JPH0444476B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a dial pulse sending circuit used in a central office line trunk interface 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 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, while the extension side interface is becoming increasingly computerized, the central office line side interface still uses 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.

Conventionally, relay contacts have been used to send out dial pulses in central office trunk interface circuits. An example is shown in FIG. here,
L ₁ and L ₂ are subscriber line (office line) inlet terminals, RL is a dial pulse sending relay that operates based on dial signals, RL is a contact of the RL relay, SW is a call path switch, TEL ₁ to TEL _o is a terminal telephone, R is a spark absorption resistor, C is a spark absorption capacitor, T is an audio coupling transformer, and RA is an incoming signal detection circuit. Relay contact rl is connected in series to station wires L ₁ and L ₂ ,
Based on the calling operation of the terminal telephone TEL (for example, TEL ₁ ), the central office lines L ₁ and L ₂ are captured via the telephone path switch SW, and then the line loop is established by dialing and turning on and off this RL relay. The dial pulse was sent out by making and breaking the . R and C are for absorbing the spark discharge generated by the relay contact RL. In this circuit, a current of about 12mA must flow through the RL relay,
Conventionally, mercury relays have been widely used, but they are expensive, large in size, must be mounted upright, and there are restrictions on the direction in which they can be mounted. Relays other than mercury relays have no directionality, but are similar in price and size, and have the disadvantage of being less durable. Further, since the capacitor C for absorbing sparks requires sufficient withstand voltage, a large capacitor is required. Next, since the transformer T is also required to pass a current of about 120 mA, it is required to be expensive and large in size. Since such large components are used, the mounting area is large and the cost of the components is high. Also,
Since the inductance of the transformer cannot be set large and coupling due to leakage magnetic flux occurs between the transformers, it is difficult to obtain crosstalk characteristics with a low leakage level below a predetermined value. This is the biggest reason why it is difficult to computerize central office line trunk circuits.

An electronic circuit has been proposed to overcome the drawbacks of the conventional example shown in FIG. 1 (Japanese Patent Publication No. 58-2512). In addition, the inventors of the present application have disclosed a circuit in which a dial pulse sending circuit is formed using a semiconductor switch element in Japanese Patent Application No. 61-59581 (Japanese Unexamined Patent Publication No. 62-217794) and Japanese Patent Application No. 61-59582 (Japanese Patent Application No. 61-59582). (Kokai No. 62-217755).

However, in this known circuit and the circuit according to the prior application, there is a non-negligible attenuation of the speech voice current in the dial pulse sending circuit, and when the distance to the station is short, the transistor in the dial pulse sending circuit saturates, causing the transmission of voice current. This has the disadvantage that the waveform of the pulse is deformed.

(Objective of the Invention) The object of the present invention is to reduce the voltage drop caused by the semiconductor switch element, to ignore the attenuation of the speech voice current, and to transmit an undeformed pulse waveform even when the distance to the station is short. An object of the present invention is to provide a dial pulse sending circuit with a small circuit configuration.

(Structure of the Invention) To achieve this objective, the dial pulse sending circuit of the present invention uses a diode bridge for converting DC current from a central office line into a DC output with a constant polarity, and a collector-emitter path of a transistor. A dial pulse sending circuit is arranged between a DC loop forming circuit having a DC forming path and is controlled on and off by a dial signal to send dial pulses to the central office line via the diode bridge. a series circuit formed by connecting a resistor in series to a parallel circuit in which an optical coupling element to be controlled and a capacitor are connected in parallel, and connected in parallel with the DC forming path; and a parallel circuit of the optical coupling element and the capacitor. a first switch element circuit driven by the connection point with the resistor and formed to pass direct current but block alternating current; and an output side of the diode bridge driven by the first switch element circuit. A second channel formed and connected to perform the operation of sending out the dial pulse by disconnecting and connecting the direct current to the direct current forming path.
The first switch element circuit is connected so as to clamp the potential at the connection point between the parallel circuit of the photocoupler and the capacitor and the resistor to the potential of a smoothing capacitor that smoothes the output voltage of the diode bridge. The structure includes a clamping diode that prevents the switch circuit element from becoming saturated.

