JPS60182898A - Trunk line trunk circuit - Google Patents

Abstract

PURPOSE:To send out an ideal waveform-shaped dial pulse by separating practically a charge/discharge circuit in a DC shunt circuit from a circuit when a relay for forming a DC loop is turned on to generate a dial pulse. CONSTITUTION:A relay K2 and diodes D6-D8 are added to a DC shunt circuit 5. When the relay K1 for forming a DC loop is turned on to generate a dial pulse, a collector current of a transistor TR rises rapidly because a DC voltage is applied to the base of a transistor TR through the diodes D7 and D8, and the relay K2. As a result, a trunk line current represents an ideal intermittent waveform having rapid-rising characteristic without delay, with respect to the relay K1 intermission.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a central office line trunk circuit used in a private branch exchange or the like.

[Technical background of the invention]

As is well known, central office line trunk circuits used in private branch exchanges, etc., transmit and receive voice signals between the central office and the exchange, and also provide direct current loops to the central office current in order to respond to outgoing and incoming calls. It has the function of forming.

FIG. 1 is a diagram showing an example of a conventional office line trunk circuit. In the figure, the station line trunker/return circuit is connected to station 1 by two lines L 1 + L 2 . The DC equivalent circuit of station 1 can be represented by a DC voltage source Es (usually a 48V DC source) and an internal resistor R8, as shown, and a line L1.

The DC resistance of L can be expressed as RL. 2 is station 1
incoming signal from (typically 16 Hz, 100Vrm
This is an AC signal detection circuit of the order of magnitude a, and is composed of a capacitor c1, a resistor R1, a photocoupler PH1, and a diode D8 connected in parallel to the primary side of the photocoupler PH.

An incoming call detection circuit 3 is connected to the secondary side of the photocoupler PI (1). 4 is a relay circuit having 1 as a relay for forming a DC loop when responding to an incoming signal or transmitting an incoming signal, and 5 is a DC is a DC shunt circuit that exhibits low resistance and high resistance in terms of AC.This DC shunt circuit 5 is
It is composed of a transistor TR forming a DC path, a photodischarge circuit consisting of a resistor R2 and a capacitor C2 connected to each other, and an emitter resistor R3, and all DC current from the station 1 flows through this DC shunt circuit 5. being done. Reference numeral 6 denotes a rectifier circuit consisting of four diodes rD2 to D, which allow the DC shunt circuit 5 to operate normally regardless of the polarity of the current flowing through the line L11L. 7 is an AC shunt circuit that exhibits low resistance in AC and high resistance in DC;
The voice signal from the station 1 with a DC current superimposed thereon passes through the AC shunt circuit 7, and is sent to the switch frame 8 in the exchange. communicated.

In the above configuration, when an incoming call signal arrives from station 1 and the called party responds by taking off-hook of the telephone, relay KX closes and a DC loop is formed with station 1, while an AC The shunt circuit 7 and the switch frame 8 form a communication path between the office line trunk and the other party's telephone, thereby allowing communication between the office 1 and the extension telephone.

On the other hand, when the dial pulse is sent out, the relay is closed in conjunction with the off-hook by the caller, and a DC loop is formed with the station 1. If you perform a dial operation in this state, the relay will be activated the number of times corresponding to the dialed number.
is intermittent. FIG. 2 shows signal waveforms of various parts when dialing the number "2" is performed, for example. As shown in FIG.
Intermittent twice in the interval from ~t4. As a result, a dial pulse is sent to station 1.

[Problems with background technology]

By the way, the DC shunt circuit 5 includes a transistor TR'! through which the DC current from the station 1 flows. i- However, the pace of this transistor TR is similar to that of resistor R8 and capacitor C2.
) is connected to the connection point P between the resistor R8 and the capacitor C2 of the charging/discharging circuit. A bias voltage obtained from the direct current from station 1 is applied to the pace of this transistor TR via a resistor R8, so that the alternating current signal superimposed on the direct current from station 1 causes the transistor Prevents the pace potential of TR from fluctuating,
The AC resistance between the collector and emitter of the transistor TR is increased so that only a DC component flows through the transistor TR. Therefore, the charging/discharging circuit consisting of this resistor R2 and capacitor C2 is an essential element.

However, the existence of this charging/discharging circuit has the disadvantage that the dial 79 pulse waveform is deformed when dial pulses are sent out. That is, in the waveform diagram shown in FIG. 2, when the relay is turned off at time t0, no voltage is applied to the DC shunt circuit 5. Therefore, the voltage vc2 charged in the capacitor C2 is transferred to the transistor TR
It is discharged through the path of pace→emitter→resistor R3, and therefore the pace potential vB decreases with the characteristics shown in FIG. 2(b).

