the formation of a DC loop in the DC loop forming circuit, and the second photocoupler
PC ₅ and the fourth photocoupler PC ₆ are configured to control off the first switching element Q ₁ and the second switching element Q ₂ at the time of dial break, and the first photocoupler PC ₃ and the third photocoupler The light receiving side element of PC ₄ is configured to obtain a polarity inverted output.

Further, the polarity reversal detection circuit of the present invention shown in FIG. 4, which can be used when the polarity of the central office line is known in advance, can be used in the central office line trunk of the switching equipment connected to the central office lines L ₁ and L ₂ . Inside, the first photocoupler
A first series detection circuit configured by a series connection of a switching element Q ₂ controlled by a light emitting side element of PC ₄ and a light receiving side element of a second photocoupler PC ₆ and a resistor R ₇ , and a third photocoupler PC The second element consists of a series connection of the light-emitting side element of ₇ and a resistor R _{of 12} .
The DC loop forming circuit (L ₁ -1-2-3-1
−L ₂ ) is connected to the office line in parallel with
The first photocoupler PC ₄ and the third photocoupler PC ₇ are used to detect the formation of a DC loop in the DC loop formation circuit, and the second photocoupler
PC ₆ is configured to turn off the switching element Q ₂ at the time of dial break, and is configured to obtain a polarity inverted output from the light receiving side elements of the first photocoupler PC ₄ and the third photocoupler PC ₇ . .

(Effects of the Invention) As explained above, according to the present invention, since the current on the light emitting diode side of the photocoupler can be reduced, it is possible to configure a polarity reversal detection circuit using an inexpensive photocoupler. A compact subscriber line interface can be provided. Furthermore, there is an advantage that the DC impedance of the station lines L ₁ and L ₂ is not substantially affected. In particular, the present invention is suitable for cases where the polarity of L ₁ and L ₂ is unknown.
It has the advantage that it can be applied even in obvious cases and can be used for all telephone devices.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional polarity reversal detection circuit, FIG. 2 is a circuit diagram showing an example of a conventional polarity reversal detection circuit, FIG. 3 is a circuit diagram showing an example of the present invention, and FIG. The figure is a circuit diagram showing another embodiment of the present invention. L ₁ , L ₂ ... central line, 1 ... diode bridge,
2...Electronic sink circuit, 3...Dial pulse sending circuit, RA...Incoming call detection circuit, T, _T1 ...Transformer, C, _C1 , _C2 ...Capacitor, PC ₁ to _{PC 7}
... Photocoupler, D ₁ , D ₂ , D ₃ , D ₄ ... Diode, Q ₁ , Q ₂ , Q ₃ ... Transistor, R, R ₁ ...
R ₁₄ ...Resistor, SW...Call path switch, TEL ₁ ~
TELn...Terminal telephone.

Claims (1)

[Scope of Claims] 1. A switching element controlled by a light-emitting side element of a first photocoupler and a light-receiving side element of a second photocoupler and a resistor connected in series in a central office line trunk of a switching device connected to a central office line. The first configured by the connection
and a second series detection circuit constituted by a series connection of the light-emitting side element of the third photocoupler and a resistor so that they have opposite polarities and are parallel to the DC loop forming circuit of the central office line trunk. is connected to the central office line, the first photocoupler and the third photocoupler are used to detect the formation of a DC loop in the DC loop formation circuit, and the second photocoupler controls the switching element to turn off at the time of dial break. A polarity reversal detection circuit configured to perform a polarity reversal detection circuit, and configured to obtain a polarity reversal output from the light-receiving side elements of the first photocoupler and the third photocoupler. 2 In the central office line trunk of a switching device connected to the central office line, a first switching element controlled by the light-emitting side element of the first photocoupler and the light-receiving side element of the second photocoupler is connected in series with a resistor. A second series detection circuit configured by a resistor and a first series detection circuit connected in series, a second switching element controlled by the light-emitting side element of the third photocoupler and the light-receiving side element of the fourth photocoupler, and a resistor. The detection circuits are connected to the central office line so as to be parallel to the DC loop forming circuit of the central office line trunk with opposite polarities, and the first photocoupler and the third photocoupler are connected to the DC loop forming circuit of the DC loop forming circuit. The second photocoupler and the fourth photocoupler are configured to turn off the first switching element and the second switching element when the dial breaks, and the first photocoupler and the third photocoupler are used for detection. A polarity reversal detection circuit configured to obtain a polarity reversal output from the light receiving side element.