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

FIG. 2 shows an embodiment of the present invention. here,
T ₁ is the audio coupling transformer, C ₁ is the transformer's DC current blocking capacitor, 1 is the diode bridge,
2 is an electronic sink circuit that exhibits a resistance value of about 50 to 300 ohms in direct current and a value close to infinity in alternating current, and 3 is an electronic dial pulse sending circuit.
Note that R ₁ and R ₂ both have a resistance value of about 10 kΩ, and resistor R ₃ has a resistance value of, for example, about 20 Ω. The electronic sink circuit 2 is used as a DC loop forming circuit in which the collector-emitter paths of the Darlington-connected transistors Q ₁ and Q ₂ serve as DC forming paths, and is required to flow a DC current but not an AC current. Ru. For this reason, the voltage between AB in the figure is configured to be divided by resistors R ₁ and R ₂ when the dial signal (HIGH) is present, and the charging current i ₂ at that time is accumulated in capacitor C ₂ and smoothed. This input drives transistors Q ₁ and Q ₂ of the sink circuit. Point D in the figure is the above-mentioned smoothing voltage. PC ₁ is a photocoupler that constitutes an optical coupling switch. When the dial signal (HIGH) is input, the transistor
Q ₅ turns on and photocoupler PC ₁ operates.

Now, based on the calling operation of the terminal phone TEL (for example TEL ₁ ), the central office line is connected via the call path switch SW.
The case where L ₁ and L ₂ are captured and then the dial is operated will be explained in order. Point D shows a predetermined smoothed voltage during dial make, but when dial breaks, current i ₃ in the figure attempts to discharge through photocoupler PC ₁ , transistors Q ₁ and Q ₂ , and resistors R ₂ and R ₃ . When discharge occurs, the charge on capacitor _C2 is lost. In this state, when the next dial make occurs, capacitor C ₂ is charged first, so
It is not possible to immediately drive the electronic sink circuit 2 to form a DC loop. Therefore, when the dial breaks, photocoupler PC ₁ is turned off and the current i ₃
Make sure that it does not flow. As a result of the above, the capacitor _C2 remains charged during the dial break. When the next dial make occurs, the electronic sink circuit 2 is immediately driven to form a DC loop.

Here, it seems that even without the electronic dial pulse sending circuit 3, the electronic sink circuit 2 having the transistors _Q1 and _Q2 , which are controlled on and off by the photocoupler _PC1 , can send out dial pulses. However, if there is no electronic dial pulse sending circuit 3, LOW is input to the dial sending signal at dial break, transistor _Q5 is turned off, photocoupler _PC1 is turned off, and therefore transistors _Q2 and _Q1 are also turned off. Therefore, the voltage between AB increases to a value close to the local voltage of 48V. This causes a current to flow through resistor _R1 to charge _C2 , making it impossible to obtain an accurate break pulse. Therefore, an electronic dial pulse sending circuit 3 is provided,
It is necessary to prevent the current that charges C ₂ from flowing during dial break.

Next, the electronic dial pulse sending circuit 3 will be explained. When the dial signal (HIGH) is input during dial sending, it is inverted by the inverter (INV) and the inverted output becomes LOW.

Supports dial operation when dial makeup
When the TTL level or C/MOS level dial signal input is inverted by the inverter INV and becomes LOW, the operation is [Q ₆ OFF → PC ₂ OFF → Q ₃ ON → Q ₄ ON], and [L ₁ → diode bridge 1-electronic sink circuit 2 → Q ₄ → diode bridge 1 → L ₂ ]
A loop is created and output as a make signal. Next, at the time of dial break, when the dial signal input mentioned above is inverted by the inverter INV and becomes HIGH,
The operation is [Q ₆ ON → PC ₂ ON → Q ₃ OFF → Q ₄ OFF], and [L ₁ → electronic sink circuit 2 → Q ₄ (OFF) →
L ₂ ] loop is opened and output as a break signal. In addition, for the loop that has become "open",
The paths of [R ₄ → D ₂ → collector/emitter of PC ₂ ] enter in parallel. If the resistance R ₄ is set to a value sufficiently higher than 100 kΩ (for example, 200 kΩ), the condition of 100 kΩ or more required for the station to detect a break can be satisfied.