Next, when the relay is turned on at time t2, voltage is again applied to the DC shunt circuit 5, and the capacitor C2 is charged through the resistor R8. However, as a general characteristic of transistors, during the time ΔT until the voltage between the pace and emitter reaches approximately 0.7V, no collector current of the transistor TR flows at all, and even after that, the pace potential vB of the transistor TR increases slowly in response to the charging time constant of resistor R2 and capacitor C2, so the collector current does not rise suddenly. As a result, the local current IL has a waveform with a slow rise as shown in Figure 2 (C), and the rise characteristics of the local current IL also change depending on the line resistance RL. However, if the line resistance RL varies depending on the length of the line, there is a drawback that the make rate of the dial pulse changes.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a central office line trunk circuit which eliminates the above ml' drawback, can send out an ideal dial pulse waveform, and which prevents the make rate from changing due to line resistance.

[Summary of the invention]

In the present invention, in order to eliminate the above-mentioned adverse effects caused by the charging/discharging circuit in the DC shunt circuit when transmitting a dial signal, the entire pace bias voltage of the transistor is applied to the pace without going through the resistance of the charging/discharging circuit. A DC shunt circuit is provided with a first means for stopping the charging and a second means for preventing a capacitor of the charging/discharging circuit from being charged by the bias voltage applied via the first means. The above objectives have been achieved.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

FIG. 3 is a circuit diagram showing an embodiment of the central office line trunk circuit according to the present invention, and the only difference is that relay 2 and diodes D6 to D are added to the DC shunt circuit 5 of the circuit shown in FIG. This is different from

That is, a diode p6 is connected between the connection point of the resistor R2 and the capacitor C2 constituting the charge/discharge circuit and the pace of the transistor TR, and its cathode is connected to the pace side of the transistor TR, and one end is connected to the capacitor C8. Between the other end of the resistor R2 and the base of the transistor TR, a series circuit consisting of diodes D, D, and a relay is connected to the can-1 of the diode D and D8.
Both I and I are connected as the pace side of the transistor TR.

In the above configuration, the □ on the relay is as shown in Figure 4 (,)
As shown in FIG. 2(, ), the switch is turned off between time points t□ and t2 and between t and t4.

As shown in FIG. 4(b), the relay 8 is turned on from time t0, which is slightly before time t1, to time t, which is after time t4. Therefore, when the relay is turned off at time t□, the voltage vc2 charged in the capacitor C1 passes through the path of the diode D6 → the pace of the drain zoster TR → the emitter → the resistor R3, as shown in FIG. 4(c). However, when the relay is turned on at time t, the DC voltage is transferred from the line L1 to the diodes D, D, and the relay without passing through the resistor R2.
Since the potential VB is applied to the pace of the transistor TR via the potential VB, the rise of the pace potential VB becomes steep as shown in FIG. 4(c). On the other hand, since a diode D6 is connected between the pace of the transistor TR and the capacitor C3 with its cathode on the pace side, the diode Dy+D
There is no risk that capacitor C2 will be charged by the pace bias voltage applied to @ and the relay via 2, and therefore the collector current of transistor TR is
As a result, the local current IL rises rapidly at the fourth
As shown in Figure (d), the relay exhibits an ideal intermittent waveform with a steep rise characteristic with no delay in response to an intermittent 1, and the make rate of the dial pulse changes depending on the line resistance RL. There will be nothing to do.

〔Effect of the invention〕

As explained above, in the present invention, when the relay for forming a DC loop is turned on to generate a dial pulse, the charging/discharging circuit of the DC shunt circuit is substantially disconnected from the circuit. There is an advantage that the make rate does not change due to line resistance, and dial pulses having an extremely ideal waveform shape can be sent out.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional central office line trunk circuit.
FIG. 2 is a signal waveform diagram of each part thereof, FIG. 3 is a circuit diagram showing an embodiment of the central office line trunk circuit according to the present invention, and FIG. 4 is a signal waveform diagram of each part thereof. DESCRIPTION OF SYMBOLS 1... Station, 2... Incoming signal detection circuit, 3... Incoming call detection circuit, 4... Relay circuit for direct current loop formation, 5...
...DC shunt circuit, 6... Rectifier circuit, 7... AC shunt circuit, 8... Switch frame.

Claims (2)

[Claims] (1) A DC shunt circuit that includes a transistor that forms a DC path and allows only a DC component to pass through is provided, and this DC shunt circuit has the base of the transistor connected in series with a resistor and a capacitor that perform charging and discharging in a similar manner. In a central office line trunk circuit connected to a connection point between the resistor and the capacitor of the circuit, and configured such that a bias voltage obtained from the DC component is applied to the base via the resistor, a dial. a first means for applying the bias voltage to the base without passing through the resistor; and charging the capacitor with the bias voltage applied through the first means when sending a pulse. A central office line trunk circuit comprising second means for preventing. (2) The office line trunk circuit according to claim (1), wherein the first means and the second means are composed of diodes.