In this way, by simultaneously controlling the photocouplers PC ₁ and PC ₂ with the dial pulse signal, the dial signal can be sent out.

During a call, the dial out signal is HIGH and the inverter INV output is LOW. Therefore, [Q ₆ OFF → PC ₂ OFF], [L ₁ (L ₂ ) → diode bridge 1 → R ₄ → D ₂ → base emitter of Q ₃ → R ₅ → base emitter of Q ₄ → Current flows in the path of diode bridge 1 → L ₂ (L ₁ )] and transistors Q ₃ and Q ₄ are turned on, so [collector-emitter of Q ₃ → R ₅ → base-emitter of Q ₄ ]
The path of L ₁ , L ₂ via diode bridge 1
enter in parallel. Even if _R5 is set to about 1kΩ so that transistor _Q4 is turned on sufficiently, the base of transistor _Q3 is smoothed by the circuit of _R4 , _D2 , and _C3 .
No alternating current flows through the collector of _Q3 , and alternating current signals such as audio are not attenuated by transistor _Q4 .

Note that when the distance to the station is short, the base current of transistor Q ₃ increases, and the voltage between the collector and emitter of transistor Q ₃ decreases, so the transistor
Q ₃ approaches saturation. Here, if a large amplitude AC signal is input without diode D ₁ , since capacitor C ₃ has a value of about 0.015 μF, sufficient smoothing will not be achieved and the AC current will flow to the base of transistor Q ₃ and the transistor Since Q ₃ is saturated, the peak portion of the waveform of the transmitted pulse will be deformed. However, if diodes D ₁ and D ₂ are connected as shown in Figure 2, the capacitance of capacitor C ₂ will be 2.2 μF.
Since this is large, smoothing is sufficiently performed and no AC signal appears at point D. Since the potential at point E is equal to the potential at point D, no AC signal appears at point E and transistor Q ₃
saturation is prevented, and pulses without waveform deformation can be transmitted.

In the embodiment shown in Fig. 2, the photocoupler has a circuit configuration that does not require a large withstand voltage.
This is advantageous in terms of cost reduction.

(Effects of the Invention) As explained above, according to the present invention, when transmitting a dial signal, the dial pulse is transmitted by a semiconductor element driven by an optical coupling element, without using a relay contact, so it is smaller in size and lower in cost. This has the advantage that it is free from restrictions such as mounting direction, and also has the effect that ancillary components such as spark prevention are unnecessary. Further, the voltage drop caused by the semiconductor switch element is small. Furthermore, the attenuation of the speech voice current is negligible, and even when the distance to the station is short, it is possible to send out a pulse waveform without deformation.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an example of a conventional dial pulse sending circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. 1...Diode bridge, 2...Electronic sink circuit (DC loop forming circuit), 3...Electronic dial pulse sending circuit, RA...Incoming call detection circuit, _L1 , _L2 ...
Local line, PC ₁ , PC ₂ ...Photocoupler (optical coupling element),
Q ₁ , Q ₂ , Q ₃ , Q ₄ , Q ₅ , Q ₆ ...Transistor, SW
…Call path switch, TEL ₁ ~ TEL _o …Terminal telephone.

Claims (1)

[Scope of Claims] 1. Between a diode bridge for converting DC current from a station line into a DC output of constant polarity and a DC loop forming circuit having a DC forming path formed by a collector-emitter path of a transistor. placed,
In a dial pulse sending circuit that is controlled on and off by a dial signal and sends a dial pulse to the office line via the diode bridge, a parallel circuit in which an optical coupling element and a capacitor that are controlled on and off by the dial signal are connected in parallel. A series circuit formed by connecting a resistor in series with the DC current forming path and a connection point between the parallel circuit of the optical coupling element and the capacitor and the resistor is driven to allow direct current to pass through, but to generate an alternating current. a first switch element circuit formed to block the output of the dial; a second switch element circuit formed and connected to perform a pulse sending operation; a smoothing circuit for smoothing the output voltage of the diode bridge; and a clamping diode connected to clamp the potential of the capacitor to prevent saturation of the first switch circuit element.